Positive electrode sheet, secondary battery comprising the same, and use of thermal expansion material

Abstract

The application provides a positive electrode tab, a secondary battery containing the positive electrode tab, and a use of a thermal expansion material. The positive electrode tab comprises a current collector and a coating layer formed on the current collector, wherein the coating layer comprises a thermal expansion material. The positive electrode tab of the present disclosure uses the thermal expansion material, so that the positive electrode active material can fall off from the current collector at an abnormally high temperature, forming a direct open circuit, hindering the subsequent continuous exothermic reaction, and thus greatly improving the safety performance of the secondary battery.

Description

TECHNICAL FIELD

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

[0002] In recent years, secondary batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0003] However, although the field and range of application of secondary batteries are increasingly expanding, in actual application, the secondary batteries are prone to shrinkage or melting of the separator, resulting in short circuit of the positive and negative electrodes, and then causing the internal release of a large amount of heat in the battery cell, leading to thermal runaway, and even causing fire or explosion. Therefore, the existing positive electrode sheet of the secondary battery still needs to be improved. SUMMARY

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

[0005] To achieve the above-mentioned purpose, the present application provides a positive electrode sheet, which uses a coating layer including a thermal expansion material, so that the instantaneous heat release reaction caused by direct short-circuiting of the positive and negative electrodes can be avoided, and the safety of the secondary battery is greatly improved.

[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 layer formed on the current collector, the coating layer comprising a thermal expansion material.

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

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

[0011] a current collector;

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

[0013] a second coating layer formed on the first coating layer.

[0014] When the two-coating structure is adopted, the direct disconnection between the positive and negative electrodes can be achieved by making the first coating fall off, thereby hindering the subsequent sustained exothermic reaction. Therefore, compared with the single-coating structure of the first aspect, the amount of the 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 effectively expand and quickly achieve the direct disconnection between the positive and negative electrodes, 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, and 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, and most preferably 110 μm; and / or

[0018] The weight ratio of the first coating to the second coating 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, and it will be difficult to effectively expand and quickly achieve the direct disconnection 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 adversely affect 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 comprises expanded microspheres.

[0021] In any embodiment, the initial expansion temperature of the expanded microspheres is 100-120℃, and preferably 110℃. If the initial expansion temperature is too low, the coating may expand too early, which will affect normal battery operation; if the initial expansion temperature is too high, the coating may expand too late, which will be difficult to quickly achieve the 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 the unexpanded state is 2-25 μm, preferably 5-15 μm, and more preferably 9-10 μm; and / or

[0023] The expansion microspheres have an expansion ratio of 5-20 times, preferably 10 times, at 100-120°C.

[0024] If the median particle size of the expansion microspheres in the unexpanded state is too low, the initial expansion temperature will be too low, the coating will expand too early, 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 direct disconnection between the positive and negative electrodes, thereby failing to effectively hinder the exothermic reaction.

[0025] If the expansion ratio of the expansion microspheres at 100-120°C is too low, the expansion will not be effective, it will be difficult to quickly achieve direct disconnection between the positive and negative electrodes, and thus the exothermic reaction cannot be effectively hindered; if the expansion ratio is too large, it may cause premature expansion, affecting the normal operation of the battery. In any embodiment, the expansion microspheres comprise at least one of polyacrylonitrile, poly N,N-dimethyl acrylamide, poly glycidyl methacrylate, poly methacrylic acid, poly methacrylonitrile, poly methyl acrylate, and poly acrylic acid.

[0026] The 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] The fourth aspect of the present application provides a use of a thermal expansion material for preparing a coating formed on a current collector of a positive electrode sheet.

[0028] In any embodiment, the thermal expansion material comprises expansion microspheres.

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

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

[0031] The expansion microspheres have an expansion ratio of 5-20 times, preferably 10 times, at 100-120°C.

[0032] In any embodiment, the expansion microspheres comprise at least one of polyacrylonitrile, poly N,N-dimethyl acrylamide, poly glycidyl methacrylate, poly methacrylic acid, poly methacrylonitrile, poly methyl acrylate, and poly acrylic acid. DETAILED DESCRIPTION

[0033] Hereinafter, the embodiments of the positive electrode tab, the secondary battery including the positive electrode tab, and the use of the thermal expansion material of the present application will be described in detail as appropriate. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repeated description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0034] The ranges in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The ranges defined in this manner can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand manner of describing each and every number that is contained in the range, wherein a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand manner of describing each and every number that is contained in the range. In addition, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and the like.

