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Lithium ion cathode materials research is one of the most pressing and challenging aspects of lithium ion battery development today, currently holding the most potential for improvement in terms of cell energy density, electrical performance and safety. Lithium ion cells contain many complex material structures and chemical reactions, some wanted and some unwanted, with the most significant bottleneck being the capacity, voltage, stability and cost of the cathode material itself.

The main ingredient that makes a lithium ion cell hazardous and risky of fire or explosion is the highly electronegative cathode material needed for positive electrode function. The cathode consists of a strong oxidizing agent needed to absorb incoming lithium cations from the electrolyte and electrons from the external circuit during discharge. To do this the cathode material contains a high level of oxygen bonded in various structures with metal atoms such as cobalt, nickel, vanadium, chromium, aluminum or manganese or in the form of a metal phosphate such as iron phosphate. The danger of having so many oxygen atoms in the cathode material is that a high temperature failure event could release the oxygen in a vicious fiery reaction or explosive burning with the often volatile hydrocarbon based electrolyte forming a perfect self contained fire triangle consisting of heat, fuel and oxygen!

Another strong oxidizing agent is sulfur which has the same valance configuration as oxygen and can be used in high energy density lithium-sulfur systems as are currently being developed by a few American companies such as Sion Power, Polyplus and Oxis Energy. The main drawback of a sulfur based cathode is that some of the intermediary LiSx compounds are solvent in the electrolyte commonly used in lithium ion cells causing the cathode and electrolyte to deteriorate, plus they often use a high capacity lithium metal anode in order to match the high capacity of the sulfur cathode and must therefore also deal with the uneven plating problems associated with lithium metal anodes. The theoretical energy density of the lithium sulfur system is very high up to 2500 Whr/kg with a practical energy density more in the range of 300-500 Whr/kg.

Synthesis of most common cathode materials are lithium containing in the discharged state and are the only source of lithium within the cell upon construction. After construction the first charge is called the formation charge where the cathode is slowly delithiated to form the Solid Electrolyte Interphase (SEI) layer against the typically carbon anode. The SEI layer is formed from components in the electrolyte and lithium from the cathode. Additional lithium is also irreversibly lost into the carbon anode itself for a total irreversible first charge capacity loss of 20% or more.

Table 1 gives a basic comparison of a number of cathode materials commonly used today. The best cathode materials have both high capacity and high voltage versus lithium to give maximum energy density, as well as low cost, low toxicity and high cycle life.

Table 1

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The cathode is the positive electrode in an electrochemical cell. During discharge, its job is to absorb incoming electrons from the external electrical circuit by either taking cations (positive ions) in from the electrolyte or by emitting anions (negative ions) out into the electrolyte.

Nickel-cadmium and nickel-metal-hydride cells both use the same positive nickel-oxyhydroxide, NiOOH, cathode material to emit negative hydroxide anions, OHʇ, out into the electrolyte during discharge via the cathode reaction NiOOH + H¿O + eʇ ↓ Ni(OH)¿ + OHʇ. The outgoing OHʇ anions are dissolved into the electrolyte to be re-absorbed through oxidization at the negative anode electrode which consists of pure cadmium in a nickel-cadmium cell, forming cadmium-hydroxide via the anode reaction Cd + 2OHʇ ↓ Cd(OH)¿ + 2eʇ. In the case of a nickel-metal-hydride cell, the anode material is a metal-alloy-hydroxide, MH, that is oxidized back to just a metal-alloy and water via the anode reaction MH + OHʇ ↓ M + H¿O + eʇ.

