Positive electrode material and positive electrode pre-lithiated battery comprising same

Abstract

Provided in the present disclosure is a positive electrode material, containing a positive electrode active material, a conductive agent and a binder, the positive electrode active material consisting of a positive electrode main material and a lithium supplementing agent, the positive electrode main material being selected from at least one of lithium iron phosphate and lithium manganese iron phosphate, and the lithium supplementing agent being selected from at least one of lithium manganate and a lithium-rich manganese-based material. On the basis of the total weight of the positive electrode active material, the mixing weight ratio of the positive electrode main material to the lithium supplementing agent is: 70:30≤positive electrode main material: lithium supplementing agent≤99.9:0.1. A positive electrode coating is formed by means of a double-layer synchronous coating process, the content of the lithium supplementing agent in the surface layer being a wt %, the content thereof in the bottom layer being b wt %, and the total content of the lithium supplementing agent in the positive electrode active material being within the range of 0.1-30%. Correspondingly, further disclosed in the present disclosure is a positive electrode pre-lithiated battery comprising the positive electrode material. The pre-lithiation technology for positive electrode materials of lithium-ion batteries provided by the present disclosure significantly improves the usable cycle capacity, rate capability and cycle stability of batteries, and has important application value and promotion prospects.

Description

A cathode material and a cathode pre-lithiated battery including the same. Technical Field

[0001] This disclosure relates to the field of lithium-ion battery technology, and in particular to a cathode material and a pre-lithiated cathode battery including the same. Background Technology

[0002] With the increasing demand for clean energy in modern society, lithium-ion batteries, as a highly efficient and environmentally friendly energy storage device, have become an important energy choice for electric vehicles, portable devices, and other fields. The performance of the cathode material directly affects key indicators such as battery energy density and cycle life.

[0003] Traditional cathode materials (such as lithium iron phosphate) are widely used in lithium-ion batteries due to their high stability and safety. Lithium manganese iron phosphate further improves energy density compared to lithium iron phosphate. However, the formation of a solid electrolyte interphase (SEI) film and irreversible changes in the electrode structure during the first charge reduce the discharge capacity of the cathode, leading to a decrease in the overall energy density of the battery.

[0004] Pre-lithiation of the cathode can compensate for lithium-ion loss and improve the initial discharge capacity. To improve the performance of lithium-ion batteries, research on cathode material pre-lithiation technology has become one of the current research hotspots. However, traditional lithium replenishment agents exhibit poor conductivity and cycle performance after delithiation, increase the mass of inactive materials in the cell, and further reduce the overall energy density of the battery.

[0005] Existing technology CN116632215A discloses a cathode material, its preparation method, and its application. The cathode material is in the form of a core plus a double-layer lithium-supplementing coating: a cathode material core (composed of polypropylene polymers, lithium manganese oxide, etc.), a first coating layer covering the cathode material core (composed of lithium-rich manganese-based materials), and a second coating layer covering the first coating layer (composed of conductive polymers and lithium-ion conductive materials). However, this existing technology focuses on coating the surface of the cathode active material particles with lithium-rich manganese and other materials at the microscale. Its structural design is relatively complex, and many factors affect battery performance (for example, the actual ion diffusion of lithium ions through the coating layer may also lead to a deterioration in battery performance). Furthermore, this existing technology only focuses on improving the cycle stability of some materials and does not study the improvement of overall performance such as cell energy, cycle life, and rate capability.

[0006] Therefore, there is a need for a simple pre-lithiation technology for lithium-ion battery cathode materials that offers improved overall performance. Summary of the Invention

[0007] Based on the technical problems existing in the background art, the present disclosure aims to provide a simple pre-lithiation technology for lithium-ion battery cathode materials, and improve the overall battery performance such as cell energy, cycle, rate, etc. by studying the blending of the lithium supplement agent material and the main cathode material at the macroscopic scale (without modifying or modifying the material structure at the microscopic particle scale).

[0008] In a first aspect, the present disclosure provides a cathode material, which includes a cathode active material, a conductive agent, and a binder. Among them, the cathode active material is composed of a main cathode material and a lithium supplement agent. The main cathode material is selected from at least one of lithium iron phosphate and lithium manganese iron phosphate, and the lithium supplement agent is selected from at least one of lithium manganate and lithium-rich manganese-based materials; based on the total weight of the cathode active material, the blending weight ratio of the main cathode material to the lithium supplement agent is: 70:30 ≤ main cathode material: lithium supplement agent ≤ 99.9:0.1.

[0009] In some embodiments, the molecular formula of lithium iron phosphate is: LiFePO4.

[0010] In some embodiments, the molecular formula of lithium manganese iron phosphate is: LiMn 0.5 , , 0.5 , <​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Mn 0.5 O2.

[0017] In some embodiments, the molecular formula of lithium manganese oxide is LiMn2O4.

[0018] In some implementations, the cathode material is lithium iron phosphate as described herein.

[0019] In some embodiments, the cathode material is lithium manganese iron phosphate as described herein.

[0020] In some embodiments, the cathode material is a combination of lithium iron phosphate and lithium manganese iron phosphate as described herein.

