A monolithic battery and a method of screening battery materials

Abstract

The application provides a monolithic battery and a screening method of battery materials, wherein the monolithic battery comprises a positive electrode sheet, a negative electrode sheet and a reference electrode, the reference electrode is arranged between the positive electrode sheet and the negative electrode sheet, and a diaphragm is arranged between the positive electrode sheet and the reference electrode and between the negative electrode sheet and the reference electrode, so that the reference electrode is separated from the positive electrode sheet and the negative electrode sheet. In the application, the three-electrode monolithic battery has the characteristics of less material and short battery manufacturing time, which is beneficial to providing a simple and safe test means for rapid screening of battery materials, and thus the test efficiency of the operator is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a monolithic battery and a battery material screening method. BACKGROUND

[0002] Lithium ion batteries have the advantages of small volume, light weight, no memory effect, high energy density and cycle life, and are widely used in mobile electronic devices, new energy vehicles, aerospace, energy storage and other fields.

[0003] At present, the battery with poor rate performance is prone to cause the battery performance to decay quickly during the fast charging and discharging process, and in severe cases, it can cause internal short circuit of the battery and fire explosion. In the prior art, a third electrode is often provided for the soft package battery to test the negative electrode potential, and the risk of lithium precipitation of the negative electrode is detected to analyze the rate performance of the battery. However, due to the complex manufacturing process (such as hot pressing) of the soft package battery, the use of materials is more and the manufacturing time is longer, which results in high time cost and manufacturing cost when testing the battery, thereby reducing the test efficiency of the operator. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a monolithic battery and a battery material screening method. Since the three-electrode monolithic battery has the characteristics of less use of materials and shorter battery manufacturing time, it is beneficial to provide a simple and safe test means for rapid screening of battery materials, thereby improving the test efficiency of the operator.

[0005] In a first aspect, the embodiments of the present application provide a monolithic battery, which comprises: a positive electrode sheet, a negative electrode sheet and a reference electrode; the reference electrode is arranged between the positive electrode sheet and the negative electrode sheet, and a separator is arranged between the positive electrode sheet and the reference electrode and between the negative electrode sheet and the reference electrode, so that the reference electrode is separated from the positive electrode sheet and the negative electrode sheet.

[0006] In an optional embodiment of the present application, the reference electrode is obtained by plating lithium on a copper wire.

[0007] In an optional embodiment of the present application, the separator material is polyethylene or polypropylene.

[0008] In a second aspect, the embodiments of the present application also provide a battery material screening method, which is applied to the monolithic battery as described above, and the method comprises:

[0009] Collecting a voltage data set of the monolithic battery when the monolithic battery is charged and discharged at different current rates within a preset time period;

[0010] Determining the state of charge of the monolithic battery according to the current rates within the preset time period;

[0011] determining, according to the voltage data set and the state of charge of the single piece of battery, a voltage change curve of the voltage of the single piece of battery varying with the state of charge at different rates;

[0012] determining, by analyzing the voltage change curve, the battery material with the rate performance meeting the preset requirement.

[0013] In an optional embodiment of the present application, the voltage value in the voltage data set includes one of the following: a first voltage value between the positive electrode piece and the negative electrode piece, a second voltage value between the negative electrode piece and the reference electrode, and a third voltage value between the positive electrode piece and the reference electrode.

[0014] In an optional embodiment of the present application, the battery material includes one of the following: electrolyte material, positive electrode material, and negative electrode material.

[0015] In an optional embodiment of the present application, when the voltage data set includes the second voltage value between the negative electrode piece and the reference electrode, and the battery material includes the negative electrode material, the step of determining the battery material with the rate performance meeting the preset requirement by analyzing the voltage change curve includes:

[0016] obtaining a specified state of charge value;

[0017] obtaining, according to the analysis of the voltage change curve, a to-be-measured second voltage value of the single piece of battery at different rates corresponding to the specified state of charge value;

[0018] If it is detected that the to-be-measured second voltage value at all rates is greater than a preset voltage threshold, it is determined that the current negative electrode material of the single piece of battery is the battery material with the rate performance meeting the preset requirement.

[0019] In an optional embodiment of the present application, when the voltage data set includes the third voltage value between the positive electrode piece and the reference electrode, and the battery material includes the positive electrode material, the step of determining the battery material with the rate performance meeting the preset requirement by analyzing the voltage change curve includes:

[0020] determining, according to the voltage change curve, a specified third voltage value and a voltage change amplitude corresponding to the specified third voltage value;

[0021] If it is detected that the voltage change amplitude is within a preset amplitude range, it is determined that the current positive electrode material of the single piece of battery is the battery material with the rate performance meeting the preset requirement.

