Cathode additive, cathode electrode sheet, preparation method and application thereof
By using polar ester-based small molecule additives with branched alkyl structures in the positive electrode of lithium-ion batteries, the problems of electrode hardness and brittleness and reduced electronic conductivity have been solved, thereby improving the flexibility and energy density of the electrode.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NINGDE AMPEREX TECHNOLOGY LTD
- Filing Date
- 2023-09-28
- Publication Date
- 2026-06-30
AI Technical Summary
Existing lithium-ion battery positive electrode sheets are brittle and prone to breakage during winding, and residual NMP in the electrode sheets can cause problems such as gas expansion and reduced electronic conductivity.
Small molecule cathode additives containing multiple polar ester groups linked with branched alkyl structures are used. Through synergistic effects with PVDF binders, the intermolecular forces of PVDF molecules are weakened, improving molecular chain mobility. Furthermore, non-polar long-chain alkyl groups are sandwiched between PVDF molecular chains to shield polar CF bonds, thereby enhancing the electrode's flexibility and electronic conductivity.
It significantly improves the flexibility and compaction density of the positive electrode, reduces the risk of electrode breakage, and enhances the energy density and cycle performance of lithium-ion batteries.
Smart Images
Figure CN117326948B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of battery technology, and in particular to a positive electrode additive, a positive electrode sheet, a method for preparing the same, and their applications. Background Technology
[0002] Lithium-ion batteries are widely used in 3C consumer products due to their long cycle life and high energy density. With the rapid development of mobile electronic devices, the demand for the dynamic performance and long cycle life of lithium-ion batteries is increasing. Polyvinylidene fluoride (PVDF) is generally used as a binder for the positive electrode of lithium-ion batteries. However, the positive electrode sheets prepared using PVDF binders are relatively hard and brittle, posing a risk of breakage during winding. Furthermore, the compaction density (PD) of the obtained positive electrode sheets is low, significantly reducing the energy density of lithium-ion batteries.
[0003] To avoid the risk of brittle breakage during winding due to the hardness and brittleness of the positive electrode, existing technologies typically increase the amount of residual N-methylpyrrolidone (NMP) in the electrode to address this issue. Conversely, to achieve higher energy density, existing technologies usually reduce the amount of inactive material added to the electrode. However, excessive residual NMP in the electrode can lead to problems such as gas expansion and abnormal thickness in the battery cell system. Furthermore, reducing the amount of inactive material in the electrode reduces its electronic conductivity and the adhesion between the active material and the substrate. Summary of the Invention
[0004] In view of this, this application provides a positive electrode additive, a positive electrode sheet, a method for preparing the same, and its application. When the positive electrode additive is applied to the preparation of electrodes for lithium-ion batteries, it can significantly improve the flexibility of the electrode sheet, thereby increasing the compaction density of the electrode sheet.
[0005] In a first aspect, this application provides a positive electrode additive, the positive electrode additive comprising the structure shown in Formula I:
[0006]
[0007] In Equation I, R1 and R2 are each independently selected from C2-C 18 Alkyl groups.
[0008] In conjunction with Formula I, the positive electrode additive described in this application is a small molecule additive containing multiple polar ester groups linked with branched alkyl structures. The positive electrode sheet prepared using the positive electrode additive with the shown structure has excellent flexibility, which can avoid the risk of brittle breakage during the winding process due to the hardness and brittleness of the positive electrode sheet, thereby improving PD.
[0009] In some implementations, in Formula I, R1 and R2 are each independently selected from C. 12 -C 18Straight-chain alkyl groups.
[0010] Secondly, this application provides a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer including a positive active material, a binder, a conductive agent and the above-mentioned positive 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. Preferably, the mass percentage of the positive electrode additive is 0.3 wt% to 0.5 wt%. This application, by further controlling the content of the positive electrode additive in the positive electrode active material layer to a suitable degree, facilitates the control of the viscosity of the positive electrode slurry and results in a lower film resistance of the prepared positive electrode active material layer, thereby improving the cycle performance of the lithium-ion battery.
