Positive pole piece, secondary battery containing positive pole piece and application of thermal expansion material

Abstract

The invention provides a positive pole piece, a secondary battery containing the positive pole piece and application of a thermal expansion material. The positive pole piece comprises a current collector, a positive pole piece and a negative pole piece, and a coating layer formed on the current collector, wherein the coating layer comprises a thermal expansion material. According to the positive pole piece disclosed by the invention, due to the use of the thermal expansion material, the positive active material can fall off from the current collector at an abnormal high temperature to form a direct open circuit and hinder a subsequent continuous exothermic reaction, so that the safety performance of the secondary battery is greatly improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode sheet, a secondary battery containing the positive electrode sheet, and uses of a thermal expansion material. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] However, despite the increasing application of secondary batteries, in actual applications, the diaphragm of secondary batteries is prone to shrinkage or melting, resulting in a short circuit between the positive and negative electrodes, which in turn causes a large amount of heat to be released instantly inside the battery cell, causing thermal runaway, and even fire and explosion. Therefore, the positive electrode of existing secondary batteries still needs to be improved. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode plate that can control the thermal runaway of the secondary battery and improve its safety performance.

[0005] In order to achieve the above-mentioned purpose, the present application provides a positive electrode plate, which uses a coating including a thermal expansion material, so that the instantaneous exothermic reaction caused by direct short-circuiting of the positive and negative electrodes can be avoided, thereby greatly improving the safety of the secondary battery.

[0006] A first aspect of the present application provides a positive electrode sheet, wherein the positive electrode sheet comprises:

[0007] a current collector; and

[0008] A coating is formed on the current collector, the coating comprising a thermal expansion material.

[0009] In any embodiment, based on the total weight of the coating, the thermal expansion material accounts for 5-20 wt %, preferably 8-15 wt %, and more preferably 14 wt %.

[0010] A second aspect of the present application provides a positive electrode sheet, wherein the positive electrode sheet comprises:

[0011] current collector;

[0012] forming a first coating layer on the current collector, the first coating layer comprising a thermal expansion material; and

[0013] A second coating layer is formed on the first coating layer.

[0014] When a two-coat structure is used, the first coating can be peeled off to directly disconnect the positive and negative electrodes, thereby preventing the subsequent continuous exothermic reaction. Therefore, compared with the single-coat structure of the first aspect, the amount of thermal expansion material can be appropriately reduced, thereby saving costs.

[0015] In any embodiment, the thermal expansion material accounts for 40-90% by weight, preferably 45-80% by weight, and more preferably 50% by weight, based on the total weight of the first coating. If the content of the thermal expansion material is too high, the energy density will decrease; if the content of the thermal expansion material is too low, it will be difficult to expand effectively, and the direct disconnection between the positive and negative electrodes cannot be quickly achieved, thereby failing to effectively hinder the exothermic reaction.

[0016] In any embodiment, the thickness of the first coating is 0.1-30 μm, preferably 1-20 μm, more preferably 5-10 μm, most preferably 7 μm; and / or

[0017] The thickness of the second coating is 0.1-200 μm, preferably 70-150 μm, more preferably 100-120 μm, most preferably 110 μm; and / or

[0018] The weight ratio of the first coating layer to the second coating layer is 1:5-1:30, preferably 1:10-1:25, more preferably 1:15-1:20, and most preferably 1:16.

[0019] If the thickness of the first coating is too large, the content of the thermal expansion material will be too high and the energy density will decrease; if the thickness of the first coating is too small, the content of the thermal expansion material will be too low, making it difficult to expand effectively and unable to quickly achieve a direct circuit break between the positive and negative electrodes, thereby failing to effectively hinder the exothermic reaction.

[0020] If the thickness of the second coating is too large, the energy density will be too high, which will have an adverse effect on safety; if the thickness of the second coating is too small, the energy density will be too low, which will be difficult to meet actual needs. In any embodiment, the thermal expansion material includes expandable microspheres.

