Method for determining addition amount of lithium supplement agent of lithium ion battery and lithium ion battery

Abstract

The invention provides a method for determining the addition amount of a lithium supplement agent of a lithium ion battery and the lithium ion battery. The method comprises the following steps: acquiring the first discharge gram volume A and the first charge gram volume B of a first electrode active material; obtaining the gram volume C of the lithium supplement agent; obtaining a first effect Y of a second electrode active material; the capacity ratio Z of a first electrode and a second electrode in the target lithium ion battery is obtained, the first electrode comprises a first electrode active material and a lithium supplement agent, and the second electrode comprises a second electrode active material; based on the parameters A, B, C, Y and Z and a first preset formula, the optimal lithium supplementing amount X of the lithium supplementing agent in the first electrode is calculated, and the first preset formula is shown in the formula (I) # imgabs0 #, and X represents the mass ratio of the lithium supplementing agent to the sum of the first electrode active material and the lithium supplementing agent. According to the method, the optimal lithium supplementing amount of the lithium supplementing agent can be obtained in advance before the lithium ion battery is manufactured, multiple times of trial and error are not needed, the workload is effectively reduced, and the universality is good.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method for determining the amount of lithium supplement added to a lithium ion battery, and a lithium ion battery. Background Art

[0002] During the first charge of a lithium-ion battery, the electrolyte will be reduced and decomposed on the surface of the negative electrode to form a solid electrolyte interface (SEI) film. In this process, a large amount of lithium ions from the positive electrode will be consumed, resulting in a low initial coulombic efficiency of the lithium-ion battery and reducing the capacity and energy density of the lithium-ion battery. By adding lithium supplements to the electrode materials of lithium-ion batteries, the lithium loss can be offset to a certain extent, thereby improving the energy density of lithium-ion batteries. However, the energy density of lithium-ion batteries does not always increase significantly as the amount of lithium supplements added to the electrode materials increases. Usually, there is an optimal amount of lithium supplements added to the electrode materials, that is, a critical value. At this critical value, the lithium supplement can just compensate for the lithium ion loss in the lithium-ion battery. This critical value is usually called the optimal lithium supplement amount.

[0003] Related technology The method of obtaining the amount of lithium replenisher added to lithium-ion batteries is to conduct a series of gradient lithium replenisher addition experiments, and match the range of empirical results by performing X-ray diffraction (XRD) analysis on the electrode active material or measuring the resistance of the electrode membrane to obtain the optimal amount of lithium replenisher added to the electrode. This method has many trial and error times, a large workload, and a single range of applicable material systems, and it is also impossible to calculate the range of the optimal lithium replenisher in advance. Summary of the invention

[0004] The embodiments of the present application provide a method for determining the amount of lithium supplement added to a lithium ion battery and a lithium ion battery, so as to at least partially solve the above technical problems.

[0005] In a first aspect, an embodiment of the present application provides a method for determining the amount of lithium supplement added to a lithium-ion battery, comprising:

[0006] Obtaining the first discharge gram capacity A and the first charge gram capacity B of the first electrode active material;

[0007] Obtain the gram capacity C of the lithium supplement;

[0008] Obtaining the first effect Y of the second electrode active material;

[0009] Obtaining a capacity ratio Z of a first electrode to a second electrode in a target lithium-ion battery, wherein the first electrode and the second electrode have opposite polarities, the first electrode includes the first electrode active material and the lithium supplement, and the second electrode includes the second electrode active material;

[0010] The optimal lithium supplement amount X of the lithium supplement agent in the first electrode is calculated based on the parameters A, B, C, Y and Z and a first preset formula, wherein the first preset formula is shown in formula (I):

[0011]

[0012] Herein, X represents the mass ratio of the lithium supplement agent to the sum of the first electrode active material and the lithium supplement agent.

[0013] In one embodiment, obtaining the first discharge gram capacity A and the first charge gram capacity B of the first electrode active material comprises:

[0014] Providing a first half-cell, the first half-cell comprising a first test electrode; the first test electrode comprising the first electrode active material having a mass M1;

[0015] Performing a charge and discharge test on the first half-cell to obtain a discharge capacity Q11 and a charge capacity Q12 of the first half-cell;

[0016] Based on the parameters M1, Q11 and Q12, and the second preset formula and the third preset formula, respectively calculate the first discharge gram capacity A and the first charge gram capacity B of the first electrode active material;

[0017] Wherein, the second preset formula is shown in formula (II), and the third preset formula is shown in formula (III):

[0018]

[0019] In one embodiment, obtaining the gram capacity C of the lithium supplement comprises:

[0020] Providing a second half-cell, the second half-cell comprising a second test electrode; the second test electrode comprising the lithium supplement having a mass M2;

[0021] Performing a discharge test on the second half-cell to obtain a discharge capacity Q21 of the second half-cell;

[0022] The gram capacity C of the lithium supplement is calculated based on the parameters M2, Q21, and a fourth preset formula, wherein the fourth preset formula is as shown in formula (IV):

[0023]

[0024] In one embodiment, obtaining the first effect Y of the second electrode active material includes:

[0025] providing a third half-cell, the third half-cell comprising a third test electrode, the third test electrode comprising a mass M3 of the second electrode active material;

[0026] Performing a charge and discharge test on the third half-battery to obtain a discharge capacity Q31 and a charge capacity Q32 of the third half-battery;

[0027] Based on the parameters M3, Q31 and Q32, and the fifth preset formula and the sixth preset formula, the first discharge gram capacity D and the first charge gram capacity E of the second electrode active material are calculated respectively, wherein the fifth preset formula is shown in formula (V), and the sixth preset formula is shown in formula (VI):

[0028]

[0029] The first effect Y of the second electrode active material is calculated based on the parameters D, E and the seventh preset formula, wherein the seventh preset formula is shown in formula (VII):

[0030]

[0031] In one embodiment, obtaining the capacity ratio Z of the first electrode to the second electrode in the target lithium-ion battery includes:

[0032] Obtaining the surface density P1 of the first electrode and the mass content ratio L1 of the first electrode active material in the active material layer of the first electrode;

[0033] Obtaining the reversible gram capacity G1 of the first electrode active material;

[0034] Obtaining the surface density P2 of the second electrode and the mass content ratio L2 of the second electrode active material in the active material layer of the second electrode;

[0035] Obtaining the reversible gram capacity G2 of the second electrode active material;

[0036] The capacity ratio Z of the first electrode to the second electrode is calculated based on the parameters P1, L1, G1, P2, L2, G2, and an eighth preset formula, wherein the eighth preset formula is shown in formula (VIII):

[0037]

[0038] In one embodiment, obtaining the reversible gram capacity G1 of the first electrode active material includes:

[0039] Providing a fourth half-cell, the fourth half-cell comprising a fourth test electrode; the fourth test electrode comprising a mass M4 of the first electrode active material;

[0040] Performing a charge and discharge cycle test on the fourth half battery to obtain an average discharge capacity Q41 of the fourth half battery during an N1-th cycle period to an Nn-th cycle period, wherein N1 and Nn are both natural numbers greater than or equal to 2, and Nn is greater than or equal to N1;

[0041] The reversible gram capacity G1 of the first electrode active material is calculated based on the parameters M4, Q41, and the ninth preset formula, which is shown in formula (IX):

[0042]

[0043] In one embodiment, obtaining the reversible gram capacity G2 of the second electrode active material comprises:

[0044] providing a fifth half-cell, the fifth half-cell comprising a fifth test electrode; the fifth test electrode comprising a mass M5 of the second electrode active material;

[0045] Performing a charge-discharge cycle test on the fifth half-battery to obtain an average discharge capacity Q51 of the fifth half-battery during an N2-th cycle to an Nm-th cycle, wherein N2 and Nm are both natural numbers greater than or equal to 2, and Nm is greater than or equal to N2;

[0046] The reversible gram capacity G2 of the second electrode active material is calculated based on the parameters M5, Q51, and the tenth preset formula, which is shown in formula (X):

[0047]

[0048] In one embodiment, the first electrode is a positive electrode, and the first electrode active material is a positive electrode active material; the second electrode is a negative electrode, and the second electrode active material is a negative electrode active material.

[0049] In one embodiment, the lithium supplement is a positive electrode lithium supplement, and the positive electrode lithium supplement includes Li 2 O. Li 2 NiO 2 , Li 5 FeO 4 , Li 6 CoO 4 , Li 2 O 2 , Li 3 N and Li 2 At least one of S.