Lead acid cells use a lead-dioxide, PbO¿, positive cathode material to absorb positive hydrogen cations, HÄ, in from the electrolyte and are major factors in the performance and life cycling of the lead acid cell. The lead-dioxide cathode is typically alloyed with 2-10 wt% of antimony or small amounts of calcium and other elements to help strengthen and improve the soft metal’s workability during manufacturing and to help improve its cycle life characteristics, especially for deep cycle applications. During discharge, the PbO¿ cathode is converted to lead-sulfate, PbSOÁ, through a two stage reaction, stage 1) PbO¿ + 4HÄ + 2eʇ ↓ PbÆÄ + 2H¿O, followed by stage 2) PbÆÄ + SOÁÆʇ ↓ PbSOÁ. The 4HÄ component of stage 1 and the SOÁÆʇ component of stage 2 are the products of breaking sulfuric acid molecules, H¿SOÁ, from the electrolyte by the reaction 2(H¿SOÁ) ↓ 4HÄ + 2(SOÁÆʇ). This is why the acidity of the aqueous based electrolyte decreases toward plain water during discharge.

The lead acid anode undergoes a similar two stage reaction during discharge by converting lead into lead-sulfate, a funny thing how the two active components in both the anode and cathode electrode materials both become lead-sulfate, PbSOÁ, during discharge.

A major precaution for lead acid batteries is once discharged, they should never be left in the discharged state for any length of time longer than necessary because the lead-sulfate will slowly change from an amorphous structure to a crystalline structure, and once crystallized, the charge process will have great difficulty reversing the chemical reaction, as once the reversible constituents are locked up the battery loses its capacity to permanent damage. So always recharge a lead acid battery as soon as possible after any significant discharge occasion.

Also, the conversion rate of lead-sulfate from an amorphous structure to a crystalline structure increases with temperature, hence elevated temperature operating environments can be especially detrimental to lead acid type battery life.

Definition: A patent is a set of exclusive rights granted by a state (national government) to an inventor or assignee for a limited period of time in exchange for public disclosure of an invention.

Purpose: Success of a patent application results in the government granting the creator or assignee monopoly control and explicit right to preclude others from making, using, selling or offering for sale the subject matter as defined by the patent claim(s) for some limited period of time. The monopoly incentive secures the assignees right to financial benefit, helping to enable a prosperous society.

Types: There are three types of patents within the United States Patent and Trademark Office USPTO that define the general nature of an invention.

Utility patents may be granted to anyone who invents or discovers any new and useful process, machine, article of manufacture, or composition of matter, or any new and useful improvement thereof;

Design patents may be granted to anyone who invents a new, original, and ornamental design for an article of manufacture; and

Plant patents may be granted to anyone who invents or discovers and asexually reproduces any distinct and new variety of plant.

Claim(s): The most important aspect of a patent is its claim. The claim relates the invention to its commercial application, or “art”, to which the patent pertains. This is where the value of a patent lies, and is the focal point of most legal proceedings. The claim illustrates the technical use and various embodiments of the invention by setting limits on the extent of protection conferred or sought by the patent.

Protection: The current patent term in the United States is 20 years which provides a sustainable competitive advantage to the assignee, usually a commercial enterprise or corporation, to directly or indirectly commercialize their invention for profit. The patent, in and of itself, provides no legal protection to a patent holder, protection only comes in the form of an infringement lawsuit filed by a patent holder against a patent infringer, making the defense of patents a rich mans game and not a simple process.

Process: In the United States, an inventor has a period of one year to file a provisional patent application from the date of first public disclosure, first public sale, or first public offer to sell an invention. A provisional application serves as a place holder within the USPTO for the eventual filing of a non-provisional application. The provisional application applies only to utility patents and can be as short or extensive as necessary to encompass the nature of the invention including drawings, data, and descriptions, but can be void of any claim(s), oaths, or information disclosure statements.

Once opened, a provisional application can be updated and expanded upon for a period of one year during which time a full non-provisional patent application must be filed in order to benefit from the earlier filing date and support provided by the provisional application. To be useful, the material contained in the provisional filing must adequately support as best as possible the subject matter of the claim(s) made in the non-provisional application. Once granted, the patent date will become the non-provisional application filing date.

