A positive electrode sheet and a battery

Abstract

The application relates to the technical field of batteries, in particular to a positive plate and a battery comprising the same. The positive plate comprises a positive current collector, a second coating layer located on one side or both sides of the positive current collector, and a first coating layer located between the positive current collector and the second coating layer, wherein the first coating layer comprises lithium-sodium-cobalt oxide, and the second coating layer comprises a lithium-rich manganese-based material. The positive plate has low surface resistance and high rate performance; the battery comprising the positive plate has low direct-current resistance, low expansion rate and good rate performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode sheet and a battery comprising the same. BACKGROUND

[0002] The energy density of a lithium ion battery is actually dependent on the performance of the positive electrode material. With the continuous development of the field of power batteries, a single high-energy-density battery is difficult to meet the increasing performance requirements, such as fast charging and discharging performance, high-voltage performance, high and low temperature performance, etc. The current commercialized materials are mainly layered lithium cobaltate, ternary materials, spinel structure lithium manganate, olivine structure lithium iron phosphate, lithium manganese iron phosphate, etc., which are difficult to meet the increasingly comprehensive performance requirements.

[0003] The lithium-rich manganese-based material has not been commercialized yet. It has a high specific capacity (> 250 mAh / g) and energy density (> 860 Wh / kg) at high voltage (> 4.8 V), and is a kind of high-energy-density positive electrode material with good prospects. However, due to poor electrical conductivity, its application in high-rate scenarios such as fast charging and discharging is limited.

[0004] In view of the low electrical conductivity of lithium-rich manganese-based materials, the electrical conductivity can be improved at the level of the electrode sheet, such as adding a carbon bottom coating or a conductive layer containing other conductive substances on the current collector. However, this method of adding a carbon bottom coating or a conductive layer containing other conductive substances between the positive electrode active material and the current collector has the following disadvantages: (1) it reduces the adhesion between the positive electrode active material and the current collector, and the active material layer is prone to fall off during the cycle process, resulting in serious capacity decay of the battery; (2) the traditional carbon-coated electrode sheet has increased brittleness and poor flexibility, and the bottom coating layer is prone to cracking during the winding and unwinding process, and the foil is prone to wrinkling.

[0005] Therefore, it is very important to invent a battery with better rate performance and lower impedance. SUMMARY

[0006] The present application aims to overcome the above-mentioned problems existing in the prior art, and provides a positive electrode sheet and a battery comprising the same. The positive electrode sheet of the present application has low surface resistance and high rate performance; the battery obtained from the positive electrode sheet of the present application has low direct current resistance, low expansion rate and good rate performance.

[0007] The present inventors have found that by reducing the surface resistance of the positive electrode sheet and improving the rate performance of the positive electrode sheet, the rate performance of the battery can be improved and the direct current resistance of the battery can be reduced.

[0008] The inventor of the present application found that, in order to improve the rate performance of the positive plate, the rate performance of the positive plate can be improved by adding a specific coating layer including lithium sodium cobalt oxide between the positive current collector and the coating layer including the lithium-rich manganese-based material, and the surface resistance is reduced, thereby improving the rate performance of the battery. The inventor of the present application screened out a specific coating layer capable of improving the conductivity of the positive plate through a large number of in-depth studies.

[0009] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a positive plate, which comprises a positive current collector, a second coating layer located on one side or both sides of the positive current collector, and a first coating layer located between the positive current collector and the second coating layer, wherein the first coating layer comprises lithium sodium cobalt oxide, and the second coating layer comprises a lithium-rich manganese-based material.

[0010] The second aspect of the present application provides a battery, wherein the positive plate of the battery is the positive plate according to the first aspect of the present application.

[0011] Compared with the prior art, the present application has at least the following advantages:

[0012] (1) The positive plate of the present application has good rate performance;

[0013] (2) The positive plate of the present application has low surface resistance;

[0014] (3) The battery of the present application has low direct current resistance (DCR);

[0015] (4) The battery of the present application has good rate performance;

[0016] (5) The battery of the present application has low expansion rate.

[0017] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Fig. 1 shows a SEM cross-sectional schematic diagram of a positive plate provided by the present application.

[0019] Figure 2 Fig. 2 shows an XRD schematic diagram of a positive plate provided by the present application.

[0020] Figure 3 Fig. 3 shows a rate performance diagram of the batteries obtained in Example 1 and Comparative Example 1.

[0021] Figure 4 Fig. 4 shows a comparison diagram of the diffraction pattern of the lithium sodium cobalt oxide prepared in Example 1 and the O2 phase lithium cobalt oxide standard card.

[0022] Figure 5Fig. 1 shows a comparison between the diffraction pattern of the lithium-rich manganese-based material prepared in Example 1 of the present application and the O3 phase lithium nickelate standard card. DETAILED DESCRIPTION

[0023] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the present application, and are not intended to limit the present application.

[0024] The first aspect of the present application provides a positive electrode sheet, which comprises a positive electrode current collector, a second coating layer on one side or both sides of the positive electrode current collector, and a first coating layer between the positive electrode current collector and the second coating layer, wherein the first coating layer comprises lithium-sodium-cobalt oxide, and the second coating layer comprises a lithium-rich manganese-based material.

