Composition of negative electrode material for power lithium-ion battery
As one of the main components of lithium-ion batteries, the negative electrode has a direct impact on and limits the electrochemical performance and application range of the battery system, such as the active components of the material, the size, morphology, and electrode composition of the active particles. At present, the anode materials used in lithium-ion batteries include carbon materials (graphite carbon materials, non-graphite carbon materials) anodes and non-carbon materials (alloy anodes and metal oxides) anodes. Non-graphite anode materials mainly include silicon (Si)-based materials, lithium titanate (Li4Ti5O12) and tin (Sn)-based materials.
Carbon/graphite material has a high theoretical specific energy (372mAh/g), is cheap and easy to obtain, and the preparation process is mature, so it is widely used. However, the first charge of the carbon/graphite negative electrode will form a solid electrolyte membrane (SEI) on the surface of the carbon particles, resulting in a loss of battery capacity, and the amount of solid electrolyte membrane (SEI) generated increases with the increase in the number of charge and discharge cycles, and the internal impedance of the battery increases. , The specific energy and power performance are reduced. The modification methods of graphite anode materials include surface oxidation, surface coating, element doping and so on. According to the type of coating material, surface coating includes surface carbon coating, metal and its oxide coating, polymer coating and so on. Carbon coating includes soft carbon coating and hard carbon coating (resin coating).
In theory, some metals or metalloids that can form alloys with lithium can be used as anode materials for lithium-ion batteries, such as Si, Ge, Sn, Pb, Al, etc. These materials are collectively referred to as alloy anode materials. Compared with graphite, the theoretical lithium storage capacity of alloy anode materials is large, and the lithium storage potential is low. The theoretical capacity of silicon (Si) is as high as 4200mAh/g, which is much higher than graphite and other carbon anode materials. It is the highest theoretical capacity among various alloy materials currently studied; the voltage of lithium insertion into silicon is lower than 0.5v, and the insertion process There is no co-intercalation of solvent molecules, which is very suitable as a negative electrode material for lithium-ion batteries. At present, the preparation methods of silicon materials mainly include chemical vapor deposition, vacuum evaporation, thermal spraying, and sputtering. However, in terms of process maturity, stability, controllability, efficiency and cost, magnetron sputtering technology is better than Other methods.
Lithium titanate (Li4Ti5O12) has a spinel structure. When used as a negative electrode material for lithium-ion batteries, it has a small volume change, a very stable structure, excellent cycle performance and a stable discharge voltage, and a higher electrode voltage. It is a raw material for preparation More abundant, and the price is cheap. However, the capacity is smaller than that of the carbon anode material, and the potential is too high relative to the metal lithium electrode. At present, the synthesis methods of lithium titanate (Li4Ti5O12) mainly include solid-phase reaction method and sol-gel method.
Development status of various anode materials:
Natural graphite: has been tried in batches
Advantages: mature technology and supporting process, low cost.
Disadvantages: the specific energy has reached the limit, the cycle performance and rate performance are poor, and the safety performance is poor.
Artificial graphite: has been applied in small batches
Advantages: mature technology and supporting process, good cycle performance.
Disadvantages: low specific energy, poor rate performance, and poor safety performance.
Mesocarbon microspheres: Has been used in batches
Advantages: mature technology and supporting processes, good rate performance, and good cycle performance.
Disadvantages: low specific energy, poor safety performance, and high cost.
Hard Carbon: Trial in small batches
Advantages: high reversible capacity, large capacity improvement space, good rate performance, and good safety performance.
Disadvantages: immature technology and supporting processes, low first-time efficiency, high cost, and poor processing performance.
Lithium titanate: Trial in small batches
Advantages: excellent rate performance, excellent high and low temperature performance, excellent cycle performance, and excellent safety performance.
Disadvantages: immature technology and supporting process, high cost, low specific energy.
Metal alloys: development stage
Advantages: high reversible capacity, large capacity improvement space, and good safety performance.
Disadvantages: immature technology and supporting processes, low first-time efficiency, high cost, poor processing performance, poor cycle performance and rate performance.