Aqueous positive electrode slurry, preparation method thereof, positive electrode plate, secondary battery and electric device

Abstract

The invention provides water-based positive electrode slurry, a preparation method thereof, a positive electrode plate, a secondary battery and an electric device. The water-based positive electrode slurry comprises water and functional substances dispersed in the water, the functional substances comprise a positive electrode active material, a hydrophobic modified fast ion conductor and a water-based binder, and the hydrophobic modified fast ion conductor is attached to at least part of the surface of the positive electrode active material. The surface hydrophilic capacity of the hydrophobic modified fast ion conductor is reduced, so that the water stability is improved; after the water-based positive electrode slurry forms a film layer of a positive electrode plate, the hydrophobic modified fast ion conductor improves the ion conductivity of the film layer, so that the direct-current impedance of the secondary battery is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to an aqueous positive electrode slurry, a preparation method thereof, a positive electrode sheet, a secondary battery, and an electrical device. Background Art

[0002] Currently, the positive electrode sheets of commercial lithium-ion batteries are basically obtained by coating an oil-based slurry of an N-methylpyrrolidone-polyvinylidene fluoride (NMP-PVDF) system. However, the NMP solvent has problems such as harming human health, being difficult to recycle, and polluting the environment during the electrode preparation process, which limits the manufacture and application of lithium batteries around the world. At the same time, with the increase in the prices of NMP and PVDF, the production cost problem of lithium batteries has become increasingly serious.

[0003] To solve the above problems, an aqueous positive electrode system using deionized water as a slurry solvent has attracted much attention. The large swelling of the aqueous binder results in a decrease in the porosity of the positive electrode sheet and an increase in the tortuosity, further deteriorating the ion conduction. Summary of the Invention

[0004] The present application provides an aqueous positive electrode slurry, a preparation method thereof, a positive electrode sheet, a secondary battery, and an electrical device to improve the ion conductivity of the positive electrode sheet prepared from the aqueous positive electrode slurry.

[0005] In a first aspect of the present application, there is provided an aqueous positive electrode slurry, which includes water and functional substances dispersed in the water. The functional substances include a positive electrode active material, a hydrophobic modified fast ion conductor, and an aqueous binder, and at least a part of the surface of the positive electrode active material is attached with the hydrophobic modified fast ion conductor.

[0006] The aqueous positive electrode slurry of the present application contains a hydrophobic modified fast ion conductor, and the hydrophilic ability of the surface of the hydrophobic modified fast ion conductor is decreased, thereby improving its water stability; after the aqueous positive electrode slurry forms a film layer of the positive electrode sheet, the hydrophobic modified fast ion conductor therein improves the ion conductivity of the film layer, thereby reducing the DC impedance of the secondary battery.

[0007] In any implementation manner of the first aspect, the hydrophobic modified fast ion conductor includes a fast ion conductor matrix and a hydrophobic modifier. The hydrophobic modifier has a hydrophobic group, and the modifier is attached to at least a part of the surface of the fast ion conductor matrix and the hydrophobic group is exposed on the surface of the hydrophobic modified fast ion conductor.

[0008] In any implementation manner of the first aspect, the Dv50 particle size of the hydrophobic modified fast ion conductor is 5 nm - 50 nm.

[0009] In any embodiment of the first aspect, the fast ion conductor matrix includes one or more of NASICON structure oxide solid electrolyte materials, garnet structure oxide solid electrolyte materials, and perovskite structure oxide solid electrolyte materials.

[0010] In any embodiment of the first aspect, the NASICON structure oxide solid electrolyte material includes Li 1+x’ Al x’ Ti 2-x’ (PO 4 ) 3 material, Li 1+x’ Al x’ Ge 2-x’ (PO 4 ) 3 material, doped element-containing Li 1+x’ Al x’ Ge 2-x’ (PO 4 ) 3 material, doped element-containing Li 1+x’ Al x’ Ti 2-x’ (PO 4 ) 3 material, at least one of 0 ≤ x’ ≤ 0.75.

[0011] In any embodiment of the first aspect, the garnet structure oxide solid electrolyte material includes Li 7-a’ La 3 A 2-a’ O 12 material and doped element-containing Li 7-a’ La 3 A 2-a’ O 12 material, at least one of 0 ≤ a’ ≤ 1, A includes at least one of Ta, Zr, and Nb.

[0012] In any embodiment of the first aspect, the perovskite structure oxide solid electrolyte material includes Li 3b’ La 2 / 3-b’ TiO 3 material, Li 3b’ Nb 2 / 3-b’ TiO 3 material, doped element-containing Li 3b’ La 2 / 3-b’ TiO 3 material and doped element-containing Li 3b’ Nb 2 / 3-b’ TiO 3 material, at least one of 0.06 ≤ b’ ≤ 0.14.

[0013] In any embodiment of the first aspect, the doping element includes any one or more of Zr, La, and Si.

[0014] In any embodiment of the first aspect, the hydrophobic modifier includes any one or more of solid fatty acids and organosiloxanes; optionally, the solid fatty acids include any one or more of lauric acid, palmitic acid, oleic acid, myristic acid, and stearic acid, and the organosiloxanes include any one or more of polydimethylsiloxane, amino silicone oil, and polyoxyethylene ether trisiloxane.

[0015] In any embodiment of the first aspect, in the functional material, the weight content of the hydrophobic modified fast ion conductor is 0.01% - 2%, optionally 0.05% - 0.5%; the weight content of the fast ion conductor matrix in the hydrophobic modified fast ion conductor is 70% - 90%.

[0016] In any embodiment of the first aspect, the Dv50 particle size of the positive electrode active material is 0.5 μm - 50 μm; optionally, in the functional material, the weight content of the positive electrode active material is 95% - 97%; optionally, the positive electrode active material includes Li m H a Fe x D d P y E e O z G g , Li(Ni x” Co y” Mn z’ Al a” Cu b Zn c Ti d )O 2 or several of them, H includes at least one element of Al, Na, K, or Mg; D includes at least one element of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti, or V; E includes at least one element of B, S, Si, or N; G includes at least one element of S, F, Cl, or Br; m is selected from the range of 0.5 to 1.15; a is selected from the range of 0 to 0.1; x is selected from the range of 0.5 to 1; d is selected from the range of 0 to 0.5; y is selected from the range of 0.5 to 1; e is selected from the range of 0 to 0.5; z is selected from the range of 3.5 to 4; g is selected from the range of 0 to 0.5; x + y + z + a + b + c + d = 1, 0.5 ≤ x < 1, 0.05 ≤ y < 1, 0 ≤ z < 0.5, 0 ≤ a ≤ 0.1, 0 ≤ b ≤ 0.1, 0 ≤ c ≤ 0.1, 0 ≤ d ≤ 0.1.

