Lithium supplementing negative electrode, lithium battery, manufacturing method of lithium supplementing negative electrode and manufacturing method of lithium battery, and electric equipment

Abstract

The invention provides a lithium supplement negative electrode, a lithium battery, a manufacturing method of the lithium supplement negative electrode and electric equipment. The lithium supplementing negative electrode comprises a current collector and negative electrode material layers arranged on the surface of at least one side of the current collector, a lithium supplementing layer is further arranged on the side, away from the current collector, of at least one negative electrode material layer, a lithium supplementing agent in the lithium supplementing layer comprises metal lithium, and each negative electrode material layer comprises a negative electrode active material, a modifier and a binder, and when the lithium is intercalated by 1-2%, the potential of the regulator is at least 0.1 V higher than that of the negative active material. The regulator is introduced to promote the lithium element from the lithium supplement layer to be quickly and transversely diffused from the lithium-rich region negative electrode material layer to the lithium-poor region negative electrode material layer after the lithium supplement negative electrode is in contact with an electrolyte, so that the lithium element is uniformly distributed in the negative electrode material layer, and the cycle performance of the lithium battery is effectively improved.

Description

Technical Field

[0001] This application relates to the field of lithium battery negative electrode lithium replenishment technology, specifically to a lithium replenishment negative electrode, a lithium battery, its manufacturing method, and electrical equipment. Background Technology

[0002] With economic and technological development, industries such as portable electronic devices (e.g., mobile phones, tablets) and electric vehicles are placing higher demands on the cycle life of lithium-ion batteries. Adding lithium replenishing agents that provide active lithium to the lithium battery system beforehand can compensate for the irreversible loss of active lithium during the initial cycle and subsequent cycles, thereby improving the battery's cycle life.

[0003] Among the many lithium replenishment methods, directly bonding lithium powder or lithium foil to the surface of the negative electrode is a relatively direct and effective method. However, lithium powder or lithium foil replenishment both suffer from the problem of uneven distribution of lithium elements on the negative electrode after the lithium replenishing agent is delithiated, which makes these lithium replenishment solutions unable to effectively improve the cycle performance of the battery. Summary of the Invention

[0004] In view of this, this application provides a lithium-replenishing negative electrode that can improve the problem of uneven distribution of lithium elements in the negative electrode derived from lithium metal replenishing agents, as well as a lithium battery using the lithium-replenishing negative electrode, a method for manufacturing the same, and an electrical device thereof.

[0005] The first aspect of this application provides a lithium-replenishing negative electrode, the lithium-replenishing negative electrode comprising a current collector and a negative electrode material layer disposed on at least one side surface of the current collector, at least one side of the negative electrode material layer opposite to the current collector further comprising a lithium-replenishing layer, the lithium-replenishing agent in the lithium-replenishing layer comprising a metallic lithium layer, the negative electrode material layer comprising a negative electrode active material, a modifier and a binder, wherein the potential of the modifier when lithium is intercalated by 1-2% is at least 0.1V higher than the potential of the negative electrode active material when lithium is intercalated by 1-2%.

[0006] Introducing the aforementioned regulator into the negative electrode material layer of the lithium-filled negative electrode can increase the potential difference between the lithium-rich region negative electrode material layer with a high degree of lithium intercalation and the lithium-poor region negative electrode material layer with a low degree of lithium intercalation, promoting the lateral diffusion of lithium elements from the lithium-rich region to the lithium-poor region. After a period of diffusion, the lithium elements extracted from the lithium-filled layer can be uniformly distributed in the negative electrode material layer, thereby improving the battery cycle performance.

[0007] Secondly, this application provides a lithium battery comprising the lithium-filled negative electrode and electrolyte described in the first aspect of this application. Optionally, the lithium battery includes a lithium-filled negative electrode, a positive electrode, and an electrolyte and a separator located between the lithium-filled negative electrode and the positive electrode.

[0008] After the electrolyte is injected, the lithium battery can be left to stand and soak, which allows the lithium element in the lithium replenishing agent to be uniformly embedded in the negative electrode material layer, thereby ensuring good cycle performance of the lithium battery.

[0009] Thirdly, this application provides a method for manufacturing a lithium battery, comprising:

[0010] The lithium-filled negative electrode, separator, and positive electrode sheet described in the first aspect of this application are stacked together to form a battery cell;

[0011] An electrolyte is injected into the cell, and after standing, forming, and aging, a lithium battery is obtained.

[0012] The above-mentioned method for manufacturing lithium batteries with lithium-added negative electrodes is simple and convenient. It does not require special electrochemical treatment of the assembled lithium batteries. Simply letting the cells filled with electrolyte stand and soak them is enough to allow the lithium elements in the lithium-added agent to be uniformly embedded in the negative electrode material layer, thereby making the lithium battery have good cycle performance.

[0013] Fourthly, this application provides a lithium battery manufactured using the method described in the third aspect of this application. This lithium battery exhibits good cycle performance.

[0014] Fifthly, this application provides an electrical device that includes the lithium battery described in the second aspect of this application or the lithium battery described in the fourth aspect of this application.

[0015] The electrical equipment is powered by the aforementioned lithium battery. Due to the superior cycle performance of the lithium battery, the electrical equipment has a strong market competitiveness. Attached Figure Description

[0016] Figure 1A and Figure 1B These are schematic diagrams of two structures of the lithium-filled anode provided in the embodiments of this application.

[0017] Figure 2 It shows Figure 1A and Figure 1B A top view of the lithium supplement layer 13.

[0018] Figure 3 The lithium content at different locations in the lithium diffusion effect experiment of the negative electrode samples of Example 2 and Comparative Example 1 was summarized. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings.

