Date: 2025-03-24 hits: 178
The low capacity of lithium battery cells is a complex problem that involves the interaction of multiple factors. This article comprehensively analyzes the reasons for the low capacity of lithium battery cells from multiple aspects such as positive electrode materials, negative electrode materials, electrolytes, separators, current collectors, electrode active materials, electrolyte decomposition, and design and processes, and proposes corresponding solutions. Through in-depth exploration of these factors, this article aims to provide theoretical support and practical guidance for optimizing the capacity of lithium battery cells.
A. Introduction
The problem of low capacity of lithium battery cells seriously restricts their performance and service life. Low capacity not only affects the battery's endurance, but may also lead to rapid degradation of battery performance. This article will comprehensively analyze the reasons for the low capacity of lithium battery cells from multiple perspectives and propose corresponding solutions.
B. Analysis of the reasons for low capacity of lithium battery cells
1. Structural changes of positive electrode materials
The positive electrode material undergoes structural changes during lithium ion extraction and insertion, resulting in a decrease in capacity. Specifically manifested as:
Phase transfer and bulk structure change: During the charging and discharging process, the positive electrode material undergoes a compositional change, resulting in changes in lattice parameters and grain breakage, thereby reducing its electrochemical performance.
Oxidation state change: Metal elements are oxidized to high oxidation states during lithium removal, further exacerbating the structural damage of the material.
2. Structural changes of negative electrode materials
Negative electrode materials (such as graphite and silicon-based materials) also undergo significant changes during cycling:
Formation and thickening of SEI film: During the first charge and discharge process, an SEI clock film will form on the negative electrode surface, which is irreversible and leads to capacity loss.
Volume expansion and pulverization: During the process of lithium extraction and deintercalation, the volume expansion of silicon-based negative electrodes can reach 320%, leading to material pulverization and subsequent capacity degradation
Reduced graphitization degree: The graphitization degree of graphite negative electrode decreases during the cycling process, leading to a decrease in ion and electron conductivity, further exacerbating capacity decay.
3. Mismatch between electrolyte and negative electrode material
The compatibility between electrolyte and negative electrode material has a significant impact on battery capacity:
The SEI film is not dense or stable: The mismatch between the electrolyte and the negative electrode material may cause the SEI film to be too thick or unstable, thereby consuming a large amount of active lithium solvent molecules. Decomposition: Some solvents (such as PC) may react with the graphite negative electrode, causing the graphite layer to peel off and further reducing the capacity
4. Membrane degradation
The separator plays a role in separating the positive and negative electrodes and allowing lithium ions to pass through the battery, and its degradation can significantly affect the capacity:
Pore blockage: Electrolyte decomposition products and active material particles may block the pores of the membrane, hindering ion transport.
Structural degradation: During high temperature or cycling, the diaphragm structure may degrade, leading to an increase in internal resistance of the battery.
5. Collecting fluid rot
Current collectors (such as copper foil) may corrode during over discharge or cycling processes
Copper dissolution and deposition: Overdischarge may cause the copper current collector to dissolve and deposit on the negative electrode surface, hindering the insertion and extraction of lithium ions.
Increased internal resistance: Corrosion of the current collector can lead to an increase in battery internal resistance, further reducing capacity
6. Loss of electrode active materials
During the cycling process, electrode materials may experience structural damage caused by mechanical stress, such as lattice collapse. The repeated deintercalation of lithium ions in the positive and negative electrode materials can lead to mechanical stress on the electrode particles, resulting in lattice collapse. Active material detachment: Mechanical stress may also cause the active material to detach from the current collector, further reducing the battery capacity.
7. Electrolyte decomposition
Electrolyte may undergo oxidation or decomposition reactions during circulation:
Decreased mass transfer capacity: The decomposition of electrolyte can lead to a decrease in its mass transfer capacity, thereby reducing battery performance.
Increased internal resistance: Decomposition products may form an unstable interface layer on the electrode surface, further increasing the internal resistance of the battery.
8. Design and process issues
Battery design and production processes may also lead to low capacity:
Improper material matching: The mismatch between the negative electrode and the electrolyte may lead to lithium deposition, thereby reducing the capacity.
Insufficient optimization of chemical formation process: Insufficient optimization of chemical formation process may lead to non dense SEI film, which in turn affects battery performance.
Improper selection of separators: Using low-cost separators may lead to a decrease in battery performance, especially during the manual winding process, which may introduce defects.
C. Solution
1. Optimize material matching: Choose an electrolyte with good compatibility with the negative electrode material and ensure the stability of the material interface performance.
2. Improve production process: Optimize the formation process to ensure the density and uniformity of SEI film, while improving the stability of slurry dispersion and coating process.
3. Enhance battery design: Optimize battery module design, reduce circulating current, and lower battery internal resistance.
4. Developing new materials: researching high conductivity and low expansion negative electrode materials (such as silicon carbon composite materials) to improve battery cycling stability.
D. Conclusion
The low capacity of lithium battery cells is a complex problem, involving the interaction of multiple factors such as positive electrode materials, negative electrode materials, electrolytes, separators, current collectors, electrode active materials, electrolyte decomposition, and design and process. By optimizing material matching, improving production processes, enhancing battery design, and developing new materials, the problem of low capacity can be effectively solved, and the performance and service life of lithium batteries can be improved. Future research should further explore the mechanisms of these toxic interactions, providing more comprehensive theoretical support and practical guidance for optimizing the performance of lithium batteries.
