Positive electrode additive, positive electrode plate and use

Abstract

A positive electrode additive, a positive electrode plate and the use. The positive electrode additive comprises a structure of formula I, wherein R1 in the formula I comprises a group of a formula a and / or a formula b, and R 2 comprises a group of a formula c. When the positive electrode additive is applied to the preparation of a positive electrode plate, the adhesion between a positive electrode active material layer and a positive electrode current collector and the cohesion between positive electrode active materials can be significantly improved, and the positive electrode additive can effectively improve the electronic conductive network of the positive electrode active material layer, reduce the resistance of a diaphragm, and facilitate the improvement of the cycling service life of a lithium ion battery.

Description

Cathode additives, cathode plates and applications

[0001] This application claims priority to the Chinese patent application filed on September 27, 2023, with application number 2023112646038 and invention name “Positive Electrode Additives, Positive Electrode Sheets and Applications”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a positive electrode additive, a positive electrode plate, and applications. Background Art

[0003] Lithium-ion batteries are widely used in consumer electronics due to their long cycle life and high energy density. With the rapid development of mobile electronic devices, demand for improved kinetic performance and long cycle life is increasing. Polyvinylidene fluoride (PVDF) is commonly used as a positive electrode binder in lithium-ion batteries. However, the bonding strength of positive electrodes prepared using PVDF is weak, significantly impacting the cycle life of lithium-ion batteries.

[0004] Summary of the Invention

[0005] In view of this, the present application provides a positive electrode additive, a positive electrode plate and an application. When the positive electrode additive is used in the preparation of the plate of a lithium-ion battery, it can significantly improve the bonding force between the active material layer and the current collector of the lithium-ion battery. The positive electrode additive has electronic conductivity, which can improve the electronic conductivity and reduce the membrane resistance, which is beneficial to improving the cycle life of the lithium-ion battery.

[0006] In a first aspect, the present application provides a positive electrode additive, wherein the positive electrode additive comprises a structure shown in Formula I:

[0007] In Formula I, R1 includes a group represented by Formula a and / or Formula b, and R2 includes a group represented by Formula c;

[0008] Wherein, * represents the connecting end. Combined with Formula I, the positive electrode additive described in the present application is a three-dimensional network macromolecular positive electrode additive containing a benzene ring and a triazine ring structure. The positive electrode additive described in the present application has high adhesion, and is particularly conducive to forming covalent bonds with the hydrated hydroxyl groups on the surface of the aluminum foil substrate, thereby improving the adhesion between the active material layer and the current collector. At the same time, the positive electrode additive shown in Formula I in the present application is used for the positive electrode active material layer, which can effectively improve the electron transport network of the active material layer and reduce the membrane resistance.

[0009] In some embodiments, the molecular weight of the positive electrode additive is 600,000 to 800,000.

[0010] In a second aspect, the present application provides a positive electrode plate, which includes a positive electrode current collector and a positive electrode active material layer arranged on at least one side of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material, a binder, a conductive agent and the above-mentioned positive electrode additives.

[0011] In some embodiments, the mass percentage of the positive electrode additive is 0.05 wt % to 0.5 wt % based on the mass of the positive electrode active material layer.

[0012] The present application regulates the content of the positive electrode additive in the positive electrode active material layer to be appropriate, and controls the molecular weight of the positive electrode additive to be within an appropriate range. On the one hand, it is beneficial to regulate the viscosity of the positive electrode slurry to be appropriate. On the other hand, it makes the sheet resistance of the prepared positive electrode active material layer lower, thereby improving the cycle performance of the lithium-ion battery.

[0013] The inventors of this application also found in their research that the cohesive force of the positive electrode plates prepared using PVDF binder is relatively small, resulting in significant rebound of the plates after cold pressing, causing serious loss of PD (compacted density) after capacity, and leading to a reduction in the energy density of lithium-ion batteries.

[0014] In order to solve the above technical problems, in some embodiments of the present application, the positive electrode active material includes Co element and optional T element, and the T element is selected from at least one of Ni, Mn, Al, Mg, Ti, Zr, La, Y, Mo, V, Cu, Zn, Ga, Nb, Cr, Ba, W, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd or Ca, and the binder includes F element.

