Solid-State Batteries I

On January 9, NIO unveiled a solid-state battery with an energy density of 360Wh/kg and a range of more than 1,000 km. This move set off thousands of waves in the capital market, and even lithium battery concept stocks also suffered a heavy fall. Solid-state batteries are a type of battery technology. Unlike lithium-ion batteries and lithium-ion polymer batteries, which are commonly used today, solid-state batteries are batteries that use solid electrodes and electrolytes.

High safety

The liquid electrolyte in liquid lithium-ion batteries is a safety hazard. The State Administration for Market Regulation ordered the recall of 33,281 new energy vehicles in 2019. A total of 6,217 NEVs were recalled due to power battery problems, accounting for 18.68 percent of the total NEV recalls this year. Power battery is one of the main hidden dangers under the main trigger condition of battery runaway.

Battery explosion or self-explosion is a common safety accident in electric vehicles, which is mainly caused by thermal control loss. Battery spontaneous combustion is caused by a short circuit of power battery in an overcharge, low or high-temperature environment. In a very short period of time, the battery gives off a lot of heat, igniting the electrolyte inside the battery and eventually causing the battery to catch fire. There is an urgent need for battery safety in the new energy vehicle market, which produces 1 million vehicles a year. Although the probability of battery problems is small, in a large market base, battery problems can become the norm. Therefore, the requirements for safety will be higher and higher, and the choice of battery combustion without fire may become the unanimous choice of the car factory. Because solid electrolyte replaces liquid electrolyte and diaphragm in liquid lithium-ion battery, accidents caused by unstable electrolyte are avoided, which has higher safety.

High Energy Density

Relying on the existing power battery system, the energy density of the battery in the future is difficult to meet the national requirements. At present, China's power battery cathode materials are changing from lithium iron phosphate to ternary system, high nickel ternary system development. The industrialization of anode materials is still concentrated in graphite and silicon-based materials. According to some battery suppliers, the energy density of lithium-ion power batteries is expected to increase to more than 300Wh/kg in the next five years, but the existing ternary system is difficult to achieve above 350Wh/kg.

The high energy density of solid-state batteries is expected to solve the range anxiety problem of new energy vehicles. The electrochemical window of solid-state batteries can reach more than 5V, higher than the 4.2V of liquid lithium-ion batteries, allowing matching of high-energy positive electrodes and improving the theoretical energy density. Since solid-state batteries do not require an electrolyte or a diaphragm, the weight and size of the battery pack will be reduced.

Commercialization of All-Solid-State Batteries Has Still a Long Way to Go

The development of solid-state battery technology needs to be gradual, the liquid electrolyte content gradually reduced, and eventually the formation of all-solid-state battery. According to the classification of electrolyte, lithium batteries can be divided into liquid, semi-solid, quasi-solid and all-solid four types, of which semi-solid, quasi-solid, and all-solid are collectively referred to as solid-state battery. During the solid-state battery iteration, the liquid electrolyte content will be reduced from 20wt% to 0wt%, the negative electrode of the battery will be gradually replaced by a lithium metal plate, the energy density of the battery is expected to increase to 500Wh /kg, and the operating temperature range of the battery will be expanded by more than three times. Nio released the battery is actually a semi-solid battery, still need to use electrolyte, diaphragm, electrolyte content is less than 10%. A solid-state battery will be the high point of lithium-ion technology, and a semi-solid battery is the necessary path for solid-state battery iteration.

Therefore, it is too early for the market to worry about the substitution of solid-state batteries for liquid batteries. The commercialization of all-solid-state batteries has just begun, but there is no mass production capacity. At the same time, the market demand for solid-state batteries is still very low, and the road to the commercialization of all-solid-state batteries is very long.

Current Situation of Global All-Solid Lithium Battery Industrialization

The research of solid-state lithium metal battery first appeared in the 1970s, and in the next 40 years, solid-state lithium battery has been widely studied in the world. Later, due to technical bottlenecks such as low ionic conductivity and poor interfacial compatibility of solid electrolyte, the commercialization process was restricted, and the research of all-solid lithium battery was stalled at the end of the 20th century.

The Data show that from 1995 to 2015, a total of 1,082 overseas patents were applied in the field of all-solid lithium batteries. During 1996-2007, the research on the commercialization of liquid lithium batteries to produce solid lithium batteries remained sluggish. Since 2007, the technology of liquid lithium batteries has become mature, and the ceiling of safety performance and energy density has gradually emerged. Overseas mainstream research institutions have increased their research efforts on solid lithium batteries. 2007 saw a resurgence in research and development of all-solid lithium batteries. Since 2007, overseas patent applications for all-solid-state lithium batteries have grown at a compound annual rate of 35.3%.

Solid electrolyte systems can be divided into organic and inorganic systems. Organic electrolyte is relatively simple and mainly consists of PEO, while inorganic system can be subdivided into oxide system and sulfide system.

Japan has a mature solid battery research system, especially in the field of all solid lithium batteries with sulfide. Of the top 10 overseas patent applications, nine are from Japan and one is from South Korea. Toyota Corporation of Japan filed the most patents, 218, accounting for 20.15 percent of the total. In June 2018, Japan's New Energy Industry Technology Integrated Development Agency announced that it would cooperate with academic institutions and enterprises to jointly develop the next generation of all-solid-state lithium batteries for electric vehicles in the next five years.

In 2011, Bollore realized the commercialization of polymer solid-state lithium batteries. The all-solid-state lithium battery prepared by France Bollore is the earliest case that polymer all-solid-state lithium battery is applied to electric vehicles in the world, and it is applied to urban rental electric vehicles. However, the biggest problem with polymer all-solid-state lithium batteries is low ionic conductivity. The French company Bollore uses heating devices to heat the batteries for normal use, which on the one hand brings safety risks, on the other hand, it also raises the cost. China's research on solid-state lithium battery started relatively late, but through the cooperation of various enterprises and the continuous attempts of universities and research institutions, the domestic solid-state battery research ranks the second tier in the world.

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