Method for evaluating an electrode

Abstract

The embodiment of the application discloses an evaluation method of an electrode, which comprises the following steps: obtaining an initial active lithium amount of a symmetrical battery to be measured; the material of a working electrode and a counter electrode of the symmetrical battery is graphite; performing a plurality of charging and discharging process controls on the symmetrical battery to obtain a residual active lithium amount; evaluating the graphite electrode of the symmetrical battery based on the initial active lithium amount and the residual active lithium amount; in each charging and discharging process, the symmetrical battery is charged and discharged by using a larger first charging rate and a first discharging rate, so that the counter electrode and the working electrode complete delithiation, the symmetrical battery is charged to a second voltage, so that the solid electrolyte interface film of the counter electrode completes electrical decomposition, and the symmetrical battery is discharged to a fourth voltage, so that the solid electrolyte interface film of the working electrode completes electrical decomposition. The application accelerates the time of each charging and discharging process and the consumption speed of lithium ions, thereby accelerating the evaluation speed of the graphite electrode.

Description

Technical Field

[0001] This application relates to, but is not limited to, the field of battery technology, and in particular to a method for evaluating an electrode. Background Technology

[0002] Lithium-ion batteries experience a slow decline in lifespan and aging degradation during use. For lithium-ion systems in related technologies, such as lithium iron phosphate batteries, lithium nickel cobalt manganese oxide batteries, sodium batteries, and solid-state batteries, the lifespan degradation is caused by the instability of the solid electrolyte interphase (SEI) film on the graphite surface of the negative electrode. During battery charging and discharging, structural damage and repair processes occur (the solid electrolyte interphase film repeatedly breaks down and regenerates, accelerating lithium consumption), leading to the loss of active lithium in the lithium-ion battery and consequently reducing its lifespan. In related technologies, the assessment of lithium-ion battery lifespan has not focused on the lithium loss from the graphite material. Summary of the Invention

[0003] In view of this, embodiments of this application provide at least one method for evaluating an electrode.

[0004] The technical solution of this application embodiment is implemented as follows:

[0005] This application provides an electrode evaluation method, including:

[0006] The initial active lithium content of the first symmetric cell to be tested was obtained; the working electrode and counter electrode of the first symmetric cell were both made of graphite.

[0007] The remaining active lithium was obtained by controlling the charge and discharge process of the first symmetrical battery multiple times.

[0008] The graphite electrode of the first symmetric cell was evaluated based on the initial and remaining active lithium content; wherein:

[0009] Each charge and discharge cycle includes:

[0010] After charging the first symmetrical battery to a preset first voltage using a preset first charging rate, the first symmetrical battery is then charged to a second voltage using a preset second charging rate, thus completing the charging process. Specifically, lithium removal is performed on the electrode at the first voltage, and electrolysis of the solid electrolyte interface film on the electrode is performed at the second voltage.

[0011] After charging is completed, the first symmetrical battery is discharged to the third voltage using a preset first discharge rate, and then discharged to the fourth voltage using a preset second discharge rate; at the third voltage, the working electrode completes delithiation; at the fourth voltage, the solid electrolyte interface film of the working electrode completes electrolysis.

[0012] The first discharge rate and the first charge rate are both in the range of 0.33C to 1.0C, and the second charge rate and the second discharge rate are both in the range of 0.01C to 0.05C.

[0013] This application provides an electrode evaluation method, including:

[0014] The initial active lithium content of the second symmetric cell to be tested was obtained; the working electrode and counter electrode of the second symmetric cell were both made of lithium nickel cobalt manganese oxide.

[0015] The remaining active lithium content was obtained by controlling the charge-discharge process of the second symmetric battery multiple times.

[0016] The lithium nickel cobalt manganese oxide electrode of the second symmetric cell was evaluated based on the initial active lithium content and the remaining active lithium content.

[0017] Each charge and discharge cycle includes:

[0018] After charging the second symmetrical battery to a preset fifth voltage using a preset first charging rate, the second symmetrical battery is charged under constant voltage at the fifth voltage. The charging process is completed when the charging current is less than or equal to the current corresponding to the preset second charging rate.

[0019] After charging is completed, the second symmetrical battery is discharged to the sixth voltage using the preset first discharge rate. Then, the second symmetrical battery is subjected to constant voltage discharge at the sixth voltage. The discharge process is completed when the discharge current is less than or equal to the current corresponding to the preset second discharge rate.

[0020] The first discharge rate and the first charge rate are both in the range of 0.33C to 1.0C, and the second charge rate and the second discharge rate are both in the range of 0.01C to 0.05C.

[0021] In this embodiment, firstly, both the working electrode and the counter electrode are made of graphite. By controlling the first symmetrical battery through multiple charge-discharge processes, both the working electrode and the counter electrode can experience lithium loss, thereby accelerating the evaluation speed of the graphite electrode. Secondly, in each charge-discharge control process, a larger first charging rate is used to charge the first symmetrical battery, allowing the counter electrode to quickly complete lithium removal, thus accelerating the time of one charge cycle. A second charging rate is then used to charge the first symmetrical battery, causing the solid electrolyte interface film of the counter electrode to undergo electrolytic decomposition, accelerating the lithium-ion consumption rate. This accelerates the lithium-ion consumption rate while simultaneously accelerating the one charge cycle. Then, a larger first discharge rate is used to discharge the first symmetrical battery, causing the working electrode to quickly complete lithium removal, thus accelerating the one discharge cycle. A second discharge rate is then used to discharge the first symmetrical battery, causing the solid electrolyte interface film of the working electrode to undergo electrolytic decomposition, accelerating the lithium-ion consumption rate. This accelerates the lithium-ion consumption rate while simultaneously accelerating the one discharge cycle. These processes accelerate the evaluation speed of the graphite electrode.

[0022] It should be understood that the above general description and the following detailed description are merely exemplary and explanatory, and are not intended to limit the technical solutions of this application. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with this application and, together with the specification, serve to explain the technical solutions of this application.

[0024] Figure 1 A schematic diagram illustrating the implementation process of an evaluation method for a graphite electrode provided in this application embodiment;

[0025] Figure 2 A schematic diagram illustrating the implementation process of an evaluation method for a lithium nickel cobalt manganese oxide electrode provided in this application embodiment;

[0026] Figure 3 An assembly schematic diagram of a first symmetrical battery provided in an embodiment of this application;

[0027] Figure 4 A schematic diagram illustrating the relationship between the electrode potential and the degree of lithium intercalation in graphite, provided for an embodiment of this application;

[0028] Figure 5 A schematic diagram illustrating the evaluation results of a graphite electrode provided in an embodiment of this application;

[0029] Figure 6 A schematic diagram illustrating the evaluation results of matching the same graphite with different electrolytes, provided for an embodiment of this application;

[0030] Figure 7 This is a schematic diagram of the electrode potential of a lithium nickel cobalt manganese oxide material as a function of the degree of lithium intercalation, provided in an embodiment of this application.

[0031] Figure 8 This is a schematic diagram illustrating the evaluation results of a lithium nickel cobalt manganese oxide electrode provided in an embodiment of this application. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application are further described in detail below with reference to the accompanying drawings and embodiments. The described embodiments should not be regarded as limitations on this application. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] In the following description, references are made to “some embodiments,” which describe a subset of all possible embodiments. However, it is understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0034] The terms “first / second / third” are used merely to distinguish similar objects and do not represent a specific ordering of objects. It is understood that “first / second / third” may be interchanged in a specific order or sequence where permitted, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used herein is for descriptive purposes only and is not intended to limit the scope of this application.

[0036] This application provides an electrode evaluation method. Figure 1 This is a schematic diagram illustrating the implementation process of an evaluation method for a graphite electrode provided in an embodiment of this application, as shown below. Figure 1 As shown, the method includes the following steps S101 to S103:

[0037] Step S101: Obtain the initial active lithium content of the first symmetric cell to be tested; the working electrode and counter electrode of the first symmetric cell are both made of graphite.

[0038] Here, a symmetrical cell refers to a type of battery system in which the positive and negative electrodes are made of the same material. These are commonly used in electrochemical research, performance evaluation, and failure analysis. The first symmetrical cell is a symmetrical cell in which both the positive and negative electrodes are made of graphite material; it can also be called a graphite symmetrical cell.

[0039] The working electrode (WE) usually refers to the electrode being studied or tested, such as graphite or other target materials. The working electrode is used to observe electrochemical behavior, such as lithium insertion / deintercalation, interfacial impedance, polarization, etc.

[0040] The counter electrode (CE) is the electrode on the other side made of the same material as the working electrode. It does not provide a reference potential and is generally used as the counter electrode of the current loop to complete charge balance.

[0041] In one embodiment, if the object of study is graphite material serving as the negative electrode of a battery, the electrode connected to the negative electrode channel of the charging device can be used as the working electrode; correspondingly, the electrode connected to the positive electrode channel of the charging device can be used as the counter electrode. In another embodiment, if the object of study is ternary material serving as the positive electrode of a battery, the electrode connected to the negative electrode channel of the charging device can be used as the working electrode; correspondingly, the electrode connected to the positive electrode channel of the charging device can be used as the counter electrode.

[0042] In this embodiment, it is assumed that the initial degree of lithium intercalation of the working electrode is x, and the initial degree of lithium intercalation of the counter electrode is y. The sum of x and y is 1, where x and y take values ​​in the range [0, 1]. For example, the initial degree of lithium intercalation of the working electrode is 30%, and the initial degree of lithium intercalation of the counter electrode is 70%; or the initial degree of lithium intercalation of the working electrode is 60%, and the initial degree of lithium intercalation of the counter electrode is 40%; or the initial degree of lithium intercalation of both the working electrode and the counter electrode is 50%; and so on. If the sum of x and y is greater than 1, lithium plating will occur during subsequent charging.

[0043] In practice, a stacked battery needs to be assembled based on graphite and lithium iron phosphate electrodes. By adjusting the discharge capacity of the stacked battery, a target graphite electrode with a lithium intercalation degree of x is obtained, and this target graphite electrode is used as the working electrode. The counter electrode is prepared following the same process. The stacked battery is used as a pretreatment battery; its purpose is to obtain the target graphite electrode. In another example, a coin cell can also be used as the pretreatment battery; when using a coin cell, a larger coin cell needs to be fabricated.