[0015] In the positive electrode additive shown in Formula I of the present application, the amino and hydroxyl groups in its structure can form strong coordination and chelation with the Co element in the positive electrode active material. At the same time, the hydroxyl / amino / imino group (at least one of the three) in the positive electrode additive shown in Formula I can also form dense hydrogen bonds with the F element in the binder, and cooperate synergistically, thereby improving the cohesion of the positive electrode active material layer, which is beneficial to reducing the rebound of the electrode after cold pressing and improving the PD after the capacity of the lithium-ion battery.

[0016] In some embodiments, the positive electrode active material includes lithium cobalt oxide and / or lithium nickel cobalt manganese oxide, and the binder includes polyvinylidene fluoride.

[0017] In some embodiments, in the positive electrode active material, the molar amount of the Co element is recorded as m1, the molar amount of the T element is recorded as m2, and 90%≤m1 / (m 1+ m2)≤100%.

[0018] In some embodiments, the bonding force between the positive electrode active material layer and the positive electrode current collector is 35 N / m to 65 N / m. In this case, the positive electrode sheet has good structural stability, which is conducive to improving the cycle performance of the lithium-ion battery.

[0019] In some embodiments, the cohesive force of the positive electrode active material layer is 70 N / m to 100 N / m, which is conducive to obtaining a high PD after capacity, greatly improving the energy density of the lithium-ion battery.

[0020] In some embodiments, the sheet resistance of the positive electrode plate is 0.2Ω to 0.3Ω. It can be seen that the positive electrode additive represented by Formula I of the present application can effectively improve the electronic conductivity of the conductive network of the plate.

[0021] In a third aspect, the present application provides an electrochemical device, which includes the above-mentioned positive electrode plate.

[0022] In a fourth aspect, the present application provides an electronic device comprising the above-mentioned electrochemical device.

[0023] The beneficial effects brought about by the technical solutions provided in some embodiments of the present application include at least the following: The present application provides a positive electrode additive having a structure shown in Formula I. The special structure of the positive electrode additive gives it high adhesion, and it can form a covalent bond with the hydrated hydroxyl groups on the surface of the aluminum foil substrate, thereby improving the bonding force between the active material layer and the current collector. The addition of the positive electrode additive is beneficial to improving the electronic conductive network of the positive electrode active material layer and reducing the membrane resistance. At the same time, when it is applied to a positive electrode sheet containing cobalt in the positive electrode active material, the hydroxyl and amino groups in the positive electrode additive can also strongly coordinate with the cobalt element in the positive electrode active material. Moreover, the hydroxyl / amino / imino groups in the positive electrode additive can form dense hydrogen bonds with the F element in PVDF, thereby improving the cohesion of the positive electrode active material layer, which is beneficial to obtaining a high PD after capacity, thereby improving the energy density of the lithium-ion battery and improving the cycle performance of the electrochemical device. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0025] In the prior art, to prevent electrode powder loss and film release, researchers generally use a higher amount of PVDF in the positive electrode, hoping to solve these problems by improving the adhesion of the positive electrode. To achieve higher energy density lithium-ion batteries, researchers generally try to increase the initial compaction density (PD) of the electrode or reduce the amount of inactive material added to the electrode, hoping to improve the energy density of lithium-ion batteries. However, increasing the amount of PVDF added will reduce the energy density of lithium-ion batteries. A higher initial compaction density of the electrode will lead to severe breakage of the active material particles. The new cross-sections generated by the particle breakage during high-temperature storage and cycling increase the side reactions with the electrolyte, seriously deteriorating the electrical performance of the lithium-ion battery. Reducing the amount of inactive material added to the electrode will reduce the electronic conductivity of the electrode and the adhesion between the active material and the substrate.

[0026] In order to solve the above technical problems, the present application proposes a positive electrode additive, a positive electrode plate and applications.

[0027] Cathode additives

[0028] The positive electrode additive includes a structure shown in Formula I:

[0029] In Formula I, R1 includes a group represented by Formula a and / or Formula b, and R2 includes a group represented by Formula c;

[0030] In some embodiments, the molecular weight of the positive electrode additive is 600,000 to 800,000. For example, the molecular weight of the positive electrode additive is 600,000, 650,000, 700,000, 750,000, 800,000, or a range consisting of any two of the above values.

