Method of assessing moisture in a battery cell

Abstract

The application provides a kind of method for evaluating the moisture of battery cell, and it relates to the technical field of battery.The method for evaluating the moisture of battery cell provided by the application comprises: carrying out aging treatment on the battery cell after liquid injection sealing, collecting the gas in the battery cell after aging treatment and detecting the content of carbon dioxide in the gas;The number of battery cells is at least 3;carry out formation on the battery cell after aging treatment, collect the gas in the battery cell after formation and detect the content of hydrogen in the gas;fit the content of carbon dioxide and hydrogen, and obtain a fitting curve;carry out the aging treatment on the same type of battery cell to be tested after liquid injection sealing, collect the gas in the battery cell to be tested after aging treatment and detect the content of carbon dioxide in the gas, and then calculate the content of hydrogen according to the fitting curve to evaluate the moisture of the battery cell to be tested.The method is safe, simple, efficient and not affected by external environment.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method for evaluating the moisture content of battery cells. Background Technology

[0002] Currently, the moisture content of battery cells is generally evaluated using a moisture meter, with the meter temperature typically set to around 170°C to detect the evaporated moisture. However, many battery cells, during the early stages of manufacturing, are prone to crystallization of water on the cell electrodes if left for extended periods or exposed to high humidity environments. This moisture evaporates at temperatures above 200°C, making it impossible to accurately detect with a moisture meter. Another method is to assess the influence of moisture by analyzing the peak intensity in the dQ / dv curve, but this curve is affected by many factors, such as temperature and pressure.

[0003] Therefore, it is necessary to find a testing method that provides more comprehensive and rigorous data and is less susceptible to external factors in order to effectively evaluate the moisture content of battery cells.

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

[0005] The purpose of this invention is to provide a method for evaluating the moisture content of battery cells, so as to solve the above-mentioned technical problems.

[0006] To achieve the above objectives, the following technical solution is adopted:

[0007] This invention provides a method for assessing the moisture content of battery cells, comprising the following steps:

[0008] a. After the battery cells are filled and sealed, they are aged. After aging, the gas inside the battery cells is collected and the carbon dioxide content in the gas is detected. The number of battery cells is at least 3.

[0009] b. Perform formation on the battery cell after step a, collect the gas inside the battery cell after formation and detect the hydrogen content in the gas;

[0010] c. Fit the carbon dioxide content and hydrogen content to obtain a fitting curve;

[0011] d. Perform the aging treatment on the same type of battery cell after liquid injection and sealing. After aging treatment, collect the gas inside the battery cell and detect the carbon dioxide content in the gas. Then, calculate the hydrogen content according to the fitted curve to evaluate the moisture content of the battery cell.

[0012] As a further technical solution, the aging treatment temperature is 25-45℃ and the time is 12-48h.

[0013] As a further technical solution, the formation current is 0.1 to 1C, the temperature is 35 to 55°C, and the formation charging is cut off to 50% to 100% SOC.

[0014] As a further technical solution, gas chromatography is used to detect carbon dioxide or hydrogen in the gas.

[0015] As a further technical solution, y = ae is adopted. bx The carbon dioxide and hydrogen content are fitted; where a and b are constants.

[0016] As a further technical solution, the battery cell includes a lithium-ion battery cell or a sodium-ion battery cell;

[0017] The types of battery cells include wound battery cells or laminated battery cells.

[0018] As a further technical solution, the battery cell includes a positive electrode, a negative electrode, a separator, and an electrolyte;

[0019] The electrolyte comprises 10%–15% LiPF6 (lithium hexafluorophosphate), 0%–1% VC (ethylene carbonate), 0%–3% PS (1,3-propanesulfonate lactone), 0%–1% DTD (ethylene sulfate), 5%–10% FEC (fluoroethylene carbonate), 0%–1% LiBOB (lithium dioxolane borate), 0%–1% TMSP (tris(trimethylsilane) phosphate), 0%–2% LiFSI (lithium difluorosulfonylimide), with the remainder being solvent;

[0020] The solvent includes one or more of EC (ethylene carbonate) and EMC (ethyl potassium carbonate).