[0050] In one embodiment, the positive electrode active material includes at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

[0051] In one embodiment, the negative electrode active material includes at least one of graphite and silicon carbon.

[0052] In a second aspect, an embodiment of the present application provides a lithium-ion battery, comprising a first electrode and a second electrode, wherein the first electrode comprises a first electrode active material and a lithium supplement, and the mass ratio T of the lithium supplement to the sum of the first electrode active material and the lithium supplement is greater than or equal to the optimal lithium supplement amount X calculated according to the above-mentioned method for determining the amount of lithium supplement added to the lithium-ion battery.

[0053] Beneficial effects of the embodiments of the present application:

[0054] In the method for determining the amount of lithium supplementer added to a lithium ion battery provided in an embodiment of the present application, parameters A, B, C, Y, and Z can be obtained in the design stage of the lithium ion battery, so that the optimal lithium supplement amount X of the lithium supplementer can be obtained in advance before the lithium ion battery is manufactured.

[0055] In addition, the method for determining the amount of lithium supplementer added to a lithium ion battery provided in the embodiment of the present application does not require multiple trial and error, thereby effectively reducing the workload, and the method for determining the amount of lithium supplementer added to a lithium ion battery can be applied to the calculation of the amount of lithium supplementer added to a variety of material systems, and has good versatility.

[0056] In addition, when designing a lithium-ion battery, by setting the amount of lithium replenisher added to the lithium-ion battery to be greater than or equal to the optimal lithium replenisher amount X, not only the energy density of the lithium-ion battery can be improved, but also the cycle performance of the lithium-ion battery can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0058] Figure 1 It is a flow chart of a method for determining the amount of lithium supplement added to a lithium-ion battery provided in an embodiment of the present application. DETAILED DESCRIPTION

[0059] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0060] In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In the present application, unless otherwise stated, the directional words used, such as "upper" and "lower", generally refer to the upper and lower parts of the device in actual use or working state, specifically the drawing direction in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0061] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0062] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0063] The terms "comprises," "includes," or any other variation thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0064] In the description of the embodiments of the present application, words such as "example" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "example" or "for example" in the embodiments of the present application is not to be interpreted as being more preferred or having more advantages than another embodiment or design. The use of words such as "example" or "for example" is intended to present relative concepts in a clear manner.

[0065] To facilitate understanding of the scheme of the present application, the spline curves and arrows used in the drawings are explained here: the components indicated by the spline curves without arrows are solid components, that is, components with solid structures; the components indicated by the spline curves with arrows are virtual components, that is, components without solid structures.

[0066] First, see Figure 1 The present application provides a method for determining the amount of lithium supplement added to a lithium ion battery, comprising the following steps:

[0067] S1, obtaining the first discharge gram capacity A and the first charge gram capacity B of the first electrode active material;

[0068] S2, obtaining the gram capacity C of the lithium supplement;

[0069] S3, obtaining the first effect Y of the second electrode active material;

[0070] S4, obtaining a capacity ratio Z of a first electrode to a second electrode in a target lithium-ion battery, wherein the first electrode and the second electrode have opposite polarities, the first electrode includes a first electrode active material and a lithium supplement, and the second electrode includes a second electrode active material;

[0071] S5. Calculate the optimal lithium supplement amount X of the lithium supplement agent in the first electrode based on the parameters A, B, C, Y and Z and a first preset formula, wherein the first preset formula is shown in formula (I):

[0072]

[0073] Wherein X represents the mass ratio of the lithium supplement agent to the sum of the first electrode active material and the lithium supplement agent.

[0074] It should be noted that the polarity of the electrode can be positive or negative, and the first electrode can be a positive electrode or a negative electrode. When the first electrode is a positive electrode, the second electrode is a negative electrode; when the first electrode is a negative electrode, the second electrode is a positive electrode.

[0075] The first electrode includes a first electrode active material and a lithium supplement, and the second electrode includes a second electrode active material. When the first electrode is a positive electrode, the first electrode active material is a positive electrode active material, the lithium supplement is a positive electrode lithium supplement, and the second electrode active material is a negative electrode active material; when the first electrode is a negative electrode, the first electrode active material is a negative electrode active material, the lithium supplement is a negative electrode lithium supplement, and the second electrode active material is a positive electrode active material.

[0076] The first coulombic efficiency of a battery (abbreviated as first efficiency) refers to the ratio of the actual capacity released by the battery during the first charge and discharge process to its theoretical capacity.

[0077] The first effect of the whole battery is closely related to the first effect of the positive and negative electrodes in the whole battery and the reaction process inside the whole battery. Usually, the first effect of the whole battery is equal to the ratio of the first discharge capacity to the first charge capacity. The first effect of the positive electrode (referred to as the positive electrode first effect) refers to the capacity conversion efficiency of the positive electrode during the first charge and discharge process. The first effect of the positive electrode is equal to the ratio of the actual capacity released by the positive electrode to the theoretical capacity of the positive electrode. The first effect of the negative electrode (referred to as the positive electrode first effect) refers to the capacity conversion efficiency of the negative electrode during the first charge and discharge process. The first effect of the negative electrode is equal to the ratio of the actual capacity released by the negative electrode to the theoretical capacity of the negative electrode.

[0078] According to the principle of the first effect balance of the whole battery: in order to achieve the positive electrode first effect = negative electrode first effect, it is necessary to ensure that the amount of lithium ion migration of the positive and negative electrodes is equal during the first charge and discharge process of the whole battery.

[0079] However, during the first charge of the full battery, a solid electrolyte interface (SEI) film will form on the negative electrode surface, consuming some lithium ions, resulting in a decrease in the number of lithium ions available for subsequent charge and discharge cycles, thereby reducing the initial efficiency of the negative electrode. Taking lithium iron phosphate batteries as an example, the initial efficiency of the negative electrode of lithium iron phosphate batteries is generally lower than that of the positive electrode.

[0080] To this end, a lithium supplement can be added before the first charge and discharge of the entire battery. The lithium supplement will release additional lithium ions during the first charge and discharge process to compensate for the lithium ions lost at the negative electrode due to processes such as the formation of the SEI film, thereby improving the initial efficiency of the entire battery.

[0081] Theoretically, to make the first effect of the positive electrode of the whole battery equal to the first effect of the negative electrode of the whole battery, it is necessary to comprehensively consider factors such as the characteristics of the positive electrode active material, the characteristics of the negative electrode active material, the amount of lithium replenishment of the lithium replenisher, and the specific design of the battery. For example, the amount of lithium replenisher required can be calculated based on the amount of lithium ion loss during the formation of the SEI film on the negative electrode. The general calculation idea is:

[0082] First, determine the amount of active lithium loss in the negative electrode (active lithium loss = (1-negative electrode first effect) × mass of negative electrode active material × negative electrode charging gram capacity), and then calculate the theoretical mass of lithium supplement that needs to be added based on the gram capacity of the lithium supplement (theoretical lithium supplement addition amount = active lithium loss / lithium supplement gram capacity).

[0083] Based on the above principle, the present application embodiment proposes a calculation formula for calculating the optimal lithium replenishing amount of the lithium replenishing agent in the electrode, as shown in formula (I):

[0084]

[0085] In formula (I), A is the first discharge gram capacity of the first electrode active material, B is the first charge gram capacity of the first electrode active material, C is the gram capacity of the lithium supplement, and Y is the first efficiency of the second electrode active material. These parameters are all inherent property parameters of the material and can be obtained by looking up the table in advance or experimental measurement. Z is a parameter that can be set manually according to demand when designing the target lithium-ion battery. Z of different target lithium-ion batteries may be different. Specifically, Z is the N / P (Negative / Positive) ratio, and the calculation formula of the N / P ratio is: (negative electrode active material gram capacity * negative electrode surface density * negative electrode active material content) / (positive electrode active material gram capacity * positive electrode surface density * positive electrode active material content). In this calculation formula, the negative electrode active material gram capacity and the positive electrode active material gram capacity are inherent property parameters of the material, which can be obtained by looking up the table in advance or experimental measurement, while the negative electrode surface density, negative electrode active material content, positive electrode surface density and positive electrode active material content are design parameters, which can be obtained in advance according to demand.

[0086] It can be seen that in the method for determining the amount of lithium supplementer added to a lithium ion battery provided in the embodiment of the present application, in formula (I), only X is an unknown quantity, and parameters A, B, C, Y, and Z can be obtained in the design stage of the target lithium ion battery, so that the optimal amount of lithium supplementer can be obtained in advance before the target lithium ion battery is manufactured.

