- LiCoO2 is the first commercial use for positive material and also the most normal and largest consumption recently days. This material has the excellent electrochemical properties, such as first cycle irreversible, small capacity loss, high efficiency on charge and discharge, good thermal stability, long cycle life and 3.6v working voltage. But cobalt has higher cost and lacks of resource, in order to reduce the cost of battery, cheaper materials with little cobalt or no cobalt must to be developed.
- LiNiO2 has the good advantage in price and reserves, and its real capacity has been closed to 70-80% of the theoretical capacity. LiNiO2 has the excellent advantages of lower discharge rate, no environment pollution and lower requirements for electrolyte. But its initial discharge efficiency is just about 85%, in addition, thermal stability of battery may cause some safety problems. To achieve a better practical effect, the discharge and charge efficiency and thermal stability need to be improved. At the same time, production methods should be adapted to the requirements of industrial production.
- Lithium Manganese Oxide(LiMn2O4)
LiMn2O4 not only has advantage on price, but also has the advantage of good safety, no environment pollution, low toxicity and easy recovery, high working voltage and lower cost. The three-dimensional tunnel structure is more conducive to the intercalation and deintercalation of lithium ion battery than ratio of intercalation compounds. However, the compatibility of LiMn2O4 and electrolyte is not good, and the cycle life under high temperature and high voltage is also a problem. LiMn2O4 is the main research object and the most promising positive material for lithium ion batteries at present and in the future.
The key lies in the Negative Material can reversibly intercalate and deintercalate lithium ion. This kind of material should have the best possible low electrode voltage, the ion has the high diffusion rate, the high degree of reversibility, the good electrical conductivity and the thermodynamic stability. At present, carbon materials are mainly used in the Negative Material.
- Soft carbonThe arrangement of soft carbon layered structure is disordered, so it’s difficult to embed and deintercalate from Li ion. At the same time, due to the larger surface, forming more SEI layer, so there is a large irreversible capacity to loss. In addition, during the process of discharge, the voltage change is large.
- Hard carbonHard carbon has a very high lithium intercalation capacity, but the vast majority of the lithium potential is 0V, so it is difficult to control the precipitation of metal lithium.
Electrolyte is the carrier of lithium ion in the reaction process. In order to meet the requirements of lithium ion battery performance , the use of the lithium ion battery should meet the following requirements:
- The ionic conductivity of lithium ion conduction is as high as possible;
- The potential range of electrochemical stability is as wide as possible;
- Good thermal stability, the use of the temperature range as wide as possible;
- Good chemical stability, and collection of fluid inside battery and reactive substancesthe have no reaction;
- Good safety and low toxicity, it is best to biodegradable;
- Low price.
Separator is between positive and negative electrodes, which is mainly to prevent the positive and negative electrode connect directly resulting the battery internal short circuit. Polyolefin porous film used in lithium ion batteries, the thickness is about 25um. The Performance requirements are:
- Good stability in the use of electrolytes；
- Do not absorb moisture；
- Have excellent insulation to the positive and negative electrode；
- Ionic conductivity；
- Enough mechanical strength；
- With the hot melt：When the temperature is about 130℃, the diaphragm has the function of organizing ion penetration and automatic termination of battery discharge. This function is very important for the safety of the battery.
Due to the above conditions, the most commonly used diaphragm is PP (polypropylene) /PE (polyethylene) bilayer microporous film.