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Solid-state Lithium Battery: Upgrade Energy Density And Safety

- Nov 06, 2018 -

Solid-state lithium battery

Experts believe that all-solid-state lithium-ion batteries use solid electrolytes instead of traditional organic liquid electrolytes, and it is expected to solve battery safety problems fundamentally. It is an ideal chemical power source for electric vehicles and large-scale energy storage.

Traditional liquid lithium batteries are referred to by scientists as "rocking-type batteries". The two ends of the rocking chair are the positive and negative poles of the battery, and the middle is electrolyte (liquid). The lithium ion is like an excellent athlete running back and forth between the positive and negative poles, and the battery charging and discharging process is completed during the movement.

However, this seemingly interesting structure has hidden dangers. According to incomplete statistics, there were 10 burning accidents in electric vehicles in the first half of this year. A firefighting unit concluded that the most common main scene of combustion of new energy vehicles is the combustion during charging. In addition, the battery will also burn during driving or stopping.

Not long ago, at the second seminar on the development direction of energy storage battery technology held in Beijing, experts on the issue of current batteries, the experts suggested that solid-state batteries are relatively ideal choices in the future, and how to improve their energy density and safety. The aspect proposes a development path.

Inheritable liquid lithium battery "river and lake status"

Why does the liquid lithium battery explode frequently? Some experts have analyzed that the traditional lithium battery may have lithium dendrite working under high current, which may cause the short circuit to break the diaphragm; the electrolyte is an organic liquid, which will intensify at high temperatures. Side reactions, oxidative decomposition, gas generation, and tendency to burn.

In recent years, academia and industry believe that the use of solid-state batteries is relatively safe in terms of safety, depending on their ability to inherit the status of liquid lithium batteries.

Experts believe that all-solid-state lithium-ion batteries use solid electrolytes instead of traditional organic liquid electrolytes, and it is expected to solve battery safety problems fundamentally. It is an ideal chemical power source for electric vehicles and large-scale energy storage.

Since the solid-state lithium battery technology uses a glass compound made of lithium or sodium as a conductive substance, it replaces the electrolyte of the conventional lithium battery, and greatly increases the energy density of the lithium battery. The use of a solid electrolyte can reduce the flammability of the battery. Although there are some combustion components in the battery, the solid electrolyte can prevent combustion, and thus the solid electrolyte does not cause combustion compared to the conventional organic battery system battery.

So how does the solid electrolyte of a solid-state battery work? According to experts, its density and structure allow more charged ions to accumulate at one end, conducting more current, which in turn increases battery capacity. Therefore, under the same amount of electricity, the solid-state battery will become smaller. Moreover, since there is no electrolyte in the solid-state battery, the storage will become easier. When it is used on a large device such as a car, there is no need to add additional cooling tubes, electronic controls, etc., which not only saves cost but also effectively reduces weight. 

Scientific research and application go hand in hand

The introduction of solid electrolyte into lithium batteries is to break through the limitations of current organic electrolytes and improve the energy density, power, temperature range and safety of batteries. Experts at the meeting suggested that to achieve these goals, it is still necessary to first solve the existing electrolyte materials themselves and some problems with the electrode interface.

Yan Jun, an associate researcher at the Shanghai Institute of Ceramics, Chinese Academy of Sciences, said that in recent years, our laboratory has mainly developed lithium-sulfur battery systems using solid electrolytes. After the metal lithium was modified with a solid electrolyte, it was found that the cycle stability of the battery was greatly improved. The researchers proposed a dual-electrolyte system lithium-sulfur battery concept, using a solid electrolyte with a lithium-ion conductive property LAGP system, using a small amount of liquid electrolyte between the positive and negative electrodes for interface wetting, the test results can be seen, the first discharge specific capacity can Compared with the ordinary liquid lithium-sulfur battery, the theoretical capacity is more than 80%, especially in terms of charge and discharge efficiency, which is basically close to 100%, and there is no problem of shuttle effect in the liquid lithium-sulfur battery.

In order to further solve the safety problem of the battery, we pass this interface through gelation, so as to ensure that there is no electrolyte flowing inside, and the modification by the polymer can also buffer the volume effect during the cycle.

Li Liangliang, an associate professor at Tsinghua University's School of Materials, said that the R&D team is currently working on a prototype of an oxide solid electrolyte and a solid-state lithium battery. It uses a ternary positive electrode, a solid electrolyte membrane and a graphite load as a negative electrode. The energy density and safety of the battery are very good. The drop was less than 10%, and the capacity remained 81% after thousands of cycles. Solid-state batteries have high energy density and good safety, enabling long-term cycling.

Hefei Boao Guoxing Energy Technology Co., Ltd. Dr. Zheng Mingsen pointed out that the laminated high-capacity solid-state polymer lithium-ion battery currently developed has a relatively simple structure, few nodes, no management system, and only needs to be connected in series when assembling the battery pack. in parallel. Some solid electrolytes are used to replace the traditional liquid electrolyte to solve the leakage of the battery and the post-collision combustion problem, which improves the safety of the battery. At present, the 1GWh energy storage demonstration power station is established in Crowne Plaza Hefei, and the unit module of 1000 kW energy can be supplied through 184 single cores. After 8 months of operation, there is no air conditioning to cool down, and the battery capacity is not attenuated.

Of course, solid-state battery development is still on the road, and there are still some key issues to be broken. Experts said that the application of solid batteries in the field of energy storage needs to take into account factors such as long life and safety. In addition, problems such as volumetric effects, stability, and interface compatibility during long-term cycling are also addressed. More detailed research is being conducted on key core issues.