Einstein nói về khoa học và đạo Phật

 "The religion of the future will be a cosmic religion. It would transcend a person God and avoid dogmas and theology. Covering both the natural and the spiritual, it should be based on a religious sense, arising from the experience of all things, natural and spiritual, as a meaningful unity. Buddhism answers this description

If there is any religion that would cope with modern scientific needs, it would be Buddhism. Buddhism requires no revision to keep it up to date with recent scientific finding. Buddhism need no surrender its view to science, because it embrances science as well as goes beyond science"

  

"Tôn giáo của tương lai sẽ là một tôn giáo toàn cầu, vượt lên trên mọi thần linh, giáo điều và thần học. Tôn giáo ấy phải bao quát cả phương diện tự nhiên lẫn siêu nhiên, đặt trên căn bản của ý thức đạo lý, phát xuất từ kinh nghiệm tổng thể gồm mọi lĩnh vực trên trong cái nhất thể đầy đủ ý nghĩa. Phật giáo sẽ đáp ứng được các điều kiện đó"

Nếu có một tôn giáo nào đương đầu với các nhu cầu của khoa học hiện đại thì đó là Phật giáo. Phật giáo không cần xét lại quan điểm của mình để cập nhật hóa với những khám phá mới của khoa học. Phật giáo không cần phải từ bỏ quan điểm của mình để xu hướng theo khoa học, vì Phật giáo bao hàm cả khoa học cũng như vượt qua khoa học"

Perovskites and Perovskite Solar Cells

The rapid improvement of perovskite solar cells has made them the rising star of the photovoltaics world and of huge interest to the academic community. Since their operational methods are still relatively new, there is great opportunity for further research into the basic physics and chemistry around perovskites. Furthermore, there is huge potential for engineering better, more efficient solar cells which are expected to reach in excess of 20% power conversion efficiency.

Why are perovskite solar cells so significant?

There are two key graphs which demonstrate why perovskite solar cells have attracted such prominent attention in the short time since the breakthrough paper of 2012[1].

The first of these graphs, which uses data taken from NREL solar cell efficiency tables, demonstrates the power conversion efficiencies of the perovskite based devices over recent years in comparison to other technologies.

The graph shows a meteoric rise compared to most other technologies over a relatively short period of time. Although it could be argued that more resources and better infrastructure for solar cell research has been available in the last few years, the dramatic rise in efficiency is still incredibly significant and impressive. This suggests that with continued research, efficiency of perovskite based solar cells can continue to rise at this rate over the coming years.

The second key graph below is the open circuit voltage compared to the band gap for a range of technologies that the perovskites compete with.

This graph demonstrates how much of a photon’s energy is lost in the conversion process from light to electricity. For standard excitonic-based, organic-based solar cells this loss can be as high as 50% of the absorbed energy. However, for the perovskite based solar cells the loss is far less. Perovskite based solar cells are fast approaching the same level of photon energy utilisation as the current leading monolithic crystalline technologies such as silicon and GaAs. Furthermore, they also have the potential for much lower processing costs.

The maximum photon energy utilisation (defined as the open circuit voltage Voc divided by the optical bandgap Eg) for common single junction solar cells material systems.

Currently, there is not known to be a significant negative aspect of perovskite based solar cells. Although lifetimes of the cells aren’t yet proven, there is no evidence to suggest their lifetime is any less than that of pure organic devices. The use of lead in perovskite compounds is not ideal, but it is used in much smaller quantities than that which is currently present in either lead or cadmium based batteries and there is potential for a lead alternative to be used in perovskite compounds instead. Finally, there has also been little discussion of the optical density of these materials which, although higher than silicon, is still lower than other active materials. As a result, the perovskite devices require thicker light-harvesting layers which may cause some fabrication limitations; particularly for solution processed devices where creating such thick layers with high uniformity can be difficult.

A key development will therefore be the improvement of precursor materials for solution based perovskite deposition and associated coating and processing techniques. Although at present the best perovskite solar cells are vacuum deposited, solution processed devices will ultimately yield lower production costs. While vacuum based processes are relatively easy to scale up, the capital equipment cost of doing so can rapidly become astronomical.

To enable a truly low cost-per-watt will require perovskite solar cells to have the much heralded trio of high efficiency, long lifetimes and low manufacturing costs. This has not yet been achieved for other thin film technologies but perovskite based devices so far demonstrate enormous potential for achieving this.

What are perovskites?

The term perovskite and perovskite structure are often used interchangeably. Technically, perovskite is a type of mineral that was first found in the Ural Mountains and named after Lev Perovski who was the founder of the Russian Geographical Society. A perovskite structure is any compound that has the same structure as the perovskite mineral.

True perovskite (the mineral) is formed of calcium, titanium and oxygen in the form CaTiO3. Meanwhile, a perovskite structure is anything that has the generic form ABX3 and the same crystallographic structure as perovskite (the mineral). However, since most people in the solar cell world aren’t involved with minerals and geology, perovskite and perovskite structure are used interchangeably.

The perovskite lattice arrangement is demonstrated below, but it must be considered that, as with many structures in crystallography, it can be represented in multiple ways. The simplest way to think about a perovskite is as a large atomic or molecular cation (positively charged) of type A in the centre of a cube. The corners of the cube are then occupied by atoms B (also positively charged cations) and the faces of the cube are occupied by a smaller atom X with negative charge (anion).

A generic perovskite structure of the form ABX3. Note however that the two structures are equivalent – the left hand structure is drawn so that atom B is at the <0,0,0> position while the right hand structure is drawn so that atom (or molecule) A is at the <0,0,0> position. Also note that the lines are a guide to represent crystal orientation rather than bonding patterns.

Dependant on which atoms/molecules are used in the structure, perovskites can have an impressive array of interesting properties including superconductivity, giant magnetoresistane, spin dependent transport (spintronics) and catalytic properties. Perovskites therefore represent an exciting playground for physicists, chemists and material scientists.

