Active substance volume fraction detection method, system, device and storage medium

Abstract

The present invention provides a method, system, device, and storage medium for detecting the volume fraction of active material. The detection method includes: discharging or charging a battery in stages using the GITT method to obtain several sets of measured negative electrode open-circuit voltages and state-of-charge (SOC) of graphite electrodes; generating a first curve of negative electrode open-circuit voltage-SOC based on the several sets of negative electrode open-circuit voltages and SOCs; generating a second curve based on a first-order equation of negative electrode open-circuit voltage-negative electrode lithium insertion amount; fitting the second curve to the first curve to obtain a linear coefficient between negative electrode lithium insertion amount and SOC; and calculating the active material volume fraction of the graphite electrode based on the measured thickness and area of ​​the graphite electrode, the theoretical maximum lithium ion concentration, the Faraday constant, the full capacity, and the linear coefficient. The present invention can calculate the active material volume fraction based on theoretical value fitting without disassembling the battery to test the electrode piece. This method is simple to operate, has high parameter accuracy, and is harmless to the battery itself.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium iron phosphate batteries, and in particular to a method, system, device and storage medium for detecting the volume fraction of an active substance. Background Art

[0002] Due to the instability of the power output of new energy systems, energy storage systems are needed, leading to the widespread use of lithium-ion batteries. Graphite is often used as the negative electrode in lithium-ion batteries. This negative electrode, composed of the active material graphite, a binder, and additives, exhibits different voltage levels during the lithium insertion process, depending on the amount of lithium inserted.

[0003] The active material volume fraction is a crucial parameter in electrochemical models and plays a crucial role in calculating battery capacity. Existing methods only measure the elemental ratios within the electrode, but graphite, binders, and additives all contain carbon, making it impossible to directly determine the active material volume fraction. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defect in the prior art that the volume fraction of active substances cannot be directly obtained, and to provide a method, system, device and storage medium for detecting the volume fraction of active substances.

[0005] The present invention solves the above technical problems through the following technical solutions:

[0006] The present invention provides a method for detecting the volume fraction of an active substance, comprising:

[0007] The battery is discharged or charged in stages using the GITT (galvanostatic intermittent titration) method to obtain several sets of measured negative electrode open circuit voltages and SOCs (state of charge) of the graphite electrodes; the change in battery capacity in each stage is a preset capacity change value;

[0008] generating a first curve of negative electrode open circuit voltage-SOC according to the plurality of sets of negative electrode open circuit voltages and SOCs;

[0009] Generate a second curve according to the first-order equation of negative electrode open circuit voltage-negative electrode lithium insertion amount;

[0010] Fitting the second curve to the first curve to obtain a linear coefficient between the amount of lithium inserted into the negative electrode and the SOC;

[0011] The active material volume fraction of the graphite electrode is calculated based on the measured thickness and area of ​​the graphite electrode, the theoretical maximum lithium ion concentration, the Faraday constant, the full capacity and the linear coefficient.

[0012] Preferably, the preset capacity change value includes a first capacity change value, a second capacity change value and a third capacity change value;

[0013] The discharging or charging operation of the battery in stages by the GITT method includes:

[0014] Step S111: After the battery is fully charged, it is left to stand for a first preset time;

[0015] Step S112: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is the first capacity change value, and leaving the battery in a static state for a second preset time;

[0016] Step S113, repeatedly executing step S112, so that the number of executions of step S112 reaches a first preset number;

[0017] Step S114: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is the second capacity change value, and leaving the battery in a static state for a third preset time;

[0018] Step S115: Repeat step S114 until the number of executions of step S114 reaches a second preset number of times;

[0019] Step S116: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is the third capacity change value or the battery voltage is less than a preset first voltage threshold, and then leaving the battery in standstill for a fourth preset time period;

[0020] Step S117: Repeat step S116 until step S116 is executed more than a third preset number of times and the battery voltage is less than the first voltage threshold.

[0021] Preferably, the preset capacity change value includes a fourth capacity change value, a fifth capacity change value and a sixth capacity change value;

[0022] The discharging or charging operation of the battery in stages by the GITT method includes:

[0023] Step S118: After discharging the battery to zero power, the battery is left to stand for a fifth preset time period;

[0024] Step S119: setting the charging current to the rated current to perform a charging operation so that the battery capacity change is the fourth capacity change value, and leaving the battery in standstill for a sixth preset time;

[0025] Step S1110: Repeat step S119 until the number of executions of step S119 reaches a fourth preset number of times;

[0026] Step S1111: setting the charging current to the rated current to perform a charging operation so that the battery capacity change is the fifth capacity change value, and leaving the battery to stand for a seventh preset time;

[0027] Step S1112: Repeat step S1111 until the number of executions of step S1111 reaches a fifth preset number of times;

[0028] Step S1113: Setting the charging current to the rated current to perform a charging operation so that the battery capacity change is the sixth capacity change value or the battery voltage is greater than a preset second voltage threshold, and then standing for an eighth preset time period;

[0029] Step S1114: Repeat step S1113 until step S1113 is executed more than a sixth preset number of times and the battery voltage is greater than the second voltage threshold.

[0030] Preferably, when the SOC is less than 90%, the positive electrode open circuit voltage is 3.42 volts, and the negative electrode open circuit voltage is expressed by the following formula:

[0031] OCPn=OCPp-OCV=3.42-OCV;

[0032] Wherein, OCPn represents the negative electrode open circuit voltage, OCPp represents the positive electrode open circuit voltage, and OCV represents the battery voltage measured after sufficient rest;

[0033] The first-order equation of the negative electrode open circuit voltage-negative electrode lithium insertion amount is expressed by the following formula:

[0034]

[0035] Wherein, OCPn represents the open circuit voltage of the negative electrode, and STOn represents the amount of lithium embedded in the negative electrode.