[0022] In an optional embodiment of the present application, the method further includes:

[0023] acquire a first ohmic impedance, a first film forming impedance and a first charge transfer impedance of a positive electrode sheet in the single sheet battery, and a second ohmic impedance, a second film forming impedance and a second charge transfer impedance of a negative electrode sheet;

[0024] if it is detected that the first ohmic impedance, the first film forming impedance and the first charge transfer impedance are all within the corresponding first preset impedance range, it is determined that the battery material for preparing the positive electrode sheet of the single sheet battery meets the preset requirement;

[0025] if it is detected that the second ohmic impedance, the second film forming impedance and the second charge transfer impedance are all within the corresponding second preset impedance range, it is determined that the battery material for preparing the negative electrode sheet of the single sheet battery meets the preset requirement.

[0026] In an optional embodiment of the present application, the method further comprises:

[0027] if it is detected that any one of the first ohmic impedance, the first film forming impedance and the first charge transfer impedance is beyond the corresponding first preset impedance range, it is determined that the battery material of the positive electrode sheet does not meet the preset requirement;

[0028] if it is detected that any one of the second ohmic impedance, the second film forming impedance and the second charge transfer impedance is beyond the corresponding second preset impedance range, it is determined that the battery material of the negative electrode sheet does not meet the preset requirement.

[0029] The embodiments of the present application provide a single sheet battery and a screening method of battery material, wherein the single sheet battery comprises a positive electrode sheet, a negative electrode sheet and a reference electrode, the reference electrode is arranged between the positive electrode sheet and the negative electrode sheet, and a diaphragm is arranged between the positive electrode sheet and the reference electrode and between the negative electrode sheet and the reference electrode, so that the reference electrode is separated from the positive electrode sheet and the negative electrode sheet. In the present application, the three-electrode single sheet battery has the characteristics of less material and short battery manufacturing time, which is beneficial to provide a simple and safe testing method for rapid screening of battery material, and thus the testing efficiency of the operator is improved.

[0030] Further, the screening of battery material is performed by using the single sheet battery, more comprehensive data information can be collected, the purpose of rapid detection and battery material screening is achieved, the cost is low, the efficiency is high, and the screening precision is high.

[0031] In order to make the above objectives, characteristics and advantages of the present application more apparent, more understandable, the following preferred embodiments are specifically described, and the accompanying drawings are referred to, and the detailed description is as follows. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0033] Figure 1 A schematic diagram of a monolithic battery structure provided by an embodiment of the present application;

[0034] Figure 2 A flowchart of a battery material screening method provided by an embodiment of the present application;

[0035] Figure 3 A schematic diagram of voltage change in a voltage data set provided by an embodiment of the present application;

[0036] Figure 4 A schematic diagram of a voltage change curve provided by an embodiment of the present application;

[0037] Figure 5 A schematic diagram of another voltage change curve provided by an embodiment of the present application;

[0038] Figure 6 A schematic diagram of another voltage change curve provided by an embodiment of the present application;

[0039] Figure 7 A schematic diagram of another monolithic battery structure provided by an embodiment of the present application;

[0040] Figure 8 A schematic diagram of voltage change in another voltage data set provided by an embodiment of the present application. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, every other embodiment obtained by those skilled in the art without creative labor belongs to the scope of the present application.

[0042] In the description of the embodiments of the present application, it should be noted that the terms "upper", "lower", "left", "right", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the application is usually placed, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0043] In the description of the embodiments of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "provided with", "mounted", "communicated", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0044] Firstly, the application scenarios applicable to the present application are introduced. The present application can be applied to the field of batteries, among which lithium ion batteries have the advantages of small volume, light weight, no memory effect, high energy density and cycle life, and are widely used in mobile electronic devices, new energy vehicles, aerospace, energy storage and other fields.

[0045] At present, the battery with poor rate performance is prone to cause the battery performance to decay quickly during the charging and discharging process, and in severe cases, it can cause internal short circuit of the battery and fire explosion. In the prior art, a third electrode is often provided for the soft package battery to test the negative electrode potential, and the risk of lithium precipitation of the negative electrode is detected to analyze the rate performance of the battery. However, due to the complex manufacturing process (such as hot pressing) of the soft package battery and the long manufacturing time, the time cost and manufacturing cost of testing the battery are high, which reduces the test efficiency of the operator.

[0046] Based on this, the embodiments of the present application provide a single battery and a battery material screening method. Since the three-electrode single battery has the characteristics of less material consumption and short battery manufacturing time, it is beneficial to provide a simple and safe testing method for rapid screening of battery materials, thereby improving the test efficiency of the operator. Further, by using the single battery to screen the battery material, more comprehensive data information can be collected, thereby achieving the purpose of rapid detection and battery material screening, with low cost, high efficiency and high screening accuracy.

