Method for evaluating effective replenishment level of active ions in secondary ion battery

Abstract

A method for evaluating the effective replenishment level of active ions in a secondary ion battery, the secondary ion battery being a first battery, and a corresponding secondary ion battery without replenished active ions being a second battery, and the method comprising: obtaining a discharge capacity C2 of the first battery within a nominal voltage range; charging the first battery and the second battery to respective preset voltages U, such that anode potentials of the first and second batteries are equal at the preset voltages U, and calculating a charging capacity difference C1 between the first battery and the second battery at the time; and calculating the sum C3 of the charging capacity difference C1 and the discharge capacity C2, where C3 is used to represent the total effective capacity of active ions in the first battery.

Description

A method for evaluating the effective replenishment level of active ions in secondary ion batteries

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410142206.1, filed on February 1, 2024, entitled “A method for evaluating the effective replenishment level of active ions in a secondary ion battery,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a method for evaluating the effective replenishment level of active ions in a secondary ion battery. Background Art

[0004] In secondary ion batteries, during the first lithium insertion process of the anode active material, the electrolyte undergoes a reduction reaction on the particle surface to form a solid electrolyte interface film (SEI), thereby consuming the cathode active ions (such as active lithium or active sodium), affecting the specific capacity of the cathode active material and reducing the energy density of the battery.

[0005] Pre-lithiation or pre-sodiumization technologies are used to supplement the electrode materials with lithium or sodium. The active lithium or sodium released during charging compensates for the initial irreversible lithium or sodium loss, forming the SEI film on the anode surface to improve the reversible cycle capacity and cycle life of the secondary ion battery. The lithium or sodium supplementation technology can be used to optimize the performance of the secondary ion battery's anode, cathode, separator, electrolyte, and current collector.

[0006] Although lithium or sodium supplementation can improve battery energy density and cycle performance, the amount of lithium or sodium supplementation is not necessarily better. Excessive or insufficient amounts will affect battery performance. Therefore, accurately evaluating the effective amount and efficiency of active ion supplementation is crucial for pre-lithiation or pre-sodiumization technologies.

[0007] Summary of the Invention

[0008] The present application provides a method for evaluating the effective replenishment level of active ions in a secondary ion battery, so as to more accurately evaluate the effective replenishment effect of the active ions.

[0009] The present application provides a method for evaluating the effective replenishment level of active ions in a secondary ion battery, wherein the secondary ion battery is a first battery, and the corresponding secondary ion battery that has not been replenished with active ions is a second battery. The evaluation method includes: obtaining the discharge capacity C2 of the first battery during discharge in a nominal voltage range; charging the first battery and the second battery to their respective preset voltages U, and at the preset voltage U, the anode potential of the first battery and the anode potential of the second battery are equal, and calculating the charge capacity difference C1 between the first battery and the second battery at this time; calculating the sum C3 of the charge capacity difference C1 and the discharge capacity C2, C3 being used to characterize the total effective capacity of the active ions of the first battery.

[0010] In any embodiment, the evaluation method includes: obtaining a curve, including: obtaining a first curve and a second curve of the charging process or the discharging process of the first battery and the second battery in the nominal voltage range and the discharge capacity C2 of the first battery, the first curve and the second curve are both full charging process curves or full discharging process curves, the first curve is the anode potential-battery voltage curve of the first battery, and the second curve is the anode potential-battery voltage curve of the second battery; obtaining a voltage interval U1, including: determining the battery voltage interval U1 of the first battery corresponding to the portion of the first curve and the second curve with the same curve shape in the same anode potential range 1-1 and the battery voltage interval U of the second battery 2-1 Obtaining the capacity difference C1, including: obtaining the charging capacity of the first battery and the second battery when the first battery and the second battery are respectively charged to their respective preset voltages U, wherein the preset voltage U of the first battery is U 1-1 The preset voltage U of the second battery is U 2-1 , calculating the charge capacity difference C1 between the first battery and the second battery at this time; obtaining the total effective capacity of active ions, including: calculating the sum C3 of the charge capacity difference C1 and the discharge capacity C2.

[0011] In any embodiment, the process of obtaining the capacity difference C1 includes: discharging the first battery and the second battery and then charging them to their respective preset voltages U, and calculating the charge capacity difference C1 between the first battery and the second battery at this time, wherein the first battery is discharged to the nominal lower limit voltage, and the second battery is discharged to an anode potential of 1V-2.5V or discharged until the anode potential reaches the SEI film decomposition potential.

[0012] In any embodiment, the discharge rate is selected from any rate between 0.02C and 0.1C.

[0013] In any embodiment, the batteries are charged to a preset voltage U at any rate between 0.02C and 0.1C.

[0014] In any embodiment, the preset voltage U of the first battery is the median voltage value of U1-1, and the preset voltage U of the second battery is U 2-1 The median voltage value.

[0015] In any embodiment, the process of determining U1-1 and U2-1 includes: translating the voltage value t1 of the first curve and / or translating the voltage value t2 of the second curve along the coordinate line where the battery voltage is located, so that the first curve and the second curve overlap in the battery voltage interval U', when the translation is in the direction of lower battery voltage, t1 and t2 are negative values, when the translation is in the direction of higher battery voltage, t1 and t2 are positive values, optionally, t1 and t2 meet any one or more of the following conditions: 0V≤|t1|��≤2.0V, 0V≤|t2|��≤2.0V, 0V≤|t1|��+|t2|��≤2.0V; calculating U according to the following formula 1-1 and U 2-1 , U 1-1 =U'-t1,U 2-1 =U'-t2.

[0016] In any embodiment, the process of obtaining the curve also includes the process of obtaining a third curve and a fourth curve of the charging process or the discharging process in the nominal voltage interval, the third curve and the fourth curve are both full charging process curves or full discharging process curves, the third curve is the SOC-battery voltage curve of the first battery, and the fourth curve is the SOC-battery voltage curve of the second battery; the evaluation method also includes determining the first battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the third curve 1-2 , determine the second battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the fourth curve 2-2 ; Determine U 1-1 and U 1-2 Overlapping voltage interval U1; determine U 2-1 and U 2-2 Overlapping voltage interval U2; in the process of obtaining the charging capacity difference C1, the preset voltage U of the first battery is any value in U1, and the preset voltage U of the second battery is any value in U2.

[0017] In any embodiment, the preset voltage U of the first battery is the median voltage value of U1 , and the preset voltage U of the second battery is the median voltage value of U2 .

[0018] In any embodiment, the curve acquisition process includes: performing a charging process or a discharging process on the first battery and the second battery at the same rate in a nominal voltage range, respectively, to acquire the first curve and the second curve.

[0019] In any embodiment, the rate of the charging process or the discharging process is selected from any rate between 0.02C and 0.1C.

[0020] In any embodiment, the evaluation method further includes the step of recording the discharge capacity C4 of the second battery, and the evaluation method further includes the process of calculating the active ion replenishment efficiency, the active ion replenishment efficiency A=(C3-C4) / C5, wherein C5 is the theoretical active ion replenishment capacity.

[0021] In any embodiment, the reference electrode is a conductive wire having an active material layer on its surface, the diameter of the conductive wire is 50 μm-100 μm, and the thickness of the active material layer is 10 μm-50 μm.

[0022] In any embodiment, the reference electrode is a copper wire, a copper wire with a lithium-plated layer on its surface, a copper wire with a sodium-plated layer on its surface, a copper wire coated with a lithium iron phosphate layer on its surface, a copper wire coated with a lithium titanate layer on its surface, or a copper wire coated with a sodium vanadium phosphate layer on its surface.

[0023] In any embodiment, when the reference electrode is a copper wire, before evaluation, the positive electrode of the first battery is used as the positive electrode, the copper wire is used as the negative electrode, and the constant current of 10 μA is charged for 1 hour to electroplate the copper wire of the first battery, and the positive electrode of the second battery is used as the positive electrode, the copper wire is used as the negative electrode, and the constant current of 10 μA is charged for 1 hour to electroplate the copper wire of the second battery.

[0024] In any embodiment, when the reference electrode is a copper wire coated with a lithium iron phosphate layer, a copper wire coated with a lithium titanate layer, or a copper wire coated with a sodium vanadium phosphate layer, the evaluation method also includes a process of first activating the reference electrode, and the process of activating the reference electrode includes: charging the first battery and the second battery to a battery voltage corresponding to 50±5% SOC, respectively.

[0025] In any embodiment, the first battery and the second battery are full batteries, and the secondary ion battery is a lithium ion secondary battery or a sodium ion secondary battery.

