Method for evaluating high-temperature storage performance of ternary and composite system soft package battery cells

Abstract

The application provides a method for evaluating high-temperature storage performance of a ternary and composite system soft package battery cell, and relates to the technical field of batteries.The method for evaluating high-temperature storage performance of a ternary and composite system soft package battery cell provided by the application comprises the following steps: pumping air from a formed to-be-tested battery cell and a test battery cell, and detecting the proportion of ethylene in the air as y; then sequentially aging and grading the test battery cell, and then placing the test battery cell in a 55 DEG C temperature environment for 28 days, and calculating the growth rate of the AC resistance of the battery cell before and after the placement as x; then fitting x and y to obtain a fitting curve, and calculating the growth rate of the AC resistance of the to-be-tested battery cell according to the fitting curve.The method has high efficiency, can accurately realize detection of the ACR change rate of the high-temperature storage of the battery cell, and improves the development efficiency of the battery cell.

Description

Technical Field

[0001] This invention relates to the field of biotechnology, and in particular to a method for evaluating the high-temperature storage performance of ternary and composite soft-pack battery cells. Background Technology

[0002] When ternary and composite soft-pack cells are stored at high temperatures, the increased side reactions can affect the change in AC internal resistance (ACR). Rapid increase in ACR can lead to increased heat generation during the actual charging and discharging of the cell, which can easily cause cell failure. Currently, the high-temperature storage performance is generally judged by actual testing of ACR changes, but this method is time-consuming.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for evaluating the high-temperature storage performance of ternary and composite soft-pack battery cells, so as to solve the above-mentioned technical problems.

[0005] To achieve the above objectives, the following technical solution is adopted: In a first aspect, the present invention provides a method for evaluating the high-temperature storage performance of ternary and composite soft-pack battery cells, comprising the following steps: After formation, the test cell and the cell to be tested are evacuated, and the proportion of ethylene in the gas is measured as y. Then, the test cell is aged and capacity tested in sequence, and the cell is fully charged after capacity testing. Then, it is placed in a temperature environment of 45~65℃ for 14~56 days, and the growth rate of AC internal resistance of the cell before and after the storage is calculated as x. Then, x and y are fitted to obtain a fitting curve, and the growth rate of AC internal resistance of the test cell is calculated based on the fitting curve.

[0006] As a further technical solution, the formation process is as follows: charging at a constant current rate of 0.1 to 1C to 70% to 100% SOC at a temperature of 35 to 55°C.

[0007] As a further technical solution, the proportion of ethylene in the gas is detected by gas chromatography.

[0008] As a further technical solution, the aging temperature is 25~55℃ and the aging time is 12~48h.

[0009] As a further technical solution, the capacity grading includes: charging and discharging at a rate of 0.5 to 1C at a temperature of 25 to 45°C, with the state of charge (SOC) of the battery cells in the cabinet ranging from 20% to 60% under the capacity grading.

[0010] As a further technical solution, the AC internal resistance was measured at room temperature before and after being left to stand.

[0011] As a further technical solution, the fitted curve is y=ax 2 +bx+c; Where a, b, and c are constants.

[0012] As a further technical solution, the positive electrode of the battery cell is composed of a current collector and a positive electrode active material layer coated on the current collector; The current collector includes aluminum foil.

[0013] The positive electrode active material layer includes a positive electrode active material, a conductive agent, a dispersant, and a binder; The positive electrode active material includes ternary materials or lithium battery positive electrode materials; The conductive agent includes one or more of carbon black or carbon nanotubes; The dispersant includes one or more of PVP, polyether dispersants, or polyester dispersants; The adhesive includes PVDF.

[0014] As a further technical solution, the negative electrode of the battery cell is composed of a current collector and a negative electrode active material layer coated on the current collector; The current collector includes copper foil; The active material layer includes a negative electrode active material, a conductive agent, a thickener, and a binder; The negative electrode active material includes one or more of graphite or hard carbon; The conductive agent includes one or more of carbon black or carbon nanotubes; The thickener includes CMC; The adhesive includes one or more of PAA or SBR.

