Application status and patent analysis of polyethylene oxide solid polymer electrolyte

Application status and patent analysis of polyethylene oxide solid polymer electrolyte

Lithium batteries are the power source for electric vehicles, but traditional liquid lithium-ion batteries have great safety hazards and low energy density problems. How to further improve the safety and cruising range of electric vehicles is also the primary problem faced by designers and manufacturers. The solid-state lithium battery using solid polymer electrolyte (SPE) can fundamentally solve the above-mentioned bottleneck problem.

PEO has been studied the earliest and most in solid polymer electrolytes, and its industrialization is the fastest. Because of its good compatibility with lithium negative electrodes and relatively good chemical stability, companies that use PEO solid polymer electrolytes to produce solid lithium batteries include the German Bosch Group that acquired SEEO, the French Bollore company, and the Quebec company of Canada.

The European lithium iron phosphate solid-state lithium battery technology comes from the Quebec Hydropower Research Institute in Canada. The Quebec Hydropower Research Institute of Canada began research on PEO solid electrolyte-based solid-state lithium batteries in 1979, with a cumulative investment of US$1.5 billion. The first generation of solid-state technology has been transferred to the French company Bollore. The company’s solid-state lithium battery has an energy density of up to 200W·h/kg. At present, the second-generation solid-state technology is also mature, the energy density can reach 250W·h/kg (80A·h, 3.5V platform), and the capacity of 2000 cycles (100% DOD) remains 80%, showing excellent cycle stability. The technical route of the battery: the negative electrode of the battery is lithium with a thickness of 39μm; the positive electrode is lithium iron phosphate (LiFePO4) with a thickness of 66μm; the polymer electrolyte is a PEO/LITFSI polymer electrolyte system. The charging and discharging rate is 1/3C, the working temperature range is 60~80℃, the energy density of the battery pack is 150W·h/kg, the cruising range is 250km, and the design life is 11 years (calculated by driving 100km per day). Currently, solid-state lithium battery technology has been successfully commercialized in France. The French company Bollore took the lead in industrializing PEO solid polymer electrolytes and applying them to solid-state batteries. Pennsylvania has already cooperated with the French Autolib automobile company, and Autolib will produce Bluecar for it. Bluecar uses lithium metal polymer solid-state batteries (Figure 1), with a top speed of 130km/h and a cruising range of up to 250km, which is enough for this car to travel back and forth between two cities. Bluecar officially entered the car rental market in Paris, France in October 2011, and now there are nearly 5,000 cars roaming the streets of Paris.

Application status and patent analysis
Figure 1 – Composition diagram of the solid-state battery used by French Bluecar

The US SEEO company developed solid-state lithium battery samples, which were acquired by the German Bosch Group in 2015. Its technical route is also based on PEO-based solid polymer electrolyte, the battery cell energy density is 220W·h/kg. The battery pack energy density is 130~150W·h/kg, and the output voltage is 3.42V.

SEEO has applied for a number of invention patents on PEO-based solid polymer electrolytes. In US20160336620 A1, the applicant reduces the melting point of PEO by introducing fluorine-containing functional groups on the PEO segment, which is even comparable to liquid electrolytes at room temperature. Compared with traditional electrolytes, the solid polymer electrolyte has higher safety performance and better flame retardant performance. The copolymer can be used in the field of lithium battery polymer electrolytes.

The patent US 20170092983 A1 reports that the battery performance of the PS-PEO block copolymer electrolyte has been significantly improved compared to the polydimethylphenoxane lithium salt polymer electrolyte. Patent US 20160301101A1 uses perfluoropolyether grafted with cyclic carbonate at the end, and then combined with lithium bistrifluoromethanesulfonimide to be used as a high-performance flame-retardant polymer electrolyte for alkali metal batteries. Among them, by adjusting the content of lithium salt (mass fraction of 5% to 30%), different ionic conductivity can be achieved.

Solid-state lithium batteries have very good application prospects under high temperature conditions, such as being used as power sources for deep-sea drilling. International PCT patent WO 2011146670 A1 reports a solid polymer electrolyte that can be used in high-temperature lithium batteries. The electrolyte is based on polydimethylphenoxane and other polymers with a high softening point (greater than 201℃). At the same time, these materials have a microphase structure, one phase provides ion conduction, and the other phase provides mechanical strength to ensure safety. Lithium batteries assembled with this electrolyte can operate safely at high temperatures (>110°C).

Application status and patent analysis of polyethylene oxide solid polymer electrolyte

Among domestic enterprises, CATL New Energy Technology Co., Ltd. (CATL) has a good working foundation in solid-state lithium batteries. At the Twelfth International Battery Technology Exchange Conference in 2016, Dr. Liang Chengdu reported on the latest progress of CATL in solid-state battery research (Figure 2). Patent CN 106299470 A reports a lithium salt of boron clathrate anion that can be used in polymer electrolytes (including PEO). The lithium salt contains negative charges, has a high degree of delocalization, has a large volume, and has good flexibility. It can be mixed with PEO to obtain a solid electrolyte, which can be used to assemble a solid battery. Compared with the prior art, the solid electrolyte adopting the lithium salt can simultaneously have higher ion conductivity and lithium ion migration number. TYCORUN ENERGY ups manufacturers in china is also a recommended company for purchasing lithium batteries.

Application status and patent analysis of polyethylene oxide solid polymer electrolyte
Figure 2 – CATL polymer solid-state lithium battery performance test