[0087] In addition, the method for determining the amount of lithium supplementer added to a lithium ion battery provided in the embodiment of the present application does not require multiple trial and error, thereby effectively reducing the workload, and the method for determining the amount of lithium supplementer added to a lithium ion battery can be applied to the calculation of the amount of lithium supplementer added to a variety of material systems, and has good versatility.

[0088] In formula (I), X is the optimal lithium supplement amount of the lithium supplement agent, which is the mass ratio of the lithium supplement agent to the sum of the first electrode active material and the lithium supplement agent. Here, the optimal lithium supplement amount X is the critical value of the amount of lithium supplement agent added. At this critical value, the effect of the lithium supplement agent is most obvious and the energy density is improved the most; if the amount of lithium supplement agent added is lower than the critical value, the lithium supplement agent may not be able to completely compensate for the loss of lithium ions; if the amount of lithium supplement agent added exceeds this critical value, although lithium ions can be further supplemented, the effect of improving energy density will no longer be significant.

[0089] When the amount of lithium supplement added exceeds the critical value, although the effect on improving energy density is limited, the excess lithium supplement can continuously replenish the lithium ion loss caused by changes in the electrode material structure and electrolyte decomposition during the lithium-ion battery cycle.

[0090] That is to say, after exceeding this critical value, the active lithium released by the lithium supplement is mainly used to improve the cycle performance. Because the lithium supplement can help maintain the stability and electrochemical activity of the electrode material, this continuous lithium ion supplement can reduce the capacity decay of the lithium-ion battery during long-term cycling, thereby improving the cycle performance of the lithium-ion battery.

[0091] Therefore, when designing a target lithium-ion battery, the amount of lithium supplement added in the target lithium-ion battery is usually set to be greater than or equal to the optimal lithium supplement amount X, which can not only improve the energy density of the target lithium-ion battery, but also improve the cycle performance of the target lithium-ion battery.

[0092] Since the added mass (in g) of the first electrode active material can be artificially designed in advance during the target lithium-ion battery design stage, the added mass (in g) of the lithium supplement agent can also be obtained when the optimal lithium supplement amount X (in %) is determined.

[0093] The following description is made by taking the example that the first electrode is a positive electrode, the first electrode active material is a positive electrode active material, the second electrode is a negative electrode, and the second electrode active material is a negative electrode active material.

[0094] The method for determining the amount of lithium supplement added to a lithium ion battery provided in the embodiment of the present application has a wide range of applications and can be applied to various lithium ion battery systems and calculation of the amount of lithium supplement added of different lithium supplements.

[0095] As an example, the first electrode active material is a positive electrode active material, and the positive electrode active material includes at least one of lithium iron phosphate (LFP), lithium iron manganese phosphate (LMFP), lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt aluminum oxide (NCA).

[0096] As an example, the lithium replenisher is a positive electrode lithium replenisher, and the positive electrode lithium replenisher includes Li 2 O. Li 2 NiO 2 , Li 5 FeO 4 , Li 6 CoO 4 , Li 2 O 2 , Li 3 N and Li 2 At least one of S.

[0097] As an example, the second electrode active material is a negative electrode active material, and the negative electrode active material includes at least one of graphite and silicon carbon.

[0098] In some embodiments, the first discharge gram capacity A and the first charge gram capacity B of the first electrode active material can be obtained by experiment. Specifically, the step of obtaining the first discharge gram capacity A and the first charge gram capacity B of the first electrode active material, that is, step S1, includes:

[0099] S11, providing a first half-cell, the first half-cell comprising a first test electrode; the first test electrode comprising a first electrode active material having a mass M1;

[0100] S12, performing a charge and discharge test on the first half battery to obtain a discharge capacity Q11 and a charge capacity Q12 of the first half battery;

[0101] S13, based on the parameters M1, Q11 and Q12, and the second preset formula and the third preset formula, respectively calculate the first discharge gram capacity A and the first charge gram capacity B of the first electrode active material, wherein the second preset formula is shown in formula (II), and the third preset formula is shown in formula (III):

[0102]

[0103] Usually, the polarity of the first test electrode is the same as the polarity of the first electrode, and the first test electrode does not contain a lithium supplement.

[0104] The first discharge capacity in grams A and the first charge capacity in grams B of the first electrode active material measured by the above method are the first discharge capacity in grams and the first charge capacity in grams, respectively. This method is simple and reliable, and the measured results can continue to be applicable to the design of other lithium-ion batteries using the first electrode active material, further improving the development efficiency of lithium-ion batteries.

[0105] It can be understood that the lithium-ion battery in the design is the target lithium-ion battery, the first electrode is the electrode in the target lithium-ion battery, and the first test electrode is the electrode of the first half-cell used in the test process. Usually, the target lithium-ion battery is a full cell, and the first half-cell is a half-cell. The first electrode and the first test electrode have the same polarity and contain the same electrode active material, but the composition of the active material layer of the first electrode and the active material layer of the first test electrode are different. For example, the active material layer of the first electrode contains a lithium supplement, while the active material layer of the first test electrode does not contain a lithium supplement.

[0106] As an example, the first electrode is a positive electrode, the first test electrode is also a positive electrode, the first electrode active material is a positive electrode active material, and the measurement process of the first discharge gram capacity A and the first charge gram capacity B of the first electrode active material includes:

[0107] S11. Weigh the cathode active material with a mass of M1, mix the cathode active material with a conductive agent (such as carbon black, carbon nanotubes, etc.) and a binder (such as polyvinylidene fluoride) in proportion, add a solvent (such as N-methylpyrrolidone), and stir evenly to make an electrode slurry. Coat the electrode slurry on the cathode current collector (such as aluminum foil), and prepare a cathode sheet (i.e., the first test electrode) through processes such as drying, rolling, and cutting. After drying, the electrode slurry forms an active material layer. Assemble the prepared cathode sheet, anode sheet (usually a lithium sheet), and separator together into a button cell (i.e., the first half cell), and then inject an appropriate amount of electrolyte. In this step, maintain a dry and dust-free environment during the battery assembly process to avoid moisture and impurities from affecting the test results.

[0108] S12. Set the test parameters, mainly including the voltage range and rate parameters (such as 0.1C, 0.2C, 1C, etc.); perform constant current charge and discharge on the button cell according to the set test parameters, and record the voltage, current, and time during the charge and discharge process to obtain the discharge capacity Q11 and the charge capacity Q12. In this step, a battery test system, such as an electrochemical workstation or a battery tester, can be used to summarize the test process to accurately control the charge and discharge parameters and record the data. In addition, during the test process, the set test parameters are related to the type of cathode active material and can be set according to different cathode active materials. Exemplarily, if the cathode active material is lithium iron phosphate, the voltage range can be set to 2.0V - 3.75V. In other embodiments, other charge and discharge methods other than constant current charge and discharge can also be adopted, which are not limited herein.

[0109] S13. Calculate the first discharge specific capacity A and the first charge specific capacity B of the cathode active material according to Equation (Ⅱ) and Equation (Ⅲ).

[0110] In some embodiments, the specific capacity C of the lithium supplement agent can be obtained through experiments. Specifically, the steps to obtain the specific capacity C of the lithium supplement agent, that is, step S2, include:

[0111] S21. Provide a second half cell, and the second half cell includes a second test electrode, and the second test electrode contains a lithium supplement agent with a mass of M2;

[0112] S22. Perform a discharge test on the second half cell to obtain the discharge capacity Q21 of the second half cell;

[0113] S23. Based on the parameters M2, Q21, and a fourth preset formula, calculate the specific capacity C of the lithium supplement agent. The fourth preset formula is shown in Equation (Ⅳ):

[0114]

[0115] Usually, the polarity of the second test electrode is the same as that of the first electrode, and the second test electrode does not contain the first electrode active material.

[0116] The gram capacity C of the lithium supplement measured by the above method is the discharge gram capacity. The method is simple and reliable, and the measured results can continue to be applicable to the design of other lithium-ion batteries using the lithium supplement, further improving the development efficiency of lithium-ion batteries.

[0117] It can be understood that the second test electrode is the electrode of the second half-cell used in the test process, and the second half-cell is usually also a half-cell. The first electrode and the second test electrode have the same polarity, but they contain different electrode active materials. The electrode active material in the first electrode is the first electrode active material, and the electrode active material of the second test electrode is a lithium supplement.