[0021] In any embodiment, the initial expansion temperature of the expandable microspheres is 100-120° C., preferably 110° C. If the initial expansion temperature is too low, the coating may expand too early, affecting the normal operation of the battery; if the initial expansion temperature is too high, the coating may expand too late, making it difficult to quickly achieve direct disconnection between the positive and negative electrodes, thereby failing to effectively hinder the exothermic reaction.

[0022] In any embodiment, the median particle size of the expanded microspheres in a non-expanded state is 2-25 μm, preferably 5-15 μm, more preferably 9-10 μm; and / or

[0023] The expansion multiple of the expanded microspheres at 100-120° C. is 5-20 times, preferably 10 times.

[0024] If the median particle size of the expandable microspheres in the non-expanded state is too low, the initial expansion temperature will be too low, the coating will expand prematurely, and the normal operation of the battery will be affected; if the median particle size is too large, the initial expansion temperature will be too high, the coating will expand too late, and it will be difficult to quickly achieve a direct circuit break between the positive and negative electrodes, and thus the exothermic reaction cannot be effectively hindered.

[0025] If the expansion multiple of the expandable microspheres at 100-120°C is too low, it is difficult to expand effectively, and it is impossible to quickly achieve a direct disconnection between the positive and negative electrodes, and thus it is impossible to effectively hinder the exothermic reaction; if the expansion multiple is too large, it may cause premature expansion and affect the normal operation of the battery. In any embodiment, the expandable microspheres include at least one of polyacrylonitrile, poly-N,N-dimethylacrylamide, poly-glycidyl methacrylate, poly-methacrylic acid, poly-methacrylonitrile, poly-methyl acrylate and poly-acrylic acid.

[0026] A third aspect of the present application provides a secondary battery, wherein the secondary battery comprises the positive electrode sheet according to the first aspect or the second aspect.

[0027] A fourth aspect of the present application provides a use of a thermal expansion material for preparing a coating, wherein the coating is formed on a current collector of a positive electrode sheet.

[0028] In any embodiment, the thermally expandable material comprises expandable microspheres.

[0029] In any embodiment, the initial expansion temperature of the expanded microspheres is 100-120°C, preferably 110°C.

[0030] In any embodiment, the median particle size of the expanded microspheres in a non-expanded state is 2-25 μm, preferably 5-15 μm, more preferably 9-10 μm; and / or

[0031] The expansion multiple of the expanded microspheres at 100-120° C. is 5-20 times, preferably 10 times.

[0032] In any embodiment, the expanded microspheres include at least one of polyacrylonitrile, poly-N,N-dimethylacrylamide, polyglycidyl methacrylate, polymethacrylic acid, polymethacrylonitrile, polymethyl acrylate and polyacrylic acid. DETAILED DESCRIPTION

[0033] Hereinafter, the embodiments of the positive electrode sheet of the present application, the secondary battery containing the positive electrode sheet, and the use of the thermal expansion material are appropriately described in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are 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 facilitate the understanding of those skilled in the art.

[0034] " Scope " in the present application is limited in the form of lower limit and upper limit, and a 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 a special range. The scope limited in this way can be including end values ​​or not including end values, and can be combined arbitrarily, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for a particular parameter, it is understood that the scope of 60-110 and 80-120 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 listed, the following scope can be fully expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0036] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0037] Unless otherwise stated, the words “comprises,” “includes,” “has,” “contains” or any other variations thereof mentioned in this application are intended to cover a non-exclusive inclusion.

[0038] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0039] If there is no special explanation, the indefinite articles "a" and "an" before the elements or components in this application have no limitation on the quantity requirement (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the number is obviously intended to be limited to the singular form.

[0040] Further, in the following specification, reference will be made to a number of expressions, which are defined as having the following meanings.

[0041] The term "positive electrode sheet" refers to an electrode sheet having a high potential that contains active materials that undergo a reduction reaction during discharge.

[0042] The term "current collector" refers to any conductive substrate capable of conducting current to an electrode during discharge or charge of a secondary battery.

[0043] The term "thermal expansion material" refers to a material whose volume expands rapidly after being heated. It is well compatible with other substances in the coating and can use its rapid expansion property to allow the positive electrode active material to fall off the current collector at abnormally high temperatures, forming a direct short circuit and hindering subsequent continuous exothermic reactions.