[0044] The initial active lithium content is the total amount of lithium ions in the first symmetric cell to be tested that can participate in the electrochemical reaction before the test.

[0045] In some embodiments, to study the performance of graphite materials, a first symmetric cell in which both the working electrode and the counter electrode are made of graphite can be subjected to cycle testing. Since both the working electrode and the counter electrode of the first symmetric cell are made of graphite, lithium loss can occur at both electrodes during cycle testing, thus accelerating the evaluation of the graphite electrode.

[0046] In some implementations, the working electrode and the counter electrode have the same degree of lithium insertion, both being 50%.

[0047] Step S102: Perform multiple charge-discharge processes on the first symmetrical battery to obtain the remaining active lithium content;

[0048] In some embodiments, the remaining active lithium content can characterize the amount of lithium ions that can still participate in electrochemical reactions after the charge-discharge process of the first symmetric battery. In one example, the remaining active lithium content can be the total amount of lithium ions remaining in the first symmetric battery that can participate in electrochemical reactions after each charge-discharge process; that is, determining the remaining active lithium content for each charge-discharge process. In another example, the remaining active lithium content can also be the total amount of lithium ions remaining in the first symmetric battery that can participate in electrochemical reactions after multiple charge-discharge processes.

[0049] In some embodiments, during each charge-discharge process of the first symmetric battery, when the working electrode and counter electrode are at a high potential, the solid electrolyte interface film on the graphite surface undergoes electrolysis, and active lithium is consumed to repair the solid electrolyte interface film, thereby accelerating the consumption of active lithium and thus accelerating the evaluation of the graphite electrode of the first symmetric battery.

[0050] Step S103: Evaluate the graphite electrode of the first symmetric cell based on the initial active lithium content and the remaining active lithium content.

[0051] In some embodiments, multiple target graphite electrodes can be fabricated using various graphite materials, and a corresponding first symmetrical battery can be fabricated based on each target graphite electrode, thus obtaining multiple first symmetrical batteries. Each of the multiple first symmetrical batteries is subjected to multiple charge-discharge process controls to obtain the remaining active lithium amount corresponding to each first symmetrical battery. Based on the initial active lithium amount and the remaining active lithium amount corresponding to each first symmetrical battery, the graphite electrode of the corresponding first symmetrical battery is evaluated, thereby realizing the evaluation of the graphite material corresponding to the graphite electrode.

[0052] Assuming a first symmetric battery has an initial active lithium content of q1, a cycle count of J, and a remaining active lithium content of q2, the evaluation index can be calculated as (q1-q2) / J, where q1-q2 represents the lithium consumption. In this case, the evaluation index represents the lithium consumption in one charge-discharge cycle. The smaller the (q1-q2) / J, the better the performance of the graphite electrode in the first symmetric battery. For a first symmetric battery, a threshold r0 can be set for this evaluation index. When the calculated evaluation index is less than this threshold r0, the graphite electrode in the first symmetric battery is considered to be a qualified graphite electrode.

[0053] When a group of first symmetrical cells includes multiple first symmetrical cells, the evaluation index corresponding to each first symmetrical cell is calculated. One approach is to identify graphite electrodes with evaluation indices greater than the threshold r0 as meeting the requirements. Another approach is to sort the evaluation indices of the group of first symmetrical cells and identify the top n indices as meeting the requirements.

[0054] In a relatively ideal situation, for a group of first symmetric cells, if the number of cycles is the same, then the evaluation index = q2 / q1. At this time, the evaluation index represents the remaining active lithium ratio. The larger the remaining active lithium ratio, the better the performance of the graphite electrode in the first symmetric cell.

[0055] In a more ideal scenario, assuming that multiple first symmetric batteries have the same initial active lithium content and the same number of cycles, the evaluation index can also be the remaining active lithium content. The first symmetric battery with a larger remaining active lithium content has better performance of its graphite electrode. The graphite material corresponding to the graphite electrode with better performance is determined to be a graphite material that meets the requirements. In this way, the graphite material that meets the requirements can be screened out.

[0056] Each charge / discharge process includes the following steps S111 and S112:

[0057] Step S111: After charging the first symmetrical battery to a preset first voltage using a preset first charging rate, charge the first symmetrical battery to a second voltage using a preset second charging rate to complete the charging process; wherein, lithium removal is completed on the electrode under the first voltage; and electrolysis is completed on the solid electrolyte interface film of the electrode under the second voltage.

[0058] Here, the first charging rate is the charging rate that enables rapid lithium removal from the counter electrode, and this first charging rate can be in the range of 0.33C to 1.0C. The second charging rate is the charging rate that enables continuous decomposition and repair of the solid electrolyte interface film of the counter electrode, and this second charging rate can be in the range of 0.01C to 0.05C. The first charging rate is considered a high rate compared to the second charging rate, which is considered a low rate.

[0059] In some embodiments, charging the first symmetrical battery at a preset first charging rate allows for rapid delithiation of the counter electrode. By the time the first symmetrical battery is charged to a first voltage, delithiation of the counter electrode is complete. During the charging process of the first symmetrical battery from the preset first voltage to a second voltage at a second charging rate, the solid electrolyte interface film of the counter electrode continuously decomposes and repairs. The first voltage is the voltage at which delithiation of the counter electrode is complete, for example, a voltage between +0.3 and +0.5V; the second voltage is the maximum cutoff voltage for charging the first symmetrical battery, for example, a voltage between +2.5V and +3.0V.

[0060] In related technologies, the charging and discharging process, especially the charging or discharging process, uses a small rate, such as 0.05C, for charging or discharging cycle control. This results in a long charging and discharging time. That is, unlike the embodiment of this application, which uses two different charging rates in the charging process and two different discharging rates in the discharging process, and uses a large rate for charging or discharging in one stage, the charging or discharging process can be accelerated.

[0061] In some embodiments, during the first charge of the first symmetrical battery, since the degree of lithium intercalation of the working electrode and the counter electrode is the same, the potentials of the two electrodes are the same, and the initial voltage of the first symmetrical battery is close to 0 volts (V). During the charging process, for the graphite first symmetrical battery, the potential of the working electrode is close to 0V; therefore, the voltage of the first symmetrical battery can be considered as the potential of the counter electrode. As the first symmetrical battery is charged, the degree of lithium intercalation of the working electrode increases, while the degree of lithium intercalation of the counter electrode decreases. When the lithium intercalated inside the counter electrode is completely deintercalated, the voltage of the first symmetrical battery reaches a first voltage. Continuing to charge the first symmetrical battery to a second voltage causes the solid electrolyte interface film of the counter electrode to continuously decompose and repair, consuming lithium ions.

[0062] Step S112: After charging is completed, the first symmetrical battery is discharged to a third voltage using a preset first discharge rate, and then discharged to a fourth voltage using a preset second discharge rate; under the third voltage, the working electrode completes delithiation; under the fourth voltage, the solid electrolyte interface film of the working electrode completes electrolysis.

[0063] Here, the first discharge rate is the discharge rate that enables rapid lithium removal from the working electrode, and this first discharge rate can be in the range of 0.33C to 1.0C. The second discharge rate is the discharge rate that enables continuous decomposition and repair of the solid electrolyte interface film of the working electrode, and this second discharge rate can be in the range of 0.01C to 0.05C. The first discharge rate is considered a high rate compared to the second discharge rate, which is considered a low rate.

[0064] In some embodiments, charging the first symmetrical battery at a preset second charging rate allows for rapid delithiation of the working electrode. By the time the first symmetrical battery is charged to a third voltage, the working electrode has already completed delithiation. During the discharge of the first symmetrical battery from the preset third voltage to the fourth voltage at a second discharge rate, the solid electrolyte interface film of the working electrode continuously decomposes and repairs.

[0065] Among them, the third voltage is the negative first voltage, the fourth voltage is the minimum voltage of the first symmetrical battery discharge, and the fourth voltage is the negative second voltage.

[0066] Generally, the operating voltage of a full cell (lithium iron phosphate-graphite) is +2.5V to +3.65V. When a full cell is over-discharged, the anode potential of the full cell will continue to rise, leading to the decomposition of the solid electrolyte interface film and affecting the operating state of the full cell. Therefore, in related technologies, when using full cells to evaluate graphite materials, it is not possible to accelerate the lithium-ion consumption rate by over-discharging the full cell.

[0067] In this embodiment of the application, the graphite material is evaluated using a first symmetric graphite cell. The lithium-ion consumption rate can be accelerated by amplifying the cutoff voltage of the first symmetric cell (e.g., amplifying it to +2.5V), thereby accelerating the evaluation efficiency of the graphite material.

[0068] In one example, a single charge-discharge cycle of a graphite electrode within the operating range consumes 0.01% of lithium. In the first symmetric cell, where graphite electrodes are located on both sides, the lithium consumption during a single charge-discharge cycle is 2 × 0.01%. After over-lithiation of the graphite electrode leading to the decomposition of the solid electrolyte interfacial film, the lithium consumption during a single charge-discharge cycle exceeds 5 × 0.01%. In the first symmetric cell, after over-lithiation causing the decomposition of the solid electrolyte interfacial film, the lithium consumption during a single charge-discharge cycle approaches 10 × 0.01%. Therefore, the performance of the graphite electrode can be rapidly evaluated.

[0069] In this embodiment, firstly, both the working electrode and the counter electrode are made of graphite. By controlling the first symmetrical battery through multiple charge-discharge processes, both the working electrode and the counter electrode can experience lithium loss, thereby accelerating the evaluation speed of the graphite electrode. Secondly, in each charge-discharge control process, a larger first charging rate is used to charge the first symmetrical battery, allowing the counter electrode to quickly complete lithium removal, thus accelerating the time of one charge cycle. A second charging rate is then used to charge the first symmetrical battery, causing the solid electrolyte interface film of the counter electrode to undergo electrolytic decomposition, accelerating the lithium-ion consumption rate. This accelerates the lithium-ion consumption rate while simultaneously accelerating the one charge cycle. Then, a larger first discharge rate is used to discharge the first symmetrical battery, causing the working electrode to quickly complete lithium removal, thus accelerating the one discharge cycle. A second discharge rate is then used to discharge the first symmetrical battery, causing the solid electrolyte interface film of the working electrode to undergo electrolytic decomposition, accelerating the lithium-ion consumption rate. This accelerates the lithium-ion consumption rate while simultaneously accelerating the one discharge cycle. These processes accelerate the evaluation speed of the graphite electrode.

