Electrode sheet, secondary battery, and electric device

Abstract

An electrode sheet, a secondary battery, and an electric device. The electrode sheet comprises an active material layer, the active material layer containing a first binder and a second binder, the first binder comprising an alkali metal polymer salt, the bonding strength of the second binder being greater than that of the first binder, the weight percentage of the alkali metal polymer salt in the active material layer being A, the weight percentage of the second binder in the active material layer being B, and A and B satisfying: 0<A+B≤5%.

Description

Electrode, secondary battery and electrical device

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311633510.8, filed on December 1, 2023, entitled “Electrode, Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a pole piece, a secondary battery and an electrical device. Background Art

[0004] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0005] In recent years, the application of secondary batteries, represented by lithium-ion batteries, has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have achieved significant development, higher requirements have been placed on their energy density, cycle performance, and safety performance.

[0006] Summary of the Invention

[0007] Based on this, the present application provides a pole piece, a secondary battery and an electrical device. By improving the pole piece, the cycle performance and fast charging performance of the secondary battery can be improved.

[0008] In order to achieve the above-mentioned object, the first aspect of the present application provides a pole piece, comprising an active material layer, wherein the active material layer comprises a first binder and a second binder, wherein the first binder comprises an alkali metal polymer salt, and the bonding strength of the second binder is greater than that of the first binder, and the weight proportion of the alkali metal polymer salt in the active material layer is A, and the weight proportion of the second binder in the active material layer is B, and the relationship between A and B satisfies: <A+B≤5%。

[0009] The active material layer of the electrode comprises a first binder and a second binder, wherein the first binder comprises an alkali metal polymer salt, wherein the alkali metal polymer salt included in the first binder is conducive to the increase of alkali metal ions (i.e., active ions) in the active material layer, thereby facilitating the improvement of the cycle performance. And because the bonding strength of the second binder is greater than that of the first binder, by using the first binder and the second binder in combination and making the weight ratio of the two meet the above range, the bonding strength of the first binder can be effectively enhanced by utilizing the relatively higher bonding property of the second binder, thereby facilitating the improvement of the bonding force of the electrode and making the bonding force at a relatively high level, reducing the demoulding problem of the electrode during use, improving the stability of the electrode, and thus improving the cycle stability of the battery.

[0010] In addition, alkali metal ions (such as lithium ions) can be dissociated from the alkali metal polymer salt, which can increase the content of alkali metal ions in the active material layer and realize the transmission of alkali metal ions on the molecular chain of the first binder; at the same time, by using the first binder in combination with the second binder, the dissociated alkali metal ions can be further transmitted on the molecular chain of the second binder, which can effectively shorten the time for the alkali metal ions to be transmitted to the current collector, reduce polarization accumulation, and thereby improve the transmission efficiency of the alkali metal ions, thereby improving the fast charging capability of the battery.

[0011] In some embodiments of the present application, the relationship between A and B satisfies: 0.3≤B / A≤8.5.

[0012] In the active material layer of the electrode, the weight ratio B / A of the alkali metal polymer salt to the second binder is within the above range, which is beneficial to improving the bonding force of the electrode, thereby improving the stability of the electrode; it is also beneficial to reducing the influence of the polyacrylate on the uniformity of the dispersion of the slurry particles in the active material layer, thereby improving the cycle performance of the electrode.

[0013] In some embodiments of the present application, the active material layer further includes a dispersant.

[0014] In some embodiments of the present application, the weight proportion of the dispersant in the active material layer is C,0 <C≤1.5%。

[0015] The active material layer contains a dispersant, and the weight ratio of the dispersant is controlled to meet the above range, which is beneficial to improving the dispersion uniformity of the slurry particles in the active material layer of the electrode and making the dispersion uniformity at a relatively high level, thereby helping to improve the cycle performance of the electrode.

[0016] In some embodiments of the present application, the following conditions are satisfied between A, B and C: <A+B+C≤6%。

[0017] When the weight ratios of the alkali metal polymer salt, the second binder, and the dispersant satisfy the above ranges, while improving the adhesion of the electrode sheet and the uniformity of the dispersion of the slurry particles in the active material layer of the electrode sheet, it can also reduce the occupation of the active materials contained in the active material layer by the above various additives, and improve the capacity of the active materials and the electrode sheet.

[0018] In some embodiments of the present application, the average molecular weight M of the alkali metal polymer salt satisfies: 3000 ≤ M ≤ 100,000, and 1.2 ≤ B / A ≤ 8.5.

[0019] When the average molecular weight of the alkali metal polymer salt is within the range of 3000 ≤ M ≤ 100,000, its own adhesion is relatively low; in the positive electrode active material layer, when the alkali metal polymer salt is used as a binder in combination with the second binder, and the weight ratio thereof and the weight ratio of the second binder satisfy 1.2 ≤ B / A ≤ 8.5, the adhesion of the electrode sheet can be effectively improved, the problem of demolding during the use of the electrode sheet can be reduced, and the stability of the electrode sheet can be improved.

[0020] In some embodiments of the present application, C satisfies: 0.2 ≤ C ≤ 1%.