[0021] In some embodiments, the lithium supplement is the lithium-rich manganese-based material described herein.

[0022] In some embodiments, the lithium supplement is lithium manganese oxide as described herein.

[0023] In some embodiments, the lithium supplement is a combination of lithium manganese oxide and lithium-rich manganese-based materials as described herein.

[0024] In this disclosure, by controlling the mixing weight ratio of the cathode main material to the lithium replenisher in the cathode active material, it is beneficial to balance the improvement of usable cycle capacity, rate performance, and cycle stability, thereby achieving a comprehensive optimization of battery performance. Based on this, this disclosure controls the mixing weight ratio of the cathode main material to the lithium replenisher in the cathode active material between 70:30 and 99.9:0.1. When the mixing weight ratio of the cathode main material to the lithium replenisher is less than 70:30, the low first-cycle coulombic efficiency of the lithium replenisher leads to an excessively low overall first-cycle coulombic efficiency of the battery. To meet safety requirements, it is necessary to appropriately increase the battery's N / P ratio and negative electrode load (the ratio of negative electrode capacity to positive electrode capacity), resulting in a decrease in the overall energy density of the battery. Furthermore, due to the relatively lower cycle stability of the lithium replenisher compared to the cathode main material, the overall cycle stability of the battery decreases. When the weight ratio of the cathode material to the lithium replenisher is greater than 99.9:0.1, the lithium replenisher content is too low, which prevents the cathode material from fully utilizing its capacity and the lithium replenisher itself from providing sufficient cycle capacity, resulting in an insignificant improvement in overall capacity. The lithium replenisher is insufficient to compensate for the loss of active lithium during cycling, resulting in an insignificant improvement in the overall cycle stability of the battery. The lithium replenisher content is too low, which cannot effectively improve the overall conductivity of the cathode, resulting in an insignificant improvement in the rate performance of the battery.

[0025] Preferably, the mixing weight ratio of the positive electrode material to the lithium replenisher is 80:20 ≤ positive electrode material : lithium replenisher ≤ 99.5 : 0.5. More preferably, the mixing weight ratio of the positive electrode material to the lithium replenisher is 85:15 ≤ positive electrode material : lithium replenisher ≤ 99:1. In an exemplary embodiment, the mixing weight ratio of the positive electrode material to the lithium replenisher can be 98.9 : 1.1. Even more preferably, the mixing weight ratio of the positive electrode material to the lithium replenisher is 85:15 ≤ positive electrode material : lithium replenisher ≤ 98:2. In an exemplary embodiment, the mixing weight ratio of the positive electrode material to the lithium replenisher can be 96.7 : 3.3 or 90.2 : 9.8.

[0026] In this disclosure, controlling the content of the positive electrode active material (composed of the main positive electrode material and lithium supplement) in the positive electrode material is beneficial to improving the positive electrode capacity. Based on this, the content of the positive electrode active material is controlled at 90 to 99% by weight, based on the total weight of the positive electrode material. When the content of the positive electrode active material is less than 90% by weight, the overall capacity and energy density of the positive electrode are low; when the content of the positive electrode active material is greater than 99% by weight, the content of conductive agent and binder is insufficient, the manufacturing of the positive electrode sheet is difficult, the conductivity is insufficient, and the overall capacity of the positive electrode cannot be fully realized.

[0027] Preferably, based on the total weight of the positive electrode material, the content of the positive electrode active material is 90 to 99% by weight, more preferably 93 to 98.5% by weight, more preferably 95 to 98% by weight, and even more preferably 96 to 98% by weight.

[0028] In this disclosure, controlling the content of the conductive agent in the cathode material is beneficial to improving the conductivity of the cathode and maximizing its capacity. Based on this, the content of the conductive agent is controlled to be 0.5% to 5% by weight, using the total weight of the cathode material as a basis. When the conductive agent content is less than 0.5% by weight, the conductivity of the cathode is insufficient, and the overall capacity of the cathode cannot be fully utilized; when the conductive agent content is greater than 5% by weight, the content of the active material in the cathode is too low, and the cathode capacity is not effectively utilized, resulting in the cathode capacity not being maximized.

[0029] Preferably, based on the total weight of the positive electrode material, the content of the conductive agent is 0.5 to 5% by weight, preferably 0.75 to 4% by weight, more preferably 1 to 3% by weight, and even more preferably 1.5 to 3% by weight.

[0030] In this disclosure, controlling the binder content in the cathode material helps reduce the manufacturing difficulty of the cathode, improve the quality of the cathode sheet, and maximize the cathode capacity. Based on this, the binder content is controlled at 0.5 to 5% by weight, using the total weight of the cathode material as a baseline. When the binder content is less than 0.5% by weight, the cathode active material and conductive agent cannot be effectively bonded, making cathode sheet manufacturing difficult; when the binder content is greater than 5% by weight, the content of cathode active material and conductive agent is insufficient, resulting in insufficient conductivity and a low overall cathode capacity.