Jurisdiction: For a small company with limited time and money, the largest and most fruitful market to apply for patent protection is the USA. Then depending on the nature of the invention, potential for profit, and further need for protection, additional applications can be made with other jurisdictions around the world as deemed necessary. Unfortunately there is no such thing as an international patent.

To be safe, all filings should be made as early as possible since most jurisdictions consider anything filed one year past any public disclosure makes the invention public domain, and voids any right for patent protection.

Cost: For a small entity, if done by oneself working directly with the USPTO, and preferably written by the inventor, filing for a patent is initially more of a time consuming process than a financial expense. For a small business, the cost to file a provisional patent is only US $110, plus the cost of a non-provisional patent which is US $165. After which, the bulk of the expense becomes the patent maintenance fees of US $490 due after 3.5 years, US $1,240 due after 7.5 years, and US $2,055 due after 11.5 years. All costs are double for non-small entities.

Metallic lithium rechargeable battery technology was first developed prior to 1970 and is still being pursued today by companies such as the Bolloré Group of France who recently acquired Avestor from Hydro Quebec in March of 2007 and Sion Power of Arizona with their Lithium Sulfur system. The defining aspect of lithium battery technology is that the anode itself is made of pure lithium metal in the form of a foil. During discharge, lithium ions dissolve from the surface of the foil and transfer to the cathode via the electrolyte. During charge, the lithium ions transfer back to the anode to be electroplated back onto the surface of the lithium foil, reforming as pure lithium metal once again, losing their status as “ions”.

Benefits of metallic lithium anodes are they are light weight and have high reversible capacity of 3,860 mAh/g. Problems are they are highly alkali in nature causing them to react with the organic electrolyte forming a passivation layer on their surface which leads to non-uniform plating of lithium during the charging process and formation of dendrites causing short circuits and serious safety problems due to localized hot spots. To overcome these problems, researchers in the 1970’s began studying the use of anode intercalation materials to replace metallic lithium. The new anode materials operate in the same fashion as existing cathode materials in that they hold the lithium atoms by insertion site diffusion, except that the anode materials do it at a much lower voltage closer to that of metallic lithium. Hence the lithium “ion” battery was born, where lithium atoms remain separate from one another at all times while residing in either the anode or cathode electrodes, eliminating the trouble of uneven metallic plating and its associated problems.

Lithium ion cells are termed rocking-chair cells because the lithium ions rock back and forth during charging and discharging between the anode and the cathode intercalation materials. Anode intercalation materials have much lower reversible capacities compared to metallic lithium, but the benefits of improved safety and much higher cycle life quickly outweigh the drawbacks in most applications.

The electrochemical potential of anode and cathode materials are measured relative to pure metallic lithium reference electrodes representing zero Volts, such that when a cell is constructed from an anode material with 0.3 Volts potential and a cathode material with 4.0 Volts potential, relative to metallic lithium, the resulting cell voltage is calculated by the difference, 4.0–0.3=3.7 Volts.

The most common anode material in use today is carbon in its layered form as graphite or in its glassy amorphous form as hard carbon. Carbon is cheap, light, environmentally friendly, has high reversible capacity of 372 mAh/g,  excellent cycling characteristics, and low electrochemical potential relative to metallic lithium in the range of 0.2-1.0 Volts, helping to maintain an overall high cell voltage when mated with other various cathode materials. Problems with carbon anodes are they are voluminous and have high irreversible first charge capacity loss in the range of 20%.

A less popular anode intercalation material is lithium titanate used by Toshiba and Altairnano, these metal oxide materials have low capacities of only 150 mAh/g and high electrochemical potentials of around 1.5 Volts resulting in a much lower energy density cell. Benefits are very good cycle life, stable electrolyte, and high power characteristics.

New silicon anode materials have very high theoretical capacities up to 4,200 mAh/g, exceeding that of even pure lithium, and voltage potentials below 1.0 Volts, but suffer from high mechanical stressing during the lithiation-delithiation processes, resulting in rapidly fading capacity loss during cycling. Other promising areas for new anode material developments include other silicides, nitrides, and lithium metal alloys.