[0015] As a further technical solution, the electrolyte of the battery cell includes: LiPF6 10~15wt%, FEC 5~10wt%, TMSP 0~1wt%, DTD 0~1wt%, VC 0~1wt%, EC 5~15wt%, EMC 10~20wt%, DEC 5~10wt%, with the balance being EC.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for evaluating the high-temperature storage performance of ternary and composite soft-pack battery cells. The method determines the change rate of the high-temperature storage ACR of the battery cell based on the proportion of ethylene in the formation gas. This method is highly efficient and can accurately detect the change rate of the high-temperature storage ACR of the battery cell, thereby improving the development efficiency of the battery cell. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 The fitted curve for Experiment Example 1; Figure 2 This is the fitted curve for Experiment Example 2. Detailed Implementation

[0019] The embodiments and examples of the present invention will be described in detail below. However, those skilled in the art will understand that the following embodiments and examples are for illustrative purposes only and should not be considered as limiting the scope of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise specified, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0020] In a first aspect, the present invention provides a method for evaluating the high-temperature storage performance of ternary and composite systems (e.g., NCM or NCM+LMFP / LFP / LMO) pouch cells, comprising the following steps: After formation, the test cell and the cell to be tested are evacuated, and the proportion of ethylene in the gas is measured as y. Then, the test cell is aged and capacity tested in sequence, and the cell is fully charged after capacity testing. Then, it is placed in a temperature environment of 45~65℃ for 14~56 days, and the growth rate of AC internal resistance of the cell before and after the storage is calculated as x. Then, x and y are fitted to obtain a fitting curve, and the growth rate of AC internal resistance of the test cell is calculated based on the fitting curve.

[0021] The inventors discovered a correlation between the proportion of ethylene in the gas produced during battery cell formation and the rate of change of its high-temperature storage ACR (Acoustic Reduction Rate). Based on this, the present invention determines the rate of change of the battery cell's high-temperature storage ACR by measuring the proportion of ethylene in the gas produced during formation. This method is highly efficient and can accurately detect the rate of change of the battery cell's high-temperature storage ACR, thereby improving the efficiency of battery cell development.

[0022] In some optional embodiments, the formation process is as follows: charging at a constant current rate of 0.1 to 1C (e.g., 0.1C, 0.5C, or 1C) to 70% to 100% SOC (e.g., 70% SOC, 80% SOC, or 100% SOC) at a temperature of 35 to 55°C (e.g., 35°C, 45°C, or 55°C).

[0023] In some alternative implementations, the proportion of ethylene in the gas is detected by gas chromatography.

[0024] In some optional embodiments, the aging temperature is 25~55°C (for example, but not limited to 25°C, 35°C or 55°C), and the aging time is 12~48h (for example, but not limited to 12h, 24h or 48h).

[0025] In some optional embodiments, the capacity grading includes: charging and discharging at a rate of 0.5 to 1C at a temperature of 25 to 45°C, so that the state of charge (SOC) of the battery cells is in the range of 20% to 60% after the capacity grading (the SOC of the battery is in the range of 20% to 60% after charging and discharging).

[0026] In some alternative implementations, the AC internal resistance is measured at room temperature before and after being left to stand.

[0027] In some alternative implementations, the fitted curve is y=ax 2 +bx+c; Where a, b, and c are constants.

[0028] Using this curve for fitting yields more accurate results.

[0029] In some alternative embodiments, the positive electrode of the battery cell consists of a current collector and a layer of positive active material coated on the current collector; The current collector includes, but is not limited to, aluminum foil, or coated aluminum foil. The thickness of the aluminum foil is 8~16μm, for example, but not limited to 8μm, 12μm or 16μm.

[0030] The positive electrode active material layer includes a positive electrode active material, a conductive agent, a dispersant, and a binder; The positive electrode active material includes, but is not limited to, ternary materials (NCM) or lithium battery positive electrode materials (LMFP / LFP / LMO). The conductive agent includes, but is not limited to, one or more of carbon black or carbon nanotubes; The dispersant includes, but is not limited to, one or more of PVP, polyether dispersants, or polyester dispersants; The adhesive includes, but is not limited to, PVDF.

