Composite slurry, composite positive electrode, composite diaphragm and lithium battery

Abstract

The invention relates to the technical field of lithium batteries, in particular to composite slurry, a composite positive electrode, a composite diaphragm and a lithium battery. The composite slurry comprises functional components and a solvent, wherein the functional components comprise a first functional additive, a second functional additive and a dispersing agent; wherein the first functional additive is a film-forming additive of which the HOMO energy level is greater than or equal to-9.2 eV; and the second functional additive is selected from lithium-containing phosphate and / or oxide solid electrolyte. The composite slurry provided by the invention is used for a positive electrode and / or a diaphragm through the synergistic effect of various functional additives so as to improve the thermal safety and the electrochemical performance effect of a lithium battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a composite slurry, a composite cathode, a composite separator, and a lithium battery. Background Technology

[0002] Lithium-ion batteries are widely used in the energy storage field due to their high operating voltage, high specific energy, long cycle life and no memory effect. With the development of new energy vehicles, higher demands are being placed on the performance of lithium-ion batteries, especially in terms of safety performance.

[0003] When lithium batteries reach a high charging cutoff voltage, especially close to the critical state of charge (SOC), the cells are prone to thermal runaway and failure under extreme abuse conditions (such as needle penetration and hot boxes) due to factors such as oxygen evolution of the positive electrode material, high-voltage stability of the electrolyte, and heat accumulation.

[0004] Currently, traditional methods improve the electrochemical performance and structural stability of lithium-ion batteries by modifying the cathode material through coating or adding functional additives to the electrolyte. However, these methods often only improve a single aspect of safety performance and have limited effectiveness in full-size, high-capacity cells. For example, CN116799291A discloses a method for coating cathode materials with a solid electrolyte, in which solid electrolyte powder slurry is mixed with a cathode substrate and annealed to obtain a modified cathode material. These methods involve long coating times, complex control conditions, and limited improvement in thermal safety performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the risks and problems of existing lithium batteries, such as fire and explosion, when subjected to extreme abnormal conditions such as compression, heating or puncture. This invention provides a composite slurry, a composite cathode, a composite separator, and a lithium battery. The composite slurry, through the synergistic effect of multiple functional additives, is used in the cathode and / or separator to improve the thermal safety and electrochemical performance of the lithium battery.

[0006] To achieve the above objectives, the first aspect of the present invention provides a composite slurry, the composite slurry comprising: a functional component containing a first functional additive, a second functional additive and a dispersant, and a solvent; The first functional additive is a film-forming additive with a HOMO energy level ≥ -9.2 eV; the second functional additive is selected from solid electrolytes containing lithium phosphate and / or oxides.

[0007] Preferably, the functional component further includes phosphazene flame retardant additives as a third functional additive.

[0008] The inventors of this invention have discovered that by adding a variety of functional additives to the composite slurry, and through the synergistic effect of each component, a comprehensive effect can be achieved in improving the battery's thermal box and needle penetration performance, thereby enhancing the overall thermal safety performance of the battery. Furthermore, the entire addition process is highly compatible with the trial production process and does not increase the cost of battery trial production.

[0009] Specifically, in the composite slurry provided by this invention, the first functional additive is a film-forming additive with a HOMO energy level ≥ -9.2 eV. Its main function is to participate in the formation of the positive electrode CEI interface, thereby improving the stability of the positive electrode interface, suppressing the side reactions at the positive electrode-electrolyte interface, and increasing the battery thermal runaway T2 temperature. The second functional additive is selected from solid electrolytes containing lithium phosphate and / or oxides. Its main function is to coat the positive electrode material or act as a separator coating, reducing the short-circuit current and improving needle penetration safety by controlling electron transport. In particular, it is combined with phosphazene flame retardant additives as the third functional additive. Its main functions are gas-phase flame retardancy (free radical capture and dilution effect) and condensed-phase flame retardancy (promoting char formation and physical isolation). The two-phase flame retardancy synergistic effect reduces the battery thermal runaway T3 temperature. The electron cloud arrangement of phosphazene groups can change the electron cloud arrangement of the first functional additive, reducing the reaction energy barrier through synergistic effect and promoting its preferential reaction. In addition, by adding dispersants and solvents, the functional additives of each component can achieve uniform dispersion and avoid sedimentation.

[0010] A second aspect of the present invention provides a composite positive electrode, wherein the composite positive electrode contains the functional components of the above-mentioned composite slurry and a positive electrode active material.

[0011] A third aspect of the present invention provides a composite diaphragm, the composite diaphragm comprising the above-mentioned composite slurry.

[0012] A fourth aspect of the present invention provides a lithium battery comprising the above-mentioned composite positive electrode and / or the above-mentioned composite separator.

[0013] Compared with the prior art, the present invention has the following advantages: (1) The composite slurry provided by the present invention improves the thermal safety performance and electrical performance of the battery as a whole through the interfacial modification effect of the first functional additive, the safety enhancement effect of the second functional additive, and especially the synergistic effect of the flame retardant effect of the third functional additive. At the same time, the entire addition process is highly compatible with the trial production process and does not increase the battery trial production cost.

[0014] (2) The composite slurry provided by the present invention is used for positive electrode mixing and / or separator coating of lithium batteries. By adjusting the content / coating amount of the composite slurry, the capacity, cycle performance and safety performance of lithium batteries can be effectively improved. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] In this invention, unless otherwise specified, "first," "second," and "third" do not indicate a sequence or limit the specific materials or steps; they are merely used to distinguish or indicate that these are not the same material or step. For example, "first functional additive," "second functional additive," and "third functional additive" are only used to indicate that these are not the same functional additive.

[0017] The first aspect of the present invention provides a composite slurry, the composite slurry comprising: a functional component containing a first functional additive, a second functional additive and a dispersant, and a solvent; The first functional additive is a film-forming additive with a HOMO energy level ≥ -9.2 eV; the second functional additive is selected from solid electrolytes containing lithium phosphate and / or oxides.

[0018] In this invention, unless otherwise specified, HOMO energy level ≥ -9.2 eV refers to the energy level of the highest occupied molecular orbital ≥ -9.2 eV; HOMO energy level parameters are measured using ultraviolet photoelectron spectroscopy.

[0019] In this invention, the first functional additive has a wide range of selection, as long as it meets the above-mentioned limitations. Preferably, the first functional additive is a film-forming additive selected from at least one of lithium phosphate salts, lithium borate salts, lithium sulfide salts, borate esters, phosphate esters, and vinylidene unsaturated organic compounds.

[0020] In some specific embodiments of the present invention, preferably, the first functional additive is selected from at least one of lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxoborate, lithium tetrafluoroborate, lithium difluorosulfonylimide (LiFSI), lithium trifluoromethylsulfonylimide (LiTFSI), tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, vinylene carbonate (VC), and vinyl sulfate.

