Determination method and design method for liquid injection amount of battery

Abstract

The invention relates to the technical field of battery manufacturing, and discloses a battery liquid injection amount determination method and a battery liquid injection amount design method. The battery liquid injection amount determination method comprises the steps that a plurality of samples are provided, and the samples comprise fresh batteries of the same kind and batteries subjected to different cycle capacity fading; measuring the liquid absorption amount of the plurality of samples; the electrolyte excess coefficient of the battery after cycle capacity fading is calculated through the formula K = (delta VLAC + delta VLAA) / (VLAC0 + VLAA0); fitting a curve of multiple groups of calculated data to obtain a relation curve of the K value and the attenuation; 20% of attenuation is substituted into the relation curve, a corresponding K value is obtained through calculation, the calculated K serves as a coefficient k and is substituted into a formula Vin = (VLAC0 + VLAA0 + VLAS0) + k * (VLAC0 + VLAA0), and the liquid injection amount Vin is obtained. The method can accurately determine the appropriate liquid injection amount of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery manufacturing, and more particularly, to a method for determining the electrolyte injection volume of a battery and a design method therefor. Background Art

[0002] In the existing electrolyte injection process, the amount of electrolyte injected is usually determined based on static parameters such as the porosity of the electrode sheet and the density of the electrolyte. However, during the actual cycling process, the liquid absorption behavior of the battery cell is dynamically affected by the following factors:

[0003] 1. Changes in the microstructure of the electrode sheet: During the cycling process, the expansion / contraction of the electrode sheet causes dynamic changes in the porosity, affecting the infiltration and retention of the electrolyte.

[0004] 2. Consumption by side reactions: Side reactions such as the growth of the SEI film and the decomposition of the electrolyte cause a continuous reduction in the effective electrolyte.

[0005] 3. Lack of feedback on attenuation and liquid absorption amount: The traditional method does not establish a direct relationship between the cycling attenuation rate and the liquid absorption amount, and it is impossible to reverse-correct the injection volume based on the capacity attenuation data.

[0006] The defects of the existing technology include: over-injection of electrolyte causes gas generation and leakage, under-injection accelerates capacity attenuation, and there is a lack of prediction ability for long-term cycling performance. If a large number of batteries with different injection volumes are used for cycling experiments to determine the optimal injection volume, this method causes large losses to the battery samples and has a long cycle, which is not conducive to improving the economic benefits of the enterprise.

[0007] In view of this, the present invention is specifically proposed. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for determining the electrolyte injection volume of a battery and a design method therefor, aiming to improve at least one of the problems mentioned in the background art.

[0009] The present invention is implemented as follows:

[0010] In a first aspect, the present invention provides a method for determining the electrolyte injection volume of a battery, including:

[0011] Providing a plurality of samples, where the plurality of samples include fresh batteries of the same type of battery and batteries after different cycle capacity attenuations;

[0012] Measuring the liquid absorption amount of the plurality of samples;

[0013] Calculating the electrolyte excess coefficient of the battery after cycle capacity attenuation through the formula K = (ΔV LAC + ΔV LAA ) / (V LAC0 + V LAA0 ), where in the formula, ΔV LAC , ΔV LAArespectively represent the liquid absorption increase of the positive electrode and negative electrode of the battery after cycling, with the unit of cm 3 , V LAC0 , V LAA0 respectively represent the liquid absorption of the positive electrode and negative electrode of the fresh battery, with the unit of cm 3 ;

[0014] Fitting curves with the K values and corresponding attenuation amounts of multiple batteries with different cycle capacity attenuations to obtain the relationship curve between the K value and the attenuation amount;

[0015] Substitute the attenuation amount value of 20% indicating the late stage of cycling into the relationship curve, calculate the corresponding K value, and use it as the coefficient k;

[0016] Substitute the coefficient k into the formula V in =(V LAC0 +V LAA0 +V LAS0 )+k×(V LAC0 +V LAA0 ) to obtain the injection volume V in , where in the formula, V LAS0 is the liquid absorption of the separator of the fresh battery, with the unit of cm 3 .

