For lithium-ion battery anode applications, the ultimate value of ground and spheroidized graphite lies in its electrochemical performance, which directly determines the energy density, service life, rate capability and safety of finished battery cells. After precision grinding, shaping and spheroidization modification, graphite particles with controlled particle size, optimized morphology and modified surface properties need to be systematically tested to verify whether they meet the design requirements of anode materials. As a leading provider of graphite processing equipment and technology with 19 years of engineering excellence, JACAN Powder Equipment applies standardized electrochemical evaluation systems throughout its process development and product quality control. Combined with its four-step core process featuring 10–50μm precision grinding, ≥0.85 sphericity and 99.9%+ purity, JACAN has formed a complete testing methodology that covers laboratory-level precise characterization and industrial-scale batch quality verification.
Core electrochemical performance indicators for ground graphite
Before conducting specific tests, it is necessary to clarify the core electrochemical indicators corresponding to graphite processing quality, so as to match appropriate testing methods for different performance dimensions.
- First-cycle coulombic efficiency: Reflects the irreversible lithium consumption during the first charge-discharge cycle, and is highly sensitive to graphite purity, surface defects and moisture content. JACAN’s strict control of ≥99.9% purity and ≤0.5% moisture in the pretreatment stage is mainly aimed at improving this indicator.
- Specific capacity: Divided into gravimetric specific capacity (mAh/g) and volumetric specific capacity (mAh/cm³). The former reflects the intrinsic lithium storage capacity of graphite, and the latter is closely related to particle sphericity and tap density. The ≥0.85 sphericity standard of JACAN’s spheroidization process directly serves the improvement of volumetric specific capacity.
- Rate capability: Describes the capacity retention performance of graphite under high-current charge-discharge conditions, and is mainly affected by particle size distribution, surface structure and lithium-ion diffusion kinetics.
- Cycle stability: Refers to the capacity retention rate after long-term charge-discharge cycles, representing the long-term service life of the anode, and depends on the stability of the solid electrolyte interphase (SEI) film and the integrity of graphite layered structure.
- Interfacial impedance: Characterizes the resistance of lithium-ion migration at the electrode-electrolyte interface, and is an important indicator for evaluating SEI film properties and reaction kinetics.
Standard test workflow: from sample preparation to cell assembly
Electrochemical performance testing of graphite anode materials must follow a standardized sample preparation and battery assembly process to eliminate process errors and ensure the reliability of test results.
1. Electrode preparation
First, prepare the working electrode using the ground graphite sample as the active material. The typical formula for laboratory testing is 90 wt% graphite active material, 5 wt% conductive agent (such as acetylene black or Super P) and 5 wt% binder (usually polyvinylidene fluoride, PVDF). The materials are mixed with N-methyl-2-pyrrolidone (NMP) as solvent and stirred uniformly to form a stable slurry.
The slurry is then coated on copper foil current collector with controlled areal density, and dried under vacuum to remove residual solvent. After drying, the electrode sheet is calendered to a target compaction density to simulate the actual electrode manufacturing process. For ground graphite with high sphericity, higher compaction density can be achieved without particle crushing, which is also an important verification point of the spheroidization process effect.
2. Coin cell assembly
Laboratory electrochemical performance testing is usually carried out with CR2032-type coin half-cells, using metal lithium foil as the counter electrode. The assembly process must be completed in an argon-filled glove box with water and oxygen content below 0.1 ppm to avoid performance degradation caused by moisture and oxygen pollution, which also corresponds to the strict moisture control in JACAN’s production process.
The assembly sequence includes stacking the working electrode, separator, lithium counter electrode and current collector in sequence, injecting a certain amount of carbonate-based electrolyte, and then sealing the cell. The assembled cells need to stand for 12–24 hours at constant temperature to ensure that the electrolyte fully infiltrates the electrode and separator, so as to obtain stable test results.
Core test methods for electrochemical characterization
1. Galvanostatic charge-discharge test
As the most basic and widely used test method, galvanostatic charge-discharge test can obtain most key performance indicators of graphite anodes. The test is carried out on a battery tester, with the voltage window generally set to 0.01–1.5 V vs. Li/Li⁺.
- First-cycle performance test: The cell is charged (lithium intercalation) at a low current rate of 0.1C to 0.01 V, then held at constant voltage until the current drops to 0.05C, and then discharged (lithium deintercalation) at 0.1C to 1.5 V. By calculating the ratio of discharge capacity to charge capacity, the first-cycle coulombic efficiency is obtained, and the reversible gravimetric specific capacity is determined at the same time.
- Rate capability test: The cells are cycled at gradually increasing current rates, such as 0.2C, 0.5C, 1C, 2C and 5C, and the discharge capacity at each rate is recorded. The capacity retention rate at high rate relative to 0.2C capacity is used to evaluate the rate performance of graphite. For ground graphite products, reasonable particle size grading can effectively improve rate capability without excessive loss of first-cycle efficiency.