[0036] Preferably, the volume fraction of the active substance is expressed by the following formula:

[0037] STOn=k*SOC+c;

[0038] ε act,n =Q full / (A n *L n *F*C n,max *k);

[0039] Wherein, STOn represents the amount of lithium embedded in the negative electrode, k represents the linear coefficient, c represents the calculation constant, SOC represents SOC, ε act,n represents the volume fraction of the active material, Q full Indicates the full capacity of the battery, A nrepresents the area of ​​the graphite electrode, L n represents the thickness of the graphite electrode, F represents the Faraday constant, C n,max Indicates the theoretical maximum lithium ion concentration.

[0040] Preferably, the detection method further comprises:

[0041] The porosity of the graphite electrode is measured by mercury intrusion porosimetry;

[0042] The volume fraction of the active material in the total solids and the volume fraction of the binder, additives, etc. in the total solids are calculated based on the porosity and the volume fraction of the active material.

[0043] Preferably, the volume fraction of the active substance in the total solids and the volume fraction of the binder, additives, etc. in the total solids are expressed by the following formula:

[0044] Φ act,n =ε act,n / (1-ε k );

[0045] Φ inact,n =1-Φact,n;

[0046] Among them, ε act,n represents the volume fraction of the active material, ε k represents the porosity of the graphite electrode, Φ act,n Indicates the volume fraction of active substances in the total solids, Φ inact,n Indicates the volume fraction of binders, additives, etc. in the total solids.

[0047] The present invention also provides a system for detecting the volume fraction of an active substance, comprising:

[0048] The charge and discharge module is used to discharge or charge the battery in stages using the GITT method to obtain several sets of measured negative electrode open circuit voltages and SOCs of the graphite electrodes; wherein the battery capacity change in each stage is a preset capacity change value;

[0049] A first curve generating module, configured to generate a first curve of negative electrode open circuit voltage-SOC according to the plurality of sets of negative electrode open circuit voltages and SOCs;

[0050] A second curve generating module is used to generate a second curve according to a first-order equation of negative electrode open circuit voltage-negative electrode lithium insertion amount;

[0051] a fitting module, configured to fit the second curve to the first curve to obtain a linear coefficient between the amount of lithium embedded in the negative electrode and the SOC;

[0052] An active material volume fraction calculation module is used to calculate the active material volume fraction of the graphite electrode based on the measured thickness and area of ​​the graphite electrode, the theoretical maximum lithium ion concentration, the Faraday constant, the full capacity and the linear coefficient.

[0053] Preferably, the preset capacity change value includes a first capacity change value, a second capacity change value and a third capacity change value;

[0054] The charging and discharging module is specifically used to perform the following steps:

[0055] Step S111: After the battery is fully charged, it is left to stand for a first preset time;

[0056] Step S112: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is the first capacity change value, and leaving the battery in a static state for a second preset time;

[0057] Step S113, repeatedly executing step S112, so that the number of executions of step S112 reaches a first preset number;

[0058] Step S114: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is the second capacity change value, and leaving the battery in a static state for a third preset time;

[0059] Step S115: Repeat step S114 until the number of executions of step S114 reaches a second preset number of times;

[0060] Step S116: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is the third capacity change value or the battery voltage is less than a preset first voltage threshold, and then leaving the battery in standstill for a fourth preset time period;

[0061] Step S117: Repeat step S116 until step S116 is executed more than a third preset number of times and the battery voltage is less than the first voltage threshold.

[0062] Preferably, the preset capacity change value includes a fourth capacity change value, a fifth capacity change value and a sixth capacity change value;

[0063] The charging and discharging module is specifically used to perform the following steps:

[0064] Step S118: After discharging the battery to zero power, the battery is left to stand for a fifth preset time period;

[0065] Step S119: setting the charging current to the rated current to perform a charging operation so that the battery capacity change is the fourth capacity change value, and leaving the battery in standstill for a sixth preset time;

[0066] Step S1110: Repeat step S119 until the number of executions of step S119 reaches a fourth preset number of times;

[0067] Step S1111: setting the charging current to the rated current to perform a charging operation so that the battery capacity change is the fifth capacity change value, and leaving the battery to stand for a seventh preset time;

[0068] Step S1112: Repeat step S1111 until the number of executions of step S1111 reaches a fifth preset number of times;

[0069] Step S1113: Setting the charging current to the rated current to perform a charging operation so that the battery capacity change is the sixth capacity change value or the battery voltage is greater than a preset second voltage threshold, and then standing for an eighth preset time period;

[0070] Step S1114: Repeat step S1113 until step S1113 is executed more than a sixth preset number of times and the battery voltage is greater than the second voltage threshold.

[0071] Preferably, when the SOC is less than 90%, the positive electrode open circuit voltage is 3.42 volts, and the negative electrode open circuit voltage is expressed by the following formula:

[0072] OCPn=OCPp-OCV=3.42-OCV;

[0073] Wherein, OCPn represents the negative electrode open circuit voltage, OCPp represents the positive electrode open circuit voltage, and OCV represents the battery voltage measured after sufficient rest;

[0074] The first-order equation of the negative electrode open circuit voltage-negative electrode lithium insertion amount is expressed by the following formula:

[0075]

[0076] Wherein, OCPn represents the open circuit voltage of the negative electrode, and STOn represents the amount of lithium embedded in the negative electrode.

[0077] Preferably, the volume fraction of the active substance is expressed by the following formula:

[0078] STOn=k*SOC+c;

[0079] ε act,n =Q full / (A n *L n *F*C n,max *k);

[0080] Wherein, STOn represents the amount of lithium embedded in the negative electrode, k represents the linear coefficient, c represents the calculation constant, SOC represents SOC, εact,n represents the volume fraction of the active material, Q full Indicates the full capacity of the battery, A n represents the area of ​​the graphite electrode, L n represents the thickness of the graphite electrode, F represents the Faraday constant, C n,max Indicates the theoretical maximum lithium ion concentration.

[0081] Preferably, the detection system further comprises:

[0082] A porosity measurement module, used to measure the porosity of the graphite electrode by mercury intrusion porosimetry;

[0083] The total solid volume fraction calculation module is used to calculate the volume fraction of the active substance in the total solid and the volume fraction of the binder, additives, etc. in the total solid according to the porosity and the volume fraction of the active substance.