[0017] In an alternative embodiment, the multiple samples include multiple groups with different injection volumes, and each group with different injection volumes includes a fresh battery and a battery with different cycle capacity attenuations of the same type of battery;

[0018] Take the average value of the K values of multiple groups with different injection volumes at the same attenuation amount and fit the curve with the corresponding attenuation amount to obtain the relationship curve.

[0019] In an alternative embodiment, the test method for the liquid absorption of the sample is as follows:

[0020] Disassemble the sample and measure the thickness of the active layer of the electrode;

[0021] Calculate the porosity of the electrode according to the true density and the measured thickness of the active layer of the electrode;

[0022] Calculate the liquid absorption of the electrode according to the formula V LA =h×A×ε, where h is the thickness of the active layer of the electrode, with the unit of μm, A is the area of the active layer of the electrode, with the unit of cm 2 , and ε is the porosity of the electrode.

[0023] In an alternative embodiment, the battery is a lithium iron phosphate or NMC ternary battery.

[0024] In an alternative embodiment, the battery is a lithium iron phosphate or NMC ternary battery.

[0025] In an alternative embodiment, the values of the different cycle capacity attenuations are 5%, 10%, 15% and 20% respectively.

[0026] In an alternative embodiment, the batteries after different cycle capacity attenuations are the batteries after charge and discharge cycling at 0.8 - 1.2C at 23 - 48°C.

[0027] In an alternative embodiment, k is 0.159 - 0.236, or k is 0.165 - 0.256.

[0028] In a second aspect, the present invention provides a method for designing a battery, including the method for determining the liquid injection amount of the battery as described in any one of the foregoing embodiments.

[0029] The present invention has the following beneficial effects:

[0030] The method provided by the present invention takes the cycle attenuation rate as the objective function, and reversely deduces the liquid injection amount to form a reverse design link of "performance requirements → process parameters". The method provided by the present invention can determine a better liquid injection amount with fewer battery samples, reducing the waste of electrolyte; the battery obtained by this design has a better cycle life; this method has wide applicability, can be compatible with the optimization of the liquid injection process of solid-state batteries, and is suitable for high-challenge scenarios such as high voltage and fast charging. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be 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 therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0032] Figure 1 A curve model established with the cycle attenuation rate and the growth rate of the electrode sheet liquid absorption (electrolyte excess coefficient K) of the 1# battery in Example 1 as data;

[0033] Figure 2 A curve model established with the cycle attenuation rate and the growth rate of the electrode sheet liquid absorption (electrolyte excess coefficient K) of the 2# battery in Example 1 as data;

[0034] Figure 3 A curve model established with the cycle attenuation rate and the growth rate of the electrode sheet liquid absorption (electrolyte excess coefficient K) of the 3# battery in Example 1 as data;

[0035] Figure 4 A curve model established with the cycle attenuation rate and the growth rate of the electrode sheet liquid absorption (electrolyte excess coefficient K) of the 4# battery in Example 1 as data;

[0036] Figure 5 The curve model established with the cycle attenuation rate of the 5# battery and the liquid absorption growth rate of the electrode sheet (electrolyte excess coefficient K) in Example 1 as data;

[0037] Figure 6 The curve model established with the average value of the cycle attenuation rate and the liquid absorption growth rate of the electrode sheet (electrolyte excess coefficient K) of each group of batteries in Example 1 as data;

[0038] Figure 7 The cycle curves of each group of batteries with different liquid injection amounts in Example 1.

[0039] Figure 8 The curve model established with the cycle attenuation rate of the 6# battery and the liquid absorption growth rate of the electrode sheet (electrolyte excess coefficient K) in Example 2 as data;

[0040] Figure 9 The curve model established with the cycle attenuation rate of the 7# battery and the liquid absorption growth rate of the electrode sheet (electrolyte excess coefficient K) in Example 2 as data;

[0041] Figure 10 The curve model established with the cycle attenuation rate of the 8# battery and the liquid absorption growth rate of the electrode sheet (electrolyte excess coefficient K) in Example 2 as data;