[0021] When the average molecular weight of the alkali metal polymer salt is within the range of 3000 ≤ M ≤ 100,000, due to its relatively short chain length and the electrostatic repulsion between the carboxyl groups in its molecular structure, the dispersion uniformity between the slurry particles in the active material layer can be at a relatively moderate level. In this case, by controlling the weight ratio of the dispersant to satisfy 0.2 ≤ C ≤ 1%, on the one hand, the dispersion uniformity between the slurry particles can be further improved to reach a relatively higher level, thereby further improving the cycle performance of the electrode sheet. On the other hand, the amount of the dispersant can be minimized to minimize its occupation of the active materials in the active material layer, thereby improving the capacity of the active materials and the electrode sheet. In addition, some dispersants are insulating materials, and when the addition amount is relatively large, it will affect the conductivity of the electrode sheet; when the weight ratio of the dispersant satisfies 0.2 ≤ C ≤ 1%, the influence on the conductivity of the electrode sheet can also be minimized, and the conductivity of the electrode sheet can be improved.

[0022] In some embodiments of the present application, the average molecular weight M of the alkali metal polymer salt satisfies: 100,000 < M ≤ 400,000, and 0.8 ≤ B / A ≤ 8.1.

[0023] When the average molecular weight of the alkali metal polymer salt is between 100,000 and 400,000, its own adhesion is moderate; in the positive electrode active material layer, the alkali metal polymer salt is used as a binder in combination with a second binder, and the weight ratio thereof to the weight ratio of the second binder satisfies 0.8 ≤ B / A ≤ 8.1, which can further improve the adhesion of the electrode sheet, make the slurry particles in the active material layer contact well with the current collector, and further enhance the adhesion between the slurry particles, reduce the shedding of the slurry particles during the charge and discharge cycle of the electrode sheet, so as to further improve the kinetic performance and stability of the electrode sheet.

[0024] In some embodiments of the present application, C satisfies: 0.4 ≤ C ≤ 1.2%.

[0025] When the average molecular weight of the alkali metal polymer salt is between 100,000 and 400,000, the length of its chain is moderate at this time. During the process of preparing it into a slurry and using it for the electrode sheet, there will be a certain degree of aggregation between the slurry particles, which will reduce the dispersion uniformity between the slurry particles to a certain extent. In this case, by controlling the weight ratio of the dispersant to satisfy 0.4 ≤ C ≤ 1.2%, it can improve the dispersion uniformity between the slurry particles to a certain extent, thereby improving the cycle performance of the electrode sheet to a certain extent; and can minimize the amount of the dispersant, minimize its occupation of the active material in the active material layer, so as to improve the capacity of the active material and the electrode sheet.

[0026] In some embodiments of the present application, the average molecular weight M of the alkali metal polymer salt satisfies: 400,000 < M ≤ 3,000,000, and 0.3 ≤ B / A ≤ 6.6.

[0027] When the average molecular weight of the alkali metal polymer salt is 400,000 < M ≤ 3,000,000, it already has a certain degree of adhesion by itself. In the active material layer, when it is used in combination with a second binder, the weight ratio thereof to the weight of the second binder satisfies 0.3 ≤ B / A ≤ 6.6, which can make the adhesion of the electrode sheet reach a relatively higher level, make the slurry particles in the active material layer contact better with the current collector, and further enhance the adhesion between the slurry particles, reduce the shedding of the slurry particles during the charge and discharge cycle of the electrode sheet, so as to further improve the kinetic performance and stability of the electrode sheet.

[0028] In some embodiments of the present application, C satisfies: 0.7 < C ≤ 1.5%.

[0029] When the average molecular weight of the alkali metal polymer salt is 400,000 to 3,000,000, although the high molecular weight alkali metal polymer salt has relatively high adhesion, due to its relatively long chain length, during the process of preparing it into a slurry and using it for the electrode sheet, the slurry particles will aggregate and become larger due to the bridging effect between the molecular chains of the alkali metal polymer salt. As a result, the dispersion uniformity between the slurry particles is easily reduced, affecting the cycle performance of the battery. In this case, by controlling the weight percentage of the dispersant to satisfy 0.7 < C ≤ 1.5%, the dispersion uniformity between the slurry particles can be effectively improved, thereby improving the cycle performance of the electrode sheet; and the amount of the dispersant can be minimized, minimizing its occupation of the active material in the active material layer, so as to improve the capacity of the active material and the electrode sheet.

[0030] The mass percentage content of the alkali metal element contained in the first binder is m, and 3% ≤ m ≤ 8.9%.

[0031] Controlling the mass percentage of the alkali metal element in the first binder within the above range can promote the transport of the dissociated alkali metal ions on the molecular chains of the first binder and the second binder, shorten the time for the alkali metal ions to transport to the current collector, reduce the polarization accumulation, and thus improve the kinetic performance of the secondary battery. In some embodiments of the present application, the alkali metal polymer salt includes alkali metal polyacrylate;

[0032] Optionally, the alkali metal polyacrylate includes one or more of lithium polyacrylate, sodium polyacrylate, and potassium polyacrylate.