[0012] In some embodiments, the boiling point of the cathode additive is between 300°C and 800°C. Therefore, the cathode additive described in this application has the characteristic of low volatility.
[0013] In some embodiments, the binder contains CF bonds. Preferably, the binder comprises polyvinylidene fluoride (PVDF). The multiple symmetrically arranged polar ester groups in the cathode additive of this application facilitate synergistic interaction with the CF bonds in PVDF, resulting in mutual solubility. Furthermore, the symmetrical structural arrangement further weakens the intermolecular forces of PVDF, improves the mobility of PVDF molecular chains, lowers the glass transition temperature of PVDF, and thus improves the flexibility of the electrode, solves the problem of electrode hardness and brittleness, and improves PD (Power Generation).
[0014] In some embodiments, the molecular weight of the binder is between 800,000 and 1,200,000. Preferably, the molecular weight of PVDF is 1,000,000. In this case, it is more conducive to the insertion of the positive electrode additive between the PVDF molecular chains, so that the non-polar long-chain alkyl groups in the positive electrode additive are sandwiched between the PVDF molecular chains, shielding the polar CF bonds in PVDF, reducing the intermolecular forces of PVDF molecular chains, and further improving the flexibility of the electrode sheet; and this small molecule additive (i.e., the positive electrode additive) can absorb moisture in the air, and has a lubricating and moisturizing effect. During the cold pressing process, it is conducive to the slippage of the main material particles, reducing damage to the aluminum foil, and further improving PD.
[0015] In some embodiments, the adhesion force between the positive electrode active material layer and the positive electrode current collector is 28.5 N / m to 29.5 N / m. Therefore, the positive electrode additive described in this application improves the flexibility of the positive electrode sheet without reducing the adhesion force between the positive electrode active material layer and the positive electrode current collector.
[0016] In some embodiments, the film resistance of the positive electrode is 0.2Ω to 0.25Ω. It is evident that the positive electrode additive described in this application can improve the flexibility of the positive electrode while also enhancing its electronic conductivity.
[0017] Thirdly, this application provides a method for preparing the above-mentioned positive electrode sheet, including the following steps:
[0018] The positive electrode active material, binder, conductive agent and the positive electrode additive are dispersed in a non-aqueous solution and stirred to obtain a positive electrode slurry. The solid content of the positive electrode slurry is 65wt% to 75wt%, and the viscosity of the positive electrode slurry is 3900mPa·s to 6100mPa·s.
[0019] In some embodiments, 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 (95.5–97):(1–2):(1–2):(0.05–0.5).
[0020] Thirdly, this application provides an electrochemical device, which includes the aforementioned positive electrode plate.
[0021] Fourthly, this application provides an electronic device comprising the electrochemical device described above.
[0022] The beneficial effects of the technical solutions provided in some embodiments of this application include at least the following: When the positive electrode additive described in this application is applied to the preparation of lithium-ion battery electrodes, it can significantly improve the flexibility of the electrodes. The multiple symmetrical polar ester groups in the positive electrode additive facilitate their interaction with the CF bonds in PVDF, resulting in mutual solubility, weakening the intermolecular forces of the binder molecular chains, reducing the crystallinity of PVDF, increasing molecular chain mobility, lowering the glass transition temperature, improving the flexibility of the electrodes, and solving the problem of electrode hardness and brittleness. Furthermore, the non-polar long-chain alkyl groups in the positive electrode additive are sandwiched between PVDF molecular chains, shielding the polar CF bonds in PVDF, reducing the intermolecular forces of PVDF molecular chains, and improving the flexibility of the electrodes. Additionally, the positive electrode additive can absorb moisture from the air, possessing lubricating and moisturizing properties; the cold pressing process facilitates the slippage of the main material particles, reducing damage to the aluminum foil and improving the electrode's power dissipation (PD). Detailed Implementation
[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.
[0024] Positive electrode additives
[0025] The positive electrode additive comprises the structure shown in Formula I:
[0026]
[0027] In Equation I, R1 and R2 are each independently selected from C2-C 18 Alkyl groups.
