Lithium supplementing positive plate as well as preparation method and application thereof

Abstract

The invention provides a lithium supplement positive plate and a preparation method and application thereof, the lithium supplement positive plate comprises a current collector and a positive active layer arranged on the current collector, and the positive active layer comprises a positive material, a first lithium supplement agent and a second lithium supplement agent. The first lithium supplement agent and the second lithium supplement agent are matched in the positive electrode active layer, and the content ratio of the first lithium supplement agent and the second lithium supplement agent is controlled in a proper range, so that the negative influence of a single lithium supplement agent in the battery use process can be avoided while the advantages of the two lithium supplement agents are exerted; and the gas production phenomenon in the lithium supplementing process is effectively inhibited while the battery capacity is improved.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of lithium-ion batteries, and in particular to a lithium-supplemented positive electrode sheet, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium replenishment technology is an effective means of increasing the energy density of lithium-ion batteries, while also improving their cycle life and energy storage performance. Currently, commonly used lithium replenishment technologies include negative electrode replenishment, positive electrode replenishment, electrolyte replenishment, separator replenishment, current collector replenishment, and electrochemical replenishment. Among these, positive electrode replenishment technology involves directly adding a positive electrode replenisher to the positive electrode slurry. This technology places lower demands on the replenishment process and eliminates the need for modifications to the production environment and equipment, making it more suitable for existing lithium-ion battery manufacturing processes.

[0003] The commonly used positive electrode lithium supplements are lithium-rich transition metal oxides. The delithiation process is accompanied by the oxidation of the transition metal, which leads to an increase in the valence of the transition metal. At the same time, there is also the phenomenon of precipitation of oxygen or oxygen free radicals. The highly oxidized lithium supplement residues remaining in the positive electrode sheet will increase the risk of side reactions when in contact with the electrolyte, thereby increasing the risk of gas production during battery use, especially in high-temperature environments. In addition, these high-valent lithium supplement residues will produce a large amount of flammable gas when triggering thermal abuse (such as needle puncture, collision, etc.), thereby increasing the risk of thermal runaway and increasing the safety risk of the battery during use. Summary of the Invention

[0004] In view of this, the present application provides a lithium-supplemented positive electrode sheet, a preparation method thereof, and an application thereof. The lithium-supplemented positive electrode sheet uses a first lithium-supplementing agent and a second lithium-supplementing agent in the positive electrode active layer and controls the content ratio of the two within an appropriate range. While giving full play to the advantages of the two lithium-supplements, it can avoid the negative effects of a single lithium-supplementing agent during the use of the battery, improve the battery capacity, and effectively suppress the gas production during the lithium-supplementing process.

[0005] In a first aspect, the present application provides a lithium-supplemented positive electrode sheet, comprising a current collector and a positive electrode active layer disposed on the current collector, wherein the positive electrode active layer comprises a positive electrode material, a first lithium supplement agent, and a second lithium supplement agent; the volume change amplitude of the first lithium supplement agent before and after the first delithiation is greater than the volume change amplitude of the second lithium supplement agent before and after the first delithiation; the first charge gram capacity of the first lithium supplement agent is greater than the first charge gram capacity of the second lithium supplement agent; the first discharge gram capacity of the first lithium supplement agent is less than the first discharge gram capacity of the second lithium supplement agent; in the lithium-supplemented positive electrode sheet after the first delithiation, the volume ratio of the first lithium supplement agent to the second lithium supplement agent is 1:(0.2-3).

[0006] In an embodiment of the present application, in the lithium-supplemented positive electrode sheet after the first delithiation, the volume ratio of the first lithium-supplementing agent to the second lithium-supplementing agent is 1:(0.3-3).

[0007] In an embodiment of the present application, the volume of the first lithium supplement after the first delithiation is 40%-90% of the volume before the first delithiation, and the volume of the second lithium supplement after the first delithiation is 60%-98% of the volume before the first delithiation.

[0008] In an embodiment of the present application, the porosity of the first lithium replenisher after the first delithiation is 5%-60%, and the porosity of the second lithium replenisher after the first delithiation is 1%-40%; the porosity of the second lithium replenisher after the first delithiation is less than the porosity of the first lithium replenisher after the first delithiation.

[0009] In an embodiment of the present application, the first charge gram capacity of the first lithium supplement agent is in the range of 400mAh / g-1200mAh / g, and the first charge and discharge efficiency of the first lithium supplement agent is in the range of 1%-14%; and / or, the first charge gram capacity of the second lithium supplement agent is in the range of 240mAh / g-550mAh / g, and the first charge and discharge efficiency of the second lithium supplement agent is in the range of 15%-45%.

[0010] In the embodiment of the present application, the first lithium supplement includes one or more of Li5FeO4, Li2O, Li6CoO4, Li5ReO6 and Li4CoO4; and / or the second lithium supplement includes Li2NiO2, Li2CuO2, Li2RuO3, Li2MnO3, Li2MoO3 and Li 0.65 Ni 1.35 One or more of O2.

[0011] In the embodiment of the present application, in the lithium-supplemented positive electrode sheet, the sum of the volumes of the first lithium-supplementing agent and the second lithium-supplementing agent accounts for 0.1%-8% of the volume of the positive electrode active layer.

[0012] In an embodiment of the present application, the particle size D50 of the first lithium supplement agent is 3 μm-15 μm; and / or the particle size D50 of the second lithium supplement agent is 4 μm-23 μm.

[0013] In an embodiment of the present application, the positive electrode material includes one or more of lithium manganese iron phosphate, lithium iron phosphate, lithium nickel manganese oxide and a ternary positive electrode material; the ternary positive electrode material includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

[0014] In an embodiment of the present application, the positive electrode active layer further includes a conductive agent; the conductive agent includes one or more of conductive graphite, carbon black, acetylene black, super-P, carbon nanotubes, graphene, Ketjen black and VGCF.