[0047] Please refer to Figure 1 , Figure 1A structural schematic diagram of a single-cell battery provided by an embodiment of the present application is shown in FIG. 1. Figure 1 As shown in FIG. 1, the single-cell battery provided by the embodiment of the present application includes a positive electrode sheet, a negative electrode sheet, and a reference electrode. The reference electrode is disposed between the positive electrode sheet and the negative electrode sheet, and a separator is disposed between the positive electrode sheet and the reference electrode and between the negative electrode sheet and the reference electrode, so that the reference electrode is separated from the positive electrode sheet and the negative electrode sheet.

[0048] Here, the positive electrode material of the positive electrode sheet includes, but is not limited to, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, or a ternary compound coated on an aluminum foil. The negative electrode material of the negative electrode sheet includes, but is not limited to, graphite or lithium titanate coated on a copper foil. The separator material is polyethylene or polypropylene.

[0049] Specifically, the reference electrode is obtained by plating lithium on a copper wire (plating lithium current I≤20μA, plating lithium time t≤12h). The reference electrode is an electrode used as a reference for comparison when measuring the electrode potential of various electrodes. The electrode to be measured and the reference electrode with an accurately known electrode potential value form a battery, and the voltage value of the battery is measured to calculate the electrode potential of the electrode to be measured. The electrode reaction on the reference electrode must be a single reversible reaction, and the electrode potential must be stable and reproducible.

[0050] In the embodiment of the present application, when developing a single-cell battery, the key is to place the reference electrode between the positive electrode sheet and the negative electrode sheet, and to separate the reference electrode from the positive electrode sheet and the negative electrode sheet with separators. The positive electrode can be an aluminum foil coated with lithium iron phosphate, and the negative electrode can be a copper foil coated with graphite. After packaging with an aluminum plastic film and injecting electrolyte, the copper wire is plated with lithium to obtain the reference electrode, so as to obtain a three-electrode single-cell battery.

[0051] Furthermore, the three-electrode single-cell battery after plating lithium has the characteristics of simple structure, less material, small size, short manufacturing time, low development cost, more comprehensive voltage data between electrodes, etc. It is mainly used in the development and testing of batteries to quickly and accurately screen battery materials and match material systems, and is safe and simple to operate. It not only improves the testing efficiency of the operator, but also enables in-depth analysis of the performance of the battery.

[0052] Due to the single cell in the embodiment of the present application has the advantages of less material, short manufacturing time, convenient and safe test, etc., the single cell is more suitable for preliminary electrical performance analysis of battery materials than soft package battery, aluminum shell battery, etc., has high stability and reliability, and can be used for long cycle test. Further, the single cell combined with three electrode technology can be used to quickly detect the kinetics, rate charge performance, positive / negative electrode impedance change, etc. of the battery material, so as to achieve the purpose of screening the battery material. In addition, after long cycle test, the positive and negative electrodes can be respectively tested by Electrochemical Impedance Spectroscopy (EIS) to provide reliable information for battery failure analysis.

[0053] Based on this, the embodiment of the present application provides a battery material screening method. Please refer to Figure 2 , Figure 2 The battery material screening method provided by the embodiment of the present application is applied to a single cell as shown in Figure 1 , and the method comprises:

[0054] S201, collecting a voltage data set of the single cell when the single cell is charged and discharged at different current rates in a preset time period.

[0055] S202, determining the state of charge of the single cell according to the current at different rates in the preset time period.

[0056] S203, determining a voltage change curve of the voltage of the single cell at different rates changing with the state of charge according to the voltage data set and the state of charge of the single cell.

[0057] S204, determining the battery material with rate performance meeting the preset requirement by analyzing the voltage change curve.

[0058] The battery material screening method provided by the embodiment of the present application collects more comprehensive data information by using the single cell as shown in Figure 1 , and performs battery material screening, which can achieve the purpose of rapid detection and battery material screening, has low cost, high efficiency, and high screening accuracy.

[0059] The above steps are exemplarily described as follows:

[0060] In step S201, a voltage data set of the single cell when the single cell is charged and discharged at different current rates in a preset time period is collected.

[0061] Here, the preset time period refers to the time period during which a single battery is monitored for charging and discharging at different current rates. This can be set according to the actual test conditions. The current rate (C) represents the battery's charging and discharging capacity. For example, different current rates include: 0.5C, 0.75C, 1C, 1.5C, and 2C.

[0062] The voltage dataset includes multiple voltage values, which may include one of the following: a first voltage value between the positive and negative electrodes, a second voltage value between the negative electrode and the reference electrode, and a third voltage value between the positive electrode and the reference electrode. For example, the voltage dataset may include multiple first voltage values ​​obtained during charging and discharging at different current rates, or it may include multiple second voltage values ​​obtained during charging and discharging at different current rates, or it may include multiple third voltage values ​​obtained during charging and discharging at different current rates; the voltage dataset may also include multiple first voltage values ​​and multiple second voltage values ​​obtained during charging and discharging at different current rates, or it may include multiple second voltage values ​​and multiple third voltage values ​​obtained during charging and discharging at different current rates, etc.; the voltage dataset may also include multiple first voltage values, multiple second voltage values, and multiple third voltage values ​​obtained during charging and discharging at different current rates.