[0084] Preferably, the volume fraction of the active substance in the total solids and the volume fraction of the binder, additives, etc. in the total solids are expressed by the following formula:

[0085] Φ act,n =ε act,n / (1-ε k );

[0086] Φ inact,n =1-Φact,n;

[0087] Among them, ε act,n represents the volume fraction of the active material, ε k represents the porosity of the graphite electrode, Φ act,n Indicates the volume fraction of active substances in the total solids, Φ inact,n Indicates the volume fraction of binders, additives, etc. in the total solids.

[0088] The present invention also provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the aforementioned method for detecting the volume fraction of active material when executing the computer program.

[0089] The present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the aforementioned method for detecting the volume fraction of active material.

[0090] The positive progress of the present invention is that: the battery is discharged or charged in stages by the GITT method, a first curve of the negative electrode open circuit voltage-SOC is generated according to several sets of measured data, a second curve is generated according to the first-order equation of the negative electrode open circuit voltage-negative electrode lithium insertion amount, the second curve is fitted to the first curve to obtain the linear coefficient of the negative electrode lithium insertion amount and SOC, and the active material volume fraction of the graphite electrode is calculated according to the measured thickness and area of ​​the graphite electrode, the theoretical maximum lithium ion concentration, the Faraday constant, the full capacity and the linear coefficient. There is no need to disassemble the battery to test the electrode piece, and the measured data can be fitted based on the theoretical value to obtain the linear coefficient, and then the active material volume fraction is calculated. The operation is simple, the parameter accuracy is high, and there is no damage to the battery itself. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Figure 1 This is a flow chart of the method for detecting the volume fraction of active material according to Example 1 of the present invention.

[0092] Figure 2 These are the first and second curve examples of the method for detecting the volume fraction of active material in Example 1 of the invention.

[0093] Figure 3 This is an example of the fitting results of the first curve and the second curve of the method for detecting the volume fraction of active material in Example 1 of the invention.

[0094] Figure 4 This is a flowchart of a specific implementation of step S11 of the method for detecting the volume fraction of active material according to Example 1 of the present invention.

[0095] Figure 5 This is a flow chart of another specific implementation of step S11 of the method for detecting the volume fraction of active material in Example 1 of the present invention.

[0096] Figure 6 This is a flow chart of a specific implementation of the method for detecting the volume fraction of active substances according to Example 1 of the present invention.

[0097] Figure 7 Schematic diagram of the modules of the active material volume fraction detection system of Example 1 of the present invention.

[0098] Figure 8 This is a schematic structural diagram of an electronic device according to embodiment 3 of the present invention. DETAILED DESCRIPTION

[0099] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples.

[0100] Example 1

[0101] This embodiment provides a method for detecting the volume fraction of active substances, referring to Figure 1 , detection methods include:

[0102] Step S11: Discharge or charge the battery in stages using the GITT method to obtain several sets of measured negative electrode open circuit voltages and SOCs of the graphite electrodes, wherein the battery capacity change in each stage is a preset capacity change value.

[0103] Step S12: generating a first negative electrode open circuit voltage-SOC curve according to a plurality of sets of negative electrode open circuit voltages and SOCs.

[0104] Step S13: generating a second curve according to a first-order equation of negative electrode open circuit voltage-negative electrode lithium insertion amount.

[0105] Step S14: Fit the second curve to the first curve to obtain a linear coefficient between the amount of lithium embedded in the negative electrode and the SOC.

[0106] Step S15: Calculate the active material volume fraction of the graphite electrode based on the measured thickness and area of ​​the graphite electrode, the theoretical maximum lithium ion concentration, the Faraday constant, the full capacity, and the linear coefficient.

[0107] The battery is intermittently discharged (or charged) using the GITT method, and the maximum voltage during the static period is taken as the open circuit voltage (OCV) of the current SOC. Since the battery is fully static at each stage to eliminate polarization, its open circuit voltage (OCV) is only related to the positive electrode open circuit voltage (OCP_p (sto_p)) and the negative electrode open circuit voltage (OCP_n (sto_n)). Its value is the difference between the positive and negative electrodes.

[0108] When SOC>0.9, OCV increases, which is caused by the negative electrode open circuit voltage OCPp (the corresponding negative electrode lithium insertion amount STOp tends to 0); when SOC≤0.9, OCPp=3.42V (volts). Therefore, when SOC≤0.9, OCV=3.42V-OCPn.

[0109] Data such as the thickness, area, and porosity of the graphite electrode are parameters that need to be controlled during battery production and can usually be obtained from the battery manufacturer. If this data is not obtained from the battery manufacturer, it can also be obtained by disassembling and measuring a battery. This data is applicable to all batteries of the same specification (the same model from the same manufacturer). Because the slurry concentration and drying rate may vary during production, the volume fraction of active material in batteries of the same specification may vary, resulting in certain deviations.

[0110] The thickness of the graphite electrode is measured as L n , the area of ​​the graphite electrode is A n, the theoretical maximum lithium ion concentration is C n,max , the Faraday constant is F, the capacity change of the battery is ΔQ, and the volume fraction of the active material is ε act,n , the amount of lithium embedded in the negative electrode is STOn, and the change in the amount of lithium embedded in the negative electrode is ΔSTOn. According to the law of charge conservation, we can get:

[0111] ΔQ=A n *L n *ε act,n *F*C n,max *ΔSTOn

[0112] Where ΔQ = Q full *ΔSOC

[0113] STOn=ΔSTOn+STOn_0

[0114] SOC=ΔSOC+SOC_0

[0115] Q full represents the full-charge capacity of the battery, ΔSOC represents the change in SOC, STOn_0 represents the initial value of the lithium insertion amount, and SOC_0 represents the initial value of SOC. The position of the initial value in the curve is not limited here.

[0116] Then, STOn=Q full *ΔSOC / (A n *L n *ε act,n *F*C n,max )+STOn_0

[0117] Q full 、A n 、L n , ε act,n , F, C n,max , STOn_0 are constants and can be simplified to:

[0118] STOn=k*ΔSOC+STOn_0

[0119] =k*SOC+STOn_0-k*SOC_0

[0120] =k*SOC+c

[0121] k represents the linear coefficient, and c represents the calculation constant. Since STOn_0 and SOC_0 are constants, STOn and ΔSOC are linearly related, which means that STOn and SOC are also linearly related.