[0017] In any embodiment of the first aspect, the weight content of the aqueous binder in the functional material is 0.1%-5%, optionally 2%-4%; optionally, the aqueous binder includes any one or more of methylcellulose and its salts, xanthan gum and its salts, chitosan and its salts, alginic acid and its salts, polyacrylamide, or acrylonitrile-acrylic acid copolymer and its derivatives; further optionally, the aqueous binder is acrylonitrile-acrylic acid copolymer, and more optionally, the number average molecular weight of the acrylonitrile-acrylic acid copolymer is 300,000-2,000,000.

[0018] In any embodiment of the first aspect, the functional material further includes a dispersant. The dispersant is used to improve the dispersibility of the hydrophobic modified fast ion conductor with a hydrophobic group in the aqueous positive electrode slurry, and further achieve the purpose of improving its adhesion effect on the surface of the positive electrode active material.

[0019] In any embodiment of the first aspect, the weight content of the dispersant in the functional material is 0.01%-0.7%, optionally 0.1%-0.5%; further optionally, the dispersant includes one or more of cationic dispersants and amphoteric dispersants; more optionally, the dispersant includes one or more of polyethyleneimine, polyethylene glycol octyl phenyl ether, styrene maleic anhydride copolymer, amino silicone oil, and polyvinylpyridine.

[0020] In any embodiment of the first aspect, the functional material further includes a conductive agent; optionally, the weight percentage content of the conductive agent in the functional material is 0.1%-5%, optionally 0.5%-3%; further optionally, the conductive agent includes one or more of conductive carbon black, conductive graphite, graphene, and carbon nanotubes. The conductive agent is used to further reduce the resistivity of the formed positive electrode sheet and improve the charge and discharge performance of the battery cell.

[0021] In any embodiment of the first aspect, the solid content of the aqueous positive electrode slurry is 40%-90%, optionally 50%-70%; and / or, the rotational viscosity of the aqueous positive electrode slurry at 25°C is 100 cp-10,000 cp, optionally 3,000 cp-7,000 cp.

[0022] The second aspect of the present application provides a method for preparing an aqueous positive electrode slurry, wherein the preparation method includes:

[0023] Kneading the positive electrode active material, the modified fast ion conductor, the optional conductive agent, and the optional first part of the dispersant to form a first mixture;

[0024] Mixing the first mixture, the aqueous binder, the optional remaining dispersant, and water to obtain the aqueous positive electrode slurry, and the weight ratio of the first part of the dispersant to the remaining dispersant is 6:4-9:2.

[0025] The third aspect of the present application provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. The positive electrode film layer includes a film layer formed by drying the aqueous positive electrode slurry provided in any embodiment of the first aspect above.

[0026] In any embodiment of the third aspect, the water contact angle of the positive electrode sheet is 70° - 90°.

[0027] The fourth aspect of the present application provides a secondary battery, which includes a positive electrode sheet, wherein the positive electrode sheet includes the positive electrode sheet provided in any embodiment of the third aspect above.

[0028] In any embodiment of the third aspect, the DC resistance DCR of the secondary battery is 1.30 Ω - 1.58 Ω, preferably 1.30 Ω - 1.45 Ω.

[0029] The fifth aspect of the present application provides an electrical device, which includes a secondary battery, and the secondary battery includes the secondary battery provided in any embodiment of the fourth aspect above. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the drawings.

[0031] Figure 1 It is a schematic structural diagram when the hydrophobic modified fast ion conductor in the aqueous positive electrode slurry provided in an embodiment of the present application adheres to the surface of the LFP positive electrode active material.

[0032] Figure 2 It is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0033] Figure 3 It is Figure 2 The exploded view of the secondary battery according to an embodiment of the present application shown.

[0034] Figure 4 It is a schematic diagram of a battery module according to an embodiment of the present application.

[0035] Figure 5 It is a schematic diagram of a battery pack according to an embodiment of the present application.

[0036] Figure 6 It is Figure 5 The exploded view of the battery pack according to an embodiment of the present application shown.

[0037] Figure 7It is a schematic diagram of an electrical device powered by a secondary battery according to an embodiment of the present application.

[0038] In the drawings, the drawings are not drawn to actual scale.

[0039] Description of reference numerals:

[0040] 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Secondary battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Specific embodiments

[0041] The embodiments of the present application will be further described in detail below with reference to the drawings and examples. The following detailed description of the examples and the drawings are used to exemplarily illustrate the principles of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0042] Hereinafter, embodiments of the aqueous positive electrode paste, its preparation method, positive electrode sheet, secondary battery, and electrical device of the present application specifically disclosed will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary details are omitted. For example, there may be cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily long and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0043] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 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, 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 specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0044] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0045] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all steps of the present application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0047] Unless otherwise specified, the terms "comprising" and "including" mentioned in the present application are open-ended. For example, the "comprising" and "including" may mean that other components not listed may also be included or comprised.

[0048] Unless otherwise specified, in the present application, the term "or" is inclusive. For example, 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) while B is true (or exists); or both A and B are true (or exist).

[0049] [Secondary battery]

[0050] A secondary battery, also known as a rechargeable battery or a storage battery, refers to a battery that can activate the active material by charging after discharging.

[0051] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During the charge and discharge process of the battery, active ions (such as lithium ions) are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows active ions to pass through. The electrolyte is between the positive electrode plate and the negative electrode plate, mainly to conduct active ions.

[0052] As described above, the swelling of the water-based binder in the water-based positive electrode slurry is large, deteriorating the ionic conductivity of the positive electrode sheet. In order to improve the above-mentioned ionic conductivity, the inventors of the present application attempted to add a fast ion conductor to the water-based positive electrode slurry. However, due to the high water sensitivity of the fast ion conductor, the advantages of fast ion conduction were greatly reduced. In order to fully exert the ionic conduction advantages of the fast ion conductor and reduce its water sensitivity, in the first embodiment of the present application, a water-based positive electrode slurry is provided. The water-based positive electrode slurry includes water and a functional material dispersed in the water. The functional material includes a positive electrode active material, a hydrophobically modified fast ion conductor, and a water-based binder. At least part of the surface of the positive electrode active material is attached with a hydrophobically modified fast ion conductor.

[0053] The water-based positive electrode slurry of the present application contains a hydrophobically modified fast ion conductor. The hydrophilic ability of the surface of the hydrophobically modified fast ion conductor is reduced, thereby improving its water stability. After the water-based positive electrode slurry forms the film layer of the positive electrode sheet, the hydrophobically modified fast ion conductor therein improves the ionic conductivity of the film layer, thereby reducing the DC impedance of the secondary battery.