[0031] Preferably, based on the total weight of the positive electrode material, the binder content is 0.5 to 5% by weight, preferably 0.75 to 4% by weight, more preferably 1 to 3% by weight, and even more preferably 1.5 to 3% by weight.

[0032] In some embodiments, the conductive agent in the positive electrode material is selected from at least one of carbon black (e.g., Ketjen black), acetylene black, carbon nanotubes, metal powder, graphene, carbon fiber, and conductive ceramics.

[0033] In some embodiments, the binder in the positive electrode material is selected from at least one of carboxymethyl cellulose, polypropylene, polyethylene, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, and styrene-butadiene rubber.

[0034] In this disclosure, the lithium supplement can form a differentiated distribution in the surface and bottom layers of the positive electrode sheet.

[0035] In some implementations, the content of the surface lithium replenisher is higher than that of the bottom lithium replenisher. This structure helps the surface lithium replenisher near the electrolyte interface to rapidly release lithium ions during the first charge of the battery, preferentially compensating for lithium loss caused by the formation of the SEI film on the negative electrode and the adjustment of the positive electrode structure. The lower content of the bottom lithium replenisher helps maintain the electrical contact stability between the electrode and the current collector, reduces side reactions, and improves cycle performance. Preferably, the weight ratio of the positive electrode material to the lithium replenisher in the surface layer is 70:30 ≤ positive electrode material : lithium replenisher ≤ 85:15, and the weight ratio of the positive electrode material to the lithium replenisher in the bottom layer is 85:15 ≤ positive electrode material : lithium replenisher ≤ 99.9:0.1. More preferably, the weight ratio of the positive electrode material to the lithium replenisher in the surface layer is 80:20 ≤ positive electrode material : lithium replenisher ≤ 90:10, and the weight ratio of the positive electrode material to the lithium replenisher in the bottom layer is 90:10 ≤ positive electrode material : lithium replenisher ≤ 99.5:0.5.

[0036] In some embodiments, the content of the surface lithium replenisher is lower than that of the bottom lithium replenisher. The bottom lithium replenisher is closer to the current collector side, which can stably release lithium ions over a longer time scale, maintain lithium balance during battery operation, reduce lithium concentration gradient fluctuations, and reduce capacity decay. Simultaneously, the lower content of the surface lithium replenisher can mitigate the risk of side reactions at the electrolyte interface and improve thermal stability. Preferably, the mixing weight ratio of the positive electrode material to the lithium replenisher in the surface layer is 85:15 ≤ positive electrode material : lithium replenisher ≤ 99.9 : 0.1, and the mixing weight ratio of the positive electrode material to the lithium replenisher in the bottom layer is 70:30 ≤ positive electrode material : lithium replenisher ≤ 85:15. More preferably, the mixing weight ratio of the positive electrode material to the lithium replenisher in the surface layer is 90:10 ≤ positive electrode material : lithium replenisher ≤ 99.5 : 0.5, and the mixing weight ratio of the positive electrode material to the lithium replenisher in the bottom layer is 80:20 ≤ positive electrode material : lithium replenisher ≤ 90:10.

[0037] In a second aspect, this disclosure provides a positive electrode pre-lithiation battery comprising the positive electrode material described herein. Preferably, the positive electrode pre-lithiation battery further comprises a negative electrode material, a separator, and an electrolyte.

[0038] In some embodiments, the negative electrode material includes a negative electrode active material (e.g., graphite), a conductive agent, and a binder.

[0039] In some embodiments, the diaphragm material is selected from at least one of polyethylene, polyvinyl chloride, polypropylene, and polystyrene. In an exemplary embodiment, the diaphragm material is polyethylene. In an exemplary embodiment, the diaphragm material is polyvinyl chloride. In an exemplary embodiment, the diaphragm material is polypropylene. In an exemplary embodiment, the diaphragm material is polystyrene. In an exemplary embodiment, the diaphragm material is selected from two of polyethylene, polyvinyl chloride, polypropylene, and polystyrene. In an exemplary embodiment, the diaphragm material is selected from three of polyethylene, polyvinyl chloride, polypropylene, and polystyrene. In an exemplary embodiment, the diaphragm material is polyethylene, polyvinyl chloride, polypropylene, and polystyrene.

[0040] In some embodiments, the electrolyte is selected from at least one of gel electrolytes, solid electrolytes, and electrolyte solutions. In some embodiments, the electrolyte is an electrolyte solution. In some embodiments, the electrolyte solution is a lithium-ion battery electrolyte containing a lithium salt and an organic solvent. In some embodiments, the lithium-ion battery electrolyte is composed of a lithium salt and an organic solvent. In some embodiments, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium trifluoromethanesulfonate, lithium bis(pentafluoroethylsulfonylimide), lithium bis(trifluoromethanesulfonylimide), lithium bis(fluorosulfonylimide), lithium difluoro(bis(oxalato)phosphate), and lithium tetrafluoro(oxalato)phosphate. In some embodiments, the organic solvent is selected from at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), dimethoxyethane (DME), and tetrahydrofuran (THF).