[0021] In some embodiments of the present invention, preferably, the D of the first functional additive... 50The wavelength is 300-50000 nm, for example, 300 nm, 500 nm, 800 nm, 1000 nm, 2000 nm, 5000 nm, 8000 nm, 10000 nm, 12000 nm, 15000 nm, 18000 nm, 20000 nm, 25000 nm, 30000 nm, 50000 nm, and any value within the range of any two values, preferably 500-20000 nm. In this invention, the above-mentioned D... 50 If the size is too small, it is easy to cause dust and clumping. 50 Excessive volume will prolong the dissolution time.

[0022] In this invention, if the first functional additive is a solid, then it relates to D. 50 Otherwise, D is not involved. 50 .

[0023] In this invention, D 50 The parameters can be measured using conventional testing methods in the field, such as laser particle size analysis (PSD) / scanning electron microscopy (SEM).

[0024] In some embodiments of the present invention, preferably, the room temperature conductivity of the second functional additive is ≥10. -10 S / cm.

[0025] In this invention, the above-mentioned conductivity is electronic conductivity; the conductivity parameter is measured using a powder resistance meter at room temperature, which is 25±2℃.

[0026] In some embodiments of the present invention, preferably, the D of the second functional additive... 50 The wavelength is 5-500 nm, for example, 5 nm, 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 300 nm, 500 nm, and any value within the range of any two values, preferably 20-200 nm. In this invention, the above-mentioned D... 50 Both excessively large and small values ​​can affect the state of the composite slurry, making it prone to sedimentation or agglomeration, which in turn affects the electrochemical performance of the battery.

[0027] In some embodiments of the present invention, preferably, the lithium-containing phosphate has an olivine structure and is selected from at least one of lithium iron phosphate (such as LiFePO4, abbreviated as LFP), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0028] In the present invention, in the composite materials of lithium iron phosphate and carbon, lithium manganese phosphate and carbon, and lithium manganese iron phosphate and carbon, carbon exists in a blended form with lithium iron phosphate / lithium manganese phosphate / lithium manganese iron phosphate to form a composite material, and the blending amount of carbon is 0.5 - 3 wt%; alternatively, carbon is coated on the surface of lithium iron phosphate / lithium manganese phosphate / lithium manganese iron phosphate to form a composite material, and the thickness of the carbon coating layer is 1 - 10 nm.

[0029] In some embodiments of the present invention, preferably, the oxide solid electrolyte is selected from at least one of garnet-type oxide solid electrolytes, perovskite-type oxide solid electrolytes, LISICON-type solid electrolytes, and NASICON-type solid electrolytes.

[0030] In the present invention, the garnet-type oxide solid electrolyte is selected from Li7La3Zr2O 12 and its derivative systems, including but not limited to Li7La3Zr2O 12 (abbreviated as LLZO), and its derivative systems also include Li 6.5 La3Zr 1.5 Ta 0.5 O 12 (LLZTO), etc.

[0031] In the present invention, the perovskite-type oxide solid electrolyte is selected from Li 3x La 2 / 3-x TiO3 and its derivative systems, 0 < x < 2 / 3, including but not limited to Li 0.5 LaTiO3 (abbreviated as LLTO), Li 0.34 La 0.51 TiO 2.94 , etc.

[0032] In the present invention, the LISICON-type solid electrolyte is selected from LiM2(PO4)3 and its derivative systems, M is selected from Ti, Zr, Ge, including but not limited to LiTi2(PO4)3 (abbreviated as LTP), LiGe2(PO4)3 (abbreviated as LGP), LiZr2(PO4)3 (abbreviated as LZP), Li3Zr2Si2PO 12 (abbreviated as LZSP), Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (abbreviated as LATP), Li 14 Zn(GeO4)4, etc.

[0033] In the present invention, the NASICON-type solid electrolyte is selected from Li 3+y M’ y M’’ 1-yO4 and its derivative systems, M' is selected from Si and / or Ge; M'' is selected from P and / or As, 0 < y < 1, including but not limited to Li 10 GeP2S 12 (abbreviated as LGPS), Li 1.5 Al 0.5 Ge 1.5 (PO4)3 (abbreviated as LAGP), etc.

[0034] In some embodiments of the present invention, preferably, the dispersant is selected from at least one of cetyltrimethylammonium bromide (CTAB), octyltrimethylammonium bromide, polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), sodium dodecylbenzenesulfonate (SDBS), and sodium dodecyl sulfate (SDS).

[0035] In some embodiments of the present invention, preferably, the solvent is selected from at least one of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc), 1,3-dioxolane (DOL), dimethylformamide (DMF), methanol, and ethanol.

[0036] In some embodiments of the present invention, preferably, the functional component further includes a phosphazene-based flame retardant additive as the third functional additive.

[0037] In some embodiments of the present invention, preferably, the D of the third functional additive 50 is 50 - 10000 nm, for example, 50 nm, 80 nm, 100 nm, 200 nm, 500 nm, 600 nm, 800 nm, 1000 nm, 2000 nm, 5000 nm, 8000 nm, 10000 nm, and any value within the range composed of any two numerical values, preferably 100 - 1000 nm. In the present invention, the above D 50 being too large or too small will affect the dispersibility. If it is too large, it is easy to settle and the distribution is uneven; if it is too small, it is easy to agglomerate and difficult to disperse evenly, resulting in a reduction in the flame retardant effect.

[0038] In the present invention, the third functional additive not only has a flame retardant effect but also contains a phosphazene group.

[0039] In some embodiments of the present invention, preferably, the third functional additive is selected from at least one of hexaphenoxycyclotriphosphazene, ethoxypentafluorocyclophosphazene, hexafluorocyclotriphosphazene, hexamethoxycyclotriphosphazene, methoxypentafluorocyclotriphosphazene, unsaturated alkoxycyclotriphosphazene, and a linear polymer containing a phosphazene group.

[0040] In the present invention, preferably, in the composite slurry, the functional components include a first functional additive, a second functional additive, and a dispersant, or the functional components include a first functional additive, a second functional additive, a dispersant, and a third functional additive.

[0041] In some embodiments of the present invention, preferably, in the composite slurry, the mass ratios of the components in the functional components satisfy: 0 < a < 0.4, 0 < b < 0.95, 0 < c < 0.05, 0 ≤ d < 0.05, and a + b + c + d = 1, where a, b, c, and d are the mass ratios of the first functional additive, the second functional additive, the dispersant, and the third functional additive, respectively.