[0025] The redox reaction of the mixed anions and cations of the lithium-rich manganese-based material can reach a specific capacity of more than 250 mAh / g at a high voltage (>4.6 V), but due to the presence of Li2MnO3 non-electrochemical active nanodomains, the electronic conductivity of the lithium-rich manganese-based material is relatively low, and the rate performance is poor. The lithium-sodium-cobalt oxide has high powder conductivity and low lithium ion migration energy, and can release more than 90% of lithium ions at a high voltage (>4.6 V), and has good rate performance.

[0026] The inventors of the present application found that by adding a first coating layer comprising lithium-sodium-cobalt oxide between the positive electrode current collector and the second coating layer comprising a lithium-rich manganese-based material, the positive electrode sheet can have low surface resistance and high rate performance. This is because during the increase of the charge rate, the lithium-sodium-cobalt oxide in the first coating layer can quickly release lithium ions, thereby playing a role in supplementing the amount of lithium removal, avoiding the problem of polarization caused by the slow lithium removal of the lithium-rich manganese-based material; during the increase of the discharge rate, the lithium-sodium-cobalt oxide in the first coating layer can play a role in accepting the high-speed electron flow of the positive electrode current collector, thereby avoiding the problem of interface polarization caused by the slow lithium ion intercalation due to the poor conductivity of the lithium-rich manganese-based material and the inability to quickly accept electrons for reduction reaction. At the same time, compared with the technology of improving the conductivity of the electrode sheet by coating a carbon base coating layer, the composite coating positive electrode sheet of the present application does not face the problem of active material layer peeling caused by poor adhesion between different coating layers and poor adhesion between the first coating layer and the positive electrode current collector, and the coating layer is not prone to cracking during the winding and unwinding process; and the first coating layer and the second coating layer both belong to the active material layer, and the conductive agent and the binder in the two coating layers can form a good conductive and adhesive network, and have good cycle stability.

[0027] By using the above-mentioned method to improve the rate performance of the positive electrode sheet, the positive electrode sheet can already achieve lower surface resistance and better rate performance than the prior art. In order to further improve the effect, one or more of the technical features can be further optimized.

[0028] The positive electrode sheet can be a composite positive electrode sheet. The composite positive electrode sheet means that the positive electrode sheet comprises two layers of coating. The first coating layer comprises lithium-sodium-cobalt oxide, which is located between the positive electrode current collector and the second coating layer; and the second coating layer comprises lithium-rich manganese-based material, which is located on one side or both sides of the positive electrode current collector.

[0029] For example, the SEM cross-sectional schematic diagram of the positive electrode sheet provided by the present application is shown in Figure 1 It can be seen that the right side is the positive electrode current collector, the left side is the second coating layer comprising lithium-rich manganese-based material, and the middle is the first coating layer comprising lithium-sodium-cobalt oxide.

[0030] In an example, in the XRD pattern of the positive electrode sheet, there is a characteristic peak in the range of 20°-22.6°, which is a superlattice diffraction peak unique to the lithium-rich manganese-based material.

[0031] For example, in the XRD pattern of the positive electrode sheet, as shown in Figure 2 there is a characteristic peak in the range of 20°-22.6°, and all the characteristic peaks appearing in this range are superlattice diffraction peaks unique to the lithium-rich manganese-based material. The appearance of the superlattice diffraction peak proves that the positive electrode sheet contains the lithium-rich manganese-based material. Further, the characteristic peak in the range of 20°-22.6° and the following corresponding lithium-rich manganese-based material diffraction peaks can more accurately prove that the positive electrode sheet contains the lithium-rich manganese-based material.

[0032] For example, in the XRD pattern of the positive electrode sheet, as shown in Figure 2 there is a coincidence peak (denoted as peak1) of the (002) crystal face diffraction peak of the lithium-sodium-cobalt oxide and the (003) crystal face diffraction peak of the lithium-rich manganese-based material, which exists in the range of 17.5°-19.5°, and the diffraction intensity of the coincidence peak is I peak1 . The coincidence peak means that the diffraction peak of the lithium-sodium-cobalt oxide coincides with the diffraction peak of the lithium-rich manganese-based material. The coincidence means that the diffraction peak of the lithium-sodium-cobalt oxide completely coincides with the diffraction peak of the lithium-rich manganese-based material.

[0033] For example, in the XRD pattern of the positive electrode sheet, as shown in Figure 2 there are diffraction peaks in the range of 42°-50°, wherein the (104) crystal face diffraction peak of the lithium-rich manganese-based material exists in the range of 43°-45°, and the diffraction intensity of the diffraction peak is I 104 , and the (103) crystal face diffraction peak of the lithium-sodium-cobalt oxide exists in the range of 46.7°-47.5°, and the diffraction intensity of the diffraction peak is I 103 .

[0034] For example, in the XRD pattern of the positive electrode sheet, as shown in Figure 2 the (015) crystal face diffraction peak of the lithium-rich manganese-based material exists in the range of 48° to 49.2°, and the diffraction intensity of the diffraction peak is I 015 , a diffraction peak exists in the range of 57° to 63°, wherein the (107) crystal face diffraction peak of the lithium-rich manganese-based material exists in the range of 57.6° to 59.2°, and the diffraction intensity of the diffraction peak is I 107 , the (105) crystal face diffraction peak of lithium sodium cobalt oxide exists in the range of 61.1° to 62.3°, and the diffraction intensity of the diffraction peak is I 105 .