[0070] In some implementations, the scheme of this application can also be used to evaluate the performance of different electrolytes.

[0071] In some embodiments, each charge-discharge process further includes the following steps S121 to S124:

[0072] Step S121: After charging the first symmetrical battery to the first voltage using the first charging rate, perform the first stage of resting.

[0073] Specifically, lithium removal from the electrode is completed when the first symmetrical battery is charged to the first voltage; the first stage of resting refers to the stage of stabilizing the state of the first symmetrical battery after it has been charged to the first voltage.

[0074] In some implementations, after the first symmetrical battery is charged to the first voltage at the first charging rate, it can be left to stand for a period of time (e.g., 5 minutes) to allow the electric field, concentration field and temperature field inside the first symmetrical battery to become stable and uniform, providing stable conditions for subsequent charging.

[0075] Step S122: After completing the first stage of resting and charging the first symmetrical battery to the second voltage using the second charging rate, perform the second stage of resting.

[0076] Specifically, when the first symmetrical battery is charged to the second voltage, the solid electrolyte interface film of the electrode is electrolyzed; the second stage of settling refers to the stage of stabilizing the state of the first symmetrical battery after it has been charged to the second voltage.

[0077] In some implementations, after the first symmetrical battery is charged to the second voltage using the second charging rate, the first symmetrical battery completes the charging phase of one charge-discharge process. After being left to stand for a period of time (e.g., 5 minutes), the electric field, concentration field, and temperature field inside the first symmetrical battery tend to be stable and uniform, providing stable conditions for the subsequent discharge process.

[0078] Step S123: After completing the second stage of resting and discharging the first symmetrical battery to the third voltage using the first discharge rate, the third stage of resting is completed.

[0079] Here, the working electrode completes lithium removal when the first symmetrical cell is discharged to the third voltage; the third stage of resting refers to the stage of discharging the first symmetrical cell to the third voltage and stabilizing the state of the first symmetrical cell.

[0080] In some implementations, after discharging the first symmetrical battery to the third voltage at the first discharge rate, it can be left to stand for a period of time (e.g., 5 minutes) to allow the electric field, concentration field and temperature field inside the first symmetrical battery to become stable and uniform, providing stable conditions for subsequent discharge.

[0081] Step S124: After completing the third stage of resting, discharge the first symmetrical battery to the fourth voltage using the second discharge rate.

[0082] In some implementations, after the first symmetrical battery is discharged to the fourth voltage using the second discharge rate, the first symmetrical battery has completed a complete charge-discharge process and can be left to stand for a period of time (e.g., 5 minutes). The electric field, concentration field and temperature field inside the first symmetrical battery tend to be stable and uniform, providing stable conditions for the next charge-discharge process.

[0083] In this embodiment, by charging the first symmetrical battery to a first voltage using a first charging rate and then letting it stand for a period of time, charging the first symmetrical battery to a second voltage using a second charging rate and then letting it stand for a period of time, and discharging the first symmetrical battery to a third voltage using a first discharging rate and then letting it stand for a period of time, the electric field, concentration field, and temperature field inside the first symmetrical battery at each stage can be made more stable and uniform, providing stable conditions for subsequent charging and discharging, thereby improving the stability and accuracy of evaluating the graphite electrode of the first symmetrical battery.

[0084] In some embodiments, the process of controlling the first symmetrical battery to perform multiple charge-discharge cycles in step S102 above to obtain the remaining active lithium may include the following step S131:

[0085] Step S131: For each charge and discharge process, the discharge capacity obtained by discharging the first symmetrical battery is determined as the remaining active lithium amount in the charge and discharge process.

[0086] In some implementations, during each charge and discharge cycle, lithium ions in the first symmetrical battery migrate between the working electrode and the counter electrode, participate in electrochemical reactions, and realize the storage and release of electrical energy. The more remaining active lithium, the more lithium ions can participate in electrochemical reactions, thereby releasing more electrical energy, i.e., the larger the discharge capacity. Therefore, the remaining active lithium in the charge and discharge cycle can be determined based on the discharge capacity of the first symmetrical battery during each charge and discharge cycle.

[0087] In some implementations, the more cycles the first symmetrical battery undergoes in its charge-discharge process, the more irreversible chemical reactions occur inside the battery, leading to the loss of active lithium. For example, the solid electrolyte interface film on the surface of the working electrode and the counter electrode continuously decomposes and repairs, continuously consuming lithium ions, thereby reducing the amount of remaining active lithium. Therefore, as the number of cycles increases, the discharge capacity of a single charge-discharge process becomes smaller.

[0088] In this embodiment of the application, by determining the discharge capacity in each charge-discharge process as the remaining active lithium amount in that charge-discharge process, the remaining active lithium amount corresponding to each charge-discharge process can be accurately obtained, thereby enabling the evaluation of the graphite electrode based on the remaining active lithium amount in multiple charge-discharge processes.

[0089] In some embodiments, the evaluation of the graphite electrode of the first symmetric cell based on the initial active lithium content and the remaining active lithium content in step S103 above includes at least one of the following steps S141 and S142:

[0090] Step S141: Determine the remaining active lithium ratio for each charge-discharge process based on the ratio of the remaining active lithium to the initial active lithium; evaluate the graphite electrode of the first symmetric battery based on the remaining active lithium ratio for each charge-discharge process.

[0091] In some embodiments, the ratio of the remaining active lithium amount in each charge-discharge process to the initial active lithium amount can characterize the proportion of the remaining active lithium amount in each charge-discharge process to the initial active lithium amount, i.e., the active lithium remaining ratio. This active lithium remaining ratio can be used to evaluate the capacity retention capability and cycle life decay rate of the first symmetric battery. Therefore, the graphite electrode of the first symmetric battery can be evaluated based on the active lithium remaining ratio in each charge-discharge process.

[0092] In some implementations, for the same number of cycles, the higher the remaining proportion of active lithium, the better the performance of the graphite electrode; the lower the remaining proportion of active lithium, the worse the performance of the graphite electrode.

[0093] In some implementations, multiple first symmetric batteries can be made using various graphite materials; the remaining active lithium ratio of the multiple first symmetric batteries in each charge-discharge cycle is determined; and under the same cycle number, the graphite electrode performance of the first symmetric battery with a larger remaining active lithium ratio is better, while the graphite electrode performance of the first symmetric battery with a smaller remaining active lithium ratio is worse.

[0094] In one example, the working electrode and counter electrode of the first symmetrical battery A are both made of graphite A, and the working electrode and counter electrode of the first symmetrical battery B are both made of graphite B. The first symmetrical battery A and the first symmetrical battery B are subjected to 30 charge-discharge cycles respectively. By comparing the remaining active lithium ratio of the first symmetrical battery A and the first symmetrical battery B during each charge-discharge cycle, after 30 charge-discharge cycles, if the remaining active lithium ratio of the first symmetrical battery A is greater than that of the first symmetrical battery B, the performance of graphite A is better than that of graphite B; if the remaining active lithium ratio of the first symmetrical battery A is less than that of the first symmetrical battery B, the performance of graphite A is worse than that of graphite B.

[0095] Step S142: Determine the lithium consumption for each charge-discharge process based on the difference between the initial active lithium quantity and the remaining active lithium quantity for each charge-discharge process; evaluate the graphite electrode of the first symmetric battery based on the lithium consumption for each charge-discharge process.

[0096] In some embodiments, the difference between the initial active lithium amount and the remaining active lithium amount in each charge-discharge process can characterize the lithium consumption in each charge-discharge process. This lithium consumption can be used to evaluate the loss of lithium ions and the degree of degradation of the first symmetric battery during multiple charge-discharge processes. Therefore, the graphite electrode of the first symmetric battery can be evaluated based on the lithium consumption in each charge-discharge process.

[0097] In some implementations, for the same number of cycles, the higher the lithium consumption, the worse the performance of the graphite electrode; the lower the lithium consumption, the better the performance of the graphite electrode.

[0098] In some implementations, multiple target graphite electrodes can be fabricated using various graphite materials, and a first symmetrical battery can be fabricated based on each target graphite electrode, thus obtaining multiple first symmetrical batteries. The lithium consumption of each first symmetrical battery in each charge-discharge cycle is determined. Under the same cycle number, the graphite electrode performance of the first symmetrical battery with a higher lithium consumption is worse, and the graphite electrode performance of the first symmetrical battery with a lower lithium consumption is better.

[0099] In one example, the working electrode and counter electrode of the first symmetrical battery A are both made of graphite A, and the working electrode and counter electrode of the first symmetrical battery B are both made of graphite B. The first symmetrical battery A and the first symmetrical battery B are subjected to 30 charge-discharge cycles respectively. By comparing the lithium consumption of the first symmetrical battery A and the first symmetrical battery B during each charge-discharge cycle, after 30 cycles, if the lithium consumption of the first symmetrical battery A is greater than that of the first symmetrical battery B, the performance of graphite A is worse than that of graphite B; if the lithium consumption of the first symmetrical battery A is less than that of the first symmetrical battery B, the performance of graphite A is better than that of graphite B.

[0100] In this embodiment, the graphite electrode of the first symmetric battery is accurately evaluated by the ratio of the remaining active lithium to the initial active lithium in each charge-discharge process, or by the difference between the initial active lithium and the remaining active lithium in each charge-discharge process.

[0101] In some embodiments, obtaining the initial active lithium content of the first symmetric cell to be tested in step S101 above includes the following step S151:

[0102] Step S151: The sum of the lithium intercalation amount of the working electrode and the counter electrode of the first symmetric cell is determined as the initial active lithium amount.

[0103] Here, the initial active lithium content refers to the total amount of mobile lithium ions that can participate in the electrochemical reaction before the first charge and discharge process of the first symmetric battery.

[0104] In some embodiments, the initial active lithium content can be the initial lithium intercalation content of the working electrode and the counter electrode of the first symmetric cell.