[0020] Currently, lithium replenishment methods for battery negative electrodes can be mainly divided into lithium powder replenishment and lithium foil replenishment. When using lithium powder as the lithium source, the lithium powder is directly dry-rolled onto the negative electrode surface, making it difficult to control the uniform distribution of lithium powder across the entire negative electrode sheet. When using lithium foil as the lithium source, it is difficult to process lithium foil with a thickness below 5μm, while the thickness of the negative electrode is generally required to be below 5μm. Since the lithium foil thickness is 5μm, patterned lithium replenishment (i.e., ordered region lithium replenishment) using lithium foil is necessary. For example, multiple lithium foil strips are rolled onto the negative electrode sheet at intervals. In this method, the lithium foil is non-uniformly distributed on the negative electrode sheet. From the above analysis, it can be seen that both lithium powder replenishment and lithium foil replenishment suffer from the problem of uneven lithium distribution.

[0021] For lithium-filled graphite anode sheets with uneven lithium distribution, after electrolyte injection, lithium will embed into the underlying graphite layer and the surrounding graphite layers. Due to the low lithium storage platform of graphite, the potential drops to around 0.8V when 1% lithium is embedded, and around 0.2V when 10% is embedded. The degree of lithium embedding differs between the underlying graphite and the surrounding graphite (graphite in the initial anode sheet not covered by the lithium-filling material). The graphite layer not directly beneath the lithium has less lithium embedding, with a potential of around 0.8V, while the graphite directly beneath the lithium has more lithium embedding, with a potential of around 0.2V. The voltage difference between the two is approximately 0.6V. This potential difference is the driving force for lithium to diffuse outwards after embedding in the graphite layer. Considering the resistance of graphite particles and the diffusion path, this driving force is relatively low, making it difficult for lithium to diffuse rapidly outwards, resulting in a difficult-to-achieve uniform lithium distribution on the anode. To address this issue, the industry typically activates the battery through multiple charge-discharge cycles to adjust lithium distribution. However, this method not only wastes energy significantly, but also reduces the potential difference between lithium-rich and lithium-poor regions due to polarization after lithium intercalation in graphite (i.e., reduces the diffusion driving force of lithium on the electrode), making it more difficult to achieve a uniform lithium distribution on the negative electrode. Therefore, this application provides a lithium-added negative electrode that promotes uniform lithium distribution on the negative electrode, a lithium battery, and a method for manufacturing the same. A battery cell using this lithium-added negative electrode can easily achieve a uniform lithium distribution on the negative electrode after being immersed in electrolyte for a period of time, without the need for additional activation treatment.

[0022] Please see also Figure 1A and Figure 1B This is a schematic diagram of two structures of the lithium-filled negative electrode provided in the embodiments of this application. The lithium-filled negative electrode 10 includes a current collector 11 and a negative electrode material layer 12 disposed on at least one side of the current collector 11. At least one negative electrode material layer 12 is further provided with a lithium-filling layer 13 on the side opposite to the current collector 11. The lithium-filling layer 13 includes a lithium-filling agent, which includes metallic lithium. The negative electrode material layer 12 includes a negative electrode active material 120, a regulator 121, and a binder. The regulator 121 has a potential at least 0.1V higher than the potential of the negative electrode active material 120 at 1-2% lithium intercalation.

[0023] To ensure uniform distribution of lithium extracted from the lithium replenishment layer 13 within the negative electrode material layer 12, this application introduces a regulator 121 to adjust the lithium distribution effect in the negative electrode material layer 12. The potential of this regulator 121 after a small amount of lithium intercalation is at least 0.1V higher than that of the negative electrode active material 120 at the same degree of lithium intercalation (e.g., 1-2%). Thus, its presence increases the potential of the negative electrode material layer in the lithium-poor region with low lithium intercalation. Conversely, in the lithium-rich region of the negative electrode material layer with high lithium intercalation (e.g., 5-20%), the high degree of lithium intercalation in the negative electrode active material leads to a higher potential for the regulator 121. The high degree of lithium intercalation results in minimal potential change in this region. Overall, the presence of regulator 121 increases the potential difference between the lithium-rich region (high lithium intercalation) and the lithium-poor region (low lithium intercalation). This increased potential difference enhances the driving force for lateral diffusion of lithium from the lithium-rich region to the lithium-poor region within the negative electrode material layer 12. After a period of diffusion, the distribution of lithium extracted from the supplementary lithium layer 13 within the negative electrode material layer 12 becomes more uniform, significantly reducing the risk of lithium plating and minimizing active lithium loss during the first and subsequent cycles, thus improving the battery's cycle performance. Furthermore, due to the large potential difference between the lithium-rich and lithium-poor regions of the negative electrode material layer 12, uniform distribution of lithium within the negative electrode material layer can be achieved simply by wetting the supplementary lithium anode 10 with the electrolyte for a period of time. This eliminates the need for additional activation treatment after battery formation to promote lithium diffusion within the negative electrode.

[0024] Among them, the terms "lithium-rich region" and "lithium-poor region" are relative concepts. For example, in the prepared lithium-replenishing anode 10, the lithium-rich region can refer to the part of the anode material layer covered by more lithium replenishing agent, and the lithium-poor region can refer to the part of the anode material layer covered by less lithium replenishing agent; or the lithium-rich region can refer to the area of ​​the anode material layer covered by lithium replenishing agent, and the lithium-poor region can refer to the area of ​​the anode material layer not covered by lithium replenishing agent.

[0025] In this application, since the potential of the regulator 121 after a small amount of lithium intercalation is higher than that of the negative electrode active material 120, lithium originating from the lithium replenishment layer preferentially intercalates into the regulator 121 and then into the negative electrode active material 120; while in the process of lithium removal from the battery negative electrode, the lithium intercalated in the negative electrode active material 120 is removed first, and the lithium intercalated in the regulator 121 is removed later or does not remove during normal battery operation.