[0035] According to a specific embodiment, the positive electrode sheet satisfies 1.2 < I peak1 / I 104 < 2.5 (for example, 1.4, 1.5, 1.8, 2.0, 2.2) and / or 3 < I 104 / I 103 < 10 (for example, 4, 5, 6, 7, 8, 9). When the positive electrode sheet satisfies the above formula, the positive electrode sheet has higher specific capacity and better rate performance.

[0036] In an example, 1.8 < I peak1 / I 104 < 2.5 and 5 < I 104 / I 103 < 8.

[0037] According to a specific embodiment, the positive electrode sheet satisfies 0.8 < I 103 / I 015 < 2.0 and / or 0.8 < I 107 / I 105 < 2.0.

[0038] According to a specific embodiment, in the XRD pattern of the positive electrode sheet, the half-peak width of the overlapping peak existing in the range of 17.5° to 19.5° is 0.15 to 0.35, and / or the half-peak width of the crystal face diffraction peak of the lithium-rich manganese-based material existing in the range of 43° to 45° is 0.3 to 0.45.

[0039] In an example, in the XRD pattern of the positive electrode sheet, the half-peak width of the overlapping peak existing in the range of 17.5° to 19.5° is 0.15 to 0.35 (for example, 0.15, 0.17, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35). The half-peak width of the overlapping peak represents the peak width at half the maximum diffraction intensity of the overlapping peak.

[0040] In one example, the half-peak width of the crystal face diffraction peak of the lithium-rich manganese-based material in the range of 43°-45° is 0.3-0.45 (for example, 0.3, 0.32, 0.35, 0.37, 0.4, 0.42, 0.45). The half-peak width of the diffraction peak represents the peak width at the half of the maximum diffraction intensity of the diffraction peak.

[0041] In one example, the lithium-sodium-cobalt oxide is an O2-phase lithium-sodium-cobalt composite layered oxide with a P63mc crystal structure. As shown in FIG. 1, by comparing the XRD diffraction pattern of the lithium-sodium-cobalt oxide of the present application with the standard card of the O2-phase lithium cobalt oxide, it can be seen that the lithium-sodium-cobalt oxide is an O2-phase lithium-sodium-cobalt oxide. Figure 4

[0042] In one example, the lithium-sodium-cobalt oxide is a single-crystal-like irregular morphology, as shown in FIG. 2. As shown in FIG. 2, the shape of the lithium-sodium-cobalt oxide in the first coating layer can be seen. Figure 1

[0043] In one example, the median particle size of the lithium-sodium-cobalt oxide is 4-8 μm (4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm). By limiting the median particle size of the lithium-sodium-cobalt oxide, the surface resistance of the positive electrode sheet can be further reduced, and the rate performance can be improved.

[0044] In one example, the chemical formula of the lithium-sodium-cobalt oxide is Li x Na y Co 1-z A z O2, wherein 0.8

[0045] The lithium-sodium-cobalt oxide can be obtained by commercial purchase or prepared by a conventional preparation process.

[0046] According to a specific embodiment, the lithium-sodium-cobalt oxide can be prepared by the following method:

[0047] (1) Co-precipitation method plus high-temperature sintering method to prepare A element doped (Co 1-z A z ​​)304 precursor: soluble cobalt salt (such as cobalt sulfate, cobalt nitrate, cobalt oxalate, etc.) and A element-containing salt (such as sulfate, nitrate, etc.) are dissolved in deionized water according to the Co:A molar ratio of (1-z):z to prepare a salt solution; a precipitant (such as sodium carbonate, sodium hydroxide, sodium oxalate, sodium bicarbonate, etc.) and a complexing agent (such as ammonia, etc.) are dissolved in deionized water to prepare a mixed alkali solution; then the salt solution and the mixed alkali solution are simultaneously and uniformly added to deionized water for co-precipitation reaction, and then the precipitate is filtered, washed, and dried to obtain (Co 1-z A z )CO3 or (Co 1-z A z )(OH)2 powder; the (Co 1-z A z )CO3 or (Co 1-z A z )(OH)2 powder is subjected to first sintering, cooled to room temperature after sintering, ground and sieved to obtain (Co 1-z A z )304 precursor;

[0048] (2) high-temperature sintering method for preparing Na m Co 1-z A z O2: the precursor prepared in step (1) is mixed with Na2CO3 powder according to the Na:Co molar ratio of (0.8-1):1, and the mixed powder is subjected to second sintering, and cooled to room temperature after sintering to obtain Na m Co 1-z A z O2 intermediate product containing Na;

[0049] (3) molten salt ion exchange method for preparing the lithium-sodium-cobalt oxide Li x Na y Co 1-z A z O2: the Na m Co 1-z A z O2 intermediate product containing Na prepared in step (2) is mixed with lithium-containing molten salt (such as lithium chloride, lithium hydroxide, lithium nitrate, etc.) according to the Li:Na molar ratio of (5-15):1, and the mixed slurry is subjected to ion exchange reaction, and after the reaction is completed, the mixed slurry is filtered, washed, and dried to obtain the lithium-sodium-cobalt oxide Li x Na y Co 1-z A z O2.

[0050] In an example, the concentration of the salt solution in step (1) is 0.2-2.5 mol / L. In an example, the concentration of the salt solution in step (1) is 0.2-2.5 mol / L.

