New Developments in All-Solid-State Batteries
With the rapid development of the new energy vehicle industry, innovation in battery technology has become a core driving force for industrial upgrading. All-solid-state batteries, in particular, are widely considered a key direction for next-generation power batteries due to their advantages such as high safety, high energy density, and long cycle life. However, what exactly constitutes a “solid-state battery”? The industry has long lacked a unified technical definition standard.
On May 22, 2025, the China Society of Automotive Engineers officially released the “All-Solid-State Battery Certification Method” (T/CSAE 434-2025), the first group standard for all-solid-state batteries and marking a key step forward in the technical specification of all-solid-state batteries.
1. What is an all-solid-state battery?
According to the standard definition, an all-solid-state battery is a battery system in which a solid electrolyte entirely transfers ions between the positive and negative electrodes. Compared to currently mainstream lithium-ion batteries with liquid or gel electrolytes, all-solid-state batteries eliminate the flammable liquid electrolyte, thereby fundamentally improving battery safety.
2. Technical Principles: Core Breakthroughs and Characterization Methods of Solid-State Batteries
2.1 Technological Transition from Liquid to Solid All-solid-state batteries (ASSBs) achieve breakthroughs in both energy density and safety by replacing traditional liquid electrolytes with solid-state electrolytes. Their core advantage stems from innovative electrolyte materials: sulfide electrolytes have a room-temperature ionic conductivity of 10⁻³ S/cm, approaching that of liquid electrolytes, and are compatible with lithium metal anodes (theoretical capacity of 3860 mAh/g), boosting energy density to over 500 Wh/kg. Oxide electrolytes (such as LLZO) exhibit excellent thermal stability (decomposition temperature >600°C), fundamentally eliminating the risk of thermal runaway. However, high impedance caused by poor solid-solid interface contact remains a major challenge. The contact resistance between traditional oxide electrolytes and electrodes can reach 1000 Ω·cm², requiring interface modification (such as LiPO₃ coating) to be reduced to below 10 Ω·cm².
2.2 Key Electrochemical Characterization Techniques:
Electrochemical impedance spectroscopy (EIS) is a core method for analyzing the interfacial properties of solid-state batteries. By applying an AC signal between 10 mHz and 1 MHz, a Nyquist plot can be obtained, which includes the bulk resistance (Rb), interfacial charge transfer resistance (Rct), and double-layer capacitance (Cdl). Ionic conductivity is calculated using the formula: σ = L/(Rb×A), where L is the electrolyte thickness (cm), A is the electrode area (cm²), and Rb is the bulk resistance (Ω). Using this method, a team from Tsinghua University discovered that the ionic conductivity of a sulfide electrolyte at 50°C is three orders of magnitude higher than at room temperature, providing a promising basis for high-temperature energy storage applications.
The differential capacity curve (dQ/dV) reveals electrochemical reaction mechanisms through the differential of capacity with respect to voltage (dQ/dV = ΔQ/ΔV). For example, the characteristic peaks of the NCM811 cathode at 3.7 V and 4.0 V correspond to phase transitions during Li⁺ insertion and extraction. The peak shift (>50 mV) during cycling can be used as a quantitative indicator of capacity decay. Experiments have shown that after 2000 cycles of solid-state batteries, the dQ/dV peak area decay rate is linearly correlated with the capacity retention rate (R² = 0.92).
The Neware 4/8 series battery testing system is designed for high-precision battery testing and supports research in a variety of application scenarios, including 3C batteries, solid-state batteries, and battery materials. Featuring a four-range design, it offers measurement accuracy of ±0.05% F.S., meeting precision testing requirements from microamperes (μA) to room amperes (mA). This portable battery testing solution with a Type-C power interface adds CV and EIS testing capabilities to meet electrochemical testing needs. In addition to standard charge and discharge testing capabilities, it also integrates EIS, DCIR, CV, pulse simulation, and other test functions to meet comprehensive testing needs.