How much better? Let’s take a look.

There are four main rechargeable chemistries used today, lead acid, nickel cadmium, nickel metal hydride, and lithium ion, and conditions vary for how each is characterized in terms of capacity. Lead acid are tested using a C/20 discharge rate, while NiCd, NiMH, and lithium ion are all tested using a C/5 discharge rate. NiCd cells typically exceed their rated capacity by up to 10%, while NiMH often miss their rated capacity by up to 10%, and if we compress the discharge rate of lead acid testing from C/20 to C/5 making all things equal, we get a reduction in capacity of about 20%. So accounting for all these variations and adjustments, Table 1 roughly compares the chemistries on an even basis.

The lithium ion values represent a large format type manganese based cathode system similar to what are currently available from LG Chem and other manufacturers for electric vehicle applications.

Table 1

At present, lithium ion offers nearly an order of magnitude more, or 10 times the energy return over their lifetime than the next best chemistry NiMH, and nearly 25 times more than lead acid. Development work around the older chemistries is mainly complete now and stagnant, while development work around lithium ion technology is still young and fast paced, currently attracting thousands of scientist and researchers from around the world working toward yet to be discovered improvements and unlocking tremendous potential that still exists.

Practically, lithium ion energy density could be improved by a factor of 2-3 over the next 5-10 years, while cycle life improvement could also be doubled or quadrupled during the same period, resulting in an overall improvement by another factor of 5-10 from today.

As well as having superior “Energy Life-Cycle Product”, lithium ion cells have many other superior features that are both electrically and physically attractive in areas concerning discharge profile, charge-discharge efficiency, cost, manufacturing, environmental, and recycling.

Designation of the anode and cathode in a rechargeable cell are defined during the discharge process. The anode always refers to the negative electrode and the cathode always refers to the positive electrode, even though the reverse is actually true during charging, where the anode becomes the cathode and the cathode becomes the anode by definition of the terms anode and cathode. Common battery lingo maintains the anode cathode designations derived from the discharge process be applied when both discharging and charging in order to avoid confusion.

During discharge, the negative anode electrode is oxidized (loss of electrons is oxidation) and it is the source of electrons, while the positive cathode electrode is reduced (gain of electrons is reduction) and it is the receiver of electrons. Each electrode depends upon the other electrode to maintain a balance of flow of electrons. The number of electrons provided by the anode must equal the number of electrons received by the cathode.  Electrode materials are often described by their mAh/g capacity ratings, from which the amount of each material required for the construction of a balanced cell can be calculated.

During discharge, the number of electrons transferred in the external electric circuit from the anode to the cathode equals the number of ions (positive or negative atoms/molecules) that must be transferred by the cell’s internal electrolyte. The electrolyte is ionically conductive, but electronically non-conductive. The ionically conductive electrolyte completes the electro-chemical circuit by carrying only ions between the active cathode and anode materials. The electrode-electrolyte-electrode interfaces are where all the real action occurs within the cell, and these two interfaces determine much of the cells characteristics and features such as cell voltage, capacity, power capability, cycle life, calendar life, self discharge, temperature effects, safety, and more.

During charging, the anode and cathode reactions are reversed by forcing electrons to flow opposite in direction than they flowed during discharge. The charger must apply a voltage across the cells’ terminals that is higher in potential than the open circuit cell voltage in order to generate electron flow back into the anode from the cathode, electro-chemically reversing the chemical reaction that took place during the discharge phase. During charging the electrolyte must also reverse function and shuttle ions back from the cathode to the anode.

Simple, build an SUV that runs on batteries and electric motors, then burn that same gasoline at more than double the efficiency of an ICE in a thermal power generating station to generate electricity to charge the batteries.