[0051] In an example, the co-precipitation reaction in step (1) has a pH of 7-12 and a temperature of 50-60°C.

[0052] In an example, the first sintering in step (1) has a temperature of 500-600°C and a time of 4-8h.

[0053] In an example, the second sintering in step (2) has a temperature of 800-1000°C and a time of 20-40h, and the sintering atmosphere of the second sintering is an oxygen atmosphere.

[0054] In an example, the ion exchange reaction has a temperature of 150-300°C, a reaction time of 8-48h, and a reaction atmosphere of air.

[0055] In an example, the lithium-rich manganese-based material is an O3-phase lithium-rich manganese material having an R-3m crystal structure. As shown in Figure 5 by comparing the XRD diffraction pattern of the lithium-rich manganese-based material of the present application with the O3-phase lithium nickelate standard card, it can be seen that the lithium-rich manganese-based material is an O3-phase lithium-rich manganese material.

[0056] In an example, the lithium-rich manganese-based material is a spherical particle, as shown in Figure 1 It can be seen that the lithium-rich manganese-based material in the second coating on the far left is a spherical particle.

[0057] In an example, the lithium-rich manganese-based material has a median particle size of 6-15μm (e.g., 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm).

[0058] In an example, the lithium-rich manganese-based material has a chemical formula of xLi2MnO3·(1-x)LiMO2, wherein 0

[0059] The lithium-rich manganese-based material can be obtained by commercial purchase or prepared by a conventional preparation process.

[0060] According to a specific embodiment, the lithium-rich manganese-based material can be prepared by the following method:

[0061] (a) dissolving a soluble salt of element M in water, and respectively preparing a precipitant solution and a complexing agent solution or a mixed solution of the two, and passing the prepared precipitant solution and complexing agent solution or mixed solution of the two into a reaction kettle with deionized water as a bottom liquid (the amount of the bottom liquid is 25% to 35% of the volume of the reaction kettle), and controlling the temperature, pH and stirring speed in the reaction kettle, to carry out a co-precipitation reaction; after the reaction is completed, the precipitate is washed and dried to obtain a precursor of the lithium-rich manganese-based material;

[0062] (b) mixing the precursor of the lithium-rich manganese-based material of step (a) with a lithium source to obtain a mixture;

[0063] (c) sintering the mixture of step (b), and after cooling, grinding and sieving to prepare the lithium-rich manganese-based material.

[0064] In an example, the soluble salt in step (a) is selected from one or more of a sulfate salt, a nitrate salt, a phosphate salt, an oxalate salt, an acetate salt, and a citrate salt of element M.

[0065] In an example, the concentration of the soluble salt of element M in step (a) is 0.5 to 4 mol / L.

[0066] In an example, the precipitant in step (a) is selected from one or more of sodium carbonate, sodium hydroxide, potassium carbonate, potassium hydroxide, ammonium carbonate and ammonium bicarbonate.

[0067] In an example, the complexing agent in step (a) is selected from aqueous ammonia (aqueous solution of ammonia gas, chemical formula NH3·H2O).

[0068] In an example, in the mixed solution in step (a), the concentration of the precipitant is 0.5 to 8 mol / L, and the concentration of the complexing agent is 0.01 to 8 mol / L.

[0069] In an example, the temperature of the co-precipitation reaction in step (a) is 45 to 65°C, the pH is 7.0 to 12.0, and the reaction time is 5h to 50h, and the co-precipitation reaction is carried out under stirring at a stirring speed of 50 to 1500 rpm, and the co-precipitation reaction is carried out under air or nitrogen, preferably under nitrogen, which can prevent Mn 2+ from being oxidized.

[0070] In an example, the lithium source in step (b) is selected from one or more of lithium carbonate and lithium hydroxide.

[0071] In one example, the molar ratio of Li:TM in step (b) is (1.2-1.6):1 (e.g., 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1), where TM is the transition metal in the precursor of the lithium-rich manganese-based material, i.e., including Mn in Li2Mn03and M in LiM02.

[0072] In one example, the sintering in step (c) is two-stage sintering, the first stage sintering temperature is 450-500°C (e.g., 450°C, 460°C, 470°C, 480°C, 490°C, 500°C), and the first stage sintering time is 4-5h (e.g., 4h, 4.5h, 5h); the second stage sintering temperature is 870-890°C (e.g., 870°C, 880°C, 890°C), and the second stage sintering time is 12-18h (e.g., 12h, 13h, 14h, 15h, 16h, 17h, 18h).

[0073] In one example, the sintering in step (c) is performed in air or oxygen.

[0074] In one example, the positive electrode current collector is selected from one or more of single-bright aluminum foil, double-bright aluminum foil, and porous aluminum foil.

[0075] According to one specific embodiment, the first coating layer comprises a first conductive agent and a first binder.

[0076] In one example, the first conductive agent is selected from one or more of graphite, carbon black, acetylene black, graphene, and carbon nanotube.

[0077] In one example, the first binder is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylate, and polyacrylic acid.

[0078] In one example, the content of the lithium-sodium-cobalt oxide is 90-97wt% and the content of the first conductive agent is 1-3wt% based on the total weight of the first coating layer. The content of the first binder can be adjusted within a range. For example, when the weight content of the lithium-sodium-cobalt oxide and the first conductive agent is less than 100%, the portion less than 100% is supplemented with the first binder.

