Method of determining optimal operating mode of battery cell

Abstract

This invention relates to the field of battery testing technology and discloses a method for determining the optimal operating mode of a battery cell. The method includes: taking multiple battery cells from the same batch for aging experiments; disassembling the cells at multiple gradients of state of harmlessness (SOH); recording the weight M and thickness D of each cell before disassembly; weighing the battery cell assembly to obtain n; determining the electrolyte weight m = M - n at the SOH; and determining the electrolyte consumption Δm = m0 - m0 of the aged cell at the SOH. ， The thickness expansion rate y = (D - D0) / D0 is used to fit the relationship between Δm, y, and SOH. Based on this relationship, the gap width H of the cell for any SOH value can be calculated as H = D0 * (y + 1) - ΔV / A. When the cell is working, it is positioned within the gap, and its width is dynamically adjusted to H according to the change in SOH of the battery. The method provided by this invention can obtain the optimal working mode of the cell and improve its service life.

Description

Technical Field

[0001] This invention relates to the field of battery testing technology, and more specifically, to a method for determining the optimal operating mode of a battery cell. Background Technology

[0002] During the cycling process, lithium-ion batteries undergo irreversible phase transitions and structural damage to their active materials, while the electrolyte continuously decomposes and is consumed on the electrode surfaces, leading to a gradual decrease in battery capacity. Electrolyte consumption is one of the key factors contributing to battery aging. When the electrolyte is insufficient to adequately wet the positive and negative electrodes, lithium-ion transport is hindered, internal resistance increases sharply, and capacity decay accelerates.

[0003] As the cycle continues, the electrolyte is consumed, creating tiny gaps inside the cell. These gaps are filled with residual free electrolyte, but because this portion of electrolyte is not effectively adsorbed by the electrode material, its utilization rate is low, and it cannot effectively replenish the consumed electrolyte.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining the optimal operating mode of a battery cell, and to provide an effective method for dynamically adjusting the internal environment of the battery cell, especially the electrolyte distribution, throughout the entire battery life.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a method for determining the optimal operating mode of a battery cell, comprising: Multiple cells from the same batch were subjected to aging tests. The cells were disassembled at multiple gradient SOH conditions, and the weight M and thickness D of each cell before disassembly were recorded. The disassembled battery cell assembly is cleaned to remove residues, then dried and weighed to obtain the weight n. The electrolyte weight m = Mn at this SOH is then obtained. The electrolyte consumption Δm of the aged battery cell at this SOH is Δm = m0 - m, where m0 is the electrolyte mass in the fresh battery cell. The thickness expansion rate y of the aged battery cell at this SOH is y = (D - D0) / D0, where D0 is the thickness of the fresh battery cell. By fitting the linear relationship between Δm and SOH, and fitting the linear relationship between y and SOH, two sets of relationships are obtained. Based on the two sets of relationships, the electrolyte consumption mass and thickness expansion rate corresponding to different SOH values ​​can be determined respectively. Based on the electrolyte consumption mass, the volume reduction ΔV of the electrolyte can be calculated. Based on ΔV, electrode area A, and thickness expansion rate y, the gap width H of the cell corresponding to this SOH value can be calculated as H = D0*(y+1)-ΔV / A. When the battery cell is working, it is placed in a gap. When the cell's SOH is 100%, the width of the gap is the same as the cell's thickness, which is D0. By applying a dynamic preload, the width of the gap is dynamically adjusted with the change of the battery's SOH. The adjustment amount of the gap width is the D0-H value corresponding to that SOH.

[0007] In an optional implementation, data in the range of 100% to 70% SOH are collected to fit the linear relationship between Δm and SOH, and the linear relationship between y and SOH.

[0008] In an optional embodiment, the positive electrode active material of the battery cell is lithium iron phosphate.

[0009] In an optional implementation, when the positive electrode active material of the battery cell is lithium iron phosphate, the linear relationship between Δm and SOH and the linear relationship between y and SOH are fitted to obtain the linear formulas Δm=a*SOH+b and y=c*SOH+d in the SOH range of 100%~70%.