[0041] In this paper, controlling the content of negative electrode active material (e.g., graphite) in the negative electrode material is beneficial to improving the capacity of the negative electrode. Based on this, the content of negative electrode active material is controlled at 80 to 99.8% by weight, taking the total weight of the negative electrode material as the baseline. When the content of negative electrode active material (e.g., graphite) is less than 80% by weight, the overall capacity and energy density of the negative electrode are low; when the content of negative electrode active material (e.g., graphite) is greater than 99.8% by weight, the content of conductive agent and binder is insufficient, the manufacturing of the negative electrode sheet is difficult, the conductivity is insufficient, and the overall capacity of the negative electrode cannot be fully realized.

[0042] Preferably, the content of the negative electrode active material (e.g., graphite) is 80 to 99.8% by weight, preferably 90 to 98.5% by weight, more preferably 93 to 98% by weight, and even more preferably 95 to 98% by weight, based on the total weight of the negative electrode material.

[0043] In this disclosure, controlling the content of the conductive agent in the negative electrode material is beneficial to improving the conductivity of the negative electrode and maximizing its capacity. Based on this, the content of the conductive agent is controlled to be between 0.1% and 10% by weight, using the total weight of the negative electrode material as a basis. When the conductive agent content is less than 0.1% by weight, the conductivity of the negative electrode is insufficient, and the overall capacity of the negative electrode cannot be fully utilized; when the conductive agent content is greater than 10% by weight, the content of the active material in the negative electrode is too low, and the capacity of the negative electrode is not effectively utilized, resulting in the negative electrode capacity not being maximized.

[0044] Preferably, based on the total weight of the negative electrode material, the content of the conductive agent is 0.1 to 10% by weight, preferably 0.2 to 5% by weight, more preferably 0.3 to 4% by weight, and even more preferably 0.5 to 3.5% by weight.

[0045] In this disclosure, controlling the binder content in the negative electrode material helps reduce the manufacturing difficulty of the negative electrode, improve the quality of the negative electrode sheet, and maximize the negative electrode capacity. Based on this, the binder content is controlled to be 0.1% to 10% by weight, using the total weight of the negative electrode material as a benchmark. When the binder content is less than 0.1% by weight, the negative electrode active material and conductive agent cannot be effectively bonded, making the manufacturing of the negative electrode sheet difficult; when the binder content is greater than 10% by weight, the content of the negative electrode active material and conductive agent is insufficient, resulting in insufficient conductivity and a low overall negative electrode capacity.

[0046] Preferably, based on the total weight of the negative electrode material, the binder content is 0.1 to 10% by weight, preferably 0.2 to 5% by weight, more preferably 0.3 to 4% by weight, and even more preferably 0.5 to 3.5% by weight.

[0047] In some embodiments, the conductive agent in the negative electrode material is selected from at least one of carbon black (e.g., Ketjen black), acetylene black, carbon nanotubes, metal powder, graphene, carbon fiber, and conductive ceramics.

[0048] In some embodiments, the binder in the negative electrode material is selected from at least one of carboxymethyl cellulose, polypropylene, polyethylene, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, and styrene-butadiene rubber.

[0049] Unless otherwise stated herein or in obvious contradiction with the context, any combination of features described herein may be used; any feature or combination of features described for the cathode material of the first aspect also applies to the cathode pre-lithiation battery of the second aspect, and vice versa.

[0050] Compared to traditional cathode pre-lithiation, this disclosure designs the mixing amount of each component in the cathode material so that the contained lithium replenishing agent can achieve the dual function of replenishing lithium for the main cathode active material in the first charge and discharge cycle, and can also provide additional usable cycle capacity after lithium replenishment so as to participate in the overall charge and discharge cycle of the battery as a cathode active material, thereby improving the overall rate performance and cycle stability of the battery. Detailed Implementation

[0051] The specific embodiments described herein are provided to illustrate this disclosure in an exemplary manner and are not intended to limit this disclosure in any way, which includes, but is not limited to, the specific embodiments described herein.

[0052] Unless the context otherwise requires, singular terms include plural forms and plural terms include singular forms. Generally, the terms described herein are those commonly known and used by those skilled in the art.

[0053] As used herein, expressions such as “comprising,” “including,” “containing,” and “having” are open-ended, indicating that in addition to the listed elements, components, or steps, there are other unlisted elements, components, or steps that do not materially affect the essential novelty of the method or product disclosed herein. Unless otherwise expressly stated, the expressions “comprising,” “including,” “containing,” and “having” also cover the case of “consisting of,” meaning that it may consist solely of the listed elements, components, or steps.

[0054] As used herein, the term "and / or" in the phrase "A and / or B" is intended to include: both A and B, A or B, (alone) A and (alone) B. Similarly, the term "and / or" in the phrase "A, B and / or C" is intended to cover implementations such as: A, B and C; A, B or C; A or C; A or B; B or C; A and C; A and B; B and C; (alone) A; (alone) B; and (alone) C.

[0055] As used herein, the terms "first," "second," "third," etc., are used only to distinguish between structures or elements mentioned in this disclosure and are not intended to limit the position, importance, etc. of any structure or element.