[0028] In some embodiments, in Formula I, R1 and R2 are each independently selected from C. 12 -C 18 Straight-chain alkyl groups.
[0029] Preparation method of positive electrode additive
[0030] For example:
[0031] Pentaerythritol and branched carboxylic acid compounds were mixed, and an appropriate amount of ammonium sulfate was added. The mixture was reacted at 160℃~200℃ and 250rpm~350rpm for 60h~80h with mechanical stirring. After the reaction was completed, an appropriate amount of desiccant was added, and the mixture was filtered to obtain the positive electrode additive.
[0032] Positive electrode sheet
[0033] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a positive active material, a binder, a conductive agent, and the aforementioned positive additives.
[0034] In some embodiments, the mass percentage of the positive electrode additive is from 0.05 wt% to 0.5 wt%, based on the mass of the positive electrode active material layer. Exemplarily, 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 of any two of the above values. Preferably, the mass percentage of the positive electrode additive is from 0.3 wt% to 0.5 wt%.
[0035] In some embodiments, the molecular weight of the adhesive is between 800,000 and 1,200,000. Exemplarily, the molecular weight of the adhesive is 800,000, 850,000, 900,000, 950,000, 1,000,000, 1,050,000, 1,100,000, 1,150,000, 1,200,000 or any combination of two of the above values.
[0036] In some embodiments, the adhesive contains CF bonds. Preferably, the adhesive comprises polyvinylidene fluoride.
[0037] In some embodiments, the positive electrode active material in the positive electrode active material layer may be selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and compounds obtained by adding other transition metals or non-transition metals to the above compounds.
[0038] In some embodiments, the positive current collector can be made of materials such as metal foil or porous metal plate, for example, foil or porous plate of metals or alloys thereof such as aluminum, copper, nickel, titanium or iron, such as Al (aluminum) foil.
[0039] In some embodiments, the adhesion force between the positive electrode active material layer and the positive electrode current collector is between 28.5 N / m and 29.5 N / m. Exemplarily, the adhesion force between the positive electrode active material layer and the positive electrode current collector is 28.5 N / m, 28.8 N / m, 29 N / m, 29.2 N / m, 29.3 N / m, 29.5 N / m, or a range consisting of any two of the above values.
[0040] In some embodiments, the film resistance of the positive electrode is from 0.2Ω to 0.25Ω. Exemplarily, the film resistance of the positive electrode is 0.2Ω, 0.22Ω, 0.23Ω, 0.25Ω, or a range consisting of any two of the above values.
[0041] Preparation method of positive electrode sheet
[0042] The method for preparing the positive electrode sheet includes at least the following steps:
[0043] The positive electrode active material, binder, conductive agent and the positive electrode additive are dispersed in a non-aqueous solution and stirred to obtain a positive electrode slurry. The solid content of the positive electrode slurry is 65wt% to 75wt%, and the viscosity of the positive electrode slurry is 3900mPa·s to 6100mPa·s. 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 (95.5~97):(1~2):(1~2):(0.05~0.5).
[0044] The above-mentioned positive electrode slurry is uniformly coated on one surface of the positive electrode current collector and dried to obtain a positive electrode sheet with one side coated with positive electrode active material. Then, the above operation steps are repeated on the other surface of the positive electrode current collector to obtain a positive electrode sheet with positive electrode active material coated on both sides.
[0045] For example, the viscosity of the positive electrode slurry is 3900 mPa.s, 3950 mPa.s, 4000 mPa.s, 4500 mPa.s, 5000 mPa.s, 5500 mPa.s, 6000 mPa.s, 6100 mPa.s or any two of the above values.
[0046] other
[0047] The negative electrode sheet can be a lithium metal sheet, or it can include a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector.
[0048] The negative electrode active material layer typically includes the negative electrode active material and optional conductive agents and binders.
[0049] Exemplary examples include one or more of natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO, Li-Sn alloys, Li-Sn-O alloys, Li-Al alloys, or metallic lithium; conductive agents include one or more of conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers; and binders include 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, this application is not limited to these materials, and other materials that can be used as negative electrode active materials, conductive agents, and binders in lithium-ion batteries may also be used.