[0042] In some embodiments of the present invention, further preferably, 1 ≤ b / a ≤ 30, for example, 1, 2, 3, 5, 8, 10, 12, 15, 18, 20, 25, 30, and any value within the range composed of any two numerical values, preferably 2 ≤ b / a ≤ 15. In the present invention, if b / a is too small, the interfacial stability deteriorates, and the overall thermal safety performance deteriorates; if b / a is too large, the internal resistance of the battery increases, and both the electrochemical performance and the thermal safety performance deteriorate.

[0043] In some embodiments of the present invention, further preferably, 0.001 ≤ c / b ≤ 0.05, for example, 0.001, 0.005, 0.008, 0.01, 0.012, 0.015, 0.018, 0.02, 0.025, 0.028, 0.03, 0.04, 0.05, and any value within the range composed of any two numerical values, preferably 0.005 ≤ c / b ≤ 0.03. In the present invention, if c / b is too small, the particles in the composite slurry are prone to agglomeration and sedimentation, resulting in poor quality of the electrode sheet, low ionic conductivity, high interfacial impedance, and poor electrochemical performance; if c / b is too large, too much dispersant hinders the transport of electrons and ions, significantly increases the interfacial impedance, and severely damages the electrical performance.

[0044] In some embodiments of the present invention, further preferably, 0 ≤ d / a ≤ 0.25, for example, 0, 0.01, 0.03, 0.05, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, and any value within the range composed of any two numerical values, preferably 0.05 ≤ d / a ≤ 0.25, more preferably 0.1 ≤ d / a ≤ 0.25. In the present invention, if d / a is too small, the internal resistance increases and the battery capacity decreases; if d / a is too large, the improvement of the thermal safety performance is not obvious.

[0045] In some embodiments of the present invention, preferably, the content of functional components in the composite slurry is 3-50 wt%, for example, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 40 wt%, 50 wt%, and any value within the range of any two values, preferably 5-30 wt%.

[0046] In this invention, the above-mentioned functional component content refers to the mass ratio of the functional components in the composite slurry, that is, functional component content = (mass of the first functional additive + mass of the second functional additive + mass of the dispersant + mass of the third functional additive) / (mass of the first functional additive + mass of the second functional additive + mass of the dispersant + mass of the third functional additive + mass of the solvent) × 100%.

[0047] In some embodiments of the present invention, preferably, the viscosity of the composite slurry is 1-3000 mPa·s, for example, 1 mPa·s, 5 mPa·s, 10 mPa·s, 50 mPa·s, 100 mPa·s, 200 mPa·s, 500 mPa·s, 800 mPa·s, 1000 mPa·s, 1200 mPa·s, 1500 mPa·s, 2000 mPa·s, 2500 mPa·s, 3000 mPa·s, and any value within the range of any two values, preferably 100-1000 mPa·s.

[0048] In this invention, the above viscosity parameters can be measured using conventional testing methods in the art, such as measuring them with a viscometer at room temperature.

[0049] In some embodiments of the present invention, preferably, the D of the composite slurry 50 The range is 5-5000nm, for example, 5nm, 10nm, 50nm, 80nm, 100nm, 200nm, 300nm, 500nm, 800nm, 1000nm, 2000nm, 3000nm, 5000nm, and any value within the range of any two values, preferably 20-1000nm.

[0050] In this invention, the above-mentioned D 50 Excessive viscosity of the composite slurry can lead to poor flowability, resulting in scratches or pinholes during coating and a risk of agglomeration. Ultimately, this can cause insufficient electrode density and affect charge / discharge efficiency. The aforementioned D 50 If the particles are too small, the specific surface area of ​​the particles will be large, the composite slurry will easily thicken, the coating will be prone to cracking, and the adhesion and mechanical strength will be reduced.

[0051] In this invention, the D of the composite slurry 50It refers to the median particle size of the particles in the composite slurry after mixing of each component.

[0052] In some embodiments of the present invention, preferably, the composite slurry includes a first functional additive, a second functional additive, a dispersant, and a solvent.

[0053] In some other embodiments of the present invention, preferably, the composite slurry includes a first functional additive, a second functional additive, a third functional additive, a dispersant, and a solvent.

[0054] In the present invention, there is a relatively wide selection range for the preparation method of the composite slurry, as long as the first functional additive, the second functional additive, the third functional additive, the dispersant, and the solvent are mixed evenly.

[0055] In some embodiments of the present invention, preferably, the composite slurry is prepared by the following method: S1. Perform a first mixing on the second functional additive, the dispersant, and the solvent to obtain a mixed slurry; S2. Perform a second mixing on the mixed slurry, the first functional additive, and an optional third functional additive to obtain a composite slurry.

[0056] In the present invention, in the composite slurry, the mass ratio of the first functional additive, the second functional additive, the dispersant, and the third functional dispersant in the functional components satisfies a:b:c:d, where 0 < a < 0.4, 0 < b < 0.95, 0 < c < 0.05, 0 ≤ d < 0.05, and a + b + c + d = 1.

[0057] In the present invention, preferably, in step S1, the conditions for the first mixing include: the rotation speed is 1000 - 2500 rpm, preferably 1800 - 2000 rpm, the time is 20 - 60 min, preferably 30 - 50 min; the temperature is 15 - 40 °C, preferably 20 - 30 °C.

[0058] In the present invention, preferably, in step S2, the conditions for the second mixing include: the rotation speed is 1000 - 2500 rpm, preferably 1800 - 2000 rpm, the time is 30 - 90 min, preferably 40 - 60 min; the temperature is 15 - 40 °C, preferably 20 - 30 °C.

[0059] The second aspect of the present invention provides a composite cathode, and the composite cathode contains the functional components of the above composite slurry and a cathode active material.

[0060] In the present invention, the above composite slurry is added to the composite cathode in a blending manner.

[0061] In some embodiments of the present invention, preferably, the content of the composite slurry in the composite positive electrode, based on the content of functional components, is 0.1-5 wt%, for example, 0.1 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 3 wt%, 5 wt%, and any value within any range of any two values, preferably 0.5-3 wt%. In the present invention, if the amount of the above-mentioned composite slurry is too large, it is easy to increase the internal resistance of the battery and affect the battery capacity; if the amount of the above-mentioned composite slurry is too small, it will not achieve the effect of improving thermal safety performance.

[0062] In some embodiments of the present invention, preferably, after the charging and discharging process, the composite slurry, based on the content of functional components, coats the surface of the positive electrode active material with a coating degree ≥60%, for example, 60%, 65%, 70%, 75%, 80%, 82%, 85%, 90%, and any value within the range of any two values, preferably ≥80%.