[0044] The term "expandable microspheres" refers to microsphere particles with a core-shell spherical structure that can be thermally expanded and foamed, wherein the core contains low-boiling-point alkanes as a foaming agent and the shell is a thermoplastic high molecular polymer.

[0045] The term "positive electrode active material" refers to an active material on the positive electrode side of a secondary battery that can reversibly occlude and release (representatively, insert and desorb) a chemical species (here, lithium ions) that serves as a charge carrier.

[0046] The term "conductive agent" refers to a conductive additive compounded to improve conductivity.

[0047] The term "binder" refers to an additive for bonding active materials to each other or to a current collector to maintain an electrode structure.

[0048] The term "secondary battery" is meant to include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

[0049] As mentioned above, the secondary batteries in the prior art still have the problem of being unable to effectively control thermal runaway, which needs to be solved urgently.

[0050] Positive electrode

[0051] In order to at least partially solve one or more of the above problems and other potential problems, a first exemplary embodiment of the present application provides a positive electrode sheet, wherein the positive electrode sheet includes:

[0052] a current collector; and

[0053] A coating is formed on the current collector, the coating comprising a thermal expansion material.

[0054] Since a coating including a thermal expansion material is used in the positive electrode plate, the instantaneous exothermic reaction caused by a direct short circuit between the positive and negative electrodes can be avoided by shedding the coating, thereby greatly improving safety.

[0055] In some embodiments, based on the total weight of the coating, the thermal expansion material accounts for 5-20% by weight, preferably 8-15% by weight, and more preferably 14% by weight, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% by weight, or any value therebetween. If the content of the thermal expansion material is too high, the energy density will decrease; if the content of the thermal expansion material is too low, it will be difficult to expand effectively, and it will be impossible to quickly achieve a direct disconnection between the positive and negative electrodes, and thus the exothermic reaction will not be effectively hindered.

[0056] In some embodiments, the coating layer includes a positive electrode active material, a conductive agent, a binder, and the thermal expansion material.

[0057] In some embodiments, based on the total weight of the coating, the positive electrode active material accounts for 70-90% by weight, preferably 80% by weight, for example, it can be 71% by weight, 72% by weight, 73% by weight, 74% by weight, 75% by weight, 76% by weight, 77% by weight, 78% by weight, 79% by weight, 80% by weight, 81% by weight, 82% by weight, 83% by weight, 84% by weight, 85% by weight, 86% by weight, 87% by weight, 88% by weight, 89% by weight, 90% by weight or any value therebetween; and / or

[0058] The conductive agent accounts for 1-5% by weight, preferably 2-4% by weight, more preferably 3% by weight, for example, 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, or any value therebetween; and / or

[0059] The binder accounts for 1-5% by weight, preferably 2-4% by weight, more preferably 3% by weight, for example, 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, or any value therebetween; and / or

[0060] The thermal expansion material accounts for 5-20% by weight, preferably 8-15% by weight, and more preferably 14% by weight. For example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% by weight or any value therebetween.

[0061] If the content of the positive electrode active material is too low, the energy density will be too low; if the content of the positive electrode active material is too high, the conductivity and bonding properties will be reduced.

[0062] If the conductive agent content is too low, the conductivity will be too low; if the conductive agent content is too high, it will have an adverse effect on energy density and adhesion.

[0063] If the binder content is too low, the bonding performance will not meet the requirements; if the binder content is too high, it will have an adverse effect on the energy density and conductivity.

[0064] In order to at least partially solve the above problems and one or more of other potential problems, a second exemplary embodiment of the present application provides another positive electrode sheet, wherein the positive electrode sheet includes:

[0065] current collector;

[0066] forming a first coating layer on the current collector, the first coating layer comprising a thermal expansion material; and

[0067] A second coating layer is formed on the first coating layer.

[0068] When a two-coat structure is used, the first coating can be peeled off to directly disconnect the positive and negative electrodes, thereby preventing the subsequent continuous exothermic reaction. Therefore, compared with the single-coat structure of the first aspect, the amount of thermal expansion material can be appropriately reduced, thereby saving costs.