[0050] For example, the negative current collector can be made of materials such as metal foil or porous metal plate, for example, using foil or porous plate of metals or alloys of them such as copper, nickel, titanium or iron, such as copper foil.
[0051] 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 may be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is coated on a negative electrode current collector, and the negative electrode sheet is obtained by processes such as drying and cold pressing.
[0052] There are no particular restrictions on the separator membrane. Any well-known porous separator membrane with electrochemical and chemical stability can be selected, such as one or more single-layer or multi-layer films made of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF).
[0053] The electrolyte includes organic solvents, lithium electrolyte salts, and additives. This application does not impose specific limitations on its types; selection can be made according to actual needs.
[0054] For example, the organic solvents mentioned above include 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), butenyl 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.
[0055] For example, the above-mentioned electrolyte lithium salt includes one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium bistrifluoromethanesulfonylimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), or LiTFOP (lithium tetrafluorooxalate phosphate).
[0056] The electrolyte may optionally include other additives, which can be any additive that can be used in lithium-ion secondary batteries. This invention does not impose specific limitations and can select additives according to actual needs. As an example, the additives may be one or more of the following: vinylene carbonate (VC), ethylene ethylene carbonate (VEC), succinate (SN), adiponitrile (AND), 1,3-propenesulfonate lactone (PST), tris(trimethylsilane) phosphate (TMSP), or tris(trimethylsilane) borate (TMSB).
[0057] Electrochemical device
[0058] The electrochemical device of this application may include any device in which an electrochemical reaction occurs, and specific examples include all types of primary or secondary batteries. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.
[0059] electronic devices
[0060] The electronic device of this application includes any of the electrochemical devices described above. The electronic device of this application can be used in, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.
[0061] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Unless otherwise stated, all parts, percentages and ratios listed below are by weight, and all raw materials used are commercially available or synthesized by conventional methods.
[0062] Example 1-1
[0063] Preparation of positive electrode additives
[0064] 1 mol pentaerythritol and 4 mol 2-ethylbutyric acid were added to a 500 mL flask, followed by 0.1 mol ammonium sulfate. The mixture was reacted at 180 °C and 300 rpm for 72 h with mechanical stirring. After the reaction was completed, 5 mol anhydrous CaCl2 was added, and the mixture was filtered through a 200 nm filter membrane to obtain the positive electrode additive.
[0065] Preparation of positive electrode sheet
[0066] LiCoO2 (positive electrode active material), PVDF binder (molecular weight 100w), conductive carbon black (conductive agent), and positive electrode additives (see Table 1) were dispersed in NMP solvent and stirred until homogeneous to obtain a positive electrode slurry with a solid content of 70wt% and a viscosity of 3960mPa·s. The mass ratio of LiCoO2, PVDF, conductive carbon black, and positive electrode additives in the solid components was 95.9:2:2:0.1 (the sum of the mass percentages of the positive electrode active material and the positive electrode additives was 96%). The above positive electrode slurry was uniformly coated on one surface of a 9μm thick aluminum foil for positive electrode current collectors and dried at 120°C to obtain a single-sided positive electrode sheet with a positive electrode active material layer thickness of 75μm. The above operation steps were then repeated on the other surface of the same aluminum foil to obtain a double-sided positive electrode sheet coated with positive electrode active material. After coating, the positive electrode sheet is cold-pressed and then cut into sheets with a size of 70mm×800mm for later use.
[0067] Preparation of negative electrode sheet
[0068] Graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 97.6:1.1:1.3, and deionized water was added as a solvent. After stirring evenly, a negative electrode slurry with a solid content of 70 wt% was obtained. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil current collector and dried at 120°C to obtain a single-sided negative electrode sheet with a 110 μm thick negative electrode active material layer. The above steps were repeated on the other surface of the copper foil to obtain a double-sided negative electrode sheet with a negative electrode active material layer. The coated negative electrode sheet was cold-pressed and then cut into sheets with a size of 74 mm × 800 mm for later use.