[0063] Therefore, the embodiments of this application can simultaneously collect the second voltage value between the negative electrode and the reference electrode and the third voltage value between the positive electrode and the reference electrode, which helps to monitor the negative electrode and the positive electrode simultaneously, thereby realizing the simultaneous analysis and testing of the positive electrode material and the negative electrode material, achieving the purpose of screening battery materials with high rate performance for lithium-ion batteries, greatly saving the amount of raw materials used, reducing R&D expenses, and saving material screening time.

[0064] In this embodiment of the application, a voltage data acquisition device can be used to collect voltage datasets. For example, Figure 3 As shown, Figure 3 This is a schematic diagram of voltage changes in a voltage data set provided in an embodiment of this application. The voltage acquisition device collects the voltage data set of a single battery during charging and discharging within 100,000 seconds, following the sequence of 0.5C discharge → 0.5C charge → 0.5C discharge → 0.75C charge → 0.5C discharge → 1C charge → 0.5C discharge → 1.5C charge → 0.5C discharge → 2C charge → 0.5C discharge. This allows for the separate monitoring of the potentials of the positive / negative electrode, positive / reference electrode, and negative / reference electrode during testing.

[0065] In the above steps, the first voltage value between the positive plate and the negative plate, the second voltage value between the negative plate and the reference electrode, and the third voltage value between the positive plate and the reference electrode can be collected by the voltage collector. The rate performance of the electrochemical system (positive electrode, negative electrode and electrolyte) of the test battery can be determined according to the change of the collected voltage values. If the voltage change amplitudes of the positive plate and the negative plate to the reference electrode are within the preset amplitude range, it is determined that the current positive electrode, negative electrode and electrolyte material of the single battery meet the preset requirements of the battery material in terms of rate performance. The purpose of material screening can be achieved through single factor test. The preset requirements can be determined according to the requirements of the battery that can be mass-produced, or can be determined according to actual needs.

[0066] In step S202, the state of charge of the single battery is determined according to the current of different rates within a preset time period.

[0067] Here, the state of charge (SOC) is the ratio of the remaining capacity of the battery after a period of use or long-term storage to the capacity of its fully charged state, commonly expressed in percentage. Its value range is 0-1, when SOC=0, it indicates that the battery is completely discharged, when SOC=1, it indicates that the battery is fully charged. The state of charge can be predicted by using discharge test method, open circuit voltage method, ampere-hour integral method, Kalman filter method, neural network method, etc. In the embodiment of the application, the state of charge is predicted by using the ampere-hour integral method. The ampere-hour integral method is simple and reliable in calculation, and can estimate the state of charge of the battery in real time.

[0068] In addition, the ampere-hour integral method and the open circuit voltage method can also be combined to estimate the state of charge of the battery. The open circuit voltage method is used to estimate the initial state of charge of the battery, and the ampere-hour integral method is used for real-time estimation. Related correction factors are added in the calculation formula to improve the calculation accuracy.

[0069] In step S203, according to the voltage data set and the state of charge of the single battery, the voltage change curve of the voltage of the single battery at different rates changing with the state of charge is determined.

[0070] Here, on the basis of steps S201 and S202, the voltage change curve of the voltage of the single battery at different rates changing with the state of charge can be fitted based on the obtained voltage data set and the state of charge of the single battery.

[0071] Specifically, the voltage change curve can include the voltage change curve of the voltage between the positive electrode of the single battery and the reference electrode changing with the state of charge, and can also include the voltage change curve of the voltage between the negative electrode of the single battery and the reference electrode changing with the state of charge.

[0072] For example, as shown in Figure 4 and Figure 6 In Figure 4 , a plurality of voltage change curves of the voltage between the negative electrode and the reference electrode changing with the state of charge when charging and discharging at different current rates are shown, wherein each voltage change curve corresponds to a different charging and discharging rate; in Figure 6 , a plurality of voltage change curves of the voltage between the positive electrode and the reference electrode changing with the state of charge when charging and discharging at different current rates are shown, wherein each voltage change curve corresponds to a different charging and discharging rate.

[0073] In step S204, the battery material whose rate performance meets the preset requirement is determined by analyzing the voltage change curve.

[0074] Here, the rate performance is the charging performance at different currents. The greater the charging rate, the faster the battery performance degradation, and when the charging and discharging rate of the battery is too different, it will exacerbate the consistency decay of the battery pack. The selection and proportioning of the battery material can be made according to the actual needs to obtain the battery material whose rate performance meets the preset requirement.

[0075] Among them, the battery material includes one of the following: electrolyte material, positive electrode material and negative electrode material.