[0033] In some embodiments of the present application, the second binder includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylic acid, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0034] In some embodiments of the present application, the dispersant includes one or more of polyethylene glycol, hydroxypropyl methyl cellulose, polyvinylpyrrolidone, sodium dodecylsulfonate, carboxymethyl starch, polyethylenebenzyltrimethylammonium salt, polyethylene glycol octylphenyl ether, polystyrene sulfonic acid, polypropylene maleic acid, methylene dimethyl naphthalene disulfonate, polyethyleneimine, N-methylpyrrolidone, carboxymethyl cellulose, and carboxymethyl cellulose salt. Optionally, the carboxymethyl cellulose salt includes sodium carboxymethyl cellulose and / or potassium carboxymethyl cellulose.

[0035] In some embodiments of the present application, the active material layer further includes an active material, and the active material includes one of a positive electrode active material and a negative electrode active material.

[0036] The second aspect of the present application further provides a secondary battery, including the electrode sheet of the first aspect of the present application.

[0037] A third aspect of the present application provides an electrical device comprising the secondary battery according to the second aspect of the present application.

[0038] The electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0039] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive work. In the drawings:

[0041] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0042] FIG. 2 is an exploded view of the battery cell according to one embodiment of the present application shown in FIG. 1 .

[0043] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0044] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0045] FIG5 is an exploded view of the battery pack shown in FIG4 according to an embodiment of the present application.

[0046] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0047] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0048] Below, some embodiments of the electrode, secondary battery and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0049] " range " disclosed in the present application can be limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be including end value or excluding end value, and any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that the scope of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are also listed, then the following range can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range " a to b " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 and 5" are listed herein, and "0 to 5" is merely an abbreviation for a combination of these values. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2 to 10," this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0050] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0051] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0052] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0053] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible inherent logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0054] In the present application, in the open technical features or technical solutions described with words such as “contain”, “include”, and “include”, unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that also include additional members in addition to the listed members. For example, A' includes a1', a2', and a3'. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of “A' consists of a1', a2', and a3'” and the feature or solution of “A' includes not only a1', a2', and a3', but also other members”. In the present application, unless otherwise specified, A' (such as B') means that B' is a non-limiting example of A', and it can be understood that A' is not limited to B'.

[0055] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0056] Electrode sheets are a crucial component of batteries, and their binder reduces their expansion. Currently, commonly used binders in electrode sheets exhibit poor adhesion between particles and between particles and the current collector, leading to mold release issues and poor stability during use. Furthermore, current electrode sheets and batteries suffer from poor fast-charging performance.

[0057] In order to solve the above technical problems, the present application provides a pole piece, which improves the bonding strength of the pole piece while also improving the fast charging performance of the pole piece and the battery by regulating the weight ratio of the alkali metal polymer salt and the binder contained in the active material layer.

[0058] In a first aspect, the present application provides a pole piece comprising an active material layer, wherein the active material layer comprises a first binder and a second binder, wherein the first binder comprises an alkali metal polymer salt, and the bonding strength of the second binder is greater than that of the first binder, and the weight proportion of the alkali metal polymer salt in the active material layer is A, and the weight proportion of the second binder in the active material layer is B, and the relationship between A and B satisfies: <A+B≤5%。

[0059] It can be understood that the "bonding strength" mentioned in this application refers to the stress required to cause the interface between the adhesive in the adhesive part and the adherend or its vicinity to be destroyed under the action of external force.

[0060] It can be understood that the above-mentioned electrode sheets may include positive electrode sheets or negative electrode sheets. When the electrode sheets are respectively positive electrode sheets or negative electrode sheets, the corresponding active material layers are respectively positive electrode active material layers or negative electrode active material layers.

[0061] The active material layer of the electrode comprises a first binder and a second binder, wherein the first binder comprises an alkali metal polymer salt, wherein the alkali metal polymer salt included in the first binder is conducive to the increase of alkali metal ions (i.e., active ions) in the active material layer, thereby facilitating the improvement of the battery cycle performance. And since the bonding strength of the second binder is greater than that of the first binder, by using the first binder and the second binder in combination and making the weight ratio of the two meet the above range, the bonding strength of the first binder can be effectively enhanced by utilizing the relatively higher bonding property of the second binder, thereby facilitating the improvement of the bonding force of the electrode and making the bonding force at a relatively high level, reducing the demoulding problem of the electrode during use, improving the stability of the electrode, and thus improving the cycle stability of the battery.

[0062] In addition, alkali metal ions (such as lithium ions) can be dissociated from the alkali metal polymer salt, which can increase the content of alkali metal ions in the active material layer and realize the transmission of alkali metal ions on the molecular chain of the first binder; at the same time, by using the first binder in combination with the second binder, the dissociated alkali metal ions can be further transmitted on the molecular chain of the second binder, which can effectively shorten the time for the alkali metal ions to be transmitted to the current collector, reduce polarization accumulation, and thereby improve the transmission efficiency of the alkali metal ions, thereby improving the fast charging capability of the battery.

[0063] In some embodiments, the active material layer further comprises a dispersant.

[0064] In some embodiments, the weight percentage of the dispersant in the active material layer is C, where 0 < C ≤ 1.5%. For example, C can be 0.1%, 0.3%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5% or within the range composed of any of the above values.