[0031] Preparation method of positive electrode additive

[0032] For example:

[0033] Compound a (containing a group represented by formula a) and / or compound b (containing a group represented by formula b) is mixed with compound c (containing a group represented by formula c), an organic solvent is added, and the mixture is placed in an oil bath environment, stirred at 550 rpm to 650 rpm at a temperature of 160° C. to 200° C. for 68 h to 74 h, washed, and dried to obtain the product.

[0034] Positive electrode

[0035] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a binder, a conductive agent and the above-mentioned positive electrode additives.

[0036] In some embodiments, the mass percentage of the positive electrode additive is 0.05 wt % to 0.5 wt % based on the mass of the positive electrode active material layer. For example, the mass percentage of the positive electrode additive is 0.05 wt %, 0.08 wt %, 0.1 wt %, 0.15 wt %, 0.2 wt %, 0.25 wt %, 0.3 wt %, 0.35 wt %, 0.4 wt %, 0.45 wt %, 0.5 wt %, or a range consisting of any two of the foregoing values.

[0037] In some embodiments, the positive electrode active material includes Co element and optionally T element, wherein the T element is selected from at least one of Ni, Mn, Al, Mg, Ti, Zr, La, Y, Mo, V, Cu, Zn, Ga, Nb, Cr, Ba, W, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd or Ca, and the binder includes F element.

[0038] Illustratively, the positive electrode active material is selected from one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and compounds obtained by adding other transition metals or non-transition metals to the above compounds.

[0039] For example, the positive electrode current collector may be made of a metal foil or a porous metal plate, for example, a foil or a porous plate made of a metal such as aluminum, copper, nickel, titanium, or iron, or an alloy thereof, such as Al (aluminum) foil.

[0040] In some embodiments, the positive electrode active material includes lithium cobalt oxide and / or lithium nickel cobalt manganese oxide, and the binder includes polyvinylidene fluoride.

[0041] Specifically, in some embodiments, the positive electrode active material includes lithium cobalt oxide, in other embodiments, the positive electrode active material includes lithium nickel cobalt manganese oxide, and in other embodiments, the positive electrode active material includes not only lithium cobalt oxide but also lithium nickel cobalt manganese oxide.

[0042] In some embodiments, in the positive electrode active material, the molar amount of the Co element is recorded as m1, the molar amount of the T element is recorded as m2, and 90%≤m1 / (m 1+ m2)≤100%.

[0043] In some embodiments, the bonding force between the positive electrode active material layer and the positive electrode current collector is 35 N / m to 65 N / m. For example, the bonding force between the positive electrode active material layer and the positive electrode current collector is 35 N / m, 40 N / m, 45 N / m, 50 N / m, 55 N / m, 60 N / m, 65 N / m, or a range consisting of any two of the foregoing values.

[0044] In some embodiments, the cohesive force of the positive electrode active material layer is 70 N / m to 100 N / m. For example, the cohesive force of the positive electrode active material layer is 70 N / m, 75 N / m, 80 N / m, 85 N / m, 90 N / m, 95 N / m, 100 N / m, or a range consisting of any two of the foregoing values.

[0045] In some embodiments, the sheet resistance of the positive electrode sheet is 0.2Ω to 0.3Ω. For example, the sheet resistance of the positive electrode active material layer is 0.2Ω, 0.22Ω, 0.24Ω, 0.25Ω, 0.26Ω, 0.28Ω, 0.3Ω, or a range consisting of any two of the above values.

[0046] Preparation method of positive electrode sheet

[0047] The method for preparing the positive electrode sheet comprises at least the following steps:

[0048] The positive electrode active material, the binder, the conductive agent and the positive electrode additive are dispersed in a non-aqueous solution, stirred and mixed to obtain a positive electrode slurry, the solid content of the positive electrode slurry is 65wt% to 75wt%, the viscosity of the positive electrode slurry is 3000mPa.s to 8000mPa.s, and based on the solid content in the positive electrode slurry, the mass ratio of the positive electrode active material, the binder, the conductive agent and the positive electrode additive is (95.5~96):(1.8~2.2):(1.8~2.2):(0.05~0.5).