[0063] In this invention, the aforementioned coating degree refers to the ratio of the area of ​​the composite slurry loaded on the surface of the positive electrode active material, based on the content of functional components, to the surface area of ​​the positive electrode active material; it is generally measured using a scanning electron microscope (SEM) method.

[0064] In some embodiments of the present invention, preferably, the content of the positive electrode active material in the composite positive electrode is ≥70wt%, preferably 70-99wt%, for example, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 92.5wt%, 95wt%, 98wt%, 99wt%, and any value within any range of any two values.

[0065] In some embodiments of the present invention, preferably, the D of the positive electrode active material 50 The size is 0.5-25μm, preferably 1-10μm.

[0066] In some embodiments of the present invention, preferably, the positive electrode active material is selected from lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel manganese oxide, lithium-rich manganese-based positive electrode materials, and at least one of the above-mentioned material modification compounds.

[0067] In this invention, the lithium manganese oxide is selected from layered lithium manganese oxide and / or spinel lithium manganese oxide; the lithium nickel manganese oxide is selected from spinel lithium manganese oxide.

[0068] In this invention, the aforementioned lithium nickel cobalt manganese oxide includes, but is not limited to, LiNi. 1 / 3 Co1 / 3 Mn 1 / 3 O2 (abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (abbreviated as NCM523), Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 (abbreviated as LRM), LiNi 0.5 Co 0.25 Mn 0.25 O2 (abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (abbreviated as NCM811), LiNi 0.8 Co 0.15 Mn 0.05 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, etc.

[0069] In this invention, the aforementioned lithium nickel cobalt aluminum oxide includes, but is not limited to, LiNi. 0.85 Co 0.15 Al 0.05 O2, LiNi 0.9 Co 0.05 Al 0.05 O2, etc.

[0070] In this invention, the composite cathode, in addition to the cathode active material and composite slurry, also contains a conductive agent and a binder.

[0071] In this invention, preferably, the composite positive electrode further includes 0-15 wt% of a conductive agent and 0-15 wt% of a binder; more preferably, it further includes 0.5-5 wt% of a conductive agent and 0.5-5 wt% of a binder.

[0072] In this invention, unless otherwise specified, the total content of the positive electrode active material, the composite slurry (based on the content of functional components), the conductive agent and the binder in the composite positive electrode is 100 wt%.

[0073] In this invention, the conductive agent includes, but is not limited to, acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, Ketjen black, vapor-grown carbon fiber (VGCF), etc.; the binder includes, but is not limited to, polyvinylidene fluoride (PVDF), acrylonitrile copolymer (LA133), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), polyamide-imide (PAI), polyethyleneimine (PEI), polyimide (PI), and tert-butyl polyacrylate-triethoxyvinylsilane (TBATEVS), etc.

[0074] In some embodiments of the present invention, the composite positive electrode is prepared by the following method: mixing positive electrode active material, the above-mentioned composite slurry, conductive agent, binder and solvent to obtain a positive electrode slurry coated on at least one side of the positive electrode current collector, and drying to obtain a composite positive electrode containing a positive electrode active material layer; wherein, the thickness of the positive electrode active material layer is 50-200 μm, for example, 50 μm, 70 μm, 90 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, and any value in any range of any two values, preferably 50-100 μm.

[0075] In this invention, the above-mentioned thickness parameters can be measured using conventional testing methods in the art, such as transmission electron microscopy (TEM).

[0076] A third aspect of the present invention provides a composite diaphragm, the composite diaphragm comprising the above-mentioned composite slurry.

[0077] In this invention, the composite slurry is added to the composite membrane by coating.

[0078] In some embodiments of the present invention, preferably, the coating amount of the composite slurry in the composite membrane, based on the content of functional components, is 1-5 g / m. 2 For example, 1g / m 2 1.5g / m 2 2g / m 2 3g / m 2 4g / m 2 5g / m 2 And any value within the range of any two values, preferably 2-4 g / m 2 .

[0079] In this invention, coating amount refers to the amount of coating relative to 1m. 2The coating amount of the above composite separator based on the content of the functional components is 1-5 g, preferably 2-4 g.

[0080] In some embodiments of the present invention, the composite separator is prepared by the following method: coating the above composite slurry on at least one side of the separator base film, and drying to obtain the composite separator.

[0081] In the present invention, the above separator base film is selected from at least one of polyethylene (PE), polypropylene (PP), and polyethylene / polypropylene / polyethylene.

[0082] The fourth aspect of the present invention provides a lithium battery, which contains the above composite positive electrode and / or the above composite separator.

[0083] In the present invention, the lithium battery includes, but is not limited to, liquid lithium batteries, solid-liquid hybrid lithium batteries, and all-solid-state lithium batteries.

[0084] According to a particularly preferred embodiment of the present invention, a composite slurry, the composite slurry includes: a functional component composed of a first functional additive, a second functional additive, a dispersant, and a third functional additive, and a solvent; Among them, the first functional additive is a film-forming additive with a HOMO energy level ≥ -9.2 eV; the second functional additive is selected from lithium-containing phosphates and / or oxide solid electrolytes; the third functional additive is selected from phosphazene flame retardant additives; Among them, in the functional component, the mass ratio of each component satisfies: 0 < a < 0.4, 0 < b < 0.95, 0 < c < 0.05, 0 ≤ d < 0.05, and a + b + c + d = 1, where a, b, c, and d are the mass ratios of the first functional additive, the second functional additive, the dispersant, and the third functional additive, respectively; Among them, 1 ≤ b / a ≤ 30, 0.001 ≤ c / b ≤ 0.05, 0 ≤ d / a ≤ 0.25.

[0085] The present invention will be described in detail below through examples.

[0086] Example 1 (1) Put 12.6 g of the second functional additive (Li 1.3 Al 0.3 Ti 1.7 (PO4)3, D 50 is 100 nm, and the conductivity at 25 °C is 10 -3 S / cm), 0.189 g of the dispersant polyethylene glycol, and 100 g of the solvent NMP in a sealed container, and mix for 30 min at 2000 rpm at 25 °C to obtain a mixed slurry; The above-mentioned mixed slurry, 4.2g of the first functional additive (lithium dioxoborate, HOMO energy level -7.5eV, D) was added. 50 (1000nm) and 0.4667g of the third functional additive (hexaphenoxycyclotriphosphazene, D) 50 The slurry (500 nm) was placed in a sealed container and mixed for 40 min at 2000 rpm at 25°C to obtain a composite slurry P1 with a functional component content of 14.86 wt%. In the aforementioned composite slurry P1, the mass percentage of the first functional additive a is 0.240, the mass percentage of the second functional additive b is 0.722, the mass percentage of the dispersant c is 0.011, and the mass percentage of the third functional additive d is 0.027. (2) The positive electrode active material (LiNi) 0.9 Co 0.05 Mn 0.05 O2, D 50 A composite slurry P1 (with a thickness of 8 μm), conductive agent carbon black, and binder PVDF are mixed with solvent water in a mass ratio of 90:1.5:4.25:4.25 to obtain a positive electrode slurry. This slurry is then coated onto aluminum foil and dried to form a positive electrode active material layer with a thickness of 70 μm, thus obtaining the composite positive electrode Q1.

