Eight Key Differences Between Semi-Solid and All-Solid-State Batteries: A Comprehensive Comparison of Safety, Energy Density, Manufacturing Complexity, Cost, and Charging Performance

EV Insight Daily Unknown

Overview

Semi-solid and all-solid-state batteries fundamentally differ in electrolyte composition and function. Semi-solid batteries contain a small amount of liquid or gel electrolyte, acting as a bridging technology to incrementally improve existing lithium-ion battery limitations. In contrast, all-solid-state batteries completely replace liquid electrolytes with solid ones, targeting significant leaps in safety, energy density, and charging performance. These differences impact eight key characteristics including manufacturing complexity, cost, and suitability for lithium metal anodes.

In Depth

Key Findings

Semi-solid-state batteries and all-solid-state batteries are both next-generation battery technologies, yet they exhibit fundamental differences in electrolyte composition and function. Semi-solid-state batteries, containing a small amount of liquid or gel electrolyte, act as a ‘bridging technology’ that partially improves the limitations of existing lithium-ion batteries. In contrast, all-solid-state batteries aim to be the ‘ultimate battery’ by completely replacing liquid electrolytes with solid ones, promising revolutionary advancements in safety, energy density, and charging performance.

Technical/Clinical Details

There are eight key differences between these two battery types:

• Electrolyte Composition: Semi-solid-state batteries typically contain 5% to 20% liquid electrolyte, whereas all-solid-state batteries use less than 5%, ideally 0%, liquid electrolyte.
• Safety: All-solid-state batteries inherently offer higher safety by eliminating flammable liquids, significantly reducing the risk of thermal runaway. Semi-solid-state batteries also improve safety by reducing liquid electrolyte content, but not to the same extent.
• Energy Density: All-solid-state batteries can achieve the highest theoretical energy densities (over 500 Wh/kg) when combined with lithium metal anodes. Semi-solid-state batteries also improve energy density through high-performance materials but have limitations.
• Manufacturing Complexity: All-solid-state batteries present significant manufacturing challenges due to solid-solid interface issues and the need for high-pressure stacking processes. Semi-solid-state batteries are relatively easier to transition to from existing technologies.
• Cost: Currently, the manufacturing cost of all-solid-state batteries is very high, posing a major barrier to mass production. Semi-solid-state batteries can leverage existing manufacturing infrastructure to some extent, offering a cost advantage.
• Charging Performance: All-solid-state batteries can achieve ultra-fast charging if high-speed lithium ion transport is realized. Semi-solid-state batteries also allow for fast charging but are constrained by their liquid electrolyte component.
• Separator Design: In all-solid-state batteries, the solid electrolyte itself often acts as the separator, allowing for thinner designs and higher energy density. Semi-solid-state batteries still require a porous separator.
• Compatibility with Lithium Metal Anodes: All-solid-state batteries are better at suppressing dendrite growth from lithium metal anodes, which is advantageous for achieving higher capacities. Dendrite issues may persist in semi-solid-state batteries.

Background & Context

The evolution of battery technology is crucial for extending the range and adoption of electric vehicles (EVs) and for integrating renewable energy sources. As the technical limits of liquid-electrolyte lithium-ion batteries become apparent, there is a strong demand for safer and higher-performing alternatives. Semi-solid-state batteries are positioned as an ‘intermediate step’ from current technologies to all-solid-state batteries, facilitating earlier market entry and risk diversification. Conversely, all-solid-state batteries are the long-term ultimate goal, attracting massive investments from governments and leading corporations worldwide.

Strategic Significance & Outlook

In the coming years, semi-solid-state batteries are expected to be gradually introduced into the EV market, balancing performance and cost. Meanwhile, research and development for all-solid-state batteries will continue, focusing on resolving fundamental issues such as interface resistance, volumetric changes, and manufacturing costs. In the long term, all-solid-state batteries hold the potential to become mainstream across a wide range of applications, from mobile devices to EVs and grid-scale energy storage. However, achieving both technological breakthroughs and economic viability will be essential for this vision to materialize.

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