[0065] In the active material layer, controlling the weight percentage of the dispersant to meet the above range is beneficial to improving the dispersion uniformity of the slurry particles in the active material layer of the electrode sheet and keeping the dispersion uniformity at a relatively high level, thereby being beneficial to improving the cycling performance of the electrode sheet.

[0066] In some embodiments, the following is satisfied between A and B: 0.3 ≤ B / A ≤ 8.5. For example, B / A can be 0.3, 0.5, 0.7, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5 or within the range composed of any of the above values.

[0067] In the active material layer of the electrode sheet, when the weight ratio B / A of the alkali metal polymer salt to the second binder is within the above range, it is beneficial to both improving the adhesion of the electrode sheet, thereby enhancing the stability of the electrode sheet, and reducing the influence of the alkali metal polymer salt on the dispersion uniformity of the slurry particles in the active material layer, and improving the cycling performance of the electrode sheet.

[0068] In some embodiments, the following is satisfied among A, B, and C: 0 < A + B + C ≤ 6%. For example, A + B + C can be 0.1%, 0.3%, 0.7%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6% or within the range composed of any of the above values.

[0069] When the weight percentages of the alkali metal polymer salt, the second binder, and the dispersant meet the above range, while improving the adhesion of the electrode sheet and the dispersion uniformity of the slurry particles in the active material layer of the electrode sheet, it can also reduce the occupation of the active material contained in the active material layer by the above various additives, and improve the capacity of the active material and the electrode sheet.

[0070] In some embodiments, one of the following relationships can be satisfied among A, B, and C: A + B + C = 6%, 0 < A + B ≤ 5%, 0 < C ≤ 1.5%; A + B + C = 5%, 0 < A + B ≤ 5%, 0 < C ≤ 1.5%; 0 < A + B + C ≤ 6%, A + B = 5%, 0 < C ≤ 1.5%; 0 < A + B + C ≤ 6%, A + B = 4%, 0 < C ≤ 1.5%; 0 < A + B + C ≤ 6%, 0 < A + B ≤ 5%, C = 1.5%; 0 < A + B + C ≤ 6%, 0 < A + B ≤ 5%, C = 1%.

[0071] When the weight proportions of the alkali metal polymer salt, the second binder and the dispersant all meet the above ranges, it is beneficial to simultaneously improve the stability, cycle performance and capacity of the electrode; and while improving the performance, the preparation cost of the electrode can also be controlled at a relatively low level.

[0072] In some embodiments, the average molecular weight M of the alkali metal polymer salt satisfies: 3000≤M≤100,000, and 1.2≤B / A≤8.5.

[0073] In some embodiments, 0.2≤C≤1%.

[0074] It should be noted that the average molecular weight M of the alkali metal polymer salt in this application refers to the number average molecular weight of the alkali metal polymer salt.

[0075] In some embodiments, the average molecular weight M of the alkali metal polymer salt can be 3,000, 5,000, 7,000, 9,000, 10,000, 20,000, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, or a range thereof.

[0076] In some embodiments, B / A may be 1.2, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, or a range consisting of any of the foregoing values.

[0077] In some embodiments, C may be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range consisting of any of the foregoing values.

[0078] When the average molecular weight of an alkali metal polymer salt is between 3,000 and 100,000, its own binding strength is relatively low. In the positive electrode active material layer, using the alkali metal polymer salt as the first binder in combination with the second binder, with the weight ratio of the alkali metal polymer salt to the second binder satisfying the ratio of 1.2 ≤ B / A ≤ 8.5, can effectively improve the bonding strength of the electrode, reduce the problem of demolding during use, and enhance the stability of the electrode.

[0079] Meanwhile, when the average molecular weight of the alkali metal polymer salt is between 3,000 and 100,000, due to its relatively short chain length and the electrostatic repulsion between carboxyl groups in its molecular structure, the dispersion uniformity among the slurry particles in the active material layer can be at a relatively moderate level. In this case, by controlling the weight percentage of the dispersant to satisfy 0.2 ≤ C ≤ 1%, on the one hand, the dispersion uniformity among the slurry particles can be further improved to reach a relatively higher level, thereby further enhancing the cycling performance of the electrode. On the other hand, the dosage of the dispersant can be minimized to minimize its occupation of the active material in the active material layer, thereby enhancing the capacity of the active material and the electrode. In addition, some dispersants are insulating materials, and when the addition amount is relatively large, it will affect the conductivity of the electrode; when the weight percentage of the dispersant satisfies 0.2 ≤ C ≤ 1%, its influence on the conductivity of the electrode can also be minimized, enhancing the conductivity of the electrode.

[0080] In some embodiments, the average molecular weight M of the alkali metal polymer salt satisfies: 100,000 < M ≤ 400,000, and 0.8 ≤ B / A ≤ 8.1.

[0081] In some embodiments, 0.4 ≤ C ≤ 1.2%.

[0082] In some embodiments, the average molecular weight M of the alkali metal polymer salt can be 200,000, 300,000, 400,000 or within the range composed of any of the above values.

[0083] In some embodiments, B / A can be 0.8, 1, 1.3, 1.5, 1.7, 2, 2.3, 2.5, 2.7, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.1 or within the range composed of any of the above values.