3. Standard: liquid substances must be less than 1%
3.1 Technical logic of the judgment threshold
The standard uses “weight loss rate <1%” as the core criterion for all-solid-state batteries, which is due to the difference in thermal stability between liquid electrolytes and solid electrolytes. The boiling point of ester electrolytes (such as EC/DMC) is usually <150℃, and they can be completely volatilized within 6 hours in a vacuum environment at 120℃; while the mass loss of solid electrolytes (such as Li₇La₃Zr₂O₁₂) under this condition is <0.1%. Experimental data shows that when the liquid content exceeds 1%, the interfacial impedance will increase by more than 30%, and the cycle life will decrease to less than 500 times, verifying the rationality of the 1% threshold.
3.2 Key parameters of the test method
The standard test process includes three core links:
(1) Pretreatment: Charge and discharge cycles are performed at a rate of 0.1C (25℃±2℃, relative humidity ≤0.035%) until the capacity change is ≤3% for two consecutive times, simulating the actual use state.
(2) Break design: The square battery is broken at the explosion-proof valve (length ≥ 10% of the longest side length), and the soft-pack battery is broken at the side seal, with an exposure time of ≤ 5 minutes.
(3) Vacuum drying: Heat at 120±5℃ for 6 hours under a vacuum of -0.095~-0.1 MPa. The liquid content is calculated by the weight loss rate: η = (m₀ – m₁)/m₀ × 100%, where m₀ is the initial mass and m₁ is the mass after drying.
3.3 Experimental methods and equipment: from standard testing to solutions
Neware has launched a solid-state battery testing solution. Neware’s charge and discharge testing equipment has high-precision current and voltage control functions, which can achieve precise adjustment of the charge and discharge process and optimize battery performance. It can be linked with a temperature chamber (temperature control system) and work in conjunction with the battery performance testing software BTS8.0 to control the battery test environment temperature and reduce the impact of temperature fluctuations on interface stability.
Neware’s solid-state battery mold is suitable for solid-state battery testing. Its simple structure makes it easy to operate and can be used in a glove box. It is made of PEEK, a high-strength and corrosion-resistant material, to ensure mold durability and chemical stability. Its excellent sealing allows it to be used with pressure sensors. During solid-state battery manufacturing, the mold applies a specific pressure to help establish close contact between the solid electrolyte and electrode materials, thereby improving the battery’s conductivity and overall performance.
Solid-state battery molds play a critical role in battery assembly. Their precise positioning ensures stable positioning of battery components during the charge and discharge cycle, significantly reducing the risk of component displacement and damage, thereby improving overall battery performance and reliability. Solid-state battery testing can be performed in an all-in-one test chamber to create a constant temperature environment to ensure consistent battery testing, or by setting different temperature environments to test the battery’s temperature performance, improving testing efficiency and repeatability.
Neware’s all-in-one product series combines charge and discharge testing with temperature control for battery testing. This allows for simultaneous constant temperature testing and high and low temperature testing, comprehensively evaluating the performance and thermal stability of solid-state batteries at varying temperatures. This provides critical data for determining a battery’s high-temperature tolerance or low-temperature startup capability, thereby driving breakthroughs and developments in solid-state battery technology for extreme environmental applications.
● All-in-one design: Integrating charge and discharge testing with temperature control streamlines laboratory testing processes, reduces wiring complexity between devices, and provides a more streamlined and efficient testing environment.
● Temperature control: Constant temperature testing ensures consistent and repeatable experimental conditions. Providing precise temperature control, the system allows for battery cycle life evaluation under defined temperature cycling conditions.
4. Industry Significance Behind the Standard
Previously, so-called “solid-state battery” products have emerged in droves, but with diverse technology approaches (such as semi-solid, quasi-solid, and fully solid-state), consumers and automakers have struggled to discern their true performance.
The introduction of this standard will regulate market promotion, prevent “pseudo-solid-state” batteries from misleading consumers, promote technological research and development, guide companies towards true fully solid-state breakthroughs, foster industry chain collaboration, and provide a unified evaluation basis for material, battery cell, and vehicle manufacturers.
5. Challenges and Future of All-Solid-State Batteries
Despite the promising prospects of all-solid-state batteries, their industrialization still faces numerous challenges, such as high interfacial impedance, high production costs, and insufficient fast-charging performance. The release of this standard not only clarifies the technical definition but also provides important guidance for industry research and development.
In the future, with continued advancements in materials innovation (such as sulfide and oxide electrolytes) and process technology, all-solid-state batteries are expected to be the first to achieve commercial application in high-end electric vehicles, energy storage systems, and other fields.
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