[0026] In any embodiment, the evaluation method comprises:

[0027] The first battery and the second battery are provided with a reference electrode, and the reference electrode is used to monitor the anode potential of the first battery and the second battery during the charge and discharge process. The first battery and the second battery are both full batteries, and the reference electrode is a copper wire, a copper wire plated with lithium, a copper wire plated with sodium, a copper wire coated with lithium iron phosphate, a copper wire coated with lithium titanate, or a copper wire coated with sodium vanadium phosphate. The diameter of the copper wire is 50 μm-100 μm, and the thickness of the active material layer on the copper wire is 10 μm-50 μm. When the reference electrode is a copper wire, during the evaluation Before the evaluation, the positive electrode of the first battery is used as the positive electrode, the copper wire is used as the negative electrode, and the constant current is 10 μA for charging for 1 hour to electroplate the copper wire of the first battery. The positive electrode of the second battery is used as the positive electrode, the copper wire is used as the negative electrode, and the constant current is 10 μA for charging for 1 hour to electroplate the copper wire of the second battery. When the reference electrode is a copper wire coated with lithium iron phosphate, a copper wire coated with lithium titanate, or a copper wire coated with sodium vanadium phosphate, the first battery and the second battery are respectively charged to a battery voltage corresponding to 50±5% SOC to activate the reference electrode.

[0028] Charging the first battery and the second battery in a nominal voltage range at any rate between 0.02C and 0.1C, obtaining an anode potential-battery voltage curve and an SOC-battery voltage curve of the first battery, as well as an anode potential-battery voltage curve and an SOC-battery voltage curve of the second battery, defining the anode potential-battery voltage curve of the first battery as a first curve, defining the anode potential-battery voltage curve of the second battery as a second curve, defining the SOC-battery voltage curve of the first battery as a third curve, and defining the SOC-battery voltage curve of the second battery as a fourth curve;

[0029] Determine the battery voltage interval U of the first battery corresponding to the portion of the first curve and the second curve with the same curve shape in the same anode potential interval 1-1 and the battery voltage interval U of the second battery 2- 1, where U is determined 1-1 and U 2-1 The process includes: translating the voltage value t1 of the first curve and / or the voltage value t2 of the second curve along the coordinate line where the battery voltage is located, so that the first curve and the second curve overlap in the battery voltage interval U', when the translation is in the direction of lower battery voltage, t1 and t2 are negative values, when the translation is in the direction of higher battery voltage, t1 and t2 are positive values, and optionally t1 and t2 meet any one or more of the following conditions: 0V≤|t1|≤2.0V, 0V≤|t2|≤2.0V, 0V≤|t1|+|t2|≤2.0V; calculating U according to the following formula 1-1 and U 2-1 , U 1-1 =U'-t1,U 2-1 =U'-t2;

[0030] Determine the first battery voltage interval U corresponding to the curve segment whose slope does not exceed 400% SOC / battery voltage in the third curve 1-2 , determine the second battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the fourth curve 2-2 ;

[0031] Determine a voltage interval U1 where U1-1 and U1-2 overlap, and determine a voltage interval U2 where U2-1 and U2-2 overlap;

[0032] Discharging the first battery and the second battery at a discharge rate selected from any rate between 0.02C and 0.1C, wherein the first battery is discharged to a nominal lower limit voltage, and the second battery is discharged to an anode potential of 1V to 2.5V or to a decomposition potential of the SEI film, and recording the discharge capacity C2 of the first battery and the discharge capacity C4 of the second battery; obtaining the charge capacities of the first battery and the second battery when the first battery and the second battery are respectively charged to a preset voltage U at any rate between 0.02C and 0.1C, wherein the preset voltage U of the first battery is a median voltage value of U1, and the preset voltage U of the second battery is a median voltage value of U2, and calculating the charge capacity difference C1 between the first battery and the second battery at this time;

[0033] The total effective capacity C3 of active ions of the first battery is calculated using formula (I): formula (I) C3 = C1 + C2;

[0034] The active ion replenishment efficiency is calculated using formula (II): A = (C3-C4) / C5, where C5 is the theoretical active ion replenishment capacity, C5 = m×k, m is the mass of the additional active ion material provided, and k is the gram capacity. When the additional active ion material provided is lithium metal, k = 3.86 Ah / g; when the additional active ion material provided is sodium metal, k = 1.165 Ah / g.

[0035] In any embodiment, the evaluation method comprises:

[0036] The first battery and the second battery are provided with a reference electrode, and the reference electrode is used to monitor the anode potential of the first battery and the second battery during the charge and discharge process. The first battery and the second battery are both full batteries, and the reference electrode is a copper wire, a copper wire plated with lithium, a copper wire plated with sodium, a copper wire coated with lithium iron phosphate, a copper wire coated with lithium titanate, or a copper wire coated with sodium vanadium phosphate. The diameter of the copper wire is 50 μm-100 μm, and the thickness of the active material layer on the copper wire is 10 μm-50 μm. When the reference electrode is a copper wire, during the evaluation Before the evaluation, the positive electrode of the first battery is used as the positive electrode, the copper wire is used as the negative electrode, and the constant current is 10 μA for charging for 1 hour to electroplate the copper wire of the first battery. The positive electrode of the second battery is used as the positive electrode, the copper wire is used as the negative electrode, and the constant current is 10 μA for charging for 1 hour to electroplate the copper wire of the second battery. When the reference electrode is a copper wire coated with lithium iron phosphate, a copper wire coated with lithium titanate, or a copper wire coated with sodium vanadium phosphate, the first battery and the second battery are respectively charged to a battery voltage corresponding to 50±5% SOC to activate the reference electrode.

[0037] The first battery and the second battery are charged and discharged in a nominal voltage range at any rate between 0.02C and 0.1C, and an anode potential-battery voltage curve and an SOC-battery voltage curve of the first battery, as well as an anode potential-battery voltage curve and an SOC-battery voltage curve of the second battery are obtained during the discharge process. The discharge capacity C4 of the second battery is recorded, and the anode potential-battery voltage curve of the first battery is defined as a first curve, the anode potential-battery voltage curve of the second battery is defined as a second curve, the SOC-battery voltage curve of the first battery is defined as a third curve, and the SOC-battery voltage curve of the second battery is defined as a fourth curve.

[0038] Determine the battery voltage interval U of the first battery corresponding to the portion of the first curve and the second curve with the same curve shape in the same anode potential interval 1-1 and the battery voltage interval U of the second battery 2- 1, where U is determined 1-1 and U 2-1 The process includes: translating the voltage value t1 of the first curve and / or the voltage value t2 of the second curve along the coordinate line where the battery voltage is located, so that the first curve and the second curve overlap in the battery voltage interval U', when the translation is in the direction of lower battery voltage, t1 and t2 are negative values, when the translation is in the direction of higher battery voltage, t1 and t2 are positive values, and optionally t1 and t2 meet any one or more of the following conditions: 0V≤|t1|≤2.0V, 0V≤|t2|≤2.0V, 0V≤|t1|+|t2|≤2.0V; calculating U according to the following formula 1-1 and U 2-1 , U 1-1 =U'-t1,U 2-1 =U'-t2;

[0039] Determine the first battery voltage interval U corresponding to the curve segment whose slope does not exceed 400% SOC / battery voltage in the third curve 1-2 , determine the second battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the fourth curve 2-2 ;

[0040] Determine a voltage interval U1 where U1-1 and U1-2 overlap, and determine a voltage interval U2 where U2-1 and U2-2 overlap;

[0041] Obtain the discharge capacity C2 of the first battery when discharged to the nominal lower limit voltage at any rate between 0.02C and 0.1C, and obtain the discharge capacity C4 of the second battery when discharged to an anode potential of 1V to 2.5V or discharged until the anode potential reaches the SEI film decomposition potential at any rate between 0.02C and 0.1C; Obtain the charge capacities of the first battery and the second battery when the first battery and the second battery are respectively charged to a preset voltage U at any rate between 0.02C and 0.1C, wherein the preset voltage U of the first battery is the median voltage value of U1, and the preset voltage U of the second battery is the median voltage value of U2, and calculate the charge capacity difference C1 between the first battery and the second battery at this time;

[0042] The total effective capacity C3 of active ions of the first battery is calculated using formula (I): formula (I) C3 = C1 + C2;

[0043] The active ion replenishment efficiency A is calculated using formula (II): A = (C3-C4) / C5, where C5 is the theoretical active ion replenishment capacity, C5 = m×k, m is the mass of the additional active ion material provided, and k is the gram capacity. When the additional active ion material provided is lithium metal, k = 3.86 Ah / g; when the additional active ion material provided is sodium metal, k = 1.165 Ah / g.

[0044] In the present application, the first battery and the second battery are respectively charged to a preset voltage U so that the two batteries are charged to the same anode potential. The charge capacity difference C1 between the first battery and the second battery at this time is calculated. This C1 is the capacity difference between the first battery and the second battery caused by lithium supplementation. The sum of this capacity difference C1 and the aforementioned discharge capacity C2 can accurately represent the total effective capacity of active ions in the lithium-supplemented first battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0046] FIG. 1 shows the lithium cycling of the second battery during charge and discharge in one embodiment.

[0047] FIG. 2 shows the lithium cycling of the first battery during charge and discharge in one embodiment.

[0048] FIG3 shows a graph of anode potential-full cell voltage of a LFP lithium-supplemented battery and a non-lithium-supplemented battery according to Example 1 of the present application.

[0049] FIG4 shows a SOC-full battery voltage curve diagram of the LFP lithium supplemented battery and the non-lithium supplemented battery of Example 1 of the present application.