[0069] In some embodiments, based on the total weight of the first coating, the thermal expansion material accounts for 40-90% by weight, preferably 45-80% by weight, and more preferably 50% by weight, for example, 40% by weight, 41% by weight, 42% by weight, 43% by weight, 44% by weight, 45% by weight, 46% by weight, 47% by weight, 48% by weight, 49% by weight, 50% by weight, 51% by weight, 52% by weight, 53% by weight, 54% by weight, 55% by weight, 56% by weight, 57% by weight, 58% by weight, 59% by weight, 60% by weight, 61 wt%, 62 wt%, 63 wt%, 64 wt%, 65 wt%, 66 wt%, 67 wt%, 68 wt%, 69 wt%, 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt% or any value therebetween. If the content of the thermal expansion material is too high, the energy density will decrease; if the content of the thermal expansion material is too low, it will be difficult to expand effectively, and it will be impossible to quickly realize a direct disconnection between the positive and negative electrodes, thereby failing to effectively hinder the exothermic reaction.

[0070] In some embodiments, the first coating layer includes a conductive agent, a binder, and the thermal expansion material described above.

[0071] In some embodiments, based on the total weight of the first coating, the conductive agent accounts for 1-15% by weight, preferably 10% by weight, for example, 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight or any value therebetween; and / or

[0072] The binder accounts for 5-50% by weight, preferably 40% by weight, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87% %, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, or any value therebetween; and / or

[0073] The thermal expansion material accounts for 40-90% by weight, preferably 45-80% by weight, and more preferably 50% by weight. For example, it can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90% by weight or any value therebetween. In some embodiments, the second coating layer includes a positive electrode active material, a conductive agent, and a binder.

[0074] In some embodiments, based on the total weight of the second coating, the positive electrode active material accounts for 90-98 weight%, preferably 97 weight%, for example, 91 weight%, 92 weight%, 93 weight%, 94 weight%, 95 weight%, 96 weight%, 97 weight%, 98 weight% or any value therebetween; and / or

[0075] The conductive agent accounts for 0.5-5% by weight, preferably 1% by weight, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5% by weight or any value therebetween; and / or

[0076] The binder accounts for 1-5% by weight, for example, 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight or any value therebetween.

[0077] If the content of the positive electrode active material is too low, the energy density will be too low; if the content of the positive electrode active material is too high, the conductivity and bonding properties will be reduced.

[0078] In the first coating layer and the second coating layer, if the content of the conductive agent is too low, the conductivity will be too low; if the content of the conductive agent is too high, it will have an adverse effect on the energy density and adhesion.

[0079] If the binder content is too low, the bonding performance will not meet the requirements; if the binder content is too high, it will have an adverse effect on the energy density and conductivity.

[0080] In some embodiments, the thickness of the first coating is 0.1-30 μm, preferably 1-20 μm, more preferably 5-10 μm, and most preferably 7 μm, for example, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm or any value between these values; and / or

[0081] The thickness of the second coating is 0.1-200 μm, preferably 70-150 μm, more preferably 100-120 μm, most preferably 110 μm, for example, 0.1 μm, 1 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm; and / or

[0082] The weight ratio of the first coating layer to the second coating layer is 1:5-1:30, preferably 1:10-1:25, more preferably 1:15-1:20, and most preferably 1:16.

[0083] If the thickness of the first coating is too large, the content of the thermal expansion material will be too high and the energy density will decrease; if the thickness of the first coating is too small, the content of the thermal expansion material will be too low, making it difficult to expand effectively and unable to quickly achieve a direct circuit break between the positive and negative electrodes, thereby failing to effectively hinder the exothermic reaction.

[0084] If the thickness of the second coating is too large, the energy density will be too high, which will have an adverse effect on safety; if the thickness of the second coating is too small, the energy density will be too low, which will be difficult to meet actual needs.

[0085] There is no particular limitation on the type of "positive electrode active material" in the first and second exemplary embodiments, and those commonly used in the art may be used. Typically, the positive electrode active material is selected from at least one of the following groups: lithium cobalt-based oxides, lithium nickel cobalt manganese-based oxides, lithium nickel cobalt aluminum-based oxides, and lithium iron phosphate, but is not limited thereto. Moreover, depending on the desired use, the positive electrode active material may be doped with one or more different elements.