[0118] As an example, the first electrode is a positive electrode, the second test electrode is also a positive electrode, the lithium supplement is a positive electrode lithium supplement, and the measurement process of the gram capacity C of the lithium supplement includes:

[0119] S21. Weigh the positive electrode lithium supplement with a mass of M2, mix the positive electrode lithium supplement with a conductive agent (such as carbon black, carbon nanotubes, etc.) and an adhesive (such as polyvinylidene fluoride) in proportion, add a solvent (such as N-methylpyrrolidone) and stir evenly to form an electrode slurry. Coat the electrode slurry on the positive electrode collector (such as aluminum foil), and prepare the positive electrode sheet (i.e., the second test electrode) by drying, rolling, cutting and other processes. Assemble the prepared positive electrode sheet, negative electrode sheet (usually a lithium sheet) and diaphragm together into a button cell (i.e., the second half cell); then inject an appropriate amount of electrolyte.

[0120] S22, set the test parameters, mainly including the discharge starting voltage (usually the highest discharge voltage of the positive electrode lithium supplement) and the cut-off voltage (usually the lowest discharge voltage of the positive electrode lithium supplement), and select appropriate rate parameters (such as 0.1C, 0.2C, 1C, etc.); under the set test parameters, the button battery is discharged at a constant current, and the voltage, current and time of the discharge process are recorded to obtain the discharge capacity Q21. In this step, a battery testing system, such as an electrochemical workstation or a battery tester, can be used to summarize the test process to accurately control the charge and discharge parameters and record the data. In addition, during the test process, the set test parameters are related to the type of positive electrode lithium supplement, and can be set according to different lithium supplements.

[0121] S23. Calculate the gram capacity C of the positive electrode lithium supplement according to formula (IV).

[0122] In some embodiments, the first effect Y of the second electrode active material can be obtained by experiment. Specifically, the step of obtaining the first effect Y of the second electrode active material, that is, step S3, includes:

[0123] S31, providing a third half-cell, wherein the third half-cell comprises a third test electrode, and the third test electrode comprises a second electrode active material having a mass M3;

[0124] S32, performing a charge and discharge test on the third half battery to obtain a discharge capacity Q31 and a charge capacity Q32 of the third half battery;

[0125] S33, based on the parameters M3, Q31 and Q32, and the fifth preset formula and the sixth preset formula, respectively calculate the first discharge gram capacity D and the first charge gram capacity E of the second electrode active material, wherein the fifth preset formula is shown in formula (V), and the sixth preset formula is shown in formula (VI):

[0126]

[0127] S35, calculating the first effect Y of the second electrode active material based on the parameters D, E and the seventh preset formula, the seventh preset formula is shown in formula (VII):

[0128]

[0129] Usually, the polarity of the third test electrode is the same as that of the second electrode, and the third test electrode does not contain a lithium supplement.

[0130] The first efficiency Y of the second electrode active material measured by the above method is the first efficiency of charge withdrawal. The method is simple and reliable, and the measured results can continue to be applicable to the design of other lithium-ion batteries using the second electrode active material, further improving the development efficiency of lithium-ion batteries.

[0131] It can be understood that the second electrode is an electrode in the target lithium-ion battery, and the third test electrode is an electrode of the third half-cell used in the test process. Usually, the target lithium-ion battery is a full battery, and the third half-cell is a half-cell. The second electrode and the third test electrode have the same polarity and contain the same electrode active material, but the composition of the active material layer of the second electrode and the active material layer of the third test electrode can be the same or different.

[0132] As an example, the second electrode is a negative electrode, the third test electrode is also a negative electrode, the second electrode active material is a negative electrode active material, and the measurement process of the first effect Y of the second electrode active material includes:

[0133] S31. Weigh the negative electrode active material with a mass of M3, mix the negative electrode active material with a conductive agent (such as carbon black, carbon nanotubes), and an adhesive (such as sodium carboxymethyl cellulose, styrene-butadiene rubber) in proportion, add a solvent (such as water) and stir evenly to form an electrode slurry. The electrode slurry is coated on the negative electrode collector (such as copper foil), and a negative electrode sheet (i.e., the third test electrode) is prepared by drying, rolling, cutting and other processes. After the electrode slurry is dried, it forms an active material layer. The prepared negative electrode sheet, positive electrode sheet (usually a lithium sheet) and separator are assembled into a button cell (i.e., the third half-cell); then an appropriate amount of electrolyte is injected.

[0134] S32, set the test parameters, mainly including the voltage range and rate parameters (such as 0.1C, 0.2C, 1C, etc.); perform constant current charge and discharge on the button battery according to the set test parameters, and record the voltage, current and time of the charge and discharge process to obtain the discharge capacity Q31 and the charge capacity Q32. In this step, a battery testing system, such as an electrochemical workstation or a battery tester, can be used to summarize the test process to accurately control the charge and discharge parameters and record the data. In addition, during the test process, the set test parameters are related to the type of negative electrode active material and can be set according to different negative electrode active materials. Exemplarily, if the negative electrode active material is graphite, the voltage range can be set to 0.005V~2.0V. In other embodiments, other charging and discharging methods besides constant current charging and discharging can also be used, which are not limited here.

[0135] S33, according to formula (V) and formula (VI), calculate the first discharge gram capacity D and the first charge gram capacity E of the negative electrode active material. Here, the first discharge gram capacity D and the first charge gram capacity E are the first discharge gram capacity after deducting electricity and the first charge gram capacity after deducting electricity, respectively.

[0136] S34. Calculate the first efficiency Y of the negative electrode active material according to formula (VII).

[0137] In some embodiments, the step of obtaining the capacity ratio Z of the first electrode to the second electrode in the target lithium-ion battery, that is, step S4, includes:

[0138] S41, obtaining the surface density P1 of the first electrode and the mass content ratio L1 of the first electrode active material in the active material layer of the first electrode;

[0139] S42, obtaining the reversible gram capacity G1 of the first electrode active material;

[0140] S43, obtaining the surface density P2 of the second electrode and the mass content ratio L2 of the second electrode active material in the active material layer of the second electrode;

[0141] S44, obtaining the reversible gram capacity G2 of the second electrode active material;

[0142] S45, calculating the capacity ratio Z of the first electrode to the second electrode based on the parameters P1, L1, G1, P2, L2, G2, and an eighth preset formula, the eighth preset formula is shown in formula (VIII):

[0143]

[0144] In formula (VIII), the surface density P1 of the first electrode, the surface density P2 of the second electrode, the mass content ratio L1 of the first electrode active material in the active material layer of the first electrode (i.e., the loading of the first electrode active material in the first electrode), and the mass content ratio L2 of the second electrode active material in the active material layer of the second electrode (i.e., the loading of the second electrode active material in the second electrode) are artificially designed parameters when the target lithium-ion battery is designed. The above parameters may vary for different target lithium-ion batteries, and the reversible gram capacity G1 of the first electrode active material and the reversible gram capacity G2 of the second electrode active material can be obtained by looking up a table or by measuring the charge, so that Z is a value that can be obtained in advance.

[0145] In some embodiments, the step of obtaining the reversible gram capacity G1 of the first electrode active material, i.e., step S42, includes:

[0146] S421, providing a fourth half-cell, wherein the fourth half-cell includes a fourth test electrode, and the fourth test electrode includes a first electrode active material with a mass M4;

[0147] S422, performing a charge and discharge cycle test on the fourth half battery to obtain an average discharge capacity Q41 of the fourth half battery during the N1th cycle period to the Nnth cycle period, wherein N1 and Nn are both natural numbers greater than or equal to 2, and Nn is greater than or equal to N1;

[0148] S423, based on the parameters M4, Q41, and the ninth preset formula, the reversible gram capacity G1 of the first electrode active material is calculated. The ninth preset formula is shown in formula (IX):

[0149]

[0150] Usually, the polarity of the fourth test electrode is the same as that of the first electrode, and the fourth test electrode does not contain a lithium supplement.

[0151] The gram capacity of the first electrode active material measured by the above method is the reversible gram capacity G1, which can more accurately reflect the reversible energy storage performance of the first electrode active material. The method is simple and reliable, and the measured results can continue to be applicable to the design of other lithium-ion batteries using the first electrode active material, further improving the development efficiency of lithium-ion batteries.

[0152] It can be understood that the fourth test electrode is an electrode of a fourth half-cell used in the test process, and usually the fourth half-cell is also a half-cell. The first electrode and the fourth test electrode have the same polarity and both contain the same electrode active material, but the composition of the active material layer of the first electrode and the active material layer of the fourth test electrode are different. For example, the active material layer of the first electrode contains a lithium supplement, while the active material layer of the fourth test electrode does not contain a lithium supplement.