[0054] At least part of the surface of the positive electrode active material is attached with a hydrophobically modified fast ion conductor. This combination of the above form not only improves the level of exertion of the ion-conducting performance of the hydrophobically modified fast ion conductor on the one hand, but also can form a protective effect on the positive electrode active material, reducing the direct contact between the positive electrode active material and water. Furthermore, the compositional stability of the positive electrode active material is improved, and the cycle performance of the battery cell is improved. Taking the phosphate-based positive electrode material as an example, lithium ions and iron ions are easily precipitated from the phosphate-based positive electrode material particles in water, resulting in a decrease in the cycle performance of the battery cell. At the same time, when the phosphate-based positive electrode material meets water, it generates high-resistivity Li 2 CO 3 which precipitates on the surface of the lithium iron phosphate particles, deteriorating the electron conduction. Therefore, the coating of the above-mentioned hydrophobically modified fast ion conductor effectively reduces ion precipitation and the generation of high-resistivity Li 2 CO 3 and can effectively improve the cycle performance of the battery cell prepared from the water-based positive electrode slurry and reduce the surface resistivity of the positive electrode active material in the battery cell, improving the charge and discharge ability of the battery cell.

[0055] In some embodiments of the present application, the hydrophobically modified fast ion conductor includes a fast ion conductor matrix and a hydrophobically modifying agent. The hydrophobically modifying agent has a hydrophobic group. The hydrophobically modifying agent is attached to at least part of the surface of the fast ion conductor matrix and the hydrophobic group is exposed on the surface of the modified fast ion conductor. Modifying the fast ion conductor matrix with a hydrophobically modifying agent not only retains the high ion conductivity of the fast ion conductor but also provides adjustable hydrophobicity for it. When using this hydrophobically modified fast ion conductor to attach to the surface of the positive electrode active material (taking lithium iron phosphate as an example), its structure can refer to Figure 1 .

[0056] In some embodiments of the present application, the Dv50 particle size of the hydrophobic modified fast ion conductor is 5 nm - 50 nm; in some embodiments of the present application, the Dv50 particle size of the positive electrode active material is 0.5 μm - 50 μm, so that the hydrophobic modified fast ion conductor is more likely to adhere to at least part of the surface of the positive electrode active material to form a coating on the positive electrode active material.

[0057] The fast ion conductor matrix for the present application can be selected from conventional fast ion conductors. In some embodiments, the above fast ion conductor matrix includes one or more of NASICON structure oxide solid electrolyte materials, garnet structure oxide solid electrolyte materials, and perovskite structure oxide solid electrolyte materials; optionally, the NASICON structure oxide solid electrolyte material includes Li 1+x’ Al x’ Ti 2-x’ (PO 4 ) 3 materials, Li 1+x’ Al x’ Ge 2-x’ (PO 4 ) 3 materials, doped element-containing Li 1+x’ Al x’ Ge 2-x’ (PO 4 ) 3 materials, doped element-containing Li 1+x’ Al x’ Ti 2-x’ (PO 4 ) 3 materials, at least one of 0 ≤ x' ≤ 0.75; the garnet structure oxide solid electrolyte material includes Li 7-a’ La 3 A 2-a’ O 12 materials and doped element-containing Li 7-a’ La 3 A 2-a’ O 12 materials, at least one of 0 ≤ a' ≤ 1; the perovskite structure oxide solid electrolyte material includes Li 3b’ La 2 / 3-b’ TiO 3 materials, Li 3b’ Nb 2 / 3-b’ TiO 3 materials, doped element-containing Li 3b’ La 2 / 3-b’ TiO 3 materials and doped element-containing Li 3b’ Nb 2 / 3-b’ TiO 3At least one of the materials, 0.06 ≤ b’ ≤ 0.14; optionally, the doping elements include any one or more of Zr, La, and Si.

[0058] The above NASICON-structured oxide solid electrolyte materials include, but are not limited to, LiTi 2 (PO 4 ) 3 、Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 、Li 1.2 Al 0.2 Ti 1.8 (PO 4 ) 3 、Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 、Li 1.3 Al 0.3 Ge 1.7 (PO 4 ) 3 。

[0059] The above garnet-structured oxide solid electrolyte materials include, but are not limited to, Li 7 La 3 Zr 2 O 12 、Li 6 La 3 Zr 1 O 12 、Li 7 La 3 Nb 2 O 12 、Li 7 La 3 Ta 2 O 12 、Li 6 BaLa 3 Zr 2 O 12 。

[0060] The perovskite-structured oxide solid electrolyte materials include, but are not limited to, Li 0.33 Nb 0.56 TiO 3 、Li 0.34 Nb 0.56 Ti 0.99 Al 0.01 O 3 。

[0061] The modifiers used in this application can be substances commonly used in the art for hydrophobic modification. In some embodiments, the above-mentioned modifiers include any one or more of solid fatty acids and organosiloxanes; optionally, the solid fatty acids include any one or more of lauric acid, palmitic acid, oleic acid, myristic acid, and stearic acid, and the organosiloxanes include any one or more of polydimethylsiloxane, amino silicone oil, and polyoxyethylene ether trisiloxane.

[0062] The preparation method of the hydrophobic modified fast ion conductor of this application can refer to conventional techniques, such as in-situ polymerization or coupling of some functional substances containing hydrophobic groups such as solid fatty acids and organosiloxanes on the surface of the fast ion conductor by hydrothermal method, sol-gel method, etc., to achieve the purpose of hydrophobicity.

[0063] The hydrophobic modified fast ion conductor is mainly added to make up for the defects brought by the water-based binder or improve the performance of the positive electrode active material. In some embodiments, among the above-mentioned functional substances, the weight content of the hydrophobic modified fast ion conductor is 0.01%-2%, such as 0.01%, 0.03%, 0.05%, 0.1%, 0.3%, 0.5%, 0.7%, 1%, 1.5% or 2%, and it can be selected as 0.05%-0.5%, and further selected as 0.1%-0.5%. It can not only give full play to the role of the hydrophobic modified fast ion but also avoid the decrease in the specific capacity of the formed positive electrode sheet due to excessive use.

[0064] In some embodiments, the weight content of the fast ion conductor matrix in the hydrophobic modified fast ion conductor is 70%-90%. The fast ion conductor matrix is used to provide sufficient ion conduction function, and the modifier content of the hydrophobic modified fast ion conductor within the above weight content range is more appropriate. It can not only provide an effective amount of hydrophobic groups but also avoid the need for more complex means to make the components in the water-based positive electrode slurry mix evenly due to excessive hydrophobic groups.