[0076] Specifically, the electrolyte needs to meet the performance indicators of high electrical conductivity, good thermal stability, high chemical stability, wide electrochemical window, wide working temperature range, good safety, etc. The main components of the electrolyte are solvents, solutes and additives, etc. Raw materials are prepared by proportioning under certain conditions. The positive electrode material includes but is not limited to: lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide or ternary compound coated on aluminum foil. The negative electrode material includes but is not limited to: graphite or lithium titanate coated on copper foil. The above battery materials can be selected and proportioned according to the actual needs of the user to obtain the battery material whose rate performance meets the preset requirement.

[0077] In an optional embodiment, when the voltage data set includes a second voltage value between the negative electrode sheet and the reference electrode, and the battery material includes a negative electrode material, step S204 includes:

[0078] Step 2041, obtaining a specified state of charge value;

[0079] Here, the specified state of charge value can be summarized according to the actual work experience of the operator.

[0080] Step 2042, obtaining the to-be-measured second voltage value of the single battery at different rates corresponding to the specified state of charge value by analyzing the voltage change curve;

[0081] Based on the voltage change curve, multiple second voltage values ​​corresponding to a specified state of charge can be obtained, and each second voltage value corresponds to a different charging rate.

[0082] Step 2043: If the second voltage value to be tested is detected to be greater than the preset voltage threshold at all rates, then the current negative electrode material of the single cell is determined to be a battery material whose rate performance meets the preset requirements.

[0083] Here, the preset voltage threshold can be derived from the operator's actual work experience. If all the second voltage values ​​are detected to be greater than the preset voltage threshold, then the current negative electrode material of the single cell is determined to be a battery material whose rate performance meets the preset requirements.

[0084] For example, such as Figure 4 As shown, with the increase of SOC, reaching between 0.6 and 0.7, such as when SOC is 0.75, the voltage value corresponding to 0.75, determined based on the voltage change curves corresponding to 1.5C and 2C, is less than 0V. This indicates that the battery material (negative electrode material) has an adverse effect on the rate charging performance. Above 0V is normal, while below 0V there is a risk of lithium plating (the preset voltage threshold is 0V). Based on this, the selection of battery materials can have some reference value. For example, to achieve high-rate performance, this particular battery material cannot be selected. Therefore, by changing the battery materials of a single cell (such as electrolyte material, positive electrode material, and negative electrode material), the voltage value on the voltage change curve corresponding to any rate can be greater than 0V. Figure 5 As shown, this battery material can be selected, which will help in the subsequent development of high-rate batteries. That is, the above method can be used to match appropriate battery materials, then the battery can be tested, and the battery materials can be selected accordingly.

[0085] Through the above method, the embodiments of this application can analyze the lithium plating risk of the negative electrode based on the second voltage value between the collected negative electrode sheet and the reference electrode, which helps to realize the analysis and testing of negative electrode materials, achieve the purpose of screening negative electrode materials with high rate performance for lithium-ion batteries, greatly save the amount of battery materials used for testing single cells, reduce R&D expenses, and save battery material screening time.

[0086] In an optional embodiment, when the voltage dataset includes a third voltage value between the positive electrode and the reference electrode, and the battery material includes a positive electrode material, step S204 further includes:

[0087] Step 2044: Based on the voltage change curve, determine the specified third voltage value and the voltage change amplitude corresponding to the specified third voltage value;

[0088] The specified third voltage value refers to any value within the voltage range corresponding to the minimum voltage change and the largest capacity change determined from the voltage change curve. The largest capacity change refers to any capacity within the capacity range that is far from the maximum capacity change and deviates from the preset capacity threshold. The voltage change amplitude refers to the difference between the minimum and maximum values ​​of the voltage range. The preset capacity threshold can be determined by the tester based on the values ​​corresponding to the battery requirements.

[0089] Step 2045: If the detected voltage change is within the preset range, then determine that the current positive electrode material of the single cell is a battery material whose rate performance meets the preset requirements.

[0090] Here, determining that the current positive electrode material of a single cell meets the preset requirements for rate performance means that using this positive electrode material enables the single cell to meet the following: under the condition that the charge and discharge voltage platform is relatively stable, the specified third voltage value changes very little at different charge and discharge rates.

[0091] It is known that when the charging and discharging voltage plateau is relatively stable, the higher the plateau voltage, the better. Under different charging rates, the smaller the change in plateau voltage, the better. Here, we use this rule to judge whether the positive electrode material of a single battery cell meets the requirements of the plateau voltage change law.

[0092] The preset amplitude range can be determined by the tester based on the values ​​required by the battery.

[0093] In addition, the platform capacity ratio can be used for judgment. If the platform capacity ratio is detected to be within a preset ratio range, it is determined that the current cathode material of the single battery cell meets the platform voltage requirements. The platform capacity ratio refers to the total percentage of charge and discharge capacity within the platform voltage range, and the preset ratio range can be determined by the tester based on the corresponding values ​​for the battery requirements.