[0122] The second curve is generated by using the first-order equation of negative electrode open circuit voltage-negative electrode lithium insertion amount because the first-order equation is relatively simple and easy to fit, while the equation with tanh (a calculation method) and exp (a calculation method) is not intuitive and difficult to fit.

[0123] Figure 2 Examples of the first curve and the second curve are shown, where the solid line is the first curve and the dotted line is the second curve. Figure 3 The figure shows an example of the fitting results, where the solid line is the first curve and the dashed line is the second curve after fitting. Since STOn and SOC are linearly related, adjusting the k value can make STOn and SOC correspond one to one.

[0124] Through image fitting, the relationship between the negative electrode open circuit voltage and SOC is converted into the relationship between the negative electrode open circuit voltage and the negative electrode lithium insertion amount. The volume fraction of active material is calculated using the slope (i.e., linear coefficient) between the negative electrode lithium insertion amount and SOC after fitting.

[0125] In this embodiment, the battery is discharged or charged in stages using the GITT method, a first curve of the negative electrode open circuit voltage-SOC is generated according to several sets of measured data, a second curve is generated according to the first-order equation of the negative electrode open circuit voltage-negative electrode lithium insertion amount, the second curve is fitted to the first curve to obtain a linear coefficient between the negative electrode lithium insertion amount and the SOC, and the active material volume fraction of the graphite electrode is calculated according to the measured thickness and area of ​​the graphite electrode, the theoretical maximum lithium ion concentration, the Faraday constant, the full capacity and the linear coefficient. Without disassembling the battery to test the electrode piece, the measured data can be fitted based on the theoretical value to obtain the linear coefficient, and then the active material volume fraction is calculated. The operation is simple, the parameter accuracy is high, and there is no damage to the battery itself.

[0126] In a specific implementation, the preset capacity change value includes a first capacity change value, a second capacity change value and a third capacity change value.

[0127] Reference Figure 4 , the “discharging or charging the battery in stages by the GITT method” in step S11 includes:

[0128] Step S111: After fully charging the battery, leave it alone for a first preset time.

[0129] Step S112: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is a first capacity change value, and leaving the battery to rest for a second preset time.

[0130] Step S113: Repeat step S112 until the number of executions of step S112 reaches a first preset number of times.

[0131] Step S114 : setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is a second capacity change value, and leaving the battery to rest for a third preset time.

[0132] Step S115: Repeat step S114 until the number of executions of step S114 reaches a second preset number of times.

[0133] Step S116: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is a third capacity change value or the battery voltage is less than a preset first voltage threshold, and then standing for a fourth preset time.

[0134] Step S117: Repeat step S116 until the number of executions of step S116 is greater than a third preset number of times and the battery voltage is less than the first voltage threshold.

[0135] Among them, for lithium iron phosphate batteries, the battery can be fully charged at 0.5*rated current (C) and 3.65V constant current and constant voltage, that is, first charge it at 0.5C constant current, and then charge it to full capacity at 3.65V constant voltage. Volt constant current and constant voltage charging is an existing technology and will not be repeated here.

[0136] The first preset time length can be 2 hours, the second preset time length can be 1 hour, the first capacity change value can be 1% of the full capacity, the first preset number of times can be 5 times, the second capacity change value can be 5% of the full capacity, the third preset time length can be 1 hour, the second preset number of times can be 17 times, the third capacity change value can be 1% of the full capacity, the fourth preset time length can be 2 hours, the third preset number of times can be 10 times, and the first voltage threshold can be 2.5 volts.

[0137] The capacity change value can be controlled by the discharge time. For example, if the discharge is performed at the rated current for 36 seconds, the capacity change value is 1% of the full capacity.

[0138] The first preset duration, the second preset duration, the first capacity change value, the first preset number of times, the second capacity change value, the third preset duration, the second preset number of times, the third capacity change value, the fourth preset duration, the third preset number of times and the first voltage threshold can be set according to actual needs.

[0139] During specific implementation, the preset capacity change values ​​include a fourth capacity change value, a fifth capacity change value, and a sixth capacity change value.

[0140] Reference Figure 5 , the “discharging or charging the battery in stages by the GITT method” in step S11 includes:

[0141] Step S118: After discharging the battery to zero power, the battery is left to stand for a fifth preset time period.

[0142] Step S119: setting the charging current to the rated current to perform a charging operation so that the battery capacity change is a fourth capacity change value, and leaving the battery to stand for a sixth preset time period.

[0143] Step S1110: Repeat step S119 until the number of executions of step S119 reaches a fourth preset number of times.

[0144] Step S1111: setting the charging current to the rated current to perform a charging operation so that the battery capacity change is a fifth capacity change value, and leaving the battery to stand for a seventh preset time period.

[0145] Step S1112: Repeat step S1111 until the number of executions of step S1111 reaches a fifth preset number of times.

[0146] Step S1113: Set the charging current to the rated current to perform a charging operation so that the battery capacity change is a sixth capacity change value or the battery voltage is greater than a preset second voltage threshold, and then stand for an eighth preset time period.

[0147] Step S1114: Repeat step S1113 until the number of executions of step S1113 is greater than a sixth preset number of times and the battery voltage is greater than a second voltage threshold.

[0148] Among them, the fifth preset time length can be 2 hours, the fourth capacity change value can be 1% of the full capacity, the sixth preset time length can be 1 hour, the fourth preset number of times can be 5 times, the fifth capacity change value can be 5% of the full capacity, the seventh preset time length can be 1 hour, the fifth preset number of times can be 17 times, the sixth capacity change value can be 1% of the full capacity, the eighth preset time length can be 1 hour, the second voltage threshold can be 3.65 volts, and the sixth preset number of times can be 10 times.

[0149] The capacity change value can be controlled by the charging time. For example, charging at the rated current for 36 seconds means the capacity change value is 1% of the full capacity.

