The selection of cell materials is related to product performance, safety and cycle life.
1. Selection of cathode materials
The selection of cathode materials for lithium-ion batteries should meet the following requirements:
The electrode potential relative to lithium is high, the composition of the positive electrode material does not change with the potential, and the ionic conductivity and electronic conductivity are high, which is conducive to reducing the internal resistance of the battery. The intercalation and deintercalation of lithium ions are reversible, and the volume change accompanying the reaction is small. The diffusion rate of lithium ions is fast, and good cycle characteristics and high current characteristics can be obtained. In addition, it has good contact performance with organic electrolytes and binders, and good thermal stability, which is beneficial to prolong battery life and improve safety performance.
2. Selection of anode material
In the 1980s, it was found that the potential of the intercalation reaction of lithium in carbon materials is close to that of lithium, and it is not easy to react with organic solvents and has good cycle performance. Using carbon material as the negative electrode, when charging and discharging, the lithium in the solid phase will undergo intercalation and deintercalation reaction.
The selected carbon anode material should meet the following requirements: (1) High lithium storage capacity. (2) The intercalation and deintercalation reactions of lithium in carbon are fast, that is, the diffusion coefficient of lithium ions in the solid phase is large, and the moving impedance at the electrode/electrolyte interface is small. (3) The existence of lithium ions in the electrode material is stable. (4) During the charge-discharge cycle of the battery, the volume change of the carbon anode material is small. (5) High electronic conductivity. (6) The carbon material does not dissolve in the electrolytic solution.
3. Selection of electrolyte
The electrolyte used in lithium ion batteries is an ionic conductor in which electrolyte lithium salt is dissolved in an organic solvent. Although there are many types of organic solvents and lithium salts, the ones that can really be used in lithium-ion batteries are very limited.
The selection of electrolyte should meet the following requirements: (1) High ionic conductivity. (2) The lithium ion migration number should be close to 1. (3) The potential range of electrochemical stability is wide. (4) There must be an electrochemical stability window of 0~5V. (5) Good thermal stability and wide operating temperature range. (6) The chemical properties are stable, and there is no chemical reaction with the current collectors and tactile substances in the battery. (7) Safe, low toxicity and biodegradable. The inorganic anion conductive salts currently developed mainly include three categories: LiBF4, LiPF6, and LiAsF6.
4. Selection of isolation film
The main function of the separator is to separate the positive and negative electrodes of the battery to prevent short circuit due to contact between the two electrodes, and also has the function of allowing electrolyte ions to pass through. The material of the separator is non-conductive, and its physical and chemical properties have a great influence on the performance of the battery. Different types of batteries use different separators. For the lithium-ion battery series, since the electrolyte is an organic solvent system, an organic solvent-resistant separator material is required, and a high-strength thin-film polyolefin porous membrane is generally used.
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