[0049] The positive electrode slurry is evenly coated on one surface of the positive electrode collector and dried to obtain a positive electrode sheet coated with positive electrode active material on one side. The above operation steps are then repeated on the other surface of the positive electrode collector to obtain a positive electrode sheet coated with positive electrode active material on both sides.

[0050] Illustratively, the viscosity of the positive electrode slurry is 3000 mPa.s, 3500 mPa.s, 4000 mPa.s, 4500 mPa.s, 5000 mPa.s, 5500 mPa.s, 6000 mPa.s, 6500 mPa.s, 7000 mPa.s, 7500 mPa.s, 8000 mPa.s or a range consisting of any two of the above values.

[0051] other

[0052] The negative electrode plate may be a metal lithium plate, or may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0053] The negative electrode active material layer generally includes a negative electrode active material and optionally a conductive agent and a binder.

[0054] Illustratively, the negative electrode active material includes one or more of natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Li-Al alloy, or metallic lithium; the conductive agent includes one or more of conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers; and the binder includes one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, or carboxymethyl cellulose (CMC). However, the present application is not limited to these materials, and other materials that can be used as negative electrode active materials, conductive agents, and binders for lithium-ion batteries may also be used.

[0055] For example, the negative electrode current collector may be made of a metal foil or a porous metal plate, for example, a foil or a porous plate made of a metal such as copper, nickel, titanium, or iron, or an alloy thereof, such as copper foil.

[0056] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the negative electrode active material and optional conductive agent and binder are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is then coated on the negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying and cold pressing.

[0057] There is no particular limitation on the isolation membrane. Any known porous structure isolation membrane with electrochemical stability and chemical stability can be selected, such as a single-layer or multi-layer film of one or more of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride (PVDF).

[0058] The electrolyte includes an organic solvent, an electrolyte lithium salt, and an additive. The present application does not impose any specific restrictions on the type of the electrolyte, and the electrolyte can be selected according to actual needs.

[0059] Illustratively, the organic solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) or diethyl sulfone (ESE), preferably two or more.

[0060] Exemplarily, the electrolyte lithium salt includes one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatophosphate) or LiTFOP (lithium tetrafluorooxalatophosphate).

[0061] The electrolyte may optionally include other additives, which may be any additive that can be used as a lithium-ion secondary battery additive. The present invention is not particularly limited thereto and may be selected based on actual needs. For example, the additive may be one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), succinonitrile (SN), adiponitrile (ADN), 1,3-propylene sultone (PST), tris(trimethylsilyl)phosphate (TMSP), or tris(trimethylsilyl)borate (TMSB).

[0062] electrochemical devices

[0063] The electrochemical device of the present application may include any device that generates an electrochemical reaction, and specific examples thereof include all kinds of primary batteries or secondary batteries. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0064] electronic devices

[0065] The electronic device of the present application includes any of the above-mentioned electrochemical devices of the present application. The electronic device of the present application can be used for, but is not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0066] The following examples and comparative examples are given to illustrate the embodiments of the present application in more detail. Unless otherwise stated, the parts, percentages and ratios listed below are all based on weight, and the raw materials used are commercially available or synthesized according to conventional methods.

[0067] Example 1-1

[0068] Preparation of positive electrode additives

[0069] 1 mol of 1,3,5-triimino-2,4,6-trihydroxybenzene and 1 mol of cyanuric chloride were added to a 2000 mL three-necked round-bottom flask, followed by the addition of 1000 mL of dimethyl sulfoxide. The mixture was placed in an oil bath at 180°C and mechanically stirred at 600 rpm for 72 h. After the reaction, the mixture was washed with methanol and dimethyl sulfoxide in sequence. Finally, the obtained solid powder was dried in a vacuum drying oven at 60°C for 24 h to obtain a positive electrode additive.