[0010] In an optional embodiment, the disassembled battery cell assembly is cleaned with a solvent, wherein the solvent is DMC.

[0011] In an optional implementation, the average density of the electrolyte is known to be ρ, and ΔV can be calculated using Δm / ρ=ΔV.

[0012] In an optional implementation, during the entire operation of the battery cell, at least 7 SOH values ​​are uniformly set within the range of 100% to 70% SOH. The Δm and y values ​​corresponding to each SOH value are determined according to the aforementioned formula, and the corresponding H value is determined according to the Δm and y values. The SOH value of the battery is monitored in real time. When the set SOH value is reached, the current width of the gap is adjusted to H.

[0013] The present invention has the following beneficial effects: By studying the relationship between the state of health (SOH) of the battery cell and the amount of electrolyte consumed, a formula was obtained between the two. Based on this formula, the amount of electrolyte consumed under different health states can be determined. Furthermore, based on the amount of electrolyte consumed, the volume change of the battery cell under the current state can be determined. After obtaining the volume change, a dynamic preload was applied to the battery cell, gradually reducing its width. The reduction value matched the width of the battery cell corresponding to the volume change. This allowed the free electrolyte originally stored in the tiny gaps in the separator and electrodes to be squeezed out. Due to capillary action and pressure, the electrolyte was redistributed and infiltrated into the pores of the electrode materials that required more electrolyte, thereby replenishing the consumed electrolyte, improving the lithium-ion transport environment, and thus extending the battery cell's lifespan. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the working state of the battery cell of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0017] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0018] This invention provides a method for determining the optimal operating mode of a battery cell, comprising: Multiple cells from the same batch were subjected to aging tests. The cells were disassembled at multiple gradient SOH conditions, and the weight M and thickness D of each cell before disassembly were recorded. The disassembled battery cell assembly is cleaned to remove residues, then dried and weighed to obtain weight n. The electrolyte weight m = Mn at SOH is then obtained. The electrolyte consumption Δm of the aged battery cell at SOH is Δm = m0 - m, where m0 is the electrolyte mass in the fresh battery cell. The thickness expansion rate y of the aged battery cell at SOH is y = (D - D0) / D0, where D0 is the thickness of the fresh battery cell. By fitting the linear relationship between Δm and SOH, and fitting the linear relationship between y and SOH, two sets of relationships are obtained. Based on the two sets of relationships, the electrolyte consumption mass and thickness expansion rate corresponding to different SOH values ​​can be determined respectively. Based on the electrolyte consumption mass, the volume reduction ΔV of the electrolyte can be calculated. Based on ΔV, electrode area A, and thickness expansion rate y, the gap width H of the cell corresponding to this SOH value can be calculated as H = D0*(y+1)-ΔV / A. like Figure 1 As shown, when the battery cell is working, the battery cell is placed in the gap. When the battery cell SOH is 100%, the width of the gap is the same as the thickness of the battery cell, which is D0. By applying a dynamic pre-tightening force, the width of the gap is dynamically adjusted with the change of battery SOH. The adjustment amount of the gap width is the D0-H value corresponding to that SOH.

[0019] The method provided by this invention obtains a relationship between the state of health (SOH) of the battery cell and the amount of electrolyte consumed. Based on this relationship, the amount of electrolyte consumed under different health states can be determined. Furthermore, based on the amount of electrolyte consumed, the volume change of the battery cell under the current state can be determined. After obtaining the volume change, a dynamic preload is applied to the battery cell to reduce its width. The reduction value matches the width of the battery cell corresponding to the volume change. This allows the free electrolyte originally stored in the tiny gaps in the separator and electrodes to be squeezed out. Due to capillary action and pressure, the electrolyte is redistributed and wetted into the pores of the electrode materials that require more electrolyte, thereby replenishing the consumed electrolyte, improving the lithium-ion transport environment, and thus extending the battery cell's service life.