[0026] In this embodiment, the regulator 121 that meets the above requirements may include one or more of iron phosphate, iron oxide, iron sulfide, zinc sulfide, and lithium titanate, but is not limited thereto. Iron phosphate, after a small amount of lithium intercalation, has a higher potential than iron oxide, iron sulfide, and lithium titanate at the same degree of lithium intercalation. The presence of iron phosphate is more conducive to increasing the potential difference between the lithium-rich region negative electrode material layer and the lithium-poor region negative electrode material layer with a low degree of lithium intercalation, thereby enabling rapid and uniform lithium replenishment in the negative electrode material layer 12. Furthermore, iron phosphate can be obtained from spent lithium iron phosphate batteries, and its application in the lithium-replenishing negative electrode provides a new application direction for the recycling of lithium iron phosphate batteries. Iron oxide and iron sulfide have a large specific capacity for lithium intercalation, and their addition amount in the negative electrode material layer 12 can be relatively low, thereby improving the energy density of the lithium battery made using the aforementioned lithium-replenishing negative electrode 10.

[0027] In this embodiment, the relationship between the regulator 121 and the lithium replenishing agent satisfies the following condition: the product of the mass of the lithium replenishing agent and its delithiation specific capacity is greater than the product of the mass of the regulator 121 and its lithium insertion specific capacity. For example, if the mass of the lithium replenishing agent is denoted as m1g, the delithiation specific capacity of the lithium replenishing agent is denoted as C1 mAh / g, the mass of the regulator 121 is denoted as m2g, and the lithium insertion specific capacity of the regulator 121 is denoted as C2 mAh / g, then m1×C1>m2×C2. Thus, the lithium replenishment capacity provided by the lithium replenishing agent is higher than the total capacity of the regulator 121, ensuring that even after the regulator 121 is fully lithium-intercalated, there is still excess lithium available for the formation of the SEI film on the electrode. Furthermore, the product of the mass of the lithium replenishing agent and its delithiation specific capacity is less than the product of the negative electrode active material 120 and its lithium insertion specific capacity. This avoids excessively high lithium replenishment capacity provided by the lithium replenishing agent, which could cause lithium plating on the negative electrode and affect battery safety performance. Typically, the lithium intercalation specific capacity of iron phosphate is approximately 150 mAh / g; that of lithium titanate is approximately 165 mAh / g; the lithium intercalation specific capacity of iron oxides is 500–1000 mAh / g; and that of iron sulfides is 600–1000 mAh / g. The delithiation specific capacity of elemental lithium is 3860 mAh / g.

[0028] In this embodiment, the mass of the regulator 121 is less than 10% of the mass of the negative electrode active material 120. In some embodiments, the mass of the regulator 121 can be 0.5%-8% of the mass of the negative electrode active material 120. Specifically, the mass of the regulator 121 is 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, etc., of the negative electrode active material 120. A suitable mass ratio between the regulator 121 and the negative electrode active material 120 ensures that lithium from the lithium replenishment layer 13 is sufficiently homogenized in the negative electrode material layer 12, thereby reducing lithium plating, reducing irreversible consumption of active lithium from the positive electrode active material, and improving the cycle performance of the battery. Further, in some embodiments of this application, the mass of the regulator 121 is 0.5%-5% of the mass of the negative electrode active material 120. In this case, the lithium battery made using this lithium-added negative electrode 10 can not only have good cycle performance, but also high capacity utilization and high energy density.

[0029] In this embodiment, the negative electrode active material 120 includes one or more of carbon-based materials, silicon-based materials, tin-based materials, and phosphorus-based materials, but is not limited thereto. The carbon-based material may include one or more of graphite, hard carbon, soft carbon, and mesophase carbon microspheres. The graphite includes natural graphite and / or artificial graphite. The silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon materials, and silicon alloys. The tin-based material may include one or more of elemental tin, tin-carbon materials, tin oxide, and tin alloys. The phosphorus-based material may include one or more of red phosphorus, black phosphorus, and phosphorus compounds.

[0030] It should be noted that when the negative electrode active material 120 includes two or more materials, the statement that "the potential of the regulator 121 at 1-2% lithium intercalation is at least 0.1V higher than the potential of the negative electrode active material 120 at 1-2% lithium intercalation" can be understood as: at least some of the negative electrode active materials 120 need to meet this condition; it is not mandatory for all the negative electrode active materials to meet it, although it is best if all the negative electrode active materials 120 meet this condition. That is, the potential of the regulator 121 at 1-2% lithium intercalation is at least 0.1V higher than the potential of at least some of the negative electrode active materials 120 at 1-2% lithium intercalation.

[0031] In some embodiments of this application, the negative electrode active material 120 includes at least graphite. The regulator 121 has a potential greater than 1V when lithium is intercalated at 1-2%. Thus, the potential of the regulator 121 when lithium is intercalated at 1-2% is 0.2V higher than the potential of graphite when lithium is intercalated at 1-2%.

[0032] In other embodiments of this application, the negative electrode active material 120 may also include one or more of hard carbon, soft carbon, mesophase carbon microspheres, silicon-based materials, tin-based materials, phosphorus-based materials, etc., but is not limited thereto.

[0033] In the negative electrode material layer 12, the negative electrode active material 120 and the regulator 121 are in a uniformly blended state. Figure 1A The example uses a negative electrode material layer 12 on one side of the current collector 11. Figure 1B The diagram illustrates the use of negative electrode material layers 12 on both sides of the current collector 11. Furthermore, Figure 1B In the present invention, each of the two negative electrode material layers 12 has a lithium replenishment layer 13 on the side away from the current collector 11; however, it is understood that in other embodiments of the present invention, one of the two negative electrode material layers 12 may have a lithium replenishment layer 13 on the side away from the current collector 11, while the other may not have a lithium replenishment layer 13.

