Liquid-State vs. Solid-State Batteries From Principles to Industry—A Comprehensive Overview of the True Evolutionary Path of Lithium-Ion Technology

When it comes to lithium batteries, we interact with liquid lithium-ion batteries almost every day—whether it’s the smartphone in our pocket, the electric vehicle we use for daily commutes, or portable power banks and outdoor energy storage systems for home use. In recent years, “solid-state batteries” have been popping up frequently at new-car launch events and tech industry news, carrying with them the aura of “next-generation cutting-edge technology”—offering longer battery life, higher safety, and the promise of never spontaneously combusting. It all sounds like the ultimate answer to battery technology.

However, many people’s understanding of solid-state batteries still remains at the literal level—simply that the electrolyte has changed from liquid to solid. In reality, this seemingly minor difference in terminology masks profound disparities across the board: in terms of internal battery structure, core performance, manufacturing costs, and industry maturity. Moreover, solid-state batteries themselves are not a single, uniform type; ranging from semi-solid designs that retain a small amount of liquid to fully solid-state batteries that are virtually free of any liquid, these technologies represent a world of difference compared to conventional liquid-electrolyte batteries.

Today, we’ll thoroughly explore liquid batteries and solid-state batteries—from their underlying principles and performance comparisons to the current industry landscape and common misconceptions—so you can truly understand the direction of lithium battery evolution.

I. The Most Fundamental Distinction: The Electrolyte—Lithium Ions’ “Highway”

The core working principle of lithium batteries is the back-and-forth “migration” of lithium ions between the positive and negative electrodes: During charging, lithium ions detach from the positive electrode and “move” to the negative electrode, where they are embedded and stored; during discharging, they return to the positive electrode, releasing electrical energy. The electrolyte serves as the “transport channel” for these lithium-ion movements, and its physical state is the key criterion for distinguishing between liquid- and solid-state batteries.

1. Traditional liquid batteries: a “highway” soaked in liquid

The lithium iron phosphate and ternary lithium batteries we use in our daily lives both belong to the category of liquid-state lithium batteries. Their electrolyte is an organic solution in which lithium salts are dissolved—much like a well-mixed “conductive brine”—that fills the entire interior of the battery cell, completely soaking the positive electrode, negative electrode, and separator.

The advantages of liquid electrolytes are quite intuitive: they exhibit excellent wettability, allowing them to make thorough contact with electrode material particles, resulting in low resistance to lithium-ion transport and high conductivity. However, their drawbacks are equally critical: organic electrolytes have low flash points, are highly flammable and volatile, and also possess corrosive properties—making them the root cause behind lithium battery fires and explosions. Once a cell is damaged and leaks, or if an internal short circuit triggers high temperatures, the electrolyte can become a “catalyst” that accelerates thermal runaway.

2. Solid-state batteries: “Directed Channels” in Solid Electrolytes

The electrolyte in solid-state batteries is a solid material. The mainstream approaches fall into three major categories: oxides, sulfides, and polymers. Lithium ions conduct through the crystal lattice channels or grain boundaries within the solid. Based on the residual proportion of internal liquid electrolyte, solid-state batteries can actually be divided into three technological stages, with decreasing maturity and increasing performance in sequence:

• Semi-solid-state battery

Also known as hybrid solid-liquid batteries, these batteries feature a liquid electrolyte content ranging from 5% to 20%. They use solid-state materials as the primary structural framework while retaining a small amount of liquid to enhance the interfacial contact between the electrodes and the electrolyte. This is currently the most mature solid-state technology route for industrialization.

• Quasi-solid-state battery

The liquid electrolyte accounts for 1%-5% and represents a transitional state, with properties and structure more closely resembling those of all-solid-state materials.

• All-solid-state battery

With the liquid electrolyte accounting for less than 0.5% and no free-flowing liquid inside the cell, this is a true “solid-state battery.”