[0087] Example 2 The method is the same as in Example 1, except that... In step (1), 0.4667g of the third functional additive (hexaphenoxycyclotriphosphazene, D) is not added. 50 With a wavelength of 500 nm, and other conditions remaining the same, composite slurry P2 was obtained; In the aforementioned composite slurry P2, the mass percentage of the first functional additive a is 0.247, the mass percentage of the second functional additive b is 0.742, and the mass percentage of the dispersant c is 0.011. In step (2), composite slurry P1 is replaced with composite slurry P2, and the other conditions are the same, to obtain composite cathode Q2.

[0088] Example 3 The method is the same as in Example 1, except that... In step (1), the first functional additive is replaced with tris(trimethylsilyl)borate, which has a HOMO energy level of -6.5eV. Under the same conditions, composite slurry P3 is obtained. In the aforementioned composite slurry P3, the mass percentage of the first functional additive a is 0.240, the mass percentage of the second functional additive b is 0.722, the mass percentage of the dispersant c is 0.011, and the mass percentage of the third functional additive d is 0.027. In step (2), composite slurry P1 is replaced with composite slurry P3, and the other conditions are the same, to obtain composite cathode Q3.

[0089] Example 4 The method is the same as in Example 1, except that... In step (1), the amounts of the first functional additive, the second functional additive, the dispersant and the third functional additive are adjusted, and the other conditions are the same, to obtain composite slurry P4. In the aforementioned composite slurry P4, the mass percentage of the first functional additive a is 0.047, the mass percentage of the second functional additive b is 0.934, the mass percentage of the dispersant c is 0.014, and the mass percentage of the third functional additive d is 0.005. In step (2), composite slurry P1 is replaced with composite slurry P4, and the other conditions are the same, to obtain composite cathode Q4.

[0090] Example 5 The method is the same as in Example 1, except that... In step (1), the amounts of the first functional additive, the second functional additive, the dispersant and the third functional additive are adjusted, and the other conditions are the same, to obtain composite slurry P5. In the aforementioned composite slurry P5, the mass percentage of the first functional additive a is 0.618, the mass percentage of the second functional additive b is 0.309, the mass percentage of the dispersant c is 0.005, and the mass percentage of the third functional additive d is 0.068. In step (2), composite slurry P1 is replaced with composite slurry P5, and the other conditions are the same, to obtain composite cathode Q5.

[0091] Example 6 The method is the same as in Example 1, except that... In step (1), the amounts of the first functional additive, the second functional additive, the dispersant and the third functional additive are adjusted, and the other conditions are the same, to obtain composite slurry P6. In the aforementioned composite slurry P6, the mass percentage of the first functional additive a is 0.235, the mass percentage of the second functional additive b is 0.707, the mass percentage of the dispersant c is 0.011, and the mass percentage of the third functional additive d is 0.047. In step (2), composite slurry P1 is replaced with composite slurry P6, and the other conditions are the same, to obtain composite cathode Q6.

[0092] Example 7 The method is the same as in Example 1, except that... In step (1), the amounts of the first functional additive, the second functional additive, the dispersant and the third functional additive are adjusted, and the other conditions are the same, to obtain composite slurry P7. In the aforementioned composite slurry P7, the mass percentage of the first functional additive a is 0.229, the mass percentage of the second functional additive b is 0.685, the mass percentage of the dispersant c is 0.01, and the mass percentage of the third functional additive d is 0.076. In step (2), composite slurry P1 is replaced with composite slurry P7, and the other conditions are the same, to obtain composite cathode Q7.

[0093] Example 8 The method is the same as in Example 1, except that... In step (1), the amounts of the first functional additive, the second functional additive, the dispersant and the third functional additive are adjusted, and the other conditions are the same, to obtain composite slurry P8. In the aforementioned composite slurry P8, the mass percentage of the first functional additive a is 0.235, the mass percentage of the second functional additive b is 0.704, the mass percentage of the dispersant c is 0.035, and the mass percentage of the third functional additive d is 0.026. In step (2), composite slurry P1 is replaced with composite slurry P8, and the other conditions are the same, to obtain composite cathode Q8.

[0094] Example 9 The method is the same as in Example 1, except that... In step (1), the amounts of the first functional additive, the second functional additive, the dispersant and the third functional additive are adjusted, and the other conditions are the same, to obtain composite slurry P9. In the aforementioned composite slurry P9, the mass percentage of the first functional additive a is 0.243, the mass percentage of the second functional additive b is 0.729, the mass percentage of the dispersant c is 0.001, and the mass percentage of the third functional additive d is 0.027. In step (2), composite slurry P1 is replaced with composite slurry P9, and the other conditions are the same, to obtain composite cathode Q9.

[0095] Example 10 The method is the same as in Example 1, except that... In step (1), the second functional additive is adjusted to LiMn. 0.6 Fe 0.4 (PO4), its D 50 The wavelength is 100 nm, and the conductivity at 25℃ is 10. -3S / cm; and adjust the dosage of the first functional additive, the second functional additive, the dispersant and the third functional additive, while keeping the other conditions the same, to obtain composite slurry P10. In the aforementioned composite slurry P10, the mass percentage of the first functional additive a is 0.089, the mass percentage of the second functional additive b is 0.888, the mass percentage of the dispersant c is 0.013, and the mass percentage of the third functional additive d is 0.01. In step (2), composite slurry P1 is replaced with composite slurry P10, and the other conditions are the same, to obtain composite cathode Q10.

[0096] Example 11 The method is the same as in Example 1, except that... In step (1), Li 1.3 Al 0.3 Ti 1.7 (PO4)3 of D 50 The nm wavelength was adjusted to 600 nm, and all other conditions remained the same, to obtain composite slurry P11. In the aforementioned composite slurry P11, the mass percentage of the first functional additive a is 0.240, the mass percentage of the second functional additive b is 0.722, the mass percentage of the dispersant c is 0.011, and the mass percentage of the third functional additive d is 0.027. In step (2), composite slurry P1 is replaced with composite slurry P11, and the other conditions are the same, to obtain composite cathode Q11.