[0015] In an embodiment of the present application, the positive electrode active layer further includes a binder; the binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyacrylate, lithium polyacrylate and sodium polyacrylate.

[0016] In the embodiment of the present application, the initial charging capacity of the lithium-supplemented positive electrode sheet is 0.25%-13% greater than that of the positive electrode sheet to which the first lithium-supplementing agent and the second lithium-supplementing agent are not added.

[0017] The second aspect of the present application further provides a method for preparing the lithium-supplemented positive electrode sheet provided in the first aspect of the present application, comprising:

[0018] Mixing the positive electrode material, the first lithium replenishing agent and the second lithium replenishing agent to prepare a lithium replenishing positive electrode active slurry;

[0019] The lithium-replenishing positive electrode active slurry is placed on a current collector to obtain a lithium-replenishing positive electrode sheet.

[0020] In the embodiment of the present application, the sum of the mass of the first lithium supplement agent and the second lithium supplement agent is 0.1%-7.4% of the mass of the positive electrode material.

[0021] In an embodiment of the present application, the mass ratio of the first lithium supplement agent to the second lithium supplement agent is (0.1-10):1.

[0022] The third aspect of the present application provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, and a separator and an electrolyte located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes the lithium-supplemented positive electrode sheet provided in the first aspect of the present application or the lithium-supplemented positive electrode sheet prepared by the preparation method provided in the second aspect of the present application.

[0023] A fourth aspect of the present application provides an electrical device, which includes a lithium-ion battery as provided in the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A flow chart of a method for preparing a lithium-supplemented positive electrode sheet provided in one embodiment of the present application;

[0025] Figure 2 A schematic structural diagram of a lithium-ion battery provided in one embodiment of the present application.

[0026] Explanation of Figure Numbers

[0027] 100 - lithium-ion battery; 101 - positive electrode; 102 - negative electrode; 103 - electrolyte; 104 - separator. DETAILED DESCRIPTION

[0028] The present application is further described in detail below in conjunction with preferred embodiments, but the protection scope of the present application is not limited to the following specific embodiments.

[0029] In this application, all professional terms have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this application.

[0030] Lithium replenishment technology is an effective means of increasing the energy density of lithium-ion batteries, while also improving their cycle life and energy storage performance. Currently, commonly used lithium replenishment technologies include negative electrode replenishment, positive electrode replenishment, electrolyte replenishment, separator replenishment, current collector replenishment, and electrochemical replenishment. Among these, positive electrode replenishment technology involves directly adding the positive electrode replenisher to the positive electrode slurry during the homogenization process. This technology places lower demands on the replenishment process, eliminates the need for modifications to the production environment and equipment, and is more suitable for existing lithium-ion battery manufacturing processes.

[0031] The commonly used positive electrode lithium supplements are lithium-rich transition metal oxides. The delithiation process is accompanied by the oxidation of the transition metal, which leads to an increase in the valence of the transition metal. At the same time, there is also the phenomenon of precipitation of oxygen or oxygen free radicals. The highly oxidized lithium supplement residues remaining in the positive electrode sheet will increase the risk of side reactions when in contact with the electrolyte, thereby increasing the risk of gas production during battery use, especially in high-temperature environments. In addition, these high-valent lithium supplement residues will produce a large amount of flammable gas when triggering thermal abuse (such as needle puncture, collision, etc.), thereby increasing the risk of thermal runaway and increasing the safety risk of the battery during use.

[0032] In response to the above problems, the present application provides a lithium-supplemented positive electrode sheet, a preparation method thereof, and an application thereof. The lithium-supplemented positive electrode sheet uses a first lithium-supplementing agent and a second lithium-supplementing agent in the positive electrode active layer and controls the content ratio of the two within an appropriate range. While giving full play to the advantages of the two lithium-supplementing agents, it avoids the negative effects of a single lithium-supplementing agent during battery use, improves the battery capacity, and effectively suppresses the gas production during the lithium-supplementing process.

[0033] The present application provides a lithium-supplementing positive electrode sheet, comprising a current collector and a positive electrode active layer disposed on the current collector. The positive electrode active layer comprises a positive electrode material, a first lithium supplement, and a second lithium supplement. In an embodiment of the present application, the volume change amplitude of the first lithium supplement before and after the first delithiation is greater than the volume change amplitude of the second lithium supplement before and after the first delithiation; and the first charge gram capacity of the first lithium supplement is greater than the first charge gram capacity of the second lithium supplement. In an embodiment of the present application, the volume change amplitude refers to the ratio of the difference between the volume of the first lithium supplement and the second lithium supplement particles before and after the first delithiation to the volume before the first delithiation. After the first charge delithiation of the first lithium supplement and the second lithium supplement in the positive electrode active layer of the lithium-supplementing positive electrode sheet provided by the present application, at least a portion of the lithium-rich first lithium supplement and the second lithium supplement becomes oligolithium metal oxide residues after delithiation, causing the first lithium supplement and the second lithium supplement to collapse and decrease in volume after the first delithiation. The first lithium supplement in the present application has a larger initial charge capacity than the second lithium supplement. Therefore, as the main lithium supplement active substance in the positive electrode active layer, the first lithium supplement has a greater contribution to the improvement of the battery capacity. Due to the release or precipitation of oxygen and oxygen free radicals in the first lithium supplement during the delithiation process, the first lithium supplement has a larger volume change before and after the first delithiation than the second lithium supplement. Therefore, by adding a second lithium supplement with a smaller volume change before and after the first delithiation to the positive electrode active layer, the gas production problem of the first lithium supplement during the delithiation process can be effectively alleviated, thereby improving the safety performance of the battery. In the embodiment of the present application, in the lithium supplement positive electrode sheet after the first delithiation, the volume ratio of the first lithium supplement to the second lithium supplement is 1: (0.2-3). In some specific embodiments, the volume ratio of the first lithium replenisher to the second lithium replenisher in the lithium replenisher positive electrode sheet can be, for example, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.5, 1:2, 1:2.5, or 1:3. The present application controls the volume ratio of the first lithium replenisher to the second lithium replenisher in the lithium replenisher positive electrode sheet within an appropriate range, thereby controlling the content ratio of the first lithium replenisher to the second lithium replenisher, thereby maximizing the synergistic lithium replenishment effect of the two, so that the lithium replenisher positive electrode sheet has a good lithium replenishment effect while also having high safety, thereby increasing the energy density, cycle life, and safety performance of the battery.