To put it in a simple analogy: A liquid battery is like a water-filled hose—lithium ions freely swim around in the water, moving quickly, but if the hose develops a crack, it’ll leak and could even catch fire. A semi-solid battery is akin to a sponge that’s fully saturated with water; the liquid is firmly held in place by a solid framework, so it can’t flow freely. In contrast, a solid-state battery is like a solid, conductive rod—lithium ions move exclusively within the solid material itself. With no liquid present at all, there’s simply no basis for leakage or combustion.

II. Changes in Internal Structure: From the “Four-Piece Set” to the “Three-Piece Set”

The change in electrolyte morphology directly restructures the internal architecture of the battery, gradually simplifying the core components from the classic “four major parts” to the “three major parts.”

1. Liquid lithium battery: the classic four-part structure

The core of a traditional liquid-cell battery consists of four essential components, none of which can be missing:

• Positive electrode

Lithium compound materials serve as a “reservoir” for lithium ions.

• Negative electrode

Currently, the mainstream material is synthetic graphite, which serves as the “storage station” for lithium ions after charging.

• Diaphragm

A porous plastic film on the first layer physically separates the positive and negative electrodes to prevent short circuits, while allowing only lithium ions to pass through.

• Liquid electrolyte

It fills the internal voids of the battery cell and is responsible for the conduction and transport of lithium ions.

These four components are assembled by winding or stacking and then encapsulated in an aluminum casing or a soft-pack housing, thus forming a complete liquid electrolyte cell. Due to the presence of liquid, the cell must reserve space for electrolyte injection and expansion cushioning, resulting in relatively low internal volume utilization.

2. All-solid-state batteries: a minimalist structure with no separator and no electrolyte.

All-solid-state batteries completely abandon liquid electrolytes and traditional plastic separators; the core components are reduced to just three:

• Composite cathode

The cathode material is mixed with solid-state electrolyte powder to create ion-transport pathways within the electrode.

• Solid electrolyte layer

Taking on two roles in one—both conducting lithium ions and serving as a separator to prevent short circuits—a single material with dual functions;

• Negative electrode

Lithium metal anodes can be used directly, no longer constrained by the capacity limitations of graphite materials, thus achieving a significant leap in energy density.

Without any liquid electrolyte or separate diaphragm, the battery’s internal structure is entirely solid. This not only eliminates at the source the material basis for leakage and combustion but also significantly simplifies the cell structure, leaving room for further improvement in volumetric utilization.

3. Semi-solid-state batteries: An improved solution compatible with existing production lines

Semi-solid-state batteries represent an intermediate approach that balances performance and cost: Most designs still retain traditional separators, but a solid-electrolyte coating is applied to the separator’s surface. The amount of liquid electrolyte is significantly reduced and is adsorbed and immobilized by the solid skeleton, losing its fluidity altogether.

The greatest advantage of this structure is that it allows for the maximum possible reuse of existing production equipment and processes used in liquid batteries, eliminating the need to completely rebuild the production lines. As a result, it enables the fastest pace of industrial implementation.

III. Hardcore Performance Showdown: The Real Gaps Across Five Key Dimensions

The underlying structural differences will ultimately translate into the performance experience that users can perceive. We’ve conducted a comprehensive comparison across five key dimensions: safety, energy density, fast charging and low-temperature performance, cycle life, and volumetric utilization.

1. Safety: From “Passive Firefighting” to “Inherent Safety”

Safety is the most critical advantage of solid-state batteries—and also their irreplaceable value.

The safety logic of liquid batteries is: Passive protection Because the electrolyte is highly flammable, the industry can only minimize the damage after thermal runaway occurs by adopting measures such as adding thermal insulation layers, installing pressure relief valves, equipping cooling systems, and designing explosion-proof valves. However, once severe compression, puncture, or internal short circuit occurs and the electrolyte leaks, it still easily triggers intense combustion or even an explosion.