[0069] Preparation of electrolyte
[0070] In a glove box filled with a dry argon atmosphere, organic solvents propylene carbonate (PC), diethyl carbonate (DEC), and ethylene carbonate (EC) were mixed in a mass ratio of 1:1:1. Lithium hexafluorophosphate (LiPF6) was then added to the above mixed organic solvents to dissolve and mix evenly to obtain an electrolyte with a LiPF6 concentration of 1.15 mol / L.
[0071] Preparation of the separating membrane
[0072] A porous polyethylene film with a thickness of 16 μm was used as the separator.
[0073] Preparation of lithium-ion batteries
[0074] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked sequentially and then wound to obtain an electrode assembly. After the tabs are welded, the electrode assembly is placed in an aluminum-plastic film and dried in a vacuum oven at 80°C for 12 hours to remove moisture. Then, the prepared electrolyte is injected, and the battery undergoes vacuum sealing, settling, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), capacity testing, and shaping processes to obtain a lithium-ion battery. Unless otherwise specified, the preparation process in this application can be carried out using conventional techniques in the field.
[0075] Test method:
[0076] (1) Viscosity test
[0077] The viscosity of the cathode slurry was tested using a digital rotational viscometer (Shanghai Jingtian Electronic Instruments Co., Ltd., LVDV1). A suitable rotor and rotation speed were selected based on the slurry being measured. The rotor was slowly inserted into the slurry for immersion. When the slurry level was in the center of the rotor groove, the rotational viscometer was started. After two minutes, when the reading remained unchanged, the reading was recorded as the viscosity of the prepared cathode slurry, in mPa·s.
[0078] (2) Adhesion test
[0079] Take the cold-pressed positive electrode sheet and punch it using a mold to obtain a test strip with a length of 100mm and a width of 20mm. Clean the surface of the steel plate with alcohol, and attach double-sided tape (NITTO.NO5000NS) with a length of 55mm to 70mm and a width of 20mm to the steel plate, ensuring no air bubbles are formed. Place the test strip centered on the double-sided tape, with the test side facing down. Use crepe tape (high-tack masking tape) to connect and fix a paper strip with a length of 50mm to 75mm and a width equal to the test strip to one end of the test strip. Manually push a 2kg rubber roller back and forth on the test strip 4 times to obtain the test sample. Test the sample using a tensile testing machine (Instron 3365). The test sample is fixed on the test stage, then the paper tape is folded upwards at 90° and secured with a clamp. The tensile testing machine then slowly pulls the paper tape at a speed of 10 mm / min until the positive electrode active material layer on the double-sided adhesive surface separates from the positive electrode current collector, ending the test. The average tensile force in the stable region is recorded as the adhesive force between the positive electrode active material layer and the positive electrode current collector, expressed in N / m.
[0080] (3) PD calculation
[0081] After determining the capacity of the battery cell electrode, use a stamping die to cut 12 small round pieces (1540.25 mm² in area). 2 After zeroing the electronic scale, use tweezers to place the cut small round pieces onto the weighing platform and record the weight of each small round piece: 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 positions: top, bottom, left, and right: 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 64h 71 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 The average thickness of each small circular piece is calculated as h1, h2, h3, h4, h5, h6, h7, h8, h9, h. 10 h 11 h 12 The formula is used to calculate the value of each small disc. The average value of the 12 small circular PDs is recorded as the PD for each embodiment or comparative example.
[0082] (4) Diaphragm resistance test
[0083] The resistance of the electrode film after cold pressing was tested using the Yuaneng Technology electrode resistance meter (BER2500). Before use, the resistance and pressure were reset. The electrode was placed under the probe for testing, and the average value of the resistance measured at 12 different positions was recorded as the resistance value of the film.
