Introduction of Electric Bike Lithium Battery

Brief introduction of lithium battery types

Lithium-ion batteries can be divided into two categories: liquid lithium-ion batteries (LIB) and polymer lithium-ion batteries (LIP for short). Polymer lithium-ion batteries can be divided into solid polymer electrolyte lithium-ion batteries, gel polymer electrolyte lithium-ion batteries and lithium-ion batteries made of polymer cathode materials; According to the cathode materials, it is divided into lithium cobaltate, lithium manganate, lithium nickelate, ternary materials, lithium iron phosphate, etc. Most of the mobile power supplies are made of lithium manganate. Like our usual mobile phone batteries, many of them are made of lithium manganate and lithium cobaltate.

At present, the mainstream materials in the electric vehicle market are ternary lithium batteries (lithium nickel cobalt manganate (nichomn) O2), lithium manganate (LiMn2O4) and lithium iron phosphate (LiFePO4). At present, the most promising anode materials used in power lithium ion batteries are mainly modified lithium manganate (LiMn2O4), lithium iron phosphate (LiFePO4) and lithium nickel cobalt manganate (Li (Ni, Co, Co, Li) Ternary li-polymer of ternary lithium battery is a lithium battery whose positive electrode material is lithium nickel cobalt manganate (Li(NiCoMn)O2). The precursor product of ternary composite positive electrode material takes nickel salt, cobalt salt and manganese salt as raw materials, and the ratio of nickel cobalt manganese in it can be adjusted according to actual needs. Compared with lithium cobaltate battery, the battery with ternary material as positive electrode has higher safety, balanced capacity and safety, and better cycle performance than normal lithium cobaltate. In the early stage, due to technical reasons, its nominal voltage was only 3.5-3.6V, which limited its application range. But up to now, with the continuous improvement of formula and perfect structure, the nominal voltage of the battery has reached 3.7V, and its capacity has reached or exceeded the level of lithium cobalt oxide battery. SANYO, PANASONIC, SONY, LG and SAMSUNG, the world's five major battery brands, have introduced ternary batteries. A considerable number of notebook battery lines have replaced the previous lithium cobaltate batteries with ternary batteries. In terms of SANYO and SAMSUNG column batteries, the production of lithium cobaltate batteries has been completely discontinued and turned to ternary batteries. At present, most small high-rate power batteries at home and abroad use ternary cathode materials. Lithium manganate battery is a battery whose positive electrode is made of lithium manganate. The nominal voltage of lithium manganate battery is 2.5~4.2v V. Lithium manganate battery is widely used for its low cost and good safety. 

lithium manganate battery has a nominal voltage of 3.7v, the internal resistance of the finished product is ≤ 200mω, and the product size is max19.2 * 56.5 * 69.5mm.

The cathode material with low cost, good safety and low temperature performance, but its material itself is unstable and easy to decompose to generate gas, so it is mostly used in mixing with other materials to reduce the cost of batteries. However, its cycle life decays rapidly, it is prone to bulge, its high temperature performance is poor, and its life is relatively short. It is mainly used for large and medium-sized batteries and power batteries, and its nominal voltage is 3.7V. Common problems, such as bulging batteries and flatulence, are the outflow of electrolyte.

The full name of lithium iron phosphate battery is lithium iron phosphate lithium ion battery, which is too long. Because its performance is especially suitable for power application, the word "power" is added to its name, namely lithium iron phosphate power battery. Some people also call it "lithium iron (LiFe) power battery".

High efficiency output: standard discharge is 2 ~ 5 C, continuous high current discharge can reach 10C, and instantaneous pulse discharge (10S) can reach 2～5C;

Good performance at high temperature: the internal temperature is as high as 95℃ when the external temperature is 65℃, and the temperature can reach 160℃ when the battery is discharged, so the structure of the battery is safe and intact;

Even if the inside or outside of the battery is damaged, the battery does not burn, does not explode and has the best safety;

Excellent cycle life, after 500 cycles, its discharge capacity is still greater than 95%; The cycle life of the battery pack should be 800 ~ 2000 times.