The safety logic of solid-state batteries is... Inherently safe Solid-state electrolytes themselves are non-flammable, non-volatile, and leak-proof. Even if the battery cell is pierced or subjected to compression and deformation, there will be no leakage of liquid leading to spreading combustion. Public test data show that solid-state battery cells, when subjected to needle-penetration, compression, and high-temperature chamber tests, mostly exhibit only slight heating—without catching fire or exploding. In contrast, liquid-electrolyte battery cells of the same specifications readily undergo thermal runaway and catch fire under identical testing conditions.

2. Energy density: The ceiling differs by nearly a factor of two.

Energy density directly determines the amount of energy a battery can store per unit volume or weight, which in turn affects the driving range of electric vehicles and the degree of slimness and lightness in consumer electronics.

• Lithium liquid battery

After years of technological iteration, the energy density has nearly reached the theoretical upper limit of material systems. The energy density of conventional ternary batteries is around 300–350 Wh/kg, while that of lithium iron phosphate batteries is approximately 180–230 Wh/kg; there is very limited room for further breakthroughs in this regard.

• Semi-solid-state battery

Through structural optimization and material adjustments, the energy density of single cells can generally reach 350–400 Wh/kg, an increase of more than 30% compared to liquid ternary batteries, easily enabling electric vehicles to achieve a range of 1,000 kilometers.

• All-solid-state battery

Because it can be paired with a lithium-metal anode, completely breaking through the capacity limit of graphite anodes, the theoretical energy density of a single cell could reach over 500 Wh/kg—nearly twice that of today’s mainstream liquid batteries. If this technology fully matures, electric vehicles with a range exceeding 1,500 kilometers and smartphones requiring only one charge per week will become a reality.

3. Fast Charging and Low-Temperature Performance: Solid-State Batteries Aren't Universally Superior

Many people assume that solid-state batteries outperform liquid electrolyte batteries in every aspect. However, when it comes to fast charging and low-temperature performance, the two actually each have their own strengths and weaknesses.

Fast charging capabilityAspect:After years of optimization, fast-charging technology for liquid batteries has become highly mature at room temperature, with charging from 30% to 80% typically achievable in under 30 minutes. However, the fast-charging performance of all-solid-state batteries varies significantly depending on the specific technological approach: The sulfide-based approach boasts an ionic conductivity that is nearly comparable to that of liquid electrolytes, giving it tremendous potential for ultra-fast charging and theoretically enabling even faster charging speeds than liquid batteries. In contrast, the oxide-based approach exhibits relatively low ionic conductivity at room temperature, resulting in slower fast-charging performance compared to liquid batteries.

Low-temperature performanceAspect:In environments below -20℃, the viscosity of liquid electrolytes in conventional batteries rises sharply, significantly reducing lithium-ion activity and often leaving the battery’s range reduced to just 50% or 60%. Solid-state batteries, on the other hand, exhibit better thermal stability and experience much less capacity degradation at low temperatures. In particular, semi-solid-state batteries generally maintain a capacity retention rate of over 80% even at -20℃, markedly enhancing the driving experience during winter in northern regions.

4. Cycle life: Significant differences across the entire lifecycle

The cycle life determines the service life of a battery and is one of the key performance indicators for energy storage and power batteries.

During repeated charge-discharge cycles, the electrolyte in liquid batteries continuously undergoes side reactions with the electrode materials, gradually depleting and aging. Meanwhile, the active materials slowly detach from the electrodes. Typically, conventional liquid ternary batteries have a cycle life of about 2,000 to 3,000 cycles, while lithium iron phosphate batteries can last for 3,000 to 5,000 cycles. If the battery is frequently subjected to high-power fast charging or used in high- or low-temperature environments, its lifespan will degrade even more rapidly. In everyday use, electric vehicles intended for home use typically show a noticeable drop in capacity after 3 to 5 years, while consumer electronics usually experience such capacity degradation within 1 to 3 years.

Solid-state batteries do not have a liquid electrolyte to corrode the electrodes, resulting in minimal side reactions at the solid-solid interface and much slower degradation of active materials. Currently, mass-produced solid-state batteries typically achieve cycle lives exceeding 5,000 cycles, while high-quality laboratory samples can even reach over 10,000 cycles, with very slow capacity fade throughout their entire lifecycle. This means that devices equipped with solid-state batteries can enjoy significantly longer service lives, greatly reducing the frequency of battery replacements and ultimately lowering long-term usage costs.