- Cycle life test: The cells are cycled continuously at a fixed rate (usually 1C) for hundreds of cycles, and the discharge capacity of each cycle is recorded. The capacity retention rate after a specified number of cycles is used to evaluate cycle stability. Graphite with optimized surface modification and high sphericity can maintain a stable SEI film during cycling, thus showing excellent capacity retention.
2. Cyclic voltammetry (CV)
Cyclic voltammetry tests the response current of the electrode under linearly scanned voltage, which is used to analyze the redox characteristics and reaction kinetics of graphite. The test usually scans at a slow scan rate (such as 0.1 mV/s) within the voltage window of 0–1.5 V.
By analyzing the position and shape of lithium intercalation/deintercalation peaks, the polarization degree of the electrode and the reversibility of the reaction can be judged. The peak current change during the initial cycles can also reflect the formation process of SEI film. For ground graphite with more surface defects, the CV curve will show obvious irreversible current in the first cycle, corresponding to low first-cycle efficiency.
3. Electrochemical impedance spectroscopy (EIS)
Electrochemical impedance spectroscopy applies a small amplitude AC sinusoidal signal to the cell in a wide frequency range, and obtains the impedance spectrum of the system by measuring the ratio of AC voltage to current. Through equivalent circuit fitting, the test can distinguish ohmic resistance, SEI film resistance and charge transfer resistance.
EIS is an important method to evaluate the interface properties of graphite anodes. Lower SEI resistance and charge transfer resistance indicate better electrolyte compatibility and faster reaction kinetics. JACAN’s surface modification process improves the interface state of graphite, which can be directly verified by EIS tests.
4. Advanced kinetic characterization
For in-depth mechanism research, more refined test methods can be adopted. Galvanostatic Intermittent Titration Technique (GITT) can calculate the lithium-ion diffusion coefficient inside graphite particles, which is used to evaluate the influence of particle size and crystal structure on diffusion kinetics. Differential capacity (dQ/dV) analysis can amplify subtle changes in the charge-discharge curve, and is often used to analyze phase transition behavior and polarization evolution during cycling.
Industrial quality control and rapid testing scheme
For large-scale industrial production, full laboratory testing of each batch of products takes a long cycle and cannot meet the needs of real-time quality control. Therefore, the industry usually adopts a two-level verification system combining rapid physical characterization and standard electrochemical confirmation.
1. Indirect evaluation by physical property indicators
In daily production, physical indicators that are easy to measure quickly, such as particle size distribution, sphericity, tap density, specific surface area (BET), purity and moisture, are used as routine inspection items. Through long-term data accumulation, the corresponding relationship between these physical indicators and electrochemical performance can be established, so as to quickly judge whether the product performance meets the standard.
For JACAN’s production lines, online monitoring of particle size and sphericity after classification, combined with offline rapid detection of purity and moisture, can realize preliminary quality screening of each batch of products, greatly improving quality control efficiency.
2. Standardized batch verification
Each batch of finished products needs to be sampled for standard coin cell electrochemical testing as the final quality release basis. The test strictly follows unified operating procedures and parameter settings to ensure the comparability of test results between different batches. For high-end anode products, full-cell tests using commercial cathode materials are also required to simulate the actual battery application scenario more accurately.
Key control points for reliable test results
The electrochemical performance of graphite is highly sensitive to test conditions. To obtain accurate and comparable results, the following control points must be strictly observed.
First, ensure sample representativeness. Ground graphite powder has a certain particle size distribution, so sampling must follow standardized procedures to avoid test deviation caused by sample inhomogeneity. Good batch consistency of products, as guaranteed by JACAN’s precision classification process, is the basis for stable test results.
Second, standardize the whole preparation process. Parameters such as slurry formula, coating areal density, compaction density, electrolyte dosage and assembly process must be kept consistent among different test groups, otherwise the difference in preparation technology will mask the performance difference of graphite materials themselves.
Third, control the test environment uniformly. The test temperature has a significant impact on electrochemical reaction kinetics, so the test must be carried out in a constant temperature environment. The standing time after cell assembly should also be unified to ensure consistent electrolyte infiltration degree.
Finally, set up parallel samples. At least 3–5 parallel cells are prepared for each sample, and abnormal data are excluded to take the average value, so as to reduce the accidental error of the test.
Testing the electrochemical performance of ground graphite is a systematic work covering sample preparation, battery assembly, multi-dimensional characterization and industrial quality control. It is not only the core means to verify the effect of grinding and spheroidization processes, but also the final standard to measure whether graphite anode materials meet the application requirements.
From laboratory precision characterization to industrial batch quality control, JACAN has established a complete electrochemical evaluation system based on its 19 years of process accumulation and verification by 1,200+ global clients. This system supports the continuous optimization of its four-step core process, and ensures that each batch of graphite products with 10–50μm particle size, ≥0.85 sphericity and 99.9%+ purity can deliver stable and excellent electrochemical performance. For the lithium-ion battery anode industry, standardized electrochemical testing methods are the technical foundation for promoting process upgrading and ensuring product reliability.