[0034] In this application, the metallic lithium used as a lithium supplement can include elemental lithium or lithium alloys. The lithium alloy can include, but is not limited to, at least one of lithium-silicon alloys, lithium-sodium alloys, lithium-potassium alloys, lithium-aluminum alloys, lithium-tin alloys, and lithium-indium alloys. Elemental lithium can include lithium powder or lithium foil. Lithium powder or lithium foil can be added to the negative electrode using existing methods, such as directly rolling lithium powder onto the negative electrode material layer 12 to form a lithium powder layer, or rolling slits or patterned lithium foil onto the negative electrode material layer 12 to form a lithium foil layer. In some embodiments of this application, the lithium supplement layer 13 is a lithium foil layer. See also... Figure 2 , Figure 2 This diagram shows a top view of the lithium replenishment layer 13 in this configuration. The lithium replenishment layer 13 comprises multiple strip-shaped lithium foils, which are spaced apart on the negative electrode material layer 12. Figure 2 The negative electrode material layer 12 is not shown in the figure.

[0035] In this application, the binder contained in the negative electrode material layer 12 helps the negative electrode active material 120 and the regulator 121 to adhere stably to the current collector 11. The binder may be selected from one or more of styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), sodium alginate, polyacrylic acid (PAA) or its salts, polyacrylates (such as polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, etc.), polyacrylamide (PAM), polyvinyl alcohol (PVA), polyimide (PI), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), etc., but is not limited thereto.

[0036] In some embodiments of this application, the negative electrode material layer 12 further includes a conductive agent. The presence of the conductive agent can enhance the electron conduction rate of the negative electrode material layer 12 and improve its kinetic performance. The conductive agent may include one or more of carbon black (such as acetylene black, Ketjen black, Super-P), carbon nanotubes, carbon nanofibers, graphene, etc.

[0037] The current collector 11 used for the lithium anode 10 may include a metal foil or a carbon-coated metal foil. The metal foil may be a single-element metal foil or a metal alloy foil. In some embodiments, the current collector 11 may be a copper foil or a carbon-coated copper foil.

[0038] This application also provides a lithium battery, which includes the lithium-filled negative electrode described in the first aspect of this application and an electrolyte.

[0039] The lithium battery includes a lithium-filled negative electrode, a positive electrode, and an electrolyte and a separator located between the lithium-filled negative electrode and the positive electrode.

[0040] After the electrolyte is injected and the battery is allowed to stand and soak, the lithium element in the lithium replenishing agent can be uniformly embedded in the negative electrode material layer, thereby ensuring good cycle performance of the lithium battery.

[0041] During charging, lithium ions are extracted from the positive electrode active material layer in the positive electrode, pass through the electrolyte, and then embed into the negative electrode active material in the negative electrode. During discharging, lithium ions are extracted from the negative electrode active material in the negative electrode, pass through the electrolyte, and then embed into the crystal lattice of the positive electrode active material.

[0042] Because the negative electrode material layer of the lithium-ion battery contains the aforementioned regulator, and this regulator has a higher lithium intercalation potential than the negative electrode active material at the same degree of lithium intercalation, during the delithiation process, the lithium intercalated in the regulator will be delithiated later than the lithium intercalated in the negative electrode active material. Therefore, after the lithium battery is fully discharged (i.e., the lithium intercalated in the negative electrode active material is basically delithiated), the residual lithium element in the negative electrode material layer will be higher than that of an un-lithiped battery and also higher than that of a lithium-ion battery without the aforementioned regulator added to the negative electrode material. In the embodiment of this application, after the lithium battery is fully discharged, the lithium element content in the negative electrode material layer 12 is 0.1wt%-1.7wt%. This is beneficial to improving the cycle performance of the lithium battery. Furthermore, from the perspective of the electrode sheet, after the lithium-ion layer of the aforementioned lithium-ion electrode sheet is delithiated, the lithium element content of the negative electrode material layer in the fully delithiated state is 0.1wt%-1.7wt%.

[0043] This application also provides a method for manufacturing a lithium battery, including:

[0044] The lithium-added negative electrode, separator, and positive electrode sheet described in the embodiments of this application are stacked sequentially to form a battery cell;

[0045] An electrolyte is injected into the cell, and after standing, forming, and aging, a lithium battery is obtained.

[0046] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side thereon. For lithium batteries, the positive active material may include one or more of lithium-based transition metal oxides (such as lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide) and polyanionic lithium-containing positive electrode materials (such as lithium iron phosphate (LFP) and lithium manganese iron phosphate (LFMP)). The separator may be any separator material used in existing batteries. Exemplarily, the separator may include, but is not limited to, single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, triple-layer PP / PE / PP, non-woven fabric, glass fiber, etc.

[0047] In this application, a battery can be assembled by injecting electrolyte into the battery cell. The assembled lithium battery also includes a battery casing, which contains the aforementioned battery cell and electrolyte. The battery assembly process includes: inserting the aforementioned battery cell into the battery casing (such as an aluminum-plastic casing), injecting electrolyte into the battery casing, and then sealing the battery casing. The electrolyte may include a non-aqueous organic solvent, lithium salt, and optional electrolyte additives. Electrolyte additives can be added according to actual needs.