[0020] Optionally, data in the range of 100%~70% SOH are collected to fit the linear relationship between Δm and SOH, and the linear relationship between y and SOH.

[0021] As the number of charge-discharge cycles increases, the active materials in lithium-ion batteries gradually degrade, leading to a reduction in reversible capacity. When the state of equilibrium (SOH) drops to 70%, the battery's actual performance significantly decreases. Low SOH is often accompanied by increased internal resistance and poorer thermal stability, increasing the risk of overheating and thermal runaway. Especially in high-current charge-discharge scenarios, aging batteries are more prone to safety hazards. Therefore, throughout the cell's lifespan, to avoid the safety risks of sudden failure, batteries typically cease operation when their performance reaches 70% SOH, at which point they no longer meet usage requirements. Thus, data from the 70% SOH range were collected to fit curves.

[0022] Optionally, the positive electrode active material of the battery cell is lithium iron phosphate. Battery cells using this positive electrode active material are suitable for determining their optimal operating mode using the method provided by this invention.

[0023] Batteries degrade slowly in the early stages of aging, but the capacity decay rate accelerates once they enter the degradation stage (such as electrolyte decomposition, SEI film thickening, and lithium dendrite growth). Optionally, when the positive electrode active material of the battery cell is lithium iron phosphate, the linear relationships between Δm and SOH, and y and SOH are fitted to obtain the linear formulas Δm=a*SOH+b and y=c*SOH+d in the SOH range of 100%~70%.

[0024] Optionally, the disassembled battery cell assembly is cleaned using a solvent, wherein the solvent is dimethyl carbonate (DMC). The solvent is used to wash away residual electrolyte and lithium salts and other byproducts from the electrodes and separator.

[0025] After solvent cleaning, the disassembled battery cell components (electrodes, separators, etc.) are placed in a dryer and dried to constant weight, and their dry weight n is measured.

[0026] Alternatively, given the average density of the electrolyte as ρ, ΔV can be calculated using Δm / ρ=ΔV.

[0027] Optionally, during the entire operation of the battery cell, at least 7 SOH values ​​are uniformly set within the range of 100% to 70% SOH. The Δm value corresponding to each SOH value is determined according to the aforementioned formula, and the corresponding H value is determined according to Δm and y values. The SOH value of the battery is monitored in real time. When the set SOH value is reached, the current width of the gap is adjusted to H.

[0028] It should be noted that in practical applications, the more point values ​​set within the 100%~70% SOH range, the more frequently the gap width can be adjusted, and the longer the battery cell's lifespan. During experiments, manual adjustment can be used when the battery cell's SOH reaches the set value. After industrialization, a dedicated electronic control fixture can be considered, incorporating the aforementioned relationship formula, to dynamically adjust the gap width based on the formula, thereby further improving the battery cell's lifespan.

[0029] Example 1 Twenty-eight battery cells from the same batch were selected. The positive electrode active layer composition, by mass percentage, was 95.1% lithium iron phosphate, 0.3% dispersant, 2.3% SP, 0.3% CNT, and 2.0% PVDF; the negative electrode active layer composition, by mass percentage, was 95% graphite, 2.0% SP, 1.3% CMC, and 1.7% SBR; the separator was PP ceramic; and the electrolyte was LiPF6. The negative electrode area A was 568.17 cm². 2 The average density ρ of the electrolyte is 1.20 g / cm³. 3 .

[0030] The 28 cells were divided into 7 groups of 4 cells each. The initial average thickness D0 and electrolyte volume m0 of each group were recorded. An aging test was conducted on all cells. The aging degree of each group was different. The 7 groups were aged to SOH of 97%, 95%, 90%, 85%, 80%, 75%, and 70%, respectively. The aging test was conducted by 1C charge and discharge with a rest time of 30 minutes.

