Description
1. Swelling behavior of the lithium ion battery(LIB)
During the charging and discharging process of lithum-ion batteries(LIBs) as lithium ions are intercalated ordeintercalated into the electrodes, the LIBs will expandand contract. Ideally, the intercalation and deintercalation of lithium ions are reversible, but in the actual cycle process, there is always a part of lithium ions that cannot be extracted from the electrodes or deposits on the surface of the anode as an insoluble by product during the cycle, resulting in irreversible swelling of or other more serious consequences, such as the deformation of the LIBs, the fragmentation of material particles, the rupture of the solid electrolyte interphase(SEI), and the consumption of electrolyte. Thus the swelling behavior of the LIB becomes an impotant indicator for evaluating the reliability of the battery. During the production process, the particle size, binder and must be optimized in advance. For the next generation anode materials with higher energy density such as silicon and lithium metal theswelling ratios ot these materials are much greater than that of the graphite anode. Therefore. how to accu.rately and effectively evaluate the swelling behavior of the LIBs made by these new anode materials becomes more important, which can guide the design of the LIB pack and improve the space utilizatior under the premise of safety.
On the other hand, the lithium plating also can cause the expansion of LIBs. Thus, how to identify the lithium plating window under different charging rate and temperature by the expansion behavior of LIBs is very helpful for the developments of the fast charging technology, sectional charging technology and other charging strategies.
2. Traditional Methods for Swelling Evaluation
- Disassemble different—condition cells and measure the thickness of the cell and electrodes by micrometer;
- Li plating window judgment: Through the disassembly of full charged cell to judge the lithium precipitation on electrode surface by visual inspection;
- Destructive Test: It is a cell consuming destructive test, and there is a higher safety risk and higher operation cost because the dry environment and professional people are required;
- Non in-site Test: Only the thickness data on several specific states can be acquired, the swelling behavior of cells cannot be described systemically; Big Deviation for lithium plating window assessment: Not every lithium plating SOC and potential in different rate can be quantified.
3. Swelling behavior of the lithium ion battery(LIB)
- In-situ swelling analysis system: Combined with the highly stable automatic platform and the high-precision thickness and mechanical sensors, it can achieve long-term stability and accurately detect the expansion thickness and the expansion force under different conditions.
- Multi-function test modes: the constant pressure and constant gap test modes can be realized for the cell, and the performance of the cell under different stress conditions can be evaluated.
- High precision control: The traditional fixture will generate ~70um deformation under the constant gap testing mode, which leads to the inaccurate swelling force test. However. the in-situ SWE series analysis system of IEST can control the change of the gap within ~1um by active modulation, and record the accurate swelling force during the constant gap testing mode.
4. Software
5. Applications
Applications
1. Application cases-Material Evaluations
1.1 Swelling behavior analysis of different anode materials
- Two types of anode material batteries with the same design and capacity, of which the full charge swelling and irreversible swelling thickness of B are significantly greater than that of At which can be used to screen and evaluate battery anode materials with swelling requirements;
- The swelling difference of three different anode material cells can be used to study the in-situ swelling process mechanism of anode materials during charge and discharge.
1.2 Swelling behavior analysis of different binder
- Comparison of the swelling behaviors of four LIBs made by different binders, the level of irreversible swellingis the same, and the main difference lies in the single-cvcle swelling thickness. In which the binder-C has the best swelling suppression effect. Thus, it can be used for evaluating and screening different binder materials.
2. Li-plating Analysis
2.1 Non-destructive Li-plating window judgment
- Compared with normal li-intercalation curve, the Li-plating swelling curve reaches inflection point when reaching Li-plating voltage, accordingly accurate Li-plating rate, voltage and SOC window will be acquired.
2.2 Application of step charge
- Quantitate the Li-plating voltage and Li-plating SOC window under a certain Li-plating rate, guide the echelon fast charging technology effectively, and realize the safe fast charging through the moderate charging strategies.
3. Application of cell structure
- Two models are used to evaluate the swelling of different anode cells, and the comparison law is basically the same as A> C> B.
- Because the two sides of the winding are bound, the crimping stress caused by the lateral swelling accumulates in the middle, so that the thickness increases with the cycle, and the four sides of the lamination are not bound, so the crimp stress of the group A pole piece with larger lateral swelling is released during the cycle, and the thickness decreases with the cycle. (Single-sided anode).
- In-situ Swelling can be used to deeply analyze the influence of process on stress and strain.
4. Process conditions
4.1 Different pressure conditions
- Properly increasing the pressure can reduce the irreversible swelling ratio of the battery;
- During the charging process, the two inflection points of the swelling curve correspond to the two peaks of the differential capacity curve, indicating that the swelling of the battery is related to the phase transition of deintercalation of lithium.
4.2 Different temperature conditions
- No matter the temperature rises from room temperature(25°C)up to 45°C and 60’C, or drops to 0°C, the irreversible swelling of the cell increases. However, the causes of irreversible swelling may be different under high temperature and low temperature conditions.
4.3 Different stress conditions
- In the range of 5000N, with the increase of the stress, the swelling stress of the cell increases gradually, which leads to the increase of the polarization of the cell and the deterioration of the dynamic performance. Therefore, we must pay attention to the influence of the initial stress in the design of the cell packing.
4.4 Thickness and stress changing during charge-discharge
- In-suit swelling analyzer(SWE) was used to monitor the changes of swelling thickness and swelling force of flexible cell in constant pressure and constant gap mode. It was found that the curves of swelling thickness and swelling force were related to the structural phase transition during charge-discharge process.
- This in-suit analysis method can be used by lithium researchers to analyze the swelling behavior of cells with different systems and production processes, so as to design cells with better performance.
Video
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