[0086] Non-limiting examples of the positive electrode active material include the following compounds:

[0087] Li a A 1-b B b D2 (where 0.90≤a≤1.8 and 0≤b≤0.5)

[0088] Li a E 1-b B b O 2-c D c (where 0.90≤a≤1.8, 0≤b≤0.5 and 0≤c≤0.05)

[0089] LiE 2-b B b O 4-c D c (where 0≤b≤0.5 and 0≤c≤0.05)

[0090] Li a Ni 1-b-c Co b B c D α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α≤2)

[0091] Li a Ni l-b-c Co b B c O 2-α F α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α<2)

[0092] Li a Ni 1-b-c Co b B c O 2-αF2 (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α<2)

[0093] Li a Ni 1-b-c Mn b B c D α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α≤2)

[0094] Li a Ni 1-b-c Mn b B c O 2-α F α (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α<2)

[0095] Li a Ni 1-b-c Mn b B c O 2-α F2 (where 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α<2)

[0096] Li a Ni b E c G d O2 (where 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5 and 0.001≤d≤0.1)

[0097] Li a Ni b Co c Mn d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5 and 0.001≤e≤0.1)

[0098] Li a NeG b O2 (where 0.90≤a≤1.8 and 0.001≤b≤0.1)

[0099] Li a CoG b O2 (where 0.90≤a≤1.8 and 0.001≤b≤0.1)

[0100] QO2

[0101] QS2

[0102] LiQS2

[0103] V2O5

[0104] LiV2O5

[0105] LiIO2

[0106] LiNiVO4

[0107] Li (3-f) J2(PO4)3(0≤f≤2)

[0108] In the above chemical formula, A may be Ni, Co, or a combination thereof; B may be Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D may be O, F, S, P, or a combination thereof; E may be Co, Mn, or a combination thereof; F may be F, S, P, or a combination thereof; G may be Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q may be Ti, Mo, Mn, or a combination thereof; I may be Cr, V, Fe, Sc, Y, or a combination thereof; and J may be V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0109] Preferably, the positive electrode active material is at least one selected from the following group: lithium cobalt oxide, lithium nickel cobalt manganese oxide and lithium iron phosphate.

[0110] There is no particular limitation on the type of the "conductive agent" in the first and second exemplary embodiments, and those commonly used in the art can be used. Typically, the conductive agent is selected from at least one of the following groups: natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, graphene, mesoporous ordered carbon, activated carbon, metal powder, metal fiber and conductive polymer.

[0111] There is no particular limitation on the type of "binder" in the first and second exemplary embodiments described above, and those commonly used in the art can be used. Typically, the binder is selected from at least one of the following groups: carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polybutadiene, butyl rubber, fluororubber, polyoxyethylene, polyvinyl alcohol, polyacrylic acid and its salts, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acryl resin, phenolic resin, epoxy resin, polyurethane, polyolefin, copolymers of propylene and olefins having 2 to 8 carbon atoms, copolymers of (meth) acrylic acid and (meth) alkyl acrylates, polystyrene butadiene copolymers, and chlorinated rubber.

[0112] In some embodiments, the thermal expansion material in the first and second exemplary embodiments described above includes expanded microspheres.

[0113] In some embodiments, the initial expansion temperature of the expandable microspheres is 100-120°C, preferably 110°C, for example, 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C, 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C, 120°C or any value therebetween. If the initial expansion temperature is too low, the coating may expand too early, affecting the normal operation of the battery; if the initial expansion temperature is too high, the coating may expand too late, making it difficult to quickly achieve direct disconnection between the positive and negative electrodes, thereby failing to effectively hinder the exothermic reaction.

[0114] In some embodiments, the median particle size of the expanded microspheres in the non-expanded state is 2-25 μm, preferably 5-15 μm, more preferably 9-10 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm or any value between these values; and / or

[0115] The expansion multiple of the expanded microspheres at 100-120° C. is 5-20 times, preferably 10 times, for example, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 times, 12 times, 13 times, 14 times, 15 times, 16 times, 17 times, 18 times, 19 times, 20 times or any value in between these values.