[0042] Figure 11 The curve model established with the cycle attenuation rate of the 9# battery and the liquid absorption growth rate of the electrode sheet (electrolyte excess coefficient K) in Example 2 as data;

[0043] Figure 12 The curve model established with the cycle attenuation rate of the 10# battery and the liquid absorption growth rate of the electrode sheet (electrolyte excess coefficient K) in Example 2 as data;

[0044] Figure 13 The curve model established with the average value of the cycle attenuation rate and the liquid absorption growth rate of the electrode sheet (electrolyte excess coefficient K) of each group of batteries in Example 2 as data;

[0045] Figure 14 The cycle curves of each group of batteries with different liquid injection amounts in Example 2. Detailed implementation manners

[0046] 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. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can all be obtained as conventional products through commercial purchase.

[0047] The features and performance of the present invention will be further described in detail below in conjunction with the embodiments.

[0048] A method for determining the injection volume of a battery provided by an embodiment of the present invention includes:

[0049] Providing a plurality of samples, the plurality of samples including fresh batteries of the same type of battery and batteries after different cycle capacity attenuations;

[0050] Measuring the liquid absorption of the plurality of samples;

[0051] Calculating the electrolyte excess coefficient of the battery after cycle capacity attenuation through the formula K = (ΔV LAC +ΔV LAA ) / (V LAC0 +V LAA0 ), where in the formula, ΔV LAC and ΔV LAA respectively represent the liquid absorption increase of the positive electrode plate and the negative electrode plate of the battery after cycling, with the unit cm 3 , and V LAC0 and V LAA0 respectively represent the liquid absorption of the positive electrode plate and the negative electrode plate of the fresh battery, with the unit cm 3 ;

[0052] Fitting a curve with the K values of a plurality of batteries after different cycle capacity attenuations and the corresponding attenuation amounts to obtain a relationship curve between the K value and the attenuation amount;

[0053] Substituting the attenuation amount value of 20% indicating the late stage of cycling into the relationship curve, calculating the corresponding K value, and taking it as the coefficient k;

[0054] Substituting the coefficient k into the formula V in = (V LAC0 +V LAA0 +V LAS0 )+k×(V LAC0 +V LAA0 ) to obtain the injection volume V in , where in the formula, V LAS0 is the liquid absorption of the separator of the fresh battery, with the unit cm 3 .

[0055] The method provided by the present invention takes the cycle attenuation rate as the objective function, reversely derives the injection volume, and forms a reverse design link of "performance requirements → process parameters". The method provided by the present invention can determine a better injection volume with fewer battery samples, realize precise injection control of the battery, reduce the waste of electrolyte; the battery obtained through this design has a better cycle life; this method has wide applicability and can be compatible with the optimization of the injection process of solid-state batteries and adapt to high-challenge scenarios such as high voltage and fast charging.

[0056] It should be noted that the injection volume V in obtained through the above methodis the preferred value of the liquid injection volume, which provides a reference for the design of the liquid injection volume. It should be understood that injecting liquid according to the numerical range near V in can enable the battery to have better cycle performance. For example, this numerical range is 0.9V in to 1.1V in .

[0057] For batteries with the same electrode sheet and the same separator but different liquid injection volumes, the k values are not very different under the same capacity attenuation. Therefore, the method provided by the present invention can be used for the same type of battery to determine the k value and further determine the preferred liquid injection volume V in .

[0058] Preferably, although the k values of the same type of batteries with different liquid injection volumes are not very different, there may be slight differences. Therefore, in order to improve the accuracy, multiple samples include multiple groups with different liquid injection volumes, and each group of the different liquid injection volume groups includes fresh batteries of the same type of battery and batteries after different cycle capacity attenuations; at the same attenuation amount, the average value of the k values of multiple different liquid injection volume groups is fitted with the corresponding attenuation amount to obtain the relationship curve.

[0059] Optionally, through research, it is found that based on the formula V in =(V LAC0 +V LAA0 +V LAS0 )+k×(V LAC0 +V LAA0 ), when the k value is 0.159 - 0.236, or k is 0.165 - 0.256, the battery obtained by injecting liquid according to the calculated liquid injection volume has better cycle performance.