[0084] In some embodiments, C can be 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.1, 1.2 or within the range composed of any of the above values.

[0085] When the average molecular weight of the alkali metal polymer salt is between 100,000 and 400,000, its own adhesion force is moderate. In the positive electrode active material layer, when the alkali metal polymer salt is used as the first binder in combination with the second binder, and the weight percentage thereof and the weight percentage of the second binder satisfy 0.8 ≤ B / A ≤ 8.1, the adhesion force of the electrode can be further improved, the contact between the slurry particles in the active material layer and the current collector is good, and the adhesion between the slurry particles and particles is further enhanced, reducing the shedding of the slurry particles during the cyclic charge and discharge process of the electrode, so as to further enhance the kinetic performance and stability of the electrode.

[0086] Meanwhile, when the average molecular weight of the alkali metal polymer salt is between 100,000 and 400,000, its chain length is moderate at this time. During the process of preparing it into a slurry and using it for the electrode sheet, there will be a certain degree of agglomeration between the slurry particles, which will reduce the dispersion uniformity between the slurry particles to a certain extent. In this case, by controlling the weight ratio of the dispersant to satisfy 0.4 ≤ C ≤ 1.2%, it can not only improve the dispersion uniformity between the slurry particles to a certain extent, thereby improving the cycle performance of the electrode sheet to a certain extent; but also minimize the dosage of the dispersant, minimize its occupation of the active material in the active material layer, so as to improve the capacity of the active material and the electrode sheet. At the same time, it can also minimize the influence of the dispersant on the conductivity of the electrode sheet and improve the conductivity of the electrode sheet.

[0087] In some embodiments, the average molecular weight M of the alkali metal polymer salt satisfies: 400,000 < M ≤ 3,000,000, and 0.3 ≤ B / A ≤ 6.6.

[0088] In some embodiments, 0.7 < C ≤ 1.5%.

[0089] In some embodiments, the average molecular weight M of the alkali metal polymer salt can be 500,000, 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,500,000, 2,000,000, 2,500,000, 3,000,000 or within the range composed of any of the above values.

[0090] In some embodiments, B / A can be 0.3, 0.5, 0.8, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.6 or within the range composed of any of the above values.

[0091] In some embodiments, C can be 0.8, 0.9, 1.1, 1.2, 1.3, 1.4, 1.5 or within the range composed of any of the above values.

[0092] When the average molecular weight of the alkali metal polymer salt is between 400,000 and 3,000,000, it already has a certain degree of adhesiveness by itself. In the active material layer, when it is used in combination with the second binder as the first binder, making its weight ratio and the weight ratio of the second binder satisfy 0.3 ≤ B / A ≤ 6.6 can make the adhesion force of the electrode sheet reach a relatively higher level, make the contact between the slurry particles in the active material layer and the current collector better, and further improve the adhesion between the slurry particles and particles, reduce the shedding of the slurry particles during the cyclic charge and discharge process of the electrode sheet, so as to further improve the kinetic performance and stability of the electrode sheet. In addition, since the cost of the alkali metal polymer salt is relatively high when its average molecular weight is relatively high, therefore, by controlling B / A within the above range, it is also beneficial to reduce the preparation cost of the battery.

[0093] Meanwhile, when the average molecular weight of the alkali metal polymer salt is 400,000 to 3,000,000, although the high molecular weight alkali metal polymer salt has relatively high adhesion, due to its relatively long chain length, during the process of preparing it into a slurry and using it for the electrode sheet, the slurry particles will agglomerate and become larger due to the bridging effect between the molecular chains of the alkali metal polymer salt. As a result, the dispersion uniformity between the slurry particles is likely to be reduced, affecting the cycle performance of the battery. In this case, by controlling the weight percentage of the dispersant to satisfy 0.7 < C ≤ 1.5%, the dispersion uniformity between the slurry particles can be effectively improved, thereby improving the cycle performance of the electrode sheet; and the amount of the dispersant can be minimized as much as possible, minimizing its occupation of the active material in the active material layer, so as to improve the capacity of the active material and the electrode sheet.

[0094] The average molecular weight of the alkali metal polymer salt has the meaning well-known in the art and can be tested by methods known in the art. For example, referring to the standard GB / T21863 - 2008 "Gel Permeation Chromatography (GPC) Using Tetrahydrofuran as Eluent", it can be tested using a gel permeation chromatograph (GPC, model LC - 20ADXR).

[0095] In some embodiments, the mass percentage content of the alkali metal element contained in the first binder is m, and 3% ≤ m ≤ 8.9%. For example, m can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 8.9% or within the range composed of any of the above values.

[0096] The alkali metal polymer salt can dissociate into alkali metal ions. By making the mass percentage content of the alkali metal element in the first binder be 3% - 8.9%, the content of alkali metal ions in the active material layer can be increased, and further promote the transport of alkali metal ions on the molecular chains of the first binder and the second binder, further shortening the time for alkali metal ions to transport to the current collector, reducing the polarization accumulation, and then improving the transport efficiency of alkali metal ions and further improving the fast charging ability of the battery.

