Examine the three major failure phenomena of liquid lithium batteries and how to fill the gap of solid state batteries

Examine the negative reactions of the lithium batteries during cycling, We can summarize the effects of these reactions into three major battery degradation scenarios and observe the effects of solid-state decomposition on the degradation phenomena: 1. Capacity loss During the cycle, due to the volume expansion or contraction of the positive and negative electrodes, the SEI membrane will crack and proliferate continuously, and the proliferating process of the SEI membrane will consume active lithium, resulting in the decrease of the overall capacity and the increase of the internal resistance of the battery. In addition, during charging, the cathode is in a high oxidation state, and the reduction phase transition is prone to occur. Transition metals such as cobalt ions in the framework are precipitated to the electrolyte and diffused to the anode, which catalyzes the further growth of SEI film, resulting in the consumption of active lithium and reversible capacity loss due to the destruction of the cathode structure. In the negative electrode, the potential of the negative electrode becomes lower, Li + diffuses from the positive electrode and inserts into the negative electrode. When the temperature is too low or the charging current is too high, the insertion speed of lithium decreases, and the lithium precipitates directly on the surface of the negative electrode. The polarization effect is more dramatic, which causes not only the loss of active lithium and the increase of internal resistance, but also the formation of fatal "lithium dendrite". Theoretically, all-solid-state batteries do not move the ions themselves, so irreversible reactions will be reduced, If a solid electrolyte which is electrochemically stable with lithium is used, the SEI and electrolyte deterioration can also be alleviate, and that extent of capacity degradation caused by the consumption of lithium ion during charging and discharging can be effectively reduce, and the generation of lithium dendrites can be further reduced or suppressed. For example, the garnet-structured lithium lanthanum zirconium oxide (LLZO) in the oxide electrolyte has excellent chemical stability, and the solid polymer electrolyte is still composed of lithium salt And the chemical stability of the polymer electrolyte is similar to that of the liquid polymer electrolyte. For the problem of capacity degradation, Increasing energy density is another solution that reduces user inconvenience, If the overall capacity of the battery can jump dramatically, even if part of the capacity is lost, a relatively large residual capacity can still support the operation of the device, while the high safety and stability of solid electrolyte allow lithium batteries to have high activity, high energy density anode materials, the theoretical capacity density of lithium metal can reach 3, 830 mAh/g, 4200 mAh/g of silicon anode material can be obtain, It is about ten times higher than the lithium carbon layer compound, which makes the energy density of power batteries reach the national standard of 300 Wh/kg in 2020, even 400 Wh/kg in 2025. At present, the leading research of lithium metal or silicon negative electrode in solid-state battery industry mainly includes France Bollor é, Korea SDI and Taiwan Light Energy, and the market estimates that consumers can use this kind of high-energy battery in 2022. 2, that increase in volume expansion volume is mainly due to the high oxidation state of the positive electrode dure charging, the free oxygen in the crystal lattice is apt to be oxidized with the electrolyte after precipitation, Carbon dioxide and oxygen are produced, which gradually cause bulging in a charging and discharging cycle, and the decomposition of electrolyte is accelerated when the voltage is higher than 4.35 V (ternary system) or high temperature environment, resulting in continuous expansion of the battery, affecting the configuration of components in the device at least, and causing fire and explosion when the structure of the battery is damaged. The solid electrolyte is not easy to oxidize with the cathode because of its chemical stability Can slow down the decomposition of electrolyte, rate of gasification, greatly reducing the degree of volume expansion, in addition to, the solid electrolyte is capable of withstanding voltages in excess of 5 V without decomposition, As a matt of fact, raising that voltage of a single cell can save part of the BMS and the shunt, and greatly increase the energy density and the cost of the module, which has attracted Nissan and other enterprises to invest in research and development for more than 10 years, but the problem of decomposition of electrolyte unde high voltage cannot be solved for a long time. The solid-state battery camp has already implemented this technology. Earlier this year, Huineng Technologies published the BiPolar + battery pack technology on CES, directly in the stack pole layer of the packaging material. A single battery can reach 85.2 volts, more than 20 kWh, and only four batteries are needed to drive the entire vehicle, so a large number of connecting wires are saved, and the battery pack volume is reduced by 50%. Fig. 1, Package 3 of Solid State Battery of Luminescent Energy Technology, Thermal runaway is the most hazardous and unpredictable risk for lithium batteries, When the battery is damaged by external forces causing a short circuit or internal short circuit, In case of overcharge, the temperature inside the battery rises, Once it reaches 130 degrees, the SEI film begins to disintegrate, As that organic electrolyte is directly contac with the high-activity positive and negative electrodes, As a consequence, a large numb of decomposition and exothermic reactions occur, which lead to an increase in that speed of the temperature and the internal pressure, a large amount of gas is generated, which causes the battery to expand rapidly, and the positive electrode disintegrates aft reaching the critical temperature, thereby releasing more heat energy and oxygen, and the chain reaction of heating, decomposition and exothermic reactions is intensified after many factors are superposed, and finally fires and explosions occur. If the original 150 degrees or so will start to produce large A polymer electrolyte and spacer membrane containing an amount of flammable gas and thermal energy are replaced with a "solid electrolyte" which is slow to vaporize at high temperatures and is non-flammable, the chain reaction of thermal runaway can be blocked and the occurrence of fire and explosion accidents can be avoided, which is similar to drawing fuel from the bottom of a bush. However, the thermal stability of different electrolyte systems is quite different, for example, the ignition point of oxide ceramic electrolyte is more than 1,000 degrees, and the thermal runaway reaction can be completely blocked; The solid polymer electrolyte will begin to disintegrate at about 280 degrees Celsius, the worst thermal stability, has not yet seen solid polymer batteries in more than 300 degrees Celsius still maintain a stable test record. Fig. 2 thermal runaway separation and thermal release proces inside that battery As can be seen from the runaway proces of the lithium battery described above, most of the side reactions are due to the chemical and high temperature instability of the organic electrolyte, even if the insulating coating of the electrode layer is seen from time to time, Research and Development of Flame Retardant Additives, it is still palliative, This is also the reason why the market focus has gradually shifted from ternary batteries to solid-state batteries in recent years, using the stability of solid electrolyte to create new energy vehicles with high safety, longer battery life and more ideal endurance, breaking through the development barriers faced by lithium batteries for decades, and enhancing the replaceability of electric vehicles to fuel vehicles. In addition, the Electric Vehicle Substandard Committee issued a draft of the national safety standard "Safety Requirements for Electric Vehicles" last year, The design and testing methods of thermal management and parts flame retardant are proposed. Driven by the market and policy, the safety standards and control system of the industry are becoming more and more complete. It is expected that the new energy vehicles will achieve essential stability as soon as possible And safety, for driving and passengers' lives and property to provide protection, replacement for China's clean energy development to add power.