[0105] In some embodiments, since the lithium intercalation levels of the working electrode and the counter electrode are pre-adjusted to the same amount, the initial active lithium amount is the sum of the lithium intercalation amounts of the working electrode and the counter electrode, or the initial active lithium amount is twice the lithium intercalation amount of the working electrode.

[0106] In this embodiment, the initial active lithium content is determined by the sum of the lithium intercalation amount of the working electrode and the counter electrode of the first symmetric battery. Thus, the graphite electrode of the first symmetric battery can be accurately evaluated by using the initial active lithium content as a reference.

[0107] In some embodiments, in order to evaluate the compatibility of different graphite materials with the same electrolyte, or the different performances of different graphite materials with the same electrolyte, the above method further includes the following steps S161 to S163:

[0108] Step S161: Obtain the initial active lithium content of a set of first symmetric cells to be tested; the parameters of the graphite materials of the working electrode and counter electrode of each first symmetric cell in the set of first symmetric cells are different;

[0109] Here, the parameters of graphite materials include graphitization degree, coating thickness, and coating integrity.

[0110] In some implementations, in order to evaluate the performance of graphite materials with different parameters, a set of first symmetric cells with different graphite materials are made using graphite materials with different parameters.

[0111] In some embodiments, the working electrode and counter electrode of each first symmetrical cell in a group of first symmetrical cells are both graphite. The degree of lithium intercalation of the working electrode and the counter electrode can be the same or different, and the initial active lithium content can be determined by the sum of the lithium intercalation content of the working electrode and the counter electrode.

[0112] Step S162: For the group of first symmetrical batteries, perform multiple charge and discharge processes on each first symmetrical battery to obtain the remaining active lithium amount corresponding to each first symmetrical battery.

[0113] In some implementations, the charge and discharge processes of multiple first symmetric cells made of graphite materials with different parameters can be controlled to evaluate the performance of the graphite electrodes of the multiple first symmetric cells.

[0114] In some implementations, when controlling the multiple charge-discharge process of each first symmetric cell, the remaining amount of active lithium in each first symmetric cell during each charging process is determined.

[0115] Step S163: Based on the initial active lithium content of each first symmetrical battery and the remaining active lithium content corresponding to each first symmetrical battery, determine the lithium consumption result corresponding to the graphite electrode in each first symmetrical battery; based on the lithium consumption result corresponding to the graphite electrode in each first symmetrical battery, determine the first symmetrical battery in each first symmetrical battery whose graphite electrode meets the lithium consumption performance requirements as the first symmetrical battery that meets the test requirements.

[0116] Here, the lithium consumption results corresponding to the graphite electrodes can reflect the lithium consumption of each graphite electrode in each first symmetric cell.

[0117] In some implementations, for multiple first symmetric cells, under the same initial active lithium content and the same number of cycles, the lithium consumption of the corresponding graphite electrode is determined by calculating the difference between the initial active lithium content and the remaining active lithium content of each first symmetric cell, thus obtaining the lithium consumption results of the graphite electrodes for multiple first symmetric cells. A higher lithium consumption corresponding to the graphite electrode indicates poorer lithium consumption performance; conversely, a lower lithium consumption indicates better lithium consumption performance.

[0118] In some implementations, for multiple first symmetric cells, under the same initial active lithium amount and the same number of cycles, the remaining active lithium ratio corresponding to the graphite electrode is determined by calculating the ratio between the remaining active lithium amount and the initial active lithium amount of each first symmetric cell, thus obtaining the lithium consumption result corresponding to the graphite electrode for multiple first symmetric cells. A higher remaining active lithium ratio corresponding to the graphite electrode indicates better lithium consumption performance; conversely, a lower remaining active lithium ratio indicates poorer lithium consumption performance.

[0119] In some implementations, for multiple first symmetric cells, under the same initial active lithium content and the same number of cycles, the remaining active lithium content of each first symmetric cell can be directly compared to obtain the lithium consumption results corresponding to the graphite electrodes of the multiple first symmetric cells. If the remaining active lithium content corresponding to the graphite electrode is larger, the lithium consumption performance of the graphite electrode is better; if the remaining active lithium content corresponding to the graphite electrode is smaller, the lithium consumption performance of the graphite electrode is worse.

[0120] In some embodiments, the lithium consumption performance of the graphite electrode in each first symmetrical cell can be scored based on the initial active lithium content and the remaining active lithium content of each first symmetrical cell, thereby obtaining the lithium consumption results corresponding to the graphite electrodes of multiple first symmetrical cells. A higher score indicates better lithium consumption performance of the graphite electrode; conversely, a lower score indicates poorer lithium consumption performance.

[0121] In the embodiments of this application, the lithium consumption result corresponding to the graphite electrode in each first symmetrical cell can be determined by any method based on the initial active lithium amount of each first symmetrical cell and the remaining active lithium amount corresponding to each first symmetrical cell. This application does not limit this.

[0122] In some implementations, the above evaluation can be used to select a graphite electrode that meets the lithium consumption performance requirements from a variety of graphite electrodes with different parameters.

[0123] In this embodiment, graphite electrodes made from graphite materials with different parameters are used to form a first symmetrical battery. The charging and discharging process of the first symmetrical battery is controlled to determine the remaining active lithium amount of each first symmetrical battery. The graphite electrodes with different parameters are evaluated by the initial active lithium amount and the remaining active lithium amount of each first symmetrical battery, so as to select a graphite material that meets the lithium consumption performance requirements.

[0124] In some embodiments, in order to evaluate the compatibility of the same graphite material with different electrolytes, or the performance of different electrolytes on the same graphite material, the above method further includes the following steps S171 to S173:

[0125] Step S171: Obtain the initial active lithium content of a group of first symmetric batteries to be tested; the parameters of the graphite material of the working electrode and the counter electrode of each first symmetric battery in the group are the same; the electrolytes of each first symmetric battery are different.

[0126] In some implementations, different electrolytes directly affect the film formation effect of the solid electrolyte interface film of the graphite electrode, as well as the repair effect of the solid electrolyte interface film during charging and discharging. Therefore, even with the same parameters of graphite material, the lithium consumption performance of different electrolytes is not consistent.

[0127] To evaluate the compatibility of the electrolyte with the graphite material or the performance of the electrolyte under the same graphite material conditions, a set of first symmetric cells with different electrolytes were prepared using graphite materials with the same parameters.

[0128] In some embodiments, the working electrode and counter electrode of each first symmetrical cell in a group of first symmetrical cells are both graphite. The degree of lithium intercalation of the working electrode and the counter electrode can be the same or different, and the initial active lithium content can be determined by the sum of the lithium intercalation content of the working electrode and the counter electrode.

[0129] Step S172: For the group of first symmetrical batteries, perform multiple charge and discharge processes on each first symmetrical battery to obtain the remaining active lithium amount corresponding to each first symmetrical battery.

[0130] In some implementations, the charge-discharge process of multiple first symmetric batteries made of graphite materials with the same parameters and different electrolytes can be controlled to evaluate the impact of the electrolytes of multiple first symmetric batteries on lithium consumption performance.

[0131] In some implementations, the remaining amount of active lithium in each first symmetric cell is determined during each charge-discharge process control of each first symmetric cell.

[0132] Step S173: Based on the initial active lithium content of each first symmetrical battery and the remaining active lithium content of each first symmetrical battery, determine the lithium consumption result of the electrolyte in each first symmetrical battery; based on the lithium consumption result of the electrolyte in each first symmetrical battery, determine the first symmetrical battery in which the electrolyte meets the lithium consumption performance requirements as the first symmetrical battery that meets the test requirements.

[0133] Here, the lithium consumption results corresponding to each electrolyte can reflect the lithium consumption of each electrolyte in each first symmetric cell.

[0134] In some implementations, for multiple first symmetric batteries, under the same initial active lithium amount and the same number of cycles, the lithium consumption of the corresponding electrolyte is determined by calculating the difference between the initial active lithium amount and the remaining active lithium amount of each first symmetric battery, thus obtaining the lithium consumption results of the electrolyte for multiple first symmetric batteries. A higher lithium consumption rate for the electrolyte indicates poorer lithium consumption performance; conversely, a lower lithium consumption rate indicates better lithium consumption performance.

[0135] In some implementations, for multiple first symmetric batteries, under the same initial active lithium amount and the same number of cycles, the remaining active lithium ratio of the electrolyte is determined by calculating the ratio between the remaining active lithium amount and the initial active lithium amount of each first symmetric battery, thus obtaining the lithium consumption result of the electrolyte for multiple first symmetric batteries. A higher remaining active lithium ratio in the electrolyte indicates better lithium consumption performance; conversely, a lower remaining active lithium ratio indicates poorer lithium consumption performance.

[0136] In some implementations, for multiple first symmetric batteries, under the same initial active lithium content and the same number of cycles, the remaining active lithium content of each first symmetric battery can be directly compared to obtain the lithium consumption results corresponding to the electrolyte of multiple first symmetric batteries. If the remaining active lithium content of the electrolyte is larger, the lithium consumption performance of the electrolyte is better; if the remaining active lithium content of the electrolyte is smaller, the lithium consumption performance of the electrolyte is worse.

[0137] In some embodiments, the lithium consumption performance of the electrolyte in each first symmetrical cell can be scored based on the initial active lithium content and the remaining active lithium content of each first symmetrical cell, thereby obtaining the lithium consumption results corresponding to the electrolytes of multiple first symmetrical cells. A higher score indicates better lithium consumption performance, while a lower score indicates poorer lithium consumption performance.

[0138] In the embodiments of this application, the lithium consumption result of the electrolyte in each first symmetrical battery can be determined by any method based on the initial active lithium amount of each first symmetrical battery and the remaining active lithium amount of each first symmetrical battery respectively. This application does not limit this.

[0139] In some implementations, through the above evaluation, an electrolyte that meets the lithium consumption performance requirements can be selected from a variety of different electrolytes, that is, an electrolyte that meets the compatibility requirements with the graphite material.

[0140] In this embodiment, the charging and discharging process of multiple first symmetrical batteries made of graphite material with the same parameters and different electrolytes is controlled to determine the remaining active lithium amount of each first symmetrical battery. The performance of various electrolytes is evaluated by the initial active lithium amount and the remaining active lithium amount of each first symmetrical battery in order to select an electrolyte that meets the performance requirements.

