Analysis and influence of low voltage in lithium battery formation process-Dongguan Xuanli electronics Co., LTD

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Analysis and influence of low voltage in lithium battery formation process

537 2024-04-02

First, the common reasons for poor low voltage

1. Problems related to the electrolyte

Decomposition or volatilization: The electrolyte concentration is too high, impurities (such as metal ions), or the temperature is out of control, resulting in decomposition, and gases (such as CO₂, Li₂CO₃) to increase the internal resistance and reduce the voltage.

Poor infiltration: the viscosity of the electrolyte is too high or the proportion of additives is unbalanced, resulting in uneven wetting of the electrode material, a decrease in the utilization rate of active substances, and an increase in resistance during charging and discharging.

2. The electrode material is defective

Poor uniformity: positive and negative powder agglomeration, uneven coating thickness, resulting in local active substances can not fully react, uneven voltage distribution.

Fluid contamination/oxidation: aluminum foil/copper foil surface oxidation or foreign body attachment, increase contact resistance, hinder electron transmission.

3. Improper process parameters

Abnormal current density: excessive current causes local overheating and accelerates electrolyte decomposition; Too low current results in incomplete formation and defects of SEI film.

Voltage curve control error: wrong cut-off voltage setting (too high resulting in lithium evolution, too low resulting in capacity loss).

4. Equipment and environmental factors

Poor sealing: leakage in the formation cabinet leads to electrolyte volatilization or moisture intrusion, destroying the SEI film.

Temperature management failure: The accuracy of the temperature sensor is insufficient or the heating/cooling system is faulty, causing local temperature difference abnormalities and affecting the reaction rate.

Excessive humidity: Environmental moisture causes water molecules to embed in the graphite layer and react with lithium ions to form LiOH·nH₂O, irreversible capacity loss.

5. Structural defects

Internal short circuit/diaphragm damage: dislocation of the pole plate and pinholes in the diaphragm during assembly lead to current short circuit and increased energy loss.

Poor packaging: the shell is not tightly sealed, the electrolyte leaks or gas escapes, and the internal pressure of the battery cell is unbalanced.

Second, the impact of low voltage on the battery cell

1. Capacity and energy density decrease

The utilization rate of active substances is low (such as poor electrode infiltration areas), the effective storage of lithium is reduced, and the nominal capacity cannot reach the design value.

SEI film defects lead to the obstruction of lithium ion transport, and the capacity attenuation accelerates during the cycle.

2. Shortened cycle life

Local lithium evolution or dendrite growth punctures the diaphragm, triggering an internal short circuit and increasing the risk of thermal runaway.

Continuous decomposition of electrolyte results in thickening of solid electrolyte interface (SEI) layer, accumulation of internal resistance, and decrease of charge and discharge efficiency.

3. Potential security risks

Gas precipitation leads to cell expansion and shell bulge, which may break or leak in serious cases.

Under the condition of high internal resistance, the temperature of high current discharge increases sharply, and the risk of thermal management failure increases.

4. Poor consistency

The proportion of low-voltage cells between batches increases, affecting the voltage balance of modules/battery packs and reducing system reliability.

Third, solutions and preventive measures

1. Optimize the electrolytic liquid system

Choose low viscosity, high ionic conductivity electrolyte (such as LiFSI based solvent).

Control the impurity content (metal ions ≤1ppm), add stable additives (such as VC, DTD).

2. Improve electrode preparation process

Ultrasonic dispersion and ball milling were used to improve powder dispersion and reduce agglomeration.

Optimize coating parameters (such as coating speed, oven temperature) to ensure uniform electrode thickness.

Clean collector surfaces (e.g. plasma treatment) to reduce contact resistance.

3. Fine process control

Step control of formation current (such as 0.1C precharge →0.2C constant current) to avoid overreaction.

The cutoff voltage is precisely controlled in combination with the CCCV mode (e.g. ternary material 4.25V vs graphite 3.65V).

4. Upgrade the environment and devices

Use a clean workshop environment with humidity ≤1%RH and temperature 25±2℃.

Equipped with constant temperature forming cabinet (±0.5℃ accuracy) and online gas detection system.

5. Quality monitoring and feedback mechanism

Implement real-time monitoring of the formation process (such as voltage-time curve analysis) to screen abnormal cells.

In situ testing (e.g. XRD, EIS) was used to locate the defect root and iterate the process parameters.

summarize：

The low voltage of the forming process is mainly caused by the synergistic effect of electrolyte, electrode material, process parameters and environment, which directly affects the capacity, life and safety of the cell. By systematically optimizing materials, processes and equipment, and establishing a closed-loop quality control system, the consistency and performance of cells can be significantly improved.

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