[0031] In some alternative embodiments, the negative electrode of the battery cell consists of a current collector and a negative electrode active material layer coated on the current collector; The current collector comprises copper foil, or copper foil with a coating. The thickness of the aluminum foil is 3~12μm, for example, but not limited to 3μm, 8μm or 12μm; The active material layer includes a negative electrode active material, a conductive agent, a thickener, and a binder; The negative electrode active material includes, but is not limited to, one or more of graphite or hard carbon; The conductive agent includes, but is not limited to, one or more of carbon black or carbon nanotubes; The thickener includes, but is not limited to, CMC; The adhesive includes, but is not limited to, one or more of PAA or SBR.

[0032] In some optional embodiments, the electrolyte comprises: LiPF6 10~15wt%, FEC 5~10wt%, TMSP 0~1wt%, DTD 0~1wt%, VC 0~1wt%, EC 5~15wt%, EMC 10~20wt%, DEC 5~10wt%, with the balance being EC.

[0033] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0034] Example 1 A method for evaluating the high-temperature storage performance of ternary and composite pouch cells includes the following steps: Formation: Charge to full charge at a constant current rate of 0.1~1C at a temperature of 35~55℃; After formation, the test cell and the cell under test are evacuated, and the proportion of ethylene in the gas is measured as y. Then, the test cell is aged and capacity-divided in sequence. After capacity-dividing, the cell is fully charged. Then, it is placed in a 55°C environment for 28 days, and the growth rate of the AC internal resistance of the cell before and after the storage is calculated as x. Then, x and y are fitted to obtain a fitting curve, and the growth rate of the AC internal resistance of the test cell is calculated based on the fitting curve.

[0035] Experimental Example 1 Cells 1-1 to 1-4 were tested and fitted according to the method in Example 1. The results are shown in Table 1 and... Figure 1 As shown, the fitted curve is y = -0.7699x. 2- 0.9177x + 0.8535. Cells 1-1 to 1-4 were prepared using the same process, and the positive electrode, negative electrode, separator, and electrolyte are as follows: Positive electrode sheet: includes current collector (aluminum foil) and positive electrode active material layer coated on the current collector; the composition of the positive electrode active material layer is (LMFP:NCM=3:7) 96.2%, SP 1.3%, CNTs 0.7%, PVDF 1.6%, PVP 0.2%; Negative electrode sheet: includes a current collector (copper foil) and a negative electrode active material layer coated on the current collector. The composition of the negative electrode active material layer is: graphite 95.4%, SP 1.5%, CMC 1.3%, SBR 1.8%; Separator: 9μm PE + 3μm CCS (i.e., a 3μm ceramic coating is provided on a 9μm PE separator). Electrolyte: LiPF6 13wt%, EC 35wt%, FEC 10wt%, TMSP 0.3wt%, DTD 0.7wt%, VC 0.8wt%, EC 12.2wt%, EMC 19wt%, DEC 9wt%.

[0036] Table 1

[0037] Two test cells, prepared using the same process as the aforementioned cells, were then tested using the method described in Example 1. The ethylene content was measured to be 50.21% and 67.8%, respectively. Based on the fitting formula, the ACR growth rates were calculated to be 30.49% and 16.77%, respectively. The actual tested ACR growth rates were 30.51% and 16.76%, respectively. It is evident that the ACR growth rate calculated by the method of this invention is close to the actual test results, indicating that the method of this invention is accurate.