[0048] The purpose of static soaking after electrolyte injection into the battery cell is primarily to ensure that the electrolyte in the newly assembled battery fully wets the cell, facilitating subsequent formation. Furthermore, static soaking also ensures that the metallic lithium in the lithium replenishment layer 13 of the aforementioned lithium-replenishing negative electrode 10 is uniformly embedded in the negative electrode material layer 12, achieving a uniform distribution of lithium elements in the negative electrode material layer 12, eliminating the need for additional electro-cycling activation treatment to promote lithium diffusion in the negative electrode sheet. In this embodiment, the static soaking temperature can be 20-50°C, and the soaking time can be 12-72 hours. In some embodiments, static soaking is performed at 45°C for 24 hours.

[0049] The purpose of formation is to form a solid electrolyte interface (SEI) film on the surface of the negative electrode material layer to block side reactions between the negative electrode material and the electrolyte. The formation process is not limited by temperature; it can be carried out at room temperature or at a suitable high temperature (e.g., 45-50°C). Furthermore, formation can be a one-step process or a stepped formation involving two or more charging stages. In some embodiments of this application, the formation process is as follows: first, charging at 0.05C for 2 hours, then charging at a constant current and constant voltage of 0.2C to 100% SOC. When the positive electrode active material of the lithium battery is lithium iron phosphate, the second step of formation is charging at a constant current and constant voltage of 0.2C to 3.8V, with a cutoff current of 0.05C.

[0050] Post-formation aging treatment can make the properties and composition of the SEI film formed after formation more stable, ensuring the stability of the electrochemical performance of the lithium battery. Aging can be carried out at room temperature or at high temperature. In some embodiments of this application, the aging is performed by standing at 40-50℃ for 24-72 hours. Specific aging temperatures can be 40℃, 42℃, 45℃, 48℃, or 50℃, etc. Specific aging times can be 24h, 28h, 32h, 36h, 40h, 42h, 48h, 54h, 60h, 66h, 70h, etc.

[0051] In some embodiments of this application, after the aging process, a capacity grading process is also included. Capacity grading involves sorting the batteries by capacity and screening their performance. This process allows for a more uniform capacity distribution and ensures more stable discharge performance. In some embodiments, the capacity grading process may include: discharging at 1 / 3C to a voltage of 2V, then charging at 1 / 3C constant current and constant voltage to 100% SOC, repeated three times. Specifically, when the positive electrode active material of the lithium battery is lithium iron phosphate, the charging process specifically involves charging at 1 / 3C constant current to 3.8V, then charging at 3.8V constant voltage to a cutoff current of 0.05C. It should be noted that after the above aging process, the aged battery needs to be cooled for a period of time before performing this capacity grading process.

[0052] Using the above-mentioned lithium-added anode to manufacture lithium batteries is a simple and convenient manufacturing method. It does not require special electrochemical treatment of the assembled lithium battery. Simply letting the battery cell filled with electrolyte stand and soak it allows the lithium metal additive to be uniformly embedded in the anode material layer and initially form an SEI film. This reduces or avoids the irreversible consumption of active lithium from the positive electrode active material during the formation of the SEI film. Furthermore, due to the more uniform lithium distribution, the battery has better cycle performance.

[0053] It should be noted that after the above formation, the lithium replenishment layer 13 in the lithium replenishment anode is basically no longer present (the metallic lithium in the lithium replenishment layer 13 has been embedded in the anode material layer 12). Therefore, the anode of the lithium battery after leaving the factory basically does not have the above-mentioned lithium replenishment layer, and an SEI film has been formed on the surface of the anode.

[0054] This application also provides a lithium battery manufactured using the above-described manufacturing method.

[0055] Since the lithium battery in this embodiment is made using the above-mentioned lithium-added negative electrode, it can have higher initial cycle efficiency and better cycle performance.

[0056] This application provides an electrical device that includes a lithium battery manufactured using the above-described method.

[0057] The electrical equipment is powered by the aforementioned lithium battery. Due to the good cycle performance of the lithium battery, the electrical equipment has a strong market competitiveness.

[0058] In this application embodiment, the electrical equipment includes, but is not limited to, one or more of the following: 3C products (such as mobile phones, laptops, tablets, wearable devices, etc.) or electric vehicles (such as electric cars, electric motorcycles, electric bicycles, etc.).

[0059] The technical solution of this application will be further described below with reference to several embodiments.

[0060] Example 1

[0061] The fabrication of a lithium-ion anode includes: 1) adding iron phosphate powder to graphite to obtain a mixed powder; wherein the mass of iron phosphate is 0.5% of the mass of graphite, and the potential of iron phosphate at 1% lithium intercalation (3.2V) is 2.4V higher than that of graphite at 1% lithium intercalation; adding the mixed powder, conductive carbon black, and binder CMC to water at a mass ratio of 100:4.4:1.6, mixing evenly to obtain a mixed slurry; coating the mixed slurry onto the opposite surfaces of a copper foil, baking to form a negative electrode material layer, and then rolling to obtain the negative electrode sheet body, wherein the double-sided areal density of the negative electrode material layer is 203 g / m². 2 2) Lithium foil with a thickness of 5μm and a width of 3mm is slit and rolled onto the opposite sides of the above-mentioned negative electrode body at intervals of 5mm to obtain a lithium-added negative electrode. The lateral dimensions of the lithium-added negative electrode are 62mm × 73mm.

[0062] The manufacture of a lithium battery includes:

[0063] (1) Preparation of the positive electrode sheet: Lithium iron phosphate powder, conductive agent (specifically conductive carbon black), and binder PVDF are added to a certain amount of N-methylpyrrolidone (NMP) in a mass ratio of 100:2:2 and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector aluminum foil, baked to form a positive electrode active material layer, and then rolled to obtain a positive electrode sheet, wherein the single-sided areal density of the positive electrode active material layer on the positive electrode sheet is 200 g / m². 2 The lateral dimensions of the positive electrode are 61mm × 72mm.