[0056] As used herein, “above” and “below” include the number itself. For example, “above one” (equivalent to “at least one”) means “one or more”, while “multiple” (equivalent to “at least two”) means “two or more”.

[0057] As used herein, when dealing with numerical values ​​or ranges of numerical values, unless otherwise expressly stated or the context is contradictory, the following applies: the range of values ​​provided herein should be understood to include the endpoint values, each intermediate value, and one-tenth of the unit of the lower limit; the range excluding one or both endpoints is also covered within the scope of this disclosure; the upper and lower limits of the range or subranges of numerical values ​​provided herein can be arbitrarily combined; and each particular value provided is considered to be modified by “about” to indicate a range covering the particular value plus / minus 20%.

[0058] Unless otherwise defined herein, the scientific and technical terms used in connection with this disclosure have the meanings commonly understood by those skilled in the art.

[0059] The chemicals used in the examples and comparative examples are as follows.

[0060] cathode materials

[0061] Lithium manganese iron phosphate (LiMn) 0.4 Fe 0.6PO4: Synthesized by Hefei Guoxuan High-Tech Power Energy Co., Ltd., used as the main cathode material.

[0062] Lithium-rich manganese-based 0.3Li₂MnO₃·0.7LiNi 0.5 Mn 0.5 O2: Synthesized by Hefei Guoxuan High-Tech Power Energy Co., Ltd., as a lithium supplement.

[0063] Polyvinylidene fluoride (PVDF): HSV900 manufactured by Arkema SA, used as an adhesive.

[0064] Carbon black Super P (SP): Super P manufactured by Imerys SA, used as a conductive agent.

[0065] N-Methylpyrrolidone: EQ-Lib-NMP manufactured by Shenzhen Kejing Zhida Technology Co., Ltd.

[0066] Aluminum foil: purchased from Shenzhen Kejing Zhida Technology Co., Ltd.

[0067] Anode material

[0068] Graphite: Synthesized by Hefei Guoxuan High-Tech Power Energy Co., Ltd., used as the negative electrode active material.

[0069] Carboxymethyl cellulose (CMC): EQ-Lib-CMC manufactured by Shenzhen Kejing Zhida Technology Co., Ltd., is used as a binder.

[0070] Styrene-butadiene rubber (SBR): EQ-Lib-SBR SBR2919 manufactured by Shenzhen Kejing Zhida Technology Co., Ltd., is used as an adhesive.

[0071] Copper foil: Purchased from Shenzhen Kejing Zhida Technology Co., Ltd.

[0072] diaphragm

[0073] Diaphragm: Celgard 2325 manufactured by Celgard, LLC

[0074] electrolytes

[0075] Ethylene carbonate (EC): Sigma Aldrich 809950, used as a solvent.

[0076] Dimethyl carbonate (DMC): Sigma Aldrich 517127, used as a solvent.

[0077] Ethyl methyl carbonate (EMC): Sigma Aldrich 754935, used as a solvent.

[0078] Lithium hexafluorophosphate (LiPF6): Purchased from Sigma Aldrich as a lithium salt.

[0079] Vinyl sulfate (VC): Purchased from Sigma Aldrich as an additive.

[0080] Example 1

[0081] (1) Preparation of cathode materials

[0082] 89% of LiMn 0.4 Fe 0.6 PO4, 3% of 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2 and 5% SP and 3% PVDF (total weight 10 kg by weight) are mixed, and N-methylpyrrolidone solvent is added and stirred into a uniform slurry. This slurry is then coated onto a 12-micron thick aluminum foil, rolled, and slit to obtain the positive electrode material.

[0083] (2) Preparation of negative electrode materials

[0084] 90% graphite, 5% conductive agent SP, 2% binder CMC, and 3% binder SBR (total weight 10 kg) were mixed evenly, and deionized water was added as a solvent. The slurry was then coated onto an 8-micron thick copper foil, dried, and rolled and slit to obtain the negative electrode material.

[0085] (3) Preparation of electrolyte

[0086] In an argon-filled glove box (oxygen < 0.1 ppm, moisture < 0.1 ppm), EC:DMC:EMC in a weight ratio of 20:40:40 were mixed evenly, and 13% by weight of lithium hexafluorophosphate was slowly added. After complete dissolution, 2% of vinyl sulfate (VC) additive was added and stirred evenly to obtain the electrolyte.

[0087] (4) Battery manufacturing

[0088] In a dry environment with the dew point controlled below -60℃, the positive electrode, separator, and negative electrode are stacked in sequence, ensuring that the separator completely separates the positive and negative electrodes and that the negative electrode completely covers the positive electrode. The stacked electrodes are then used to make a cell, which is hot-pressed and sealed in an aluminum-plastic film with adhesive tabs. After baking until the moisture content is within acceptable limits, the electrolyte is injected into the soft-pack cell. Subsequently, the cell is sealed, formed, aged a second time, and capacity tested to obtain an experimental battery for testing.

[0089] (5) Performance Testing

[0090] As described below, a series of electrical performance tests were conducted on the prepared experimental battery, including indicators such as charge-discharge cycles, rate performance, cycle stability, and storage performance at different temperatures and cutoff voltages.