[0065] In some embodiments of this application, among the functional substances, the weight content of the positive electrode active material is 95%-97%; optionally, the positive electrode active material includes Li m H a Fe x D d P y E e O z G g 、Li(Ni x” Co y” Mn z’ Al a Cu b Zn c Ti d )O 2One or more of the following, H includes at least one element of Al, Na, K or Mg; D includes at least one element of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti or V; E includes at least one element of B, S, Si or N; G includes at least one element of S, F, Cl or Br; m is selected from the range of 0.5 to 1.15; a is selected from the range of 0 to 0.1; x is selected from the range of 0.5 to 1; d is selected from the range of 0 to 0.5; y is selected from the range of 0.5 to 1; e is selected from the range of 0 to 0.5; z is selected from the range of 3.5 to 4; g is selected from the range of 0 to 0.5; x” + y” + z’ + a + b + c + d = 1, 0.5 ≤ x” < 1, 0.05 ≤ y” < 1, 0 ≤ z’ < 0.5, 0 ≤ a ≤ 0.1, 0 ≤ b ≤ 0.1, 0 ≤ c ≤ 0.1, 0 ≤ d ≤ 0.1. Thereby, the formed positive electrode sheet has a higher specific capacity.

[0066] The main function of the water-based binder is to bond. The more the amount used, the stronger the bonding effect. However, the more the amount used, the smaller the porosity of the positive electrode sheet and the greater the tortuosity of the pores, resulting in a greater ion transport barrier. In some embodiments, the weight content of the water-based binder in the above functional materials is 0.1% - 5%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4% or 5%, and can be selected as 2% - 4%; by controlling the above weight content, the influence on ion transport is reduced as much as possible on the basis of maintaining the bonding effect. In some embodiments, optionally, the water-based binder includes any one or more of methyl cellulose and its salts, xanthan gum and its salts, chitosan and its salts, alginic acid and its salts, polyacrylamide, or acrylonitrile-acrylic acid copolymer and its derivatives. To further increase the areal density of the positive electrode film layer in the positive electrode sheet, further optionally, the water-based binder is acrylonitrile-acrylic acid copolymer. The above acrylonitrile-acrylic acid copolymer has a stronger bonding force and meets the requirements of a higher areal density. Considering the construction convenience, more preferably, the number-average molecular weight of the acrylonitrile-acrylic acid copolymer is 300000 - 2000000.

[0067] In some embodiments of the present application, in order to improve the adhesion uniformity and adhesion force of the hydrophobic modified fast ion conductor on the surface of the positive electrode active material, the functional material further includes a dispersant; optionally, the weight content of the dispersant in the functional material is 0.01%-0.7%, such as 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6% or 0.7%, optionally 0.1%-0.5%; further optionally, the dispersant includes one or more of cationic dispersants and amphoteric dispersants; more optionally, the dispersant includes one or more of polyethyleneimine, polyethylene glycol octyl phenyl ether, styrene maleic anhydride copolymer, amino silicone oil, and polyvinyl pyridine. The dispersant is used to improve the dispersibility of the hydrophobic modified fast ion conductor with hydrophobic groups in the aqueous positive electrode slurry, thereby achieving the purpose of improving its adhesion effect on the surface of the positive electrode active material.

[0068] In some embodiments of the present application, the above-mentioned functional material further includes a conductive agent; optionally, the weight percentage content of the conductive agent in the functional material is 0.1%-5%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4% or 5%, optionally 0.5%-3%; further optionally, the conductive agent includes one or more of conductive carbon black (such as superconducting carbon black, acetylene black and Ketjen black), conductive graphite, graphene, and carbon nanotubes. The conductive agent is used to further reduce the resistivity of the formed positive electrode sheet and improve the charge and discharge performance of the battery cell.

[0069] When the solid content of the aqueous positive electrode slurry is too high and the viscosity is too large, the process difficulty of slurry coating increases; when the solid content is too low, the drying temperature and time of the electrode sheet need to be strictly controlled, otherwise it is easy to crack during drying. In some embodiments of the present application, the solid content of the above-mentioned aqueous positive electrode slurry is 40%-90%, optionally 50%-70%; and / or, the rotational viscosity of the aqueous positive electrode slurry at 25°C is 100 cp-10000 cp, optionally 3000 cp-7000 cp. The above solid content or rotational viscosity can effectively improve the coating process of the slurry and facilitate drying using conventional processes, and the structure of the electrode sheet is stable.

[0070] The second aspect of the present application provides a method for preparing an aqueous positive electrode slurry, the preparation method including: kneading the positive electrode active material, the hydrophobic modified fast ion conductor, the optional conductive agent, and the optional first part of the dispersant to form a first mixture; mixing the first mixture, the aqueous binder, the optional remaining dispersant, and water to obtain the aqueous positive electrode slurry, and the weight ratio of the first part of the dispersant to the remaining dispersant is 6:4-9:2. Most of the dispersant is used to disperse the positive electrode active material, the hydrophobic modified fast ion conductor, and the conductive agent, and a small amount is used to disperse the aqueous binder, thereby further optimizing the dispersion effect of the dispersant.

[0071] In the above preparation method, the cathode active material and the hydrophobic modified fast ion conductor are first mixed, so that the modified fast ion conductor adheres to the cathode active material with higher efficiency and greater probability, and then the function of the fast ion conductor can be better exerted.

[0072] [Cathode electrode sheet]

[0073] The second embodiment of the present application provides a cathode electrode sheet, which includes a cathode current collector and a cathode film layer provided on at least one side of the cathode current collector. The cathode film layer includes a film layer formed by drying any one of the aqueous cathode slurries in the above first embodiment.

[0074] In the cathode electrode sheet of the present application, the film layer formed by the aqueous cathode slurry has high electron and ion conductivity, and the cycle performance and charge-discharge capacity of the battery cell including it are also improved.

[0075] In some embodiments, the water contact angle of the cathode electrode sheet at 25 °C is 70° - 90°, optionally 75° - 84°, such as 70°, 72°, 74°, 75°, 76°, 79°, 80°, 82°, 83°, 84°, 86°, 87°, 88°, 89°, 90°.

[0076] The water contact angle is measured using a SINDIN solid-liquid contact angle measuring instrument.

[0077] In some embodiments, by way of example, the cathode current collector has two surfaces opposite to each other in its own thickness direction, and the cathode film layer is provided on any one or both of the two opposite surfaces of the cathode current collector.

[0078] In some embodiments, the cathode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0079] In some embodiments, the cathode electrode sheet can be prepared by the following method: dispersing the components for preparing the cathode electrode sheet, such as the cathode active material, the conductive agent, the binder, and any other components, in solvent water to form an aqueous cathode slurry; coating the aqueous cathode slurry on the cathode current collector, and after processes such as drying and cold pressing, the cathode electrode sheet can be obtained.