[0064] (2) Electrolyte preparation: Ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), and dimethyl carbonate (DMC) are mixed in a weight ratio of 1:1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0065] (3) Battery assembly: In an argon-filled glove box, the above-prepared positive electrode and lithium-filled negative electrode are stacked and separated by a PP separator to obtain a battery cell. The number of positive electrode is 3 and the number of lithium-filled negative electrode is 4. The battery cell is then encapsulated with an aluminum-plastic film and 2.6g of the above-prepared electrolyte is injected into the battery cell. The battery cell is then left to stand and soak at 45°C for 24 hours. After that, the soaked battery cell is subjected to formation and aging in sequence to obtain a lithium battery. The formation process is as follows: first, charge at 0.05C for 2 hours, then charge at 0.2C constant current and constant voltage to 3.8V, with a cutoff current of 0.05C. The aging process is as follows: place in an oven at 45°C for 48 hours.

[0066] After aging, the battery was cooled at 25°C for 6 hours, then discharged at 1 / 3C to 2V, and charged at 1 / 3C constant current and constant voltage to 3.8V, with a cutoff current of 0.05C. This charge-discharge cycle was repeated 3 times, and the discharge capacity of the third discharge was recorded as the initial discharge capacity. The lithium battery prepared in Example 1 was subjected to 500 charge-discharge cycles at a 1 / 3C rate, with a voltage range of 2V-3.8V. The capacity after 500 cycles was recorded, and the percentage obtained by dividing it by the initial discharge capacity was used as the capacity retention rate.

[0067] Example 2

[0068] The difference between Example 2 and Example 1 is that, in the fabrication of the lithium-added anode, the mass of iron phosphate powder added is 2.5% of the mass of graphite; and in the resulting lithium-added anode, the double-sided areal density of the anode material layer is 205 g / m². 2 .

[0069] The lithium-added anode obtained in Example 2 was prepared into a lithium battery using the same method as in Example 1, and its initial discharge capacity, capacity after 500 cycles, and capacity retention were tested.

[0070] Example 3

[0071] The difference between Example 3 and Example 1 is that, in the fabrication of the lithium-added anode, the mass of iron phosphate powder added is 5% of the mass of graphite; and in the resulting lithium-added anode, the double-sided areal density of the anode material layer is 208 g / m². 2 .

[0072] The lithium-added anode obtained in Example 3 was prepared into a lithium battery using the same method as in Example 1, and its initial discharge capacity, capacity after 500 cycles, and capacity retention were tested.

[0073] Example 4

[0074] The difference between Example 4 and Example 1 is that, in the fabrication of the lithium-added anode, the mass of iron phosphate powder added is 7.5% of the mass of graphite; and in the resulting lithium-added anode, the double-sided areal density of the anode material layer is 212 g / m².2 .

[0075] The lithium-added anode obtained in Example 4 was prepared into a lithium battery using the same method as in Example 1, and its initial discharge capacity, capacity after 500 cycles, and capacity retention were tested.

[0076] Example 5

[0077] The difference between Example 5 and Example 1 is that, in the fabrication of the lithium-added anode, the mass of iron phosphate powder added is 10% of the mass of graphite; and in the resulting lithium-added anode, the double-sided areal density of the anode material layer is 214 g / m². 2 .

[0078] The lithium-added anode obtained in Example 5 was prepared into a lithium battery using the same method as in Example 1, and its initial discharge capacity, capacity after 500 cycles, and capacity retention were tested.

[0079] Example 6

[0080] The difference between Example 6 and Example 2 is that, in the fabrication of the lithium-filled anode, iron phosphate powder was replaced with iron oxide Fe2O3; the mass of the added iron oxide was still 2.5% of the mass of graphite. The potential of the iron oxide at 1% lithium intercalation (2.6V) was 1.8V higher than that of graphite at 1% lithium intercalation.

[0081] The lithium-added anode obtained in Example 6 was prepared into a lithium battery using the same method as in Example 1, and its initial discharge capacity, capacity after 500 cycles, and capacity retention were tested.

[0082] Example 7

[0083] The difference between Example 7 and Example 2 is that, in the fabrication of the lithium-filled anode, iron phosphate powder is replaced with iron sulfide (FeS); the mass of the added iron sulfide is still 2.5% of the mass of graphite. The potential of the iron sulfide at 1% lithium intercalation (2.3V) is 1.5V higher than that of graphite at 1% lithium intercalation.

[0084] The lithium-added anode obtained in Example 7 was prepared into a lithium battery using the same method as in Example 1, and its initial discharge capacity, capacity after 500 cycles, and capacity retention were tested.

[0085] Example 8

[0086] The difference between Example 8 and Example 2 is that, in the fabrication of the lithium-added anode, iron phosphate powder is replaced with lithium titanate; the mass of lithium titanate added is still 2.5% of the mass of graphite. The potential of lithium titanate at 1% lithium intercalation (2V) is 1.2V higher than that of graphite at 1% lithium intercalation.

[0087] The lithium-added anode obtained in Example 8 was prepared into a lithium battery using the same method as in Example 1, and its initial discharge capacity, capacity after 500 cycles, and capacity retention were tested.

[0088] Example 9

[0089] The difference between Example 9 and Example 2 is that, in the fabrication of the lithium-added anode, iron phosphate powder is replaced with ZnS; the mass of lithium titanate added is still 2.5% of the mass of graphite. The potential of ZnS at 1% lithium intercalation (0.9V) is 0.1V higher than that of graphite at 1% lithium intercalation.