[0094] For example, a three-electrode monocell can simultaneously detect the third voltage value between the positive electrode and the reference electrode. The voltage dataset can provide the variation of the third voltage value with SOC under different charge / discharge rates. This allows for the determination of the stability of the positive electrode potential during charge / discharge, as well as the magnitude of the positive electrode polarization at different rates, providing a reliable basis for screening positive electrode materials.

[0095] For example, such as Figure 6 As shown, during charging, the third voltage between the positive electrode and the reference electrode remains stable at 80% SOC, exhibiting a wide voltage plateau. The specified third voltage also increases with increasing charging rate. The difference between 0.75C and 1C is not significant, but the polarization at 2C increases markedly, although it is still much smaller than the polarization of the negative electrode. This indicates that the battery's performance at high charging rates is limited by the negative electrode material.

[0096] The embodiment of the present application can determine whether the current positive electrode material of the single battery meets the preset requirement of the rate performance of the battery material by detecting the voltage variation range of the third voltage value between the positive electrode sheet and the reference electrode within a preset time period. The operation is simple, easy to implement, and helpful to realize the analysis and testing of the positive electrode material, so as to save the screening time of the battery material.

[0097] The embodiment of the present application can monitor the positive electrode sheet and the negative electrode sheet of the single battery. The second voltage value between the negative electrode sheet and the reference electrode and the third voltage value between the positive electrode sheet and the reference electrode are collected at the same time, and the battery material is screened, so as to determine whether the current positive electrode material or negative electrode material of the single battery is the battery material meeting the preset requirement of the rate performance. Specifically, the current positive electrode material of the single battery can be replaced by other positive electrode material, and the above method is used for the screening of the positive electrode material.

[0098] In the related scheme, the EIS can be used for selecting the battery material and testing the micro battery parameters, but the prior art cannot independently analyze the impedance between the positive electrode and the reference electrode and the impedance between the negative electrode and the reference electrode.

[0099] Based on this, the embodiment of the present application further includes the following method:

[0100] Step 601, obtaining the first ohmic impedance, the first film forming impedance and the first charge transfer impedance of the positive electrode sheet in the single battery, and the second ohmic impedance, the second film forming impedance and the second charge transfer impedance of the negative electrode sheet;

[0101] Step 602, if it is detected that the first ohmic impedance, the first film forming impedance and the first charge transfer impedance are all within the corresponding first preset impedance range, it is determined that the battery material for preparing the positive electrode sheet of the single battery meets the preset requirement; if it is detected that the second ohmic impedance, the second film forming impedance and the second charge transfer impedance are all within the corresponding second preset impedance range, it is determined that the battery material for preparing the negative electrode sheet of the single battery meets the preset requirement.

[0102] Here, the first preset impedance range includes a first preset impedance threshold, a second preset impedance threshold and a third preset impedance threshold; and the second preset impedance range includes a fourth preset impedance threshold, a fifth preset impedance threshold and a sixth preset impedance threshold. The preset impedance thresholds corresponding to the first ohmic impedance, the first film-forming impedance and the first charge transfer impedance, and the second ohmic impedance, the second film-forming impedance and the second charge transfer impedance are different, and can be defined as follows: if the first ohmic impedance is detected to be less than or equal to the first preset impedance threshold, the first film-forming impedance is detected to be less than or equal to the second preset impedance threshold, and the first charge transfer impedance is detected to be less than or equal to the third preset impedance threshold, it is determined that the battery material for preparing the positive electrode sheet of the single sheet battery meets the preset requirement; and if the second ohmic impedance is detected to be less than or equal to the fourth preset impedance threshold, the second film-forming impedance is detected to be less than or equal to the fifth preset impedance threshold, and the second charge transfer impedance is detected to be less than or equal to the sixth preset impedance threshold, it is determined that the battery material for preparing the negative electrode sheet of the single sheet battery meets the preset requirement. The preset impedance thresholds mentioned above are determined by the tester according to the corresponding numerical values of the battery requirements. Specifically, the first preset impedance threshold is greater than the fourth preset impedance threshold, the second preset impedance threshold is less than the fifth preset impedance threshold, and the third preset impedance threshold is less than the sixth preset impedance threshold.

[0103] Further, the method further includes step 603, which includes: if any one of the first ohmic impedance, the first film-forming impedance and the first charge transfer impedance is detected to be out of the corresponding first preset impedance range, it is determined that the battery material of the positive electrode sheet does not meet the preset requirement; and if any one of the second ohmic impedance, the second film-forming impedance and the second charge transfer impedance is detected to be out of the corresponding second preset impedance range, it is determined that the battery material of the negative electrode sheet does not meet the preset requirement.