Over-discharge to zero volts is not damaged;

Can be charged quickly;

Low cost;

The lithium iron phosphate battery with the same size and capacity is 1/3 of that of lead-acid battery and 1/3 of that of lead-acid battery.

There is no pollution to the environment. The battery does not contain any heavy metals and rare metals (Ni-MH batteries need rare metals), is non-toxic (SGS certification passed), is pollution-free, conforms to European ROHS regulations, and is an absolute green battery. However, there is a large amount of lead in lead-acid batteries, which will still cause secondary pollution to the environment if it is not disposed properly after being discarded, while lithium iron phosphate materials have no pollution during production and use.

Comparison of ternary lithium battery and lithium iron phosphate battery

Using the same battery structure, ternary materials and lithium iron phosphate materials were selected to make batteries, and the tests of discharge, charging and cycling were carried out under different conditions. Ternary materials have advantages in charge rate, discharge rate and discharge performance at different temperatures, while lithium iron phosphate materials have better cycling performance, and can still maintain more than 80% of the initial capacity after 5 000 cycles in 1 C.. Lithium iron phosphate battery is also superior to ternary materials in safety.

For example, conventionally, the single cell of ternary lithium battery is 800 times, and the cycle life of group battery is 400-500 times; Good low temperature performance. The cycle life of lithium iron battery cell is 2000 times, and the cycle life of group battery is 800-1000 times; Lithium iron batteries are available in 18650 cylinders (cylindrical and slightly larger in size than ternary lithium batteries), and also in soft packages.

Disadvantages of lithium iron phosphate battery: The tap density of the positive electrode of lithium iron phosphate battery is small, and the density is generally about 0.8 to 1.3. Big volume.

 Poor conductivity, slow diffusion rate of lithium ions, and low actual specific capacity when charging and discharging at high times. Low temperature performance of lithium iron phosphate battery is poor. (in a particularly cold environment, such as cold in winter in Europe, electricity can not be released at temperatures above-10℃).

Storage and maintenance of lithium batteries

It is better to discharge the lithium battery partially instead of completely, and try to avoid frequent complete discharge. It's best to unplug the battery immediately after it is fully charged.

The aging rate of lithium battery is determined by temperature and charging state. The following table illustrates the reduction of battery capacity under two parameters.

Temperature                                  charge 40%                                                charge 100%

       0°C                             98% capacity after one year                        94% capacity after one year 

      25°C                            96% capacity after one year                        80% capacity after one year             

      40°C                            85% capacity after one year                        65% capacity after one year  

      60°C                            75% capacity after one year                        60% capacity after three months

Maintenance: the ternary lithium battery is over-discharged, and the battery is also damaged when the voltage is too low. It is recommended to maintain it every three months. If possible, try to charge the battery to 40% and keep it in a cool place. In this way, the battery's own protection circuit can operate within a long storage period. If the battery is placed at high temperature after being fully charged, it will cause great damage to the battery.

Storage: Short-term storage: Store the battery in a dry, non-corrosive gas place with a temperature and humidity between-20 C and 35 C 65 20%. If the temperature and humidity are higher or lower than this temperature and humidity, the metal parts of the battery will rust or the battery will leak. 

Long-term storage: As long-term storage will accelerate the self-discharge and passivation of active substances of the battery, the ambient temperature and humidity should be between 10 C and 30 C 65 20%. At the same time, in order to reduce the negative impact of self-discharge and passivation of active substances caused by long-term storage (such as more than one year), the battery should be charged and discharged once every three months to restore its original performance.

Life: Under normal circumstances, the best service temperature of lithium battery is 20 ~25℃, so under the condition of bottom temperature, the service life of lithium battery will be reduced by half. If the normal life is 500 cycles, the bottom temperature may only be less than 300 times. If the temperature exceeds -20℃, the ternary battery may not be used at all. If the temperature exceeds -10℃, the capacity of lithium iron battery will not be released.