[0079] In one example, the content of the lithium-sodium-cobalt oxide is 92-95wt% and the content of the first conductive agent is 1.2-2.5wt% based on the total weight of the first coating layer.

[0080] According to one specific embodiment, the second coating layer comprises a second conductive agent and a second binder.

[0081] In an example, the content of the lithium-rich manganese-based material is 80-95 wt% and the content of the second conductive agent is 5-10 wt% based on the total weight of the second coating layer. The content of the second binder can be adjusted within a range. For example, when the weight content of the lithium-rich manganese-based material and the second conductive agent is less than 100%, the second binder is used to make up the difference.

[0082] In an example, the content of the lithium-rich manganese-based material is 85-90 wt% and the content of the second conductive agent is 5-8 wt% based on the total weight of the second coating layer.

[0083] The first coating layer includes the first conductive agent and the second coating layer includes the second conductive agent, and the first conductive agent and the second conductive agent together form a conductive network in the positive electrode sheet, connecting the transport of performance electrons in lithium sodium cobalt oxide and lithium-rich manganese-based material.

[0084] In an example, the second conductive agent is selected from one or more of graphite, carbon black, acetylene black, graphene and carbon nanotubes.

[0085] In an example, the second binder is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylate and polyacrylic acid.

[0086] Illustratively, the positive electrode sheet can be prepared by mixing the lithium sodium cobalt oxide, the first conductive agent and the first binder, and sufficiently homogenizing with an organic solvent to form a first coating layer slurry, coating the first coating layer slurry on one side or both sides of the surface of the positive electrode current collector to form a first coating layer, and then drying and rolling; mixing the lithium-rich manganese-based material, the second conductive agent and the second binder, and sufficiently homogenizing with an organic solvent to form a second coating layer slurry, coating the second coating layer slurry on the surface of the first coating layer to form a second coating layer, and then drying and rolling to obtain the positive electrode sheet.

[0087] In an example, the organic solvent is N-methyl pyrrolidone (NMP).

[0088] According to a specific embodiment, the thicknesses of the first coating layer and the second coating layer are H1 and H2, respectively, and H1 and H2 satisfy 0.05≤H2 / H1≤30 (for example, 0.05, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 10, 15, 20, 25, 30). When the positive current collector has the first coating layer and the second coating layer on only one side, H1 represents the thickness of the first coating layer on one side, and H2 represents the thickness of the second coating layer on one side; when the positive current collector has the first coating layer and the second coating layer on both sides, H1 represents the sum of the thicknesses of the first coating layers on both sides, and H2 represents the sum of the thicknesses of the second coating layers on both sides. When the thicknesses of the first coating layer and the second coating layer of the positive electrode sheet satisfy the above formula, the rate capability of the positive electrode sheet is improved. The thicknesses of the first coating layer and the second coating layer can be measured by the SEM cross-sectional view of the positive electrode sheet.

[0089] In an example, 1≤H2 / H1≤2.

[0090] According to a specific embodiment, the compaction density of the positive electrode sheet is 2-4 g / cm 3 (for example, 2 g / cm 3 , 2.5 g / cm 3 , 3 g / cm 3 , 3.5 g / cm 3 , 4 g / cm 3 ).

[0091] The second aspect of the application provides a battery, the positive electrode sheet of which is the positive electrode sheet of the first aspect of the application. The materials and preparation methods of the battery, except for the positive electrode sheet, can be performed in the manner of the art, and all can achieve the effects of low impedance, low expansion rate, and good rate capability.

[0092] The energy density of the battery can be 250-380 Wh / kg (for example, 250 Wh / kg, 260 Wh / kg, 270 Wh / kg, 280 Wh / kg, 290 Wh / kg, 300 Wh / kg, 310 Wh / kg, 320 Wh / kg, 330 Wh / kg, 340 Wh / kg, 350 Wh / kg, 360 Wh / kg, 370 Wh / kg, 380 Wh / kg).

[0093] In an example, the battery comprises a negative electrode sheet.

[0094] In an example, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on at least one side surface of the negative electrode current collector.

[0095] In an example, the negative electrode active material layer comprises a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0096] In an example, the negative active material is selected from one or more of artificial graphite, natural graphite, soft carbon, hard carbon, Si-O composite material, Si-C composite material, and Si negative material.

[0097] In an example, the negative conductive agent is selected from one or more of artificial graphite, natural graphite, carbon black, acetylene black, and CNT.

[0098] In an example, the negative binder is selected from one or more of carboxymethyl cellulose-Na, carboxymethyl cellulose-Li, butadiene rubber, and polyethylene.

[0099] In an embodiment, the negative current collector is a copper foil.

[0100] The battery of the present application has low direct current resistance, low expansion rate, and good rate performance due to containing the positive electrode sheet of the present application.

[0101] The present application will be described in detail below through examples. The examples described in the present application are only a part of the examples of the present application, rather than all the examples. Based on the examples in the present application, all other examples obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application.

[0102] The following examples are used to illustrate the positive electrode sheet of the present application.