[0150] The fifth preset duration, fourth capacity change value, sixth preset duration, fourth preset number of times, fifth capacity change value, seventh preset duration, fifth preset number of times, sixth capacity change value, eighth preset duration, second voltage threshold and sixth preset number of times can be set according to actual needs.

[0151] In a specific implementation, when the SOC is less than 90%, the positive electrode open circuit voltage is 3.42 volts, and the negative electrode open circuit voltage is expressed by the following formula:

[0152] OCPn=OCPp-OCV=3.42-OCV.

[0153] Among them, OCPn represents the negative electrode open circuit voltage, OCPp represents the positive electrode open circuit voltage, and OCV represents the battery voltage measured after sufficient rest.

[0154] The following formula is used to express the first-order equation of negative electrode open circuit voltage-negative electrode lithium insertion amount:

[0155]

[0156] Among them, OCPn represents the open circuit voltage of the negative electrode, and STOn represents the amount of lithium embedded in the negative electrode.

[0157] In specific implementation, the following formula is used to express the volume fraction of active substances:

[0158] STOn=k*SOC+c.

[0159] ε act,n =Q full / (A n *L n *F*C n,max *k).

[0160] Among them, STOn represents the amount of lithium inserted into the negative electrode, k represents the linear coefficient, c represents the calculation constant, SOC represents SOC, ε act,n represents the volume fraction of active material, Q full Indicates the full capacity of the battery, A n Represents the area of ​​the graphite electrode, L n represents the thickness of the graphite electrode, F represents the Faraday constant, C n,max Indicates the theoretical maximum lithium ion concentration.

[0161] When implementing it, refer to Figure 6 , the detection method also includes:

[0162] Step S16: measuring the porosity of the graphite electrode by mercury intrusion porosimetry.

[0163] Step S17: Calculate the volume fraction of the active material in the total solids and the volume fraction of the binder, additives, etc. in the total solids based on the porosity and the volume fraction of the active material.

[0164] In specific implementation, the following formula is used to express the volume fraction of active substances in the total solids and the volume fraction of binders, additives, etc. in the total solids:

[0165] Φ act,n =ε act,n / (1-ε k ).

[0166] Φ inact,n =1-Φact,n.

[0167] Among them, ε act,n represents the volume fraction of active material, ε k Indicates the porosity of the graphite electrode, Φ act,n Indicates the volume fraction of active substances in the total solids, Φ inact,n Indicates the volume fraction of binders, additives, etc. in the total solids.

[0168] Example 2

[0169] This embodiment provides a detection system for the volume fraction of active substances, referring to Figure 7 , the detection system includes:

[0170] The charge and discharge module 1 is used to discharge or charge the battery in stages using the GITT method to obtain several sets of measured negative electrode open circuit voltages and state of charge (SOC) of the graphite electrodes. The change in battery capacity during each stage is a preset capacity change value.

[0171] The first curve generating module 2 is configured to generate a first curve of negative electrode open circuit voltage-SOC according to a plurality of sets of negative electrode open circuit voltages and SOCs.

[0172] The second curve generating module 3 is used to generate a second curve according to a first-order equation of negative electrode open circuit voltage-negative electrode lithium insertion amount.

[0173] The fitting module 4 is used to fit the second curve to the first curve to obtain a linear coefficient between the amount of lithium embedded in the negative electrode and the SOC.

[0174] The active material volume fraction calculation module 5 is used to calculate the active material volume fraction of the graphite electrode based on the measured thickness and area of ​​the graphite electrode, the theoretical maximum lithium ion concentration, the Faraday constant, the full capacity and the linear coefficient.

[0175] The battery is intermittently discharged (or charged) using the GITT method, and the maximum voltage during the static period is taken as the open circuit voltage (OCV) of the current SOC. Since the battery is fully static at each stage to eliminate polarization, its open circuit voltage (OCV) is only related to the positive electrode open circuit voltage (OCP_p (sto_p)) and the negative electrode open circuit voltage (OCP_n (sto_n)). Its value is the difference between the positive and negative electrodes.

[0176] When SOC>0.9, OCV increases, which is caused by the negative electrode open circuit voltage OCPp (the corresponding negative electrode lithium insertion amount STOp tends to 0); when SOC≤0.9, OCPp=3.42V (volts). Therefore, when SOC≤0.9, OCV=3.42V-OCPn.

[0177] Data such as the thickness, area, and porosity of the graphite electrode are parameters that need to be controlled during battery production and can usually be obtained from the battery manufacturer. If this data is not obtained from the battery manufacturer, it can also be obtained by disassembling and measuring a battery. This data is applicable to all batteries of the same specification (the same model from the same manufacturer). Because the slurry concentration and drying rate may vary during production, the volume fraction of active material in batteries of the same specification may vary, resulting in certain deviations.

[0178] The thickness of the graphite electrode is measured as L n , the area of ​​the graphite electrode is A n , the theoretical maximum lithium ion concentration is C n,max , the Faraday constant is F, the capacity change of the battery is ΔQ, and the volume fraction of the active material is ε act,n , the amount of lithium embedded in the negative electrode is STOn, and the change in the amount of lithium embedded in the negative electrode is ΔSTOn. According to the law of charge conservation, we can get:

[0179] ΔQ=A n *L n *ε act,n *F*C n,max *ΔSTOn

[0180] Where ΔQ = Q full *ΔSOC

[0181] STOn=ΔSTOn+STOn_0

[0182] SOC=ΔSOC+SOC_0

[0183] Q full represents the full capacity of the battery, ΔSOC represents the change in SOC, STOn_0 represents the initial value of the lithium insertion amount, and SOC_0 represents the initial value of SOC. The position of the initial value in the curve is not limited here.

[0184] Then, STOn=Q full *ΔSOC / (A n *L n *ε act,n *F*C n,max )+STOn_0

[0185] Q full 、A n , L n , ε act,n , F, C n,max , STOn_0 are constants and can be simplified to:

[0186] STOn=k*ΔSOC+STOn_0

[0187] =k*SOC++STOn_0-k*SOC_0

[0188] =k*SOC+c

[0189] k represents the linear coefficient, and c represents the calculation constant. Since STOn_0 and SOC_0 are constants, STOn and ΔSOC are linearly related, which means that STOn and SOC are also linearly related.