[0034] In this application, the first charge gram capacity of the first lithium supplement refers to the first charge gram capacity of the first lithium supplement obtained by using the first lithium supplement as the positive electrode material of a battery to make a button battery, and then charging it to 4.3V under 0.1C conditions; the first discharge gram capacity of the first lithium supplement refers to the first discharge gram capacity of the first lithium supplement obtained by using the first lithium supplement as the positive electrode material of a battery to make a button battery, and then discharging it to 2.5V under 0.1C conditions; the first charge and discharge efficiency is the ratio of the first discharge gram capacity to the first charge gram capacity. In this application, the first charge gram capacity of the second lithium supplement refers to the first charge gram capacity of the second lithium supplement obtained by using the second lithium supplement as the positive electrode material of the battery to make a button battery, and then charging it to 4.3V under 0.1C conditions; the first discharge gram capacity of the second lithium supplement refers to the first discharge gram capacity of the second lithium supplement obtained by using the second lithium supplement as the positive electrode material of the battery to make a button battery, and then discharging it to 2.5V under 0.1C conditions; the first charge and discharge efficiency is the ratio of the first discharge gram capacity to the first charge gram capacity.

[0035] In some embodiments of the present application, in the lithium-supplemented positive electrode sheet after initial delithiation, the volume ratio of the first lithium supplement agent to the second lithium supplement agent is 1:(0.3-3). Controlling the volume ratio of the first lithium supplement agent to the second lithium supplement agent within the above range can further limit the content of the first lithium supplement agent in the lithium-supplemented positive electrode sheet to be greater than or equal to the content of the second lithium supplement agent, thereby further optimizing the synergistic lithium supplement effect of the first lithium supplement agent and the second lithium supplement agent, improving the lithium supplement efficiency of the first lithium supplement agent and the second lithium supplement agent, and further extending the cycle life of the battery while increasing the battery energy density as much as possible.

[0036] In an embodiment of the present application, the volume of the first lithium replenisher after the first delithiation is 40%-90% of the volume before the first delithiation, and the volume of the second lithium replenisher after the first delithiation is 60%-98% of the volume before the first delithiation. After the first charge and delithiation, the lithium-rich first lithium replenisher and the second lithium replenisher become oligolithium metal oxide residues after delithiation, causing the first lithium replenisher and the second lithium replenisher to collapse and change in volume after the first delithiation. The first lithium replenisher releases oxygen or precipitates oxygen free radicals during the delithiation process, resulting in a significant volume change before and after the first delithiation. The second lithium replenisher undergoes a valence change in the metal element during the delithiation process, ensuring that the oxygen element in the second lithium replenisher is tightly bound to the metal element. Therefore, oxygen evolution does not occur during the delithiation process, and compared to the first lithium replenisher, the volume change before and after the first delithiation is relatively small. The present application controls the volume change amplitude of the first lithium replenisher and the second lithium replenisher within an appropriate range, thereby ensuring the contribution of the lithium replenisher to the electrode capacity while further reducing the occurrence of gas production caused by the release of oxygen by the first lithium replenisher and the occurrence of side reactions with the electrolyte caused by the release of oxygen free radicals. In some specific embodiments of the present application, the volume of the first lithium replenisher after the first delithiation can be, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90% of the volume before the first delithiation; the volume of the second lithium replenisher after the first delithiation can be, for example, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 98% of the volume before the first delithiation.

[0037] In an embodiment of the present application, the porosity of the first lithium supplement after the initial delithiation is 5%-60%, and the porosity of the second lithium supplement after the initial delithiation is 1%-40%. Furthermore, the porosity of the second lithium supplement is less than that of the first lithium supplement. In the positive electrode active layer of the lithium-supplemented positive electrode sheet provided herein, the first and second lithium supplements undergo structural collapse after delithiation, resulting in a reduction in volume and the development of defects such as cracks and gaps within the particles. This, in turn, causes a change in the porosity of the first and second lithium supplements after the initial delithiation. The present application controls the porosity of the second lithium replenisher after the first delithiation to be within a range smaller than the porosity of the first lithium replenisher after the first delithiation, thereby further controlling the volume changes of the first and second lithium replenishers before and after the first delithiation. As a result, compared with the first lithium replenisher, the volume change of the second lithium replenisher after the first delithiation is smaller, the cracks inside the second lithium replenisher particles are fewer, and the corresponding porosity is also smaller, thereby further enhancing the synergistic effect of the first and second lithium replenishers and improving the safety performance and cycle life of the lithium replenisher positive electrode sheet. In some specific embodiments of the present application, the porosity of the first lithium replenisher after the first delithiation can be, for example, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 30%, 40%, 50%, or 60%; the porosity of the second lithium replenisher after the first delithiation can be, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 30%, or 40%.