[0116] If the median particle size of the expandable microspheres in the non-expanded state is too low, the initial expansion temperature will be too low, the coating will expand prematurely, and the normal operation of the battery will be affected; if the median particle size is too large, the initial expansion temperature will be too high, the coating will expand too late, and it will be difficult to quickly achieve a direct circuit break between the positive and negative electrodes, and thus the exothermic reaction cannot be effectively hindered.

[0117] If the expansion multiple of the expandable microspheres at 100-120°C is too low, it is difficult to expand effectively, and it is impossible to quickly achieve a direct circuit break between the positive and negative electrodes, and thus it is impossible to effectively hinder the exothermic reaction; if the expansion multiple is too large, it may cause premature expansion and affect the normal operation of the battery.

[0118] There is no particular limitation on the type of the expanded microspheres, and those commonly used in the art can be used. Typically, the expanded microspheres include at least one of polyacrylonitrile, poly-N,N-dimethylacrylamide, polyglycidyl methacrylate, polymethacrylic acid, polymethacrylonitrile, polymethyl acrylate, and polyacrylic acid.

[0119] Secondary battery

[0120] In order to at least partially solve one or more of the above problems and other potential problems, a third exemplary embodiment of the present application provides a secondary battery, wherein the secondary battery includes the positive electrode sheet according to the above first exemplary embodiment and the second exemplary embodiment.

[0121] Application of thermal expansion materials

[0122] In order to at least partially solve one or more of the above problems and other potential problems, a fourth exemplary embodiment of the present application provides a use of a thermal expansion material for preparing a coating layer, wherein the coating layer is formed on a current collector of a positive electrode sheet.

[0123] In one embodiment, the thermally expandable material comprises expandable microspheres.

[0124] In some embodiments, the initial expansion temperature of the expandable microspheres is 100-120°C, preferably 110°C, for example, 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C, 110°C, 111°C, 112°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C, 120°C or any value therebetween. If the initial expansion temperature is too low, the coating may expand too early, affecting the normal operation of the battery; if the initial expansion temperature is too high, the coating may expand too late, making it difficult to quickly achieve direct disconnection between the positive and negative electrodes, thereby failing to effectively hinder the exothermic reaction.

[0125] In some embodiments, the median particle size of the expanded microspheres in the non-expanded state is 2-25 μm, preferably 5-15 μm, more preferably 9-10 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm or any value between these values; and / or

[0126] The expansion multiple of the expanded microspheres at 100-120° C. is 5-20 times, preferably 10 times, for example, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 times, 12 times, 13 times, 14 times, 15 times, 16 times, 17 times, 18 times, 19 times, 20 times or any value in between these values.

[0127] If the median particle size of the expandable microspheres in the non-expanded state is too low, the initial expansion temperature will be too low, the coating will expand prematurely, and the normal operation of the battery will be affected; if the median particle size is too large, the initial expansion temperature will be too high, the coating will expand too late, and it will be difficult to quickly achieve a direct circuit break between the positive and negative electrodes, and thus the exothermic reaction cannot be effectively hindered.

[0128] If the expansion multiple of the expandable microspheres at 100-120°C is too low, it is difficult to expand effectively, and it is impossible to quickly achieve a direct circuit break between the positive and negative electrodes, and thus it is impossible to effectively hinder the exothermic reaction; if the expansion multiple is too large, it may cause premature expansion and affect the normal operation of the battery.

[0129] There is no particular limitation on the type of the expanded microspheres, and those commonly used in the art can be used. Typically, the expanded microspheres include at least one of polyacrylonitrile, poly-N,N-dimethylacrylamide, polyglycidyl methacrylate, polymethacrylic acid, polymethacrylonitrile, polymethyl acrylate, and polyacrylic acid.

