1. Electrode material

(1) Positive electrode material

a. On the basis of traditional cathode materials (LiCoO2, LiMn2O4, LiFePO4, etc.), develop various related derivative materials, through doping, coating, adjusting microstructure, controlling material morphology, size distribution, specific surface area, impurity content, etc. Technical means to comprehensively improve its specific capacity, rate, cyclability, compaction density, electrochemical, chemical and thermal stability.

b. Ternary materials (LiNixCoyMn1-x-y) and lithium-rich materials (Mn-based and V-based) have large development and technical research space and broad application prospects. Therefore, nickel-cobalt-manganese ternary materials, lithium-rich manganese-based vanadium-based materials, composite cathode materials with excellent performance, and high-efficiency and energy-saving polyanion group cathode materials are the mainstream of cathode materials for lithium-ion batteries in the future; development of more efficient and energy-saving new cathode materials Materials to overcome and replace the existing defective cathode materials are also a research hotspot.

c. A series of transition metal fluorides, oxides, sulfides and nitrides have been demonstrated to achieve multi-electron transfer and achieve high capacity. The electrode material that realizes the lithium storage function based on the conversion reaction mechanism has a specific capacity that is more than 2-4 times higher than that of the traditional lithium-ion battery electrode material based on the lithium ion intercalation and extraction mechanism. However, there are still many problems to be solved. There are relatively few studies on such materials, and there are still many unclear places in the mechanism.

d. Looking at the literature, some people have made organic cathode materials, which are mainly divided into conductive polymers, sulfur-containing compounds, nitroxide radical compounds and carbonyl compounds, etc. (I don’t know much about it, if there is hope for understanding can be added).

Among them, P1 and P2 are organic electrode materials (which can be small molecules or polymers), and M+ and A+ are doped positive and negative ions, usually Li+, Na+, (C4H9)4N+, Cl\CICV, PF6-, etc. P1-M+, P2+A-, PI+A-, P2-M+ are doped organic electrode materials.

(2) Negative electrode material

a. Carbon-based materials

Including important future development will focus on high-power graphite anodes and non-graphite high-capacity carbon anodes (soft carbon, hard carbon, etc.) to meet the needs of future power and high-energy batteries. Novel carbon materials: such as carbon nanotubes (CNTs), graphene, due to their special 1D and 2D flexible structures, excellent thermal conductivity and electrical conductivity, reduce their cost towards high energy density, high cycle characteristics and low cost. direction development.

b. Non-carbon materials

LTO can be analogous to carbon-based materials. Fe, Ge, Sn, Si and other metal or semiconductor materials are the current research hotspots. It can be formed around the directions of coating, surface modification, nanometerization, and compounding in order to reduce its volume expansion. Stable SEI film, the specific capacity of this type of metal material, especially Si, is very high, and it should be an ideal cathode material for next-generation lithium-ion batteries, but the problems of volume expansion and SEI instability have not been well solved. It restricts its development to a certain extent, especially the advantage of volume energy density related to graphite anode is far inferior to the theoretical calculation results, so it is not an absolute advantage in application. In the end, the anode material of lithium ion battery is likely to return to Li The element itself, lithium metal rechargeable lithium-ion batteries, all-solid-state lithium-ion batteries, lithium-sulfur batteries, and lithium-air batteries and other new batteries are being extensively studied.

2. Electrolyte materials

It is important to increase the voltage window of the electrolyte, reduce the cost, the temperature range of the electrolyte, improve the ionic conductivity of the solid electrolyte, and control the formation of a stable SEI film.

(1) Liquid electrolyte:

At this stage, LiPF6, EC plus one or more linear carbonates are generally used as solvents, and various types and occasions are tested by adding different additives, using different solvents and replacing different lithium salts, because LIPF6/ EC: The operating temperature range of the DMC electrolyte system is -20 to 50 °C. At this stage, there are also many attempts to use ionic liquids, which have a wider temperature range, lower vapor pressure, good electrochemical performance and electrochemical stability, but are very expensive (Professor Dai Hongjie’s aluminum ion battery Nature is an ionic liquid used) , and then the development of gel/solid electrolytes; secondly, high-voltage electrolytes can be solved by purifying solvents, using ionic liquids, fluorocarbonates, adding positive electrode surface film additives, etc. The same development of solid electrolytes can also significantly improve the voltage range.

(2) Gel electrolyte

Commonly used gel-type polymer electrolyte matrices are: polyacrylonitrile (PAN), polyethylene oxide (PEO), polymethacrylic acid, methyl ester (PMMA), polyvinylidene fluoride (PVDF) and the like. Gel-type polymer electrolytes have less pollution to the environment and better safety performance, and are very popular in the battery market. In recent years, the development trend is to obtain high porosity, low electrical resistance, high tear strength and better acid and alkali resistance by means of modified copolymerization or blending of nanoparticles (commonly used inorganic fillers are SiO2, Al2O3). Capability and good elasticity of the electrolyte membrane.

(3) Solid electrolyte

Solid electrolytes are generally called fast ionic conductors, which require high ionic conductivity, low electronic conductivity and low activation energy. To be honest, I think the solid electrolyte should be the final BOSS of the lithium ion electrolyte. Its proposal is to solve all the problems of the lithium ion electrolyte at this stage, so the development goal is to fundamentally solve the safety problems of the currently used lithium ion batteries and improve the Energy density, cyclability, service life, lower battery costs, and more.

3. Development and Outlook

When some problems of metal lithium dendrite and safety are solved, lithium metal is likely to become the final anode material for lithium-ion batteries. The following figure shows the development plan of lithium ion batteries from the perspective of theoretical calculation in a literature, from lithium ion batteries to lithium metal batteries, and then to lithium fuel power cells. Therefore, based on this: For lithium-ion batteries, from the perspective of increasing energy density year by year, the future development trend of rechargeable lithium-ion batteries may be:

A new generation of lithium-ion batteries using high-capacity positive electrodes, high-voltage positive electrodes, and high-capacity negative electrodes, such as LiNi1/2Mn3/2O4xLi2MnO3(1–x)LiNi1/3Co1/3Mn1/3O2 as the positive electrode and high-capacity Si-based materials as the negative electrode ion battery.

A rechargeable lithium-ion battery with metallic lithium as the negative electrode. Graphite fluoride (CF)n has an operating voltage of 2.9V and a lithium storage capacity of 800mAh/g. Li/(CF)n batteries have high mass energy density, but they cannot be cycled yet. Other lithium-ion batteries, such as Li/FeF3, Li/MnO2, Li/FeS2 batteries, can not fully meet the application requirements in terms of cycle performance, safety and other comprehensive properties.

It is expected that the first realization may be a rechargeable lithium-ion battery using metal lithium as the negative electrode and using the existing positive electrode material of lithium-ion battery.

The final developed high-energy-density battery should be a rechargeable lithium-ion battery with metal lithium as the negative electrode and O2, H2O, CO2, and S as the positive electrode.