[0035] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0036] If not specifically stated, all steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), and the like.

[0037] If not specifically stated, the "comprise", "include", "have", "contain", or any other variant thereof mentioned in the present application is intended to cover non-exclusive inclusion.

[0038] The term "or" is inclusive in this application, unless otherwise indicated. So, for example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0039] The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one." The use of "one" or "the" in the claims is not limiting to only one of the features recited in the claim. Thus, the use of "one" or "the" in the claims is not limiting to only one of the features recited in the claim.

[0040] Further, in the following description, numerous specific details are set forth to provide a thorough understanding of the present application. However, it will be apparent to one of ordinary skill in the art that the application can be practiced without these specific details. In other instances, well-known methods have not been described in detail in order not to unnecessarily obscure the present application.

[0041] The term "positive electrode sheet" refers to an electrode sheet having a high potential containing an active material that undergoes a reduction reaction during discharge.

[0042] The term "current collector" refers to any electrically 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 that rapidly expands in volume upon heating, is well compatible with other materials in the coating, and can be made to rapidly expand by its properties, so that the positive active material can be detached from the current collector at an abnormally high temperature, forming a direct short circuit, and hindering the subsequent continuous exothermic reaction.

[0044] The term "expanding microsphere" refers to a microspherical particle having a core-shell spherical structure that can be thermally expanded and foamed, with a low-boiling alkane as a foaming agent in the core and a thermoplastic polymer as the shell.

[0045] The term "positive active material" refers to an active material on the positive side of a secondary battery that can reversibly occlude and release (typically, intercalate and deintercalate) a chemical species that becomes a charge carrier (here, lithium ions).

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

[0047] The term "binder" refers to an additive that is added to bond active materials to each other or to bond active materials to a current collector, thereby maintaining the electrode structure.

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

[0049] As described above, the secondary battery in the prior art still has the problem of being unable to effectively control thermal runaway, which needs to be solved.

[0050] Positive electrode sheet

[0051] To at least partially solve one or more of the above problems and other potential problems, the first example embodiment of the present application provides a positive electrode tab, wherein the positive electrode tab comprises:

[0052] a current collector; and

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

[0054] Due to the use of the coating layer comprising the thermal expansion material in the positive electrode tab, the instantaneous heat release reaction of avoiding the direct short circuit between the positive and negative electrodes can be achieved by the coating layer falling off, thereby greatly improving the safety.

[0055] In some embodiments, the thermal expansion material accounts for 5-20 wt%, preferably 8-15 wt%, more preferably 14 wt%, of the total weight of the coating layer, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, or any value between these values. 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 is difficult to effectively expand and quickly achieve the direct circuit breaking between the positive and negative electrodes, thereby failing to effectively hinder the heat release reaction.

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

[0057] In some embodiments, the positive electrode active material accounts for 70-90 wt%, preferably 80 wt%, of the total weight of the coating layer, for example, 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 between these values; and / or

[0058] the conductive agent accounts for 1-5 wt%, preferably 2-4 wt%, more preferably 3 wt%, of the total weight of the coating layer, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or any value between these values; and / or

[0059] The binder is 1-5 wt%, preferably 2-4 wt%, more preferably 3 wt%, for example 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or any value between these values; and / or

[0060] The thermal expansion material is 5-20 wt%, preferably 8-15 wt%, more preferably 14 wt%, for example 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, or any value between these values.

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

[0062] 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, the energy density and adhesion will be adversely affected.

[0063] If the content of the binder is too low, the adhesion will not meet the requirements; if the content of the binder is too high, the energy density and conductivity will be adversely affected.

[0064] To at least partially solve one or more of the above problems and other potential problems, the second example embodiment of the present application provides another positive electrode tab, wherein the positive electrode tab comprises:

[0065] a current collector;

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

[0067] a second coating layer formed on the first coating layer.

[0068] When a two-coating layer structure is adopted, the direct disconnection between the positive and negative electrodes can be achieved by causing the first coating layer to fall off, thereby hindering the subsequent sustained exothermic reaction. Therefore, compared with the single-coating layer structure of the first aspect described above, the amount of thermal expansion material can be appropriately reduced, thereby saving costs.

[0069] In some embodiments, the thermal expansion material accounts for 40-90 wt%, preferably 45-80 wt%, more preferably 50 wt%, for example 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt%, 55 wt%, 56 wt%, 57 wt%, 58 wt%, 59 wt%, 60 wt%, 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 between these values, of 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 circuit between the positive and negative electrodes cannot be quickly realized, thereby failing to effectively hinder the exothermic reaction.