[0084] (5) Cyclic performance test
[0085] Cycle performance was evaluated by the capacity retention rate of lithium-ion batteries. After formation, the lithium-ion batteries were placed in a constant-temperature environment at 25°C and charged at a constant current of 0.6C to 4.5V, then charged at a constant voltage to the cutoff current of 0.05C. After a 3-minute rest period following full charge, they were discharged at 0.5C to 3.0V, and the discharge capacity was recorded as D0. Cycling tests were then conducted using a 0.6C charge / 0.5C discharge cycle for 500 cycles. The discharge capacity after the 500th cycle was recorded as D1. The capacity retention rate (%) of the lithium-ion battery after 500 cycles at room temperature (25°C) is calculated as D1 / D0 × 100%.
[0086] Examples 1-2 to Examples 1-19
[0087] Unlike Example 1-1, some parameters in the preparation process of the positive electrode were adjusted, as detailed in Table 1; the rest remained the same as in Example 1-1. It should be noted that the non-polar long-chain alkyl groups in Examples 1-2 to 1-18 are all non-polar straight-chain alkyl groups, and the non-polar long-chain alkyl groups in Examples 1-19 have at least one branch that is an irregularly chained alkyl group. Specifically, the structural formula of the positive electrode additive in Example 19 is as follows:
[0088]
[0089] Comparative Example 1
[0090] Unlike Example 1-1, no additives were used in the preparation of the positive electrode slurry, and the mass percentage of the positive electrode active material was 96%, while the rest was the same as in Example 1-1.
[0091] Comparative Example 2
[0092] The difference from Example 1-1 is that the additive used in the preparation of the positive electrode slurry is methyl ethyl succinate, while the rest is the same as in Example 1-1.
[0093] Table 1
[0094]
[0095] Table 2
[0096]
[0097]
[0098] By comparing Examples 1 to 18 with Comparative Example 1, and referring to Tables 1 and 2, it can be seen that when the positive electrode of the lithium-ion battery in this application contains the positive electrode additive described in this application, the film resistance of the positive electrode, the adhesion between the positive electrode active material layer and the current collector, and the capacity retention rate after 500 cycles are improved compared with Comparative Example 1. Simultaneously, the small molecule additive inserted between the PVDF molecular chains (i.e., the positive electrode additive described in this application) can weaken the intermolecular forces of PVDF molecules, improve molecular chain mobility, solve the problem of electrode brittleness, improve electrode flexibility, and significantly increase the electrode PD after capacity reduction, with a maximum PD of 4.00 g / cc, thus significantly improving the energy density of the lithium-ion battery.
[0099] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector; The positive electrode active material layer includes a positive electrode active material, a binder, a conductive agent, and a positive electrode additive; The positive electrode additive includes compounds with the structure shown in Formula I: Equation I; In Equation I, R1 and R2 are each independently selected from C2-C 18 Alkyl groups.
2. The positive electrode sheet according to claim 1, characterized in that, In Equation I, R1 and R2 are each independently selected from C. 12 -C 18 Straight-chain alkyl groups.
3. The positive electrode sheet according to claim 1, characterized in that, Based on the mass of the positive electrode active material layer, the mass percentage of the positive electrode additive is from 0.05 wt% to 0.5 wt%.
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 0.3wt% to 0.5wt%.
5. The positive electrode sheet according to claim 1, characterized in that, The molecular weight of the adhesive is between 800,000 and 1,200,000; The adhesive contains CF bonds.
6. The positive electrode sheet according to claim 1, characterized in that, The adhesive includes polyvinylidene fluoride.
7. A method for preparing a positive electrode sheet as described in any one of claims 1 to 6, characterized in that, Includes the following steps: The positive electrode active material, binder, conductive agent and the positive electrode additive are dispersed in a non-aqueous solution and stirred to obtain a positive electrode slurry. The solid content of the positive electrode slurry is 65wt% to 75wt%, and the viscosity of the positive electrode slurry is 3900mPa·s to 6100mPa·s.
8. The preparation method according to claim 7, characterized in that, 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 (95.5~97):(1~2):(1~2):(0.05~0.5).
9. An electrochemical device, characterized in that, The electrochemical device includes the positive electrode sheet according to any one of claims 1 to 6 or the positive electrode sheet prepared by the preparation method according to any one of claims 7 to 8.
10. An electronic device, characterized in that, The electronic device includes the electrochemical device of claim 9.