Solid-State Batteries vs Semi-Solid-State Batteries vs Liquid Batteries: A Comparative Analysis

As energy storage technology continues to advance, all-solid-state batteries, semi-solid-state batteries, and liquid batteries are three technologies that are actively being developed. Each has its unique characteristics and is widely regarded as a potential game changer in fields such as electric vehicles (EVs) and renewable energy storage.

Solid-state batteries can be divided into three types: semi-solid, quasi-solid, and all-solid, based on the proportion of liquid electrolyte used. Semi-solid batteries have less than 10% liquid electrolyte by weight, quasi-solid batteries have less than 5%, while all-solid-state batteries contain no liquid electrolyte at all, using solid materials for the electrolyte. Currently, all-solid-state batteries are mainly in the research and prototype stages worldwide. The shift from liquid to solid-state batteries begins with changes to the electrolyte material, leading to changes in production processes. Currently, there are three main technological routes for solid-state batteries: polymer solid-state, oxide solid-state, and sulfide solid-state. The immaturity of materials, preparation technologies, and high production costs are the main factors limiting the commercialization of all-solid-state batteries. The industry generally believes that large-scale commercialization of these batteries is still at least five years away. As a result, semi-solid-state batteries are seen as a more industry-friendly technology. In fact, many companies in Japan, South Korea, Europe, and the United States are focusing on sulfide technology for the development of all-solid-state batteries, while companies in China tend to favor oxide technology, mainly developing semi-solid-state batteries.

Here is a comparison of these three battery technologies:

1. All-Solid-State Batteries (SSBs)  

All-solid-state batteries are considered the “next generation” of energy storage. Unlike traditional liquid batteries that use liquid electrolytes, all-solid-state batteries use solid electrolytes made from materials such as ceramics, glass, or polymers. The main advantages of all-solid-state batteries include:  

Higher energy density: All-solid-state batteries can have up to three times the energy density of traditional liquid batteries, making them ideal for applications that require high power and long usage times, such as electric vehicles.

Higher safety: All-solid-state batteries are less prone to thermal runaway because the solid electrolyte is non-flammable.

Longer lifespan: Compared to traditional batteries, these batteries degrade more slowly, offering a longer service life.

However, despite their enormous potential, all-solid-state batteries face several challenges, including high production costs, complex manufacturing processes, and issues with mechanical stress and lithium dendrites in the solid electrolyte. Experts believe that while this technology holds great promise, large-scale production may take a long time.

2. Semi-Solid-State Batteries  

Semi-solid-state batteries are a hybrid technology between liquid and all-solid-state batteries. They use a gel-like electrolyte (semi-solid material) that combines some advantages of solid-state technology while retaining the flexibility of liquid electrolytes.  

Enhanced safety: The gel electrolyte in semi-solid-state batteries is less flammable than traditional liquid electrolytes, reducing the risk of fire.

Improved energy density: Although their energy density is lower than all-solid-state batteries, semi-solid batteries offer higher energy density than liquid batteries and can be produced using existing lithium-ion production lines, lowering production barriers.

Faster development: Semi-solid-state battery technology has already been tested in electric vehicles, with companies like Nio exploring its application.

However, despite these advantages, semi-solid-state batteries still fall short of all-solid-state batteries in terms of energy density and lifespan. The engineering of gel electrolytes also needs further optimization for large-scale production.

3. Liquid Batteries  

Liquid batteries, such as the widely used lithium-ion (Li-ion) batteries, have become the foundation of modern energy storage. These batteries use a liquid electrolyte to transport ions during charging and discharging.  

Mature technology: Lithium-ion batteries are currently the most commercially viable batteries, widely used in electric vehicles, smartphones, and other consumer electronics.

Lower cost: Due to years of development, the production cost of liquid batteries is relatively low, and large-scale production capacity is already in place.

However, despite their widespread use, liquid batteries have lower energy density, safety, and lifespan compared to all-solid and semi-solid batteries. Liquid electrolytes are flammable, and over time, the performance of these batteries degrades.

Timeline for Mass Production of Solid-State Batteries  

Although all-solid-state batteries have attracted significant attention, industry experts suggest that mass production may still be years away. In contrast, semi-solid-state batteries could enter the market sooner due to their compatibility with existing lithium-ion production lines, making them a likely candidate for early adoption in electric vehicles.

While all-solid-state batteries hold tremendous potential in terms of safety, energy density, and lifespan, they still face numerous challenges. Semi-solid-state batteries, with their balance of energy density, safety, and shorter development cycles, are expected to make progress in the near term. Liquid batteries, although still dominating the market, will gradually be replaced as all-solid and semi-solid-state battery technologies continue to evolve. The future of battery technology will be a gradual transition, moving from liquid batteries to semi-solid-state, and finally to all-solid-state batteries, with incremental improvements in performance, safety, and sustainability at each stage.