In the case of perovskite solar cells, the most efficient devices so far have been produced with the following combination of materials in the usual perovskite form ABX3:

• A = An organic cation - methylammonium (CH3NH3)+
• B = A big inorganic cation - usually lead(II) (Pb2+)
• X3= A slightly smaller halogen anion – usually chloride (Cl-) or iodide (I-)

Since this is a relatively general structure, these perovskite based devices can also be given a number of different names which can either refer to a more general class of materials or a specific combination. As an example of this we’ve created the below table to highlight how many names can be formed from one basic structure.

A	B	X3
Organo	Metal	Trihalide (or trihalide)
Methylammonium	Lead	Iodide (or triiodide)
	Plumbate	Chloride (or trichloride)

The perovskite name picking table: pick any one item from columns A, B or X3 to come up with a valid name. Examples include: Organo-lead-chlorides, Methylammonium-metal-trihalides, organo-plumbate-iodides etc.

The table demonstrates how vast the parameter space is for potential material/structure combinations, as there are many other atoms/molecules that could be substituted for each column. The choice of material combinations will be crucial for determining both the optical and electronic properties (e.g. bandgap and commensurate absorption spectra, mobility, diffusion lengths, etc). A simple brute-force optimisation by combinatorial screening in the lab is likely to be very inefficient at finding good perovskite structures. As such, while the field of perovskite solar cells has progressed rapidly so far with only a basic know-how of the photo physics and structural chemistry, to fully optimise devices will require far more in-depth knowledge than is currently available.

Fabrication and Measurement of Perovskite Solar Cells

Although perovskites come from a seemingly different world of crystallography, they can be incorporated very easily into a standard OPV (or other thin film) architecture. While the best perovskite structures have been vacuum deposited to give better, more uniform film qualities, this process requires the co-evaporation of the organic (methylammonium) component at the same time as the inorganic (lead halide) components. The accurate co-evaporation of these materials to form the perovskite therefore requires specialist evaporation chambers that are not available to many researchers. This may also cause the practical issues of calibration and cross-contamination between organic and non-organic sources which would be difficult to clean.

However, the development of low temperature solution deposition routes offer a much simpler method to incorporate perovskites and can even be used with existing materials sets. Although the perovskite solar cells originally came out of DSSC research, the fact that they no longer require an oxide scaffold means the field is bifurcating and that many device architectures now look very similar to thin film photovoltaics except with the active layers substituted with the perovskite. The key to enabling this is that the perovskite precursor materials use relatively polar solvents for deposition therefore an orthogonal solvent systems for the different layers can be fairly easily developed.

The below structure represents a standard (non-inverted) perovskite solar cell based upon a standard glass/ITO substrates with metal back contact. All that is required to form a working device from the perovskite are two charge selective interface layers for the electrons and holes respectively.

Many of the standard interface layers from the world of organic photovoltaics work relatively well. For example PEDOT:PSS and the PTAA-class of polymers work well as hole interface layers while PCBM, C60, ZnO and TIO2 makes an effective electron interfaces. However, the field is so new that there is a vast archive of possible interface materials to be explored. Understanding and optimising the energy levels and interactions of different materials at these interfaces offers a very exciting area of research.

Generic structure of a standard (non-inverted) perovskite solar cell

The main issue for practical device fabrication of perovskite solar cells is that of film quality and thickness. The light harvesting (active) perovskite layer needs to be several hundred nanometres thick – several times more than for standard organic photovoltaics. Unless the deposition conditions and annealing temperature are optimised rough surfaces with incomplete coverage are formed. Even with good optimisation there is still a significant surface roughness remaining, and therefore thicker interface layers than might normally be used are also required. However, the fact that efficiencies of over 11% have already been achieved for spin coated devices [2] is highly encouraging.

It is for this reason that we look forward to watching the progress of solution processed perovskite solar cells and to developing the techniques and devices to help researchers at the cutting edge.

References (please note that Ossila has no formal connection to any of the authors or institutions in these references):

[1] Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites. Michael M. Lee et al., Science magazine, Vol 338, p643-647 (2012)
[2] Morphological Control for High Performance, Solution-Processed Planar Heterojunction Perovskite Solar Cells. Giles E. Eperon et al., Advanced Materials, Vol 24, p151-157 (2014)
[3] Perovskite solar cells employing organic charge-transport layers. Olga Malinkiewicz et al., Nature Photonics, Vol 8, p128-132 (2014)

Further Reading:

Perovskite solar cell overviews:

• Hybrid solar cells- Perovskites under the Sun. Maria Antonietta Loi & Jan C. Hummelen, Nature Materials, V 12, p1087-1089 (2013)
• Perovskite-Based Solar Cells. Gary Hodes, Science magazine, Vol 342, p317-318 (2013)

A general perovskite review by Henry Snaith:

• Perovskites: The Emergence of a New Era for Low-Cost, High-Efficiency Solar Cells. Henry J. Snaith, The Journal of Physical Chemistry Letters, Vol 4, p3623-3630 (2013)

Key perovskite papers:

• Efficient organometal trihalide perovskite planar-heterojunction solar cells on flexible polymer substrates. Pablo Docampo et al., Nature Communications, Vol 4, Article 2761 (2013)
• Electron-hole diffusion lengths exceeding 1 micrometer in an organometal trihalide perovskite absorber. Samula D. Stranks et al., Science magazine, Vol 342, p341-344 (2013)
• High Charge Carrier Mobilities and Lifetimes in Organolead Trihalide Perovskites. Christian Wehrenfennig et al., Advanced Materials, Vol 26, p1584-1589 (2013)
• Low-temperature processed meso-superstructured to thin-film perovskite solar cells. Energy Environmental Science, James M. Ball et al., Vol 6, p1739-1743 (2013

Tapping Solar Power With Perovskites

Every now and again, a well-studied research topic explodes with new life. Long after carbon materials filled chapters of dated textbooks, for example, that field’s soul was reenergized around 1990 after buckyballs and carbon nanotubes were discovered. It happened again in that field about a half-dozen years ago when graphene took the world by storm. It’s happening now in photovoltaics.