[0104] Specifically, if the first ohmic impedance is detected to be greater than the first preset impedance threshold, the first film-forming impedance is detected to be greater than the second preset impedance threshold, or the first charge transfer impedance is detected to be greater than the third preset impedance threshold, it is determined that the battery material of the positive electrode sheet does not meet the preset requirement; and if the second ohmic impedance is detected to be greater than the fourth preset impedance threshold, the second film-forming impedance is detected to be greater than the fifth preset impedance threshold, or the second charge transfer impedance is detected to be greater than the sixth preset impedance threshold, it is determined that the battery material of the negative electrode sheet does not meet the preset requirement.

[0105] In addition, the charge transfer of the positive and negative electrodes needs to maintain kinetic balance. Compared with the negative electrode, too fast charge transfer of the positive electrode will cause large polarization of the negative electrode and easy lithium precipitation. The three-electrode single sheet battery in the embodiment of the application can distinguish and detect the ohmic impedance, the film-forming impedance and the charge transfer impedance of the positive electrode sheet and the negative electrode sheet. In this way, by respectively testing the charge transfer impedances of the positive electrode and the negative electrode, a basis can be provided for matching of different positive and negative electrode materials (the charge transfer impedances of the positive electrode and the negative electrode are preferably similar).

[0106] Here, with the change of battery material, SEI will change, and then the embodiments of the application can use EIS to screen the battery material after establishing the same battery, such as the screening of electrolyte.

[0107] Specifically, in step 601, the ohmic impedance R S , film forming impedance and charge transfer impedance R CT are defined as follows: wherein the ohmic resistance R S is mainly composed of the resistance of electrode material, electrolyte, diaphragm and the contact resistance of each part. The film forming impedance includes the impedance of the negative electrode electrolyte interface (SEI) and the impedance of the positive electrode electrolyte interface (CEI). The charge transfer impedance refers to the transfer resistance that can hinder or control the movement of electric charge.

[0108] In step 601, the single battery in the embodiments of the application can distinguish and detect the impedance of the positive electrode sheet and the impedance of the negative electrode sheet. The impedance here includes ohmic impedance, film forming impedance and charge transfer impedance. Specifically, the impedance between the positive electrode sheet and the reference electrode mainly includes the first ohmic impedance and the impedance R CEI of the positive electrode electrolyte interface (CEI), and the impedance of the negative electrode mainly includes the impedance R SEI of the negative electrode solid electrolyte interface (SEI) and the second charge transfer impedance.

[0109] In step 602, the three-electrode single battery technology can be used to analyze the first ohmic impedance, the first film forming impedance and the first charge transfer impedance of the positive electrode sheet, and the second ohmic impedance, the second film forming impedance and the second charge transfer impedance of the negative electrode sheet without damaging the structure of the battery.

[0110] The first ohmic impedance of the single battery is mainly from the positive electrode material, which is consistent with the characteristics of poor conductivity of lithium iron phosphate and high internal resistance of the battery. Because the conductivity of the negative electrode main material graphite is high, the second ohmic impedance of the negative electrode is relatively low.

[0111] The film forming impedance of the battery includes the impedance R CEI of the positive electrode electrolyte interface (CEI) and the impedance R SEI of the negative electrode electrolyte interface (SEI), wherein R SEI accounts for the main part. Similarly, the charge transfer impedance is also mainly from the negative electrode, indicating that the dynamic performance of the battery is mainly limited by the negative electrode. These impedance parameters have great reference value for selecting battery materials.

[0112] When selecting battery materials, it is desirable to have a small charge transfer impedance, R SEIThe impedance is stable during cycling, which allows for the screening of battery materials using both RSEI impedance and RCT impedance.

[0113] In addition, three-electrode monocells can be used to evaluate the long-cycle performance of batteries. As the number of battery uses increases, the charge transfer impedance and film formation impedance of the positive and negative electrodes increase. EIS testing of three-electrode monocells provides the impedance of each part of the positive and negative electrodes, which is used to assess the degree of battery aging and provide useful information for failure analysis.

[0114] Through the above methods, the three-electrode monocell provided in this application embodiment can be used to quickly detect changes in the kinetics, rate performance, and positive and negative electrode impedances (RS, RSEI, RCEI, and RCT) of battery materials, thereby achieving the purpose of screening battery materials and analyzing battery aging.

[0115] Furthermore, such as Figure 7 and Figure 8 As shown, in Figure 7 In this configuration, if the reference electrode 103' is placed outside the positive electrode 101' (between the non-positive electrode 101' and the negative electrode 102'), and the separator 104' is disposed between the reference electrode 103' and the positive electrode 101', and between the positive electrode 101' and the negative electrode 102', then... Figure 8 It can be seen that during the test, the detection of lithium potential at the positive and negative electrodes (especially the positive electrode) is not sensitive. This is because the distance between the reference electrode and the active surfaces (charge-discharge reaction surfaces) of the positive and negative electrode plates is relatively large, resulting in a larger compensation voltage. The detection of lithium potential at the negative electrode is also not accurate enough. Therefore, in the above embodiments of this application, placing the reference electrode between the positive and negative electrode plates (separating the reference electrode from both the positive and negative electrodes with a separator) is the optimal solution.