[0097] In some embodiments, it includes alkali metal polyacrylate.

[0098] In some embodiments, the alkali metal polyacrylate includes one or more of lithium polyacrylate (PAALi), sodium polyacrylate (PAANa), and potassium polyacrylate (PAAK).

[0099] In some embodiments, the type of the second binder is not limited and can be selected according to actual needs. For example, the second binder can include one or more of styrene-butadiene rubber and its modified compounds, polyacrylic acid, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, polyvinylidene fluoride, and polytetrafluoroethylene.

[0100] It is understood that when the electrode sheet is a positive electrode sheet, the active material layer is a positive electrode active material layer. In this case, in the positive electrode active material layer, the second binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0101] It is understood that when the electrode is a negative electrode, the active material layer is a negative electrode active material layer. In this case, in the negative electrode active material layer, the second binder may include one or more of styrene-butadiene rubber (SBR) and its modified compounds, polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0102] In some embodiments, the type of dispersant is not limited and can be selected according to actual needs. For example, the dispersant can include one or more of polyethylene glycol, hydroxypropyl methylcellulose, polyvinyl pyrrolidone, sodium lauryl sulfate, carboxymethyl starch, polyvinyl benzyl trimethyl ammonium salt, polyethylene glycol octylphenyl ether, polystyrene sulfonic acid, polypropylene maleate, sodium methylene dimethyl naphthalene sulfonate, polyethylene imine, nitrogen methyl pyrrolidone, carboxymethyl cellulose, and carboxymethyl cellulose salt.

[0103] In some embodiments, the carboxymethylcellulose salt may include sodium carboxymethylcellulose and / or potassium carboxymethylcellulose.

[0104] In some embodiments, the active material layer further includes an active material, and the active material includes one of a positive electrode active material and a negative electrode active material.

[0105] In a second aspect, the present application provides a secondary battery comprising the electrode described in the first aspect of the present application.

[0106] It can be understood that in a secondary battery, the electrode described in the first aspect of the present application can be only a positive electrode, or only a negative electrode, or it can be both a positive electrode and a negative electrode.

[0107] In some embodiments, the secondary battery may include one or more of a lithium ion battery, a sodium ion battery, and a potassium ion battery.

[0108] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0109] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0110] Positive electrode

[0111] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0112] As a non-limiting example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0113] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0114] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.85 Co 0.15 Al 0.05 O2.

[0115] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode materials in this application, unless otherwise specified, the Li content is the initial state of the material. The positive electrode material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the Li content in the positive electrode material contained in the plate will usually change. Among them, the Li content can be measured by molar content, but is not limited to this. Regarding "the Li content is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that new materials obtained by appropriate modification on the basis of the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode materials, and non-limiting examples include coating modification.

[0116] In the examples of positive electrode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar content, but is not limited to this.

[0117] In some embodiments, the positive electrode active material may also include at least one of the following materials: one or more of a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries may also be used.

[0118] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Non-limiting examples of sodium transition metal oxides may be Na x MO2, wherein M may include one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0119] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be one or more of P, S, and Si; n represents (YO4) n- valence.

[0120] Polyanionic compounds can also be sodium ions, transition metal ions, tetrahedral (YO4) n-A class of compounds containing anion units and halogen anions. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be one or more of P, S, and Si, and n represents (YO4) n- valence state; the halogen can be one or more of F, Cl and Br.

[0121] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedron unit (ZO y ) m+ and an optional halogen anion. Y can be one or more of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, which may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, and m represents (ZO y ) m+ valence state; the halogen can be one or more of F, Cl and Br.

[0122] Polyanionic compounds may include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F and Na3(VO y )2(PO4)2F 3-2y (0≤y≤1) wherein M′ in NaM′PO4F may include one or more of V, Fe, Mn and Ni.

[0123] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ). The transition metal may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Non-limiting examples of Prussian blue compounds may include Na a Me b Me' c (CN)6, wherein Me and Me' can each independently be one or more of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0124] In some embodiments, the positive electrode active material layer may further optionally include a conventional binder. As non-limiting examples, the conventional binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0125] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0126] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or two surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 to 25000 milliPa·seconds (mPa·s). When applying the positive electrode slurry, the coating unit area density on a dry weight basis (excluding the solvent) can be 15 to 35 mg / cm2 (mg / cm 2 The compacted density of the positive electrode sheet can be 3.0 to 3.6 g / cm3 (g / cm 3 ), can be selected as 3.3~3.5g / cm 3 .

[0127] Negative electrode

[0128] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0129] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0130] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0131] In some of these embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0132] In some embodiments, the negative electrode active material layer may further include a conventional binder. The conventional binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0133] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0134] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0135] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or two surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 to 10000 mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75 to 220 g / m 2 The compaction density of the negative electrode can be 1.0g / cm 3 ~1.8g / cm 3 .

[0136] electrolytes

[0137] The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0138] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0139] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorodioxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0140] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate One or more of fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0141] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0142] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0143] Isolation film

[0144] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0145] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0146] In some embodiments, the isolation film has a thickness of 6 to 40 μm, and optionally 12 to 20 μm.