[0141] In some embodiments, using the first symmetric battery prepared in this application for charge-discharge process control, and using the charge-discharge process control scheme of this application, can accelerate the lithium consumption rate of the graphite electrode, thereby accelerating the evaluation speed of the graphite electrode. Therefore, the number of cycles for evaluating the graphite electrode can be controlled within the range of 10 to 100. In some embodiments, the number of cycles for evaluating the graphite electrode can be 30.

[0142] In some embodiments, the first symmetrical cell is made using two target graphite electrodes with the same degree of lithium intercalation; the target graphite electrodes are obtained by disassembling the negative electrode of the stacked cell; the negative electrode of the stacked cell is made of graphite; and the positive electrode of the stacked cell is made of lithium iron phosphate.

[0143] In this embodiment, graphite 1 and graphite 2 with different particle sizes (e.g., particle sizes between 1 and 15 micrometers) can be used as the bottom active material and the surface active material, respectively. The negative electrode of the stacked battery is prepared by mixing graphite, conductive carbon, thickener, binder, etc., in a specific ratio. In related technologies, negative electrode sheets are mass-produced by double-sided coating. However, insufficient electrolyte contact on one side of the double-sided coating prevents the active material on that side from effectively participating in the reaction, affecting test results and making it unsuitable for direct use in coin cells, stacked batteries, etc.

[0144] In this embodiment, the positive electrode of the stacked battery uses lithium iron phosphate. In the laboratory, lithium iron phosphate with the target particle size is used as the positive electrode active material. The positive electrode of the stacked battery is prepared by mixing the positive electrode active material, conductive carbon, binder, etc. in a certain proportion. In some embodiments, the target particle size can be 1 to 10 micrometers. In related technologies, the positive electrode is made by mass-producing lithium nickel cobalt manganese oxide (LCO) electrodes. However, LCO electrodes have poor structural stability and significant lithium and structural losses, and are generally not used as counter electrodes in graphite material research. When evaluating graphite materials, it is necessary to use the more stable lithium iron phosphate material as the counter electrode to control the lithium intercalation amount.

[0145] In some embodiments, the ratio of negative electrode capacity to positive electrode capacity (CB value) is controlled to be above 1.0 during the fabrication of the stacked battery, for example, between 1.0 and 1.1.

[0146] The negative electrode capacity can be calculated as follows: First, calculate the total mass per unit area minus the current collector mass per unit area, the proportion of the negative electrode active material (graphite), and the theoretical specific capacity of the negative electrode material (graphite); then, multiply the three values ​​to determine the negative electrode capacity. For example, the theoretical specific capacity of graphite is 360 mAh / g.

[0147] The positive electrode capacity can be calculated as follows: First, calculate the total mass per unit area minus the current collector mass per unit area, the proportion of the positive electrode active material (lithium iron phosphate), and the theoretical specific capacity of the positive electrode material; then, multiply the three to determine the positive electrode capacity. For example, the theoretical specific capacity of lithium iron phosphate is 160 mAh / g.

[0148] In some embodiments, the degree of lithium intercalation in the negative electrode of the stacked battery is obtained by charging the stacked battery from a fully discharged state to half of the total discharge capacity of the stacked battery; the total discharge capacity of the stacked battery is obtained by discharging the stacked battery from a fully charged state to a fully discharged state.

[0149] In some implementations, the degree of lithium intercalation of the negative electrode of the stacked battery can be adjusted to 50% based on the total discharge capacity Q value recorded during the process of discharging the stacked battery from a fully charged state to a fully discharged state.

[0150] In some implementations, the lithium intercalation level of the stacked battery can be adjusted to 50% by charging it from a fully discharged state to half of the Q value.

[0151] In this embodiment, the degree of lithium intercalation of the negative electrode of the stacked battery can be accurately adjusted by charging the stacked battery from a fully discharged state to half of its total discharge capacity and by discharging the stacked battery from a fully charged state to a fully discharged state.

[0152] In some embodiments, the first symmetrical cell is assembled in the order of target graphite electrode, target separator, and target graphite electrode; the target separator is made by providing insulating layers on both sides of the separator, for example, the target separator is made by bonding insulating tape to both sides of the separator; the central area of ​​the insulating tape has holes of the target size cut out.

[0153] In some implementations, first cut insulating tape of the same size as the diaphragm (e.g., 45 mm × 55 mm), then use a hole punch to cut holes of the target size in the center area of ​​the cut insulating tape, and then stick the cut insulating tape to both sides of the diaphragm, ensuring that the insulating tape is aligned with the diaphragm, thus obtaining the target diaphragm.

[0154] In some embodiments, the target graphite electrode, the target separator, and the target graphite electrode are assembled in that order. The assembled device is placed in an aluminum-plastic film and an electrolyte is injected. The aluminum-plastic film is then heat-sealed using a hot press and immersed at 45 degrees Celsius for 12 hours. After being fixed by a clamp, the first symmetrical battery is obtained and kept for later use.

[0155] In related technologies, directly assembling coin cells involves the edge region of the separator participating in the lithium insertion / extraction reaction, leading to material loss in the edge region and resulting in differences in lithium consumption, thus causing poor consistency in test results. However, the embodiments of this application employ a specially designed target separator to ensure that the centroid region of the first symmetrical cell is the effective area, and the edge region does not participate in the lithium insertion / extraction reaction, avoiding lithium consumption differences caused by material loss in the edge region and improving test consistency.

[0156] In this embodiment, by attaching insulating tape of the same size to both sides of the diaphragm and cutting holes of the target size in the central area, the effective active area can be precisely controlled to the target size of the holes in the central area of ​​the insulating tape, which greatly improves the consistency and accuracy of the evaluation of the graphite electrode.

[0157] This application provides an electrode evaluation method. Figure 2 This application provides a schematic diagram of the implementation process of an evaluation method for a lithium nickel cobalt manganese oxide electrode, as illustrated in the embodiments of this application. Figure 2 As shown, the method includes the following steps S201 to S203:

[0158] Step S201: Obtain the initial active lithium content of the second symmetric cell to be tested; the working electrode and counter electrode of the second symmetric cell are both made of lithium nickel cobalt manganese oxide.

[0159] Here, the second symmetrical cell is a symmetrical cell where both the positive and negative electrodes use lithium nickel cobalt manganese oxide material, and can also be called a lithium nickel cobalt manganese oxide symmetrical cell. The second symmetrical cell is used to evaluate lithium nickel cobalt manganese oxide material.

[0160] The initial active lithium content is the total amount of lithium ions in the second symmetric cell to be tested that can participate in the electrochemical reaction before the test.

[0161] In some embodiments, the electrode of the negative electrode channel in the second symmetrical battery connected to the charging device is used as the working electrode; correspondingly, the electrode of the positive electrode channel in the second symmetrical battery connected to the charging device is used as the counter electrode.

[0162] In some embodiments, the degree of lithium intercalation of the lithium nickel cobalt manganese oxide electrode of the second symmetric cell is pre-adjusted in the same way as the degree of lithium intercalation of the graphite electrode.

[0163] In some implementations, to study the performance of lithium nickel cobalt manganese oxide (LCO) materials, a second symmetric cell, in which both the working and counter electrodes are made of LCO, can be cycle-tested. Since both the working and counter electrodes of the second symmetric cell are made of LCO, lithium loss occurs at both electrodes during cycle testing, thus accelerating the evaluation of the LCO electrode.

[0164] In some embodiments, lithium nickel cobalt manganese oxide is a type of ternary material, which may also include lithium nickel cobalt aluminum oxide. Symmetrical cells can also be prepared using lithium nickel cobalt aluminum oxide for evaluating the material.

[0165] Step S202: Perform multiple charge-discharge processes on the second symmetrical battery to obtain the remaining active lithium content;

[0166] Here, the remaining active lithium content can characterize the amount of lithium ions that can still participate in electrochemical reactions after the charging and discharging process of the second symmetric battery.

[0167] In some embodiments, during each charge-discharge process of the second symmetric battery, when the working electrode and counter electrode are at a high potential, the solid electrolyte interface film on the surface of lithium nickel cobalt manganese oxide undergoes electrolysis, and active lithium is consumed to repair the solid electrolyte interface film, thereby accelerating the consumption of active lithium and thus accelerating the evaluation of the lithium nickel cobalt manganese oxide electrode of the second symmetric battery.

[0168] In some implementations, with the same initial amount of active lithium, the amount of remaining active lithium can reflect the lithium consumption of the lithium nickel cobalt manganese oxide electrode, thereby enabling the evaluation of the lithium nickel cobalt manganese oxide material.

[0169] Step S203: Evaluate the lithium nickel cobalt manganese oxide electrode of the second symmetric cell based on the initial active lithium content and the remaining active lithium content;

[0170] In some implementations, the evaluation method for the lithium nickel cobalt manganese oxide electrode of the second symmetric cell is consistent with the evaluation method for the graphite electrode.

[0171] Each of the charging and discharging processes includes the following steps S211 and S212:

[0172] Step S211: After charging the second symmetrical battery to a preset fifth voltage using a preset first charging rate, perform constant voltage charging on the second symmetrical battery at the fifth voltage. When the charging current is less than or equal to the current corresponding to the preset second charging rate, the charging process is completed.

[0173] Here, the first charging rate is the charging rate that enables rapid lithium removal from the counter electrode, and the first charging rate can be in the range of 0.33C to 1.0C. The second charging rate is the charging rate that enables continuous decomposition and repair of the solid electrolyte interface film of the counter electrode, and the second charging rate can be in the range of 0.01C to 0.05C.

[0174] The fifth voltage is the voltage at which lithium removal is completed at the counter electrode. The value of the fifth voltage may be between 1.3V and 2.0V.

[0175] In practice, the second symmetrical battery is charged at a preset first charging rate to rapidly delithigate the counter electrode. Delithiation of the counter electrode is completed when the second symmetrical battery is charged to a fifth voltage. To further accelerate the lithium-ion consumption rate of the second symmetrical battery, constant-voltage charging continues at the fifth voltage, causing electrolytic decomposition of the solid electrolyte interface film on the counter electrode. This continues until the charging current is less than or equal to the current corresponding to the preset second charging rate, at which point the electrolytic decomposition of the solid electrolyte interface film on the counter electrode is complete. Thus, the second symmetrical battery completes one charging cycle.