[0050] FIG5 shows a graph of anode potential-full cell voltage of a NCM battery with lithium supplementation and a battery without lithium supplementation according to Example 2 of the present application.

[0051] FIG6 shows a SOC-full battery voltage curve diagram of a lithium-supplemented battery and a non-lithium-supplemented battery of the NCM of Example 2 of the present application. DETAILED DESCRIPTION

[0052] The following detailed description of the embodiments of the present application is provided in conjunction with the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present application, but are not intended to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0053] Below, with appropriate reference to the accompanying drawings, an embodiment of the method for evaluating the effective replenishment level of active ions in the secondary ion battery of the present application is described in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0054] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0055] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0056] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0057] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0058] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or comprised.

[0059] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0060] The present application provides a method for evaluating the effective replenishment level of active ions in a secondary ion battery, wherein the secondary ion battery is a first battery, and the corresponding di-ion secondary battery that has not been replenished with active ions is a second battery. The evaluation method includes: obtaining the discharge capacity C2 of the first battery during discharge in a nominal voltage range; charging the first battery and the second battery to their respective preset voltages U, and at the preset voltage U, the anode potential of the first battery and the anode potential of the second battery are equal, and calculating the charge capacity difference C1 between the first battery and the second battery at this time; and calculating the sum C3 of the charge capacity difference C1 and the discharge capacity C2, where C3 is used to characterize the total effective capacity of the active ions of the first battery.

[0061] The secondary ion battery is also called a rechargeable battery or storage battery, which refers to a battery that can be recharged to activate the active material after the battery is discharged and can continue to be used.

[0062] Typically, a secondary ion battery consists of a cathode electrode, an anode electrode, a separator, and an electrolyte. During the battery's charge and discharge process, active ions (such as lithium ions) are embedded and released back and forth between the cathode electrode and the anode electrode. The separator is placed between the cathode electrode and the anode electrode, primarily to prevent a short circuit between the cathode and anode electrodes while allowing active ions to pass through. The electrolyte, located between the cathode electrode and the anode electrode, primarily conducts active ions.

[0063] The first and second batteries are identical in design and manufacturing process, except for the use of lithium supplementation. While variations in electrode width and length are permitted, the capacities used in this application are normalized to the actual area of ​​the cathode electrode during charge and discharge.

[0064] In the present application, the first battery and the second battery are respectively charged to a preset voltage U so that the two batteries are charged to the same anode potential. The charge capacity difference C1 between the first battery and the second battery at this time is calculated. This C1 is the capacity difference between the first battery and the second battery caused by lithium supplementation. The sum of this capacity difference C1 and the aforementioned discharge capacity C2 can accurately represent the total effective capacity of active ions in the lithium-supplemented first battery.

[0065] According to the working mechanism of conventional secondary ion batteries, in some embodiments, the preset voltage is generally in the range of 2.8-3.8V.

[0066] The principle of the above-mentioned evaluation method of the present application is described below with reference to the accompanying drawings.

[0067] FIG1 shows the lithium cycle of the second battery during charge and discharge in one embodiment. As shown in FIG1 , there are filling positions representing lithium, the cathode contains 100 lithiums, the anode has 110 vacancies for lithium insertion and removal (i.e., reversible vacancies at the anode), and 10 lithium vacancies required for SEI formation. During the first charge, 100 lithiums are removed from the cathode, 10 are used for SEI film formation, and 90 are stored in reversible vacancies at the anode. When fully discharged, 90 lithiums are removed to the cathode. When charging again, the anode potential is controlled so that 40 lithiums are inserted into the anode. The anode potential represents the actual SOC of the anode. Actual SOC = lithium inserted into the anode / total amount of reversible vacancies. In FIG1 , SOC = 40 / 100 = 40%.

[0068] FIG2 shows the lithium cycle of the first battery during charge and discharge in one embodiment. As shown in FIG2 , there are filling positions representing lithium, the cathode contains 112 lithiums (including 12 supplementary lithiums), the anode has 110 vacancies for lithium insertion and removal (i.e., reversible vacancies at the anode), and 10 lithium vacancies required for SEI formation. During the first charge, 112 lithiums are removed from the cathode, 10 are used for SEI film formation, and 102 are stored in reversible vacancies at the anode. When fully discharged, 100 lithiums are removed to the cathode. During recharging, the anode potential is controlled so that a total of 40 lithiums are embedded in the anode, i.e., the actual SOC = lithium embedded in the anode / total amount of reversible vacancies. In FIG2 , SOC = 40 / 100 = 40%.

[0069] At this time, the active lithium of the lithium supplement battery C3 = C2 + C1 = 100 + (40-38) = 102.

[0070] The voltage corresponding to the same interval of the anode potential-battery voltage curve of the first battery and the second battery can be selected as the preset voltage U, thereby ensuring that the actual anode potentials of the first battery and the second battery are more accurately equal when charged to the preset voltage U.

[0071] In some embodiments of the present application, the above-mentioned evaluation method includes:

[0072] Obtaining a curve includes: obtaining a first curve and a second curve of a charging process or a discharging process of the first battery and the second battery in a nominal voltage range and a discharge capacity C2 of the first battery, wherein the first curve and the second curve are both full charging process curves or both are full discharging process curves, the first curve is an anode potential-battery voltage curve of the first battery, and the second curve is an anode potential-battery voltage curve of the second battery;

[0073] Obtaining the voltage interval U1 includes: determining the battery voltage interval U1 of the first battery corresponding to the portion of the first curve and the second curve that has the same curve shape in the same anode potential interval;1-1 and the battery voltage interval U of the second battery 2-1 ;

[0074] Obtaining the capacity difference C1 includes: obtaining the charging capacity of the first battery and the second battery when the first battery and the second battery are respectively charged to their respective preset voltages U, wherein the preset voltage U of the first battery is U 1-1 The preset voltage U of the second battery is U 2-1 Calculate the difference C1 in the charge capacity between the first battery and the second battery at this time using any value in ;

[0075] Obtaining the total effective replenishment capacity of active ions includes calculating the sum C3 of the charge capacity difference C1 and the discharge capacity C2.

[0076] The above method is used to determine the preset voltage U. The obtained charging capacity difference C1 is closer to the actual level. 1-1 And the battery voltage range U 2-1 When overlapping, the preset voltage of the first battery and the preset voltage of the second battery may be the same.

[0077] In the process of obtaining the capacity difference C1, the charge capacities of the first and second batteries can be the charge capacities corresponding to the charge voltage U during the process of obtaining the above curve. Therefore, recharging is not required during the process of obtaining the capacity difference C1. Of course, the charge capacities of the first and second batteries can also be obtained by performing separate charging according to the above conditions.

[0078] In some embodiments of the present application, the process of obtaining the capacity difference C1 includes: discharging the first battery and charging the second battery to their respective preset voltages U, and calculating the charge capacity difference C1 between the first battery and the second battery at this time, wherein the first battery is discharged to the nominal lower limit voltage, and the second battery is discharged to 1V-2.5V or discharged until the anode potential reaches the SEI film decomposition potential.

[0079] The above-mentioned SEI film decomposition potential can be accurately determined by conventional dQ / dV testing in the art, and will not be described in detail in this application.

[0080] The first battery, which has been lithium-supplemented, has more active lithium at the anode. During discharge, the cathode inserts lithium to a lower voltage, leading to greater polarization. Consequently, after discharge, the first battery has more active lithium remaining at the anode than the second battery. Therefore, discharging the first battery to the nominal lower voltage limit ensures full discharge, minimizing the amount of active lithium remaining at the anode due to incomplete discharge. This reduces the total effective capacity of active ions in the first battery.

[0081] In some embodiments, the discharge rate is selected from any rate between 0.02 C and 0.1 C. Discharging at such a low rate makes it easier to precisely control the discharge cutoff voltage, and the obtained capacity difference C1 is more accurate.

[0082] In some embodiments, the batteries are charged at any rate between 0.02C and 0.1C to a preset voltage U. The low rate charging makes it easier to accurately control the charging cut-off voltage.

[0083] The above-mentioned preset voltage U can be any value in U1. In some embodiments, the preset voltage U of the first battery is U 1-1 The median voltage value of the second battery is U 2-1 The median voltage value.

[0084] Due to different battery systems, the first curve and the second curve of the first battery and the second battery cannot be overlapped in situ. In some embodiments, U 1-1 and U 2-1 The process includes: translating the voltage value t1 of the first curve and / or the voltage value t2 of the second curve along the coordinate line where the battery voltage is located, so that the first curve and the second curve overlap in the battery voltage interval U', when the translation is in the direction of lower battery voltage, t1 and t2 are negative values, when the translation is in the direction of higher battery voltage, t1 and t2 are positive values, and optionally t1 and t2 meet any one or more of the following conditions: 0V≤|t1|≤2.0V, 0V≤|t2|≤2.0V, 0V≤|t1|+|t2|≤2.0V; calculating U according to the following formula 1-1 and U 2-1 , U 1-1 =U'-t1,U 2-1 =U'-t2. Thus, a more accurate U 1-1 and U 2- 1.