[0091] Example 2

[0092] The material was prepared and its performance tested as described in Example 1, with the difference being that in the cathode material preparation process, 83% LiMn was used... 0.4 Fe 0.6 PO4, 9% of 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2 and 5% conductive agent SP and 3% binder PVDF (total weight 10 kg by weight) are mixed, and the rest is the same as in Example 1.

[0093] Example 3

[0094] The material was prepared and its performance tested as described in Example 1, with the difference being that: in the preparation of the cathode material, 83% LiMn... 0.4 Fe 0.6 PO4, 9% of 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.5 O2 and 5% conductive agent SP and 3% binder PVDF (total weight 10 kg by weight) are mixed, and the rest is the same as in Example 1.

[0095] Example 4

[0096] The material was prepared and its performance tested as described in Example 1, with the difference being that in the cathode material preparation process, 66% LiMn was used... 0.4 Fe 0.6 PO4, 26% of 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2 and 5% conductive agent SP and 3% binder PVDF (total weight 10 kg by weight) are mixed, and the rest is the same as in Example 1.

[0097] Example 5

[0098] The material was prepared and its performance tested as described in Example 1, with the difference being that in the cathode material preparation process, 91% LiMn... 0.4 Fe 0.6 PO4, 1% of 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2 and 5% conductive agent SP and 3% binder PVDF (total weight 10 kg by weight) are mixed, and the rest is the same as in Example 1.

[0099] Example 6

[0100] The material was prepared and its performance tested as described in Example 1, with the difference that: during the preparation of the cathode material, the surface and bottom slurries were prepared according to the following ratios: the surface slurry consisted of 45.5% LiMn. 0.4 Fe 0.6 PO4, 0.5% of 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2 and 2.5% conductive agent SP, 1.5% binder PVDF (total weight 10kg, by weight%); the bottom layer is 43.5% LiMn. 0.4 Fe 0.6 PO4, 2.5% of 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2, 2.5% conductive agent SP, and 1.5% binder PVDF (total weight 10 kg) were used in a dual-channel slit extrusion die. The first channel outputs the bottom layer slurry, and the second channel outputs the top layer slurry. The bottom layer slurry was first coated onto the surface of a 12-micron thick aluminum foil, and the top layer slurry was immediately coated onto the undried bottom layer. After coating, the material was dried in a gradient temperature-controlled drying oven, rolled, and slit to obtain the positive electrode material. Other steps were the same as in Example 1.

[0101] Example 7

[0102] The material was prepared and its performance tested as described in Example 1, with the difference that: during the preparation of the cathode material, the surface and bottom slurries were prepared according to the following ratios: the surface slurry consisted of 43.5% LiMn. 0.4 Fe 0.6 PO4, 2.5% of 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2 and 2.5% conductive agent SP, 1.5% binder PVDF (total weight 10 kg, by weight %); the bottom layer is 45.5% LiMn. 0.4 Fe 0.6 PO4, 0.5% of 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2, 2.5% conductive agent SP, and 1.5% binder PVDF (total weight 10 kg) were used in a dual-channel slit extrusion die. The first channel outputs the bottom layer slurry, and the second channel outputs the top layer slurry. The bottom layer slurry was first coated onto the surface of a 12-micron thick aluminum foil, and the top layer slurry was immediately coated onto the undried bottom layer. After coating, the material was dried in a gradient temperature-controlled drying oven, rolled, and slit to obtain the positive electrode material. Other steps were the same as in Example 1.

[0103] Comparative Example 1

[0104] The material was prepared and its performance tested as described in Example 1, with the difference being that in the cathode material preparation process, 92% of LiMn was used... 0.4 Fe 0.6 PO4 and 5% conductive agent SP and 3% binder PVDF (total weight 10 kg by weight) were mixed, and the rest was the same as in Example 1.

[0105] Comparative Example 2

[0106] The material was prepared and its performance tested as described in Example 1, with the difference being that in the preparation of the cathode material, 89% LiMn was used... 0.4 Fe 0.6 PO4, 3% Li2NiO2, 5% conductive agent SP, and 3% binder PVDF (total weight 10 kg by weight) were mixed, and the rest was the same as in Example 1.

[0107] Comparative Example 3

[0108] The material was prepared and its performance tested as described in Example 1, with the difference being that in the cathode material preparation process, 60% LiMn was used... 0.4 Fe 0.6 PO4, 32% of 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2 and 5% conductive agent SP and 3% binder PVDF (total weight 10 kg by weight) are mixed, and the rest is the same as in Example 1.

[0109] Comparative Example 4

[0110] The material was prepared and its performance tested as described in Example 1, with the difference being that in the cathode material preparation process, 91.55% LiMn was used. 0.4 Fe 0.6 PO4, 0.45% of 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2 and 5% conductive agent SP and 3% binder PVDF (total weight 10 kg by weight) are mixed, and the rest is the same as in Example 1.