“It seems we’ve all been bitten by the perovskite bug,” says University of Oxford physicist Henry J. Snaith, naming the topic in photovoltaics that’s all the rage these days. Snaith leads Oxford’s Photovoltaic & Optoelectronic Device Group.

Photovoltaic devices that directly convert sunlight to electricity aren’t new. Various types of these energy transformers, which are also known as solar cells, have been around for decades. The type Snaith refers to, perovskite solar cells, has been studied intensely only in the past year and a half. During that time, numerous researchers joined the effort, attracted by these cells’ promise to be inexpensive yet high performing. These scientists quickly boosted perovskite solar cells’ electrical output. Now they are working to broaden the cells’ appeal by tailoring their chemical compositions to further boost electrical output, by improving processing methods and stability, and by figuring out why these solar cells perform so unexpectedly well.

[+]Enlarge

 

CELLULAR COMMUNICATION

Northwestern’s Chang (from left), Kanatzidis, Feng Hao, and Byunghong Lee compare solar- cell preparation methods.

Credit: Mitch Jacoby/C&EN

The stodgy, Cold War-era quality to the name “perovskite” belies the excitement engulfing this research topic. Strictly speaking, the label refers to a long-ago-discovered calcium-titanium-based mineral composed mainly of calcium titanate, CaTiO₃. Scientists use the term loosely nowadays to refer to a large class of materials that, like CaTiO₃, exhibit ABX₃ stoichiometry and adopt the perovskite crystal structure.

The perovskites rocking the photovoltaics world these days are organometal trihalides, the most commonly studied of which is CH₃NH₃PbI₃. (CH₃NH₃ is the A group in ABX₃.) The main reason for the excitement is the recent steep rate of improvement in perovskite solar-cell performance.

Some types of solar cells, for example, ones based on high-purity crystalline silicon, have long provided top-notch photovoltaic performance. The power conversion efficiency, or simply the efficiency, of these devices, which is a ratio of the light energy in to the electrical energy out, reaches around 25%. But that performance is costly, owing to the expensive materials and energy-intensive crystal growth and vapor deposition methods needed to make such cells. State-of-the-art solar cells boasting efficiencies topping 40% are available today. But those specialized research devices come with much higher price tags.

Other technologies, such as organic photovoltaic devices based on photosensitive organic polymers, made waves when they debuted in the solar-cell arena because they hold the promise of being less expensive. These devices benefit from being made via low-cost solution-phase plastics manufacturing methods.

Although the price was right for plastic solar cells, the conversion efficiency in the early-2000s time frame was only a few percent. Since then, the value has climbed slowly and now sits around 11%. Other low-cost solar-cell technologies also improved slowly during that period. But they, too, remain relatively weak converters of solar energy.

[+]Enlarge

 

SANDWICH STRUCTURE

Light passing through a transparent electrode (blue) onto a layer of a photosensitive perovskite material (red) stimulates excitations called electron-hole pairs (e^–/h⁺). The charged particles separate and diffuse through the charge-conducting layers to their respective electrodes, thereby generating electric current.

Credit: J. Phys. Chem. Lett. (micrograph)

In contrast, perovskite solar cells are following a more radical course. Almost overnight the conversion efficiency of these cells leaped from just a few percent in a forerunner to perovskite cells to more than 16% in current versions. Most of the advances were reported in 2012 and 2013. The fast-paced improvement, which hasn’t shown signs of slowing, coupled with inexpensive materials and preparation methods, prompts Snaith to declare that perovskite solar cells are poised “to break the prevailing paradigm” by combining low cost and excellent performance.

Snaith recently launched Oxford Photovoltaics, a start-up company, to commercialize this technology. The company is focusing on photovoltaic-based windows and architectural materials for buildings.

Similar to other relatively young photovoltaic technologies, perovskite solar cells can be fashioned using common wet chemistry techniques. The simplicity of making solar-cell components via liquid-phase chemical reactions and depositing the materials by methods such as spraying and spin coating may make it possible for solar-cell manufacturers to eventually replace clean rooms and sophisticated manufacturing equipment with simple benchtop processes, says Prashant V. Kamat, a professor in the University of Notre Dame’s chemistry department and radiation laboratory.

[+]Enlarge

 

VARIETY PACK

Perovskite solar cells vary from lab to lab. The set of four (top) contain tin-based perovskite materials and distinct organic dyes. The color difference in the pair on the bottom arises from a gentle heating step that induces crystallization of organo lead trihalide perovskite precursors.

Credit: Mitch Jacoby/C&EN

But even before manufacturers start building production facilities, the simplicity of perovskite solar-cell assembly is attracting many academic researchers. “Anyone can play,” Kamat says. The barrier to getting started in this field is low, he explains, because this type of research requires only standard lab equipment.

Another reason for the popularity is that perovskite photovoltaics hold much in common with—or can be viewed as an offshoot of—well-studied devices known as dye-sensitized solar cells (DSSCs). These devices are also called Grätzel cells after their inventor, Michael Grätzel of the Swiss Federal Institute of Technology, Lausanne. And DSSCs are closely related to yet another hot solar-cell technology—quantum dot solar cells (C&EN, Sept. 23, 2013, page 28). A key difference among these three cell types is the nature of the light absorber, which can be a trihalide perovskite, a dye, or inorganic quantum dots.

DSSCs feature a porous network of TiO₂ particles that have been treated with a sunlight-absorbing dye, often a ruthenium compound, and typically infused with a liquid redox-active electrolyte material. As dye molecules absorb light and become energetically excited, they inject electrons into the TiO₂ particles, which shuttle the electrons toward one of the cell’s electrodes. The molecules return to their original state via electron transfer from the redox material, which conducts positive charges, or “holes.”