[0090] The lithium-added anode obtained in Example 9 was prepared into a lithium battery using the same method as in Example 1, and its initial discharge capacity, capacity after 500 cycles, and capacity retention were tested.

[0091] To highlight the beneficial effects of this application, the following comparative examples are provided.

[0092] Comparative Example 1

[0093] The difference between Comparative Example 1 and Example 1 is that the negative electrode material layer of the lithium-added negative electrode does not contain the regulator of this application.

[0094] Specifically, the preparation of the lithium-ion anode in Comparative Example 1 includes: 1) adding graphite, conductive carbon black, and binder CMC to water at a mass ratio of 100:4.4:1.6, mixing evenly to obtain a slurry; coating the slurry onto the opposite sides of a copper foil, baking to form a negative electrode material layer, and then rolling to obtain the negative electrode sheet body, wherein the single-sided areal density of the negative electrode material layer is 101 g / m². 2 ;2) Lithium foil with a thickness of 5μm and a width of 3mm is slit and rolled onto both sides of the negative electrode material layer of the above negative electrode body at intervals of 5mm to obtain a lithium-added negative electrode.

[0095] The lithium-added anode prepared in Comparative Example 1 was used to prepare a lithium battery using the same method as in Example 1, and its initial discharge capacity, capacity after 500 cycles, and capacity retention were tested.

[0096] Comparative Example 2

[0097] The difference between Comparative Example 2 and Comparative Example 1 is that the negative electrode sheet was not replenished with lithium, that is, the lithium foil was not rolled onto the negative electrode material layer.

[0098] The negative electrode prepared in Comparative Example 2 was used to prepare a lithium battery using the same method as in Example 1, and its initial discharge capacity, capacity after 500 cycles, and capacity retention were tested.

[0099] Comparative Example 3

[0100] The difference between Comparative Example 3 and Example 2 is that, in the fabrication of the lithium-filled anode, iron phosphate powder was replaced with Cu2O; the mass of Cu2O added was still 2.5% of the mass of graphite. The potential of Cu2O at 1% lithium intercalation (0.7V) was 0.1V lower than that of graphite at 1% lithium intercalation.

[0101] The lithium-added anode prepared in Comparative Example 3 was used to prepare a lithium battery using the same method as in Example 1, and its initial discharge capacity, capacity after 500 cycles, and capacity retention were tested.

[0102] The performance test results of the lithium batteries in each embodiment and comparative example are shown in Table 1 below.

[0103] Table 1. Performance test results of lithium batteries in each embodiment and comparative example.

[0104]

[0105] As can be seen from the comparison between Comparative Example 3 and Comparative Example 1 in Table 1, when the additives introduced into the negative electrode material layer do not meet the requirements of this application, they basically cannot improve the problem of uneven lithium element distribution in the negative electrode, and thus have little effect on improving the battery cycle performance. The performance of Comparative Example 3 battery is basically similar to that of Comparative Example 2 battery without lithium replenishment agent, and even worse than that of Comparative Example 2 battery.

[0106] As can be seen from the comparison of Examples 1-5 and Comparative Example 1 in Table 1, after introducing the regulator iron phosphate that meets the requirements of this application into the negative electrode material layer, the lithium elements from the lithium replenishment layer can be more evenly distributed in the negative electrode material layer, reducing the probability of lithium plating, reducing the loss of active lithium by the battery, and the battery cycle performance is better. Moreover, the battery cycle performance is improved more and more as the amount of iron phosphate added increases. In addition, when the amount of iron phosphate added is appropriate, the total amount of lithium replenishment provided by the lithium foil is sufficient to compensate for the active lithium lost during the formation of the SEI film and the active lithium embedded in the regulator iron phosphate, and the battery capacity is very high. For example, the first discharge capacity of the battery in Examples 1-3 is higher than that of the battery in Comparative Example 1. When the amount of iron phosphate added is large, the total amount of lithium replenishment provided by the lithium foil is insufficient to compensate for the active lithium lost during the formation of the SEI film and the active lithium embedded in the regulator iron phosphate (the active lithium embedded in iron phosphate is difficult to release during the delithiation process of the negative electrode), and the battery capacity decreases. The decrease is greater as the amount of iron phosphate added increases. For example, the first discharge capacity of the battery in Examples 4-5 is lower than that of the battery in Comparative Example 1.

[0107] Furthermore, by replacing the iron phosphate material with other regulators that meet the requirements of this application, a comparison between Examples 7-9 and Comparative Example 1 also shows that the addition of these regulators can improve the battery cycle performance.

[0108] To support the effectiveness of the additives introduced into the lithium-filled electrode in improving the uneven distribution of lithium in the lithium-filled anode, the following lithium diffusion effect experiment was conducted.

[0109] Taking Example 2 as an example, 5μm thick lithium foil was directly rolled onto the single-sided coated negative electrode material layer (containing iron phosphate) of Example 1 and the single-sided coated negative electrode material layer (without iron phosphate) of Comparative Example 1 to obtain lithium-replenished negative electrodes. Each negative electrode material layer simultaneously contained a lithium-replenishing region (covered by lithium foil) and a non-lithium-replenishing region (without lithium foil). Each lithium-replenished negative electrode was placed in an aluminum-plastic film, and 2mL of the lithium-ion electrolyte used in Example 1 was added. The film was vacuum-sealed and allowed to stand at 45°C for 24 hours. Afterwards, the aluminum-plastic film was disassembled in an argon-filled glove box, the negative electrode sheet was removed, washed with dimethyl carbonate (DMC), and dried. The lithium content was then characterized. Starting from the boundary between lithium-added and non-lithiated areas, select lithium-added areas and non-lithiated areas at a certain distance from the starting point, and cut them into 2mm wide strips (parallel to the boundary). Photograph these strips and calculate their areas. Place the selected lithium-added and non-lithiated electrode samples into separate bottles with rubber stoppers of a certain volume, and inject a certain amount of water to wet the electrode samples, allowing the lithium to fully react with the water and release hydrogen gas. Extract the gas from the bottles, detect the hydrogen content using a gas chromatograph, and deduce the lithium content in the sample based on the amount of hydrogen, converting it to volume per unit area. Figure 3 Table 2 summarizes the lithium content at different locations in the lithium diffusion effect experiment of the negative electrode samples of Example 2 and Comparative Example 1.