[0130] Example

[0131] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0132] Example 1

[0133] Prepare the positive electrode sheet, the specific steps are as follows:

[0134] (1) adding super P, polyvinylidene fluoride and expanded microspheres (with an initial expansion temperature of 110° C., a median particle size of 9 μm in a non-expanded state, and an expansion multiple of 10 times at 110° C.) to N-methylpyrrolidone in a weight ratio of 1:4:5 to prepare a first slurry with a solid content of 80%;

[0135] (2) coating the first slurry on an aluminum foil positive electrode current collector, and then drying to obtain a first coating layer (7 μm thick);

[0136] (3) lithium cobalt oxide, super P and polyvinylidene fluoride were added to N-methylpyrrolidone in a weight ratio of 97:1:2 to prepare a second slurry with a solid content of 48%, and then the second slurry was coated on the first coating and dried to form a second coating (thickness of 110 μm), and then cold pressed and cut to obtain a positive electrode sheet;

[0137] The weight ratio of the first coating layer to the second coating layer is 1:16.

[0138] Example 2

[0139] Prepare the positive electrode sheet, the specific steps are as follows:

[0140] (1) adding lithium cobalt oxide, super P, polyvinylidene fluoride and expanded microspheres (with an initial expansion temperature of 110° C., a median particle size of 9 μm in a non-expanded state, and an expansion multiple of 10 times at 110° C.) to N-methylpyrrolidone in a weight ratio of 80:3:3:14 to prepare a slurry with a solid content of 48%; and

[0141] (2) The slurry was coated on an aluminum foil positive electrode current collector and dried to form a coating (117 μm thick), which was then cold pressed and cut to obtain a positive electrode sheet.

[0142] Example 3

[0143] The method is basically the same as Example 1, except that in step (1), the weight ratio of super P, polyvinylidene fluoride and expanded microspheres is 1:5:4.

[0144] Example 4

[0145] It is basically the same as Example 1, except that the thickness of the first coating layer is 10 μm, the thickness of the second coating layer is 50 μm, and the weight ratio of the first coating layer to the second coating layer is 1:5.

[0146] Example 5

[0147] It is basically the same as Example 1, except that the thickness of the first coating layer is 5 μm, the thickness of the second coating layer is 100 μm, and the weight ratio of the first coating layer to the second coating layer is 1:20.

[0148] Example 6

[0149] It is basically the same as Example 1, except that the initial expansion temperature of the expanded microspheres is 100°C.

[0150] Example 7

[0151] It is basically the same as Example 1, except that the initial expansion temperature of the expanded microspheres is 120°C.

[0152] Example 8

[0153] It is basically the same as Example 1, except that the median particle size of the expanded microspheres in the non-expanded state is 2 μm.

[0154] Example 9

[0155] It is basically the same as Example 1, except that the median particle size of the expanded microspheres in the non-expanded state is 25 μm.

[0156] Example 10

[0157] It is basically the same as Example 1, except that the expansion multiple of the expanded microspheres at 110° C. is 5 times.

[0158] Embodiment 11

[0159] It is basically the same as Example 1, except that the expansion multiple of the expanded microspheres at 110° C. is 20 times.

[0160] Example 12

[0161] The method is basically the same as Example 2, except that in step (1), the weight ratio of lithium cobalt oxide, super P, polyvinylidene fluoride and expanded microspheres is 90:2:3:5.

[0162] Embodiment 13

[0163] The method is basically the same as Example 2, except that in step (1), the weight ratio of lithium cobalt oxide, super P, polyvinylidene fluoride and expanded microspheres is 75:2:3:20.

[0164] Embodiment 14

[0165] It is basically the same as Example 2, except that the initial expansion temperature of the expanded microspheres is 100°C.

[0166] Embodiment 15

[0167] It is basically the same as Example 2, except that the initial expansion temperature of the expanded microspheres is 130°C.

[0168] Example 16

[0169] It is basically the same as Example 2, except that the median particle size of the expanded microspheres in the non-expanded state is 2 μm.

[0170] Embodiment 17

[0171] It is basically the same as Example 2, except that the median particle size of the expanded microspheres in the non-expanded state is 25 μm.

[0172] Embodiment 18

[0173] It is basically the same as Example 2, except that the expansion multiple of the expanded microspheres at 110° C. is 5 times.

[0174] Embodiment 19

[0175] It is basically the same as Example 2, except that the expansion multiple of the expanded microspheres at 110° C. is 20 times.