[0103] Example 1

[0104] (1) Preparation of components:

[0105] Positive electrode current collector: double-light aluminum foil;

[0106] First coating layer: lithium-sodium cobalt oxide 94 parts by weight, first conductive agent (conductive carbon black) 2 parts by weight, first binder (PVDF) 4 parts by weight;

[0107] Second coating layer: lithium-rich manganese-based material 88 parts by weight, second conductive agent (conductive carbon black) 6 parts by weight, second binder (PVDF) 6 parts by weight.

[0108] (2) Preparation of lithium-sodium cobalt oxide

[0109] 1) soluble cobalt salt (cobalt sulfate) and Al element containing salt (aluminum sulfate octadecahydrate) are dissolved in deionized water according to Co:Al molar ratio of 99:1 to prepare a 2 mol / L salt solution; the precipitant (sodium carbonate) and complexing agent (ammonia) are dissolved in deionized water to prepare a mixed alkali liquor, in which the concentration of sodium carbonate is 2 mol / L and the concentration of ammonia is 0.2 mol / L; then the prepared salt solution and mixed alkali liquor are simultaneously and uniformly added to deionized water for co-precipitation reaction, the pH of the co-precipitation reaction is 7.5, the temperature is 55℃, the feeding time lasts for 30h, then the precipitate is filtered, washed and dried to obtain (Co 0.99 Al 0.01 )CO3 powder; the (Co 0.99 Al 0.01 )CO3 powder is subjected to first sintering, the first sintering temperature is 500℃, the sintering time is 5h, after sintering, it is cooled to room temperature, and after grinding and sieving, (Co 0.99 Al 0.01 )3O4 precursor is obtained.

[0110] 2) the (Co 0.99 Al 0.01 )3O4 precursor prepared in step 1) is mixed with Na2CO3 powder according to Na:Co molar ratio of 0.86:0.99, and after being uniformly mixed in a mixer, it is placed in a muffle furnace for second sintering, the second sintering temperature is 850℃, the sintering time is 35h, the sintering atmosphere is oxygen atmosphere, and after sintering, it is cooled to room temperature to obtain Na 0.86 Co 0.99 Al 0.01 O2 containing Na intermediate product.

[0111] 3) the Na 0.86 Co 0.99 Al 0.01 O2 containing Na intermediate product obtained in step 2) is mixed with lithium-containing molten salt (lithium hydroxide) according to Li:Na molar ratio of 8:1, the mixed slurry is subjected to ion exchange reaction, the ion exchange reaction is carried out at 260℃, the reaction time is 12h, the reaction atmosphere is air atmosphere, after the reaction is completed, the slurry is filtered, washed, dried, ground, and sieved to obtain lithium-sodium-cobalt oxide Li 0.84 Na 0.02 Co 0.99 Al 0.01 O2.

[0112] (3) Preparation of lithium-rich manganese-based material

[0113] (a) soluble salts of element M (NiSO4, CoSO4, MnSO4) are dissolved in water to prepare a mixed salt solution, wherein the total concentration of metal ions in the mixed salt solution is 2 mol / L, Ni2+ :Co 2+ :Mn 2+ The molar ratio of Co:Mn:Li is 0.13:0.13:0.54, a mixed solution of a precipitant solution (NaCO3) and a complexing agent solution (NH3·H2O) is prepared, the concentration of the precipitant solution (NaCO3) is 2 mol / L, and the concentration of the complexing agent solution (NH3·H2O) is 0.2 mol / L; the prepared mixed solution of the precipitant and the complexing agent is introduced into a reaction kettle, deionized water is added as a bottom liquid (the amount of the bottom liquid is 30% of the volume of the reaction kettle), the above-mentioned mixed salt solution is pumped into the reaction kettle at a feeding speed of 200 mL / h using a peristaltic pump, the stirring speed is controlled to be 1000 rpm, the circulating water temperature is 50°C, the alkali liquid feeding speed is adjusted using three-stage speed regulation, the pH of the solution system is controlled to be 7.5, the feeding time lasts for 30 h, and the co-precipitation reaction is carried out under nitrogen condition; after the reaction is completed, the slurry is subjected to solid-liquid separation, then deionized water is used for centrifugal cleaning, and then drying is carried out at 120°C for 24 h, to obtain a lithium-rich manganese-based material carbonate precursor;

[0114] (b) fully mixing the lithium-rich manganese-based material carbonate precursor of step (a) with a lithium source (Li2CO3), wherein the molar ratio of Li:TM is 1.5:1, and TM is Ni, Co, and Mn;

[0115] (c) after fully mixing in a mixer, sintering is carried out in a muffle furnace, the sintering is two-stage sintering, the first-stage sintering temperature is 500°C, and the time is 5 h; the second-stage sintering temperature is 880°C, and the time is 15 h, the sintering atmosphere is oxygen, and after cooling, grinding and sieving are carried out, to obtain a lithium-rich manganese-based material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2.

[0116] (4) Preparation of the positive electrode sheet

[0117] After mixing the lithium-sodium-cobalt oxide, the first conductive agent, and the first binder, the organic solvent (N-methyl pyrrolidone) is fully homogenized to form a first coating slurry, the first coating slurry is coated on both sides of the positive electrode current collector to form a first coating layer, and then drying and rolling are carried out, and the thickness H1 of the first coating layer after rolling is 40 μm; after mixing the lithium-rich manganese-based material, the second conductive agent, and the second binder, the organic solvent (N-methyl pyrrolidone) is fully homogenized to form a second coating slurry, the second coating slurry is coated on the surface of the first coating layer to form a second coating layer, and then drying and rolling are carried out, and the thickness H2 of the second coating layer after rolling is 60 μm, to obtain the positive electrode sheet.