[0021] As a further technical solution, the positive electrode sheet includes a current collector and a positive electrode active material layer coated on the current collector; the positive electrode active material layer includes a positive electrode active material, a conductive agent, a binder, and a dispersant;

[0022] The positive electrode active material includes one or more of NCM (lithium nickel cobalt manganese oxide), LMFP (lithium manganese iron phosphate), LFP (lithium iron phosphate), or LMO (lithium manganese oxide);

[0023] The conductive agent includes one or more of carbon black (SP) or carbon nanotubes (CNTs);

[0024] The adhesive includes: PVDF (polyvinylidene fluoride);

[0025] The dispersant includes one or more of the following: PVP (polyvinylpyrrolidone), polyether dispersants, polyester dispersants, or phosphate ester dispersants.

[0026] As a further technical solution, the negative electrode sheet includes a current collector and a negative electrode active material layer coated on the current collector, wherein the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and a thickener;

[0027] The negative electrode active material includes one or more of graphite or hard carbon;

[0028] The conductive agent includes one or more of carbon black or carbon nanotubes;

[0029] The adhesive includes one or more of PAA (polyacrylic acid) or SBR (styrene-butadiene rubber);

[0030] The thickener includes CMC (carboxymethyl cellulose).

[0031] As a further technical solution, the diaphragm includes a PP diaphragm or a PE diaphragm.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The method for evaluating cell moisture provided by this invention assesses cell moisture (adsorbed water + crystallization water) by the amount of carbon dioxide produced after cell formation. This method is safe, simple, efficient, and unaffected by the external environment. Detailed Implementation

[0034] 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.

[0035] This invention provides a method for assessing the moisture content of battery cells, comprising the following steps:

[0036] a. After the battery cells are filled and sealed, they are aged. After aging, the gas inside the battery cells is collected and the carbon dioxide content in the gas is detected. The number of battery cells is at least 3.

[0037] b. Perform formation on the battery cell after step a, collect the gas inside the battery cell after formation and detect the hydrogen content in the gas;

[0038] c. Fit the carbon dioxide content and hydrogen content to obtain a fitting curve;

[0039] d. Perform the aging treatment on the same type of battery cell after liquid injection and sealing. After aging treatment, collect the gas inside the battery cell and detect the carbon dioxide content in the gas. Then, calculate the hydrogen content according to the fitted curve to evaluate the moisture content of the battery cell.

[0040] It should be noted that "same model" refers to batteries made with the same raw materials and using the same method.

[0041] The inventors discovered that the carbon dioxide production of the battery cell after aging increases with increasing cell moisture content (possibly due to the reaction of HF and residual alkali). It is known in the art that hydrogen production during the cell formation stage increases with increasing cell moisture content (moisture reacts with the electrolyte to generate hydrogen). Based on this, this invention fits the carbon dioxide production after aging and the hydrogen production after formation to obtain a fitting curve. Based on the fitting curve, the hydrogen production after formation corresponding to the carbon dioxide production after aging of the tested battery cell is calculated. The cell moisture content is then assessed based on the hydrogen production, reducing manpower and resources and avoiding the risks associated with gas extraction during formation (the battery cell has a certain state of charge after formation, and gas extraction carries risks).

[0042] In some alternative implementations, the aging treatment temperature may be, for example, but not limited to, 25°C, 35°C, or 45°C, and the time may be, for example, but not limited to, 12h, 24h, 36h, or 48h.

[0043] In some alternative implementations, the formation current may be, for example, but not limited to, 0.1C, 0.5C or 1C, the temperature may be, for example, but not limited to, 35°C, 45°C or 55°C, and the formation charge may be cut off to 50% SOC to 100% SOC, for example, to 50% SOC, 80% SOC or 50% SOC.

[0044] In some alternative implementations, gas chromatography is used to detect carbon dioxide or hydrogen in the gas.

[0045] This invention does not impose specific limitations on the fitting function. In some preferred embodiments, y = ae is used. bx The carbon dioxide and hydrogen content are fitted; where a and b are constants.

[0046] In some alternative embodiments, the battery cell includes a lithium-ion battery cell or a sodium-ion battery cell;

[0047] The types of battery cells include wound battery cells or laminated battery cells.