[0080] [Anode electrode sheet]

[0081] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0082] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on either or both of the two opposite surfaces of the negative electrode current collector.

[0083] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0084] In some embodiments, the negative electrode active material can be a negative electrode active material for batteries well-known in the art. As an example, the negative electrode active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based materials can be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials can be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0085] In some embodiments, the negative electrode film layer may also optionally include a binder. As an example, the binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0086] In some embodiments, the negative electrode film layer may also optionally include a conductive agent. As an example, the conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the negative electrode film layer may also optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0088] In some embodiments, the negative electrode sheet can be prepared in the following manner: The components for preparing the negative electrode sheet described above, such as the negative electrode active material, conductive agent, binder, and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0089] [Electrolyte]

[0090] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. There are no specific restrictions on the type of electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0091] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0092] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro(bis(oxalato))phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0093] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0094] In some embodiments, the electrolyte solution can also optionally include additives. As an example, the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and can also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0095] [Separator]

[0096] In some embodiments, the secondary battery further includes a separator. There are no particular restrictions on the type of separator in this application, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0097] In some embodiments, the material of the separator membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0098] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator membrane can be made into an electrode assembly by a winding process or a stacking process.

[0099] In some embodiments, the DC resistance DCR of the secondary battery is 1.30 Ω - 1.58 Ω, such as 1.30 Ω, 1.31 Ω, 1.32 Ω, 1.33 Ω, 1.34 Ω, 1.35 Ω, 1.36 Ω, 1.37 Ω, 1.38 Ω, 1.39 Ω, 1.40 Ω, 1.41 Ω, 1.42 Ω, 1.43 Ω, 1.44 Ω, 1.45 Ω, 1.48 Ω, 1.50 Ω, 1.42 Ω, 1.55 Ω, or 1.58 Ω, preferably 1.30 Ω - 1.45 Ω. The DCR is the value at 50% SOC (state of charge). Since the ionic conductivity of the positive electrode sheet is increased compared to the positive electrode sheet without the modified fast ion conductor, the DC resistance DCR value of the secondary battery is reduced. The above DC resistance DCR value is detected by conventional testing methods in the art. For example, during the intermittent discharge of the secondary battery, the voltage at the moment before the end of the discharge and the voltage after the discharge ends and stabilizes are tested, and the voltage difference between the two is the DC resistance of the secondary battery. Optionally, the above DCR is mainly for the phosphate-based secondary battery system.

[0100] In some embodiments, the secondary battery includes a secondary battery cell, or includes a battery module and a battery pack.

[0101] In some embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the above electrode assembly and electrolyte.

[0102] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0103] This application does not particularly limit the shape of the secondary battery cell, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 is a secondary battery cell 5 with a square structure as an example.

[0104] In some embodiments, referring to Figure 3, the outer package may include a housing 51 and a top cover assembly 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery cell 5 may be one or more, and those skilled in the art can select according to specific actual needs.

[0105] In some embodiments, the secondary battery cells can be assembled into a battery module. The number of secondary battery cells included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0106] Figure 4 is a battery module 4 as an example. Refer to Figure 4 , in the battery module 4, a plurality of secondary battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the plurality of secondary battery cells 5 can be fixed by fasteners.

[0107] Optionally, the battery module 4 may further include a housing having a receiving space, and a plurality of secondary battery cells 5 are received in the receiving space.

[0108] In some embodiments, the above battery module can be further assembled into a battery pack. The number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0109] Figure 5 and Figure 6 is a battery pack 1 as an example. Refer to Figure 5 and Figure 6 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 and form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0110] In addition, the present application also provides an electrical device, which includes the secondary battery provided by the present application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0111] As the electrical device, a secondary battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0112] Figure 7 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or a battery module can be adopted.

[0113] [Embodiment]

[0114] Hereinafter, 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 a limitation to the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0115] In the embodiments of the present application, the modified fast ion conductor is in-situ coupled with a modifier on the surface of the fast ion conductor by the sol-gel method.

[0116] Embodiment 1

[0117] Mix LiFePO 4 positive electrode lithium iron phosphate active material (Dv50 particle size is 27 μm), modified fast ion conductor stearic acid-modified Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (wherein Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3The weight content is 82%, and its Dv50 particle size is 33 nm), the conductive agent SUPER P, and the dispersant are kneaded evenly according to the weight ratio of 96.2:0.5:1:0.3 to form a first mixture; the first mixture and the aqueous binder are mixed according to the weight ratio of 98:2 and then mixed and stirred with water to obtain an aqueous positive electrode slurry with a solid content of 60%. Among them, the dispersant uses polyethyleneimine, and the aqueous adhesive uses the Indule aqueous binder LA-133. Then, the positive electrode slurry is evenly coated on the positive electrode current collector, and after drying, cold pressing, and slitting, a positive electrode plate is obtained.

[0118] Example 2

[0119] The difference from Example 1 lies in that the LiFePO4 positive electrode lithium iron phosphate active material, the modified fast ion conductor lithium stearic acid modified Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , the conductive agent SUPER P, and the dispersant are kneaded evenly according to the weight ratio of 96.2:0.1:1:0.3 to form a first mixture, and the rest are the same as in Example 1.

[0120] Example 3

[0121] The difference from Example 1 lies in that the LiFePO4 positive electrode lithium iron phosphate active material, the modified fast ion conductor lithium stearic acid modified Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , the conductive agent SUPER P, and the dispersant are kneaded evenly according to the weight ratio of 96.2:0.3:1:0.3 to form a first mixture, and the rest are the same as in Example 1.

[0122] Example 4

[0123] The difference from Example 1 lies in that the LiFePO4 positive electrode lithium iron phosphate active material, the modified fast ion conductor lithium stearic acid modified Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , the conductive agent SUPER P, and the dispersant are kneaded evenly according to the weight ratio of 96.2:0.7:1:0.3 to form a first mixture, and the rest are the same as in Example 1.

[0124] Example 5

[0125] The difference from Example 1 lies in that the LiFePO4 positive electrode lithium iron phosphate active material, the modified fast ion conductor lithium stearic acid modified Li 1.3 Al0.3 Ti 1.7 (PO 4 ) 3 , conductive agent SUPER P, and dispersant are kneaded evenly in a weight ratio of 96.2:1:1:0.3 to form a first mixture, and the rest are the same as in Example 1.

[0126] Example 6

[0127] The difference from Example 1 lies in that the LiFePO4 cathode lithium iron phosphate active material, the modified fast ion conductor lithium stearate-modified 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , conductive agent SUPER P, and dispersant are kneaded evenly in a weight ratio of 96.2:0.01:1:0.3 to form a first mixture, and the rest are the same as in Example 1.