[0153] In addition, the fourth half-battery is subjected to a charge and discharge cycle test, that is, the fourth half-battery is repeatedly subjected to multiple charge and discharge tests. Multiple times here means at least twice. When calculating the gram capacity data of the first electrode active material, the discharge capacity data of the fourth half-battery in the first charge and discharge process is usually not used, but the discharge capacity data of the fourth half-battery in other charge and discharge processes after the first charge and discharge process is used. The gram capacity data of the first electrode active material obtained at this time is the reversible gram capacity data. Usually, the reversible gram capacity of the electrode active material is less than the first discharge gram capacity or the first charge gram capacity of the electrode active material, because the growth of the SEI film, etc. during the first charge and discharge process is likely to lead to the consumption of active lithium, thereby causing the reversible gram capacity of the electrode active material to decrease in the subsequent charge and discharge process.

[0154] When calculating the reversible gram capacity G1 of the first electrode active material, the discharge capacity in one of the charge and discharge processes or the average discharge capacity of multiple charge and discharge processes can be used. In other words, the average discharge capacity Q41 of the fourth half-battery during the N1th cycle to the Nnth cycle is used to calculate the reversible gram capacity G1. Here N1 and Nn are both natural numbers greater than or equal to 2, and Nn is greater than or equal to N1. As an example, N1=Nn=2, that is, the discharge capacity of the second cycle (that is, the second charge and discharge process) is obtained and divided by 1 to obtain the average discharge capacity Q41. As an example, N1=3, Nn=7, that is, the total discharge capacity from the 3rd cycle to the 7th cycle is obtained and divided by 5 to obtain the average discharge capacity Q41.

[0155] As an example, the first electrode is a positive electrode, the fourth test electrode is also a positive electrode, the first electrode active material is a positive electrode active material, and the measurement process of the reversible gram capacity G1 of the first electrode active material includes:

[0156] S421. Weigh the positive electrode active material with a mass of M4, mix the positive electrode active material with a conductive agent (such as carbon black, carbon nanotubes, etc.) and an adhesive (such as polyvinylidene fluoride) in proportion, add a solvent (such as N-methylpyrrolidone) and stir evenly to form an electrode slurry, apply the electrode slurry on a positive electrode collector (such as aluminum foil), and prepare a positive electrode sheet (i.e., the fourth test electrode) by drying, rolling, cutting and other processes. After the electrode slurry is dried, it forms an active material layer. The prepared positive electrode sheet, negative electrode sheet (usually a lithium sheet) and diaphragm are assembled into a button cell (i.e., the fourth half cell), and then an appropriate amount of electrolyte is injected. In this step, a dry and dust-free environment is maintained during the battery assembly process to prevent moisture and impurities from affecting the test results.

[0157] S422, set the test parameters, mainly including the voltage range and rate parameters (such as 0.1C, 0.2C, 1C, etc.); under the set test parameters, perform a charge and discharge cycle test on the button battery, record the voltage, current and time of the charge and discharge cycle process, generally starting from the second or third cycle, so as to obtain the average discharge capacity Q41. In this step, a battery testing system, such as an electrochemical workstation or a battery tester, can be used to summarize the test process to accurately control the charge and discharge parameters and record data. In addition, during the test process, the set test parameters are related to the type of positive electrode active material and can be set according to different positive electrode active materials. Exemplarily, if the positive electrode active material is lithium iron phosphate, the voltage range can be set to 2.0V~3.75V, which is the main interval for the reversible insertion and extraction of lithium ions in the charge and discharge process of lithium iron phosphate materials.

[0158] S423. Calculate the reversible gram capacity G1 of the first electrode active material according to formula (IX).

[0159] In some embodiments, the step of obtaining the reversible gram capacity G2 of the second electrode active material, i.e., step S44, includes:

[0160] S441, providing a fifth half-cell, the fifth half-cell comprising a fifth test electrode, the fifth test electrode comprising a second electrode active material having a mass M5;

[0161] S442, performing a charge-discharge cycle test on the fifth half battery to obtain an average discharge capacity Q51 of the fifth half battery during the N2th cycle to the Nmth cycle, wherein N2 and Nm are both natural numbers greater than or equal to 2, and Nm is greater than or equal to N2;

[0162] S443, based on the parameters M5, Q51, and the tenth preset formula, calculate the reversible gram capacity G2 of the second electrode active material, the tenth preset formula is shown in formula (X):

[0163]

[0164] Usually, the polarity of the fifth test electrode is the same as that of the second electrode, and the fifth test electrode does not contain a lithium supplement.

[0165] The gram capacity of the second electrode active material measured by the above method is the reversible gram capacity G2, which can more accurately reflect the reversible energy storage performance of the second electrode active material. The method is simple and reliable, and the measured results can continue to be applicable to the design of other lithium-ion batteries using the second electrode active material, further improving the development efficiency of lithium-ion batteries.

[0166] It can be understood that the fifth test electrode is an electrode of a fifth half-cell used in the test process, and the fifth half-cell is usually also a half-cell. The second electrode and the fifth test electrode have the same polarity and both contain the same electrode active material, but the composition of the active material layer of the second electrode and the active material layer of the fifth test electrode may be the same or different.

[0167] In addition, the fifth half-battery is subjected to a charge-discharge cycle test, that is, the fifth half-battery is subjected to multiple charge-discharge tests repeatedly. Multiple times here means at least twice. When calculating the gram capacity data of the second electrode active material, the discharge capacity data of the fifth half-battery in the first charge-discharge process is usually not used, but the discharge capacity data of the fifth half-battery in other charge-discharge processes after the first charge-discharge process is used. The gram capacity data of the second electrode active material obtained at this time is reversible gram capacity data.

[0168] When calculating the reversible gram capacity G2 of the second electrode active material, the discharge capacity in one of the charge and discharge processes or the average discharge capacity of multiple charge and discharge processes can be used. In other words, the average discharge capacity Q51 of the fifth half-battery during the N2th cycle to the Nmth cycle is used to calculate the reversible gram capacity G2. Here, N2 and Nm are both natural numbers greater than or equal to 2, and Nm is greater than or equal to N2. As an example, N2=Nm=2, that is, the discharge capacity of the second cycle (that is, the second charge and discharge process) is obtained and divided by 1 to obtain the average discharge capacity Q51. As an example, N2=3, Nm=7, that is, the total discharge capacity from the 3rd cycle to the 7th cycle is obtained and divided by 5 to obtain the average discharge capacity Q51.

[0169] As an example, the second electrode is a negative electrode, the fifth test electrode is also a negative electrode, the second electrode active material is a negative electrode active material, and the measurement process of the reversible gram capacity G2 of the second electrode active material includes:

[0170] S441. Weigh the negative electrode active material with a mass of M5, mix the negative electrode active material with a conductive agent (such as carbon black, carbon nanotubes), and a binder (such as sodium carboxymethyl cellulose, styrene-butadiene rubber) in proportion, add a solvent (such as water) and stir evenly to form an electrode slurry; coat the electrode slurry on a negative electrode collector (such as copper foil), and prepare a negative electrode sheet (i.e., the fifth test electrode) through processes such as drying, rolling, and cutting. After the electrode slurry is dried, it forms an active material layer; assemble the prepared negative electrode sheet, positive electrode sheet (usually a lithium sheet) and separator together into a button cell (i.e., the fifth half cell); and then inject an appropriate amount of electrolyte.

[0171] S442, set the test parameters, mainly including the voltage range and rate parameters (such as 0.1C, 0.2C, 1C, etc.); under the set test parameters, perform a charge and discharge cycle test on the button battery, record the voltage, current and time of the charge and discharge cycle process, generally starting from the second or third cycle, so as to obtain the average discharge capacity Q51. In this step, a battery testing system, such as an electrochemical workstation or a battery tester, can be used to summarize the test process to accurately control the charge and discharge parameters and record the data. In addition, during the test, the set test parameters are related to the type of negative electrode active material and can be set according to different negative electrode active materials. Exemplarily, if the negative electrode active material is graphite, the voltage range can be set to 0.005V~2.0V, which covers the main potential range of graphite during the lithium ion insertion and extraction process.

[0172] S423. Calculate the reversible gram capacity G2 of the second electrode active material according to formula (X).