[0118] Example 2 group

[0119] This group of examples is used to illustrate the impact of changing the weight parts of lithium sodium cobalt oxide in the first coating and / or the weight parts of the lithium-rich manganese-based material in the second coating.

[0120] This group of examples is performed with reference to Example 1, except that the weight parts of lithium sodium cobalt oxide in the first coating and / or the weight parts of the lithium-rich manganese-based material in the second coating are changed, as shown in Table 1.

[0121] Example 3 group

[0122] This group of examples is used to illustrate the impact of changing H2 / H1.

[0123] This group of examples is performed with reference to Example 1, except that H2 / H1 is changed, as shown in Table 1.

[0124] Table 1

[0125]

[0126]

[0127] Comparative Example 1

[0128] Example 1 is used as a reference, except that there is only one coating on both sides of the positive electrode current collector, and the total thickness of the coating is 100 μm, and the composition of the coating is 88 parts by weight of the lithium-rich manganese-based material, 6 parts by weight of the second conductive agent (conductive carbon black), and 6 parts by weight of the second binder (PVDF).

[0129] Comparative Example 2

[0130] Example 2d is used as a reference, except that there is only one coating on both sides of the positive electrode current collector, and the total thickness of the coating is 100 μm, and the composition of the coating is 95 parts by weight of the lithium-rich manganese-based material, 2.5 parts by weight of the second conductive agent (conductive carbon black), and 2.5 parts by weight of the second binder (PVDF).

[0131] Comparative Example 3

[0132] Example 1 is used as a reference, except that the first coating is replaced by a conductive carbon coating of a certain thickness. The conductive carbon is nano-conductive graphite, and the thickness of the conductive carbon coating is 2.5 μm. The composition of the second coating is 88 parts by weight of the lithium-rich manganese-based material, 6 parts by weight of the second conductive agent (conductive carbon black), and 6 parts by weight of the second binder (PVDF). The total thickness of the first and second coatings is 100 μm.

[0133] Preparation Example

[0134] The positive electrode sheets obtained in the examples and comparative examples are used to prepare batteries in the following manner, respectively:

[0135] (1) Positive electrode sheet

[0136] The positive electrode sheet obtained in each of the above examples and comparative examples was used, respectively.

[0137] (2) Negative electrode sheet

[0138] A negative electrode active material (artificial graphite), a negative electrode conductive agent (carbon black), and a negative electrode binder (styrene-butadiene rubber) were mixed in a weight ratio of 96:2:2, a mixed slurry was prepared using deionized water as a solvent, and the mixed slurry was coated on both sides of a negative electrode current collector (copper foil).

[0139] (3) Electrolyte

[0140] The electrolyte includes an organic solvent, a lithium salt, and other additives. The organic solvent is EC: EMC: DEC = 1:1:1 vol%, the lithium salt is LiPF6, and the other additives are any additives that can be used as electrolyte additives in the prior art.

[0141] (4) Preparation of lithium ion battery

[0142] The positive electrode sheet of step (1), the graphite negative electrode sheet of step (2), a PE porous ceramic separator, an aluminum plastic film, and positive and negative electrode tabs were cut to the required size for a stacked battery. In a humidity environment of <10%, the positive electrode sheet and the negative electrode sheet were cut to tabs, and then stacked with the separator in the order of the positive electrode sheet, the negative electrode sheet, and the separator, and the tabs were welded. Subsequently, the battery core was placed in an aluminum plastic film punch for top-side sealing treatment. After the battery was baked at 80°C for 24 h, the electrolyte of step (3) was injected, and then aging and formation, second sealing, edge folding, sorting, and OCV were performed to obtain a stacked structure soft-pack battery.

[0143] Test example

[0144] (1) SEM test

[0145] The cross-sectional morphology of the positive electrode sheet was tested by a scanning electron microscope.

[0146] (2) XRD test

[0147] The XRD diffraction pattern of the positive electrode sheet was obtained by a Bruker D8 Advance.

[0148] (3) Rate performance test

[0149] The test environment was 25°C, the voltage range was 2.0-4.6 V, the current density was 1C = 200 mA / g, the rate test was performed, and the capacity retention rate of the rate test = the discharge specific capacity at the 30th cycle / the discharge specific capacity at the 1st cycle.

[0150] (4) Surface resistance test

[0151] The double-sided surface resistance of the rolled electrode sheet was tested using a four-probe tester, and each test was performed on the paste-coated head, middle, and tail of each electrode sheet A and C, and the average value was taken.

[0152] (5) DCR test

[0153] Before the rate test, the battery was cycled at 0.1C / 0.1C for one cycle, and the DCR at 0.1C full charge was tested, which was recorded as the DCR before the rate test. After the rate test, the battery was in a full charge state and its DCR was tested, which was recorded as the DCR after the rate test.

[0154] (6) Swelling rate test

[0155] The thickness of the battery cell was tested using a semi-automatic micrometer, and the swelling rate = (the thickness of the battery cell after the rate test - the thickness of the battery cell before the rate test) / the thickness of the battery cell before the rate test * 100%

[0156] The results obtained are recorded in Table 2.