[0031] The aged battery cells were disassembled, and the weight M and thickness D before disassembly were recorded for each group. The average value of each group was taken, resulting in 7 sets of M and D data, as shown in Table 1. The battery cell assembly (all parts except the electrolyte) was cleaned with DMC, then dried and weighed. The average weight of each group was taken, resulting in 7 sets of dry weight data n under different SOH conditions, as shown in Table 1. The electrolyte consumption Δm of the aged battery cell at this SOH is calculated as m0-m, and the results are shown in Table 1. The battery cell thickness expansion rate y = (D- The calculation results of D0) / D0 are shown in Table 1.

[0032] Table 1. Values ​​of m0, M, n, Δm, D0, D, and y for each group of cells.

[0033] By fitting the curves based on the above data, the linear formulas Δm=-81.65*SOH+81.65 and y=-0.116*SOH+0.116 were obtained in the SOH 100%~70% range.

[0034] Based on the above formula, the electrolyte consumption Δm and cell expansion rate y corresponding to SOH are determined, and the corresponding gap width H = D0*(y+1)-ΔV / A is calculated accordingly, as shown in Table 2.

[0035] Table 2. Δm, y, H, and D0-H values ​​under different SOH values.

[0036] Ten fresh cells from the same batch were divided into two groups. One group had a constant gap width of D0, while the other group had a gap width of H adjusted at different SOH stages. Aging tests were conducted on both groups of cells, and the capacity retention rate of the two groups of cells after an average of 1000 cycles was recorded, as shown in Table 3.

[0037] Table 3 Comparison of Capacity Retention Rate

[0038] As can be seen from the comparison in Table 3, the capacity retention rate of the group whose gap width changes with different SOH is significantly higher, indicating that the method provided by the present invention can significantly improve the service life of the battery cell after obtaining a better cell working mode.

[0039] Example 2 Twenty-eight battery cells from the same batch were selected. The positive electrode active layer composition, by mass percentage, was 96.1% lithium iron phosphate, 0.1% dispersant, 1.8% SP, 0.2% CNT, and 1.8% PVDF; the negative electrode active layer composition, by mass percentage, was 96.0% graphite, 1.7% SP, 0.8% CMC, and 1.5% SBR; the separator was PP; and the electrolyte was LiPF6. The electrode area A was 326.13 cm². 2 The average density ρ of the electrolyte is 1.20 g / cm³. 3 .

[0040] The 28 cells were divided into 7 groups of 4 cells each. The initial average thickness D0 and electrolyte volume m0 of each group were recorded. An aging test was conducted on all cells. The aging degree of each group was different. The 7 groups were aged to SOH of 97%, 95%, 90%, 85%, 80%, 75%, and 70%, respectively. The aging test was conducted by 1C charge and discharge with a rest time of 30 minutes.

[0041] The aged battery cells were disassembled, and the weight and thickness of each group before disassembly were recorded. The average value of each group was taken to obtain 7 sets of M and D data, as shown in Table 4. The battery cell assembly (all parts except electrolyte) was cleaned with DMC, then dried and weighed. The average weight of each group was taken to obtain 7 sets of dry weight data n under different SOH, as shown in Table 4. The electrolyte consumption Δm of the aged battery cell at this SOH is calculated as m0 - m, and the results are shown in Table 4. The battery cell thickness expansion rate y is calculated as (D - D0) / D0, and the results are shown in Table 4.

[0042] Table 4 shows the m0, M, n, Δm, D0, D, and y values ​​for each group of cells.

[0043] By fitting the curves based on the above data, the linear formulas Δm=-39.92*SOH+39.92 and y=-0.107*SOH+0.107 were obtained in the SOH 100%~70% range.

[0044] Based on the above formula, the electrolyte consumption Δm and cell expansion rate y corresponding to different SOH values ​​are determined, and the corresponding gap width H = D0*(y+1)-ΔV / A is calculated accordingly, as shown in Table 5.

[0045] Table 5. Δm, y, H, and D0-H values ​​under different SOH values.

[0046] Ten cells were divided into two groups. One group had a constant gap width of D0, while the other group had a gap width of H adjusted at different SOH stages. Aging tests were conducted on both groups of cells, and the capacity retention rate of the two groups of cells after an average of 100 cycles was recorded, as shown in Table 6.