[0097] Example 12 The method is the same as in Example 1, except that... In step (1), the third functional additive is replaced with melamine, whose D 50 With a wavelength of 500 nm and other conditions remaining the same, composite slurry P12 was obtained. In the aforementioned composite slurry P12, the mass percentage of the first functional additive a is 0.240, the mass percentage of the second functional additive b is 0.722, the mass percentage of the dispersant c is 0.011, and the mass percentage of the third functional additive d is 0.027. In step (2), composite slurry P1 is replaced with composite slurry P12, and the other conditions are the same, to obtain composite cathode Q12.

[0098] Example 13 The method is the same as in Example 1, except that... In step (1), the first functional additive is adjusted to lithium difluorophosphate, with a HOMO energy level of -8.0 eV and D 50 1000nm; Li 1.3Al 0.3 Ti 1.7 (PO4)3 of D 50 Adjust the concentration to 150 nm; use CTAB as the dispersant and ethanol as the solvent; adjust the amounts of the first functional additive, the second functional additive, the dispersant, and the third functional additive; mix at 1800 rpm for 50 min and at 1800 rpm for 60 min; keep the other conditions the same to obtain composite slurry P13. In the aforementioned composite slurry P13, the mass percentage of the first functional additive a is 0.16, the mass percentage of the second functional additive b is 0.8, the mass percentage of the dispersant c is 0.024, and the mass percentage of the third functional additive d is 0.016. In step (2), the positive electrode active material (LiCoO2, D) is added. 50 A composite slurry (8 μm thick), conductive agent carbon black, and binder PVDF are mixed with solvent water in a mass ratio of 95:0.5:2.5:2 to obtain a positive electrode slurry. This slurry is then coated onto aluminum foil and dried to form a positive electrode active material layer with a thickness of 70 μm, thus obtaining the composite positive electrode Q13.

[0099] Example 14 The method is the same as in Example 1, except that... In step (1), the first functional additive is adjusted to lithium difluorooxalate borate, with a HOMO energy level of -7.2 eV and D 50 1000nm; Li 1.3 Al 0.3 Ti 1.7 (PO4)3 of D 50 Adjust 200nm; change the third functional additive to ethoxypentafluorocyclophosphamide, its D 50 The wavelength is 800 nm; PVP is used as the dispersant and methanol is used as the solvent; the amounts of the first functional additive, the second functional additive, the dispersant and the third functional additive are adjusted; the mixture is first mixed at 2200 rpm for 30 min and then second mixed at 2200 rpm for 30 min; the other conditions are the same, and composite slurry P14 is obtained. In the aforementioned composite slurry P14, the mass percentage of the first functional additive a is 0.061, the mass percentage of the second functional additive b is 0.922, the mass percentage of the dispersant c is 0.005, and the mass percentage of the third functional additive d is 0.012. In step (2), the positive electrode active material (LiNi) is... 0.8 Co 0.15 Al 0.05 O2, D 50A composite slurry (8 μm thick), conductive agent carbon black, and binder PVDF are mixed with solvent water in a mass ratio of 92.5:1:3.5:3 to obtain a positive electrode slurry. This slurry is then coated onto aluminum foil and dried to form a positive electrode active material layer with a thickness of 70 μm, thus obtaining the composite positive electrode Q14.

[0100] Example 15 The method is the same as in Example 1, except that... In step (1), the first functional additive is adjusted to lithium bis(difluorosulfonyl)imide, with a HOMO energy level of -7.7 eV and D 50 The wavelength is 1000 nm; the second functional additive is adjusted to LiMn. 0.6 Fe 0.4 (PO4), its D 50 Adjusted to 150nm, conductivity at 25℃ is 10. -3 S / cm; The third functional additive was adjusted to hexafluorocyclotriphosphazene, whose D 50 The wavelength was 1000 nm; the dispersant used was n-octyltrimethylammonium bromide; the amounts of the first functional additive, the second functional additive, the dispersant, and the third functional additive were adjusted; the mixture was first mixed at 1500 rpm for 60 min, and then second mixed at 1800 rpm for 70 min; the other conditions were the same, and the composite slurry P15 was obtained. In the aforementioned composite slurry P15, the mass percentage of the first functional additive a is 0.089, the mass percentage of the second functional additive b is 0.887, the mass percentage of the dispersant c is 0.018, and the mass percentage of the third functional additive d is 0.006. In step (2), the positive electrode active material (LiNi) is... 0.8 Co 0.1 Mn 0.1 O2, D 50 A composite slurry P15 (with a thickness of 8 μm), conductive agent carbon black, and binder PVDF are mixed with solvent water in a mass ratio of 75:5:10:10 to obtain a positive electrode slurry. This slurry is then coated onto aluminum foil and dried to form a positive electrode active material layer with a thickness of 70 μm, thus obtaining the composite positive electrode Q15.

[0101] Comparative Example 1 The method is the same as in Example 1, except that... No step (1); In step (2), the positive electrode active material (LiNi) is... 0.9 Co 0.05 Mn 0.05 O2, D 50The composite cathode DQ1 was obtained by mixing carbon black (with a thickness of 8 μm), conductive agent carbon black, and binder PVDF in a mass ratio of 90:4.25:4.25, with other conditions remaining the same.

[0102] Comparative Example 2 The method is the same as in Example 1, except that... In step (1), without adding 4.2g of the first functional additive, the other conditions are the same, and the composite slurry DP2 is obtained; In the aforementioned composite slurry DP2, the mass percentage of the first functional additive a is 0, the mass percentage of the second functional additive b is 0.8, the mass percentage of the dispersant c is 0.012, and the mass percentage of the third functional additive d is 0.188. In step (2), composite slurry P1 is replaced with composite slurry DP2, and the other conditions are the same, to obtain composite cathode DQ2.

[0103] Comparative Example 3 The method is the same as in Example 1, except that... In step (1), without adding 12.6g of the second functional additive, and with the other conditions remaining the same, composite slurry DP3 was obtained; In the aforementioned composite slurry DP3, the mass percentage of the first functional additive a is 0.35, the mass percentage of the second functional additive b is 0, the mass percentage of the dispersant c is 0.611, and the mass percentage of the third functional additive d is 0.039. In step (2), composite slurry P1 is replaced with composite slurry DP3, and the other conditions are the same, to obtain composite cathode DQ3.

[0104] Comparative Example 4 The method is the same as in Example 1, except that... In step (1), without adding 0.189g of dispersant, and with the other conditions remaining the same, composite slurry DP4 was obtained; In the aforementioned composite slurry DP4, the mass percentage of the first functional additive a is 0.243, the mass percentage of the second functional additive b is 0.73, the mass percentage of the dispersant c is 0, and the mass percentage of the third functional additive d is 0.027. In step (2), composite slurry P1 is replaced with composite slurry DP4, and the other conditions are the same, to obtain composite cathode DQ4.