[0147] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0148] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0149] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0150] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0151] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0152] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0153] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0154] The secondary battery may be a battery module 4 or a battery pack 1 .

[0155] A battery module includes at least one battery cell. The number of battery cells contained in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0156] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0157] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0158] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0159] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0160] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0161] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0162] Figure 6 shows an example of an electric device 6. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0163] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0164] Example

[0165] Below, the embodiment of the present application is described. The embodiment described below is exemplary, is only used to explain the present application, and is not to be construed as limiting the present application. Where the technology or conditions are not specified in the embodiment, the technology or conditions described in the literature in this area or the product instructions are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0166] Example 1-1

[0167] (1) Preparation of negative electrode sheet

[0168] With a solid content of 53%, the negative electrode active materials graphite, carboxymethyl cellulose CMC, conductive carbon SP, binder SBR and lithium polyacrylate PAALi were stirred at high speed in deionized water at a weight ratio of 96:1:0.5:2:0.5 to obtain a negative electrode slurry. The weight of the obtained negative electrode slurry was controlled to 0.209 g / 1540.25 mm2 (g / 1540.25 mm2).2 ) is evenly coated on both sides of a 10μm-thick copper foil. After the slurry on the copper foil is fully dried in an environment of 50-140 degrees Celsius (°C), it is cold-pressed at a density of 1.7 grams per cubic centimeter (g / cc) to obtain a negative electrode sheet with a thickness of 0.1694 millimeters (mm). It is then cut into pieces with a width of 97 mm for later use.

[0169] (2) Preparation of positive electrode sheet

[0170] With a solid content of 62%, the positive electrode active material lithium iron phosphate LFP, the binder PVDF and the conductive carbon SP are dispersed in the solvent NMP in a weight ratio of 97:2:1 and mixed evenly to obtain a positive electrode slurry. The weight of the obtained positive electrode slurry is controlled to 0.45g / 1540.25mm 2 The slurry was evenly coated on both sides of a 15μm thick aluminum foil. After the slurry on the aluminum foil was fully dried in an environment of 50-140°C, it was cold pressed with a density of 2.6g / cc to obtain a positive electrode sheet with a thickness of 0.2384mm. It was then cut into pieces with a width of 100mm for later use.

[0171] (3) Isolation film

[0172] A 7μm thick polypropylene isolation film was selected.

[0173] (4) Preparation of electrolyte

[0174] The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC), with a volume ratio of 1:1:1. In an argon atmosphere glove box with a water content of <10 parts per million (ppm), fully dried lithium salt LiPF6 is dissolved in the organic solvent and mixed thoroughly to obtain an electrolyte solution. The concentration of the lithium salt is 1 mol / L.

[0175] (5) Preparation of batteries

[0176] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation. After winding into a square bare battery cell, an aluminum-plastic film is placed in it. After baking at 80°C to remove water, 10g of the corresponding non-aqueous electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, the finished battery is obtained.

[0177] Examples 1-2 to 1-17, Examples 2-1 to 2-15, Examples 3-1 to 3-14, Comparative Examples 1-1 to 1-4, Comparative Examples 2-1 to 2-4, and Comparative Examples 3-1 to 3-4

[0178] The preparation of the electrode and battery was similar to that of Example 1-1, except that the relevant parameters in the preparation process were adjusted, as detailed in Tables 1 to 6 below. "~" indicates that M is near the corresponding value; for example, "~4000" indicates that M is around 4000, i.e., M is approximately 4000.

[0179] Table 1

[0180] Table 2

[0181] Table 3

[0182] Table 4

[0183] Table 5

[0184] Table 6

[0185] In addition, the batteries obtained in the above examples and comparative examples were subjected to cycle performance tests, and the test results are shown in Tables 7 to 9 below.

[0186] Test section

[0187] (1) Test method for mass percentage of alkali metal elements

[0188] Take a certain mass M of alkali metal polyacrylate sample and use inductively coupled plasma emission spectroscopy (ICP) to test the mass m1 of the alkali metal element. Then, the mass percentage of the alkali metal element in the alkali metal polyacrylate is the average value = m1 / M×100%. The sample to be tested is prepared by the following method: weigh 0.2g of sample in a beaker, add 10 milliliters (mL) of concentrated HNO3 solution, place it on a 180°C hot plate and digest for 30 minutes (min). After the sample is digested for 30 minutes, cool it to room temperature, transfer the digestion solution to a 50mL volumetric flask through a funnel and make up the volume. Test according to the industry standard USEPA-6010D-2018, prepare a standard test solution, which is the multi-element standard solution of ICP analysis of the National Nonferrous Metals Testing Center. The curve concentration points are 0, 0.2, 0.5, 1.0, and 2.0 mg / L respectively. Prepare a standard solution calibration curve with the instrument, input the sample mass and volume, and then test the digested solution. Solutions outside the curve range need to be diluted before testing. Finally, the presence of elements is identified through the characteristic spectrum of elements emitted by atoms (qualitative analysis), and the content of elements is determined based on the intensity of the spectral lines (quantitative analysis).