[0038] Experimental Example 2 Cells 2-1 to 2-4 were tested and fitted according to the method in Example 1. The results are shown in Table 2 and... Figure 2 As shown, the fitted curve is y = -6.4969x. 2 + 1.2653x + 0.6533. Cells 1-1 to 1-4 were prepared using the same process, and the positive electrode, negative electrode, separator, and electrolyte are as follows: Positive electrode sheet: includes a current collector (aluminum foil) and a positive electrode active material layer coated on the current collector; the positive electrode active material layer is composed of NCM 96.2%, SP 1.3%, CNTs 0.7%, PVDF 1.6%, and PVP 0.2%; Negative electrode sheet: includes a current collector (copper foil) and a negative electrode active material layer coated on the current collector. The composition of the negative electrode active material layer is: graphite 95%, SP 1.9%, CMC 1.3%, SBR 1.8%. Membrane: 9μm PE + 3μm CCS; Electrolyte: LiPF6 15wt%, EC 34wt%, FEC 10wt%, TMSP 0.5wt%, DTD 0.5wt%, VC 1wt%, EC 12wt%, EMC 17wt%, DEC 10wt%.

[0039] Table 2

[0040] Two test cells, prepared using the same process as the aforementioned cells, were then tested using the method described in Example 1. The ethylene content was measured to be 60.12% and 67.23%, respectively. Based on the fitting formula, the ACR growth rates were calculated to be 22.97% and 17.25%, respectively. The actual tested ACR growth rates were 22.98% and 17.26%, respectively. It is evident that the ACR growth rate calculated by the method of this invention is close to the actual test results, indicating that the method of this invention is accurate.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating the high-temperature storage performance of ternary and composite soft-pack battery cells, characterized in that, Includes the following steps: After formation, the test cell and the cell to be tested are evacuated, and the proportion of ethylene in the gas is measured as y. Then, the test cell is aged and capacity tested in sequence, and the cell is fully charged after capacity testing. Then, it is placed in a temperature environment of 45~65℃ for 14~56 days, and the growth rate of AC internal resistance of the cell before and after the storage is calculated as x. Then, x and y are fitted to obtain a fitting curve, and the growth rate of AC internal resistance of the test cell is calculated based on the fitting curve.

2. The method according to claim 1, characterized in that, The formation process is as follows: charging at a constant current rate of 0.1 to 1C to 70% to 100% SOC at a temperature of 35 to 55°C.

3. The method according to claim 1, characterized in that, The proportion of ethylene in the gas was determined by gas chromatography.

4. The method according to claim 1, characterized in that, The aging temperature is 25~55℃, and the aging time is 12~48h.

5. The method according to claim 1, characterized in that, The capacity grading includes charging and discharging at a rate of 0.5 to 1C at a temperature of 25 to 45°C, with the state of charge (SOC) of the battery cells in the cabinet ranging from 20% to 60% under the capacity grading.

6. The method according to claim 1, characterized in that, The AC internal resistance was measured at room temperature before and after being left to stand.

7. The method according to claim 1, characterized in that, The fitted curve is y=ax 2 +bx+c; Where a, b, and c are constants.

8. The method according to claim 1, characterized in that, The positive electrode of the battery cell consists of a current collector and a layer of positive electrode active material coated on the current collector; The current collector includes aluminum foil; The positive electrode active material layer includes a positive electrode active material, a conductive agent, a dispersant, and a binder; The positive electrode active material includes ternary materials or lithium battery positive electrode materials; The conductive agent includes one or more of carbon black or carbon nanotubes; The dispersant includes one or more of PVP, polyether dispersants, or polyester dispersants; The adhesive includes PVDF.

9. The method according to claim 1, characterized in that, The negative electrode of the battery cell consists of a current collector and a negative electrode active material layer coated on the current collector; The current collector includes copper foil; The active material layer includes a negative electrode active material, a conductive agent, a thickener, and a binder; The negative electrode active material includes one or more of graphite or hard carbon; The conductive agent includes one or more of carbon black or carbon nanotubes; The thickener includes CMC; The adhesive includes one or more of PAA or SBR.

10. The method according to claim 1, characterized in that, The electrolyte of the battery cell comprises: LiPF6 10~15wt%, FEC 5~10wt%, TMSP 0~1wt%, DTD 0~1wt%, VC 0~1wt%, EC 5~15wt%, EMC 10~20wt%, DEC 5~10wt%, with the balance being EC.

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