[0128] Example 7

[0129] The difference from Example 1 lies in that the LiFePO4 cathode lithium iron phosphate active material, the modified fast ion conductor lithium stearate-modified 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , conductive agent SUPER P, and dispersant are kneaded evenly in a weight ratio of 96.2:2:1:0.3 to form a first mixture, and the rest are the same as in Example 1.

[0130] Example 8

[0131] The difference from Example 1 lies in that the LiFePO4 cathode lithium iron phosphate active material, the modified fast ion conductor lithium stearate-modified 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , conductive agent SUPER P, and dispersant are kneaded evenly in a weight ratio of 96.2:0.05:1:0.3 to form a first mixture, and the rest are the same as in Example 1.

[0132] Example 9

[0133] The difference from Example 1 lies in that the modified fast ion conductor is lithium stearate-modified 7 La 3 Zr 2 O 12 (where Li 7 La 3 Zr 2 O 12The weight content is 82%, and its Dv50 particle size is 37 nm), and the rest is the same as in Example 1.

[0134] Example 10

[0135] The difference from Example 1 is that the modified fast ion conductor is Li modified with stearic acid 0.33 Nb 0.56 TiO 3 (where Li 0.33 Nb 0.56 TiO 3 The weight content is 82%, and its Dv50 particle size is 21 nm), and the rest is the same as in Example 1.

[0136] Example 11

[0137] The difference from Example 1 is that the modified fast ion conductor is Li modified with amino silicone oil (Macklin A909718) 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (where Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 The weight content is 82%, and its Dv50 particle size is 33 nm), and the rest is the same as in Example 1.

[0138] Example 12

[0139] The difference from Example 1 is that the Dv50 particle size of the modified fast ion conductor is 48 nm, and the rest is the same as in Example 1.

[0140] Example 13

[0141] The difference from Example 1 is that the Dv50 particle size of the modified fast ion conductor is 7 nm, and the rest is the same as in Example 1.

[0142] Example 14

[0143] The difference from Example 1 is that the first mixture and the aqueous binder are mixed in a weight ratio of 98:4 and then mixed and stirred with water, and the rest is the same as in Example 1.

[0144] Example 15

[0145] The difference from Example 1 is that the first mixture and the aqueous binder are mixed in a weight ratio of 98:0.1 and then mixed and stirred with water, and the rest is the same as in Example 1.

[0146] Example 16

[0147] The difference from Example 1 is that the first mixture and the aqueous binder are mixed in a weight ratio of 98:5 and then mixed and stirred with water, and the rest are the same as in Example 1.

[0148] Example 17

[0149] The difference from Example 1 is that an acrylonitrile-acrylic acid copolymer with a number-average molecular weight of about 300,000 is used as the aqueous binder, and the rest are the same as in Example 1.

[0150] Example 18

[0151] The difference from Example 1 is that an acrylonitrile-acrylic acid copolymer with a number-average molecular weight of about 2,000,000 is used as the aqueous binder, and the rest are the same as in Example 1.

[0152] Example 19

[0153] The difference from Example 1 is that xanthan gum is used as the aqueous binder, and the rest are the same as in Example 1.

[0154] Example 20

[0155] The difference from Example 1 is that polyacrylamide is used as the aqueous binder, and the rest are the same as in Example 1.

[0156] Example 21

[0157] The difference from Example 1 is that the LiFePO4 cathode lithium iron phosphate active material, the modified fast ion conductor lithium stearic acid modified Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , the conductive agent SUPER P, and the dispersant are kneaded evenly in a weight ratio of 96.2:0.5:1:0.1 to form a first mixture, and the rest are the same as in Example 1.

[0158] Example 22

[0159] The difference from Example 1 is that the LiFePO4 cathode lithium iron phosphate active material, the modified fast ion conductor lithium stearic acid modified Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , the conductive agent SUPER P, and the dispersant are kneaded evenly in a weight ratio of 96.2:0.5:1:0.5 to form a first mixture, and the rest are the same as in Example 1.

[0160] Example 23

[0161] The difference from Example 1 lies in that the active material of the LiFePO4 cathode, lithium iron phosphate, the modified fast ion conductor, lithium 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , the conductive agent SUPER P, and the dispersant are kneaded evenly according to the weight ratio of 96.2:0.5:1:0.01 to form a first mixture, and the rest are the same as in Example 1.

[0162] Example 24

[0163] The difference from Example 1 lies in that the active material of the LiFePO4 cathode, lithium iron phosphate, the modified fast ion conductor, lithium 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , the conductive agent SUPER P, and the dispersant are kneaded evenly according to the weight ratio of 96.2:0.5:1:0.7 to form a first mixture, and the rest are the same as in Example 1.

[0164] Example 25

[0165] The difference from Example 1 is that polyethylene glycol octyl phenyl ether is used as the dispersant, and the rest are the same as in Example 1.

[0166] Example 26

[0167] The difference from Example 1 is that no dispersant is used, and the rest are the same as in Example 1.

[0168] Example 27

[0169] The difference from Example 1 lies in that the active material of the LiFePO4 cathode, lithium iron phosphate, the modified fast ion conductor, lithium 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , the conductive agent SUPER P, and the dispersant are kneaded evenly according to the weight ratio of 96.2:0.5:0.5:0.1 to form a first mixture, and the rest are the same as in Example 1.

[0170] Example 28

[0171] The difference from Example 1 lies in that the active material of the LiFePO4 cathode, lithium iron phosphate, the modified fast ion conductor, lithium 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3, the conductive agent SUPER P and the dispersant are kneaded evenly according to the weight ratio of 96.2:0.5:3:0.1 to form a first mixture, and the rest is the same as in Example 1.

[0172] Example 29

[0173] The difference from Example 1 is that the modified fast ion conductor used is Li modified with stearic acid 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , where the weight content of Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 is 70%, and its Dv50 particle size is 33 nm, and the rest is the same as in Example 1.

[0174] Example 30

[0175] The difference from Example 1 is that the modified fast ion conductor used is Li modified with stearic acid 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , where the weight content of Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 is 90%, and its Dv50 particle size is 33 nm, and the rest is the same as in Example 1.

[0176] Example 30

[0177] Replace the positive electrode lithium iron phosphate active material in Example 1 with NCM811, and the rest is the same as in Example 1.

[0178] Comparative Example 1

[0179] Do not use the modified fast ion conductor, and the rest is the same as in Example 1.

[0180] Comparative Example 2

[0181] Replace the modified fast ion conductor in Example 1 with the Li before modification in Example 1 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , and the rest is the same as in Example 1.