[0176] Comparative Example 1

[0177] It is basically the same as Example 1, except that expanded microspheres are not used.

[0178] Comparative Example 2

[0179] It is basically the same as Example 2, except that expanded microspheres are not used.

[0180] test

[0181] Test Standards

[0182] The positive electrode sheets of the above-mentioned Examples 1-19 and Comparative Examples 1-2 were used to prepare lithium secondary batteries, and then subjected to a 130° C. thermal abuse test. Test method: The fully charged lithium secondary battery was heated to 130° C. at a heating rate of 5° C. / min and maintained for 30 minutes.

[0183] Test Results

[0184] For specific test results, see Table 1 below.

[0185] Table 1

[0186]

[0187]

[0188] It can be clearly seen from Table 1 that, compared with Comparative Examples 1-2 which do not use expanded microspheres, Examples 1-19 which use expanded microspheres all show significant improvement in safety performance at high temperatures, thereby achieving beneficial technical effects.

[0189] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet comprises: a current collector; and A coating is formed on the current collector, the coating comprising a thermal expansion material.

2. The positive electrode sheet according to claim 1, characterized in that: Based on the total weight of the coating, the thermal expansion material accounts for 5-20 wt %, preferably 8-15 wt %, and more preferably 14 wt %.

3. A positive electrode sheet, characterized in that: The positive electrode sheet comprises: current collector; forming a first coating layer on the current collector, the first coating layer comprising a thermal expansion material; and A second coating layer is formed on the first coating layer.

4. The positive electrode sheet according to claim 3, characterized in that: Based on the total weight of the first coating layer, the thermal expansion material accounts for 40-90 wt %, preferably 45-80 wt %, and more preferably 50 wt %.

5. The positive electrode sheet according to claim 3, characterized in that: The thickness of the first coating is 0.1-30 μm, preferably 1-20 μm, more preferably 5-10 μm, most preferably 7 μm; and / or The thickness of the second coating is 0.1-200 μm, preferably 70-150 μm, more preferably 100-120 μm, most preferably 110 μm; and / or The weight ratio of the first coating layer to the second coating layer is 1:5-1:30, preferably 1:10-1:25, more preferably 1:15-1:20, and most preferably 1:

16.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The heat expandable material includes expandable microspheres.

7. The positive electrode sheet according to claim 6, characterized in that: The initial expansion temperature of the expanded microspheres is 100-120°C, preferably 110°C.

8. The positive electrode sheet according to claim 6, characterized in that: The median particle size of the expanded microspheres in a non-expanded state is 2-25 μm, preferably 5-15 μm, more preferably 9-10 μm; and / or The expansion multiple of the expanded microspheres at 100-120° C. is 5-20 times, preferably 10 times.

9. The positive electrode sheet according to claim 6, characterized in that: The expanded microspheres include at least one of polyacrylonitrile, poly-N,N-dimethylacrylamide, polyglycidyl methacrylate, polymethacrylic acid, polymethacrylonitrile, polymethyl acrylate and polyacrylic acid.

10. A secondary battery, characterized in that: The secondary battery comprises the positive electrode sheet according to any one of claims 1 to 9.

11. Use of a thermal expansion material for preparing a coating, characterized in that: The coating is formed on the current collector of the positive electrode sheet.

12. The use according to claim 11, characterized in that The heat expandable material includes expandable microspheres.

13. The use according to claim 12, characterized in that The initial expansion temperature of the expanded microspheres is 100-120°C, preferably 110°C.

14. The use according to claim 12, characterized in that The median particle size of the expanded microspheres in a non-expanded state is 2-25 μm, preferably 5-15 μm, more preferably 9-10 μm; and / or The expansion multiple of the expanded microspheres at 100-120° C. is 5-20 times, preferably 10 times.

15. The positive electrode sheet according to claim 12, characterized in that: The expanded microspheres include at least one of polyacrylonitrile, poly-N,N-dimethylacrylamide, polyglycidyl methacrylate, polymethacrylic acid, polymethacrylonitrile, polymethyl acrylate and polyacrylic acid.

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