[0085] In some embodiments, the process of obtaining the curve further includes obtaining a third curve and a fourth curve of the nominal voltage interval charging process or discharging process, the third curve and the fourth curve are both full charging process curves or full discharging process curves, the third curve is the SOC-battery voltage curve of the first battery, and the fourth curve is the SOC-battery voltage curve of the second battery; the evaluation method further includes determining the first battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the third curve 1-2 , determine the second battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the fourth curve 2-2 ; Determine U 1-1 and U 2-1 Overlapping voltage interval U1; determine U1-2 and U 2-2 Overlapping voltage interval U2; in the process of obtaining the charging capacity difference C1, the preset voltage U of the first battery is any value in U1, and the preset voltage U of the second battery is any value in U2.

[0086] Factors such as the accuracy of the charging and discharging equipment cause a deviation between the actual charge cut-off voltage and the preset voltage U. When the slope of the SOC-battery voltage curve is low, the resulting SOC deviation is small, and therefore has a smaller impact on C1. When the slope does not exceed 400% SOC / battery voltage, the slope of this curve segment is low, meaning that even if there is a certain difference between the battery's charge cut-off voltage and the preset voltage, the corresponding capacity difference C1 is less affected by the charge and discharge itself. The resulting charge and discharge difference is as close as possible to the difference caused by lithium replenishment.

[0087] In some embodiments of the present application, the preset voltage U of the first battery is the median voltage value of U1, and the preset voltage U of the second battery is the median voltage value of U2.

[0088] In some embodiments, the curve acquisition process includes: charging or discharging the first battery and the second battery at the same rate within a nominal voltage range, respectively, to acquire the first curve and the second curve.

[0089] In some embodiments, the rate of the charging process or the discharging process is selected from any rate between 0.02 C and 0.1 C. The charging process or the discharging process is performed at such a low rate to improve the accuracy of the curve.

[0090] In some embodiments, the evaluation method further includes recording the discharge capacity C4 of the second battery. The evaluation method further includes calculating the active ion replenishment efficiency, where the active ion replenishment efficiency A = (C3 - C4) / C5, where C5 is the theoretical active ion replenishment capacity. The theoretical active ion replenishment capacity can be calculated as C5 = m × k, where m is the mass of the additional active ion material provided, and k is the gram capacity. When the additional active ion material provided is lithium metal, k = 3.86 Ah / g; when the additional active ion material provided is sodium metal, k = 1.165 Ah / g.

[0091] The evaluation method of this application requires accurate anode potential. To simplify the anode potential testing method, in some embodiments, a reference electrode is provided in the first and second batteries to monitor the anode potential of the first and second batteries during charge and discharge. The battery has a built-in reference electrode, for example, provided between the cathode and anode and separated from the cathode and anode by a diaphragm.

[0092] In some embodiments, the reference electrode is a conductive wire having an active material layer on its surface. The conductive wire has a diameter of 50 μm to 100 μm, and the active material layer has a thickness of 10 μm to 50 μm. The conductive wire is preferably a metal wire, such as a copper wire; and the active material layer can be an active metal layer or an active compound layer.

[0093] In some embodiments, the reference electrode is a copper wire, a copper wire with a lithium-plated layer on its surface, a copper wire with a sodium-plated layer on its surface, a copper wire coated with a lithium iron phosphate layer on its surface, a copper wire coated with a lithium titanate layer on its surface, or a copper wire coated with a sodium vanadium phosphate layer on its surface.

[0094] In some embodiments, when the reference electrode is a copper wire, an active metal layer is plated on its surface before evaluation. For example, the copper wire of the first battery is electroplated by using the positive electrode of the first battery as the positive electrode and the copper wire as the negative electrode, and charging at a constant current of 10 μA for 1 hour. The copper wire of the second battery is electroplated by using the positive electrode of the second battery as the positive electrode and the copper wire as the negative electrode, and charging at a constant current of 10 μA for 1 hour.

[0095] In some embodiments, when the reference electrode is a copper wire coated with a lithium iron phosphate layer, a copper wire coated with a lithium titanate layer, or a copper wire coated with a sodium vanadium phosphate layer, the evaluation method also includes a process of first activating the reference electrode, and the process of activating the reference electrode includes: charging the first battery and the second battery to a battery voltage corresponding to 50±5% SOC, respectively.

[0096] To further improve the accuracy of the assessment, in some embodiments, both the first and second batteries are full cells, and the secondary ion battery is a lithium-ion secondary battery or a sodium-ion secondary battery. By directly measuring the full battery, the charge and discharge processes can fully simulate the actual battery operation, resulting in more accurate assessment results.

[0097] In some embodiments of the present application, the above-mentioned evaluation method includes:

[0098] The first battery and the second battery are provided with a reference electrode, and the reference electrode is used to monitor the anode potential of the first battery and the second battery during the charge and discharge process. The first battery and the second battery are both full batteries, and the reference electrode is a copper wire, a copper wire with a lithium-plated layer on the surface, a copper wire with a sodium-plated layer on the surface, a copper wire coated with a lithium iron phosphate layer on the surface, a copper wire coated with a lithium titanate layer on the surface, or a copper wire coated with a sodium vanadium phosphate layer on the surface. The diameter of the copper wire is 50 μm-100 μm, and the thickness of the active material layer on the copper wire is 10 μm-50 μm. When the reference electrode is a copper wire, The surface is plated with an active metal layer, for example: the positive electrode of the first battery is used as the positive electrode, the copper wire is used as the negative electrode, and the constant current is charged at 10 μA for 1 hour to electroplate the copper wire of the first battery; the positive electrode of the second battery is used as the positive electrode, the copper wire is used as the negative electrode, and the constant current is charged at 10 μA for 1 hour to electroplate the copper wire of the second battery; when the reference electrode is a copper wire coated with lithium iron phosphate, a copper wire coated with lithium titanate, or a copper wire coated with sodium vanadium phosphate, the first battery and the second battery are respectively charged to a battery voltage corresponding to 50±5% SOC to activate the reference electrode;

[0099] Charging the first battery and the second battery in a nominal voltage range at any rate between 0.02C and 0.1C, obtaining an anode potential-battery voltage curve and an SOC-battery voltage curve of the first battery, as well as an anode potential-battery voltage curve and an SOC-battery voltage curve of the second battery, defining the anode potential-battery voltage curve of the first battery as a first curve, defining the anode potential-battery voltage curve of the second battery as a second curve, defining the SOC-battery voltage curve of the first battery as a third curve, and defining the SOC-battery voltage curve of the second battery as a fourth curve;

[0100] Determine the battery voltage interval U of the first battery corresponding to the portion of the first curve and the second curve with the same curve shape in the same anode potential interval 1-1 and the battery voltage interval U of the second battery 2- 1, where U is determined 1-1 and U 2-1 The process includes: translating the voltage value t1 of the first curve and / or the voltage value t2 of the second curve along the coordinate line where the battery voltage is located, so that the first curve and the second curve overlap in the battery voltage interval U', when the translation is in the direction of lower battery voltage, t1 and t2 are negative values, when the translation is in the direction of higher battery voltage, t1 and t2 are positive values, and optionally t1 and t2 meet any one or more of the following conditions: 0V≤|t1|≤2.0V, 0V≤|t2|≤2.0V, 0V≤|t1|+|t2|≤2.0V; calculating U according to the following formula 1-1 and U 2-1 , U 1-1 =U'-t1,U 2-1 =U'-t2;

[0101] Determine the first battery voltage interval U corresponding to the curve segment whose slope does not exceed 400% SOC / battery voltage in the third curve 1-2 , determine the second battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the fourth curve 2-2 ;

[0102] Determine a voltage interval U1 where U1-1 and U1-2 overlap, and determine a voltage interval U2 where U2-1 and U2-2 overlap;

[0103] Discharging the first battery and the second battery at a discharge rate selected from any rate between 0.02C and 0.1C, wherein the first battery is discharged to a nominal lower limit voltage, and the second battery is discharged to 1V to 2.5V or discharged until the anode potential reaches the SEI film decomposition potential, and recording the discharge capacity C2 of the first battery and the discharge capacity C4 of the second battery; obtaining the charge capacities of the first battery and the second battery when the first battery and the second battery are respectively charged to a preset voltage U at any rate between 0.02C and 0.1C, wherein the preset voltage U of the first battery is the median voltage value of U1, and the preset voltage U of the second battery is the median voltage value of U2, and calculating the charge capacity difference C1 between the first battery and the second battery at this time;

[0104] The total effective replenishment capacity C3 of the active ions of the first battery is calculated using formula (I): formula (I): C3 = C1 + C2;

[0105] The active ion replenishment efficiency is calculated using formula (II): A = (C3-C4) / C5, where C5 is the theoretical active ion replenishment capacity, C5 = m×k, m is the mass of the additional active ion material provided, and k is the gram capacity. When the additional active ion material provided is lithium metal, k = 3.86 Ah / g; when the additional active ion material provided is sodium metal, k = 1.165 Ah / g.