[0182] Battery Preparation

[0183] Preparation of the negative electrode sheet: The active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water as the solvent according to a weight ratio of 96.2:0.8:0.8:1.2, and after mixing evenly, a negative electrode slurry is prepared; the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil once or multiple times, and after drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0184] Preparation of the electrolyte: In a glove box under an argon atmosphere (H 2 O <0.1 ppm, O 2 <0.1 ppm), the organic solvents ethylene carbonate (EC) / ethyl methyl carbonate (EMC) are mixed evenly according to a volume ratio of 3 / 7, and 12.5% LiPF 6 lithium salt is dissolved in the organic solvent, and after stirring evenly, the electrolyte is obtained.

[0185] Separator: A polypropylene membrane is used as the separator.

[0186] The positive electrode sheets, separators, and negative electrode sheets of each example or comparative example are stacked in sequence, with the separator placed between the positive and negative electrode sheets to play a separating role, and then wound to obtain a bare battery cell. The tabs of the bare battery cell are welded, and the bare battery cell is placed in an aluminum shell, baked at 80°C to remove water, then the electrolyte is injected and sealed to obtain a non-charged battery. The non-charged battery is then successively subjected to processes such as standing, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery products corresponding to each example and comparative example.

[0187] Testing of the solid content of the aqueous positive electrode slurry: First, dry and clean petri dishes are dried in an oven at 105°C for 30 minutes. Take them out and place them in a desiccator. After cooling to room temperature, weigh them. Sample with a ground-glass dropping bottle, and weigh 1.5 - 2 grams of the sample by the subtraction method, place it in the weighed petri dish, and make the sample evenly spread on the bottom of the container. Then place it in a forced-air constant-temperature oven adjusted to the temperature specified in the following table and bake for a certain period of time. Take it out, place it in a desiccator, cool to room temperature, and weigh. Then place it in the oven and bake for 30 minutes, take it out, place it in a desiccator, cool to room temperature, and weigh until the weight difference between the two weighings is not more than 0.01 grams (all weighings are accurate to 0.01 grams). Two samples are determined in parallel for the test, and the average value is taken.

[0188] Viscosity Test of Aqueous Positive Electrode Slurry: Prepare the liquid to be measured and place it in a beaker or straight cylindrical container with a diameter of not less than 70 mm and a height of not less than 125 mm. Accurately control the temperature of the liquid to be measured at the specified temperature of 25 °C. Carefully adjust the level of the instrument and check whether the bubble in the level of the instrument is centered to ensure that the instrument is in a horizontal working state. Select a suitable rotor and rotation speed according to the estimated liquid viscosity. Slowly adjust the lifting knob to adjust the height of the rotor in the liquid to be measured until the liquid level mark (the middle of the groove) of the rotor is flush with the liquid surface. Conduct the test according to the instrument instructions and record the data.

[0189] Water Contact Angle Test of Positive Electrode Plate at 25 °C: Measure using a SINDIN solid-liquid contact angle measuring instrument. Operate the test according to the operation instructions.

[0190] Battery Performance Test

[0191] 1. Initial Gram Capacity Test of Battery

[0192] Taking Example 1 as an example, the process of the initial gram capacity test of the battery is as follows: At 25 °C, charge the battery corresponding to Example 1 at a constant current of 1 / 3C to 3.65V, then charge it at a constant voltage of 3.65V until the current is 0.05C, let it stand for 5 minutes, and then discharge it at 1 / 3C to 2.5V. The obtained capacity divided by the tare weight of lithium iron phosphate in the positive electrode is recorded as the initial gram capacity Cw.

[0193] 2. High Rate Current Cycling Performance Test of Battery

[0194] The process of the battery capacity retention rate test is as follows: At 25 °C, charge the corresponding battery at a constant current of 25C to 3.65V, then charge it at a constant voltage of 3.65V until the current is 0.05C, let it stand for 5 minutes, and then discharge it at 25C to 2.5V, and record the initial DC resistance impedance R0. Repeat the above steps for the same battery, and at the same time record the DC resistance impedance Rn of the battery after the nth cycle. Then the growth rate Pn of the battery DCR after each cycle = Rn / R0 * 100% - 1. In this test process, the first cycle corresponds to n = 1, the second cycle corresponds to n = 2,... the 100th cycle corresponds to n = 100. The data of the battery DCR growth rate corresponding to Example 1 in Table 1 are the data measured after 100 cycles under the above test conditions, that is, the value of P100. The test processes of the comparative examples and other examples are the same as above.

[0195] 3. DC Impedance Test of Battery

[0196] The process of testing the DC impedance of the battery is as follows: The lithium-ion battery is charged at a constant current of 1.5C to 3.65V, and then charged at a constant voltage to 0.05C. It is left standing for 30 min; it is discharged at a current of 0.1C for 10 s (sampling once every 0.1 s and recording the corresponding voltage value U1), and discharged at a current of 1C for 360 s (sampling once every 0.1 s and recording the corresponding voltage value U2). The charge and discharge steps are repeated 5 times. "1C" is the current value that completely discharges the battery capacity within 1 hour. The DCR is calculated according to the following formula: R = (U2 - U1) / (1C - 0.1C). This DCR is the value at 50% SOC (state of charge).

[0197] The test results are recorded in Table 1.

[0198] Table 1

[0199] From the comparison of the example and comparative example data in Table 1, it can be seen that when the fast ion conductor Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 is added to the aqueous positive electrode slurry, the DC resistance impedance of the battery can be reduced, and the cycle performance of the battery can be improved. When the fast ion conductor is modified with a modifier, the DC resistance impedance of the battery is reduced more significantly, and the cycle performance of the battery is improved more significantly.

[0200] From the data comparison of Examples 1 to 8, it can be found that within a certain range, as the amount of the modified fast ion conductor increases, the DC resistance impedance gradually decreases, and the DCR growth rate also gradually decreases. However, when the amount of the modified fast ion conductor increases to more than 1%, the above effects cannot be further improved significantly.

[0201] Although the present application has been described with reference to the preferred embodiments, various improvements can be made to it and its components can be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. An aqueous positive electrode slurry, the aqueous positive electrode slurry comprising water and a functional material dispersed in the water, the functional material comprising a positive electrode active material, a hydrophobic modified fast ion conductor, and an aqueous binder, at least a portion of the surface of the positive electrode active material being attached with the hydrophobic modified fast ion conductor.

2. The aqueous positive electrode slurry according to claim 1, wherein, the hydrophobic modified fast ion conductor comprises a fast ion conductor matrix and a hydrophobic modifier, the hydrophobic modifier having a hydrophobic group, the modifier being attached to at least a portion of the surface of the fast ion conductor matrix and the hydrophobic group being exposed on the surface of the hydrophobic modified fast ion conductor.