[0110] from Figure 3 It can be seen that, in Example 2, after the lithium replenishment layer is delithiated, the difference in lithium content between the lithium replenishment region and the unreplenished region of the anode material layer is small (the content difference is only 0.24 mAh / cm³). 2 (See Table 2 below). This difference is significantly lower than that of the conventional lithium-added anode in Comparative Example 2 without the introduced modifier. Furthermore, in the anode sheet of Example 1, the lithium content in the non-lithiated region at different locations from the boundary between lithium-added and non-lithiated areas is essentially equal, while in Comparative Example 1, the lithium content in the non-lithiated region gradually decreases with increasing distance from the boundary between lithium-added and non-lithiated areas. These results indicate that the modifier introduced into the anode material layer in this application can effectively promote the diffusion of lithium from lithium-rich to lithium-poor regions during non-uniform lithium addition, resulting in a more uniform distribution of lithium in the anode.

[0111] In addition, the lithium diffusion effect experiment was also conducted on the lithium-added anodes of other embodiments and Comparative Example 3, and the test results are summarized in Table 2 below.

[0112] Table 2. Lithium diffusion experimental results for each embodiment and comparative example.

[0113]

[0114] A comparison of the results of Examples 1, 3-9 and Comparative Example 1 in Table 2 shows that the lithium-added negative electrodes of this application, which introduce different amounts or types of regulators into the negative electrode material layer, can effectively promote the diffusion of lithium from the lithium-added area to the un-lithiated area even when the lithium-added layer is not uniformly lithium-added, resulting in a more uniform distribution of lithium in the negative electrode. However, the additive Cu2O introduced into the negative electrode material layer of Comparative Example 3 does not promote the diffusion of lithium from the lithium-added area to the un-lithiated area or achieve a uniform distribution of lithium throughout the entire negative electrode.

[0115] The above description represents the preferred embodiments of this application, but should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A lithium supplementing negative electrode, characterized by comprising: The lithium supplement negative electrode comprises a current collector and a negative electrode material layer arranged on at least one side surface of the current collector, and at least one negative electrode material layer is further provided with a lithium supplement layer on the side away from the current collector, the lithium supplement agent in the lithium supplement layer comprises metallic lithium, the negative electrode material layer comprises a negative electrode active material, an adjusting agent and a binder, wherein the potential of the adjusting agent when 1-2% of lithium is inserted is at least 0.1V higher than the potential of the negative electrode active material when 1-2% of lithium is inserted.

2. The lithium supplementing negative electrode according to claim 1, wherein The adjusting agent comprises one or more of iron phosphate, iron oxide, iron sulfide, zinc sulfide and lithium titanate.

3. The lithium supplementing negative electrode according to claim 1, wherein The mass of the adjusting agent is less than 10% of the mass of the negative electrode active material.

4. The lithium supplement negative electrode according to claim 3, wherein The mass of the adjusting agent is 0.5%-8% of the mass of the negative electrode active material, preferably 0.5%-5%.

5. The lithium supplement negative electrode according to any one of claims 1 to 4, wherein The mass of the lithium supplement agent is m1 g, the specific capacity of the lithium supplement agent for lithium extraction is C1 mAh / g, the mass of the adjusting agent is m2 g, and the specific capacity of the adjusting agent for lithium insertion is C2 mAh / g, wherein m1xC1>m2xC2.

6. The lithium supplement negative electrode according to any one of claims 1 to 5, wherein The negative electrode active material comprises graphite.

7. The lithium supplement negative electrode according to claim 6, wherein The negative electrode active material further comprises one or more of hard carbon, soft carbon, mesocarbon microbeads, silicon-based material, tin-based material and phosphorus-based material.

8. The lithium supplement negative electrode according to any one of claims 1 to 7, wherein The metallic lithium comprises lithium powder, lithium foil or lithium alloy.

9. The lithium supplementing anode of claim 1, wherein, The lithium supplement layer is a lithium foil layer, and the lithium foil layer comprises a plurality of strip-shaped lithium foils arranged on the negative electrode material layer at intervals.

10. A lithium battery, characterized by, The lithium supplement negative electrode and the electrolyte as claimed in any one of claims 1-9.

11. The lithium battery of claim 10, wherein, After the lithium battery is discharged, the content of lithium in the negative electrode material layer is 0.1wt%-1.7wt%.

12. A method of manufacturing a lithium battery, characterized by, The lithium supplement negative electrode and the electrolyte as claimed in any one of claims 1-9. The lithium supplement negative electrode and the electrolyte as claimed in any one of claims 1-9. The lithium supplement negative electrode and the electrolyte as claimed in any one of claims 1-9.

13. A lithium battery, characterized by The lithium supplement negative electrode and the electrolyte as claimed in any one of claims 1-9.

14. An electrical device, characterized by The lithium supplement negative electrode and the electrolyte as claimed in any one of claims 1-9. The lithium supplement negative electrode and the electrolyte as claimed in any one of claims 1-9. The lithium supplement negative electrode and the electrolyte as claimed in any one of claims 1-9. The lithium supplement negative electrode and the electrolyte as claimed in any one of claims 1-9.

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