[0106] In the process of obtaining the capacity difference C1, the charge capacities of the first and second batteries can be the charge capacities corresponding to the charge to voltage U during the process of obtaining the first to fourth curves. Therefore, recharging is not required during the process of obtaining the capacity difference C1. Of course, the charge capacities of the first and second batteries can also be obtained by charging them separately according to the above conditions.

[0107] In some embodiments of the present application, the above-mentioned evaluation method includes:

[0108] The first battery and the second battery are provided with a reference electrode, and the reference electrode is used to monitor the anode potential of the first battery and the second battery during the charge and discharge process. The first battery and the second battery are both full batteries. The reference electrode is a copper wire, a copper wire with a lithium-plated layer on the surface, a copper wire with a sodium-plated layer on the surface, a copper wire coated with a lithium iron phosphate layer on the surface, a copper wire coated with a lithium titanate layer on the surface, or a copper wire coated with a sodium vanadium phosphate layer on the surface. The diameter of the copper wire is 50 μm-100 μm, and the thickness of the active material layer on the copper wire is 10 μm-50 μm. When the reference electrode is a copper wire, Before the evaluation, the copper wire of the first battery was electroplated by charging the positive electrode of the first battery and the copper wire as the negative electrode at a constant current of 10 μA for 1 hour. The copper wire of the second battery was electroplated by charging the positive electrode of the second battery and the copper wire as the negative electrode at a constant current of 10 μA for 1 hour. When the reference electrode was a copper wire coated with a lithium iron phosphate layer, a copper wire coated with a lithium titanate layer, or a copper wire coated with a sodium vanadium phosphate layer, the first battery and the second battery were respectively charged to the battery voltage corresponding to 50±5% SOC to activate the reference electrode.

[0109] The first battery and the second battery are charged and discharged in a nominal voltage range at any rate between 0.02C and 0.1C, and an anode potential-battery voltage curve and an SOC-battery voltage curve of the first battery, as well as an anode potential-battery voltage curve and an SOC-battery voltage curve of the second battery are obtained during the discharge process. The discharge capacity C4 of the second battery is recorded, and the anode potential-battery voltage curve of the first battery is defined as a first curve, the anode potential-battery voltage curve of the second battery is defined as a second curve, the SOC-battery voltage curve of the first battery is defined as a third curve, and the SOC-battery voltage curve of the second battery is defined as a fourth curve.

[0110] Determine the battery voltage interval U of the first battery corresponding to the portion of the first curve and the second curve with the same curve shape in the same anode potential interval 1-1 and the battery voltage interval U of the second battery 2-1 , where U is determined 1-1 and U 2-1 The process includes: translating the voltage value t1 of the first curve and / or the voltage value t2 of the second curve along the coordinate line where the battery voltage is located, so that the first curve and the second curve overlap in the battery voltage interval U', when the translation is in the direction of lower battery voltage, t1 and t2 are negative values, when the translation is in the direction of higher battery voltage, t1 and t2 are positive values, and optionally t1 and t2 meet any one or more of the following conditions: 0V≤|t1|≤2.0V, 0V≤|t2|≤2.0V, 0V≤|t1|+|t2|≤2.0V; calculating U according to the following formula 1-1 and U 2-1 , U 1-1 =U'-t1,U2- 1 = U'-t2;

[0111] Determine the first battery voltage interval U corresponding to the curve segment whose slope does not exceed 400% SOC / battery voltage in the third curve 1-2 , determine the second battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the fourth curve 2-2 ;

[0112] Determine a voltage interval U1 where U1-1 and U1-2 overlap, and determine a voltage interval U2 where U2-1 and U2-2 overlap;

[0113] Obtain the discharge capacity C2 of the first battery when discharged to the nominal lower limit voltage at any rate between 0.02C and 0.1C, and the discharge capacity C4 of the second battery when discharged to 1V-2.5V or discharged until the anode potential reaches the SEI film decomposition potential; Obtain the charge capacities of the first battery and the second battery when the first battery and the second battery are respectively charged to a preset voltage U at any rate between 0.02C and 0.1C, wherein the preset voltage U of the first battery is the median voltage value of U1, and the preset voltage U of the second battery is the median voltage value of U2, and calculate the charge capacity difference C1 between the first battery and the second battery at this time;

[0114] The total effective replenishment capacity C3 of the active ions of the first battery is calculated using formula (I): formula (I): C3 = C1 + C2;

[0115] The active ion replenishment efficiency A is calculated using formula (II): A = (C3-C4) / C5, where C5 is the theoretical active ion replenishment capacity, C5 = m×k, m is the mass of the additional active ion material provided, and k is the gram capacity. When the additional active ion material provided is lithium metal, k = 3.86 Ah / g; when the additional active ion material provided is sodium metal, k = 1.165 Ah / g.

[0116] The above-mentioned discharge capacity C2 can be the discharge capacity of the first battery when it is discharged to the nominal lower limit voltage during the process of obtaining the first to fourth curves. Of course, it can also be the capacity corresponding to the case of a separate discharge according to the above-mentioned conditions. The above-mentioned discharge capacity C4 can be the discharge capacity of the second battery when it is discharged to the above-mentioned voltage during the process of obtaining the first to fourth curves. Of course, it can also be the capacity corresponding to the case of a separate discharge according to the above-mentioned conditions. In the process of obtaining the capacity difference C1, the charge capacity of the first battery and the second battery can be the charge capacity corresponding to the charge to voltage U during the process of obtaining the first to fourth curves. Therefore, the process of obtaining the capacity difference C1 does not require recharging. Of course, the charge capacity of the first battery and the second battery can also be obtained by charging separately according to the above-mentioned conditions.

[0117] The above-mentioned evaluation method of the present application is applicable to the evaluation of secondary ion batteries of any composition, and the evaluation method of the present application can be used for evaluation regardless of whether the secondary ion battery is cathode lithium-supplemented, anode lithium-supplemented, electrolyte lithium-supplemented or diaphragm lithium-supplemented.

[0118] The following is an illustrative description of the components of a secondary ion battery.

[0119] [Cathode plate]

[0120] The cathode electrode generally includes a cathode current collector and a cathode film layer disposed on at least one surface of the cathode current collector, wherein the cathode film layer includes a cathode active material.

[0121] As an example, the cathode current collector has two surfaces opposite to each other in its thickness direction, and the cathode film layer is disposed on either or both of the two opposite surfaces of the cathode current collector.

[0122] In some embodiments, the cathode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0123] In some embodiments, the cathode active material may adopt cathode active materials for batteries that are well known in the art. As an example, when the secondary battery is a lithium ion secondary battery, the cathode active material may include at least one of the following materials: lithium phosphates containing olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery cathode active materials may also be used. These cathode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0124] When the secondary battery is a sodium-ion secondary battery, as an example, the cathode active material of the sodium-ion secondary battery may include at least one of the following materials: at least one of a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound. However, the present application is not limited to these materials, and other conventionally known materials that can be used as sodium-ion battery cathode active materials may also be used.

[0125] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0126] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be at least one of P, S and Si; n represents (YO4) n- valence.

[0127] Polyanionic compounds can also be sodium ions, transition metal ions, tetrahedral (YO4) n-A class of compounds containing anion units and halogen anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4) n- valence state; the halogen may be at least one of F, Cl and Br.

[0128] The polyanionic compound can also be a compound having sodium ions, tetrahedral (YO4)n-anion units, polyhedral units (ZO y ) m+ and an optional halogen anion. Y can be at least one of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, and m represents (ZO y ) m+ valence state; the halogen may be at least one of F, Cl and Br.

[0129] Polyanionic compounds include NaFePO4, Na3V2(PO4) (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0130] Prussian blue compounds can be compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0131] In some embodiments, the cathode film layer may further include a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0132] In some embodiments, the cathode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0133] In some embodiments, the cathode electrode sheet can be prepared by the following method: the above-mentioned components for preparing the cathode electrode sheet, such as the cathode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a cathode slurry; the cathode slurry is coated on the cathode current collector, and after drying, cold pressing and other processes, the cathode electrode sheet can be obtained.

[0134] [Anode plate]

[0135] The anode electrode sheet includes an anode current collector and an anode film layer disposed on at least one surface of the anode current collector, wherein the anode film layer includes an anode active material.

[0136] As an example, the anode current collector has two surfaces opposite to each other in its thickness direction, and the anode film layer is provided on either one or both of the two opposite surfaces of the anode current collector.

[0137] In some embodiments, the anode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0138] In some embodiments, the anode active material may be an anode active material for a battery that is well known in the art. As an example, the anode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as battery anode active materials may also be used. These anode active materials may be used alone or in combination of two or more.

[0139] In some embodiments, the anode film layer may further include a binder. For example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0140] In some embodiments, the anode film layer may further include a conductive agent. For example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0141] In some embodiments, the anode film layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0142] In some embodiments, the anode electrode sheet can be prepared by the following method: the components for preparing the anode electrode sheet, such as the anode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form an anode slurry; the anode slurry is coated on the anode current collector, and after drying, cold pressing and other processes, the anode electrode sheet can be obtained.