[0157] Table 2

[0158]

[0159]

[0160] As can be seen from Table 2, by comparing the examples and the comparative examples, it can be seen that the battery electrode sheet prepared from the positive electrode sheet of the examples has a reduced surface resistance of the electrode sheet, improved rate performance, reduced swelling rate, and reduced DCR growth before and after the rate test, which shows that the scheme of the present application improves the rate performance of the positive electrode sheet, reduces the surface resistance of the positive electrode sheet, thereby improving the rate performance of the battery and reducing the swelling rate of the battery.

[0161] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A positive electrode plate, characterized in that, The positive electrode includes a positive current collector, a second coating located on one or both sides of the positive current collector, and a first coating located between the positive current collector and the second coating. The first coating comprises lithium sodium cobalt oxide, and the second coating comprises a lithium-rich manganese-based material. The lithium sodium cobalt oxide is an O2-phase lithium sodium cobalt composite layered oxide, and the chemical formula of the lithium sodium cobalt oxide is Li. x Na y Co 1-z A z O2, where 0.8 < x < 1, 0 < y < 0.05, 0 < z < 0.05, and A is one or more of Al, Mg, Ti, Zr, P, Ni, and Fe.

2. The positive electrode according to claim 1, wherein, In the XRD pattern of the positive electrode, characteristic peaks exist in the range of 20° to 22.6°; and / or, in the XRD pattern of the positive electrode, there is a coincidence peak where the (002) crystal plane diffraction peak of the lithium sodium cobalt oxide coincides with the (003) crystal plane diffraction peak of the lithium-rich manganese-based material, and this coincidence peak exists in the range of 17.5° to 19.5°, with a diffraction intensity of I. peak1 Diffraction peaks exist in the range of 42° to 50°, among which the (104) crystal plane diffraction peak of the lithium-rich manganese-based material exists in the range of 43° to 45°, and the diffraction intensity of this diffraction peak is I. 104 The (103) crystal plane diffraction peak of the lithium sodium cobalt oxide exists in the range of 46.7°~47.5°, and the diffraction intensity of this diffraction peak is I. 103 .

3. The positive electrode sheet according to claim 2, wherein, The positive electrode plate satisfies 1.2 < I peak1 / I 104 <2.5 and / or 3 < I 104 / I 103 <10.

4. The positive electrode sheet according to claim 1, wherein, If the thicknesses of the first coating and the second coating are H1 and H2 respectively, then H1 and H2 satisfy 0.05 ≤ H2 / H1 ≤ 30.

5. The positive electrode according to claim 4, wherein, H1 and H2 satisfy 1 ≤ H2 / H1 ≤ 2.

6. The positive electrode according to claim 2 or 3, wherein, In the XRD pattern of the positive electrode sheet, the full width at half maximum (FWHM) of the overlapping peak existing within the range of 17.5° to 19.5° is 0.15 to 0.35, and / or the FWHM of the crystal plane diffraction peak of the lithium-rich manganese-based material existing within the range of 43° to 45° is 0.3 to 0.

45.

7. The positive electrode sheet according to any one of claims 1-3, wherein, In the XRD pattern of the positive electrode, a (015) crystal plane diffraction peak of the lithium-rich manganese-based material exists in the range of 48° to 49.2°, and the diffraction intensity of this peak is I. 015 Diffraction peaks exist in the range of 57° to 63°, among which the (107) crystal plane diffraction peak of the lithium-rich manganese-based material exists in the range of 57.6° to 59.2°, and the diffraction intensity of this diffraction peak is I. 107 A diffraction peak of the (105) crystal plane of lithium sodium cobalt oxide exists at 61.1°~62.3°, and the diffraction intensity of this peak is I. 105 .

8. The positive electrode according to claim 7, wherein, The positive electrode plate satisfies 0.8 < I 103 / I 015 <2.0 and / or 0.8 <I 107 / I 105 <2.

0.

9. The positive electrode according to claim 1, wherein, The lithium sodium cobalt oxide has a P63mc crystal structure; and / or, the lithium-rich manganese-based material is an O3-phase lithium-rich manganese material with an R-3m crystal structure; and / or, the chemical formula of the lithium-rich manganese-based material is xLi2MnO3·(1-x)LiMO2, where 0 < x < 0.5, and M includes one or more of the elements Mn, Ni, Co, Al, Mg, Zr, Ti, Nb, W, P, B, F, Y, La.

10. The positive electrode according to claim 1, wherein, The median particle size of the lithium sodium cobalt oxide is 4 to 8 μm; and / or, the median particle size of the lithium-rich manganese-based material is 6 to 15 μm.

11. The positive electrode according to claim 1, wherein, The first coating includes a first conductive agent and a first binder. Based on the total weight of the first coating, the content of the lithium sodium cobalt oxide is 90 - 97 wt%, and the content of the first conductive agent is 1 - 3 wt%; and / or, the second coating includes a second conductive agent and a second binder. Based on the total weight of the second coating, the content of the lithium-rich manganese-based material is 80 - 95 wt%, and the content of the second conductive agent is 5 - 10 wt%.

12. The positive electrode according to claim 1, wherein, The compaction density of the positive electrode sheet is 2~4 g / cm³. 3 .

13. A battery, characterized in that, The battery includes the positive electrode sheet according to any one of claims 1 - 12.

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