[0176] Step S212: After charging is completed, the second symmetrical battery is discharged to a sixth voltage using a preset first discharge rate. Then, the second symmetrical battery is subjected to constant voltage discharge at the sixth voltage. The discharge process is completed when the discharge current is less than or equal to the current corresponding to the preset second discharge rate.

[0177] Here, the first discharge rate is the charging rate that enables rapid lithium removal from the working electrode, and the first discharge rate can be in the range of 0.33C to 1.0C. The second discharge rate is the discharge rate that enables continuous decomposition and repair of the solid electrolyte interface film of the working electrode, and the second discharge rate can be in the range of 0.01C to 0.05C.

[0178] The sixth voltage is the voltage at which the working electrode completes delithiation. The sixth voltage is the negative fifth voltage.

[0179] During implementation, the second symmetrical battery is discharged at a preset first discharge rate, causing rapid lithium removal from the working electrode. Lithium removal is completed at the working electrode when the second symmetrical battery is discharged to a sixth voltage. To further accelerate the lithium-ion consumption rate of the second symmetrical battery, constant-voltage discharge is continued at the sixth voltage, causing electrolytic decomposition of the solid electrolyte interface film at the working electrode. This continues until the discharge current is less than or equal to the current corresponding to the preset second discharge rate, at which point the electrolytic decomposition of the solid electrolyte interface film at the working electrode is complete. Thus, the second symmetrical battery completes one charge-discharge cycle.

[0180] In this embodiment, firstly, both the working electrode and the counter electrode are made of lithium nickel cobalt manganese oxide. By controlling the second symmetrical battery through multiple charge-discharge processes, both the working electrode and the counter electrode can experience lithium loss, thereby accelerating the evaluation speed of the lithium nickel cobalt manganese oxide electrode. Secondly, in each charge-discharge control process, the second symmetrical battery is charged to a fifth voltage using a larger first charge rate, allowing the counter electrode to quickly complete lithium delithiation. The battery is then charged at a constant voltage at the fifth voltage, causing the solid electrolyte interface film of the counter electrode to undergo electrolytic decomposition, accelerating the lithium-ion consumption rate. This accelerates the lithium-ion consumption rate while simultaneously speeding up the first charge process. Then, the second symmetrical battery is discharged to a sixth voltage using a larger first discharge rate, allowing the working electrode to quickly complete lithium delithiation. The battery is then discharged at a constant voltage at the sixth voltage, causing the solid electrolyte interface film of the working electrode to undergo electrolytic decomposition, further accelerating the lithium-ion consumption rate. This accelerates the lithium-ion consumption rate while simultaneously speeding up the first discharge process. These processes accelerate the evaluation speed of the lithium nickel cobalt manganese oxide electrode.

[0181] The following describes the application of the embodiments of this application in a real-world scenario.

[0182] Lithium-ion batteries experience a slow decline in lifespan during use (and aging-related degradation). For lithium-ion systems in related technologies (lithium iron phosphate, lithium nickel cobalt manganese oxide, sodium batteries, solid-state batteries, etc.), the main reason for lifespan degradation is the instability of the solid electrolyte interface film on the graphite surface of the negative electrode. During battery charging and discharging, structural damage occurs, and the repair process (the solid electrolyte interface film repeatedly breaks and regenerates, accelerating lithium consumption) leads to the loss of active lithium in the lithium-ion battery, resulting in a decrease in the battery's lifespan.

[0183] Based on the above description, the best possible implementation method for quickly evaluating the lifespan of lithium-ion batteries is to conduct rapid tests on the lithium loss of their negative electrode material (i.e., graphite material).

[0184] This application provides an accelerated testing method for graphite electrodes based on a first symmetric cell. The solution differs from related technologies in the following ways: 1) In related technologies, the first symmetric cell is used for impedance detection, not for active lithium testing; 2) This application provides a feasible cycling strategy for the first symmetric cell, and based on this, by amplifying the cutoff voltage of the first symmetric cell, the solid electrolyte interface film of the graphite electrode undergoes electrolytic degradation; 3) Repeated charge-discharge operations are performed on the two electrodes of the first symmetric cell, and both electrodes experience an accelerated process. Compared to a full cell, both electrodes of the first symmetric cell are made of graphite, resulting in lithium loss. Through these differences, the solution of this application can achieve the goal of rapidly evaluating the lithium consumption of graphite materials.

[0185] The evaluation of the graphite electrode of the first symmetric cell under test can include the following three stages:

[0186] In the first stage, the degree of lithium intercalation in the graphite electrode is adjusted to obtain the target graphite electrode.

[0187] Phase Two: A test cell (corresponding to the first symmetric cell in the aforementioned embodiment) is prepared using the target graphite electrode.

[0188] Phase 3 involves conducting multiple charge-discharge cycle tests on the prepared test battery to evaluate the graphite electrode of the test battery.

[0189] The three stages are described below:

[0190] For stage one, the lithium intercalation state of the graphite electrode is adjusted to obtain the target graphite electrode;

[0191] In this embodiment, a graphite electrode with a preset lithium intercalation degree is required to prepare a first symmetrical cell as an accelerated testing cell. Therefore, it is necessary to first obtain the target graphite electrode. In this example, the target graphite electrode is obtained by disassembling it from the prepared stacked cell. The stage of obtaining the target graphite electrode includes the following three processes:

[0192] Step 1: Prepare the negative electrode of the stacked battery;

[0193] Step 2: Preparation of the positive electrode for the stacked battery;

[0194] In step 3, the above positive and negative electrodes are used to fabricate a stacked battery according to the standard process, and the target graphite electrode is obtained through the stacked battery.

[0195] Process 1, preparing the negative electrode of the stacked battery, includes the following steps:

[0196] Step 11: Take graphite 1 and graphite 2 with different particle sizes as the bottom active material and the surface active material.

[0197] In some implementations, smaller-particle-size graphite can be used as the surface active material, and larger-particle-size graphite can be used as the bottom active material.

[0198] Step 12: Take graphite, conductive carbon, thickener, and binder in a mass ratio of 96:1:1.5:1.5, and then mix them.

[0199] Graphite is the main active material in the negative electrode, responsible for storing and releasing lithium ions; conductive carbon forms a conductive network in the negative electrode, improving the conductivity of the electrode and buffering the volume change of the active material during charging and discharging; thickener can improve the viscosity and stability of the electrode slurry and prevent solid particles from settling; binder can adhere the active material to the current collector and maintain the stability of the electrode's mechanical structure and electrochemical performance.

[0200] Step 13: Add an appropriate amount of deionized water and stir for 15 minutes in a vacuum mixer to obtain the base coat A and the top coat B.

[0201] Deionized water, as a solvent, can dissolve the thickener to form a viscous solution, increasing the viscosity of the slurry and preventing solid particles from settling.

[0202] Step 14: Apply the base coat A evenly to both surfaces of the negative electrode current collector (such as copper foil) and transfer it to an oven to dry.

[0203] The current collector gathers and conducts electrons generated by the electrochemical reaction of the negative electrode active material (such as graphite or silicon) to the external circuit. Furthermore, it acts as a carrier for the negative electrode active material, supporting it and absorbing the volume change stress during charging and discharging, thus preventing damage to the electrode structure.

[0204] Step 15: Apply the topcoat B evenly over the surface of the basecoat A, and then transfer it to the oven for drying.

[0205] Step 16: Continue rolling the dried electrode sheets to obtain the negative electrode of the stacked battery, which is then kept for later use.

[0206] In some embodiments, the cathode material used in the stacked battery is lithium iron phosphate, which is prepared in the laboratory using lithium iron phosphate powder with a target particle size. In some embodiments, the target particle size can be 1 to 10 micrometers.

[0207] Step 2, preparing the positive electrode of the stacked battery, includes the following steps:

[0208] Step 21: Take the positive electrode active material (such as lithium iron phosphate) with the target particle size.

[0209] Step 22: Take a positive electrode active material: conductive carbon: binder with a mass ratio of 98:1:1 and add it to the feed.

[0210] Step 23: Add N-methylpyrrolidone (NMP) solvent and stir under vacuum for 15 minutes to obtain positive electrode slurry;

[0211] Step 24: Apply the positive electrode slurry evenly to both sides of the positive electrode current collector (such as aluminum foil) and transfer it to an oven to dry;

[0212] Step 25: Roll the dried electrode sheets to obtain the positive electrode of the stacked battery, which is then kept for later use.

[0213] In the fabrication of stacked batteries, the ratio of negative electrode capacity to positive electrode capacity (CB ratio) is controlled to be above 1.0, for example, between 1.0 and 1.1. The negative electrode capacity is determined by subtracting the mass of the current collector per unit area from the total mass per unit area, the proportion of the negative electrode active material (graphite), and the theoretical specific capacity of the negative electrode material (graphite). For example, the theoretical specific capacity of graphite is 360 mAh / g. The positive electrode capacity is determined by subtracting the mass of the current collector per unit area from the total mass per unit area, the proportion of the positive electrode active material (lithium iron phosphate), and the theoretical specific capacity of the positive electrode material. For example, the theoretical specific capacity of lithium iron phosphate is 160 mAh / g.

[0214] Step 3 involves fabricating a stacked battery using the aforementioned positive and negative electrodes according to a standard procedure, and further obtaining the target graphite electrode through the stacked battery, including:

[0215] Step 31: Fabricate a stacked battery using the above positive and negative electrodes according to the standard process, and follow the standard process of baking (110 degrees Celsius, 12 hours), liquid injection, immersion (45 degrees Celsius, 20 hours), and clamping.

[0216] Step 32: Formation of graphite electrodes.

[0217] Step 33: Obtain the target graphite electrode through stacked cells;

[0218] During the initial charge-discharge process of the stacked battery, after resting for 10 minutes, it was charged at 0.1C and the highest permissible voltage; after resting for another 10 minutes, it was discharged at 0.1C and the lowest permissible voltage; the discharge capacity of the above discharge process was recorded as the Q value; after resting for another 10 minutes, it was charged at 0.1C. Based on the recorded Q value, the lithium intercalation degree of the graphite electrode was adjusted to 50%, thus obtaining the stacked battery. The stacked battery was disassembled in a non-air environment (glove box) to obtain the target graphite electrode with a lithium intercalation degree of 50%.