[0143] [Electrolytes]

[0144] The electrolyte conducts ions between the cathode and anode electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0145] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0146] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0147] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0148] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include anode film-forming additives, cathode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0149] [Isolation film]

[0150] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0151] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0152] In some embodiments, the cathode electrode sheet, the anode electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0153] In some embodiments, the secondary battery includes a secondary battery cell, or includes a battery module and a battery pack.

[0154] [Example]

[0155] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0156] Example 1: Evaluation of LFP Secondary Batteries

[0157] Both the lithium-supplemented and non-supplemented batteries are full cells with a built-in reference electrode copper wire with a diameter of 50μm. The positive electrode material is lithium iron phosphate (LFP), the positive electrode current collector is aluminum foil, and the weight ratio of LFP, conductive agent acetylene black, and binder PVDF in the positive electrode film is 94:4:2. The negative electrode material is graphite, the negative electrode current collector is copper foil, and the weight ratio of graphite, conductive agent acetylene black, and binder styrene-butadiene rubber (SBR) + carboxymethyl cellulose (CMC) in the negative electrode film is 95:1.5:3.1:0.4. The electrolyte composition is ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC) in a weight ratio of EC:PC:DMC = 3:3:3 to form a solvent. The concentration of lithium salt LiPF6 in the electrolyte is 1 mol / L. A 12μm thick polyethylene porous membrane serves as the separator. The first battery was replenished with lithium at the positive electrode. The lithium replenishment material was lithium-rich lithium iron oxide (Li5FeO4). The mass of the replenished lithium was 0.328g and the theoretical gram capacity was 0.867Ah / g. Therefore, the theoretical active ion replenishment capacity C5 can be calculated to be 0.284Ah. The second battery was not replenished with lithium. Otherwise, it was exactly the same as the first battery. Before the test, for the lithium replenished battery, the copper wire was used as the negative electrode and the positive electrode of the lithium replenished battery was used as the positive electrode. A constant current of 10μA was applied for 1h. For the battery without lithium replenishment, the copper wire was used as the negative electrode and the positive electrode of the lithium replenished battery was used as the positive electrode. A constant current of 10μA was applied for 1h. This process will make a layer of metallic lithium on the surface of the copper wire with a thickness of about 30μm.

[0158] The LFP-supplemented and non-supplemented batteries were charged at a rate of 0.04C in the nominal voltage range of 2.5-3.65V to obtain the anode potential-cell voltage curves and SOC-cell voltage curves for the respective charging processes. Figure 3 shows the anode potential-full cell voltage curves for the LFP-supplemented and non-supplemented batteries, and Figure 4 shows the SOC-full cell voltage curves for the LFP-supplemented and non-supplemented batteries.

[0159] In Figure 3, the overlapping interval U1 of the two curves is determined to be 3.25-3.35V; in Figure 4, a voltage interval U2 with a lower slope is selected, such as 2.7-3.3V. The overlapping voltage interval of U1 and U2, determined above, is 3.25-3.3V. Any voltage within this interval can be used as the charge cutoff voltage. In this embodiment, the median value of 3.275V is selected for evaluation.

[0160] The lithium-supplemented battery and the non-lithium-supplemented battery were discharged at a rate of 0.04C, wherein the lithium-supplemented battery was discharged to the nominal lower limit voltage, and the non-lithium-supplemented battery was discharged to an anode potential of 1V. The discharge capacity C2 of the lithium-supplemented battery was recorded as 2.11Ah, and the discharge capacity C4 of the non-lithium-supplemented battery was recorded as 1.93Ah.

[0161] The lithium-supplemented and non-supplemented batteries were charged at a rate of 0.04C, with a cutoff voltage of 3.275V. According to test data, the capacity of the lithium-supplemented battery at 3.275V was 0.44Ah. The capacity at 3.275V was 0.49Ah, resulting in a capacity difference C1 of 0.05Ah. Therefore, the total effective active lithium ion capacity of the first battery is C3 = C1 + C2 = 2.16Ah. The calculated lithium-supplementation efficiency A = (C3 - C4) / C5 = 81%.

[0162] Example 2: Evaluation of NCM Secondary Batteries

[0163] Both lithium-ion batteries and non-lithium-ion batteries are full batteries with built-in reference electrode copper wire with a diameter of 50μm. The positive electrode material is LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), the positive electrode current collector is aluminum foil, the weight ratio of NCM811, conductive agent acetylene black, and binder PVDF in the positive electrode film layer is 94:4:2; the negative electrode material is graphite and silicon monoxide, (SiO), the negative electrode current collector is copper foil, the weight ratio of graphite, SiO, conductive agent acetylene black, and binder SBR+CMC in the negative electrode film layer is 67.5:22.5:1.5:7:1.5, ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC) are EC:PC:DMC=3:3:3 to form a solvent, and the concentration of lithium salt LiPF6 in the electrolyte is 1 mol / L; a 12 μm thick polyethylene porous film is used as an isolation membrane. The negative electrode of the first battery was replenished with lithium. The lithium replenishment material was metallic lithium. The mass of the replenished lithium was 0.367g and the theoretical gram capacity was 3.86Ah / g. Therefore, the theoretical active ion replenishment capacity C5 can be calculated to be 1.42Ah. The lithium replenishment process and subsequent battery production were carried out at 25°C and the humidity was <2%. The second battery was not replenished with lithium. Otherwise, it was exactly the same as the first battery. Before the test, for the lithium replenished battery, the copper wire was used as the negative electrode and the positive electrode of the lithium replenished battery was used as the positive electrode. A constant current of 10μA was applied for 1h. For the battery without lithium replenishment, the copper wire was used as the negative electrode and the positive electrode of the lithium replenished battery was used as the positive electrode. A constant current of 10μA was applied for 1h. This process will result in a layer of metallic lithium with a thickness of about 30μm on the surface of the copper wire.

[0164] The lithium-ion batteries and non-lithium-ion batteries were charged and discharged at a rate of 0.04C in the nominal voltage range of 2.5-4.2V to obtain the anode potential-cell voltage curve and SOC-cell voltage curve for each charging process. Figure 5 shows the anode potential-full cell voltage curve for the lithium-ion batteries and non-lithium-ion batteries with NCM, and Figure 6 shows the SOC-full cell voltage curve for the lithium-ion batteries and non-lithium-ion batteries with NCM.

[0165] In Figure 5, the anode potential-full cell voltage curve of the non-replenished lithium battery is shifted so that the shifted curve overlaps with the anode potential-full cell voltage curve of the replenished lithium battery at around 3.1 V. As shown in Figure 5, the shift amount is 0.16 V. The full cell voltage interval U corresponding to the overlapping portion of the anode potential-full cell voltage curve of the replenished lithium battery and the shifted anode potential-full cell voltage curve of the non-replenished lithium battery is determined. 1-1 2.9-3.5V. This 2.9-3.5V corresponds to the full battery voltage range of the lithium battery. For the full battery voltage range without lithium battery, U 1-2 The translation amount needs to be added, and the calculated value is 3.06-3.66V.

[0166] In Figure 6, the interval with a lower slope is determined, and for the full battery voltage interval U 2-1 The full battery voltage range is 2.9-3.3V without lithium battery replenishment. 2-2 It is 2.9-3.4V.

[0167] Determine the overlapping range of U1-1 and U2-1 for lithium battery replenishment is 2.9-3.3V, and do not replenish lithium battery U 2-1 and U 2-2 The overlapping range is 3.06-3.4 V. The charging cutoff voltage of the lithium-ion battery is determined to be the median of 2.9-3.3 V, 3.1 V. The charging cutoff voltage of the non-lithium-ion battery is determined to be the median of 3.1 + 0.16 V, 3.26 V, so that the lithium-ion battery and the non-lithium-ion battery are charged to the same anode potential.

[0168] The lithium-supplemented battery and the non-lithium-supplemented battery were discharged at a rate of 0.04C, wherein the lithium-supplemented battery was discharged to the nominal lower limit voltage, and the non-lithium-supplemented battery was discharged to an anode potential of 1V. The discharge capacity C2 of the lithium-supplemented battery was recorded as 4.38Ah, and the discharge capacity C4 of the non-lithium-supplemented battery was recorded as 3.25Ah.

[0169] The lithium-ion battery and the non-lithium-ion battery were charged at a rate of 0.04C. The charging cut-off voltage of the lithium-ion battery was 3.1V, and the charging cut-off voltage of the non-lithium-ion battery was 3.26V. The lithium-ion battery and the non-lithium-ion battery were charged to the same anode potential.

[0170] According to test data, the rechargeable lithium battery has a capacity of 0.07 Ah when charged to 3.1 V. The unrecharged battery has a capacity of 0.16 Ah when discharged and charged to 3.26 V. Therefore, the capacity difference C1 is 0.09 Ah. Therefore, the total active lithium ion capacity of the first battery is C3 = C1 + C2 = 4.47 Ah. The calculated recharge efficiency is A = (C3 - C4) / C5 = 86%.

[0171] Example 3: Evaluation of NCM Secondary Batteries (Effect of Temperature)

[0172] When using metallic lithium for lithium replenishment, the lithium will react with the anode electrode, causing the electrode to generate heat and the temperature to rise, intensifying the reaction between lithium and air, causing the lithium replenishment efficiency to decrease, and thus causing the active lithium in the battery to be lower than the design value and the battery life to be shorter.