In all of these types of solar cells, photoinduced excitation of electron-hole pairs and charge-transport processes work in concert to drive electrons toward one electrode and holes toward the other. These events generate a flow of electric current that can be used as a power source.

One of the shortcomings of DSSCs, especially early designs of these devices, is the thickness of the dye-coated TiO₂ films. To absorb enough sunlight to do an adequate energy conversion job, the films tend to be several micrometers thick, which poses processing challenges, especially to efforts to make thin, flexible devices. That’s where trihalide perovskites come into play.

Northwestern University’s Robert P. H. Chang, a professor of materials science and engineering, explains that one of the main attractions of these materials is that they absorb sunlight more intensely and over a broader region of the solar spectrum than other light absorbers commonly used in solar cells. As a result, perovskite-based solar cells can be thinner than other types of cells, easier to process, and potentially less expensive to manufacture.

Some of those features, which now are widely known, were uncovered in a 2009 study by Tsutomu Miyasaka, an electrochemist at Toin University of Yokohama, in Japan, and coworkers. By treating a film of TiO₂ with a solution containing CH₃NH₃I and PbI₂, the team triggered a self-assembly process that coated the oxide with a layer of CH₃NH₃PbI₃ nanocrystals, one of the perovskite materials at the center of current research efforts. They also prepared the tribromide from the corresponding brominated reagents.

The group fashioned solar cells by sandwiching the perovskite-coated oxide films together with an organic electrolyte solution between conducting glass electrodes. They found that the triiodide cell readily generated electric current with a conversion efficiency of 3.8%. The tribromide’s performance was a little weaker—3.1% (J. Am. Chem. Soc. 2009, DOI:10.1021/ja809598r).

The performance was modest, but it attracted the attention of Nam-Gyu Park, a chemical engineering professor atSungkyunkwan University, in South Korea. By optimizing various parameters, including the nature of the TiO₂ film surface and the perovskite nanocrystal size, Park’s team bumped up the conversion efficiency of the triiodide cell to 6.5% (Nanoscale2011, DOI: 10.1039/c1nr10867k).

But there was a hitch. These cells depended on an electrolyte solution that remained liquid in the finished device. Researchers had been trying for years to avoid using these liquids because they dramatically shorten cell lifetimes.

A common example of these materials, an organic solution of the iodide/triiodide (I^–/I₃^–) redox couple, a hole conductor, is corrosive and volatile and quickly decomposes trihalide perovskites. As a result, these perovskite cells worked well, but only briefly. Scientists had shown previously that noncorrosive solid electrolytes could replace their troublesome liquid-phase counterparts. But the efficiencies of solid-state DSSCs tended to be low.

Help came in the form of a hole-conducting polyaromatic ring compound in the spirobifluorene family known as spiro-OMeTAD. With that compound on hand, things started to heat up quickly. Park teamed up with Grätzel and made solid-state spiro-OMeTAD/triiodide perovskite cells that exhibited much-improved stability and conversion efficiencies measuring 9.7% (Sci. Rep.2012, DOI: 10.1038/srep00591).

And Snaith teamed up with Miyasaka, used spiro-OMeTAD as the hole-conducting layer, and deposited it on a mixed halide perovskite, CH₃NH₃PbI₂Cl. When the team made solar cells with those compounds and TiO₂, they observed conversion efficiencies near 8%, a value that just a year earlier would have turned heads. But when they replaced TiO₂ with alumina (Al₂O₃), an insulator that cannot conduct electrons to the electrode—that is, when they made a solar cell that was sure to fail—it surprisingly delivered a whopping 10.9% conversion efficiency (Science 2012, DOI: 10.1126/science.1228604).

The team proposed that alumina serves only as a high-surface-area scaffold but that it mediates formation of a layer of high-quality perovskite crystals. The group suggested that the quality of the film is likely the reason the crystals can collect and transport electrons so efficiently.

Around the same time, Chang and Northwestern colleague Mercouri G. Kanatzidis, a chemistry professor, also reported success with a solid-state solar cell featuring a perovskite material. The cell was made from dye-coated nanoporous TiO₂ and a novel light-absorbing, hole-conducting material with the perovskite structure—fluorine-doped CsSnI₃ (also an ABX₃ material). In tests of that cell, the group measured conversion efficiencies of 10.2% (C&EN, June 11, 2012, page 40).

[+]Enlarge

 

In quick succession throughout 2013, one research paper after another popped up on journal websites, each describing a perovskite solar-cell design with a twist and each reporting efficiency improvements. For example, Sang Il Seok of South Korea’s Korea Research Institute of Chemical Technology (KRICT) found that by using polytriarylamine as a hole conductor, he and his coworkers made cells that achieved 12% conversion efficiencies (Nat. Photon. 2013, DOI: 10.1038/nphoton.2013.80).

And University of Saskatchewan chemists Dianyi Liu andTimothy L. Kelly did away with the high-temperature processing step necessary for conditioning TiO₂ by replacing that oxide with a substantially thinner layer of ZnO. The team took advantage of those improvements to make flexible trihalide perovskite solar cells with conversion efficiencies in excess of 10%. They also made rigid cells that achieve efficiencies as high as 15.7% (Nat. Photon. 2013 , DOI: 10.1038/nphoton.2013.342). The highest efficiency perovskite solar cell verified to date by theNational Renewable Energy Laboratory, which is regarded internationally as the official verifier of solar-cell performance, comes from KRICT and clocks in at 16.2%.

As researchers strive to increase conversion efficiencies, they also keep busy measuring, studying, and improving other cell parameters. “The materials in these cells are complicated, and we don’t really understand how they work,” Kanatzidis says. So his group has undertaken a detailed survey of phase transitions, charge transport, and other basic properties of lead and tin perovskites (Inorg. Chem. 2013, DOI: 10.1021/ic401215x). The group is currently working on ways to improve the chemical stability of tin compounds so they can serve as durable alternatives to lead-based perovskites.