5. Volume utilization: Enhancing spatial efficiency

Liquid batteries, due to the need to reserve space for electrolyte injection and accommodate cell expansion, have an overall volume utilization rate of about 70%. In contrast, solid-state batteries, which contain no liquid and no separate separator, feature a more compact structure and can achieve a volume utilization rate of over 85%.

Simply put, for battery packs of the same size, solid-state batteries can store more energy; conversely, for the same energy demand, solid-state batteries can be made lighter and thinner, leaving more design flexibility for devices.

IV. Costs and Industrialization: The Generational Gap in Maturity

Behind the performance advantages lies a huge gap in manufacturing difficulty and cost—this is precisely the core reason why solid-state batteries, despite years of hype, have yet to achieve widespread adoption.

1. Lithium-ion batteries in liquid form: an extremely mature industrial ecosystem

After more than 30 years of industrial iteration, liquid lithium-ion batteries have developed an extremely sophisticated global supply chain—from upstream raw materials to midstream materials and down to downstream cell manufacturing. Equipment, processes, and yield rates have all been refined to exceptionally high levels.

Currently, the mass-production cost of liquid lithium batteries is approximately 0.5 to 0.8 yuan per Wh, with a cell yield exceeding 95%. Production capacity is ample, offering exceptional cost-effectiveness and making them the clear market mainstream today. The large-scale industry and mature supply chain represent liquid batteries’ strongest “moat.”

2. Semi-solid-state batteries: Can be mass-produced with minimal modifications, with clearly defined transitional properties.

The biggest advantage of semi-solid-state batteries is their exceptional compatibility with existing liquid-battery production lines: over 90% of the production equipment can be directly reused, requiring only minor modifications to processes such as electrolyte injection and formation before mass production can begin—resulting in very low costs for industrial transition.

In terms of cost, semi-solid-state batteries currently cost 15% to 30% more than liquid-state batteries of the same specifications. However, as production capacity ramps up and scale expands, costs are expected to continue declining. From an industry perspective, starting in 2024, semi-solid-state batteries have entered the stage of large-scale vehicle integration—ranging from mass-market passenger cars priced at around 100,000 yuan to high-end models costing over a million yuan—and corresponding implementation plans are already in place. This makes semi-solid-state technology the most commercially viable solid-state battery approach available today.

3. Solid-state batteries: Mass production will still take time, and costs remain high.

The manufacturing processes for all-solid-state batteries differ dramatically from those of liquid batteries. Issues such as the control of solid-solid interface impedance, the preparation of large-area electrolyte sheets, the handling of lithium-metal anodes, and the composite electrode fabrication process are all challenges that the industry has yet to fully overcome.

Currently, all-solid-state batteries are still in the pilot-scale and small-batch demonstration stages. Their mass-production yield remains low, and their manufacturing costs are several to even more than ten times higher than those of liquid batteries, meaning they are not yet ready for widespread consumer adoption. The industry generally expects that the oxide-based approach will be the fastest to reach engineering maturity, with small-batch vehicle integration anticipated around 2027. The sulfide-based approach boasts the most comprehensive performance characteristics, but its production requires a highly stringent, anhydrous and anaerobic inert environment, involving massive equipment investments. As such, large-scale commercialization is widely expected to take place around 2030.

V. Industry Endgame: Long-term Coexistence, Not Total Substitution

Many people ask: Once solid-state battery technology matures, will it completely replace liquid batteries? The answer is no. The evolution of battery technology has always been gradual rather than disruptive and revolutionary. Over the next 5 to 10 years—or even longer—liquid, semi-solid, and all-solid-state batteries will coexist for a long time, each tailored to meet different market demands.