[0048] In some alternative embodiments, the battery cell includes a positive electrode, a negative electrode, a separator, and an electrolyte;

[0049] The electrolyte comprises 10%–15% LiPF6 (lithium hexafluorophosphate), 0%–1% VC (ethylene carbonate), 0%–3% PS (1,3-propanesulfonate lactone), 0%–1% DTD (ethylene sulfate), 5%–10% FEC (fluoroethylene carbonate), 0%–1% LiBOB (lithium dioxolane borate), 0%–1% TMSP (tris(trimethylsilane) phosphate), 0%–2% LiFSI (lithium difluorosulfonylimide), with the remainder being solvent;

[0050] The solvent includes one or more of EC (ethylene carbonate) and EMC (ethyl potassium carbonate).

[0051] It should be noted that "VC (ethylene carbonate) 0-1%" means that the amount of VC added in the electrolyte is less than 1%. When it is 0, it means that no VC is added. The same applies to other substances such as PS, DTD, LiBOB, TMSP, and LiFSI.

[0052] In some alternative embodiments, the electrolyte contains 10% to 35% EC by mass and 10% to 45% EMC by mass.

[0053] In some optional embodiments, the positive electrode sheet includes a current collector and a positive electrode active material layer coated on the current collector; the positive electrode active material layer includes a positive electrode active material, a conductive agent, a binder, and a dispersant;

[0054] The positive electrode active material includes one or more of NCM, LMFP, LFP, or LMO;

[0055] The conductive agent includes one or more of carbon black or carbon nanotubes;

[0056] The adhesive includes: PVDF;

[0057] The dispersant includes one or more of the following: PVP, polyether dispersant, polyester dispersant, or phosphate ester dispersant.

[0058] In some optional embodiments, the negative electrode sheet includes a current collector and a negative electrode active material layer coated on the current collector, the negative electrode active material layer including a negative electrode active material, a conductive agent, a binder and a thickener;

[0059] The negative electrode active material includes one or more of graphite or hard carbon;

[0060] The conductive agent includes one or more of carbon black or carbon nanotubes;

[0061] The adhesive includes one or more of PAA or SBR;

[0062] The thickener includes CMC.

[0063] In some alternative embodiments, the diaphragm includes, but is not limited to, a PP diaphragm or a PE diaphragm, or other diaphragms well known to those skilled in the art.

[0064] 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.

[0065] It should be noted that in the following embodiments, "%" stands for mass percentage, which refers to the mass percentage of the substance.

[0066] Example 1

[0067] Battery cells: The difference between battery cells of the same model A1, A2, A3 and A4 lies in the moisture content of the electrode plates.

[0068] The positive electrode of the battery cell includes a current collector and a positive electrode active material layer coated on the current collector; the positive electrode active material layer is composed of: 96% positive electrode active material (LMFP:NCM=4:6), 1.3% SP, 0.7% CNTs, 1.8% PVDF, and 0.2% PVP;

[0069] The negative electrode sheet includes a current collector 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%, and SBR 1.8%.

[0070] The diaphragm is: 16μm PE + 2μm CCS (i.e., a diaphragm with a 2μm ceramic layer on a 16μm PE surface).

[0071] The electrolyte is: LiPF6: 15%, EC: 33%, EMC: 43%, VC: 0.5%, PS: 2%, DTD: 1%, FEC: 5%, LiBOB: 0.3%, TMSP: 0.2%.

[0072] The above-mentioned battery cells were subjected to the following tests:

[0073] 1. The battery cell was disassembled before electrolyte filling, and the moisture content of the positive and negative electrode plates was tested using a moisture tester. The results are shown in Table 1.

[0074] Table 1

[0075] A1 131.22 90.56 A2 112.7 87.55 A3 83.26 85.63 A4 62.91 30.4

[0076] 2. After the electrolyte was injected and sealed, the battery cells were aged at 45°C for 36 hours. Then, the aged cells were placed in an inert gas atmosphere, punctured with a syringe to remove the gas, and the gas was injected into a 0.05L–0.1L aluminum-plastic film gas bag for storage. GC gas composition testing was then performed. The test results are shown in Table 2.