Meanwhile, longtime photovoltaics researchers David Cahen and Gary Hodes, both professors at Weizmann Institute of Science, in Israel, are exploring ways to boost a key solar-cell parameter known as open-circuit voltage, V_OC. Devices with high V_OC values can capture high-energy photons and thereby exploit a broader range of the solar spectrum than can traditional cells. They also can be used to tap sunlight to directly drive electrochemical reactions.

By carefully matching the methyl ammonium lead tribromide perovskite with a hole conductor featuring handpicked electronic and optical properties, Cahen, Hodes, Eran Edri, and Saar Kirmayer made a solar cell with an open-circuit voltage measuring 1.3 V. That value is substantially higher—by several hundred millivolts—than unoptimized perovskite cells (J. Phys. Chem. Lett.2013, DOI: 10.1021/jz400348q). Just recently, the team bumped up the V_OC value further, to more than 1.5 V, by using a custom-made mixed bromide-chloride lead perovskite.

Unlike many other types of photovoltaics, in perovskites, it’s all about the chemistry, Hodes stresses. Precursor synthesis, cell assembly, and device customization are all mediated by ordinary chemistry methods, he adds, underscoring the prominent role chemists can play in this field.

Almost overnight, researchers catapulted the conversion efficiency of perovskite solar cells from a few percent to more than 16%. “It’s tough to predict where this technology will end up,” Snaith says, but it certainly has “the right ingredients” to deliver exceptional efficiencies at the lowest possible cost.

He adds, “So long as we can improve the stability of this technology, I would say we are witnessing the emergence of a contender for ultimately low-cost solar power.”

http://cen.acs.org/articles/92/i8/Tapping-Solar-Power-Perovskites.html

Lithium -carbon battery could be cost effective

The advantages of using carbon are that it is cost-effective and safe to use, and the energy output is five to eight times higher than lithium-ion batteries currently on the market. The new battery technology also performs better than two other future technologies: lithium-sulfur batteries, currently in the prototype stage, and lithium-air batteries, now under development. For example, the induced-fluorination technology could be used to produce cellphone batteries that would charge faster and last longer. The research team developed the new battery technology for energy storage using carbon nanomaterials and a process called induced fluorination.

High performance rechargeable batteries are urgently demanded for future energy storage systems. Here, we adopted a lithium-carbon battery configuration. Instead of using carbon materials as the surface provider for lithium-ion adsorption and desorption, we realized induced fluorination of carbon nanotube array (CNTA) paper cathodes, with the source of fluoride ions from electrolytes, by an in-situ electrochemical induction process. The induced fluorination of CNTA papers activated the reversible fluorination/defluorination reactions and lithium-ion storage/release at the CNTA paper cathodes, resulting in a dual-storage mechanism. The rechargeable battery with this dual-storage mechanism demonstrated a maximum discharging capacity of 2174 mAh gcarbon−1 and a specific energy of 4113 Wh kgcarbon−1 with good cycling performance.

Although Li-ion batteries (LIBs) have transformed portable electronics, the energy density and cycle life of existing LIBs, even if fully developed, remain insufficient. Reaching beyond the horizon of LIBs requires the exploration of new electrochemistry and/or new materials1. The recent popular attempts are Li-sulfur (Li-S) and Li-air (Li-O2) batteries. However, there are some formidable challenges for Li-S and Li-O2 batteries, e.g., dissolution of discharging products, poor cathode electrical conductivity, and large volume expansion upon lithiation.

Li-CFx batteries have the highest energy density among all primary lithium batteries with a theoretical specific energy of 2180 Wh kg(Li+CF)−1. A high capacity of 615 mAh gCFx−1 was also reported for the pre-synthesized CFx cathodes. It is well known that defluorination of carbon fluorides can be achieved with the assistance of lithium cations during discharging in Li-CFx batteries. However, Li-CFx batteries have attracted limited interest because of their strictly non-rechargeable nature16 and the non-environmental-friendly synthesis process for carbon fluorides, e.g., the use of F2 gas and/or catalysts under extreme temperature condition

Ragone plot, comparing Li-CNT-F batteries with other batteries in terms of weight of cathode materials.


The complex anion of [F-TPFPB]− was previously found to be reversibly intercalated in graphite with limited capacity, 60 ~ 80 mA gcarbon−1. It is the intercalation of the bulky complex anion of [F-TPFPB]− that will sterically hinder further anion intercalation and worsen the cathode specific capacity. However, in this report, the intercalation of [F-TPFPB]− was successfully suppressed, as suggested in Figure 2f, which may explain the high capacity achieved in Figure 4. The suppression of bulky [F-TPFPB]− intercalation is due to the particular induction temperature (70°C) conducted, which reduces the energy barrier for the F− release from [F-TPFPB]−, and therefore, promotes the intercalation of free F− in CNTA papers. It is also worth to note that the free fluoride ions released from [F-TPFPB]− are originally from the dissolved LiF salts, rather than from the decomposition of TPFPB molecules. It has been calculated that the energy barrier for the fluoride anion release from TPFPB (59.2 kcal/mol) is much lower than the breakdown of a true covalent bond (typically on the order of 100 kcal/mol) in TPFPB

In conclusion, they realized the induced fluorination of CNTA paper cathodes by an in-situ electrochemical induction process at 70°C and in the presence of TPFPB. The induced fluorination of CNTA papers activated the reversible fluorination/defluorination reactions and lithium-ion storage/release at the CNTA paper cathodes, resulting in a dual-storage mechanism. It is the first time that the reversible fluorination/defluorination reactions were realized at pure carbon and non-fluoride materials. In addition, the induced fluorination destructed the graphitic carbon to defective nanostructures, which further facilitated the two reversible reactions at both 70°C and 22°C. The rechargeable battery with this dual-storage mechanism demonstrated a maximum discharging capacity of 2174 mAh gcarbon−1 and a specific energy of 4113 Wh kgcarbon−1 with good cycling performance. This paper uncovers the significance of energy storage by carbon materials at high voltages, and demonstrates the Li-C-F battery system a new promising candidate for the future energy storage systems.

