Archive for October, 2009

Lithium Ion – Head and Shoulders Above The Rest

Saturday, October 24th, 2009

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

Chemistry Nominal Cell Voltage Capacity Ahr/kg C/5 discharge rate Energy Whr/kg C/5 discharge rate Life Cycles 100% DoD fade to 80% Energy Life-Cycle Product kWhr/kg
Sealed Lead Acid 2.0 12.5 25 500 13
Nickel Cadmium 1.2 31.6 38 700 27
Nickel Metal Hydride 1.2 53.3 64 500 32
Lithium Ion 3.7 39.2 145 2000 290

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.

Cell Basics, Anode, Cathode and Electrolyte Functions

Saturday, October 17th, 2009

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.

How to double the MPG of an SUV running on gasoline

Wednesday, October 14th, 2009

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.

Batteries… what’s the big deal?

Monday, October 12th, 2009

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.