[0077] Table 2

[0078] <![CDATA[H2]]> 0.29％ 0.28％ 0.22％ 0.26％ <![CDATA[CO2]]> 46.95％ 42.26％ 40.75％ 32.73％ WHAT 52.42％ 57.08％ 58.62％ 66.70％ <![CDATA[C2H4]]> 0.22％ 0.24％ 0.26％ 0.21％ <![CDATA[C3H6]]> 0.08％ 0.11％ 0.10％ 0.07％ <![CDATA[C4H8]]> 0.03％ 0.03％ 0.03％ 0.02％

[0079] 3. The above-mentioned battery cells were formed (current set to 0.2C, temperature set to 55℃, charging cutoff to 100% SOC). After formation, the battery cells were placed in an inert gas atmosphere, then punctured with a syringe to evacuate the gas, and the gas was injected into a 0.05L~0.1L aluminum-plastic film gas bag for storage. GC gas composition testing was then performed. The test results are shown in Table 3.

[0080] Table 3

[0081]

[0082]

[0083] 4. Using y = ae bx A function (where a and b are constants) was used to fit the carbon dioxide production after aging and the hydrogen production after formation treatment, resulting in a fitted curve y = 0.0426e 2.7204x ;

[0084] 5. The same type of battery cell to be tested, after being injected and sealed, undergoes the aforementioned aging treatment. After aging, the gas inside the battery cell is collected and the carbon dioxide content in the gas is detected. Then, the hydrogen content is calculated based on the fitted curve. The composition of the gas produced during aging is shown in Table 4, and the composition of the gas produced during formation is shown in Table 5.

[0085] Table 4

[0086]

[0087] Table 5

[0088]

[0089] According to the fitting formula y = 0.0426e 2.7204x When the proportion of CO2 produced during aging is 46.44%, the proportion of H2 produced is 15.068%, which is basically consistent with the actual measured value (15.07%).

[0090] Example 2

[0091] Battery cells: The difference between B1, B2, B3 and B4 batteries of the same model lies in the moisture content of the electrode plates.

[0092] The positive electrode of the battery cell includes a current collector and a positive electrode active material layer coated on the current collector; the positive electrode active material layer is composed of: 95.8% positive electrode active material (LFP:LMFP:NCM=1:2:7), 1.5% SP, 0.5% CNTs, 2% PVDF, and 0.2% PVP;

[0093] The negative electrode sheet includes a current collector and a negative electrode active material layer coated on the current collector. The composition of the negative electrode active material layer is: graphite 94.9%, SP 2%, CMC 1.3%, SBR 1.8%.

[0094] The membrane is made of 9μm PE and 3μm CCS.

[0095] The electrolyte is: LiPF6: 11%, EC: 34%, EMC: 44%, VC: 0.3%, PS: 1.5%, DTD: 0.9%, FEC: 7%, LiBOB: 0.3%, LiFSI: 1%.

[0096] The above-mentioned battery cells were subjected to the following tests:

[0097] 1. The battery cell was disassembled before electrolyte filling, and the moisture content of the positive and negative electrode plates was tested using a moisture tester. The results are shown in Table 6.

[0098] Table 6

[0099] A1 110.2 105.25 A2 109.8 100.89 A3 81.44 78.05 A4 56.37 90.66

[0100] 2. After liquid injection and sealing, the battery cells were aged at 35°C for 40 hours. The aged cells were then placed in an inert gas atmosphere, punctured with a syringe to remove the gas, and the gas was injected into a 0.05L–0.1L aluminum-plastic film gas bag for storage. GC gas composition testing was then performed. The test results are shown in Table 7.

[0101] Table 7

[0102]

[0103]

[0104] 3. The above-mentioned battery cells were formed (current set to 0.3C, temperature set to 55℃, charging cutoff to 70% SOC). After formation, the battery cells were placed in an inert gas atmosphere, then punctured with a syringe to evacuate the gas, and the gas was injected into a 0.05L~0.1L aluminum-plastic film gas bag for storage. GC gas composition testing was then performed. The test results are shown in Table 8.