[0219] Two stacked cells were prepared according to this process. The negative electrodes of the two stacked cells were removed to obtain two graphite electrodes with a lithium intercalation degree of 50%. One graphite electrode served as the working electrode of the first symmetrical cell, and the other graphite electrode served as the counter electrode of the first symmetrical cell.

[0220] It should be noted that since the degree of lithium intercalation of the graphite electrode can be adjusted based on the discharge capacity Q, the degree of lithium intercalation of the target graphite electrode can be set according to requirements, for example, set to x.

[0221] For Phase Two, the fabrication of a test cell (corresponding to the first symmetric cell in the aforementioned embodiments) using a target graphite electrode includes:

[0222] Take the target graphite electrode obtained from the above disassembly and fabricate a special diaphragm (corresponding to the target diaphragm in the previous embodiment). Assemble the target graphite electrode, target diaphragm, and target graphite electrode in that order, as follows: Figure 3 As shown, insulating tape 22 is adhered to both sides of the target diaphragm 21, and negative electrode plates 23 are on both sides of the target diaphragm. The assembled device is placed in the aluminum-plastic film and electrolyte is injected. The aluminum-plastic film is heat-sealed using a hot press and then immersed at 45 degrees Celsius for 12 hours. After being fixed by the upper clamp, the test battery can be obtained and kept for later use.

[0223] The special diaphragm can be made through the following process: First, cut insulating tape to the same size as the diaphragm (e.g., 45 mm × 55 mm). Then, using a hole punch, cut holes of the target size in the center area of ​​the cut insulating tape. Adhere the cut insulating tape to both sides of the diaphragm, ensuring that the insulating tape is aligned with the diaphragm, and you will obtain the special diaphragm.

[0224] For Phase 3, the prepared test battery was subjected to multiple charge-discharge cycle tests to evaluate the graphite electrode of the test battery.

[0225] The electrode potential of graphite is strongly correlated with the degree of lithium intercalation, such as... Figure 4 As shown, the normal operating potential of graphite is between 0 and 0.3V. The higher the electrode potential of graphite, the lower the degree of lithium intercalation; the lower the electrode potential, the higher the degree of lithium intercalation. When the electrode potential of graphite is high (>1.0V), it will cause electrodecomposition of the solid electrolyte interface film on the graphite surface, which will then consume active lithium for repair. This process accelerates the consumption of active lithium. By accelerating the process in this way, the lithium consumption performance of graphite can be quickly determined.

[0226] Based on the above description, the following test plan was set up:

[0227] Step 41, let it stand for 5 minutes;

[0228] Two graphite electrodes are connected to the two ends of the charging and discharging device, with the one connected to the negative electrode channel of the charging and discharging device being the working electrode and the other being the counter electrode.

[0229] Step 42: Charge the first symmetrical battery to be tested to the first voltage using the first charging rate;

[0230] Here, the first charging rate is selected from 0.33 to 1.0C, and the first voltage can be selected from +0.3 to +0.5 volts. The initial active lithium amount is related to the preset degree of lithium intercalation. In this embodiment, two graphite electrodes with a lithium intercalation degree of 50% can be used as the working electrode and the counter electrode, respectively. Since the two electrodes each have the same charge, the total initial active lithium amount needs to be multiplied by 2. The first voltage is between +0.3V and +0.5V.

[0231] In this embodiment of the application, the first charging rate is a higher rate than the second charging rate. The first symmetrical battery is charged to 0.3V using a higher rate. During this process, the counter electrode continuously delithiates, and the potential increases; the working electrode continuously inserts lithium, and the potential decreases.

[0232] Step 43, let it stand for 5 minutes;

[0233] Step 44: Charge the first symmetrical battery from the first voltage to the second voltage using the second charging rate;

[0234] Electrolytic decomposition of the solid electrolyte interface film at the electrode under the second voltage.

[0235] The second voltage is the cutoff voltage of the first symmetrical battery, which can be +2.5V. The second charging rate is lower than the first charging rate, ranging from 0.01 to 0.05C.

[0236] Step 45: Let it sit for 5 minutes;

[0237] Step 46: Discharge the first symmetrical battery to the third voltage using a first discharge rate of 1.0C;

[0238] During discharge, lithium insertion begins at the counter electrode, and lithium extraction begins at the working electrode. When the discharge reaches the third voltage, lithium extraction is complete at the working electrode. The third voltage can be a negative first voltage, for example, -0.4V, and the fourth voltage can be a negative second voltage, for example, -2.5V.

[0239] Step 47: Let it sit for 5 minutes;

[0240] Step 48: Discharge the first symmetrical battery from the third voltage to the fourth voltage using the second discharge rate;

[0241] Here, the second discharge rate can be 0.04C, and the fourth voltage is the cutoff voltage of the first symmetrical cell, which can be -2.5V. In this embodiment, the first symmetrical cell is discharged at a low rate of 0.04C, causing electrolytic decomposition of the solid electrolyte interface film at the working electrode, discharging to -2.5V.

[0242] Step 49, repeat steps 41 to 48.

[0243] In each cycle, the solid electrolyte interface membrane underwent electrolysis on both the counter electrode and the working electrode, resulting in double the lithium consumption loss.

[0244] The sum of the discharge capacities from steps 46 and 48 is determined as the total remaining active lithium. Normalization with the initial active lithium design yields the accelerated lithium consumption data for this graphite material. This application's solution can rapidly amplify differences in lithium consumption through short-term cycle testing, such as... Figure 5 As shown, through two sets of experiments, only 30 cycles were required to identify that the lithium consumption performance of graphite B was inferior to that of graphite A.

[0245] As can be seen from the above test scheme, initially, since both electrodes of the first symmetrical battery have the same degree of lithium intercalation, and the potentials of the working electrode and the counter electrode are the same, the initial voltage of the first symmetrical battery is close to 0V. Subsequently, the first symmetrical battery is charged, and the degree of lithium intercalation on the working electrode (the electrode connected to the negative electrode channel of the charging and discharging device) increases, while the degree of lithium intercalation on the counter electrode (the electrode connected to the positive electrode channel of the charging and discharging device) decreases. When the internal lithium intercalation on the counter electrode is completely removed, the voltage of the first symmetrical battery reaches the first voltage. Continuing to charge the first symmetrical battery causes the solid electrolyte interface film on the counter electrode to decompose until the second voltage is reached.

[0246] In addition to evaluating different types of graphite, this application embodiment can also evaluate the cycle lithium consumption of the same graphite paired with different electrolytes, thus achieving the effect of evaluating the lithium consumption performance of the electrolyte. The electrolyte directly affects the film formation effect of the solid electrolyte interface film of graphite, that is, the repair effect of the solid electrolyte interface film during use. Therefore, the lithium consumption performance of the same graphite paired with different electrolytes will also have certain differences. For example... Figure 6 As shown, by performing cycle tests on multiple identical graphite cells with different electrolytes fabricated according to the present application, it can be identified that the performance of electrolyte B is inferior to that of electrolyte A after only 30 cycles.

[0247] This application's embodiments can also evaluate ternary materials (such as lithium nickel cobalt manganese oxide), where the electrode potential is strongly correlated with the degree of lithium intercalation. Figure 7As shown, as the degree of lithium intercalation in the lithium nickel cobalt manganese oxide electrode decreases, the lithium-to-lithium potential of the lithium nickel cobalt manganese oxide electrode increases from the minimum potential (Vmin) to the maximum potential (Vmax). In the lithium nickel cobalt manganese oxide symmetrical battery (corresponding to the second symmetrical battery in the aforementioned embodiment), during charging and discharging, the degree of lithium intercalation in one electrode increases, and the lithium-to-lithium potential decreases to Vmin; the degree of lithium intercalation in the other electrode decreases, and the lithium-to-lithium potential increases to Vmax. Since the degree of lithium intercalation in the two electrodes of the symmetrical battery is the same, the initial voltage of the lithium nickel cobalt manganese oxide symmetrical battery is 0V, and after the cycle starts, the cutoff voltages are ±(Vmax-Vmin).

[0248] Preparing a lithium nickel cobalt manganese oxide symmetric cell for testing may include the following steps:

[0249] Step 51: Adjust the lithium intercalation state of the lithium nickel cobalt manganese oxide electrode to obtain the target lithium nickel cobalt manganese oxide electrode.

[0250] First, lithium nickel cobalt manganese oxide (LCO) electrodes and graphite electrodes for a lithium nickel cobalt manganese oxide-graphite stacked battery are prepared. Second, the LCO and graphite electrodes are fabricated into a lithium nickel cobalt manganese oxide-graphite stacked battery according to a standard process. Finally, the degree of lithium intercalation of the LCO electrode in the lithium nickel cobalt manganese oxide-graphite stacked battery is adjusted, and the LCO electrode with the adjusted degree of lithium intercalation is disassembled to obtain the target lithium nickel cobalt manganese oxide electrode.

[0251] Step 52: Prepare a lithium nickel cobalt manganese oxide symmetric cell using the target lithium nickel cobalt manganese oxide electrode.

[0252] The method for assembling a lithium nickel cobalt manganese oxide symmetric cell using two target lithium nickel cobalt manganese oxide electrodes is consistent with the method for fabricating a graphite symmetric cell in this application.

[0253] This application embodiment can also evaluate ternary materials (such as lithium nickel cobalt manganese oxide). First, a lithium nickel cobalt manganese oxide symmetric battery for testing is prepared. The working electrode and counter electrode of the lithium nickel cobalt manganese oxide symmetric battery are both made of lithium nickel cobalt manganese oxide material, and the lithium intercalation degree of both the working electrode and the counter electrode is 50%. The method for preparing the target lithium nickel cobalt manganese oxide electrode with a lithium intercalation degree of 50% is consistent with the method for preparing the target graphite electrode in this application. When evaluating the target lithium nickel cobalt manganese oxide electrode, graphite material is used as the counter electrode to adjust the lithium intercalation degree of the lithium nickel cobalt manganese oxide electrode to obtain the target lithium nickel cobalt manganese oxide electrode.