[0190] The second curve is generated by using the first-order equation of negative electrode open circuit voltage-negative electrode lithium insertion amount because the first-order equation is relatively simple and easy to fit, while the equation with tanh (a calculation method) and exp (a calculation method) is not intuitive and difficult to fit.

[0191] Figure 2 Examples of the first curve and the second curve are shown, where the solid line is the first curve and the dotted line is the second curve. Figure 3 The figure shows an example of the fitting results, where the solid line is the first curve and the dashed line is the second curve after fitting. Since STOn and SOC are linearly related, adjusting the k value can make STOn and SOC correspond one to one.

[0192] Through image fitting, the relationship between the negative electrode open circuit voltage and SOC is converted into the relationship between the negative electrode open circuit voltage and the negative electrode lithium insertion amount. The volume fraction of active material is calculated using the slope (i.e., linear coefficient) between the negative electrode lithium insertion amount and SOC after fitting.

[0193] In this embodiment, the battery is discharged or charged in stages using the GITT method, a first curve of the negative electrode open circuit voltage-SOC is generated according to several sets of measured data, a second curve is generated according to the first-order equation of the negative electrode open circuit voltage-negative electrode lithium insertion amount, the second curve is fitted to the first curve to obtain a linear coefficient between the negative electrode lithium insertion amount and the SOC, and the active material volume fraction of the graphite electrode is calculated according to the measured thickness and area of ​​the graphite electrode, the theoretical maximum lithium ion concentration, the Faraday constant, the full capacity and the linear coefficient. Without disassembling the battery to test the electrode piece, the measured data can be fitted based on the theoretical value to obtain the linear coefficient, and then the active material volume fraction is calculated. The operation is simple, the parameter accuracy is high, and there is no damage to the battery itself.

[0194] In a specific implementation, the preset capacity change value includes a first capacity change value, a second capacity change value and a third capacity change value.

[0195] The charge and discharge module 1 is specifically configured to perform the following steps:

[0196] Step S111: After fully charging the battery, leave it alone for a first preset time.

[0197] Step S112: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is a first capacity change value, and leaving the battery to rest for a second preset time.

[0198] Step S113: Repeat step S112 until the number of executions of step S112 reaches a first preset number of times.

[0199] Step S114 : setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is a second capacity change value, and leaving the battery to rest for a third preset time.

[0200] Step S115: Repeat step S114 until the number of executions of step S114 reaches a second preset number of times.

[0201] Step S116: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is a third capacity change value or the battery voltage is less than a preset first voltage threshold, and then standing for a fourth preset time.

[0202] Step S117: Repeat step S116 until the number of executions of step S116 is greater than a third preset number of times and the battery voltage is less than the first voltage threshold.

[0203] Among them, for lithium iron phosphate batteries, the battery can be fully charged at 0.5*rated current (C) and 3.65V constant current and constant voltage, that is, first charge it at 0.5C constant current, and then charge it to full capacity at 3.65V constant voltage. Volt constant current and constant voltage charging is an existing technology and will not be repeated here.

[0204] The first preset time length can be 2 hours, the second preset time length can be 1 hour, the first capacity change value can be 1% of the full capacity, the first preset number of times can be 5 times, the second capacity change value can be 5% of the full capacity, the third preset time length can be 1 hour, the second preset number of times can be 17 times, the third capacity change value can be 1% of the full capacity, the fourth preset time length can be 2 hours, the third preset number of times can be 10 times, and the first voltage threshold can be 2.5 volts.

[0205] The capacity change value can be controlled by the discharge time. For example, if the discharge is performed at the rated current for 36 seconds, the capacity change value is 1% of the full capacity.

[0206] The first preset duration, the second preset duration, the first capacity change value, the first preset number of times, the second capacity change value, the third preset duration, the second preset number of times, the third capacity change value, the fourth preset duration, the third preset number of times and the first voltage threshold can be set according to actual needs.

[0207] During specific implementation, the preset capacity change values ​​include a fourth capacity change value, a fifth capacity change value, and a sixth capacity change value.

[0208] The charge and discharge module 1 is specifically configured to perform the following steps:

[0209] Step S118: After discharging the battery to zero power, the battery is left to stand for a fifth preset time period.

[0210] Step S119: setting the charging current to the rated current to perform a charging operation so that the battery capacity change is a fourth capacity change value, and leaving the battery to stand for a sixth preset time period.

[0211] Step S1110: Repeat step S119 until the number of executions of step S119 reaches a fourth preset number of times.

[0212] Step S1111: setting the charging current to the rated current to perform a charging operation so that the battery capacity change is a fifth capacity change value, and leaving the battery to stand for a seventh preset time period.

[0213] Step S1112: Repeat step S1111 until the number of executions of step S1111 reaches a fifth preset number of times.

[0214] Step S1113: Set the charging current to the rated current to perform a charging operation so that the battery capacity change is a sixth capacity change value or the battery voltage is greater than a preset second voltage threshold, and then stand for an eighth preset time period.

[0215] Step S1114: Repeat step S1113 until the number of executions of step S1113 is greater than a sixth preset number of times and the battery voltage is greater than a second voltage threshold.

[0216] Among them, the fifth preset time length can be 2 hours, the fourth capacity change value can be 1% of the full capacity, the sixth preset time length can be 1 hour, the fourth preset number of times can be 5 times, the fifth capacity change value can be 5% of the full capacity, the seventh preset time length can be 1 hour, the fifth preset number of times can be 17 times, the sixth capacity change value can be 1% of the full capacity, the eighth preset time length can be 1 hour, the second voltage threshold can be 3.65 volts, and the sixth preset number of times can be 10 times.

[0217] The capacity change value can be controlled by the charging time. For example, charging at the rated current for 36 seconds means the capacity change value is 1% of the full capacity.

[0218] The fifth preset duration, fourth capacity change value, sixth preset duration, fourth preset number of times, fifth capacity change value, seventh preset duration, fifth preset number of times, sixth capacity change value, eighth preset duration, second voltage threshold and sixth preset number of times can be set according to actual needs.