1. Liquid Batteries: Holding Steady in the Affordable, Essential Market

Liquid batteries, thanks to their highly mature supply chains and extremely low costs, will continue to dominate markets where cost-effectiveness is paramount—such as mass consumer applications, affordable powertrains, and large-scale energy storage. Future R&D efforts will no longer focus on disruptive breakthroughs but rather on incremental improvements in safety and cycle life through methods like negative-electrode modification, optimization of electrolyte additives, and innovation in cell architecture. By leveraging their cost advantages, liquid batteries will maintain their stronghold in the vast existing market.

2. Semi-solid-state batteries: Seizing the incremental mid-to-high-end market

As a transitional technology, semi-solid-state batteries will first enter high-end passenger vehicles, commercial and industrial energy storage, and specialized applications—areas that have higher demands for safety and range—offering improved performance at an acceptable cost premium. As costs continue to decline, these batteries will gradually penetrate the mid-range market, serving as a bridge between liquid-electrolyte and all-solid-state technologies.

3. Solid-state batteries: Gradually expanding from high-end and specialized applications to broader markets.

All-solid-state batteries will first be deployed in high-end electric vehicles, aerospace, military equipment, and specialized energy storage applications—scenarios that have extremely high performance requirements and are relatively insensitive to price. As the industrial chain matures and costs decline year by year, these batteries will gradually expand into the consumer market. They represent the ultimate technological direction for power batteries, but widespread adoption will take a sufficiently long time.

To put it simply: Liquid batteries underpin today’s industrial foundation, semi-solid-state batteries support nearly five years of technological upgrades, and all-solid-state batteries point toward a long-term future spanning more than ten years. These three types represent different stages along the path of technological evolution—rather than being mutually exclusive alternatives.

VI. The Three Most Common Cognitive Biases

Regarding solid-state batteries, there’s a lot of exaggerated hype online. Here, we’d like to clarify three of the most common misconceptions.

Misconception 1: Solid-state batteries will never catch fire.

This statement is inaccurate. Solid-state batteries merely eliminate the biggest risk factor—the combustion of the electrolyte—but the positive and negative electrode materials themselves remain chemically active substances. If an extreme internal short circuit or overcharging/overdischarging occurs, triggering violent chemical reactions in these materials, they could still generate heat, smoke, or even catch fire. A more accurate statement would be: Solid-state batteries have a significantly lower risk of thermal runaway compared to liquid-electrolyte batteries, with a dramatic reduction in both the probability and intensity of fires, representing a qualitative leap in safety. However, this does not mean that solid-state batteries are “absolutely immune to combustion.”

Misconception 2: Solid-state batteries are the same as all-solid-state batteries.

This is the most common cognitive bias. When daily news reports talk about “mass production of solid-state batteries” or “solid-state batteries being installed in vehicles,” the vast majority are actually referring to semi-solid-state batteries. Fully solid-state batteries have not yet entered the consumer market on a large scale. There are significant differences between the two in terms of performance, cost, and maturity, and they should not be confused with each other.

Misconception 3: Solid-state batteries will soon completely replace liquid batteries.

No, that’s not going to happen. The battery industry is a capital-intensive, long-cycle sector—investing in a single cell production line often requires tens of billions of yuan—and it’s simply impossible to scrap and rebuild the entire infrastructure just because of technological advancements. Moreover, the cost and supply-chain advantages of liquid batteries cannot be surpassed in the short term. For a long time to come, the landscape will remain dominated by liquid batteries, with semi-solid batteries rapidly gaining traction and all-solid-state batteries gradually being implemented; a complete replacement won’t occur anytime soon.

From liquid to semi-solid and then to all-solid-state—this evolutionary journey of lithium batteries is, at its core, a continuous technological progression aimed at “reducing liquid content, enhancing safety, and boosting energy density.” Liquid batteries have laid the foundation for today’s global new-energy industry, while semi-solid batteries serve as a bridge toward even higher performance. And all-solid-state batteries represent the ultimate direction for power batteries. Each of these battery types has its own distinct role and inherent value. Once you understand the fundamental differences between liquid and solid-state batteries, you’ll gain a clear grasp of the true trajectory of next-generation energy technologies.