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

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

[0072] The binder can be 5-50 wt.%, preferably 40 wt.%, for example 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, 20 wt.%, 21 wt.%, 22 wt.%, 23 wt.%, 24 wt.%, 25 wt.%, 26 wt.%, 27 wt.%, 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 between these values; and / or

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

[0074] In some embodiments, the cathode active material can be 90-98 wt.%, preferably 97 wt.%, based on the total weight of the second coating, for example 91 wt.%, 92 wt.%, 93 wt.%, 94 wt.%, 95 wt.%, 96 wt.%, 97 wt.%, 98 wt.%, or any value between these values; and / or

[0075] The conductive agent can be 0.5-5 wt.%, preferably 1 wt.%, for example 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, or any value between these values; and / or

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

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

[0078] In the first coating and the second coating, 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, the energy density and adhesion will be adversely affected.

[0079] If the content of the binder is too low, the adhesion will not meet the requirements; if the content of the binder is too high, the energy density and conductivity will be adversely affected.

[0080] In some embodiments, the thickness of the first coating is 0.1-30 μm, preferably 1-20 μm, more preferably 5-10 μm, most preferably 7 μm, for example, 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 to the second coating is 1:5-1:30, preferably 1:10-1:25, more preferably 1:15-1:20, 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, and it will be difficult to effectively expand and quickly achieve direct disconnection between the positive and negative electrodes, thereby failing to effectively hinder the exothermic reaction.

[0084] If the second coating layer is too thick, the energy density will be too high, which adversely affects safety. If the second coating layer is too thin, the energy density will be too low, which makes it difficult to meet actual requirements.

[0085] There is no particular limitation regarding the type of "positive electrode active material" in the above-described first example embodiment and second example embodiment, and those commonly used in the art can be employed. Typically, the positive electrode active material is selected from at least one of the group consisting of lithium cobalt-based oxides, lithium nickel cobalt manganese-based oxides, lithium nickel cobalt aluminum-based oxides, and lithium iron phosphates, but is not limited thereto. Also, the positive electrode active material can be doped with one or more different elements depending on the intended use.

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

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

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

[0090] Li a Ni 1-b-c Co b B c D α (wherein 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 (wherein 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 NiG 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 can be Ni, Co, or a combination thereof; B can be Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D can be O, F, S, P, or a combination thereof; E can be Co, Mn, or a combination thereof; F can be F, S, P, or a combination thereof; G can be Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q can be Ti, Mo, Mn, or a combination thereof; I can be Cr, V, Fe, Sc, Y, or a combination thereof; and J can be V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

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

[0110] As for the type of the "conductive agent" in the above-described first example embodiment and second example embodiment, there is no particular limitation, and those commonly used in the art can be employed. Typically, the conductive agent is selected from at least one of the group consisting of 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] As for the type of the "binder" in the above-described first example embodiment and second example embodiment, there is no particular limitation, and those commonly used in the art can be employed. Typically, the binder is selected from at least one of the group consisting of 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 salt, polyvinyl pyrrolidone, polyepoxy chloropropane, polyphosphazene, polyacrylonitrile, polystyrene, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acryl resin, phenol resin, epoxy resin, polyurethane, polyolefinic acid, copolymer of propylene and olefin having 2-8 carbon atoms, copolymer of (meth)acrylic acid and (meth)acrylic acid alkyl ester, polystyrene butadiene copolymer, and chlorinated rubber.

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

[0113] In some embodiments, the expanded microspheres have an initial expansion temperature of 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 between these values. 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 expanded microspheres have a median particle size of 2-25 μm, preferably 5-15 μm, more preferably 9-10 μm, in the unexpanded state, 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 expanded microspheres have an expansion ratio of 5-20 times, preferably 10 times, at 100-120°C, 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 between these values.

[0116] If the median particle size of the expanded microspheres in the unexpanded state is too low, the initial expansion temperature will be too low, the coating will expand too early, affecting the normal operation of the battery; if the median particle size is too large, the initial expansion temperature will be too high, the coating will 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.

[0117] If the expansion ratio of the expanded microspheres at 100-120°C is too low, the coating may not expand effectively, making it difficult to quickly achieve direct disconnection between the positive and negative electrodes, thereby failing to effectively hinder the exothermic reaction; if the expansion ratio is too large, the coating may expand too early, affecting 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 first and second exemplary embodiments.