Dual-storage mechanism with reversible fluorination/defluorination reactions and lithium-ion storage/release occurring at CNTA paper cathode.

from : http://nextbigfuture.com

Liquid Metal Battery Stores Power After Sun Or Wind Retreat

Ambri, a Cambridge, Massachusetts startup founded by MIT researchers, is working to turn a new renewable-energy concept into a commercially viable product. Employing Liquid Metal Batteries, their goal is to store power for significantly less than current battery technologies. “If we can Get Liquid-Metal batteries down to $500 a kilowatt-hour, we’ll change the world,”Donald Sadoway, chief scientific adviser at Ambri Inc., said.

This new technology promises an alternative to the massive pumped-water systems that make up 95 percent of U.S. energy-storage capacity. At the lower price, developers will be able to build wind and solar projects that can deliver power to the grid anytime, making renewable energy as reliable as natural gas and coal without the greenhouse-gas emissions.

A major difference between Ambri’s technology and other batteries is its all-liquid design. As shown in the figure, Ambri’s cells are made of three simple components — a salt (electrolyte) which separates two distinct metal layers (electrodes). Cells operate at elevated temperature and, upon melting, these three layers self-segregate and float on top one another due to their different densities and levels of immiscibility. Initially, researchers at MIT worked with magnesium (Mg) and antimony (Sb) electrodes; Ambri is commercializing a chemistry with a higher voltage and lower cost. In a charged state, there is potential energy between the top metal layer and the bottom metal layer which creates a cell voltage. To discharge the battery, the cell voltage drives electrons from the Mg electrode, delivering power to the external load (e.g., light bulb), and the electrons return back into the Sb electrode. Internally, this causes Mg ions to pass through the salt and alloy with Sb, forming a Mg-Sb alloy. To recharge, power from an external source (e.g., wind turbine) pushes electrons in the opposite direction, pulling Mg from the Mg-Sb alloy and re-depositing Mg back onto the top layer, returning the system to three distinct liquid layers. The cell design is simple, uses low-cost materials, and the all liquid design avoids the main failure mechanisms experienced by solid components in other battery technologies.

Another major difference between Ambri’s Liquid Metal Battery and other battery technologies is its capital efficiency in manufacturing. Ambri’s factories will require one fourth to one tenth of the capital investment to produce an equivalent amount of electricity storage per year as other technologies. The active components of Ambri’s cells are housed in steel containers and cell tolerances are in millimeters not microns. Cells are put together in systems using steel racking and other basic components. Consequently, Ambri will be able to leverage workers that have experience building and assembling steel parts, a ubiquitous skill set. This gives rise to its manufacturing strategy of building Ambri’s Liquid Metal Batteries around the world through a network of manufacturers that will serve local and regional markets on a global basis.

 In the world of electricity storage, the Liquid Metal Battery technology performs like both a tractor and a race car. It can respond to regulation signals in milliseconds and can store up to twelve hours of energy and discharge it slowly over time.

Liquid electrodes offer a robust alternative to solid electrodes, avoiding common failure mechanisms of conventional batteries, such as electrode particle cracking. The all-liquid design avoids cycle-to-cycle capacity fade because the electrodes are reconstituted with each charge.

The Liquid Metal Battery operates silently, is emissions-free and has no moving parts.

Ambri’s Liquid Metal Battery technology is unique - it has distinct properties and performance capabilities - and is unlike any other battery technology in the world. As a result, Ambri has secured a strong intellectual property position. The company has filed or has licensing rights to more than 30 domestic and international patents and patent applications and continues to pursue broad coverage.

Today, the electric grid is the largest supply chain in the world with no warehouse. The electricity we use is generated moments before we use it. To keep the lights on, power grids are to meet the highest levels of demand, which occur only a few hours per year. It is hard to get enough electricity into certain areas, like big cities, leading to price spikes and threats of blackouts and brownouts. In addition, no one can control when the sun shines or when the wind blows, making it hard to operate the grid when wind and solar resources are significant contributors. As worldwide consumption is increasing and grid infrastructure is aging, a new solution is required.

The solution is Ambri’s Liquid Metal Battery — a novel grid-scale electricity storage technology. The Liquid Metal Battery will fundamentally change the way power grids are operated on a global basis. It will provide numerous benefits to multiple stakeholders across the electric system value chain:

·     Electric Utilities

·     Independent power producers

·     Transmission operators

·     End-users

The new battery will help integrate renewable resources like wind and solar, creating a cleaner electricity infrastructure; it will offset the need to build additional transmission, generation and distribution assets, which will lower electricity costs; it will enable users to reduce their electricity bills; and it will improve reliability in the face of an aging grid. Ambri’s Liquid Metal Battery will reduce the amount of generation, transmission and distribution infrastructure by enabling the electric grid to be built to meet average demand instead of peak demand.

Industry grapples with EV battery economics

Say “electric vehicle” (EV) and most people believe they immediately see an end to our foreign oil dependence. But in the role of consumers, these same people start to back off when the car purchase price approaches about $25k. That’s one reason EV sales in the U.S. fell short of expectations in 2011. While the EV market may expand a bit this year, the cost for the batteries going in EVs and plug-in electrics (PEVs) has become center stage --- and some skeptics wonder whether battery technology will ever be ready for prime time. Beyond the high cost of the technology today, there are also practical at-home and on-the-road charging issues that remain unresolved.