[0038] In an embodiment of the present application, the first charge gram capacity of the first lithium supplement is 400mAh / g-1200mAh / g, and the first charge-discharge efficiency of the first lithium supplement is 1%-14%. In some specific embodiments, the first charge gram capacity of the first lithium supplement can be, for example, 400mAh / g, 500mAh / g, 600mAh / g, 700mAh / g, 800mAh / g, 900mAh / g, 1000mAh / g, 1100mAh / g, or 1200mAh / g, and the first charge-discharge efficiency of the first lithium supplement can be, for example, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, or 14%. In an embodiment of the present application, the amount of lithium released by the first lithium supplement during the first delithiation accounts for 70%-95% of the total lithium content of the first lithium supplement. In some specific embodiments, the amount of lithium released by the first lithium supplement during initial delithiation can account for 70%, 75%, 80%, 85%, 90%, or 95% of the total lithium content of the first lithium supplement. By controlling the relevant electrochemical parameters of the first lithium supplement within the above ranges, the lithium supplement efficiency of the first lithium supplement during initial charging can be further improved.

[0039] In an embodiment of the present application, the first charge gram capacity of the second lithium supplement is 240mAh / g-550mAh / g, and the first charge and discharge efficiency of the second lithium supplement is 15%-45%. In some specific embodiments, the first charge gram capacity of the second lithium supplement can be, for example, 240mAh / g, 250mAh / g, 280mAh / g, 300mAh / g, 350mAh / g, 400mAh / g, 450mAh / g, 500mAh / g, or 550mAh / g, and the first charge and discharge efficiency of the second lithium supplement can be, for example, 15%, 20%, 25%, 30%, 35%, 40%, or 45%. In an embodiment of the present application, the amount of lithium removed from the second lithium supplement during the first delithiation accounts for 55%-88% of the total lithium content of the second lithium supplement. In some specific embodiments, the amount of lithium released by the second lithium replenisher during the first lithium removal can, for example, account for 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 88% of the total lithium content of the second lithium replenisher. By controlling the relevant electrochemical parameters of the second lithium replenisher within the above ranges, the lithium replenishment efficiency of the second lithium replenisher during battery cycling can be further improved. In this application, the first charge and discharge efficiency is the ratio of the first discharge gram capacity to the first charge gram capacity.

[0040] In an embodiment of the present application, the first charge gram capacity of the first lithium supplement is greater than the first charge gram capacity of the second lithium supplement, and the first charge and discharge efficiency of the second lithium supplement is greater than the first charge and discharge efficiency of the first lithium supplement. By controlling the first charge gram capacity and the first charge and discharge efficiency of the first and second lithium supplements within the above ranges, the present application can further enhance the battery capacity-enhancing effect of the first lithium supplement, and further enhance the advantage of the second lithium supplement's large reversible specific capacity. This allows the second lithium supplement to continuously release active lithium into the battery system during repeated charge and discharge of the battery, thereby achieving continuous lithium replenishment during the battery cycle.

[0041] In the embodiment of the present application, the first lithium supplement agent includes one or more of Li5FeO4, Li2O, Li6CoO4, Li5ReO6 and Li4CoO4. In the present application, by selecting the above metal oxides with higher oxygen content as the first lithium supplement agent, the lithium supplement effect during the first charge can be effectively exerted. In the embodiment of the present application, the second lithium supplement agent includes Li2NiO2, Li2CuO2, Li2RuO3, Li2MnO3, Li2MoO3 and Li 0.65 Ni 1.35One or more of O2. This application uses the above-mentioned metal oxides as the second lithium replenisher. These metal oxides will not produce oxygen evolution during the charge and discharge process, thereby compensating for the safety defects of the first lithium replenisher. In addition, most of the residues of these second lithium replenishers after the first delithiation are layered structures, which give them a high reversible specific capacity. During the battery cycle, active lithium is continuously released into the battery system. By making special selections and combinations of the first lithium replenisher and the second lithium replenisher, the obtained lithium replenisher positive electrode sheet has a good lithium replenishment effect during both the first charge and subsequent cycles.

[0042] In the embodiment of the present application, in the lithium-supplemented positive electrode sheet, the sum of the volumes of the first lithium-supplementing agent and the second lithium-supplementing agent accounts for 0.1%-8% of the volume of the positive electrode active layer. In some specific embodiments, the sum of the volumes of the first lithium-supplementing agent and the second lithium-supplementing agent accounts for 0.1%, 0.2%, 0.3%, 0.5%, 0.6%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8% of the volume of the positive electrode active layer. The present application controls the total amount of the first lithium-supplementing agent and the second lithium-supplementing agent in the positive electrode active layer within an appropriate range, so that the lithium-supplemented positive electrode sheet has both good lithium-supplementing effect and energy density, thereby improving the capacity and cycle life of the battery. In addition, it can also effectively improve the utilization rate of the lithium-supplementing agent, avoid the waste of the lithium-supplementing agent or the need for more negative electrode materials, effectively reduce the battery cost and improve the energy density of the battery.

[0043] In an embodiment of the present application, the particle size D50 of the first lithium supplement agent is 3 μm-15 μm; the particle size D50 of the second lithium supplement agent is 4 μm-23 μm. In some specific embodiments of the present application, the particle size D50 of the first lithium supplement agent may be, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm; the particle size D50 of the second lithium supplement agent may be, for example, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm, 22 μm, or 23 μm. In the present application, the particle size D50 is specifically Dv50, which refers to the particle size corresponding to when the cumulative particle size distribution percentage of the measured sample reaches 50%. The physical meaning is that particles with a particle size larger than it account for 50%, and particles with a particle size smaller than it also account for 50%. In the embodiment of the present application, it can be measured and calculated using SEM (Scanning Electron Microscope) combined with EDS (Energy Dispersive Spectrometer), and can also be measured using FIB-SEM (Focused Ion Beam-Scanning Electron Microscope). In the embodiment of the present application, the particle size D50 of the first lithium supplement and the second lithium supplement includes the particle size before the first delithiation, and also includes the particle size before the first delithiation, that is, the particle size of the first lithium supplement and the second lithium supplement before and after the first delithiation are both within the above range. By controlling the particle size of the first lithium replenisher and the second lithium replenisher within the above-mentioned range, the present application can, on the one hand, avoid the excessively small particle size causing the lithium replenisher to have an excessively large specific surface area, thereby causing side reactions in the electrolyte; on the other hand, it can avoid the excessively large particle size causing the lithium replenisher to form larger inert particles after delithiation, thereby hindering the transmission of lithium ions in the electrode sheet, thereby further improving the safety performance and lithium ion transmission capacity of the lithium replenisher positive electrode sheet.