[0105] Comparative Example 5 The method is the same as in Example 1, except that... In step (1), the first functional additive is replaced with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), which has a HOMO energy level of -9.5 eV. Under the same conditions, the composite slurry DP5 is obtained. In the aforementioned composite slurry DP5, the mass percentage of the first functional additive a is 0.240, the mass percentage of the second functional additive b is 0.722, the mass percentage of the dispersant c is 0.011, and the mass percentage of the third functional additive d is 0.027. In step (2), composite slurry P1 is replaced with composite slurry DP5, and the other conditions are the same, to obtain composite cathode DQ5.

[0106] Comparative Example 6 The method is the same as in Example 1, except that... In step (1), the second functional additive is replaced with boehmite, whose D 50 100nm, conductivity <10 -14 S / cm; Under the same conditions, composite slurry DP6 was obtained; In the aforementioned composite slurry DP6, the mass percentage of the first functional additive a is 0.240, the mass percentage of the second functional additive b is 0.722, the mass percentage of the dispersant c is 0.011, and the mass percentage of the third functional additive d is 0.027. In step (2), composite slurry P1 is replaced with composite slurry DP6, and the other conditions are the same, to obtain composite cathode DQ6.

[0107] Table 1

[0108] Note: In the composite slurry, b / a - the mass ratio of the second functional additive to the first functional additive; c / b - the mass ratio of the dispersant to the second functional additive; d / a - the mass ratio of the third functional additive to the first functional additive.

[0109] As shown in Table 1, compared with Comparative Examples 1-6, the composite electrode sheets prepared by Examples 1-15 using the composite slurry provided by the present invention have a lower heat release rate in DSC tests, and have a significantly better effect on improving thermal safety performance.

[0110] Test Example 1 Assemble lithium batteries: Cut the composite cathodes (Q1-Q15 and DQ1-DQ6) from Examples 1-15 and Comparative Examples 1-6 into the following shapes: F12mm round wafers are matched with separators (PE base film) and lithium sheets of corresponding sizes. They are placed in the following order: negative electrode shell - lithium sheet - separator (with a certain amount of electrolyte added) - positive electrode sheet - gasket - spring sheet - positive electrode shell. Then they are transferred to a sealing machine, pressurized to 50kPa, and assembled to obtain lithium batteries (W1-W15 and DW1-DW6).

[0111] The composite slurry P1 from Example 1 was coated onto a PE base film, resulting in a coating amount of 3 g / m. 2 The composite separator, the composite positive electrode Q1 and the negative electrode of Example 1 above are assembled to obtain the lithium battery W16, as Example 16.

[0112] The electrochemical performance of the above lithium batteries was tested under the following conditions, and the results are listed in Table 2: S1. The prepared lithium-ion battery is placed in a test cabinet (25℃) and the first-efficiency charge-discharge regime is set: charge to 4.2V with constant current and constant voltage at 0.1C, cut-off current is 0.02C, stand for 2 minutes, discharge to the specified voltage with constant current at 0.1C, stand for 2 minutes, and repeat 2 times. S2, Cyclic charge-discharge regime: Charge to 4.25V with 1C constant current and constant voltage, cut-off current is 0.02C, rest for 2min, discharge to 2.8V with 1C constant current, rest for 2min, cycle 200 times.

[0113] Test Example 2 Assembling lithium-ion pouch batteries: Lithium-ion pouch batteries were prepared using the composite positive electrodes (Q1-Q15 and DQ1-DQ6) obtained in Examples 1-15 and Comparative Examples 1-6, respectively. The specific preparation method was as follows: using the above-mentioned positive electrode sheets as positive electrodes and graphite electrodes as negative electrodes, the electrolyte was a 1 mol / L LiPF6 solution with an N / P ratio of 1.05 dissolved in a 1:1:1 volume ratio of EC / DMC / EMC. Celgard 2400 single-layer microporous PP base membrane was used as the separator or composite separator. The lithium-ion pouch batteries were assembled on a production line with strict control of water and oxygen content through processes such as rolling, die cutting, assembly, drying, electrolyte injection, formation, and capacity testing, respectively, to obtain lithium-ion pouch batteries (W'1-W'15 and DW'1-DW'6) with specifications of 10Ah-87187.

[0114] The composite slurry P1 from Example 1 was coated onto a PP base film, resulting in a coating amount of 3 g / m. 2 The composite separator, the composite positive electrode Q1 and the negative electrode of Example 1 above are graphite electrodes, and they are assembled to obtain a lithium-ion soft pack battery W'16, as Example 16.

[0115] The thermal safety performance of the above-mentioned lithium-ion pouch batteries was evaluated using hot box and nail penetration tests. The specific testing method for the hot box test is as follows, and the results are listed in Table 2: S1, Initial charging regime: Charge at a constant current and constant voltage of 0.33C to 4.2V, cut-off current of 0.02C, let stand for 60 minutes, and record voltage, internal resistance, and weight; S2. Place the battery in the battery thermal shock test chamber and complete the preparation work; S3. After the preparation is completed, raise the temperature from room temperature to 130°C at a rate of 5°C / min and hold for 60 minutes. Then raise the temperature to 140°C at a rate of 5°C / min and hold for 60 minutes. Continue this process, with each step increasing by 10°C and holding for 60 minutes at each step, until the battery fails. S4. Record voltage and temperature changes, failure temperature point, and failure time.

[0116] The specific testing method for the needle prick test is as follows: S1, Initial state charging regime: 0.33C constant current and constant voltage charging to 4.2V, cut-off current 0.05C; S2, use 5mm 3mm A 1mm high-temperature resistant steel needle (with a 45° cone angle at the tip, and a smooth surface free of rust, oxide layer, and oil) is inserted through the battery at a speed of 5mm / s from a direction perpendicular to the battery plates. The insertion point should be close to the geometric center of the pierced surface. The steel needle remains inside the battery, and the battery failure status is observed. The observation time is up to 1 hour.

[0117] Table 2

[0118] Note: In the needle penetration results, 5mm pass - the lithium battery passes the 1mm, 3mm and 5mm needle penetration tests respectively; 1mm pass, 3mm fail - the lithium battery passes only the 1mm needle penetration test, but fails the 3mm and 5mm needle penetration tests; 1mm fail - the lithium battery fails the 1mm, 3mm and 5mm needle penetration tests respectively.

[0119] As can be seen from the data in Table 1-2, compared with Comparative Examples 1-6, Examples 1-16 use the composite slurry provided by the present invention to prepare composite cathode assembled lithium batteries, which not only significantly improve thermal safety performance, but also have higher electrochemical performance.