[0173] In some embodiments, the first test electrode is the same as the fourth test electrode, and the measurement process of the first discharge gram capacity A and the first charge gram capacity B of the first electrode active material and the measurement process of the reversible gram capacity G1 of the first electrode active material can be performed in the same experiment, reducing the workload.

[0174] In some embodiments, the third test electrode is the same as the fifth test electrode, and the measurement process of the first efficiency Y of the second electrode active material and the measurement process of the reversible gram capacity G2 of the second electrode active material can be performed in the same experiment, reducing the workload.

[0175] In a second aspect, an embodiment of the present application further provides a lithium-ion battery, comprising a first electrode and a second electrode, wherein the first electrode comprises a first electrode active material and a lithium supplement, and the mass ratio T of the lithium supplement to the sum of the first electrode active material and the lithium supplement is greater than or equal to X calculated according to the above-mentioned method for determining the amount of lithium supplement added to the lithium-ion battery.

[0176] It should be noted here that the mass ratio T is the actual mass ratio of the lithium supplement in the lithium-ion battery.

[0177] By generally setting the actual mass ratio T of the lithium supplement in the lithium ion battery to be greater than or equal to the optimal lithium supplement amount X, not only the energy density of the lithium ion battery can be improved, but also the cycle performance of the lithium ion battery can be improved.

[0178] The following is a description with reference to specific embodiments.

[0179] Example 1

[0180] Calculating the optimal lithium replenishment amount X when the target lithium-ion battery is an LFP / graphite system (the optimal lithium replenishment amount here refers to the lithium replenishment amount when the energy density of the system is maximized), specifically including the following steps:

[0181] S1, obtaining the first discharge gram capacity A and the first charge gram capacity B of the positive electrode active material LFP, the steps comprising:

[0182] S11. Battery preparation process:

[0183] The positive electrode active material LFP was weighed, and the positive electrode active material LFP was mixed with a conductive agent (carbon black) and a binder (polyvinylidene fluoride) in a mass ratio of (LFP: carbon black: PVDF = 8:1:1), and a solvent (N-methylpyrrolidone) was added and stirred to form an electrode slurry.

[0184] The electrode slurry is coated on the aluminum foil current collector and prepared into an electrode sheet through drying and rolling process; the electrode sheet is cut into appropriate size to fit the button battery shell.

[0185] The prepared positive electrode sheet, negative electrode sheet (specifically lithium sheet) and separator (specifically polyethylene separator, the same below) are assembled together into a button battery; the electrolyte is injected (the electrolyte is an electrolyte system composed of lithium hexafluorophosphate as electrolyte, ethylene carbonate, dimethyl carbonate and diethyl carbonate, the same below) to make the positive electrode sheet, negative electrode sheet and separator fully infiltrated by the electrolyte.

[0186] S12. Testing process:

[0187] Set the test parameters: the voltage range is 2.0V to 3.75V, and select an appropriate discharge rate (specifically 0.1C).

[0188] Charge and discharge test: Under the set parameters, the button battery is charged and discharged at a constant current, the voltage, current and time during the charge and discharge process are recorded, and the charge capacity and discharge capacity are obtained.

[0189] S13, calculation process:

[0190] Calculate the first discharge gram capacity A, where the first discharge gram capacity A (mAh / g) = discharge capacity (mAh) / mass of positive electrode active material (g), and the results are recorded in Table 1;

[0191] The first charge gram capacity B was calculated, wherein the first charge gram capacity B (mAh / g) = charge capacity (mAh) / mass of the positive electrode active material (g). The results are recorded in Table 1.

[0192] S2. Obtain lithium supplement Li 5 FeO 4 Capacity C in grams:

[0193] S21. Battery preparation process:

[0194] Weigh an appropriate amount of positive electrode lithium supplement Li 5 FeO 4 , and the conductive agent (carbon black) and the adhesive (polyvinylidene fluoride) are mixed in a mass ratio (Li 5 FeO 4 : carbon black: polyvinylidene fluoride = 8:1:1) are mixed, and a solvent (N-methylpyrrolidone) is added and stirred evenly to prepare an electrode slurry.

[0195] The electrode slurry is coated on the aluminum foil current collector and prepared into an electrode sheet through drying and rolling process; the electrode sheet is cut into appropriate size to fit the button battery shell.

[0196] The prepared positive electrode sheet, negative electrode sheet (specifically lithium sheet) and separator are assembled together into a button battery; the electrolyte is injected so that the positive electrode sheet, negative electrode sheet and separator are fully soaked by the electrolyte.

[0197] S22, Testing process:

[0198] Set test parameters: set the discharge start voltage (usually the highest discharge voltage of the positive electrode lithium supplement, such as 4.3V) and the cut-off voltage (usually the lowest discharge voltage of the lithium supplement, such as 2.0V), and select an appropriate charge and discharge rate (such as 0.1C).

[0199] Discharge test: Under the set parameters, the button battery is discharged at a constant current, the voltage, current and time of the discharge process are recorded, and the discharge capacity is obtained.

[0200] S23, calculation process:

[0201] The gram capacity C of the positive electrode lithium replenisher is calculated, wherein the gram capacity C of the positive electrode lithium replenisher = discharge capacity (mAh) / mass (g) of the positive electrode lithium replenisher. The results are recorded in Table 1.

[0202] S3, obtaining the first effect Y of the negative electrode active material graphite, the steps comprising:

[0203] S31, battery preparation process:

[0204] Weigh an appropriate amount of negative electrode active material graphite, mix the negative electrode active material graphite with a conductive agent (carbon black) and a binder (sodium carboxymethyl cellulose CMC and styrene-butadiene rubber SBR) in a mass ratio of (graphite: carbon black: CMC: SBR = 96:2:1:1), add a solvent (water) and stir evenly to prepare an electrode slurry.

[0205] The electrode slurry is coated on the copper foil current collector and prepared into an electrode sheet through drying and rolling process; the electrode sheet is cut into appropriate size to fit the button battery shell.

[0206] The prepared negative electrode sheet, positive electrode sheet (specifically a lithium sheet) and separator are assembled together into a button battery; the electrolyte is injected so that the positive electrode sheet, negative electrode sheet and separator are fully soaked by the electrolyte.

[0207] S32, test process:

[0208] Set the test parameters: set the voltage range to 0.005V~2.0V, and select an appropriate discharge rate (specifically 0.1C).

[0209] Charge and discharge test: Under the set parameters, the button battery is charged and discharged at a constant current, the voltage, current and time of the charge and discharge process are recorded, and the charge capacity and discharge capacity are obtained.

[0210] S33, calculation process:

[0211] Calculate the first discharge capacity in grams, where the first discharge capacity in grams (mAh / g) = discharge capacity (mAh) / mass of negative electrode active material (g);

[0212] Calculate the first charge gram capacity, where the first charge gram capacity (mAh / g) = charge capacity (mAh) / mass of positive electrode active material (g);

[0213] The first efficiency Y of the negative electrode active material was calculated, wherein the first efficiency Y of the negative electrode active material = first discharge gram capacity / first charge gram capacity, and the results are recorded in Table 1.

[0214] S4. Obtain Z of a target lithium-ion battery, wherein the target lithium-ion battery is a LFP / graphite system, that is, the positive electrode of the target lithium-ion battery comprises a positive electrode active material LFP, and the negative electrode comprises a negative electrode active material graphite.

[0215] S41, obtaining the surface density P1 of the positive electrode and the mass content L1 of the positive electrode active material LFP in the positive electrode film layer of the positive electrode.

[0216] S42, obtaining the reversible gram capacity of the positive electrode active material LFP, the steps comprising:

[0217] S421, battery preparation process:

[0218] The positive electrode active material LFP was weighed, and the positive electrode active material LFP was mixed with a conductive agent (carbon black) and a binder (polyvinylidene fluoride) in a mass ratio of (LFP: carbon black: PVDF = 8:1:1), and a solvent (N-methylpyrrolidone) was added and stirred to form an electrode slurry.

[0219] The electrode slurry is coated on the aluminum foil current collector, and an electrode sheet with uniform thickness is prepared through drying and rolling process; the electrode sheet is cut into appropriate size to fit the button battery shell.

[0220] The prepared positive electrode sheet, negative electrode sheet (specifically lithium sheet) and separator are assembled together into a button battery; the electrolyte is injected so that the positive electrode sheet, negative electrode sheet and separator are fully soaked by the electrolyte.

[0221] S422, Testing process:

[0222] Set the test parameters: the voltage range is 2.0V to 3.75V, and select an appropriate discharge rate (specifically 0.1C).