[0044] In an embodiment of the present application, the positive electrode material includes one or more of lithium manganese iron phosphate, lithium iron phosphate, lithium nickel manganese oxide, and a ternary positive electrode material, wherein the ternary positive electrode material includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide. The first lithium replenisher and the second lithium replenisher in the lithium-supplemented positive electrode sheet provided herein are not particularly limited to the lithium-ion battery system and are applicable to most common lithium-ion battery systems.

[0045] In an embodiment of the present application, the positive electrode active layer further includes a conductive agent, which includes one or more of conductive graphite, carbon black, acetylene black, super-P, carbon nanotubes, graphene, Ketjen black, and VGCF. The conductivity of the lithium-supplemented positive electrode sheet can be further enhanced by selecting a suitable conductive agent and binder. In an embodiment of the present application, the positive electrode active layer further includes a binder, which includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyacrylate, lithium polyacrylate, and sodium polyacrylate. Selecting a suitable binder can further enhance the bonding strength between the positive electrode active layer and the current collector of the lithium-supplemented positive electrode sheet, as well as the bonding strength between the components within the positive electrode active layer.

[0046] In an embodiment of the present application, the initial charge capacity of the lithium-supplemented positive electrode sheet is 0.25%-13% greater than that of a positive electrode sheet to which the first and second lithium-supplementing agents are not added. In the present application, a positive electrode sheet to which the first and second lithium-supplementing agents are not added refers to a positive electrode sheet having the same composition and content of all components as the lithium-supplemented positive electrode sheet, the only difference being that the first and second lithium-supplementing agents are not added. In some specific embodiments, the initial charge capacity of the lithium-supplemented positive electrode sheet is 0.25%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, or 13% greater than that of a positive electrode sheet to which the first and second lithium-supplementing agents are not added. The lithium-supplemented positive electrode sheet provided in the present application can effectively improve its capacity while ensuring the safety performance of the battery by using the first and second lithium-supplementing agents in combination. The active lithium released by the first and second lithium replenishers partially replenishes the active lithium released from the positive electrode material that is consumed during the formation of the SEI film, and partially replenishes the reversible lithium lost in the lithium insertion sites of the positive electrode sheet. This ultimately results in a certain degree of improvement in the battery capacity after the first and second lithium replenishers are combined to replenish the lithium. In this application, the initial charge capacity of the lithium-replenished positive electrode sheet is the sum of the three charging capacities obtained by charging the lithium-replenished positive electrode sheet at 0.05C for 2 hours, then charging it to 3.8V at 0.2C, and then charging it to 4.3V at 0.03C.

[0047] In the embodiments of the present application, the DC discharge impedance of the lithium-supplemented positive electrode sheet at room temperature is 1%-30% lower than that of a positive electrode sheet without the first and second lithium-supplementing agents. The DC discharge impedance of the lithium-supplemented positive electrode sheet at -10°C is 2%-40% lower than that of a positive electrode sheet without the first and second lithium-supplementing agents. The lithium-supplemented positive electrode sheet provided in the application, by combining the first and second lithium-supplementing agents, can effectively reduce the impedance of the battery.

[0048] The lithium-supplemented positive electrode provided in the present application is compounded by using a first lithium-supplementing agent that contributes more to the capacity of the electrode and a second lithium-supplementing agent whose volume change is smaller before and after the first delithiation, and controlling their content within an appropriate range. The two work together to supplement lithium, thereby improving the capacity of the battery while also improving the safety performance and cycle life of the battery.

[0049] This application also provides a method for preparing the lithium-supplemented positive electrode sheet provided above. Figure 1 The preparation method is a flow chart, comprising:

[0050] S101. The positive electrode material, the first lithium replenishing agent and the second lithium replenishing agent are mixed to prepare a lithium replenishing positive electrode active slurry;

[0051] S102. Disposing the lithium-replenishing positive electrode active slurry on a current collector to obtain a lithium-replenishing positive electrode sheet.

[0052] In step S101, the sum of the masses of the first and second lithium replenishers is 0.1%-7.4% of the mass of the positive electrode material. In some specific embodiments, the sum of the masses of the first and second lithium replenishers can be, for example, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 7.4% of the mass of the positive electrode material. By controlling the sum of the masses of the first and second lithium replenishers within an appropriate range, the present application can ensure that the positive electrode material provides sufficient energy density for the lithium-replenishing positive electrode sheet while fully utilizing the lithium replenishing effect of the lithium replenisher, further improving the capacity and cycle life of the battery.

[0053] In an embodiment of the present application, the mass ratio of the first lithium supplement agent to the second lithium supplement agent is (0.1-10):1. In some specific embodiments, the mass ratio of the first lithium supplement agent to the second lithium supplement agent can be, for example, 0.1:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1. In some embodiments, the mass ratio of the first lithium supplement agent to the second lithium supplement agent is (1-10):1.

[0054] In some embodiments of the present application, the lithium-supplemented positive electrode active slurry in step S101 further includes a conductive agent and a binder. In the embodiments of the present application, the conductive agent can be any conductive agent known in the art, for example, one or more of conductive graphite, carbon black, acetylene black, super-P, carbon nanotubes, graphene, Ketjen black, and VGCF; the binder can be any binder known in the art, for example, one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyacrylate, lithium polyacrylate, and sodium polyacrylate.