[0219] In a specific implementation, when the SOC is less than 90%, the positive electrode open circuit voltage is 3.42 volts, and the negative electrode open circuit voltage is expressed by the following formula:

[0220] OCPn=OCPp-OCV=3.42-OCV.

[0221] Among them, OCPn represents the negative electrode open circuit voltage, OCPp represents the positive electrode open circuit voltage, and OCV represents the battery voltage measured after sufficient rest.

[0222] The following formula is used to express the first-order equation of negative electrode open circuit voltage-negative electrode lithium insertion amount:

[0223]

[0224] Among them, OCPn represents the open circuit voltage of the negative electrode, and STOn represents the amount of lithium embedded in the negative electrode.

[0225] In specific implementation, the following formula is used to express the volume fraction of active substances:

[0226] STOn=k*SOC+c.

[0227] ε act,n =Q full / (A n *L n *F*C n,max *k).

[0228] Among them, STOn represents the amount of lithium inserted into the negative electrode, k represents the linear coefficient, c represents the calculation constant, SOC represents SOC, ε act,n represents the volume fraction of active material, Q full Indicates the full capacity of the battery, A n Represents the area of ​​the graphite electrode, L n represents the thickness of the graphite electrode, F represents the Faraday constant, C n,max Indicates the theoretical maximum lithium ion concentration.

[0229] In specific implementation, the detection system also includes:

[0230] The porosity measurement module 6 is used to measure the porosity of the graphite electrode by mercury intrusion porosimetry.

[0231] The total solid volume fraction calculation module 7 is used to calculate the volume fraction of the active substance in the total solid and the volume fraction of the binder, additives, etc. in the total solid according to the porosity and the volume fraction of the active substance.

[0232] In specific implementation, the following formula is used to express the volume fraction of active substances in the total solids and the volume fraction of binders, additives, etc. in the total solids:

[0233] Φ act,n =ε act,n / (1-ε k ).

[0234] Φ inact,n =1-Φact,n.

[0235] Among them, ε act,n represents the volume fraction of active material, ε k Indicates the porosity of the graphite electrode, Φ act,n Indicates the volume fraction of active substances in the total solids, Φ inact,n Indicates the volume fraction of binders, additives, etc. in the total solids.

[0236] Example 3

[0237] Figure 8 This is a schematic diagram of the structure of an electronic device provided in Example 3 of the present invention. The electronic device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the method for detecting the volume fraction of active material in Example 1 is implemented. Figure 8 The electronic device 30 shown is only an example and should not limit the functionality and scope of use of the embodiments of the present invention.

[0238] The electronic device 30 may be a general-purpose computing device, such as a server device. Components of the electronic device 30 may include, but are not limited to, the at least one processor 31, the at least one memory 32, and a bus 33 connecting various system components (including the memory 32 and the processor 31).

[0239] The bus 33 includes a data bus, an address bus, and a control bus.

[0240] The memory 32 may include a volatile memory, such as a random access memory (RAM) 321 and / or a cache memory 322 , and may further include a read-only memory (ROM) 323 .

[0241] The memory 32 may also include a program / utility 325 having a set (at least one) of program modules 324, such program modules 324 including but not limited to: an operating system, one or more application programs, other program modules, and program data, each of which or some combination may include an implementation of a network environment.

[0242] The processor 31 executes various functional applications and data processing by running computer programs stored in the memory 32 , such as the method for detecting the volume fraction of active material in Example 1 of the present invention.

[0243] The electronic device 30 can also communicate with one or more external devices 34 (e.g., buttons, pointing devices, etc.). This communication can occur via an input / output (I / O) interface 35. Furthermore, the model-generated electronic device 30 can also communicate with one or more networks (e.g., a local area network (LAN), a wide area network (WAN), and / or a public network, such as the Internet) via a network adapter 36. As shown, the network adapter 36 communicates with other modules of the model-generated electronic device 30 via a bus 33. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with the model-generated electronic device 30, including but not limited to microcode, device drivers, redundant processors, external disk drive arrays, RAID (RAID) systems, tape drives, and data backup storage systems.

[0244] It should be noted that although several modules / modules or submodules / modules of the electronic device are mentioned in the detailed description above, this division is merely exemplary and not mandatory. In fact, according to embodiments of the present invention, the features and functions of two or more modules / modules described above may be embodied in one module / module; conversely, the features and functions of one module / module described above may be further divided and embodied by multiple modules / modules.

[0245] Example 4

[0246] This embodiment provides a computer-readable storage medium having a computer program stored thereon. When the program is executed by a processor, the method for detecting the volume fraction of active material in Example 1 is implemented.

[0247] The readable storage medium may include, but is not limited to, a portable disk, a hard disk, a random access memory, a read-only memory, an erasable programmable read-only memory, an optical storage device, a magnetic storage device, or any suitable combination thereof.

[0248] In a possible implementation, the present invention can also be implemented in the form of a program product, which includes program code. When the program product is run on a terminal device, the program code is used to enable the terminal device to execute the method for detecting the volume fraction of active substances in Example 1.

[0249] The program code for executing the present invention may be written in any combination of one or more programming languages, and may be executed entirely on the user device, partially on the user device, as an independent software package, partially on the user device and partially on a remote device, or entirely on the remote device.

[0250] Although specific embodiments of the present invention have been described above, those skilled in the art will appreciate that these are merely illustrative and that the scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, and such changes and modifications are intended to fall within the scope of the present invention.

