Lithium iron phosphate battery


The lithium iron phosphate battery or LFP battery, is a type of lithium-ion battery using lithium iron phosphate| as the cathode material, and a graphitic carbon electrode with a metallic backing as the anode. The energy density of is lower than that of lithium cobalt oxide chemistry, and also has a lower operating voltage. The main drawback of is its low electrical conductivity. Therefore, all the cathodes under consideration are actually /C. Because of low cost, low toxicity, well-defined performance, long-term stability, etc. is finding a number of roles in vehicle use, utility scale stationary applications, and backup power.

History

is a natural mineral of the olivine family. Arumugam Manthiram and John B. Goodenough first identified the polyanion class of cathode materials for lithium ion batteries. was then identified as a cathode material belonging to the polyanion class for use in batteries in 1996 by Padhi et al. Reversible extraction of lithium from and insertion of lithium into was demonstrated. Because of its low cost, non-toxicity, the natural abundance of iron, its excellent thermal stability, safety characteristics, electrochemical performance, and specific capacity it has gained considerable market acceptance.
The chief barrier to commercialization was its intrinsically low electrical conductivity. This problem was overcome by reducing the particle size, coating the particles with conductive materials such as carbon nanotubes, or both. This approach was developed by Michel Armand and his coworkers. Another approach by Yet Ming Chiang's group consisted of doping LFP with cations of materials such as aluminium, niobium, and zirconium.
MIT introduced a new coating that allows the ions to move more easily within the battery. The "Beltway Battery" utilizes a bypass system that allows the lithium ions to enter and leave the electrodes at a speed great enough to fully charge a battery in under a minute. The scientists discovered that by coating lithium iron phosphate particles in a glassy material called lithium pyrophosphate, ions bypass the channels and move faster than in other batteries. Rechargeable batteries store and discharge energy as charged atoms are moved between two electrodes, the anode and the cathode. Their charge and discharge rate are restricted by the speed with which these ions move. Such technology could reduce the weight and size of the batteries. A small prototype battery cell has been developed that can fully charge in 10 to 20 seconds, compared with six minutes for standard battery cells.
Negative electrodes made of petroleum coke were used in early lithium-ion batteries; later types used natural or synthetic graphite.

Advantages and disadvantages

The battery uses a lithium-ion-derived chemistry and shares many advantages and disadvantages with other lithium-ion battery chemistries. However, there are significant differences.
LFP contain neither nickel nor cobalt, both of which are supply constrained and expensive.
LFP chemistry offers a longer cycle life than other lithium-ion approaches.
Like nickel-based rechargeable batteries, batteries have a very constant discharge voltage. Voltage stays close to 3.2 V during discharge until the cell is exhausted. This allows the cell to deliver virtually full power until it is discharged, and it can greatly simplify or even eliminate the need for voltage regulation circuitry.
Because of the nominal 3.2 V output, four cells can be placed in series for a nominal voltage of 12.8 V. This comes close to the nominal voltage of six-cell lead-acid batteries. Along with the good safety characteristics of LFP batteries, this makes LFP a good potential replacement for lead-acid batteries in applications such as automotive and solar applications, provided the charging systems are adapted not to damage the LFP cells through excessive charging voltages, temperature-based voltage compensation, equalisation attempts or continuous trickle charging. The LFP cells must be at least balanced initially before the pack is assembled and a protection system also needs to be implemented to ensure no cell can be discharged below a voltage of 2.5 V or severe damage will occur in most instances.
The use of phosphates avoids cobalt's cost and environmental concerns, particularly concerns about cobalt entering the environment through improper disposal.
has higher current or peak-power ratings than.
The energy density of a new LFP battery is some 14% lower than that of a new battery. Also, many brands of LFPs, as well as cells within a given brand of LFP batteries, have a lower discharge rate than lead-acid or. Since discharge rate is a percentage of battery capacity a higher rate can be achieved by using a larger battery if low-current batteries must be used. Better yet, a high current LFP cell can be used.
cells experience a slower rate of capacity loss than lithium-ion battery chemistries such as cobalt or manganese spinel lithium-ion polymer batteries or lithium-ion batteries. After one year on the shelf, a cell typically has approximately the same energy density as a Li-ion cell, because of LFP's slower decline of energy density.

Safety

One important advantage over other lithium-ion chemistries is thermal and chemical stability, which improves battery safety. is an intrinsically safer cathode material than and manganese spinel, through omission of the cobalt, with its negative temperature coefficient of resistance that can encourage thermal runaway. The P–O bond in the Phosphate| ion is stronger than the Co–O bond in the ion, so that when abused, the oxygen atoms are released more slowly. This stabilization of the redox energies also promotes faster ion migration.
As lithium migrates out of the cathode in a cell, the undergoes non-linear expansion that affects the structural integrity of the cell. The fully lithiated and unlithiated states of are structurally similar which means that cells are more structurally stable than cells.
No lithium remains in the cathode of a fully charged cell. is highly resilient during oxygen loss, which typically results in an exothermic reaction in other lithium cells. As a result, cells are harder to ignite in the event of mishandling. The battery does not decompose at high temperatures.

Specifications

Transportation

Higher discharge rates needed for acceleration, lower weight and longer life makes this battery type ideal for forklifts, bicycles and electric cars. 12V LiFePO4 batteries are also gaining popularity as a second battery for a caravan, motor-home or boat.

Solar-powered lighting systems

Single "14500" LFP cells are now used in some solar-powered landscape lighting instead of 1.2 V NiCd/NiMH.
LFP's higher working voltage lets a single cell drive an LED without circuitry to step up the voltage. Its increased tolerance to modest overcharging means that can be connected to photovoltaic cells without circuitry to halt the recharge cycle. The ability to drive an LED from a single LFP cell also obviates battery holders, and thus the corrosion, condensation and dirt issues associated with products using multiple removable rechargeable batteries.
By 2013, better solar-charged passive infrared security lamps emerged. As AA-sized LFP cells have a capacity of only 600 mAh, the units shine for at most 10 hours. However, if triggering is only occasional, such units may be satisfactory even charging in low sunlight, as lamp electronics ensure after-dark "idle" currents of under 1 mA.

Other uses

Many home EV conversions use the large format versions as the car's traction pack. With the efficient power-to-weight ratios, high safety features and the chemistry's resistance to thermal runaway, there are few barriers for use by amateur home "makers". Motorhomes are often converted to lithium iron phosphate because of the high draw.
Some electronic cigarettes use these types of batteries. Other applications include flashlights, radio-controlled models, portable motor-driven equipment, amateur radio equipment, industrial sensor systems and emergency lighting.