[0055] In the embodiment of the present application, the sum of the masses of the positive electrode material, the first lithium replenisher and the second lithium replenisher accounts for 92.2%-98.3% of the total mass of the lithium replenishing positive electrode active slurry; the mass of the conductive agent accounts for 0.5%-3.8% of the total mass of the lithium replenishing positive electrode active slurry; the mass of the binder accounts for 1.2%-4% of the total mass of the lithium replenishing positive electrode active slurry; wherein the total mass of the positive electrode active slurry refers to the total mass of the slurry after removing the solvent.

[0056] The preparation method provided in this application has a simple process, a short flow, and a low preparation cost, which is conducive to large-scale industrial production.

[0057] like Figure 2 As shown, the present application also provides a lithium-ion battery 100, which includes a positive electrode sheet 101, a negative electrode sheet 102, and an electrolyte 103 and a separator 104 located between the positive electrode sheet 101 and the negative electrode sheet 102, wherein the positive electrode sheet 101 includes a lithium-supplemented positive electrode sheet as provided in the previous text of the present application or a lithium-supplemented positive electrode sheet prepared by the preparation method provided in the previous text of the present application. In an embodiment of the present application, the negative electrode sheet 102 includes a negative electrode current collector and a negative electrode active layer provided on the negative electrode current collector, and the negative electrode active material in the negative electrode material layer can be any negative electrode active material for lithium-ion batteries known in the art. In an embodiment of the present application, the negative electrode active material in the negative electrode material layer can be any negative electrode active material for lithium-ion batteries known in the art. For example, the negative electrode active material can be selected from one or more of carbon-based negative electrode active materials, silicon-based negative electrode active materials, tin-based negative electrode active materials, and lithium metal negative electrode active materials. Among them, carbon-based negative electrodes include but are not limited to natural graphite, artificial graphite, hard carbon, soft carbon, and graphene; silicon-based negative electrodes include but are not limited to silicon, silicon carbon, silicon oxide, etc.; tin-based negative electrodes include but are not limited to tin, tin carbon, tin oxide, and tin metal compounds.

[0058] The present application also provides an electrical device comprising the lithium-ion battery described above. The electrical device may be, for example, an electric car, a mobile phone, a tablet computer, a laptop computer, a wearable device (a watch, a wristband), a digital camera, or the like.

[0059] The present application is further described below with reference to several embodiments:

[0060] Example 1

[0061] Weigh 3g of the adhesive polyvinylidene fluoride and dissolve it in 60g of the solvent N-methylpyrrolidone, then add 3g of the conductive agent carbon black, mix and stir to obtain a conductive adhesive solution;

[0062] Weigh 100 g of lithium iron phosphate (LiFePO4) as the positive electrode material and add it to the conductive glue to prepare the positive electrode active slurry.

[0063] Weigh 1g of a first lithium replenisher Li5FeO4 with a particle size D50 of 6 μm and 1g of a second lithium replenisher Li2NiO2 with a particle size D50 of 12 μm and add them to the positive electrode active slurry to prepare a lithium replenishing positive electrode active slurry;

[0064] Among them, the first lithium supplement has an initial discharge capacity of 713 mAh / g and an initial discharge capacity of 43 mAh / g; the second lithium supplement has an initial discharge capacity of 413 mAh / g and an initial discharge capacity of 124 mAh / g;

[0065] The prepared lithium-replenishing positive electrode active slurry is coated on aluminum foil, and the lithium-replenishing positive electrode sheet is obtained after baking and roller pressing.

[0066] Example 2

[0067] The difference from Example 1 is that the mass of the first lithium supplement is 1.5 g, and the mass of the second lithium supplement is 0.5 g.

[0068] Example 3

[0069] The difference from Example 1 is that the mass of the first lithium supplement is 0.5 g, and the mass of the second lithium supplement is 1.5 g.

[0070] Example 4

[0071] The difference from Example 1 is that the mass of the first lithium supplement is 1.2 g, and the mass of the second lithium supplement is 0.8 g.

[0072] Example 5

[0073] The difference from Example 1 is that the first lithium supplement agent is Li6CoO4 with a particle size D50 of 10 μm, the first discharge gram capacity of the first lithium supplement agent is 977 mAh / g, and the first discharge gram capacity is 103 mAh / g; after the lithium supplement positive electrode sheet undergoes the first delithiation, the volume ratio of the first lithium supplement agent to the second lithium supplement agent is 1:0.9.

[0074] Example 6

[0075] The difference from Example 1 is that the second lithium replenisher is Li2CuO2 with a particle size D50 of 10 μm, the first discharge gram capacity of the second lithium replenisher is 406 mAh / g, and the first discharge gram capacity is 123 mAh / g; after the lithium replenisher positive electrode sheet undergoes the first delithiation, the volume ratio of the first lithium replenisher to the second lithium replenisher is 1:1.1.

[0076] Example 7

[0077] The difference from Example 6 is that the mass of the first lithium supplement agent is 2 g, and the mass of the second lithium supplement agent is 2 g; after the lithium supplement positive electrode sheet undergoes the first delithiation, the volume ratio of the first lithium supplement agent to the second lithium supplement agent is 1:0.9.

[0078] Example 8

[0079] The difference from Example 1 is that the particle size D50 of the first lithium replenisher is 13 μm, and the particle size D50 of the second lithium replenisher is 6 μm; after the lithium replenisher positive electrode sheet undergoes the first delithiation, the volume ratio of the first lithium replenisher to the second lithium replenisher is 1:0.83.

[0080] Comparative Example 1

[0081] Weigh 3g of the adhesive polyvinylidene fluoride and dissolve it in 60g of the solvent N-methylpyrrolidone, then add 3g of the conductive agent carbon black, mix and stir to obtain a conductive adhesive solution;

[0082] Weigh 100 g of lithium iron phosphate (LiFePO4) as the positive electrode material and add it to the conductive glue to prepare the positive electrode active slurry.