EV battery costs have actually declined somewhat lately. But the modest decreases won’t affect the cost of EVs for at least a year or two, says Pike Research (Boulder, Colo.); even then, the savings look to be minimal. The biggest opportunities for savings come from use of high-volume manufacturing techniques, and these aren’t practical until consumers start buying. Besides range anxiety and high price tags, some conventional economic considerations continue to be big obstacles. One big one is that early market info indicates the resale value for an EV after four years would, on a percentage basis, be much lower than that for a comparative gasoline-powered vehicle. Sadly, media claims of a “rapidly expanding” market are a stretch. But for now, some EV makers think they can make a business out of selling cars and leasing EV lithium-based batteries. Will it work?

The battery system nowadays accounts for perhaps one-third of total vehicle cost and from several hundred to a few thousand pounds of the vehicle weight. Cost and weight may become an even bigger issue because batteries are expected to expand, not get smaller.

Battery leasing seems a way out. Linked with a “hot swapping” architecture, it is one possible way to address such issues as on-the-road charging. The recharging process is problematic. Whether from home during “off-peak” hours or from highway pit stops during the day, there is no near-term way to make charging as quick as filling up with gas. The forecast from Pike Research is for 7.7 million charging stations worldwide (public, private, residential) by 2017. But right now that prediction seems somewhat optimistic.

Moreover, national coordination on charging stations might best be summed up as a jumble of confused activity. Many states have their own buyer incentives. Bucking the small gains, however, was a recent set of U.S. government incentives for installing EV chargers, converting vehicles to EVs, and buying special-category electric vehicles. (The measures expired at year’s end.) Various third-party start-ups now in the loop to facilitate growth of the EV industry are struggling. Despite some glowing forecasts, it seems as though the sale of an individual EV often boils down to the consumer’s immediate budget concerns versus those of the national budget; both appear squeezed for now.

If the polls from Pike Research are true, only 40% of consumers are currently interested in purchasing a PEV, a decline of 4% from last year. There are various architectural plans for on-the-road charging stations. But built into all these plans is an assumption of a practical limit on the number of standard battery sizes and ratings. To complicate matters further, there is a sizeable group of EV nonbelievers and detractors who think the idea of charging-on-the-go is silly and impractical.

Begetting battery bargains
The idea of leasing an EV battery is meant to quell consumer anxiety over EV range and driver concerns about leaving home for work and returning the same day. Though system integrators look at on-the-road charging stations as part of the infrastructure that makes EVs practical, for many consumers the whole concept of frequent recharging further complicates the decision to buy a vehicle. Battery makers who are ramping up face the fact that EV makers are trying to standardize quickly to facilitate high-volume production and thus must field a manufacturable product at breakneck speed. Without sufficiently high EV sales, the availability of lithium-based batteries may well outstrip the demand for them. In short, the manufacture of battery packs is expensive and carries an economic risk.

At least one automaker is testing the waters with battery leasing. As part of its ZE electric car program, Renault in France delivered its first truck vehicle, the Kangoo Van ZE, in the U.K. late last year with a leasing deal on its battery. Battery fees (perhaps a maximum of £100 a month) will be based on the user’s yearly mileage. The company indicated earlier its initial plans for the five EVs it expects to market in the UK over the next year or two is to lease the batteries for about £70 a month.

The idea is sprouting for fleet vehicles, too, although in a different way. Examples include the “Green for Free” program, from Enova (Torrance, Calif.), a manufacturer of electric and hybrid drives; and Freightliner Custom Chassis Corp. (FCCC, part of Daimler Trucks N.A., Portland, Ore.), which manufactures Class 5-8 trucks for commercial vehicle applications. The two companies are crossing the bridge from diesel to electric-powered trucks. The program, announced in November, offers buyers an FCCC All-Electric Walk-in Van (i.e., with battery) for the same price as a diesel truck. The idea is that consumers benefit from the lower cost of electricity versus diesel fuel, and they also save on maintenance over time. It’s the first program, according to Enova, that eliminates the overall incremental costs associated with purchasing and operating an all-electric vehicle. The hope is that the initiative ultimately brings both electric and hybrid vehicles to the commercial fleet market in great numbers.

The DOE thinks next-generation lithium-ion batteries can be 70% cheaper than those of today thanks to developments that include the tailoring of the solid-electrolyte interphase (SEI) layer on the anode, better electrolytes, and specially layered oxides on the cathode.

Yet not all carmakers see things this way, particularly for EVs, and particularly in the U.S. Nissan N.A. (Franklin, Tenn.), for example, first considered battery leasing back in 2009 as part of the Nissan-Renault Alliance. Back then, the company expressed optimism that battery leasing would benefit buyers of the Nissan Leaf, although it admitted its own research showed U.S. consumers might not support the idea.

But in 2010 Nissan said it had abandoned the idea, at least for the U.S.; European deals are still possible in conjunction with start-up third-party integrators such as Better Place (Palo Alto, Calif.). In any case, there’s been no change in Nissan’s strategy since its last announcement, and a spokesman for Nissan says customers see a car and its batteries as a single inseparable purchase item. Ford Motor Co. expresses the same idea regarding its newly released Focus Electric.

Nevertheless, despite such setbacks, it looks as though the leasing idea is gaining traction. Most recently, General Electric Co. said it would look into taking a role as a third-party battery-lease integrator, curiously in cooperation with Nissan. Part of the project would be to develop a battery charging infrastructure, as well as battery-to-grid systems. GE also owns a part of battery maker A123 Systems (Watertown, Mass.).

Despite naysayers, battery-swapping stations are, in fact, slowly coming online. You’d be lucky to find a dozen such highway stations in your state, and none have been particularly well publicized. The subject gets talked up more extensively in Europe, with Copenhagen hosting the first battery-swapping facility on the continent. Better Place manages it. As reported in the New York Times, the company has plans for 19 more such stations in Denmark this year, which will accommodate quick battery swaps in vehicles made by Renault. In the U.S., Tesla’s Model S sedan, due in production shortly, is said to have battery-swapping capability, and others will likely follow.