[0070] Preparation of positive electrode

[0071] LiCoO2 (positive electrode active material), PVDF (binder), conductive carbon black (conductive agent), and the prepared positive electrode additive were dispersed in NMP solvent and stirred to obtain a positive electrode slurry with a solid content of 70 wt% and a viscosity of 3000 mPa·s. The mass ratio of LiCoO2, PVDF, conductive carbon black, and the positive electrode additive in the solid components was 95.95:2:2:0.05 (the combined mass percentages of the positive electrode active material and the positive electrode additive were 96%). The positive electrode slurry was evenly coated on one surface of a 9 μm thick positive electrode current collector aluminum foil and dried at 120°C to obtain a single-sided positive electrode active material-coated positive electrode sheet with a thickness of 75 μm. The above steps were then repeated on the other surface of the positive electrode current collector aluminum foil to obtain a double-sided positive electrode sheet. The coated positive electrode sheet was cold pressed and then cut into sheets measuring 70 mm x 800 mm for later use.

[0072] Preparation of negative electrode sheet

[0073] The negative electrode active materials graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a mass ratio of 97.6:1.1:1.3. Deionized water was then added as a solvent and stirred thoroughly to produce a negative electrode slurry with a solid content of 70 wt%. The negative electrode slurry was evenly coated on one surface of a 6 μm thick negative electrode current collector copper foil and dried at 120°C to produce a single-sided negative electrode sheet coated with a 110 μm thick negative electrode active material layer. The above steps were repeated on the other surface of the negative electrode current collector copper foil to produce a double-sided negative electrode sheet coated with a negative electrode active material layer. The coated negative electrode sheet was cold pressed and then cut into sheets measuring 74 mm x 800 mm for later use.

[0074] Preparation of electrolyte

[0075] In a glove box filled with a dry argon atmosphere, the organic solvents propylene carbonate (PC), diethyl carbonate (DEC), and ethylene carbonate (EC) were mixed in a mass ratio of 1:1:1, and then lithium hexafluorophosphate (LiPF6) was added to the above organic solvents to dissolve and mix thoroughly to obtain an electrolyte with a LiPF6 concentration of 1.15 mol / L.

[0076] Preparation of isolation membrane

[0077] A porous polyethylene film having a thickness of 16 μm was used as a separator.

[0078] Preparation of lithium-ion batteries

[0079] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order and then wound to obtain an electrode assembly. After the tabs are welded, the electrode assembly is placed in an aluminum-plastic film, dried in a vacuum oven at 80°C for 12 hours to remove moisture, and then injected with the above-prepared electrolyte. After vacuum packaging, standing, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), capacity, shaping and other processes, a lithium-ion battery is obtained. In this application, unless otherwise specified, all preparations can be made with reference to conventional technical means in this field.

[0080] Test method:

[0081] (1) Viscosity test

[0082] The viscosity of the cathode slurry was measured using a digital rotational viscometer (Shanghai Jingtian Electronic Instrument Co., Ltd., LVDV 1). The appropriate rotor and rotational speed were selected based on the slurry being measured. The rotor was slowly inserted into the slurry to soak it. When the slurry level was in the middle of the rotor groove, the rotational viscometer was started. After two minutes, when the reading remained constant, the reading was read and recorded as the viscosity of the prepared cathode slurry in mPa·s.

[0083] (2) Adhesion test

[0084] Take the cold-pressed positive electrode sheet and punch it out with a mold to obtain a test specimen with a length of 100 mm and a width of 20 mm. Wipe the surface of the steel plate clean with alcohol, and stick a double-sided tape (NITTO.NO5000NS) with a length of 55 mm to 70 mm and a width of 20 mm on the steel plate. No bubbles should be generated. Stick the test specimen on the double-sided tape in the center with the test surface facing down. Use wrinkle glue (high-viscosity masking paper) to connect and fix a paper tape with a length of 50 mm to 75 mm and a width equal to the test specimen to one end of the test specimen. Push a rubber roller with a mass of 2 kg back and forth on the test specimen 4 times by hand to obtain a test sample. Use a tensile testing machine (Instron 3365) to test the sample. The test sample was secured to the test bench. The paper tape was then folded upward 90° and secured with a clamp. The tensile testing machine then slowly pulled the tape at a speed of 10 mm / min until the positive electrode active material layer on the double-sided tape surface separated from the positive electrode current collector. The test was concluded after the average tensile force in the plateau region was recorded as the bonding force between the positive electrode active material layer and the positive electrode current collector, expressed in N / m.