3. The aqueous positive electrode slurry according to claim 1, wherein, the Dv50 particle size of the hydrophobic modified fast ion conductor is 5 nm - 50 nm; optionally, the fast ion conductor matrix comprises one or more of a NASICON structure oxide solid electrolyte material, a garnet structure oxide solid electrolyte material, and a perovskite structure oxide solid electrolyte material; Optionally, the NASICON-structured oxide solid electrolyte material includes Li 1+x’ Al x’ Ti 2-x’ (PO 4 ) 3 material, Li 1+x’ Al x’ Ge 2-x’ (PO 4 ) 3 material, Li 1+x’ Al x’ Ge 2-x’ (PO 4 ) 3 material containing a doping element, Li 1+x’ Al x’ Ti 2-x’ (PO 4 ) 3 material, etc., where 0 ≤ x' ≤ 0.75; The garnet-structured oxide solid electrolyte material includes Li 7-a’ La 3 A 2-a’ O 12 material and at least one of the Li 7-a’ La 3 A 2-a’ O 12 materials containing doping elements, where 0 ≤ a’ ≤ 1, and A includes at least one of Ta, Zr, and Nb; The perovskite-structured oxide solid electrolyte material includes Li 3b’ La 2 / 3-b’ TiO 3 material, Li 3b’ Nb 2 / 3-b’ TiO 3 material, Li 3b’ La 2 / 3 -b’TiO 3 material and Li 3b’ Nb 2 / 3-b’ TiO 3 material containing at least one of the doped elements, 0.06 ≤ b’ ≤ 0.14; optionally, the doping element comprises any one or more of Zr, La, and Si.

4. The aqueous positive electrode slurry according to any one of claims 1 to 3, wherein, the hydrophobic modifier comprises any one or more of a solid fatty acid and an organosiloxane; optionally, the solid fatty acid comprises any one or more of lauric acid, palmitic acid, oleic acid, myristic acid, and stearic acid, and the organosiloxane comprises any one or more of polydimethylsiloxane, amino silicone oil, and polyoxyethylene ether trisiloxane.

5. The aqueous positive electrode slurry according to any one of claims 1 to 4, wherein, in the functional material, the weight content of the hydrophobic modified fast ion conductor is 0.01% - 2%, optionally 0.05% - 0.5%; the weight content of the fast ion conductor matrix in the hydrophobic modified fast ion conductor is 70% - 90%.

6. The aqueous positive electrode slurry according to any one of claims 1 to 5, wherein, The Dv50 particle size of the positive electrode active material is 0.5 μm - 50 μm; optionally, in the functional material, the weight content of the positive electrode active material is 95% - 97%; optionally, the positive electrode active material includes Li m H a Fe x D d P y E e O z G g , Li(Ni x” Co y” Mn z’ Al a” Cu b Zn c Ti d )O 2 or several of them, the H includes at least one element of Al, Na, K or Mg; the D includes at least one element of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti or V; the E includes at least one element of B, S, Si or N; the G includes at least one element of S, F, Cl or Br; the m is selected from the range of 0.5 to 1.15; the a is selected from the range of 0 to 0.1; the x is selected from the range of 0.5 to 1; the d is selected from the range of 0 to 0.5; the y is selected from the range of 0.5 to 1; the e is selected from the range of 0 to 0.5; the z is selected from the range of 3.5 to 4; the g is selected from the range of 0 to 0.5; x + y + z + a + b + c + d = 1, 0.5 ≤ x < 1, 0.05 ≤ y < 1, 0 ≤ z < 0.5, 0 ≤ a ≤ 0.1, 0 ≤ b ≤ 0.1, 0 ≤ c ≤ 0.1, 0 ≤ d ≤ 0.

1.

7. The aqueous positive electrode slurry according to any one of claims 1 to 6, wherein, the weight content of the aqueous binder in the functional material is 0.1% - 5%, optionally 2% - 4%; optionally, the aqueous binder comprises any one or more of methyl cellulose and its salts, xanthan gum and its salts, chitosan and its salts, alginic acid and its salts, polyacrylamide, or acrylonitrile - acrylic acid copolymer and its derivatives; further optionally, the aqueous binder is an acrylonitrile - acrylic acid copolymer, and more optionally, the number average molecular weight of the acrylonitrile - acrylic acid copolymer is 300000 - 2000000.

8. The aqueous positive electrode slurry according to any one of claims 1 to 7, wherein, The functional material further includes a dispersant; optionally, the weight content of the dispersant in the functional material is 0.01%-0.7%, optionally 0.1%-0.5%; further optionally, the dispersant includes one or more of cationic dispersants and amphoteric dispersants; more optionally, the dispersant includes one or more of polyethyleneimine, polyethylene glycol octyl phenyl ether, styrene maleic anhydride copolymer, amino silicone oil, and polyvinyl pyridine.

9. The aqueous positive electrode slurry according to any one of claims 1 to 8, wherein, The functional material further includes a conductive agent; optionally, the weight percentage content of the conductive agent in the functional material is 0.1%-5%, optionally 0.5%-3%; further optionally, the conductive agent includes one or more of conductive carbon black, conductive graphite, graphene, and carbon nanotubes.

10. The aqueous positive electrode slurry according to any one of claims 1 to 9, wherein, The solid content of the aqueous positive electrode slurry is 40%-90%, optionally 50%-70%; and / or, The rotational viscosity of the aqueous positive electrode slurry at 25°C is 100 cp - 10,000 cp, optionally 3,000 cp - 7,000 cp.

11. A method for preparing an aqueous positive electrode slurry, wherein, The preparation method includes: Kneading the positive electrode active material, the modified fast ion conductor, the optional conductive agent, and the optional first part of the dispersant to form a first mixture; Mixing the first mixture, the aqueous binder, the optional remaining dispersant, and water to obtain the aqueous positive electrode slurry, and the weight ratio of the first part of the dispersant to the remaining dispersant is 6:4 - 9:

2.

12. A positive electrode plate, comprising a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, wherein, The positive electrode film layer includes a film layer dried from the aqueous positive electrode slurry according to any one of claims 1 to 10.

13. The positive electrode plate according to claim 12 or 13, wherein, The water contact angle of the positive electrode plate is 70° - 90°.

14. A secondary battery, comprising a positive electrode plate, wherein, The positive electrode plate includes the positive electrode plate according to claim 12 or 13.

15. The secondary battery according to claim 14, wherein, The DC impedance DCR of the secondary battery is 1.30 Ω - 1.58 Ω, preferably 1.30 Ω - 1.45 Ω.

16. An electrical device, comprising a secondary battery, wherein, The secondary battery includes the secondary battery according to claim 14 or 15.

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