[0223] Charge and discharge cycle test: Under the set parameters, start the electrochemical workstation to perform charge and discharge cycle test, record the voltage, current and time of the charge and discharge cycle process, and obtain the average discharge capacity from the second cycle to the sixth cycle;

[0224] S423, calculation process:

[0225] The reversible gram capacity of the positive electrode active material is calculated, wherein the reversible gram capacity of the positive electrode active material (mAh / g) = average discharge capacity (mAh) / mass of the positive electrode active material (g).

[0226] S43, obtaining the surface density P2 of the negative electrode and the mass content L2 of the negative electrode active material graphite in the negative electrode film layer.

[0227] S44, obtaining the reversible gram capacity of the negative electrode active material graphite, the steps comprising:

[0228] S441, battery preparation process:

[0229] Weigh the negative electrode active material graphite, mix the negative electrode active material graphite with a conductive agent (carbon black) and a binder (sodium carboxymethyl cellulose CMC and styrene-butadiene rubber SBR) in a mass ratio of (graphite: carbon black: CMC: SBR = 96:2:1:1), add a solvent (water) and stir evenly to prepare an electrode slurry.

[0230] The electrode slurry is coated on the copper foil current collector and prepared into an electrode sheet through drying and rolling process; the electrode sheet is cut into appropriate size to fit the button battery shell.

[0231] The prepared negative electrode sheet, positive electrode sheet (specifically a lithium sheet) and separator are assembled together into a button battery; the electrolyte is injected so that the positive electrode sheet, negative electrode sheet and separator are fully soaked by the electrolyte.

[0232] S442, Testing process:

[0233] Set the test parameters: set the voltage range to 0.005V~2.0V, and select an appropriate discharge rate (specifically 0.1C).

[0234] Charge and discharge cycle test: Under the set parameters, start the electrochemical workstation to perform charge and discharge cycle test, record the voltage, current and time of the charge and discharge cycle process, and obtain the average discharge capacity from the second cycle to the sixth cycle;

[0235] S443, calculation process:

[0236] The reversible gram capacity of the negative electrode active material is calculated, wherein the reversible gram capacity of the negative electrode active material (mAh / g) = average discharge capacity (mAh) / mass of the negative electrode active material (g).

[0237] S45. Calculate the capacity ratio Z (i.e., N / P ratio) of the positive electrode to the negative electrode in the target lithium-ion battery using the formula:

[0238]

[0239] The calculation results are recorded in Table 1.

[0240] S5. Calculate the optimal lithium replenishment amount X of the target lithium-ion battery. The formula is:

[0241]

[0242] The calculation results are recorded in Table 1.

[0243] Example 2

[0244] Calculating the optimal lithium supplement amount X when the target lithium-ion battery is a LFP / Si-C (Si content in Si-C is 5wt%, C content is 95wt%) system, specifically includes the following steps:

[0245] S1 is the same as S1 in Example 1 and will not be described in detail here.

[0246] S2. Obtain lithium supplement Li 2 NiO 2 Capacity C in grams:

[0247] S21. Battery preparation process:

[0248] Weigh an appropriate amount of positive electrode lithium supplement Li 2 NiO2 , and the conductive agent (carbon black) and the adhesive (polyvinylidene fluoride) are mixed in a mass ratio (Li 2 NiO 2 : carbon black: polyvinylidene fluoride = 8:1:1) are mixed, and a solvent (N-methylpyrrolidone) is added and stirred evenly to prepare an electrode slurry.

[0249] The electrode slurry is coated on the aluminum foil current collector and prepared into an electrode sheet through drying and rolling process; the electrode sheet is cut into appropriate size to fit the button battery shell.

[0250] The prepared positive electrode sheet, negative electrode sheet (specifically lithium sheet) and separator are assembled together into a button battery; the electrolyte is injected so that the positive electrode sheet, negative electrode sheet and separator are fully soaked by the electrolyte.

[0251] S22, Testing process:

[0252] Set test parameters: Set the discharge start voltage (usually the positive electrode lithium supplement Li 2 NiO 2 The maximum discharge voltage is 4.5V) and the cut-off voltage (usually the positive electrode lithium supplement Li 2 NiO 2 The minimum discharge voltage is 2.0V), select an appropriate charge and discharge rate (such as 0.1C).

[0253] Discharge test: Under the set parameters, the button battery is discharged at a constant current, the voltage, current and time of the discharge process are recorded, and the discharge capacity is obtained.

[0254] S23, calculation process:

[0255] The gram capacity C of the positive electrode lithium replenisher is calculated, wherein the gram capacity C of the positive electrode lithium replenisher = discharge capacity (mAh) / mass (g) of the positive electrode lithium replenisher. The results are recorded in Table 1.

[0256] S3, obtaining the first effect Y of the negative electrode active material Si-C, the steps comprising:

[0257] S31, battery preparation process:

[0258] Weigh an appropriate amount of negative electrode active material Si-C, mix the negative electrode active material Si-C with a conductive agent (carbon black) and a binder (sodium carboxymethyl cellulose CMC and styrene-butadiene rubber SBR) in a mass ratio of (Si-C: carbon black: CMC: SBR = 96:2:1:1), add a solvent (water) and stir evenly to form an electrode slurry.

[0259] The electrode slurry is coated on the copper foil current collector and prepared into an electrode sheet through drying and rolling process; the electrode sheet is cut into appropriate size to fit the button battery shell.

[0260] The prepared negative electrode sheet, positive electrode sheet (specifically a lithium sheet) and separator are assembled together into a button battery; the electrolyte is injected so that the positive electrode sheet, negative electrode sheet and separator are fully soaked by the electrolyte.

[0261] S32, test process:

[0262] Set the test parameters: set the voltage range to 2.0V~4.5V, and select an appropriate discharge rate (specifically 0.1C).

[0263] Charge and discharge test: Under the set parameters, the button battery is charged and discharged at a constant current, the voltage, current and time of the charge and discharge process are recorded, and the charge capacity and discharge capacity are obtained.

[0264] S33, calculation process:

[0265] Calculate the first discharge capacity in grams, where the first discharge capacity in grams (mAh / g) = discharge capacity (mAh) / mass of negative electrode active material (g);

[0266] Calculate the first charge gram capacity, where the first charge gram capacity (mAh / g) = charge capacity (mAh) / mass of positive electrode active material (g);

[0267] The first efficiency Y of the negative electrode active material Si-C was calculated, wherein the first efficiency Y of the negative electrode active material = first discharge gram capacity / first charge gram capacity, and the results are recorded in Table 1.

[0268] S4. Obtain Z of a target lithium-ion battery, wherein the target lithium-ion battery is of LFP / Si-C system, that is, the positive electrode of the target lithium-ion battery comprises positive electrode active material LFP, and the negative electrode comprises negative electrode active material Si-C.

[0269] S41, obtaining the surface density P1 of the positive electrode and the mass content L1 of the positive electrode active material LFP in the positive electrode film layer of the positive electrode.

[0270] S42 is the same as S42 in Example 1 and will not be described in detail here.

[0271] S43, obtaining the surface density P2 of the negative electrode and the mass content L2 of the negative electrode active material Si-C in the negative electrode film layer.

[0272] S44, obtaining the reversible gram capacity of the negative electrode active material Si-C, the steps comprising:

[0273] S441, battery preparation process:

[0274] Weigh the negative electrode active material Si-C, mix the negative electrode active material Si-C with a conductive agent (carbon black) and a binder (sodium carboxymethyl cellulose CMC and styrene-butadiene rubber SBR) in a mass ratio of (Si-C: carbon black: CMC: SBR = 96:2:1:1), add a solvent (water) and stir evenly to form an electrode slurry.

[0275] The electrode slurry is coated on the copper foil current collector and prepared into an electrode sheet through drying and rolling process; the electrode sheet is cut into appropriate size to fit the button battery shell.

[0276] The prepared negative electrode sheet, positive electrode sheet (specifically a lithium sheet) and separator are assembled together into a button battery; the electrolyte is injected so that the positive electrode sheet, negative electrode sheet and separator are fully soaked by the electrolyte.

[0277] S442, Testing process:

[0278] Set the test parameters: set the voltage range to 2.0V~4.5V, and select an appropriate discharge rate (specifically 0.1C).