[0085] (3) Cohesion test

[0086] Take the cold-pressed positive electrode sheet and punch it out with a mold to obtain a test specimen with a length of 80 mm and a width of 20 mm. Wipe the surface of the steel plate clean with alcohol, and stick a double-sided tape (NITTO.NO5000NS) with a length of 50 mm to 60 mm and a width of 20 mm on the steel plate. No bubbles should be generated. Stick the test specimen on the double-sided tape with the test surface facing up. Stick the green glue for cohesion (Todi adhesive tape, width 20 mm * length 80 mm) in the center of the test specimen, cut a paper tape with a length of 60 mm * 20 mm width, and insert the paper tape into the gap between the test specimen and the green glue, with a cross-overlap length of ~15 mm. Push a rubber roller with a mass of 2 kg back and forth on the test specimen 4 times by hand to obtain a test sample. Use a tensile testing machine (Sansi, Instron 3365) to test the sample. The test sample was secured to the test bench. The paper tape was then folded upward 180° and secured with a clamp. The tensile testing machine then slowly pulled the tape at a speed of 10 mm / min until the green glue separated from the active material layer on the positive electrode surface. The test concluded. The average tensile force in the plateau region was recorded as the cohesive force between the positive electrode active materials, measured in N / m.

[0087] (4) PD calculation

[0088] After taking the capacity, the cell pole piece is punched out with a punch die to cut 12 small discs (area 1540.25mm 2 ), after the electronic scale is reset, use tweezers to place the punched small discs on the weighing table and record the weight of each small disc m1, m2, m3, m4, m5, m6, m7, m8, m9, m 10 、m 11 、m 12 Use a micrometer to measure the thickness of each small disc at four locations: h 11 、h 12 、h 13 、h 14 ;h 21 、h 22 、h 23 、h 24 ;h 31 、h 32 、h 33 、h 34 ;h 41 、h 42 、h 43 、h 44 ;h 51 、h 52 、h 53 、h 54 ;h 61 、h 62 、h 63 、h 64 ;h71 、h 72 、h 73 、h 74 ;h 81 、h 82 、h 83 、h 84 ;h 91 、h 92 、h 93 、h 94 ;h 101 、h 102 、h 103 、h 104 ;h 111 、h 112 、h 113 、h 114 ;h 121 、h 122 、h 123 、h 124 .

[0089] The average value of the four thicknesses of each small disc is h1, h2, h3, h4, h5, h6, h7, h8, h9, h 10 、h 11 、h 12 , calculate the value of each small disc by the formula The average value of the PD of the 12 small discs was recorded as the PD of each example or comparative example.

[0090] (5) Diaphragm resistance test

[0091] Use Yuanneng Technology's electrode resistance meter (BER2500) to test the electrode and diaphragm resistance after cold pressing. Before use, perform resistance reset and pressure reset. Place the electrode under the probe for testing, and take the average value of the resistance values ​​measured at 12 different positions as the diaphragm resistance value.

[0092] (6) Cyclic performance test

[0093] The cycle performance is evaluated by the capacity retention rate of the lithium-ion battery. The formed lithium-ion battery is placed in a constant temperature environment at 25°C, charged to 4.5V at a constant current of 0.6C, and then charged at a constant voltage to a cut-off current of 0.05C. After fully charged and left for 3 minutes, it is discharged to 3.0V at 0.5C, and the discharge capacity is recorded as D0. The cycle test is carried out with a 0.6C charge / 0.5C discharge process, and the cycle is repeated 500 times. The discharge capacity after the 500th cycle is recorded as D1. The capacity retention rate (%) of the lithium-ion battery after 500 cycles at room temperature (25°C) = D1 / D0×100%.

[0094] Example 1-2 to Example 1-25

[0095] The difference from Example 1-1 is that some parameters of the positive electrode additive and the positive electrode sheet during the preparation process are adjusted, as shown in Table 1. The rest are the same as Example 1-1.