[0047] Table 6 Comparison of Capacity Retention Rate

[0048] As can be seen from the comparison in Table 6, the capacity retention rate of the group whose gap width changes with different SOH is significantly higher, indicating that the method provided by the present invention can significantly improve the service life of the battery cell after obtaining a better battery cell working mode.

[0049] In summary, the method provided by this invention has the following characteristics: 1. Active electrolyte replenishment: It changes the passive to the active, and uses mechanical force to force the release of inefficient interstitial electrolyte and replenish it to the consumption area, which improves the electrolyte utilization rate and effectively delays the capacity decay caused by electrolyte drying.

[0050] 2. Adaptive control: The preload is no longer a fixed value, but a variable that is dynamically adjusted according to the actual health status of the battery, realizing refined management throughout the entire life cycle.

[0051] 3. Extend battery life: By maintaining good electrode wetting, the battery internal resistance is reduced, the aging rate is slowed down, and thus the battery life and cycle life are significantly extended.

[0052] 4. Improved safety: Good electrolyte distribution helps stabilize the electrode interface, reduces the risk of lithium dendrite precipitation, and improves the safety of battery use.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the optimal operating mode of a battery cell, characterized in that, include: Multiple cells from the same batch were subjected to aging tests. The cells were disassembled at multiple gradient SOH conditions, and the weight M and thickness D of each cell before disassembly were recorded. The disassembled battery cell assembly is cleaned to remove residues, then dried and weighed to obtain the weight n. The electrolyte weight m = Mn at SOH is then obtained. The electrolyte consumption Δm of the aged battery cell at SOH is Δm = m0 - m, where m0 is the electrolyte mass in the fresh battery cell. The thickness expansion rate y of the aged battery cell at SOH is y = (D - D0) / D0, where D0 is the thickness of the fresh battery cell. By fitting the linear relationship between Δm and SOH, and fitting the linear relationship between y and SOH, two sets of relationships are obtained. Based on the two sets of relationships, the electrolyte consumption mass and thickness expansion rate corresponding to different SOH values ​​can be determined respectively. Based on the electrolyte consumption mass, the volume reduction ΔV of the electrolyte can be calculated. Based on ΔV, electrode area A, and thickness expansion rate y, the gap width H of the cell corresponding to this SOH value can be calculated as H = D0*(y+1)-ΔV / A. When the battery cell is working, it is placed in a gap. When the cell's SOH is 100%, the width of the gap is the same as the cell's thickness, which is D0. By applying a dynamic preload, the width of the gap is dynamically adjusted with the change of the battery's SOH. The adjustment amount of the gap width is the D0-H value corresponding to that SOH.

2. The method according to claim 1, characterized in that, Data in the range of 100%~70% SOH were collected to fit the linear relationship between Δm and SOH, and the linear relationship between y and SOH.

3. The method according to claim 1 or 2, characterized in that, The positive electrode active material of the battery cell is lithium iron phosphate.

4. The method according to claim 2, characterized in that, When the positive electrode active material of the battery cell is lithium iron phosphate, the linear relationship between Δm and SOH and the linear relationship between y and SOH are fitted. The linear formulas Δm=a*SOH+b and y=c*SOH+d are obtained in the SOH range of 100%~70%.

5. The method according to claim 1, characterized in that, The disassembled battery cell assembly is cleaned using a solvent, namely dimethyl carbonate.

6. The method according to claim 1, characterized in that, Given that the average density of the electrolyte is ρ, ΔV can be calculated using Δm / ρ=ΔV.

7. The method according to claim 1, characterized in that, During the entire operation of the battery cell, at least 7 SOH values ​​are uniformly set within the range of 100%~70% SOH. The Δm and y values ​​corresponding to each SOH value are determined according to the aforementioned formula, and the corresponding H value is determined according to the Δm and y values. The SOH value of the battery is monitored in real time. When the set SOH value is reached, the current width of the gap is adjusted to H.

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