Jun 25, 2019 Pageview：27
At present, battery systems selected by Chinese new energy automobile manufacturers mainly include ternary materials/graphite system, lithium iron phosphate/graphite system and ternary batteries/lithium titanate system. The representative automobile enterprises that choose sanyuan battery are geely, chang 'an, baic, saic, jac, etc. The representative automobile enterprises that choose lithium iron phosphate battery are byd, and the representative automobile enterprises of sanyuan/lithium titanate battery are zhuhai yinlong.
In March 2017, the ministry of industry and information technology and other four ministries and commissions jointly promulgated the action plan for promoting the development of automobile power battery, pointing out that by 2020, the specific energy of new lithium ion power shenchi monomer is required to exceed 300Wh/Kg. The specific energy of the system aims to reach 260Wh/Kg.
Judging from the raw materials of the three kinds of batteries, the monomer specific energy exceeding 300Wh/Kg is unachievable for lithium iron phosphate and lithium titanate batteries. Currently, only ternary materials can meet such requirements. The above is a comparison of three lithium battery material systems. Although ternary battery has a higher energy density than other batteries, it USES liquid electrolyte, which is a big safety risk. There is a consensus in the industry that solid electrolytes can solve the safety problems of lithium batteries.
Solid-state batteries are not a new concept, and apple patented them back in 2012. Solid - state batteries are batteries with solid - state electrodes and solid - state electrolytes. The anode material of solid state battery is not much different from that of liquid electrolyte battery, and the anode material is mainly lithium metal, lithium alloy or graphene. All these factors combine to make a solid lithium-ion battery. At present, solid-state lithium battery can be divided into inorganic solid-state electrolyte battery and polymer solid-state lithium battery. The development of solid - state lithium battery mainly depends on the development of solid electrolyte materials.
Solid electrolyte materials
For solid-state batteries, the selection of appropriate solid-state electrolyte materials is the core content of battery design. Generally, the performance requirements for electrolytes are as follows:
(1) high room temperature conductivity;
(2) electrons cannot pass through, but lithium ions can;
(3) electrochemical window width;
(4) good compatibility with electrode materials;
(5) good thermal stability, moisture resistance, excellent mechanical properties;
(6) easy availability of raw materials, low cost, simple synthesis method.
In organic polymer-based lithium ion conductors, lithium ions "dissolve" in the polymer matrix in the form of lithium salts. Electrical conductivity is the key parameter to characterize the quality of electrolyte, and the transmission rate is mainly affected by the interaction with the substrate and the activity of the chain segment. Improving the activity of the chain segment is conducive to improving the lithium ion conductivity.
At present, the most studied polymer solid electrolyte is PEO (polyethylene oxide) and its derivatives complex lithium salt polymer electrolyte. PEO polymers also have good ionic conductivity and good processing properties at higher temperatures. However, PEO polymer electrolytes also have problems such as low ionic conductivity at room temperature and poor compatibility with lithium metal anode.
2. Inorganic solid electrolyte
Among the inorganic solid electrolyte materials, the early developed halide electrolyte has low conductivity. These early developed materials still have problems of unstable chemical properties and difficult preparation.
Both the sulfide electrolyte and the oxide electrolyte contain glass, ceramic, and glass-ceramic (glass-ceramic) materials in three different crystal states. In general, the conductivity of sulfides is often significantly higher than that of oxides of the same type due to the weak binding effect of S on Li compared with O, which is conducive to the migration of Li+.
The oxide electrolyte has high stability to air and heat, low cost of raw materials and easy to realize large-scale preparation. In the oxide electrolyte, the amorphous (glass) oxide electrolyte has low room temperature conductivity and is sensitive to water vapor in the air, so the preparation often requires high temperature quenching, which is difficult to be used in actual batteries.
In the oxide, lithium ions conduct conduction in the gap of the skeleton structure composed of much larger O2-, weakening li-o interaction, realizing the three-dimensional transmission of lithium ions and optimizing the ratio of lithium ions to vacancy concentration in the transmission channel are conducive to improving the conductivity of lithium ions. Based on these ideas, some lithium oxide conductor materials with complex structures have emerged successively, among which the representative ones include garnet type structure system, perovskite structure system and sodium fast ion conductor structure system. However, of these materials, only the garnet structure of the material system is stable to lithium metal. The materials with high conductivity in the other two structures contain Ti, Ge and other elements that can be reduced by lithium metal. In addition, garnet structure system material has good stability to air, low raw material cost and high mechanical strength of sintered body, so it has the potential to be widely used as an ideal solid electrolyte in all-solid lithium battery.
Ii. Problems to be solved
The purpose of introducing solid electrolyte into lithium battery is to break through the current limitations of organic electrolyte and improve the energy density, power density, operating temperature range and safety of battery. However, to truly achieve these goals, it is still necessary to first solve some problems existing in the existing electrolyte material itself and the interface with the electrode.
For example, the improvement of energy density requires the use of low-potential and high-capacity anode materials, as well as high-potential and high-capacity anode materials. In this case, the electrochemical window with limited polymer and sulfide is often difficult to be directly applied in the case of high voltage. Improving power density requires improving electrolyte conductivity, which is still a big problem.
All-solid lithium battery has extremely high safety, and its solid electrolyte is non-flammable, non-corrosive, non-volatile, and non-liquid leakage. At the same time, it also overcomes the phenomenon of lithium dendrite, and the probability of spontaneous combustion of automobile equipped with all-solid lithium battery will be greatly reduced. The current energy density of all-solid lithium battery is about 400Wh/Kg, and the estimated maximum potential is 900Wh/Kg. However, there are still some problems to be solved in improving the energy density and power density of solid-state batteries, which need to start from solid electrolyte and anode and cathode materials. Once these problems can be effectively solved, a new battery revolution will certainly be set off in the future.
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