[0060] Optionally, the test method for the electrolyte excess coefficient of the sample is as follows:

[0061] S1. Prepare the sample

[0062] Take batteries of the same type (same electrode sheet and separator), which can include one group of batteries or multiple groups of batteries. If it is one group of batteries, the batteries in this group are completely the same, only the cycle capacity attenuation is different;

[0063] If there are multiple groups of batteries, the liquid injection volumes between groups are different, and the batteries within each group are completely the same, only the cycle capacity attenuation is different.

[0064] The same type of battery samples within each group include fresh batteries and batteries after different cycle capacity attenuations.

[0065] S2. Disassemble the sample and measure the thickness of the active layer of the electrode sheet.

[0066] The specific method for measuring the thickness is as follows: Use a micro-CT or a thickness gauge to measure the thickness of the positive and negative electrodes, and then subtract the thickness of the current collector to obtain the thickness of the active layer.

[0067] S3. Calculate the porosity of the electrode based on the true density and the measured thickness of the active layer of the electrode.

[0068] The formula is as follows: ε = 1 - ρ coat (ω AM / ρ AM + ω CA / ρ CA + ω B / ρ B ); where ε is the porosity, ρ coat is the bulk density of the coating, with the unit of g / cm 3 , ω is the mass percentage of the coating components, ρ is the true density of the components, with the unit of g / cm 3 , and the subscripts AM, CA, and B represent the active material, the conductive agent, and the binder, respectively.

[0069] S4. Calculate the liquid absorption capacity of the electrode

[0070] Calculate the liquid absorption capacity of the electrode according to the formula V LA = h × A × ε, where V LA is the liquid absorption volume, h is the thickness of the active layer of the electrode, with the unit of μm, A is the area of the active layer of the electrode, with the unit of cm 2 , and ε is the porosity of the electrode.

[0071] S5. Calculate the excess coefficient

[0072] Calculate the electrolyte excess coefficient of the battery after cyclic capacity decay through the formula K = (ΔV LAC + ΔV LAA ) / (V LAC0 + V LAA0 ), where ΔV LAC , ΔV LAA respectively represent the increased liquid absorption amounts of the positive and negative electrodes of the battery after cycling, with the unit of cm 3 , and V LAC0 , V LAA0 respectively represent the liquid absorption amounts of the positive and negative electrodes of the fresh battery, with the unit of cm 3 .

[0073] S6. Establish a relationship model

[0074] If the battery sample only includes a group of the same type of batteries, use the calculated K value and the corresponding cyclic capacity decay coefficient to fit a binary linear relationship curve;

[0075] If the battery sample includes multiple batteries with different liquid injection amounts, the average value of the K values of multiple different liquid injection amount groups at the same attenuation amount can be fitted with the corresponding attenuation amount curve to obtain the relationship curve.

[0076] Optionally, the battery is a lithium iron phosphate or NMC ternary battery.

[0077] Further, the numerical values of different cycle capacity attenuations are 5%, 10%, 15% and 20% respectively.

[0078] Optionally, the batteries after different cycle capacity attenuations are the batteries after charge and discharge cycling at 0.8 - 1.2C (such as 0.8C, 1C or 1.2C) at 23 - 48°C (such as 23°C, 25°C, 30°C, 40°C, 45°C or 48°C).

[0079] The embodiment of the present invention provides a battery design method, including the method for determining the liquid injection amount of the battery provided by the embodiment of the present invention.

[0080] Example 1

[0081] 1. Prepare the battery

[0082] Prepare 5 groups of LiFePO4 soft-pack batteries with different liquid injection amounts, with a capacity of 25Ah, and the liquid injection amounts are known as shown in

[0083] Table 1;

[0084] Instance number 1# 2# 3# 4# 5# <![CDATA[Initial filling volume V in / cm 3 > 77.73 80.29 82.88 85.37 88.02 Initial coefficient k calculated based on the formula 0.081 0.120 0.159 0.196 0.236