[0083] Weigh 2 g of a first lithium replenisher Li5FeO4 having a particle size D50 of 6 μm and add it to the positive electrode active slurry to prepare a lithium replenishing positive electrode active slurry;

[0084] The prepared lithium-replenishing positive electrode active slurry is coated on aluminum foil, and the lithium-replenishing positive electrode sheet is obtained after baking and roller pressing.

[0085] Comparative Example 2

[0086] Weigh 3g of the adhesive polyvinylidene fluoride and dissolve it in 60g of the solvent N-methylpyrrolidone, then add 3g of the conductive agent carbon black, mix and stir to obtain a conductive adhesive solution;

[0087] Weigh 100 g of lithium iron phosphate (LiFePO4) as the positive electrode material and add it to the conductive glue to prepare the positive electrode active slurry.

[0088] Weigh 2 g of a second lithium replenisher Li2NiO2 with a particle size D50 of 12 μm and add it to the positive electrode active slurry to prepare a lithium replenishing positive electrode active slurry;

[0089] The prepared lithium-replenishing positive electrode active slurry is coated on aluminum foil, and the lithium-replenishing positive electrode sheet is obtained after baking and roller pressing.

[0090] Comparative Example 3

[0091] Weigh 3g of the adhesive polyvinylidene fluoride and dissolve it in 60g of the solvent N-methylpyrrolidone, then add 3g of the conductive agent carbon black, mix and stir to obtain a conductive adhesive solution;

[0092] Weigh 100 g of lithium iron phosphate (LiFePO4) as the positive electrode material and add it to the conductive glue to prepare the positive electrode active slurry.

[0093] Weigh 0.4 g of a first lithium replenisher Li5FeO4 with a particle size D50 of 6 μm and 1.6 g of a second lithium replenisher Li2NiO2 with a particle size D50 of 12 μm and add them to the positive electrode active slurry to prepare a lithium replenishing positive electrode active slurry;

[0094] The prepared lithium-replenishing positive electrode active slurry is coated on aluminum foil, and the lithium-replenishing positive electrode sheet is obtained after baking and roller pressing.

[0095] Charge and discharge capacity:

[0096] The first lithium supplement agent and the second lithium supplement agent in Examples 1 to 8 were respectively used as battery positive electrode materials to make button batteries, and then charged to 4.3V under 0.1C conditions to obtain the first charge gram capacity of the first lithium supplement agent and the second lithium supplement agent, respectively; the first lithium supplement agent and the second lithium supplement agent were respectively used as battery positive electrode materials to make button batteries, and then discharged to 2.5V under 0.1C conditions to obtain the first discharge gram capacity of the first lithium supplement agent and the second lithium supplement agent, respectively.

[0097] Volume change:

[0098] The lithium-replenished positive electrode sheets after the first delithiation prepared in Examples 1 to 8 and Comparative Examples 1 to 3 were tested using a FIB-SEM (Focused Ion Beam-Scanning Electron Microscope). Areas of 200 μm*200 μm in size were selected from different regions of the electrode sheet and sliced layer by layer and scanned to form multi-layer two-dimensional images. The multi-layer two-dimensional imaging data was then three-dimensionally reconstructed. The first lithium replenisher particles and the second lithium replenisher particles decreased in volume after the first delithiation, but pores remained in the electrode sheet corresponding to the spaces occupied by the first lithium replenisher particles and the second lithium replenisher particles before the first delithiation. The volume of the pores was the volume of the lithium replenisher particles occupying the space corresponding to the pores before the first delithiation. The volumes of the selected first lithium replenisher particles and the second lithium replenisher particles before and after the first delithiation were measured respectively. The volume change amplitude and porosity of the first lithium replenisher and the second lithium replenisher before and after the first delithiation, and the volume ratio of the first lithium replenisher to the second lithium replenisher after the first delithiation were calculated. The results are shown in Table 1, wherein the volume change amplitude of the first lithium replenisher before and after the first delithiation = (the volume of the first lithium replenisher after the first delithiation - the volume of the first lithium replenisher before the first delithiation) / the volume of the first lithium replenisher before the first delithiation * 100%, and the volume change amplitude of the second lithium replenisher before and after the first delithiation = (the volume of the second lithium replenisher after the first delithiation - the volume of the second lithium replenisher before the first delithiation) / the volume of the second lithium replenisher before the first delithiation * 100%.

[0099] The lithium-supplemented positive electrode sheets prepared in Examples 1 to 8 and Comparative Examples 1 to 3 were combined with negative electrodes, separators, and electrolytes to form soft-pack batteries.

[0100] Gas production performance: The soft-pack batteries prepared in Examples 1 to 8 and Comparative Examples 1 to 3 were adjusted to SOC of 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, and 0% in sequence. After storage at 60°C for 28 days, the battery weight was tested by the drainage method. The gas production performance of the battery was calculated and statistically analyzed by the weight difference. The results are shown in Table 1.

[0101] Cycle performance: The soft-pack batteries prepared in Examples 1 to 8 and Comparative Examples 1 to 3 were charged at 60°C with a cutoff current of 0.05C from 0.5CCC-CV to 3.7V and discharged at 0.5C to 2.3V. After 1000 cycles, the retention rate of the battery capacity relative to the battery capacity before cycling was checked. The results are shown in Table 1.

[0102] Rate performance: The soft-pack batteries prepared in Examples 1 to 8 and Comparative Examples 1 to 3 were charged at 25°C with a cutoff current of 0.05C from 0.5CCC-CV to 3.7V and discharged at 0.1C to 2.3V, and the capacity was recorded as C1; at 25°C, the charge condition was 0.5C CC-CV to 3.7V with a cutoff current of 0.05C and discharged at 2C to 2.3V, and the capacity was recorded as C2; the 2C / 0.1C capacity retention rate was calculated as: C2 / C1*100%, and the results are shown in Table 1.