Claims

1. A method for detecting the volume fraction of active substances, characterized in that: include: The battery is discharged or charged in stages using the GITT method to obtain several sets of measured negative electrode open circuit voltages and SOCs of the graphite electrodes; wherein the battery capacity change in each stage is a preset capacity change value; generating a first curve of negative electrode open circuit voltage-SOC according to the plurality of sets of negative electrode open circuit voltages and SOCs; Generate a second curve according to the first-order equation of negative electrode open circuit voltage-negative electrode lithium insertion amount; Fitting the second curve to the first curve to obtain a linear coefficient between the amount of lithium inserted into the negative electrode and the SOC; Calculating the active material volume fraction of the graphite electrode based on the measured thickness and area of ​​the graphite electrode, the theoretical maximum lithium ion concentration, the Faraday constant, the full capacity, and the linear coefficient; The volume fraction of the active substance is expressed by the following formula: STOn=k*SOC+c; ε act,n =Q full / (A n *L n *F*C n,max *k); Wherein, STOn represents the amount of lithium embedded in the negative electrode, k represents the linear coefficient, c represents the calculation constant, SOC represents SOC, ε act,n represents the volume fraction of the active material, Q full Indicates the full capacity of the battery, A n represents the area of ​​the graphite electrode, L n represents the thickness of the graphite electrode, F represents the Faraday constant, C n,max Indicates the theoretical maximum lithium ion concentration.

2. The method for detecting the volume fraction of active substances according to claim 1, wherein: The preset capacity change value includes a first capacity change value, a second capacity change value and a third capacity change value; The discharging or charging operation of the battery in stages by the GITT method includes: Step S111: After the battery is fully charged, it is left to stand for a first preset time; Step S112: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is the first capacity change value, and leaving the battery in a static state for a second preset time; Step S113, repeatedly executing step S112, so that the number of executions of step S112 reaches a first preset number; Step S114: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is the second capacity change value, and leaving the battery in a static state for a third preset time; Step S115: Repeat step S114 until the number of executions of step S114 reaches a second preset number of times; Step S116: setting the discharge current to the rated current to perform a discharge operation so that the battery capacity change is the third capacity change value or the battery voltage is less than a preset first voltage threshold, and then leaving the battery in standstill for a fourth preset time period; Step S117: Repeat step S116 until step S116 is executed more than a third preset number of times and the battery voltage is less than the first voltage threshold.

3. The method for detecting the volume fraction of active substances according to claim 1, wherein: The preset capacity change values ​​include a fourth capacity change value, a fifth capacity change value, and a sixth capacity change value; The GITT method discharges or charges the battery in stages, including: Step S118: After discharging the battery to zero power, the battery is left to stand for a fifth preset time period; Step S119: setting the charging current to the rated current to perform a charging operation so that the battery capacity change is the fourth capacity change value, and leaving the battery in standstill for a sixth preset time; Step S1110: Repeat step S119 until the number of executions of step S119 reaches a fourth preset number of times; Step S1111: setting the charging current to the rated current to perform a charging operation so that the battery capacity change is the fifth capacity change value, and leaving the battery to stand for a seventh preset time; Step S1112: Repeat step S1111 until the number of executions of step S1111 reaches a fifth preset number of times; Step S1113: Setting the charging current to the rated current to perform a charging operation so that the battery capacity change is the sixth capacity change value or the battery voltage is greater than a preset second voltage threshold, and then standing for an eighth preset time period; Step S1114: Repeat step S1113 until step S1113 is executed more than a sixth preset number of times and the battery voltage is greater than the second voltage threshold.

4. The method for detecting the volume fraction of active substances according to claim 1, wherein: When the SOC is less than 90%, the positive electrode open circuit voltage is 3.42 volts, and the negative electrode open circuit voltage is expressed by the following formula: OCPn=OCPp-OCV=3.42-OCV; Wherein, OCPn represents the negative electrode open circuit voltage, OCPp represents the positive electrode open circuit voltage, and OCV represents the battery voltage measured after sufficient rest; The first-order equation of the negative electrode open circuit voltage-negative electrode lithium insertion amount is expressed by the following formula: Wherein, OCPn represents the open circuit voltage of the negative electrode, and STOn represents the amount of lithium embedded in the negative electrode.

5. The method for detecting the volume fraction of active substances according to claim 1, wherein: The detection method further comprises: The porosity of the graphite electrode is measured by mercury intrusion porosimetry; The volume fraction of the active material in the total solids and the volume fraction of the binder, additives, etc. in the total solids are calculated based on the porosity and the volume fraction of the active material.

6. The method for detecting the volume fraction of active substances according to claim 5, wherein: The following formula is used to express the volume fraction of the active substance in the total solids and the volume fraction of the binder, additives, etc. in the total solids: F act,n =e act,n / (1-e k ); F inact,n =1-Φact,n; Among them, ε act,n represents the volume fraction of the active material, ε k represents the porosity of the graphite electrode, Φ act,n Indicates the volume fraction of active substances in the total solids, Φ inact,n Indicates the volume fraction of binders, additives, etc. in the total solids.

7. A system for detecting the volume fraction of active substances, characterized in that: include: The charge and discharge module is used to discharge or charge the battery in stages using the GITT method to obtain several sets of measured negative electrode open circuit voltages and SOCs of the graphite electrodes; wherein the battery capacity change in each stage is a preset capacity change value; A first curve generating module, configured to generate a first curve of negative electrode open circuit voltage-SOC according to the plurality of sets of negative electrode open circuit voltages and SOCs; A second curve generating module is used to generate a second curve according to a first-order equation of negative electrode open circuit voltage-negative electrode lithium insertion amount; a fitting module, configured to fit the second curve to the first curve to obtain a linear coefficient between the amount of lithium embedded in the negative electrode and the SOC; an active material volume fraction calculation module, configured to calculate the active material volume fraction of the graphite electrode based on the measured thickness and area of ​​the graphite electrode, the theoretical maximum lithium ion concentration, the Faraday constant, the full capacity, and the linear coefficient; The volume fraction of the active substance is expressed by the following formula: STOn=k*SOC+c; ε act,n =Q full / (A n *L n *F*C n,max *k); Wherein, STOn represents the amount of lithium embedded in the negative electrode, k represents the linear coefficient, c represents the calculation constant, SOC represents SOC, ε act,n represents the volume fraction of the active material, Q full Indicates the full capacity of the battery, A n represents the area of ​​the graphite electrode, L n represents the thickness of the graphite electrode, F represents the Faraday constant, C n,max Indicates the theoretical maximum lithium ion concentration.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the method for detecting the volume fraction of active material according to any one of claims 1 to 6 is implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for detecting the volume fraction of active material according to any one of claims 1 to 6 is implemented.

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