[0085] 2. Charge and discharge cycling

[0086] Perform charge and discharge cycling on each group of batteries with different liquid injection amounts, at 45°C, 1C charge and discharge, so that the cycle capacity attenuation rates of the battery cells in each group are 0% (i.e., no cycling), 5%, 10%, 15%, 20% respectively;

[0087] The parameters of all battery cells are shown in Table 2:

[0088] Table 2 Parameters of battery cells

[0089]

[0090]

[0091] 3. Measure the thickness of the electrode sheets: Use micro-CT to measure the thickness of the positive and negative electrode sheets during the cycling process, and disassemble some batteries to measure the initial thickness and the thickness after cycling of the positive and negative electrode sheets with a thickness measuring instrument, and record the data, as shown in Table 3.

[0092] Table 3 Thicknesses of each battery group at different attenuations

[0093]

[0094] 4. Calculate the porosity: According to the material density of the electrode sheet and the measured thickness, calculate the porosity of the electrode sheet, as shown in Table 4.

[0095] Table 4 Calculated porosities of different battery packs at different attenuations

[0096]

[0097]

[0098] 5. Determine the liquid absorption amount: According to the calculated porosity and the volume of the electrode sheet, calculate the liquid absorption amount of the electrode sheet, as shown in Table 5.

[0099] Table 5 Calculated liquid absorption amounts of different battery packs at different attenuations

[0100]

[0101] 6. Calculate the electrolyte excess coefficient: Take the change in the liquid absorption amount during the cycling process as the electrolyte excess coefficient, as shown in Table 6.

[0102] Table 6 Electrolyte excess coefficients of different battery packs at different attenuations

[0103]

[0104] Establish relationship models for the data of Group 1#, 2#, 3#, 4#, 5# and the average group in Table 6 respectively, as Figures 1 to 6 shown. Substitute the attenuation value 0.2 (20%) at the later stage of cycling into each of the fitted formulas, and the calculated results k are 0.198, 0.195, 0.195, 0.196, 0.198, 0.196 respectively.

[0105] Substitute the above calculated values into the formula V in =(V LAC0 +V LAA0 +V LAS0 )+k×(V LAC0 +V LAA0 ), and calculate to obtain that V in are 85.48, 85.31, 85.31, 85.35, 85.47 、 85.38 cm 3 . It can be seen that the calculated optimal liquid injection amounts V in obtained from the models established with the experimental data of each experimental group and the average group are very close. In the range of 85.30 - 85.50, take the data of the average group, which is approximately 85.38 cm 3 .

[0106] According to the preferred electrolyte injection volume obtained from the above calculations, it can be seen that the battery has better high-temperature cycle performance when the injection volume is around 85.38 cm 3 or so. Compare the injection volume obtained from this calculation with the injection volumes of the known groups 1#, 2#, 3#, 4#, and 5#. Among them, the injection volume of group 4# is very close to the value obtained from the calculation. Therefore, the cycle performance of the battery in group 4# among the above 5 groups of batteries should be the best.

[0107] 7. Verification

[0108] To verify the accuracy of the above results, charge and discharge the fresh batteries of groups 1#, 2#, 3#, 4#, and 5# at 45 °C and 1C, and record the number of cycles when the capacity retention rate decays to 80%, as Figure 7 shown.

[0109] From Figure 7 it can be seen that the number of cycles of group 4# is the most, exceeding 2100 cycles. This result shows that the injection volume determined by the method for determining the preferred electrolyte injection volume provided in the embodiments of the present invention is accurate and feasible.

[0110] In addition, by observing the cycle curve, it can be seen that the cycle performance of groups 3#, 4#, and 5# is the best. The k values corresponding to these three groups based on the formula V in =(V LAC0 +V LAA0 +V LAS0 )+k×(V LAC0 +V LAA0 ) are 0.159, 0.196, and 0.236 respectively. Therefore, it can be seen that when the k value is 0.159 - 0.236, manufacturing the battery according to the calculated injection volume has good cycle performance.