[0189] (2) Cyclic performance test

[0190] At 25°C, the battery was charged at a constant current of 1 / 3C to a voltage of 3.65 volts (V), then charged at a constant voltage of 3.65V to a current of 0.05C. After standing for 5 minutes, the battery was discharged at a constant current of 1C to a voltage of 2.0V. This constitutes one charge cycle, and the discharge capacity is the discharge capacity of the first cycle. The cyclic charge test is repeated as described above until the discharge capacity decays to 80% of the initial value. The cycle is completed and the total number of cycles is recorded to obtain the battery's cycle performance (cycle life).

[0191] (3) Fast charging performance test

[0192] Using Cu wire as the three electrodes, charge at a 5C charge rate until the anode potential drops to 0 millivolts (mV). Then, switch to low-rate charging, sequentially charging at 4C, 3C, 2C, and 1C, to obtain the cell's maximum charge capacity map. Starting from 0% SOC, step charge using the cell's maximum charge capacity map is performed until the cell's cutoff voltage reaches 3.8V. The time required to charge from 20% SOC to 80% SOC is recorded as the battery's fast charge time.

[0193] Table 7

[0194] Table 8

[0195] Table 9

[0196] In Tables 7 to 9 above, by comparing Examples 1-1 to 1-17 with Comparative Examples 1-1 to 1-4, comparing Examples 2-1 to 2-15 with Comparative Examples 2-1 to 2-4, and comparing Examples 3-1 to 3-14 with Comparative Examples 3-1 to 3-4, it can be seen that the cycle life of the embodiments is higher than that of the corresponding comparative examples, indicating that the present application can improve the cycle performance and fast charging performance of the battery by regulating the ratio of the first binder and the second binder in the active material layer.

[0197] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0198] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A pole piece includes an active material layer, the active material layer contains a first binder and a second binder, the first binder includes an alkali metal polymer salt, the bonding strength of the second binder is greater than that of the first binder, the weight percentage of the alkali metal polymer salt in the active material layer is A, the weight percentage of the second binder in the active material layer is B, and the relationship between A and B satisfies: 0 < A + B ≤ 5%.

2. The pole piece according to claim 1, wherein: The relationship between A and B satisfies: 0.3 ≤ B / A ≤ 8.

5.

3. The pole piece according to claim 1 or 2, wherein: The active material layer further contains a dispersant.

4. The pole piece according to claim 3, wherein: The weight percentage of the dispersant in the active material layer is C, 0 < C ≤ 1.5%.

5. The pole piece according to claim 4, wherein: The relationship among A, B and C satisfies: 0 < A + B + C ≤ 6%.

6. The pole piece according to any one of claims 2 to 5, wherein: The average molecular weight M of the alkali metal polymer salt satisfies: 3,000 ≤ M ≤ 100,000, and 1.2 ≤ B / A ≤ 8.

5.

7. The pole piece according to any one of claims 4 to 6, wherein: C satisfies: 0.2 ≤ C ≤ 1%.

8. The pole piece according to any one of claims 2 to 5, wherein: The average molecular weight M of the alkali metal polymer salt satisfies: 100,000 < M ≤ 400,000, and 0.8 ≤ B / A ≤ 8.

1.

9. The pole piece according to any one of claims 4 to 5 and 8, wherein: C satisfies: 0.4 ≤ C ≤ 1.2%.

10. The pole piece according to any one of claims 2 to 5, wherein: The average molecular weight M of the alkali metal polymer salt satisfies: 400,000 < M ≤ 3,000,000, and 0.3 ≤ B / A ≤ 6.

6.

11. The pole piece according to any one of claims 4 to 5 and 10, wherein: C satisfies: 0.7 < C ≤ 1.5%.

12. The pole piece according to any one of claims 1 to 11, wherein: The mass percentage of the alkali metal element contained in the first binder is m, 3% ≤ m ≤ 8.9%.

13. The pole piece according to any one of claims 1 to 12, wherein: The alkali metal polymer salt includes an alkali metal polyacrylate.

14. The pole piece according to claim 13, wherein: The alkali metal polyacrylate includes one or more of lithium polyacrylate, sodium polyacrylate and potassium polyacrylate.

15. The pole piece according to any one of claims 1 to 14, wherein: The second binder includes one or more of styrene-butadiene rubber and its modified compounds, polyacrylic acid, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, polyvinylidene fluoride and polytetrafluoroethylene.

16. The pole piece according to any one of claims 3 to 15, wherein: The dispersant includes one or more of polyethylene glycol, hydroxypropyl methyl cellulose, polyvinylpyrrolidone, sodium dodecyl sulfonate, carboxymethyl starch, polyvinylbenzyltrimethylammonium salt, polyethylene glycol octylphenyl ether, polystyrene sulfonic acid, polypropylene maleic acid, methylene dimethyldinaphthalene sulfonate, polyethyleneimine, N-methylpyrrolidone, carboxymethyl cellulose and carboxymethyl cellulose salt.

17. The pole piece according to any one of claims 1 to 16, wherein: The active material layer further contains an active material, and the active material includes one of a positive electrode active material and a negative electrode active material.

18. A secondary battery, which includes the pole piece according to any one of claims 1 to 17.

19. An electrical device, which includes the secondary battery according to claim 18.

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