In the U.S., most recent developments center on charging batteries. In November Nissan, in conjunction with Sumitomo, announced an early-2012 release of a dc battery charger for the U.S. that will quick-charge a Nissan Leaf in under 30 minutes. The price is $9,900 (about one-third the cost of competing chargers, says Nissan). It’s also suited to all plug-in vehicles capable of quick charging on the CHAdeMO (quick-charge) Japanese standard supported by Nissan, Mitsubishi, and Toyota, among others.

And though EV promoters think fleet vehicles have the most compelling economics for EV technology, there is a problem with this logic: natural gas prices that recently slumped to ten-year lows. The low prices make it more economical for big fleets to save fuel costs by rigging their vehicles for burning natural gas rather than replacing them with PHEV or EV versions. President Obama’s recent visit to a Las Vegas UPS facility running natural gas-powered trucks put this approach in the headlines .

Towards phosphatesBattery technology itself shines on amid occasional flare-ups about battery safety and vehicle fires. While most drivers don’t consciously worry about fires from accidents in gasoline-fueled vehicles, the idea seems to take on scary dimensions when it concerns a new technology. Current generations of EVs will mostly use lithium-ion cells, and there are signs that lithium-phosphate technology will get more attention as a way to deal with the flammability issue of lithium-oxide batteries as well as to bring longer life (EE&T, March/April 2011).

With the recent battery fire during a crash-test of the Chevy Volt fresh on their minds, designers may be changing gears in a hurry. Indeed, Chevy’s Spark, due out next year, reportedly will be using a lithium-phosphate battery supplied by A123 Systems. Early indications are that more battery makers and commercial fleet manufacturers have gone or will be going that way soon. Beyond safety considerations, there’s also the issue of total lifetime performance. “If I were a lithium-oxide salesman, I’d say we can offer you 15 to 20% more run time than a lithium phosphate,” said Bob Kanode, CEO of Valence Technology Inc., a leader in the phosphate technology. “Is that true? Yes. But the whole truth is lithium-ion oxide begins to fade quickly. On day one they may have 15 to 20% more capacity. But in six months to a year of continuous operation, they’ve dropped below the line of phosphate and will continue to decline. Phosphate is stable over a very long life.”

The DOE has hight hopes for reducing the costs of EV batteries based on its work in plug-in hybrid electric vehicle batteries. Industry is making progress on the goal of a 40-mile all-electric range battery that costs just $3,400.

The company is also the sole supplier to Electric Vehicles International (EVI, Stockton, Calif.), which manufactures electric vans and trucks. In August, EVI announced a 100-truck contract with United Parcel Service. These trucks are said to have a 90-mile range.

Indeed, fleet vehicles like those that UPS fields look like a good test bed for EVs likely to last longer than their original batteries. “A lot of people don’t know those trucks run for 20 to 25 years,” says Kanode. “And over that time, major systems are changed out several times -- diesel engines, brakes, and anything else you can imagine. But the body of the truck is well built to avoid corrosion. In this wear-out-and-replace business model, their metrics predict they would replace their first battery systems in 11 years, and again at 21 years. Lithium-oxide in this duty cycle (every day, up to 16 hours) wouldn’t last 10 years, but phosphate will.” These major factors will help make for a savings of $550,000 per truck over the 25 years, says Kanode.

Things to comeBeyond batteries, there is a lot of activity in devising the infrastructure needed to support charging stations. Pike Research expects Asian manufacturers to take an early lead in developing vehicle-to-grid charging systems. The firm also expects to see a host of wireless suppliers and equipment manufacturers new to the automotive industry make an initial thrust into both EV charger and telematics systems. These advanced schemes will fold battery monitoring chores into the communications functions such as traffic monitoring and weather forecasts that vehicular communication systems now handle.

Click image to view larger

Looking towards the next generation of battery systems, there are a slew of efforts in the lab driven by relatively unknown groups still in the “venture capital phase.” Some of the action points towards promising but largely untapped areas of battery technology for EVs. However, indications are that lithium and nickel-metal hydride should be the chemistries of choice for the near future. Other chemistries look to be several decades into the future.

A snapshot of the more relevant activity includes the Battery 500 Project at IBM’s Almaden research facility in San Jose, Calif. Researchers there are developing a lithium-air battery designed for EVs with a 500-mile range. Lithium-air, while a technology of interest since the 1970s, hasn’t been a serious EV contender for a number of reasons. But beyond its promise of high energy-density, the new battery’s success will apparently hinge heavily on the capabilities of its new electrolyte, which IBM has thus far not disclosed. Prototypes are expected next year, but how far the battery gets is anyone’s guess --- commercial manufacturing isn’t expected until 2020, by which time the EV landscape will likely be dramatically different.

Click image to view larger.

Further afield, MIT is developing a flow-battery characterized by an anode and cathode that are particles in a liquid. Researchers there have hopes the architecture can be made to accommodate most any battery chemistry. The battery’s unique structure, with physically separate charge and discharge areas, is a major factor in improving its efficiency, researchers say.

Similarly, there are high hopes for research from Nissan aimed at developing a fast-charger that does its job in 10 minutes. Commercialization is expected to take 10 years or more. EE&T

Green VERSU$ green

The U.S. Dept. of Energy (DoE) has a fairly optimistic outlook on R&D battery work as outlined in its November 2011 overview. But strategic advances in battery technology may not be in the bag even for the long term (10 years).

The DoE’s forecast in November for a factor-of-two-to-three increase in power and energy density from most likely lithium-ion based batteries by 2020 seems reasonable. But its hope that manufacturers can reduce battery costs by at least 60% appears somewhat optimistic. That’s because battery makers will be stuck in a low-volume market for awhile. Estimates are for an annual battery production capacity of 10M kW-hr by 2015 that will power 1 million EVs. Yet overall, industry’s applications for research funding from various DoE entities exceed $190M this year just for transportation batteries. That’s about double the amount awarded for each of the last two years.

Source: http://powerelectronics.com/power-electronics-systems/industry-grapples-ev-battery-economics