Solid-state Battery Separator: Key to Future Energy Storage

The Revolutionary Significance of Solid-state Batteries

Liquid electrolytes are flammable (such as organic solvents such as DMC/EC with a flash point below 40°C), have an energy density ceiling (the current maximum mass production is 350Wh/kg), and have a risk of thermal runaway (the temperature can reach 800°C during short circuit). The side reaction between the electrolyte and lithium metal will also aggravate the growth of dendrites, resulting in a decrease in cycle life. By replacing the liquid system with solid electrolytes, triple advantages can be achieved:

Intrinsic safety: the flash point of solid electrolytes is >200°C, the probability of thermal runaway is reduced by more than 95%, and there is no risk of leakage;

Energy density leap: compatible with lithium metal negative electrodes (theoretical capacity 3860mAh/g) and 5V-level high-voltage positive electrodes (such as lithium-rich manganese-based materials), the theoretical energy density exceeds 500Wh/kg;

Structural innovation: solid electrolytes simultaneously undertake ion transmission and physical isolation functions, and directly replace traditional separators in some designs.

As the core component of the solid/solid interface, it must simultaneously meet the following requirements: high ionic conductivity (>1mS/cm, close to the level of liquid electrolyte), mechanical strength (elastic modulus>6GPa to inhibit dendrite penetration), interface compatibility (forming low impedance contact with electrode materials), and partial separator structure is still retained in quasi-solid-state batteries, while all-solid-state batteries usually eliminate independent separators.

Battery Separators Products List

• PTFE Battery Separator
• PE Battery Separator
• PP Battery Separator
• PP/PE/PP Trilayers Battery Separator
• Ceramic Coated Separator (PE Base Film)
• Ceramic Coated Separator (PP Base Film)
• Cellulose Separator
• PVDF Coated Separator
• Glass Fiber Battery Separator

Technical Principles and Material Innovation of Solid-state Separators

Differences between solid-state separators and traditional LIB separators

All-solid-state batteries are reconstructed in the following ways:

Multilayer stacking design: 5-20μm solid electrolyte layer directly isolates electrodes, eliminating independent separators

Bipolar structure integration: solid electrolyte acts as both separator and current collector, increasing volume utilization by 30%

Inorganic solid electrolyte

The ion conductivity of oxide systems (such as LLZO) is 1-10mS/cm, but they are brittle (fracture toughness <2MPa·m¹/²), and nanosilver coating is required to improve the interface. The ion conductivity of sulfide systems (such as Li₃PS₄) reaches 10⁻²S/cm, but it is easy to react with water to generate H₂S.

Polymer-based composite materials

PEO-based electrolytes have excellent flexibility (elongation at break>200%), and the thermal decomposition temperature is increased to 250°C through SiO₂/Al₂O₃ nanofillers. The electrochemical window of the polycarbonate system is widened to 4.5V, which is suitable for positive electrode

Innovative design of composite separator

A 50nm LiPON inorganic layer is set on the anode side of the gradient structure to prevent dendrites, and the surface is covered with a 1μm polymer layer to optimize the interface. The sandwich structure includes a sulfide electrolyte (core layer) + a polymer protective layer (on both sides), taking into account high conductivity and processability. The bionic structure introduces a honeycomb porous ceramic skeleton, and the ion conductivity is increased by 3 times to 8.7mS/cm.

Significant Advantages of Solid-state Separators

Solid-state separators replace liquid electrolytes with solid electrolytes, fundamentally eliminating the risks of electrolyte leakage, volatilization and flammability. Its mechanical strength is significantly higher than that of traditional separators, which can effectively suppress short-circuit problems caused by lithium dendrite penetration, and its high temperature resistance (up to 150°C or above) greatly reduces the probability of thermal runaway. For example, all-solid-state batteries use non-flammable electrolytes, which can naturally isolate the positive and negative electrodes and avoid internal short circuits caused by lithium dendrites piercing the separator in traditional liquid batteries.

Physical structure optimization: The thickness of the solid electrolyte can be reduced to the micron level (such as ≤10μm), and the traditional separator can be eliminated, simplifying the packaging and cooling system, and increasing the battery volume energy density by more than 70%.

Improved material adaptability: The wide electrochemical window of the solid electrolyte (up to 5V) supports high-capacity cathode materials such as high-nickel ternary and lithium-rich manganese-based, and is compatible with lithium metal anodes, pushing the energy density to break through 500Wh/kg, doubling that of traditional liquid batteries.

3. Wide temperature range and fast charging potential

Solid electrolyte ion transport is less affected by temperature and can work stably in a wide temperature range of -30℃ to 150℃, alleviating the problem of low-temperature capacity attenuation. Although the current ionic conductivity (especially polymer/oxide system) is still lower than that of liquid electrolyte, the high ion mobility of sulfide electrolyte (close to liquid level) provides theoretical possibility for fast charging.

Future Trends and Commercialization Prospects

1. Technology integration path

Semi-solid transition solution: retain 5%-10% liquid electrolyte to optimize interface contact, compatible with existing production lines, and first applied to high-end electric vehicles in the short term.

Material system innovation: cobalt-free/low-nickel positive electrode (such as lithium-rich manganese-based) combined with silicon-based negative electrode, taking into account cost and performance; sulfide-polymer composite electrolyte may be the key to balancing conductivity and stability.

2. Material innovation direction

Silicon-based negative electrode iteration: silicon-carbon negative electrode with solid separator, through nano-sizing and pre-lithiation technology to alleviate volume expansion problem, increase cycle life to more than 1000 times.

Bionic structure design: The bionic nanopore membrane can precisely control the ion migration path. Combined with the self-healing properties of solid electrolytes, it is expected to achieve high-rate charging and discharging and long-cycle stability.