[0254] The fabricated lithium nickel cobalt manganese oxide symmetric battery was subjected to the following cycle tests, including the following steps:

[0255] Step 61, let it stand for 2 minutes;

[0256] The two electrodes are connected to the positive and negative channels of the charging and discharging device, respectively. By default, one is the working electrode and the other is the counter electrode.

[0257] Step 62: Charge to the positive fifth voltage (Vmax-Vmin) using the first charging rate of 1.0C.

[0258] In this system, the first charging rate is the maximum charging rate, which can range from 0.33 to 1.0C. Vmax is the upper limit of the lithium-ion potential of the ternary material, typically between 4.3V and 4.5V. Vmin is the lower limit of the lithium-ion potential, typically between 2.5V and 3.0V. Therefore, it can be assumed that (Vmax - Vmin) is likely between 1.3V and 2.0V. A larger (Vmax - Vmin) value, the closer it is to the limit, resulting in a stronger acceleration effect; a smaller (Vmax - Vmin) value, closer to the normal operating potential range (typically 2.7V to 4.2V), results in a weaker acceleration effect.

[0259] Step 63: Perform constant voltage charging on the nickel-cobalt-manganese lithium symmetric battery at the fifth voltage (Vmax-Vmin). Stop constant voltage charging when the charging current is less than or equal to the current corresponding to the second charging rate.

[0260] The value of the second charging rate can be between 0.01 and 0.05C;

[0261] Here, the lithium nickel cobalt manganese oxide symmetric battery is first charged at the first charging rate until the counter electrode completes delithiation. Then, the lithium nickel cobalt manganese oxide symmetric battery is charged at the fifth voltage under constant voltage until the charging current is less than or equal to the current corresponding to the second charging rate. At this point, the charging is stopped, so that the counter electrode completes the electrolytic decomposition of the solid electrolyte interface membrane.

[0262] Step 64: Let it sit for 5 minutes;

[0263] Step 65: Discharge to the sixth voltage (negative (Vmax-Vmin)) using the first discharge rate.

[0264] Step 66: Perform constant voltage discharge on the nickel-cobalt-manganese lithium symmetric battery at the sixth voltage. Stop discharging when the discharge current is less than or equal to the current corresponding to the second discharge rate.

[0265] Here, the lithium nickel cobalt manganese oxide symmetric battery is discharged at a first discharge rate of 0.33 to 1.0C until the working electrode completes delithiation. The lithium nickel cobalt manganese oxide symmetric battery is then discharged at a constant voltage at a sixth voltage. When the discharge current is less than or equal to the current corresponding to the second discharge rate (0.04C), the discharge is stopped, so that the working electrode completes the electrolytic decomposition of the solid electrolyte interface film.

[0266] Step 67, repeat steps 61 to 66.

[0267] Record the sum of the capacities of steps 65 and 66 in each cycle as the total amount of remaining active lithium.

[0268] This application's solution can rapidly amplify the lithium consumption difference of nickel-cobalt-manganese symmetric batteries through short-term cycle testing, such as... Figure 8 As shown, it can be identified that lithium nickel cobalt manganese oxide B has inferior lithium consumption performance compared to lithium nickel cobalt manganese oxide A after only 30 cycles.

[0269] It should be noted that the description of the various embodiments above tends to emphasize the differences between the various embodiments, while the similarities or similarities can be referred to each other.

[0270] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. It should be understood that in the various embodiments of this application, the sequence numbers of the above steps / processes do not imply a sequential order of execution; the execution order of each step / process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. The sequence numbers of the above embodiments of this application are merely descriptive and do not represent the superiority or inferiority of the embodiments.

[0271] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0272] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways.

[0273] The above description is merely an embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method of evaluating an electrode, characterized by, The method comprises: obtaining an initial active lithium amount of a first symmetrical battery to be tested; the materials of the working electrode and the counter electrode of the first symmetrical battery are both graphite; controlling the first symmetrical battery to undergo a plurality of charging and discharging processes to obtain a residual active lithium amount; based on the initial active lithium amount and the residual active lithium amount, evaluating the graphite electrode of the first symmetrical battery; wherein each of the charging and discharging processes comprises: after charging the first symmetrical battery to a preset first voltage at a preset first charging rate, charging the first symmetrical battery to a second voltage at a preset second charging rate to complete the charging process; wherein the counter electrode completes delithiation at the first voltage; and the solid electrolyte interface film of the counter electrode completes electrical decomposition at the second voltage; after the charging is completed, discharging the first symmetrical battery to a third voltage at a preset first discharging rate, and then discharging the first symmetrical battery to a fourth voltage at a preset second discharging rate; wherein the working electrode completes delithiation at the third voltage; and the solid electrolyte interface film of the working electrode completes electrical decomposition at the fourth voltage; wherein the first discharging rate and the first charging rate are both within a range of 0.33C to 1.0C, and the second charging rate and the second discharging rate are both within a range of 0.01C to 0.05C.

2. The method of claim 1, wherein, Each of the charging and discharging processes further comprises: after charging the first symmetrical battery to the first voltage at the first charging rate, performing a first-stage standing; after sequentially completing the first-stage standing and charging the first symmetrical battery to the second voltage at the second charging rate, performing a second-stage standing; after sequentially completing the second-stage standing and discharging the first symmetrical battery to the third voltage at the first discharging rate, performing a third-stage standing; after completing the third-stage standing, discharging the first symmetrical battery to the fourth voltage at the second discharging rate.

3. The method of claim 1, wherein, Based on the initial active lithium amount and the residual active lithium amount, evaluating the graphite electrode of the first symmetrical battery comprises: determining, based on the ratio of the residual active lithium amount to the initial active lithium amount in each of the charging and discharging processes, the active lithium residual proportion in each of the charging and discharging processes; based on the active lithium residual proportion in each of the charging and discharging processes, evaluating the graphite electrode of the first symmetrical battery.

4. The method of claim 1, wherein, Based on the initial active lithium amount and the residual active lithium amount, evaluating the graphite electrode of the first symmetrical battery comprises: determining, based on the difference between the initial active lithium amount and the residual active lithium amount in each of the charging and discharging processes, the lithium consumption amount in each of the charging and discharging processes; based on the lithium consumption amount in each of the charging and discharging processes, evaluating the graphite electrode of the first symmetrical battery.

5. The method according to any one of claims 1 to 4, characterized in that, The method further comprises: determining the initial active lithium amount as the sum of the lithium intercalation amount of the working electrode and the lithium intercalation amount of the counter electrode of the first symmetrical battery.

6. The method according to any one of claims 1 to 4, characterized in that, The method further comprises: Obtaining initial active lithium amounts of a group of first symmetric batteries to be tested; parameters of graphite materials of working electrodes and counter electrodes of each of the first symmetric batteries in the group of first symmetric batteries are different; Controlling, for each of the first symmetric batteries in the group of first symmetric batteries, a plurality of charging and discharging processes to obtain respective residual active lithium amounts of each of the first symmetric batteries; Based on the initial active lithium amounts of each of the first symmetric batteries and the respective residual active lithium amounts of each of the first symmetric batteries, lithium consumption results of the graphite electrodes in each of the first symmetric batteries are determined; based on the lithium consumption results of the graphite electrodes in each of the first symmetric batteries, a first symmetric battery in which the graphite material in each of the first symmetric batteries meets a lithium consumption performance requirement is determined as a first symmetric battery that meets a test requirement.

7. The method according to any one of claims 1 to 4, characterized in that, The method further comprises: Obtaining initial active lithium amounts of a group of first symmetric batteries to be tested; parameters of graphite materials of working electrodes and counter electrodes of each of the first symmetric batteries in the group of first symmetric batteries are different; Controlling, for each of the first symmetric batteries in the group of first symmetric batteries, a plurality of charging and discharging processes to obtain respective residual active lithium amounts of each of the first symmetric batteries; Based on the initial active lithium amounts of each of the first symmetric batteries and the respective residual active lithium amounts of each of the first symmetric batteries, lithium consumption results of the graphite electrodes in each of the first symmetric batteries are determined; based on the lithium consumption results of the graphite electrodes in each of the first symmetric batteries, a first symmetric battery in which the graphite material in each of the first symmetric batteries meets a lithium consumption performance requirement is determined as a first symmetric battery that meets a test requirement.

8. The method according to any one of claims 1 to 4, characterized in that, The number of the charging and discharging processes is in a range of 10 to 100.

9. The method according to any one of claims 1 to 4, characterized in that, The first symmetric battery is made of two target graphite electrodes with the same lithium intercalation degree; The target graphite electrode is obtained by disassembling a negative electrode of a laminated battery; the material of the negative electrode of the laminated battery is graphite material; and the material of a positive electrode of the laminated battery is lithium iron phosphate.

10. The method of claim 9, wherein, The lithium intercalation degree of the negative electrode of the laminated battery is obtained by charging the laminated battery from a fully discharged state to half of a total discharge capacity of the laminated battery; and the total discharge capacity of the laminated battery is obtained by discharging the laminated battery from a fully charged state to a fully discharged state.

11. The method of claim 9, wherein, The first symmetric battery is assembled in the order of a target graphite electrode, a target separator and the target graphite electrode; The target separator is made by arranging insulating layers on both sides of the separator.

12. A method of evaluating an electrode, characterized by, The method comprises: Obtaining an initial active lithium amount of a second symmetric battery to be tested; the materials of working electrodes and counter electrodes of the second symmetric battery are both lithium nickel cobalt manganese oxide; Controlling a plurality of charging and discharging processes of the second symmetric battery to obtain a residual active lithium amount; Based on the initial active lithium amount and the residual active lithium amount, evaluating a lithium nickel cobalt manganese oxide electrode of the second symmetric battery; Each of the charging and discharging processes comprises: After charging the second symmetrical battery to a preset fifth voltage at a preset first charging rate, the second symmetrical battery is charged at the fifth voltage, and the charging process is completed when the charging current is less than or equal to a current corresponding to a preset second charging rate; After the charging is completed, the second symmetrical battery is discharged to a sixth voltage at a preset first discharging rate, and the discharging process is completed when the discharging current is less than or equal to a current corresponding to a preset second discharging rate. The first discharging rate and the first charging rate are both in a range of 0.33C to 1.0C, and the second charging rate and the second discharging rate are both in a range of 0.01C to 0.05C.

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