[0111] Table 1: Main materials and lithium supplementing agents and their proportions in the examples and comparative examples

[0112] Electrical performance testing

[0113] The prepared soft-pack batteries were immersed for 24 hours and then formed and capacity-graded using a battery testing cabinet. The formation process involved constant current charging at 0.02C to 3.2V, followed by constant current charging at 0.1C to 3.7V, and then aging at 45℃ for 24 hours. The capacity-graded process involved constant current and constant voltage charging at 0.1C to 4.25V, with a cutoff current of 0.05C, constant current discharging at 0.1C to 2.75V, constant current and constant voltage charging at 0.33C to 4.25V, with a cutoff current of 0.05C, and then constant current discharging at 0.33C to 2.75V. After capacity grading, the batteries were cycled 500 times using a constant current and constant voltage charge-discharge cycle at 0.33C / 0.33C, with the voltage range set to 2.75-4.25V. Specific test results are shown in Table 2.

[0114] Table 2: Battery Test Results

[0115] By comparing the results of Example 1 and Comparative Example 1, it can be seen that the lithium-rich manganese-based pre-lithiated cathode material provided in this disclosure significantly improves the first discharge capacity, the capacity retention rate after 500 cycles, and the capacity retention rate at high rates in the test of pouch batteries.

[0116] By comparing the results of Example 1 and Example 2, it can be seen that an appropriate higher proportion of lithium supplement can further improve the battery cycle capacity, cycle capacity retention, and rate performance.

[0117] By comparing the results of Example 2 and Example 3, it can be seen that optimizing the lithium replenishment composition can further optimize the battery cycle capacity, cycle capacity retention rate and rate performance.

[0118] By comparing the results of Example 1 with those of Comparative Examples 1 and 2, it can be seen that both the pre-lithiation of this disclosure and the conventional pre-lithiation improve the performance of the unlithiated battery. However, the pre-lithiation of this disclosure is significantly better than the conventional pre-lithiation in terms of discharge capacity, capacity retention after 500 cycles, and capacity retention at high rates.

[0119] By comparing the results of Example 4 with those of Comparative Example 3, it can be seen that when the lithium replenishment content is too high, the coulombic efficiency of the battery in the first cycle is lower and the cycle stability is worse.

[0120] By comparing the results of Example 5 with those of Comparative Example 4, it can be seen that when the lithium replenishment content is too low, the battery's first discharge capacity, cycle stability, and rate performance are not significantly improved.

[0121] Comparing the results of Example 1 and Example 6, it can be seen that, under the condition of the same overall lithium supplementation content in the cathode, appropriately increasing the proportion of the bottom lithium supplementation helps to further improve the cycle stability of the cathode material, while maintaining a similar initial charge-discharge capacity and initial coulombic efficiency as in Example 1. This structural design effectively alleviates volume expansion and interfacial side reactions during cycling.

[0122] Comparing the results of Example 1 and Example 7, it can be seen that, under the condition of the same overall lithium replenishment content in the cathode, appropriately increasing the proportion of surface lithium replenishment helps to further improve the initial discharge specific capacity of the cathode material, while maintaining cycle stability and initial coulombic efficiency similar to those of Example 1. This structural optimization achieves a faster active lithium release pathway, which is beneficial to improving the initial energy density.

[0123] The above results demonstrate that the cathode material with a specific composition and mixed in a specific ratio, and the cathode pre-lithiation battery including the present disclosure, have improved overall performance.

[0124] This disclosure combines lithium iron phosphate (LFP) and lithium manganese iron phosphate (MFP) cathode materials with a certain proportion of lithium-rich manganese-based and lithium manganese oxide cathode materials as lithium replenishing agents. The low initial coulombic efficiency and lithium-rich characteristics of the lithium-rich manganese-based materials in this disclosure can replenish lithium to the main cathode active material during the first cycle, allowing its usable cycle capacity to be fully utilized. Meanwhile, compared to traditional cathode lithium replenishing agents, lithium manganese oxide and lithium-rich manganese-based materials have been widely studied as cathode active materials for lithium-ion batteries. As lithium replenishing agents, they can continue to participate in the overall charge-discharge cycle of the battery after the initial lithium replenishment, significantly improving the battery's energy density and cycle stability. Compared to main materials with poor conductivity such as LFP and MFP, lithium-rich manganese-based and lithium manganese oxide materials have superior conductivity, which can further improve the overall rate performance of the battery.

[0125] Therefore, the lithium-ion battery cathode material pre-lithiation technology provided in this disclosure significantly improves the usable cycle capacity, rate performance, and cycle stability of the battery by introducing lithium-rich manganese-based and lithium manganese oxide cathode materials as lithium supplementers, and has significant application value and promising prospects. With the increasing demand for clean energy, this disclosure will play a positive role in promoting the development and sustainable utilization of lithium-ion battery technology.

[0126] Although this disclosure describes exemplary embodiments of carrying out this disclosure, including the best mode of carrying out this disclosure known to the inventors, variations of the above embodiments will be apparent to those skilled in the art upon reading this disclosure. These variations can be suitably employed by those skilled in the art, and this disclosure is intended to cover variations that implement this disclosure in a manner different from that specifically described herein. Therefore, this disclosure includes all variations and equivalents of the subject matter described in the claims. Furthermore, unless otherwise stated herein or in obvious contradiction to the context, this disclosure is intended to cover any combination of all possible variations of the elements described herein.