[0121] Use of a thermal expansion material

[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 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 prematurely, 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 a direct circuit break between the positive and negative electrodes, thereby failing to effectively inhibit the exothermic reaction.

[0125] In some embodiments, the expanded microspheres have a median particle size in a non-expanded state of 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 in between; and / or

[0126] The expansion microspheres have an expansion ratio of 5-20 times, preferably 10 times, at 100-120°C, 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 between these values.

[0127] If the median particle size of the expansion microspheres in the unexpanded state is too low, the initial expansion temperature will be too low, the coating will expand too early, 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 direct disconnection between the positive and negative electrodes, thereby failing to effectively hinder the exothermic reaction.

[0128] If the expansion ratio of the expansion microspheres at 100-120°C is too low, the expansion will not be effective, and it will be difficult to quickly achieve direct disconnection between the positive and negative electrodes, thereby failing to effectively hinder the exothermic reaction; if the expansion ratio is too large, it may cause premature expansion, affecting the normal operation of the battery.

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

[0130] Examples

[0131] Hereinafter, examples of the present application will be described. The examples described below are exemplary and are intended to explain the present application, and should not be construed as limiting the present application. If a specific technique or condition is not mentioned in the examples, the technique or condition described in the literature in the art or according to the product manual is used. If the reagent or instrument used is not mentioned by the manufacturer, it is a conventional product that can be obtained by purchase on the market.

[0132] Example 1

[0133] A positive electrode sheet was prepared according to the following specific steps:

[0134] (1) Super P, polyvinylidene fluoride, and expansion microspheres (initial expansion temperature of 110°C, median particle size of 9 μm in the unexpanded state, and expansion ratio of 10 times at 110°C) were added to N-methyl pyrrolidone at a weight ratio of 1:4:5 to prepare a first slurry with a solid content of 80%;

[0135] (2) The first slurry was coated on an aluminum foil positive current collector, and then dried to obtain a first coating (thickness of 7 μm);

[0136] (3) Lithium cobaltate, super P and polyvinylidene fluoride are added to N-methylpyrrolidone in a weight ratio of 97:1:2 to prepare a second slurry having a solid content of 48%, which is then coated on the first coating layer described above and dried to form a second coating layer (thickness: 110 μm), followed by cold pressing and slitting 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] A positive electrode sheet is prepared by the following steps:

[0140] (1) Lithium cobaltate, super P, polyvinylidene fluoride and expanded microspheres (initial expansion temperature: 110°C, median particle size in non-expanded state: 9 μm, expansion ratio at 110°C: 10 times) are added to N-methylpyrrolidone in a weight ratio of 80:3:3:14 to prepare a slurry having a solid content of 48%; and

[0141] (2) The slurry described above is coated on an aluminum foil positive current collector and dried to form a coating layer (thickness: 117 μm), followed by cold pressing and slitting to obtain a positive electrode sheet.

[0142] Example 3

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

[0144] Example 4

[0145] 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] 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] The same as Example 1, except that the initial expansion temperature of the expanded microspheres is 100°C.

[0150] Example 7

[0151] 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] The method is basically the same as Example 1, except that the expansion ratio of the expanded microspheres at 110° C. is 5 times.

[0158] Example 11

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

[0160] Example 12

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

[0162] Example 13

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

[0164] Example 14

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

[0166] Example 15

[0167] The method 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] Example 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] Example 18

[0173] The same as Example 2, except that the expanded microspheres have an expansion ratio of 5 times at 110°C.

[0174] Example 19

[0175] The same as Example 2, except that the expanded microspheres have an expansion ratio of 20 times at 110°C.

[0176] Comparative Example 1

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

[0178] Comparative Example 2

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

[0180] Test

[0181] Test standards

[0182] Using the positive electrode tabs of Examples 1-19 and Comparative Examples 1-2 described above, lithium secondary batteries were respectively prepared, and then subjected to a 130°C thermal abuse test. Test method: the full-charge lithium secondary battery was heated to 130°C at a heating rate of 5°C / min, and maintained for 30 min.

[0183] Test results

[0184] Specific test results are shown in Table 1 below.

[0185] Table 1

[0186]

[0187]

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

[0189] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration and playing the same role and effects as the technical idea within the scope of the technical solutions of the present application are all included in the technical scope of the present application. Furthermore, within the scope of the main idea of the present application, other modes obtained by applying various modifications to the embodiments, or combining part of the configuration elements of the embodiments, are also included in the scope of the present application.