[0173] Example 3 uses the same electrode as Example 2. The manufacturing process is the same except that the storage temperature of the lithium-replenished battery after lithium replenishment is different, so as to test the influence of temperature on the lithium replenishment effect.

[0174] Specifically, the same positive electrode and negative electrode as in Example 2 were used. The first battery was replenished with lithium, and the lithium replenishment material was metallic lithium. The mass of the replenished lithium was 0.37g, and the theoretical gram capacity was 3.86Ah / g. Therefore, the theoretical active ion replenishment capacity C5 can be calculated to be 1.43Ah. The lithium replenishment process was carried out at 25°C and the humidity was <2%. After the lithium replenishment, the jelly roll was immediately wound to obtain the jelly roll, and then the jelly roll was placed in a 40°C incubator for 6 hours (atmospheric environment, humidity <2%) to simulate the effect of heat generation of the electrode. After the shelving was completed, the subsequent production steps were carried out at room temperature, and the process conditions were the same as in Example 2.

[0175] The testing process and data analysis were the same as in Example 2. The discharge capacity C2 of the first battery was 4.38 Ah, and the discharge capacity C4 of the unreplenished battery was 3.25 Ah. The difference in charge capacity C1 between the unreplenished and replenished batteries was 0.03 Ah. Therefore, the total active lithium ion capacity of the first battery was C3 = C1 + C2 = 4.41 Ah, and the replenishment efficiency A = (C3 - C4) / C5 = 81%.

[0176] Comparing the results with those of Example 2, we found that temperature has a significant negative impact on lithium replenishment efficiency, resulting in a reduction in the battery's active lithium ion capacity and low lithium replenishment efficiency, thus affecting the battery's lifespan. Therefore, controlling the temperature of the electrode or electrode core during and after lithium replenishment helps reduce side reactions between lithium and air, maximizes the effectiveness of the replenished metallic lithium, and ultimately achieves high lithium replenishment efficiency.

[0177] Further analysis of the data in Examples 2 and 3 also reveals that under different lithium replenishment efficiencies, there is no significant difference in the discharge capacity C2 of the lithium-replenished battery. This is because the battery's lithium replenishment amount is relatively high. At lithium replenishment efficiencies of 86% and 81%, the replenished active lithium is sufficient to compensate for the irreversible active lithium consumption of the negative electrode (mainly from SEI film formation). At this time, the battery capacity is determined by the reversible capacity of the positive electrode. Since the same electrode is used in the two embodiments, the positive electrode capacity is the same, so there is no difference in the measured C2. The above test results also illustrate that testing the total active lithium ion capacity or lithium replenishment efficiency of the lithium-replenished battery can effectively identify the lithium replenishment effect, such as whether the above-mentioned lithium replenishment temperature is abnormal. If only the discharge capacity C2 is analyzed, it is difficult to ensure that a lithium replenishment evaluation result with reference value is obtained.

[0178] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A method for evaluating the effective replenishment level of active ions in a secondary ion battery, wherein: The secondary ion battery is a first battery, and the secondary ion battery corresponding to the secondary ion battery that has not been supplemented with active ions is a second battery. The evaluation method includes: Obtaining a discharge capacity C2 of the first battery during discharge in a nominal voltage range; charging the first battery and the second battery to their respective preset voltages U, wherein at the preset voltage U, the anode potential of the first battery and the anode potential of the second battery are equal, and calculating the charge capacity difference C1 between the first battery and the second battery at this time; A sum C3 of the charge capacity difference C1 and the discharge capacity C2 is calculated, where C3 is used to represent the total effective capacity of active ions of the first battery.

2. The evaluation method according to claim 1, wherein: The evaluation method includes: Obtaining a curve includes: obtaining a first curve and a second curve of a charging process or a discharging process of the first battery and the second battery in a nominal voltage range, and a discharge capacity C2 of the first battery, wherein the first curve and the second curve are both full-charge process curves or both are full-discharge process curves, the first curve is an anode potential-battery voltage curve of the first battery, and the second curve is an anode potential-battery voltage curve of the second battery; Obtaining the voltage interval U1 includes: determining the battery voltage interval U1 of the first battery corresponding to the portion of the first curve and the second curve with the same curve shape in the same anode potential interval; 1-1 and the battery voltage interval U of the second battery 2-1 ; Obtaining the capacity difference C1 includes: obtaining the charging capacity of the first battery and the second battery when the first battery and the second battery are respectively charged to their respective preset voltages U, wherein the preset voltage U of the first battery is U 1-1 The preset voltage U of the second battery is U 2-1 Calculate the charge capacity difference C1 between the first battery and the second battery at this time using any value in ; Obtaining the total effective capacity of active ions includes calculating a sum C3 of the charge capacity difference C1 and the discharge capacity C2.

3. The evaluation method according to claim 2, wherein: The process of obtaining the capacity difference C1 includes: The first battery and the second battery are discharged and then charged to their respective preset voltages U, and the charge capacity difference C1 between the first battery and the second battery at this time is calculated, wherein the first battery is discharged to the nominal lower limit voltage, and the second battery is discharged to an anode potential of 1V-2.5V or discharged until the anode potential reaches the SEI film decomposition potential.

4. The evaluation method according to claim 3, wherein: The discharge rate is selected from any rate between 0.02C and 0.1C.

5. The evaluation method according to claim 3, wherein: The batteries are charged at any rate between 0.02C and 0.1C to the preset voltage U.

6. The evaluation method according to any one of claims 2 to 5, wherein: The preset voltage U of the first battery is U 1-1 The median voltage value of the second battery is U 2-1 The median voltage value.

7. The evaluation method according to any one of claims 2 to 5, wherein: Determine U 1-1 and U 2- 1. The process includes: Shifting the voltage value t1 of the first curve and / or the voltage value t2 of the second curve along the coordinate line where the battery voltage is located so that the first curve and the second curve overlap in the battery voltage interval U', when the shift is in the direction of lower battery voltage, t1 and t2 are negative values, when the shift is in the direction of higher battery voltage, t1 and t2 are positive values, and t1 and t2 satisfy any one or more of the following conditions: 0V≤|t1|≤2.0V, 0V≤|t2|≤2.0V, 0V≤|t1|+|t2|≤2.0V; Calculate U according to the following formula 1-1 and U 2-1 , U 1-1 =U'-t1,U 2-1 =U'-t2.

8. The evaluation method according to any one of claims 2 to 5, wherein: The curve acquisition process further includes acquiring a third curve and a fourth curve of a charging process or a discharging process in a nominal voltage range, wherein the third curve and the fourth curve are full-charge process curves or full-discharge process curves, the third curve is a SOC-battery voltage curve of the first battery, and the fourth curve is a SOC-battery voltage curve of the second battery; The evaluation method further includes determining a first battery voltage interval U corresponding to a curve segment in the third curve having a slope not exceeding 400% SOC / battery voltage. 1-2 , determine the second battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the fourth curve 2-2 ; Determine the U 1-1 and the U 1-2 Overlapping voltage interval U1; Determine the U 2-1 and the U 2-2 Overlapping voltage interval U2; in the process of obtaining the charging capacity difference C1, the preset voltage U of the first battery is any value in U1, and the preset voltage U of the second battery is any value in U2.

9. The evaluation method according to claim 8, wherein: The preset voltage U of the first battery is the median voltage value of U1 , and the preset voltage U of the second battery is the median voltage value of U2 .

10. The evaluation method according to any one of claims 2 to 5, wherein: The curve acquisition process includes: The first battery and the second battery are respectively charged or discharged at the same rate within a nominal voltage range to obtain the first curve and the second curve.

11. The evaluation method according to claim 10, wherein: The rate of the charging process or the discharging process is selected from any rate between 0.02C and 0.1C.

12. The evaluation method according to any one of claims 2 to 5, wherein: The evaluation method further comprises the step of recording the discharge capacity C4 of the second battery, The evaluation method also includes a process of calculating the active ion replenishment efficiency. Ion replenishment efficiency A = (C3-C4) / C5, where C5 is the theoretical replenishment capacity of active ions.

13. The evaluation method according to any one of claims 1 to 5, wherein: Reference electrodes are provided in the first battery and the second battery, and the reference electrodes are used to monitor the anode potentials of the first battery and the second battery during the charge and discharge process.

14. The evaluation method according to claim 13, wherein: The reference electrode is a conductive wire with an active material layer on the surface. The diameter of the conductive wire is 50 μm-100 μm, and the thickness of the active material layer is 10 μm-50 μm.