[0111] Example 2

[0112] 1. Prepare the battery

[0113] Prepare 5 groups of Li(NiCoMn)O2 soft-pack batteries with different injection volumes, with a capacity of 30 Ah, and the known injection volumes are shown in Table 7;

[0114] Instance number 6# 7# 8# 9# 10# <![CDATA[Initial filling volume V in / cm 3 > 71.10 73.67 76.26 78.83 81.43 Initial coefficient k calculated based on the formula 0.075 0.120 0.165 0.210 0.256

[0115] 2. Charge and discharge cycle

[0116] Perform charge and discharge cycles on each group of batteries with different injection volumes. Charge and discharge at 25 °C and 0.33C, so that the cycle capacity attenuation rates of the battery cells in each group are 0% (i.e., no cycle), 5%, 10%, 15%, and 20% respectively;

[0117] The parameters of all battery cells are shown in Table 8:

[0118] Table 8 Parameters of Battery Cells

[0119]

[0120] 3. Measure the thickness of the electrode sheets: Use micro-CT to measure the thickness of the positive and negative electrode sheets during the cycling process, and disassemble some batteries to measure the initial thickness and the thickness after cycling of the positive and negative electrode sheets using a thickness gauge, and record the data as shown in Table 9.

[0121] Table 9 Thicknesses of Different Battery Packs at Different Degrees of Deterioration

[0122]

[0123] 4. Calculate the porosity: Calculate the porosity of the electrode sheets based on the material density of the electrode sheets and the measured thickness, as shown in Table 10.

[0124] Table 10 Calculated Porosities of Different Battery Packs at Different Degrees of Deterioration

[0125]

[0126] 5. Determine the liquid absorption capacity: Calculate the liquid absorption capacity of the electrode sheets based on the calculated porosity and the volume of the electrode sheets, as shown in Table 11.

[0127] Table 11 Calculated Liquid Absorption Capacities of Different Battery Packs at Different Degrees of Deterioration

[0128]

[0129] 6. Calculate the electrolyte excess coefficient: Take the growth rate of the liquid absorption capacity during the cycling process as the electrolyte excess coefficient, as shown in Table 12.

[0130] Table 12 Electrolyte Excess Coefficients of Different Battery Packs at Different Degrees of Deterioration

[0131]

[0132] Establish relationship models for the data of No. 6, No. 7, No. 8, No. 9, No. 10 and the average group in Table 12 respectively, as shown in Figures 8 to 13 Substitute the decay value 0.2 (20%) at the later stage of cycling into each of the fitted formulas, and the calculated results k are 0.211, 0.212, 0.209, 0.210, 0.209, 0.210 respectively.

[0133] Substitute the above calculated values into the formula V in =(V LAC0 +V LAA0 +V LAS0 )+k×(V LAC0 +V LAA0 ) respectively, and calculate V inThey are 78.89, 78.94, 78.76, 78.82, 78.78 respectively 、 78.83 cm 3 It can be seen that the optimal liquid injection volume V obtained by calculating the model established with the experimental data of each experimental group and the average group in has very close numerical values, within the range of 78.76 - 78.94, and the data of the average value group is about 78.83 cm 3 .

[0134] According to the optimal liquid injection volume obtained from the above calculations, it can be known that the battery has better high - temperature cycle performance when the liquid injection volume is around 78.84 cm 3 . Comparing the liquid injection volume obtained by this calculation with the liquid injection volumes of the known groups 6#, 7#, 8#, 9#, and 10#, among which the liquid injection volume of group 9# is very close to the value obtained by calculation. Therefore, the cycle performance of the battery in group 9# among the above 5 groups of batteries should be the best.

[0135] 7. Verification

[0136] To verify the accuracy of the above results, the fresh batteries of groups 6#, 7#, 8#, 9#, and 10# were charged and discharged at 25°C and 1C, and the number of cycles when the capacity retention rate decayed to 80% was recorded, as Figure 14 shown.

[0137] From Figure 14 it can be seen that the number of cycles of group 9# is the most, exceeding 1600 cycles. This result shows that the liquid injection volume determined by the method for determining the optimal electrolyte liquid injection volume provided in the embodiments of the present invention is accurate and feasible.

