Cheaper solid-state battery with polymer electrolyte enters production as Sunwoda teases 700 Wh/kg energy density potential

One of the top five cell makers in China, Sunwoda, will be starting mass solid-state battery production from a pilot line this year with a capacity expansion in 2026.

The company's first generation of polymer electrolyte has resulted in a production-ready solid-state battery that offers energy density of 400 Wh/kg. This nearly doubles the average energy density of existing batteries with liquid electrolyte in mass electric vehicles or power stations like the new Anker Solix that is 50% off on Amazon, but Sunwoda's other achievement is cost.

Battery cells with solid-state technology may have higher capacities and be inherently safer thanks to the lack of volatile liquid electrolyte, but they are still rather expensive to make at lower volumes. Upon announcing its 400 Wh/kg solid-state battery, however, Sunwoda said that it will be able to mass-produce it at costs comparable to that of semi-solid batteries that have 5% liquid and 95% solid electrolyte.

These are used as a bridge technology by automakers like NIO, whose 150 kWh pack allows the ET7 sedan to cover more than 650 miles between charges. The world's biggest battery maker CATL has also pegged semi-solid state batteries as a good tradeoff between performance and price per kWh, so if Sunwoda's all-solid-state battery hits cost parity with those, automakers are certain to take note.

Besides the production-ready solid-state battery with energy density of 400 Wh/kg, China's top five cell maker has already prototyped one with 520 Wh/kg, just as Toyota, CATL, or Samsung. Its 3D composite anode helps ion transfer, while a layer with tiny bubbles containing interface repair agent fixes the solid electrolyte interphase film, and prevents dendrite growth to suppress their destructive side effects. This one will be entering production around 2027 when most of the other solid-state battery makers will be starting their own mass production process, too.

By then, however, Sunwoda expects to have reached 700 Wh/kg energy density with various prototypes, thanks to its proprietary polymer electrolyte technology. The solid-state battery energy density record was heretofore held by China's largest car exporter, Chery. It announced recently that it will have vehicles with a 600 Wh/kg solid-state battery on the road in 2027, touting the same polymer electrolyte approach.

Sunwoda's solid-state battery has a cathode porosity of just 5%, or five times less than is typical, yet its ion conductivity is increased threefold. The "nano-structured high-entropy anode" has seven times the capacity of graphite ones and has double the cycle life. Sunwoda's composite polymer electrolyte membrane greatly facilitates ion conductivity, but is also elastic and durable. The cell interface coating is flexible, too, exhibiting "high ion conduction, strong adhesion, high ductility, and self-healing," as per Sunwoda. The resulting 20 Ah cells offer longevity of 1,200 life cycles, and have already passed the nail penetration and the 200°C hot-box safety tests.

The promising technology is constantly being advanced in labs, too, as the Chinese Academy of Sciences recently announced a flexible solid-state battery prototype with polymer electrolyte that flaunts up to 86% higher energy density than the current production-ready solid-state batteries that range from 350 Wh/kg to 400 Wh/kg, depending on the maker.

The 500 Wh/kg solid-state batteries, previously thought to be the theoretical limit of the current technology, are already being tested in prototype vehicles like the Mercedes EQS that can cover 750 miles on charge, but their mass production is only slated for 2027 and in small batches for premium electric vehicles at that.