15. The evaluation method according to claim 14, wherein: The reference electrode is a copper wire, a copper wire with a lithium-plated layer on the surface, a copper wire with a sodium-plated layer on the surface, a copper wire coated with a lithium iron phosphate layer on the surface, a copper wire coated with a lithium titanate layer on the surface, or a copper wire coated with a sodium vanadium phosphate layer on the surface. When the reference electrode is a copper wire, before evaluation, the copper wire of the first battery is electroplated by charging with a constant current of 10 μA for 1 hour with the positive electrode of the first battery as the positive electrode and the copper wire as the negative electrode, and the copper wire of the second battery is electroplated by charging with a constant current of 10 μA for 1 hour; When the reference electrode is a copper wire coated with a lithium iron phosphate layer, a copper wire coated with a lithium titanate layer, or a copper wire coated with a sodium vanadium phosphate layer, the evaluation method further includes first activating the reference electrode, and the process of activating the reference electrode includes: The first battery and the second battery are respectively charged to a battery voltage corresponding to 50±5% SOC.

16. The evaluation method according to any one of claims 1 to 5, wherein: The first battery and the second battery are both full batteries, and the secondary ion battery is a lithium ion secondary battery or a sodium ion secondary battery.

17. The evaluation method according to claim 1, wherein: The evaluation method includes: The first battery and the second battery are provided with a reference electrode, and the reference electrode is used to monitor the anode potential of the first battery and the second battery during the charge and discharge process. The first battery and the second battery are full batteries. The reference electrode is a copper wire, a copper wire with lithium plating on the surface, a copper wire with sodium plating on the surface, a copper wire coated with lithium iron phosphate on the surface, a copper wire coated with lithium titanate on the surface, or a copper wire coated with sodium vanadium phosphate on the surface. The diameter of the copper wire is 50 μm-100 μm, and the thickness of the active material layer on the copper wire is 10 μm-50 μm. When the reference electrode is a copper wire Before the evaluation, the copper wire of the first battery was electroplated by charging the positive electrode of the first battery and the copper wire as the negative electrode at a constant current of 10 μA for 1 hour, and the copper wire of the second battery was electroplated by charging the positive electrode of the second battery and the copper wire as the negative electrode at a constant current of 10 μA for 1 hour; when the reference electrode was a copper wire coated with lithium iron phosphate, a copper wire coated with lithium titanate, or a copper wire coated with sodium vanadium phosphate, the first battery and the second battery were respectively charged to a battery voltage corresponding to 50±5% SOC to activate the reference electrode; Charging the first battery and the second battery in a nominal voltage range at any rate between 0.02C and 0.1C, obtaining an anode potential-battery voltage curve and an SOC-battery voltage curve of the first battery, as well as an anode potential-battery voltage curve and an SOC-battery voltage curve of the second battery, defining the anode potential-battery voltage curve of the first battery as a first curve, defining the anode potential-battery voltage curve of the second battery as a second curve, defining the SOC-battery voltage curve of the first battery as a third curve, and defining the SOC-battery voltage curve of the second battery as a fourth curve; Determine the battery voltage interval U of the first battery corresponding to the portion of the first curve and the second curve with the same curve shape in the same anode potential interval 1-1 and the battery voltage interval U of the second battery 2-1 , where U is determined 1-1 and U 2-1 The process includes: translating the voltage value t1 of the first curve and / or the voltage value t2 of the second curve along the coordinate line where the battery voltage is located, so that the first curve and the second curve overlap in the battery voltage interval U', when the translation is in the direction of lower battery voltage, t1 and t2 are negative values, when the translation is in the direction of higher battery voltage, t1 and t2 are positive values, and t1 and t2 meet any one or more of the following conditions: 0V≤|t1|≤2.0V, 0V≤|t2|≤2.0V, 0V≤|t1|+|t2|≤2.0V; calculating U according to the following formula 1-1 and U 2-1 , U 1-1 =U'-t1,U 2-1 =U'-t2; Determine the first battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the third curve 1-2 , determine the second battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the fourth curve 2-2 ; Determine the U 1-1 and the U 1-2 Overlapping voltage interval U1, determine the U 2-1 and the U 2-2 Overlapping voltage interval U2; Discharging the first battery and the second battery at a discharge rate selected from any rate between 0.02C and 0.1C, wherein the first battery is discharged to a nominal lower limit voltage, and the second battery is discharged to an anode potential of 1V to 2.5V or to an anode potential reaching an SEI film decomposition potential, and recording the discharge capacity C2 of the first battery and the discharge capacity C4 of the second battery; obtaining the charge capacities of the first battery and the second battery when the first battery and the second battery are respectively charged to the preset voltage U at any rate between 0.02C and 0.1C, wherein the preset voltage U of the first battery is a median voltage value of U1, and the preset voltage U of the second battery is a median voltage value of U2, and calculating the charge capacity difference C1 between the first battery and the second battery at this time; The total effective capacity C3 of active ions of the first battery is calculated using formula (I): formula (I): C3 = C1 + C2; The active ion replenishment efficiency is calculated using formula (II): A = (C3-C4) / C5, where C5 is the theoretical active ion replenishment capacity, C5 = m×k, m is the mass of the additional active ion material provided, and k is the gram capacity. When the additional active ion material provided is lithium metal, k = 3.86 Ah / g; when the additional active ion material provided is sodium metal, k = 1.165 Ah / g.

18. The evaluation method according to claim 1, wherein: The evaluation method includes: The first battery and the second battery are provided with a reference electrode, and the reference electrode is used to monitor the anode potential of the first battery and the second battery during the charge and discharge process. The first battery and the second battery are full batteries. The reference electrode is a copper wire, a copper wire with lithium plating on the surface, a copper wire with sodium plating on the surface, a copper wire coated with lithium iron phosphate on the surface, a copper wire coated with lithium titanate on the surface, or a copper wire coated with sodium vanadium phosphate on the surface. The diameter of the copper wire is 50 μm-100 μm, and the thickness of the active material layer on the copper wire is 10 μm-50 μm. When the reference electrode is a copper wire Before the evaluation, the copper wire of the first battery was electroplated by charging the positive electrode of the first battery and the copper wire as the negative electrode at a constant current of 10 μA for 1 hour, and the copper wire of the second battery was electroplated by charging the positive electrode of the second battery and the copper wire as the negative electrode at a constant current of 10 μA for 1 hour; when the reference electrode was a copper wire coated with lithium iron phosphate, a copper wire coated with lithium titanate, or a copper wire coated with sodium vanadium phosphate, the first battery and the second battery were respectively charged to a battery voltage corresponding to 50±5% SOC to activate the reference electrode; charging and discharging the first battery and the second battery in a nominal voltage range at any rate between 0.02C and 0.1C, obtaining an anode potential-battery voltage curve and an SOC-battery voltage curve of the first battery, as well as an anode potential-battery voltage curve and an SOC-battery voltage curve of the second battery during the discharge process, and recording a discharge capacity C4 of the second battery, defining the anode potential-battery voltage curve of the first battery as a first curve, defining the anode potential-battery voltage curve of the second battery as a second curve, defining the SOC-battery voltage curve of the first battery as a third curve, and defining the SOC-battery voltage curve of the second battery as a fourth curve; Determine the battery voltage interval U of the first battery corresponding to the portion of the first curve and the second curve with the same curve shape in the same anode potential interval 1-1 and the battery voltage interval U of the second battery 2-1 , where U is determined 1-1 and U 2-1 The process includes: translating the voltage value t1 of the first curve and / or the voltage value t2 of the second curve along the coordinate line where the battery voltage is located, so that the first curve and the second curve overlap in the battery voltage interval U', when the translation is in the direction of lower battery voltage, t1 and t2 are negative values, when the translation is in the direction of higher battery voltage, t1 and t2 are positive values, and t1 and t2 meet any one or more of the following conditions: 0V≤|t1|≤2.0V, 0V≤|t2|≤2.0V, 0V≤|t1|+|t2|≤2.0V; calculating U according to the following formula 1-1 and U 2-1 , U 1-1 =U'-t1,U 2-1 =U'-t2; Determine the first battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the third curve 1-2 , determine the second battery voltage interval U corresponding to the curve segment with a slope not exceeding 400% SOC / battery voltage in the fourth curve 2-2 ; Determine the U 1-1 and the U 1-2 Overlapping voltage interval U1, determine the U 2-1 and the U 2-2 Overlapping voltage interval U2; Obtain the discharge of the first battery to the nominal lower limit at any rate between 0.02C-0.1C voltage, obtaining the discharge capacity C2 of the second battery when discharged to an anode potential of 1V-2.5V or when discharged to the anode potential reaching the SEI film decomposition potential at any rate between 0.02C and 0.1C; obtaining the charging capacity of the first battery and the second battery when the first battery and the second battery are respectively charged to the preset voltage U at any rate between 0.02C and 0.1C, wherein the preset voltage U of the first battery is the median voltage value of U1, and the preset voltage U of the second battery is the median voltage value of U2, and calculating the charging capacity difference C1 between the first battery and the second battery at this time; The total effective capacity C3 of active ions of the first battery is calculated using formula (I): formula (I): C3 = C1 + C2; The active ion replenishment efficiency A is calculated using formula (II): A = (C3-C4) / C5, where C5 is the theoretical active ion replenishment capacity, C5 = m×k, m is the mass of the additional active ion material provided, and k is the gram capacity. When the additional active ion material provided is lithium metal, k = 3.86 Ah / g; when the additional active ion material provided is sodium metal, k = 1.165 Ah / g.

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