[0096] Comparative Example 1

[0097] The difference from Example 1-1 is that no additives are used in the preparation of the positive electrode slurry, the mass percentage of the positive electrode active material is 96%, and the rest is the same as Example 1-1.

[0098] Comparative Example 2

[0099] The difference from Example 1-1 is that, in the preparation process of the positive electrode slurry, the additive used is phenolic resin (molecular weight ≈200,000), and the rest is the same as Example 1-1.

[0100] Table 1

[0101] Table 2

[0102] In combination with Table 1 and Table 2, it can be seen from the comparison of Example 1-1 and Comparative Example 1 that when the positive electrode sheet of the lithium ion battery in the embodiment of the present application contains the positive electrode additive described in the present application, the bonding force between the positive electrode active material layer and the current collector is relatively large, and can reach more than 35 N / m, while the bonding force of Comparative Example 1 is only 28.3 N / m. Moreover, the cohesive force between the positive electrode active materials to which the positive electrode additive is added in the present application is relatively large, and the prepared lithium ion battery has a higher PD and cycle capacity retention rate.

[0103] Examples 1-2 through 1-25 further discuss the selection of the R1 group in Formula I, the positive electrode additive content, and the positive electrode additive molecular weight within appropriate ranges, all of which achieve excellent results. In particular, Example 1-10 achieves a high adhesion strength of 65 N / m between the positive electrode active material layer and the current collector, a cohesive strength of 100 N / m between the positive electrode active materials, a post-capacitance PD of 4.10 g / cc, and a 500-cycle capacity retention rate of 92.8%.

[0104] It can be seen that applying the positive electrode additive described in this application to the positive electrode plate can ensure good bonding between the positive electrode active material layer and the current collector and good cohesion between the positive electrode active materials. The lithium-ion battery made using the positive electrode plate provided by this application has higher PD and good cycle performance.

[0105] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A positive electrode additive for lithium ion batteries, characterized in that: The positive electrode additive includes a structure shown in Formula I: In Formula I, R1 includes a group represented by Formula a and / or Formula b, and R2 includes a group represented by Formula c; 2. The positive electrode additive according to claim 1, characterized in that The molecular weight of the positive electrode additive is 600,000 to 800,000.

3. A positive electrode sheet, characterized in that: The positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector; The positive electrode active material layer comprises a positive electrode active material, a binder, a conductive agent and the positive electrode additive according to any one of claims 1 to 2.

4. The positive electrode sheet according to claim 3, characterized in that: Based on the mass of the positive electrode active material layer, the mass percentage of the positive electrode additive is 0.05 wt % to 0.5 wt %.

5. The positive electrode sheet according to claim 3, characterized in that: The mass percentage of the positive electrode additive is 0.25 wt % to 0.5 wt % based on the mass of the positive electrode active material layer.

6. The positive electrode sheet according to claim 3, characterized in that: The positive electrode active material includes a Co element and an optional T element, wherein the T element is selected from at least one of Ni, Mn, Al, Mg, Ti, Zr, La, Y, Mo, V, Cu, Zn, Ga, Nb, Cr, Ba, W, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd or Ca; The binder includes F element.

7. The positive electrode sheet according to claim 6, characterized in that: The positive electrode active material includes lithium cobalt oxide and / or lithium nickel cobalt manganese oxide; The binder includes polyvinylidene fluoride.

8. The positive electrode sheet according to claim 6, characterized in that: In the positive electrode active material, the molar amount of the Co element is recorded as m1, the molar amount of the T element is recorded as m2, and 90%≤m1 / (m1+m2)≤100%.

9. The positive electrode sheet according to claim 3, characterized in that: At least one of the following conditions is met: (1) The bonding force between the positive electrode active material layer and the positive electrode current collector is 35 N / m to 65 N / m; (2) The cohesive force of the positive electrode active material layer is 70 N / m to 100 N / m; (3) The membrane resistance of the positive electrode plate is 0.2Ω to 0.3Ω.

10. An electrochemical device, characterized in that: The electrochemical device comprises the positive electrode sheet according to any one of claims 3 to 9.

11. An electronic device, characterized in that: The electronic device comprises the electrochemical device according to claim 10.

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