[0105] Table 8

[0106] <![CDATA[H2]]> 17.97％ 17.26％ 17.08％ 16.52％ <![CDATA[CO2]]> 1.65％ 2.36％ 1.71％ 1.45％ <![CDATA[CH4]]> 1.56％ 1.82％ 1.81％ 1.23％ WHAT 15.52％ 16.21％ 16.93％ 14.07％ <![CDATA[C2H6]]> 0.75％ 0.87％ 0.88％ 0.64％ <![CDATA[C2H4]]> 62.47％ 61.42％ 61.54％ 66.03％ <![CDATA[C3H8]]> 0.01％ 0.01％ 0.01％ 0.01％ <![CDATA[C3H6]]> 0.04％ 0.04％ 0.02％ 0.03％ <![CDATA[C4H 10 ]]> 0.01％ 0.01％ 0.02％ 0.01％ <![CDATA[C2H2]]> 0.00％ 0.00％ 0.00％ 0.00％

[0107] 4. Using y = ae bx A function (where a and b are constants) was used to fit the carbon dioxide production after aging and the hydrogen production after formation treatment, resulting in the fitted curve y = 0.1565e 0.3015x ;

[0108] 5. The same type of battery cell to be tested, after being injected and sealed, undergoes the aforementioned aging treatment. After aging, the gas inside the battery cell is collected and the carbon dioxide content in the gas is detected. Then, the hydrogen content is calculated based on the fitted curve. The composition of the gas produced during aging is shown in Table 9, and the composition of the gas produced during formation is shown in Table 10.

[0109] Table 9

[0110]

[0111]

[0112] Table 10

[0113]

[0114] According to the fitting formula y = 0.1565e 0.3015x When the proportion of CO2 produced during aging is 14.01%, the proportion of H2 produced is 16.325%, which is basically consistent with the actual measured value (16.28%).

[0115] 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 assessing the moisture content of a battery cell, characterized in that, Includes the following steps: a. After the battery cells are filled and sealed, they are aged. After aging, the gas inside the battery cells is collected and the carbon dioxide content in the gas is detected. The number of battery cells is at least 3. b. Perform formation on the battery cell after step a, collect the gas inside the battery cell after formation and detect the hydrogen content in the gas; c. Fit the carbon dioxide content and hydrogen content to obtain a fitting curve; d. Perform the aging treatment on the same model of battery cell after liquid injection and sealing. After aging treatment, collect the gas inside the battery cell and detect the carbon dioxide content in the gas. Then, calculate the hydrogen content according to the fitting curve to evaluate the moisture content of the battery cell. Using y=ae bx The carbon dioxide and hydrogen content were fitted; where a and b are constants. The battery cell is a lithium-ion battery cell or a sodium-ion battery cell. The type of battery cell is either a wound battery cell or a laminated battery cell.

2. The method according to claim 1, characterized in that, The aging process is carried out at a temperature of 25-45°C for 12-48 hours.

3. The method according to claim 1, characterized in that, The formation current is 0.1~1C, the temperature is 35~55℃, and the formation charge is cut off to 50%~100% SOC.

4. The method according to claim 1, characterized in that, Gas chromatography is used to detect carbon dioxide or hydrogen in a gas.

5. The method according to claim 1, characterized in that, The battery cell includes a positive electrode, a negative electrode, a separator, and an electrolyte; The electrolyte comprises 10%~15% LiPF6, 0~1% VC, 0~3% PS, 0~1% DTD, 5%~10% FEC, 0~1% LiBOB, 0~1% TMSP, 0~2% LiFSI, with the remainder being solvent; The solvent includes one or more of EC and EMC.

6. The method according to claim 5, characterized in that, The positive electrode sheet includes a current collector and a positive electrode active material layer coated on the current collector; the positive electrode active material layer includes a positive electrode active material, a conductive agent, a binder, and a dispersant; The positive electrode active material includes one or more of NCM, LMFP, LFP, or LMO; The conductive agent includes one or more of carbon black or carbon nanotubes; The adhesive includes: PVDF; The dispersant includes one or more of the following: PVP, polyether dispersant, polyester dispersant, or phosphate ester dispersant.

7. The method according to claim 5, characterized in that, The negative electrode sheet includes a current collector and a negative electrode active material layer coated on the current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and a thickener. 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 adhesive includes one or more of PAA or SBR; The thickener includes CMC.

8. The method according to claim 5, characterized in that, The diaphragm includes a PP diaphragm or a PE diaphragm.

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