[0279] Charge and discharge cycle test: Under the set parameters, start the electrochemical workstation to perform charge and discharge cycle test, record the voltage, current and time of the charge and discharge cycle process, and obtain the average discharge capacity from the second cycle to the sixth cycle;

[0280] S443, calculation process:

[0281] The reversible gram capacity of the negative electrode active material is calculated, wherein the reversible gram capacity of the negative electrode active material (mAh / g) = average discharge capacity (mAh) / mass of the negative electrode active material (g).

[0282] S45. Calculate the capacity ratio Z (i.e., N / P ratio) of the positive electrode to the negative electrode in the target lithium-ion battery using the formula:

[0283]

[0284] The calculation results are recorded in Table 1.

[0285] S5. Calculate the optimal lithium replenishment amount X of the target lithium-ion battery. The formula is:

[0286]

[0287] The calculation results are recorded in Table 1.

[0288] Table 1

[0289]

[0290] In order to verify the accuracy of the calculated optimal lithium supplement amount X, a full battery is prepared to measure actual data. Specifically, the corresponding lithium-ion battery is prepared according to the features set in each embodiment when designing the target lithium-ion battery, that is, the type and loading of the active material and the type of lithium supplement agent, as well as the surface density of the positive and negative electrodes are kept consistent with the target lithium-ion battery design. Specifically, the positive and negative electrode slurry is stirred-coated-cold pressed-sheeted and assembled into a small soft-pack battery of about 2Ah, and the formation and capacity division (charging and discharging) are carried out on the lithium battery formation equipment, and the capacity data during the formation and capacity division process and the weight of the positive and negative electrode powder in the electrode sheet are collected.

[0291] Since A, B, and Y are inherent properties of the material and the parameters are fixed, the gram capacity C' of the lithium supplement agent in the full battery can be obtained based on the measured capacity data of the soft-pack battery (full battery) during the formation and capacity division process. Substituting C' into formula (I) to calculate the corrected value X' of the optimal lithium supplement amount X, the results are recorded in Table 1. From the comparison of the optimal lithium supplement amount X and its corrected value X' in Table 1, it can be seen that the difference between the two is small, which shows that the accuracy of the optimal lithium supplement amount X calculated by the above-mentioned method for determining the amount of lithium supplement agent added for lithium-ion batteries is relatively high.

[0292] The embodiments of the present application are introduced in detail above. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A method for determining the amount of lithium supplement added to a lithium ion battery, characterized in that: include: Obtaining the first discharge gram capacity A and the first charge gram capacity B of the first electrode active material; Obtain the gram capacity C of the lithium supplement; Obtaining the first effect Y of the second electrode active material; Obtaining a capacity ratio Z of a first electrode to a second electrode in a target lithium-ion battery, wherein the first electrode and the second electrode have opposite polarities, the first electrode includes the first electrode active material and the lithium supplement, and the second electrode includes the second electrode active material; The optimal lithium supplement amount X of the lithium supplement agent in the first electrode is calculated based on the parameters A, B, C, Y and Z and a first preset formula, wherein the first preset formula is shown in formula (I): Herein, X represents the mass ratio of the lithium supplement agent to the sum of the first electrode active material and the lithium supplement agent.

2. The method for determining the amount of lithium supplement for lithium ion batteries according to claim 1, characterized in that: The step of obtaining the first discharge gram capacity A and the first charge gram capacity B of the first electrode active material comprises: Providing a first half-cell, the first half-cell comprising a first test electrode; the first test electrode comprising the first electrode active material having a mass M1; Performing a charge and discharge test on the first half-cell to obtain a discharge capacity Q11 and a charge capacity Q12 of the first half-cell; Based on the parameters M1, Q11 and Q12, and the second preset formula and the third preset formula, respectively calculate the first discharge gram capacity A and the first charge gram capacity B of the first electrode active material; Wherein, the second preset formula is shown in formula (II), and the third preset formula is shown in formula (III):

3. The method for determining the amount of lithium supplement for lithium ion batteries according to claim 1, characterized in that: The step of obtaining the gram capacity C of the lithium supplement comprises: Providing a second half-cell, the second half-cell comprising a second test electrode; the second test electrode comprising the lithium supplement having a mass M2; Performing a discharge test on the second half-cell to obtain a discharge capacity Q21 of the second half-cell; The gram capacity C of the lithium supplement is calculated based on the parameters M2, Q21, and a fourth preset formula, wherein the fourth preset formula is as shown in formula (IV):

4. The method for determining the amount of lithium supplement for lithium ion batteries according to claim 1, characterized in that: The obtaining of the first effect Y of the second electrode active material comprises: providing a third half-cell, the third half-cell comprising a third test electrode, the third test electrode comprising a mass M3 of the second electrode active material; Performing a charge and discharge test on the third half-battery to obtain a discharge capacity Q31 and a charge capacity Q32 of the third half-battery; Based on the parameters M3, Q31 and Q32, and the fifth preset formula and the sixth preset formula, the first discharge gram capacity D and the first charge gram capacity E of the second electrode active material are calculated respectively, wherein the fifth preset formula is shown in formula (V), and the sixth preset formula is shown in formula (VI): The first effect Y of the second electrode active material is calculated based on the parameters D, E and the seventh preset formula, wherein the seventh preset formula is shown in formula (VII):

5. The method for determining the amount of lithium supplement for lithium ion batteries according to claim 1, characterized in that: The step of obtaining the capacity ratio Z of the first electrode to the second electrode in the target lithium-ion battery comprises: Obtaining the surface density P1 of the first electrode and the mass content ratio L1 of the first electrode active material in the active material layer of the first electrode; Obtaining the reversible gram capacity G1 of the first electrode active material; Obtaining the surface density P2 of the second electrode and the mass content ratio L2 of the second electrode active material in the active material layer of the second electrode; Obtaining the reversible gram capacity G2 of the second electrode active material; The capacity ratio Z of the first electrode to the second electrode is calculated based on the parameters P1, L1, G1, P2, L2, G2, and an eighth preset formula, wherein the eighth preset formula is shown in formula (VIII):

6. The method for determining the amount of lithium supplement for lithium ion batteries according to claim 5, characterized in that: The obtaining of the reversible gram capacity G1 of the first electrode active material comprises: Providing a fourth half-cell, the fourth half-cell comprising a fourth test electrode; the fourth test electrode comprising a mass M4 of the first electrode active material; Performing a charge and discharge cycle test on the fourth half battery to obtain an average discharge capacity Q41 of the fourth half battery during an N1-th cycle period to an Nn-th cycle period, wherein N1 and Nn are both natural numbers greater than or equal to 2, and Nn is greater than or equal to N1; The reversible gram capacity G1 of the first electrode active material is calculated based on the parameters M4, Q41, and the ninth preset formula, which is shown in formula (IX):

7. The method for determining the amount of lithium supplement for lithium ion batteries according to claim 5, characterized in that: The obtaining of the reversible gram capacity G2 of the second electrode active material comprises: providing a fifth half-cell, the fifth half-cell comprising a fifth test electrode; the fifth test electrode comprising a mass M5 of the second electrode active material; Performing a charge-discharge cycle test on the fifth half-battery to obtain an average discharge capacity Q51 of the fifth half-battery during an N2-th cycle to an Nm-th cycle, wherein N2 and Nm are both natural numbers greater than or equal to 2, and Nm is greater than or equal to N2; The reversible gram capacity G2 of the second electrode active material is calculated based on the parameters M5, Q51, and the tenth preset formula, which is shown in formula (X):

8. The method for determining the amount of lithium supplement for lithium ion batteries according to any one of claims 1 to 7, characterized in that: The first electrode is a positive electrode, and the first electrode active material is a positive electrode active material; the second electrode is a negative electrode, and the second electrode active material is a negative electrode active material.

9. The method for determining the amount of lithium supplement for lithium ion batteries according to claim 8, characterized in that: The lithium replenisher is a positive electrode lithium replenisher, and the positive electrode lithium replenisher includes at least one of Li2O, Li2NiO2, Li5FeO4, Li6CoO4, Li2O2, Li3N and Li2S; and / or, The positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide; and / or, The negative electrode active material includes at least one of graphite and silicon carbon.

10. A lithium ion battery, characterized in that: The invention comprises a first electrode and a second electrode, wherein the first electrode comprises a first electrode active material and a lithium supplement, and a mass ratio T of the lithium supplement to the total of the first electrode active material and the lithium supplement is greater than or equal to an optimal lithium supplement amount X calculated according to the method for determining the amount of lithium supplement added for a lithium ion battery according to any one of claims 1 to 9.

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