Claims

1. A positive electrode material comprising a positive electrode active material, a conductive agent, and a binder, wherein, The positive electrode active material is composed of a positive electrode main material and a lithium supplement agent, the positive electrode main material is selected from at least one of lithium iron phosphate and lithium manganese iron phosphate, and the lithium supplement agent is selected from at least one of lithium manganate and a lithium-rich manganese-based material; the blending weight ratio of the positive electrode main material to the lithium supplement agent is 70:30≤positive electrode main material:lithium supplement agent≤99.9:0.1, based on the total weight of the positive electrode active material.

2. The positive electrode material according to claim 1, wherein, The molecular formula of the lithium iron phosphate is LiFePO4; and / or, The molecular formula of the lithium manganese iron phosphate is: LiMn x Fe 1-x PO4, wherein 0.05≤x≤0.95; and / or, The molecular formula of the lithium-rich manganese-based material is: xLi2MnO3·(1-x)LiM y N 1-y O2, wherein 0 < x < 1, 0.8 ≤ y ≤ 1, M is selected from Ni, Ni+Co, Ni+Mn or Ni+Mn+Co, and N is one or more metal elements selected from Mg, Al, Ti, W, Sb, Nb, Ta and Mo; and / or, The molecular formula of the lithium manganate is LiMn2O4.

3. The positive electrode material according to claim 1 or 2, wherein The positive electrode main material is lithium manganese iron phosphate; and / or, the lithium supplement agent is a lithium-rich manganese-based material; and / or, the blending weight ratio of the positive electrode main material to the lithium supplement agent is 70:30≤positive electrode main material:lithium supplement agent≤99.9:0.1, based on the total weight of the positive electrode active material.

4. The positive electrode material according to claim 1 or 2, wherein The content of the positive electrode active material is 90 to 99 wt%, preferably 93 to 98.5 wt%, more preferably 95 to 98 wt%, based on the total weight of the positive electrode material; the content of the conductive agent is 0.5 to 5 wt%, preferably 0.75 to 4 wt%, more preferably 1 to 3 wt%; and / or, the content of the binder is 0.5 to 5 wt%, preferably 0.75 to 4 wt%, more preferably 1 to 3 wt%.

5. The positive electrode material according to claim 1 or 2, wherein The conductive agent is selected from at least one of carbon black, acetylene black, carbon nanotubes, metal powder, graphene, carbon fiber and conductive ceramic; and / or, the binder is selected from at least one of carboxymethyl cellulose, polypropylene, polyethylene, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate and butadiene styrene rubber.

6. A positive electrode sheet for a lithium-ion battery, characterized in that, Comprise: a current collector having oppositely arranged surfaces and a bottom surface; a positive electrode active layer comprising a surface layer coated on the surface and a bottom layer coated on the bottom surface; wherein the bottom layer and the surface layer both comprise the positive electrode material according to any one of claims 1-5.

7. The positive electrode sheet according to claim 6, the mass fraction of the lithium supplement agent in the surface layer is a wt%, the mass fraction of the lithium supplement agent in the bottom layer is b wt%, a+b=100 and a≠b.

8. The cathode electrode of claim 6, wherein, The positive electrode active layer is formed by a wet-on-wet double-layer synchronous coating process, using a coating device with a double-channel slot extrusion die, the positive electrode material of the bottom layer and the positive electrode material of the surface layer are synchronously injected and sequentially coated on the current collector, and then subjected to multi-stage gradient drying and calendering treatment.

9. A positive electrode pre-lithiation battery comprising the positive electrode material according to any one of claims 1-5.

10. The battery of claim 9, wherein, The battery further comprises a negative electrode material, a separator and an electrolyte.

11. The battery of claim 10, wherein, The negative electrode material comprises graphite, a conductive agent and a binder; and / or the material of the separator is selected from at least one of polyethylene, polyvinyl chloride, polypropylene and polystyrene; and / or the electrolyte is selected from at least one of a gel electrolyte, a solid-state electrolyte and an electrolyte solution, and the electrolyte is preferably a lithium ion battery electrolyte.

12. The battery of claim 11, wherein, The content of the graphite is 80 to 99.8 wt%, preferably 90 to 98.5 wt%, more preferably 93 to 98 wt%, based on the total weight of the negative electrode material; and / or the content of the conductive agent is 0.1 to 10 wt%, preferably 0.2 to 5 wt%, more preferably 0.3 to 4 wt%; and / or the content of the binder is 0.1 to 10 wt%, preferably 0.2 to 5 wt%, more preferably 0.3 to 4 wt%.

13. The battery of claim 11 or 12, wherein, The conductive agent in the negative electrode material is selected from at least one of carbon black, acetylene black, carbon nanotubes, metal powder, graphene, carbon fiber and conductive ceramic; and / or the binder in the negative electrode material is selected from at least one of carboxymethyl cellulose, polypropylene, polyethylene, polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate and butadiene styrene rubber.

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