Introduction to the basic composition of lithium batteries

There are several basic materials inside the lithium battery: positive active material, negative active material, separator, electrolyte. Let's briefly discuss what these materials are for. It is not difficult to understand the positive and negative electrodes. To realize charge transfer, there must be positive and negative materials with a potential difference. So what is an active material? We know that batteries actually convert electrical and chemical energy to each other to achieve energy storage and release. To achieve this process, the materials of the positive and negative electrodes are required to easily participate in chemical reactions, be active, and be easy to oxidize and reduce, so as to realize energy conversion. Therefore, we need active materials to make the positive and negative electrodes of the battery. As mentioned above, lithium is our preferred material for batteries, so why not use metallic lithium as the active material of the electrode? Isn't it possible to achieve the maximum energy density? Let’s look at the above picture again. The three elements of oxygen (O), cobalt (Co) and lithium (Li) form a very stable positive electrode material structure (the ratio and arrangement in the picture are for reference only), and the carbon atoms of the negative electrode graphite The arrangement also has a very stable layered structure. The positive and negative electrode materials must not only be active, but also have a very stable structure in order to achieve orderly and controllable chemical reactions. What are the unstable results? Think of gasoline burning and bomb explosions, and the energy is violently released. The process of this chemical reaction is actually impossible to precisely control artificially, so the chemical energy becomes heat energy, which releases the energy at one time and is irreversible. Lithium in the form of metal is too lively. Most naughty children are disobedient and like to do damage. Early research on lithium batteries was really focused on using metallic lithium or its alloy as the negative electrode, but because of outstanding safety issues, other better paths had to be found. In recent years, with people's pursuit of energy density, this research direction has a trend of full blood resurrection, which we will talk about later. In order to achieve chemical stability in the process of energy storage and release, that is, the safety and long life of battery charge and discharge cycles, we need an electrode material that is active when it is to be active and stable when it is to be stable. After long-term research and exploration, people have found several lithium metal oxides, such as lithium cobaltate, lithium titanate, lithium iron phosphate, lithium manganate, nickel cobalt manganese ternary materials, etc., which can be used as the active or negative electrode of the battery. Material, to deal with the above problems. As shown in the figure above, the olivine structure of lithium iron phosphate is also a very stable cathode material structure. The deintercalation of lithium ions during charging and discharging does not cause lattice collapse. As a digression, there are indeed lithium metal batteries, but they are almost negligible compared with lithium batteries. The development of technology will ultimately serve the market. Of course, while dealing with the stability problem, it also brings serious side-uses, that is, the proportion of lithium as an energy carrier has been greatly reduced, and the energy density has dropped by more than an order of magnitude. If you have gains, you will lose. Natural way. . The negative electrode usually chooses graphite or other carbon materials as the active material. It also follows the above-mentioned principles. It requires not only a good energy carrier, but also relatively stable, and relatively rich reserves, which is convenient for large-scale manufacturing. The element is a relatively optimal solution. Of course, this is not the only solution. There are extensive researches on anode materials, which will be discussed later. What do electrolytes do? In layman's terms, it is the water in the swimming pool that allows lithium ions to swim around freely. Therefore, the ion conductivity should be high (the resistance to swimming is small), the electronic conductivity should be small (insulation), and the chemical stability should be good ( Stability is overriding), thermal stability is better (all for safety), and the potential window should be wide. Based on these principles, after long-term engineering exploration, people have found an electrolyte prepared from raw materials such as high-purity organic solvents, electrolyte lithium salts, and necessary additives under certain conditions and in certain proportions. Organic solvents include PC (propylene carbonate), EC (ethylene carbonate), DMC (dimethyl carbonate), DEC (diethyl carbonate), EMC (ethyl methyl carbonate) and other materials. Electrolyte lithium salts include LiPF6, LiBF4 and other materials. The isolation film is added to prevent the positive and negative materials from directly contacting. We hope to make the battery as small as possible and store as much energy as possible, so the distance between the positive and negative electrodes is getting smaller and smaller, and the short circuit Become a huge risk. In order to guard against the short-circuit of the positive and negative materials, causing the violent release of energy, a material must be used to separate the positive and negative electrodes. This is the origin of the separator. The isolation membrane must have good ion permeability, and it is important to open channels for lithium ions to allow them to pass freely. At the same time, it is an electronic insulator to achieve insulation between the positive and negative electrodes. At present, the diaphragms on the market mainly include single-layer PP, single-layer PE, double-layer PP/PE, and three-layer PP/PE/PP composite films. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: How long is the true life of the mobile phone battery?