[0116] This application provides a single-cell battery and a method for screening battery materials. The single-cell battery includes a positive electrode, a negative electrode, and a reference electrode. The reference electrode is disposed between the positive and negative electrodes. Separators are provided between the positive and reference electrodes, and between the negative and reference electrodes, to separate the reference electrode from both the positive and negative electrodes. In this application, the three-electrode single-cell battery has the advantages of requiring less material and having a shorter manufacturing time, which facilitates a simple and safe testing method for rapid screening of battery materials, thereby improving the testing efficiency of operators. Furthermore, using this single-cell battery for battery material screening allows for the collection of more comprehensive data, achieving rapid detection and screening of battery materials with lower cost, higher efficiency, and higher screening accuracy.

[0117] Finally, it should be noted that the above-described embodiments are merely specific embodiments of the present application, which are used to illustrate the technical solutions of the present application, but not to limit the same. The protection scope of the present application is not limited thereto. Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that any person skilled in the art can make modifications or easily think of changes to the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some of the technical features within the technical scope disclosed by the present application. The modifications, changes or replacements do not make the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for screening battery materials, characterized in that, The method is applied to a single battery, the single battery comprising a positive electrode sheet, a negative electrode sheet and a reference electrode; a diaphragm is arranged between the positive electrode sheet and the reference electrode and between the negative electrode sheet and the reference electrode, so that the reference electrode is separated from the positive electrode sheet and the negative electrode sheet; the method comprises: collecting a voltage data set of the single battery when the single battery is charged and discharged at different current rates within a preset time period; determining a state of charge of the single battery according to the current rates within the preset time period; determining a voltage change curve of the single battery at different rates according to the voltage data set and the state of charge of the single battery; the voltage values in the voltage data set include one of a first voltage value between the positive electrode sheet and the negative electrode sheet, a second voltage value between the negative electrode sheet and the reference electrode and a third voltage value between the positive electrode sheet and the reference electrode; determining a battery material with a rate performance meeting a preset requirement by analyzing the voltage change curve.

2. The method of claim 1, wherein, The battery material includes one of an electrolyte material, a positive electrode material and a negative electrode material.

3. The method of claim 1, wherein, When the voltage data set includes the second voltage value between the negative electrode sheet and the reference electrode, and the battery material includes a negative electrode material, the step of determining a battery material with a rate performance meeting a preset requirement by analyzing the voltage change curve comprises: obtaining a specified state of charge value; obtaining a to-be-tested second voltage value of the single battery at different rates corresponding to the specified state of charge value by analyzing the voltage change curve; if it is detected that the to-be-tested second voltage value at all rates is greater than a preset voltage threshold, determining that the current negative electrode material of the single battery is a battery material with a rate performance meeting a preset requirement.

4. The method of claim 1, wherein, When the voltage data set includes the third voltage value between the positive electrode sheet and the reference electrode, and the battery material includes a positive electrode material, the step of determining a battery material with a rate performance meeting a preset requirement by analyzing the voltage change curve comprises: determining a specified third voltage value and a voltage change amplitude corresponding to the specified third voltage value according to the voltage change curve; if it is detected that the voltage change amplitude is within a preset amplitude range, determining that the current positive electrode material of the single battery is a battery material with a rate performance meeting a preset requirement.

5. The method of claim 1, wherein, The method further comprises: obtaining a first ohmic impedance, a first film-forming impedance and a first charge transfer impedance of the positive electrode sheet, and a second ohmic impedance, a second film-forming impedance and a second charge transfer impedance of the negative electrode sheet in the single battery; if it is detected that the first ohmic impedance, the first film-forming impedance and the first charge transfer impedance are all within a corresponding first preset impedance range, determining that a battery material for preparing the positive electrode sheet of the single battery meets a preset requirement; if it is detected that the second ohmic impedance, the second film-forming impedance and the second charge transfer impedance are all within a corresponding second preset impedance range, determining that a battery material for preparing the negative electrode sheet of the single battery meets a preset requirement.

6. The method of claim 5, wherein, The method further comprises: if any one of the first ohmic impedance, the first film-forming impedance and the first charge transfer impedance is detected to be out of the corresponding first preset impedance range, it is determined that the battery material of the positive plate does not meet the preset requirement; if any one of the second ohmic impedance, the second film-forming impedance and the second charge transfer impedance is detected to be out of the corresponding second preset impedance range, it is determined that the battery material of the negative plate does not meet the preset requirement.

7. The method of claim 1, wherein, The reference electrode is obtained by plating lithium on a copper wire.

8. The method of claim 1, wherein, The diaphragm material is polyethylene or polypropylene.

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