[0103] Table 1

[0104]

[0105]

[0106] As can be seen from Table 1, the lithium-supplemented positive electrode sheets provided in Examples 1 to 8 of the present application can improve the battery capacity and cycle performance while effectively suppressing the gas production during the lithium replenishment process by adding a suitable first lithium replenisher and a second lithium replenisher to the positive electrode active layer and controlling the content ratio of the two within a suitable range.

[0107] The preferred embodiments are described in detail above, but the present invention is not limited to the above-mentioned specific implementation methods. Under the guidance of this application, technicians in this field can also make various forms of specific changes without departing from the scope of protection of this application, which all fall within the scope of protection of the present invention.

Claims

1. A lithium-supplemented positive electrode sheet, characterized in that: The lithium-replenishing positive electrode sheet includes a current collector and a positive electrode active layer arranged on the current collector, the positive electrode active layer includes a positive electrode material, a first lithium replenisher and a second lithium replenisher; the volume change amplitude of the first lithium replenisher before and after the first delithiation is greater than the volume change amplitude of the second lithium replenisher before and after the first delithiation; the first charge gram capacity of the first lithium replenisher is greater than the first charge gram capacity of the second lithium replenisher; the first discharge gram capacity of the first lithium replenisher is less than the first discharge gram capacity of the second lithium replenisher; in the lithium-replenishing positive electrode sheet after the first delithiation, the volume ratio of the first lithium replenisher to the second lithium replenisher is 1:(0.2-3).

2. The lithium-supplemented positive electrode sheet according to claim 1, wherein: In the lithium-supplementing positive electrode sheet, the volume ratio of the first lithium-supplementing agent to the second lithium-supplementing agent is 1:(0.3-3).

3. The lithium-supplemented positive electrode sheet according to claim 1 or 2, characterized in that: The volume of the first lithium supplement after the first delithiation is 40%-90% of the volume before the first delithiation, and the volume of the second lithium supplement after the first delithiation is 60%-98% of the volume before the first delithiation.

4. The lithium-supplemented positive electrode sheet according to any one of claims 1 to 3, characterized in that: The porosity of the first lithium replenisher after the first delithiation is 5%-60%, and the porosity of the second lithium replenisher after the first delithiation is 1%-40%; the porosity of the second lithium replenisher after the first delithiation is less than the porosity of the first lithium replenisher after the first delithiation.

5. The lithium-supplemented positive electrode sheet according to any one of claims 1 to 4, characterized in that: The first charge gram capacity of the first lithium supplement is 400mAh / g-1200mAh / g, and the first charge and discharge efficiency of the first lithium supplement is 1%-14%; and / or the first charge gram capacity of the second lithium supplement is 240mAh / g-550mAh / g, and the first charge and discharge efficiency of the second lithium supplement is 15%-45%.

6. The lithium-supplemented positive electrode sheet according to any one of claims 1 to 5, characterized in that: The first lithium supplement includes one or more of Li5FeO4, Li2O, Li6CoO4, Li5ReO6 and Li4CoO4; and / or the second lithium supplement includes Li2NiO2, Li2CuO2, Li2RuO3, Li2MnO3, Li2MoO3 and Li 0.65 Ni 1.35 One or more of O2.

7. The lithium-supplemented positive electrode sheet according to any one of claims 1 to 6, characterized in that: In the lithium-supplemented positive electrode sheet, the sum of the volumes of the first lithium-supplementing agent and the second lithium-supplementing agent accounts for 0.1% to 8% of the volume of the positive electrode active layer.

8. The lithium-supplemented positive electrode sheet according to any one of claims 1 to 7, characterized in that: The particle size D50 of the first lithium supplement agent is 3 μm-15 μm; and / or the particle size D50 of the second lithium supplement agent is 4 μm-23 μm.

9. The lithium-supplemented positive electrode sheet according to any one of claims 1 to 8, characterized in that: The positive electrode material includes one or more of lithium manganese iron phosphate, lithium iron phosphate, lithium nickel manganese oxide and a ternary positive electrode material; the ternary positive electrode material includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

10. The lithium-supplemented positive electrode sheet according to any one of claims 1 to 9, characterized in that: The positive electrode active layer also includes a conductive agent and a binder; the conductive agent includes one or more of conductive graphite, carbon black, acetylene black, super-P, carbon nanotubes, graphene, Ketjen black and VGCF; the binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyacrylate, lithium polyacrylate and sodium polyacrylate.

11. The lithium-supplemented positive electrode sheet according to any one of claims 1 to 10, characterized in that: The initial charging capacity of the lithium-supplementing positive electrode sheet is 0.25%-13% greater than that of a positive electrode sheet to which the first lithium-supplementing agent and the second lithium-supplementing agent are not added.

12. A method for preparing a lithium-supplemented positive electrode sheet according to any one of claims 1 to 11, characterized in that: include: Mixing the positive electrode material, the first lithium replenishing agent and the second lithium replenishing agent to prepare a lithium replenishing positive electrode active slurry; The lithium-replenishing positive electrode active slurry is placed on a current collector to obtain a lithium-replenishing positive electrode sheet.

13. The method for preparing a lithium-supplemented positive electrode sheet according to claim 12, wherein: The sum of the mass of the first lithium supplement agent and the second lithium supplement agent is 0.1%-7.4% of the mass of the positive electrode material; and / or the mass ratio of the first lithium supplement agent to the second lithium supplement agent is (0.1-10):

1.

14. A lithium ion battery, characterized in that: The lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, and a separator and an electrolyte located between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes the lithium-supplemented positive electrode sheet according to any one of claims 1 to 11 or the lithium-supplemented positive electrode sheet prepared by the preparation method according to any one of claims 12 to 13.

15. An electrical device, characterized in that: The electric device includes the lithium-ion battery as claimed in claim 14.

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