[0120] As can be seen from Examples 1 and Comparative Examples 1-6, Comparative Example 2 does not contain the first functional additive and cannot participate in the formation of the positive electrode CEI interface, resulting in poor positive electrode interface stability and numerous side reactions at the positive electrode and electrolyte interface; Comparative Example 3 does not contain the second functional additive and cannot regulate the electron transport path, resulting in poor positive electrode interface stability and failure to improve battery safety; Comparative Example 4 does not contain a dispersant, and the particles in the composite slurry are prone to agglomeration and sedimentation, resulting in poor electrode quality, which in turn leads to low ionic conductivity, high interfacial impedance, and deteriorated electrochemical performance. In other words, the functional components of the composite slurry provided by this invention can achieve uniform dispersion and avoid sedimentation.

[0121] Meanwhile, the first functional additive in Comparative Example 5 is a film-forming additive with a HOMO energy level < -9.2 eV. The electrolyte components will be preferentially oxidized, making it difficult for the film-forming agent to play its role and failing to form a good positive electrode CEI film. This results in poor positive electrode interface stability, numerous side reactions at the positive electrode and electrolyte interface, and the inability to improve thermal safety performance. Comparative Example 6 uses boehmite, which can only slightly delay puncture damage through physical barrier and has no ion conduction function. When needle puncture occurs, it can only improve heat resistance to a certain extent and cannot inhibit the heat spread after short circuit. In contrast, the second functional additive mentioned above is not only resistant to high temperature, but its solid-state properties can reduce side reactions with the electrolyte and increase the battery thermal runaway temperature. When needle puncture causes local thermal runaway, it can better maintain its own structural integrity, interrupt the thermal runaway process, and achieve the effect of improving battery thermal safety performance.

[0122] Therefore, the composite slurry provided by the present invention contains a first functional additive, a second functional additive, and a dispersant in its functional components, especially with the addition of a third functional additive. When the components are in a certain appropriate ratio, the lithium battery has excellent thermal safety performance and electrochemical performance. That is, through the interfacial modification effect of the first functional additive and the safety enhancement effect of the second functional additive, and especially the synergistic effect of the flame retardant effect of the third functional additive containing phosphazene groups, the overall thermal safety performance and electrical performance of the battery are improved.

[0123] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite slurry, characterized in that, The composite slurry includes: a functional component containing a first functional additive, a second functional additive, and a dispersant, and a solvent; Among them, the first functional additive is a film-forming additive with a HOMO energy level ≥ -9.2 eV; the second functional additive is selected from lithium-containing phosphates and / or oxide solid electrolytes.

2. The composite slurry according to claim 1, wherein, The first functional additive is a film-forming additive selected from at least one of lithium-containing phosphates, lithium borates, lithium sulfates, borate esters, phosphate esters, and vinylidene unsaturated organic compounds; And / or, the first functional additive is selected from at least one of lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium bis(difluoromethylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, vinylene carbonate, and vinyl sulfate.

3. The composite slurry according to claim 1 or 2, wherein, The second functional additive has a room temperature conductivity ≥10. -10 S / cm; And / or, the D of the second functional additive 50 The range is 5-500nm, preferably 20-200nm; And / or, the lithium-containing phosphate has an olivine structure and is selected from at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon; And / or, the oxide solid electrolyte is selected from at least one of garnet-type oxide solid electrolytes, perovskite-type oxide solid electrolytes, LISICON-type solid electrolytes, and NASICON-type solid electrolytes; And / or, the dispersant is selected from at least one of cetyltrimethylammonium bromide, octyltrimethylammonium bromide, polyvinylpyrrolidone, polyethylene glycol, sodium dodecylbenzenesulfonate, and sodium dodecyl sulfate.

4. The composite slurry according to any one of claims 1-3, wherein, The functional component further includes a phosphazene-based flame retardant additive as a third functional additive; And / or, the third functional additive is selected from at least one of hexaphenoxycyclotriphosphazene, ethoxypentafluorocyclophosphazene, hexafluorocyclotriphosphazene, hexamethoxycyclotriphosphazene, methoxypentafluorocyclophosphazene, unsaturated alkoxycyclotriphosphazene, and a linear polymer containing a phosphazene group; And / or, the D of the third functional additive 50 The range is 50-10000nm, preferably 100-1000nm.

5. The composite slurry according to claim 4, wherein, In the functional component, the mass ratios of each component satisfy: 0 < a < 0.4, 0 < b < 0.95, 0 < c < 0.05, 0 ≤ d < 0.05, and a + b + c + d = 1, where a, b, c, and d are the mass ratios of the first functional additive, the second functional additive, the dispersant, and the third functional additive, respectively; Preferably, 1 ≤ b / a ≤ 30, preferably 2 ≤ b / a ≤ 15; Preferably, 0.001 ≤ c / b ≤ 0.05, preferably 0.005 ≤ c / b ≤ 0.03; Preferably, 0 ≤ d / a ≤ 0.25, preferably 0.05 ≤ d / a ≤ 0.25, more preferably 0.1 ≤ d / a ≤ 0.

25.

6. The composite slurry according to any one of claims 1-5, wherein, In the composite slurry, the content of the functional component is 3 - 50 wt%, preferably 5 - 30 wt%; And / or, the viscosity of the composite slurry is 1 - 3000 mPa·s, preferably 100 - 1000 mPa·s; And / or, the D of the composite slurry 50 The range is 5-5000 nm, preferably 20-1000 nm; And / or, the composite slurry includes a first functional additive, a second functional additive, a dispersant, and a solvent; or includes a first functional additive, a second functional additive, a third functional additive, a dispersant, and a solvent.

7. A composite positive electrode, characterized in that, The composite cathode contains the functional components of the composite slurry as described in any one of claims 1-6 and the cathode active material.

8. The composite positive electrode according to claim 7, wherein, In the composite cathode, the content of the composite slurry, based on the content of functional components, is 0.1-5 wt%, preferably 0.5-3 wt%. And / or, after the charge-discharge process, the composite slurry, based on the content of functional components, coats the surface of the positive electrode active material, with a coating degree of ≥60%, preferably ≥80%; And / or, in the composite cathode, the content of the cathode active material is ≥70wt%, preferably 70-99wt%; And / or, the positive electrode active material is selected from lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese-based positive electrode material, and at least one of the above-mentioned material modification compounds.

9. A composite diaphragm, characterized in that, The composite diaphragm contains the composite slurry according to any one of claims 1-6; Preferably, in the composite membrane, the coating amount of the composite slurry, based on the content of functional components, is 1-5 g / m³. 2 Preferably 2-4 g / m 2 .

10. A lithium battery, characterized in that, The lithium battery contains the composite positive electrode as described in claim 7 or 8, and / or the composite separator as described in claim 9.

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