Internal combustion engines, or ICE powered vehicles, roll down the road plowing through the atmosphere by way of energy extracted from liquid fuels. Energy contained in liquid fuels is converted to mechanical energy by expansion of hot gases in an engine’s cylinders. The start of the power stroke converts the vaporized air-fuel mixture into extremely hot, high pressure carbon dioxide and water gases. The fuel’s state is transformed from a dense hydro-carbon chained liquid into individual species of hot CO2 and H2O gases via combustion with atmospheric oxygen.

Thermal efficiency of an ICE to deliver mechanical work from heat energy is roughly 20%, meaning that 80% of the heat energy contained in the fuel is wasted, blown out the tail pipe and radiator system. The problem with piston powered ICE vehicles is one of thermal dynamic inefficiency. Hot gases expanding in the cylinders during the power stroke cool and work is done as per Boyle’s law of gases. The expansion and cooling of hot combustion gases is how heat energy is physically converted to mechanical energy and waste heat, but because the temperature of the exhaust gases are still very high, with them goes a lot of unharnessed energy.

The solution to ICE inefficiency is simple, burn the fuel in a better method in order to extract more bang for your buck, and that better method is a thermal power generating station. A modern thermal electric power station can burn any type of fuel with a thermal efficiency as high as 48%, and when combined in a co-generating facility that uses an electric generator’s waste heat to supply nearby heating and absorptive cooling requirements, the overall efficiency of the fuel burned can be as high as 89%.

Consider also the additional energy expended during the extraction, refining, production, and delivery of gasoline and diesel fuels; a steam boiler system even when powered by coal starts to look pretty good. Large amounts of electrical energy are used by refineries during the refining processes to run pumps and provide heating. Fuel products are treated with hydrogen injection during cracking to produce lighter fuels from heavier oils. These extra energy inputs could be eliminated if the raw crude oil were simply burned directly in a co-gen facility producing combined electricity, heating, and cooling services.

When one drills down to the nuts and bolts of conventional gasoline and diesel fuels used for transportation, one finds that coal powered thermal generating stations are not really the devil they’re made out to be, and in fact, the real devil is in the extremely inefficient way our society uses oil products for transportation fuels and internal combustion engines.

It’s a huge deal and it’s about reversible energy storage. Energy is neither created nor destroyed, but can only change state. Energy is stored in batteries electro-chemically, as opposed to just chemically, as it is in fuels such as gasoline, oil, coal, natural gas, and even hydrogen. Energy stored in batteries is fundamentally different than traditional energy carriers by the fact that electro-chemical energy stored in secondary rechargeable batteries is a reversible process, whereas energy stored in fossil fuels is a non-reversible process.

Due to the shortcomings of fossil fuels not being able to reversibly store energy, we have labeled them “sources of energy” rather than “storage of energy”, and common parlance considers fossil fuels as energy sources, rather than energy carriers, which is in fact what they are. While batteries are correctly considered energy carriers, they have the added benefit of being extremely efficient and reversible.

Fossil fuels are nothing more than energy carriers that were charged millions of years ago by energy originating from the sun, trapped in plankton and other little creatures and plants for our use today. The drawback of fossil fuel energy systems is that they are not reversible. Energy released by burning hydro-carbon chains of any type is not a reversible process, once a fossil fuel has been burned to chemically extract its heat value through reaction with atmospheric oxygen to form the products of CO2 and H2O gas, the process is in no way reversible.

So, what’s the big deal about batteries? Simply put, they are incredible in their ability to easily, efficiently, and reversibly store energy. No other portable mechanism comes even close to their ability to effectively store and return large amounts of useful energy in a controlled and reversible manor. Battery energy storage and retrieval efficiency is typically between 85-95% for a complete charge-discharge cycle, meaning that for every 1000 Watt-hours of electrical power delivered to the battery of an electric scooter or electric car, that battery will return 850-950 Watt-hours of useful energy to drive the wheels, run the air conditioner, blow the heater, and play the radio… and that is quite a big deal from which future ramifications will be enormous.