[0138] In addition, by observing the cycle curves, it can be seen that the cycle performance of groups 8#, 9#, and 10# is the best. For these three groups, the corresponding k values based on the formula V in =(V LAC0 +V LAA0 +V LAS0 ) + k×(V LAC0 +V LAA0 ) are 0.165, 0.210, and 0.256 respectively. Therefore, it can be seen that when the k value is between 0.165 and 0.256, manufacturing batteries according to the calculated liquid injection volume has good cycle performance.

[0139] It can be seen from Example 1 and Example 2 that the method for determining the battery liquid injection volume provided by the present invention can be used to determine the battery liquid injection volume, and the battery manufactured according to the determined liquid injection volume has better cycle performance.

[0140] In summary, the method provided by the present invention uses the cyclic decay rate as the objective function to inversely deduce the liquid injection volume, forming a reverse design link of "performance requirements → process parameters". The method provided by the present invention can determine a better liquid injection volume with fewer battery samples, reducing the waste of electrolyte; the battery obtained through this design has a better cycle life; this method has wide applicability, can be compatible with the optimization of the liquid injection process for solid-state batteries, and is suitable for high-challenge scenarios such as high voltage and fast charging.

[0141] The foregoing are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for determining the amount of liquid injected into a battery, characterized in that: include: Providing a plurality of samples, wherein the plurality of samples include fresh batteries and batteries with different cycle capacity decay of the same battery; measuring the liquid absorption of the plurality of samples; By the formula K=(ΔV LAC +ΔV LAA ) / (V LAC0 +V LAA0 ) to calculate the electrolyte excess coefficient of the battery after the cycle capacity decay, where ΔV LAC , ΔV LAA Respectively represent the increase in liquid absorption of the positive and negative electrodes of the battery after cycling, in cm 3 , V LAC0 、V LAA0 Respectively represent the liquid absorption of the positive and negative electrodes of fresh batteries, in cm 3 ; A relationship curve between the K value and the attenuation amount is obtained by fitting a curve of the K value and the corresponding attenuation amount of multiple batteries after different cycle capacity attenuation; Substitute the attenuation value of 20% at the end of the marked cycle into the relationship curve, calculate the corresponding K value, and use it as the coefficient k; Substitute the coefficient k into the formula V in =(V LAC0 +V LAA0 +V LAS0 )+k×(V LAC0 +V LAA0 ), obtain the injection volume V in , where V LAS0 The amount of liquid absorbed by the diaphragm of a fresh battery, in cm 3 .

2. The determination method according to claim 1, characterized in that: The plurality of samples include a plurality of groups with different injection volumes, and each group of the groups with different injection volumes includes fresh batteries and batteries with different cycle capacity attenuation of the same battery; The relationship curve is obtained by taking the average value of the K values ​​of a plurality of different injection volume groups under the same attenuation amount and fitting the corresponding attenuation amount curve.

3. The determination method according to claim 1, characterized in that: The test method for the liquid absorption of the sample is: Disassembling the sample and measuring the thickness of the active layer of the electrode; The porosity of the pole piece is calculated based on the actual density and measured thickness of the active layer of the pole piece; According to the formula V LA =h×A×ε to calculate the liquid absorption of the electrode, where h is the thickness of the active layer of the electrode, in μm, and A is the area of ​​the active layer of the electrode, in cm 2 , ε is the porosity of the electrode.

4. The determination method according to claim 1, characterized in that: The battery is a lithium iron phosphate or NMC ternary battery.

5. The determination method according to claim 1, characterized in that: The battery is a lithium iron phosphate or NMC ternary battery.

6. The determination method according to claim 1, characterized in that: The values ​​of the different cycle capacity decays are 5%, 10%, 15% and 20% respectively.

7. The determination method according to claim 1, characterized in that: The battery after different cycle capacity attenuation is a battery after charge and discharge cycles at 0.8 to 1.2 C at 23 to 48° C.

8. The determination method according to claim 1, characterized in that: k is 0.159 to 0.236, or k is 0.165 to 0.

256.

9. A battery design method, characterized in that: The invention comprises a method for determining the battery liquid filling amount as described in any one of claims 1 to 8.

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