Claims

1. A positive electrode plate, characterized in that: The positive electrode plate comprises: a current collector; and forming a coating on the current collector, the coating comprising a thermal expansion material, The thermal expansion material includes expandable microspheres, the median particle size of the expandable microspheres in a non-expanded state is 9 μm-10 μm, and the expandable microspheres include at least one of polyacrylonitrile, poly N,N-dimethylacrylamide, polyglycidyl methacrylate, polymethacrylic acid, polymethacrylonitrile, polymethyl acrylate and polyacrylic acid.

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 wt% to 20 wt%.

3. 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 8 wt % to 15 wt %.

4. 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 14 wt%.

5. A positive electrode plate, characterized in that: The positive electrode plate comprises: current collector; forming a first coating layer on the current collector, the first coating layer comprising a thermal expansion material; and forming a second coating layer on the first coating layer, The thermal expansion material includes expandable microspheres, the median particle size of the expandable microspheres in a non-expanded state is 9 μm-10 μm, and the expandable microspheres include at least one of polyacrylonitrile, poly N,N-dimethylacrylamide, polyglycidyl methacrylate, polymethacrylic acid, polymethacrylonitrile, polymethyl acrylate and polyacrylic acid.

6. The positive electrode sheet according to claim 5, characterized in that: Based on the total weight of the first coating layer, the thermal expansion material accounts for 40 wt % to 90 wt %.

7. The positive electrode sheet according to claim 5, characterized in that: Based on the total weight of the first coating layer, the thermal expansion material accounts for 45 wt% to 80 wt%.

8. The positive electrode sheet according to claim 5, characterized in that: Based on the total weight of the first coating layer, the thermal expansion material accounts for 50 weight %.

9. The positive electrode sheet according to claim 5, characterized in that: The thickness of the first coating is 0.1 μm-30 μm; and / or The thickness of the second coating layer is 0.1 μm-200 μm; and / or The weight ratio of the first coating layer to the second coating layer is 1:5-1:

30.

10. The positive electrode sheet according to claim 5, characterized in that: The thickness of the first coating layer is 1 μm-20 μm; and / or The thickness of the second coating layer is 70 μm-150 μm; and / or The weight ratio of the first coating layer to the second coating layer is 1:10-1:

25.

11. The positive electrode sheet according to claim 5, characterized in that: The thickness of the first coating layer is 5 μm-10 μm; and / or The thickness of the second coating layer is 100 μm-120 μm; and / or The weight ratio of the first coating layer to the second coating layer is 1:15-1:

20.

12. The positive electrode sheet according to claim 5, characterized in that: The thickness of the first coating layer is 7 μm; and / or The thickness of the second coating layer is 110 μm; and / or The weight ratio of the first coating layer to the second coating layer is 1:

16.

13. The positive electrode sheet according to any one of claims 1 to 12, characterized in that: The initial expansion temperature of the expandable microspheres is 100°C-120°C.

14. The positive electrode sheet according to claim 13, characterized in that: The initial expansion temperature of the expanded microspheres is 110°C.

15. The positive electrode sheet according to claim 13, characterized in that: The expansion multiple of the expanded microspheres at 100° C.-120° C. is 5 to 20 times.

16. The positive electrode sheet according to claim 13, characterized in that: The expansion ratio of the expanded microspheres at 100° C.-120° C. is 10 times.

17. A secondary battery, characterized in that: The secondary battery comprises the positive electrode sheet according to any one of claims 1 to 16.

18. 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, wherein the thermal expansion material includes expanded microspheres, the median particle size of the expanded microspheres in a non-expanded state is 9 μm-10 μm, and the expanded microspheres include at least one of polyacrylonitrile, poly N,N-dimethylacrylamide, polyglycidyl methacrylate, polymethacrylic acid, polymethacrylonitrile, polymethyl acrylate and polyacrylic acid.

19. The use according to claim 18, characterized in that The initial expansion temperature of the expandable microspheres is 100°C-120°C.

20. The use according to claim 18, characterized in that The initial expansion temperature of the expanded microspheres is 110°C.

21. The use according to claim 18, characterized in that The expansion multiple of the expanded microspheres at 100° C.-120° C. is 5 to 20 times.

22. The use according to claim 18, characterized in that The expansion ratio of the expanded microspheres at 100-120° C. is 10 times.

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