Ternary positive electrode sheet for lithium battery with high safety, high capacity and long cycle, and preparation method and use thereof

Abstract

The application discloses a ternary positive plate for lithium battery with high safety, high capacity and long cycle, and a preparation method and application thereof. The positive plate comprises a current collector and a positive material layer on the surface of the current collector, wherein the positive material layer comprises ternary positive active material particles, a conductive agent, a binder and oxide solid electrolyte particles capable of conducting lithium ions; the surface capacity of the positive plate is greater than or equal to 4 mAh / cm 2 , and the particle size D50 of the oxide solid electrolyte particles is 0.1-3 microns. By adding the oxide solid electrolyte particles with a specific particle size into the positive plate, the conductive agent and the binder are matched, and for the positive plate with a surface capacity greater than or equal to 4 mAh / cm 2 , the characteristics of high safety can be considered on the premise of ensuring high capacity and good cycle performance.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, to a positive electrode sheet and its preparation method and application, and more particularly to a ternary positive electrode sheet for lithium batteries that combines high safety, high capacity and long cycle life, its preparation method, a method for improving the safety of lithium batteries, the corresponding positive electrode sheet, and lithium batteries. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, good cycle performance, long lifespan, low self-discharge, and no memory effect, making them promising candidates for power batteries. Electric vehicles, as a mode of transportation, have their driving range and safety performance being key concerns, which primarily depend on the energy density, cycle life, power density, and safety performance of the power battery.

[0003] From the perspective of energy density of power batteries and driving range of electric vehicles, nickel-containing ternary material systems have significant advantages, especially high-nickel ternary lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide materials, which have broad application prospects in power batteries. Ternary materials have advantages such as large specific capacity, long cycle life, good low-temperature performance, and abundant raw materials. Moreover, they can simultaneously overcome the problems of low capacity of lithium iron phosphate, high cost of lithium cobalt oxide, and poor stability of lithium manganese oxide. They are considered to be one of the most promising cathode materials for power lithium batteries. Therefore, high-nickel ternary materials have good application prospects in the field of electric vehicles.

[0004] Despite the numerous advantages of ternary cathode materials, they suffer from poor high-temperature stability and are prone to thermal runaway. Furthermore, the higher the nickel content in the ternary material, the worse the thermal stability. Improving the safety of ternary cathode materials is crucial for the widespread application of high-energy-density ternary lithium batteries in the power battery field and is currently one of the hot research areas.

[0005] Taking lithium nickel manganese cobalt oxide, a ternary material, as an example, its poor safety is due to the following reasons:

[0006] 1) Lithium nickel manganese cobalt oxide has a relatively low thermal decomposition temperature, high heat release, and poor thermal stability. Compared with lithium iron phosphate, lithium nickel manganese cobalt oxide has a deoxidation temperature of 200℃ and a heat release greater than 800J / g, while lithium iron phosphate has a deoxidation temperature of 270℃ and a heat release of only 124J / g, and it only decomposes on a large scale above 400℃. 2) Lithium nickel manganese cobalt oxide is relatively reactive and has strong oxidizing properties at high potentials. It is also unstable and prone to oxygen evolution, which leads to side reactions with the electrolyte, releasing a large amount of heat and easily causing thermal runaway. It also reduces the cycle life and storage life of ternary cathode materials.

[0007] The above problems are the reasons for the deterioration of the safety performance of ternary lithium batteries. How to effectively solve the safety hazards of ternary batteries and avoid thermal runaway has become an urgent problem for companies at home and abroad.

[0008] Currently, methods to improve the safety of lithium batteries mainly include: positive electrode material coating, electrolyte additives, PTC coating, insulating / flame-retardant coating, ceramic separator coating, and negative electrode material modification. For example, CN103151513B, a high-performance ternary power battery and its preparation method, discloses a nickel-cobalt-manganese lithium ternary material coated with Al2O3 to improve the safety performance of ternary batteries. However, this invention has limited effect on safety improvement at higher temperatures. CN104409681A, a method for preparing lithium-ion battery electrodes with PTC coating, discloses a method of pre-coating a temperature-sensitive pre-coating on the current collector before coating the positive or negative electrode active material. This pre-coating has good conductivity at room temperature, and its resistance increases sharply when the temperature rises, preventing the battery from heating up further, thereby improving the safety of lithium-ion batteries. However, because needle penetration thermal runaway occurs instantaneously, the mechanism of this coating often does not have time to take effect and cannot effectively improve needle penetration safety. In addition, the methods mentioned above, such as coating the cathode material, coating the ceramic separator, using electrolyte additives, constructing PTC coatings, and constructing insulating or flame-retardant coatings, will reduce the electrochemical performance of the cathode. The overall performance of the cathode material modified by these methods still needs to be optimized. On the other hand, they will also have a certain impact on the electrode or cell manufacturing process, making it difficult to scale up production.

[0009] Therefore, it is still necessary to find a modification method that can ensure higher battery safety while maintaining good electrical performance. Summary of the Invention

[0010] In view of the above-mentioned problems existing in the prior art, the purpose of the present invention is to provide a positive electrode sheet, its preparation method and application, and in particular to provide a ternary positive electrode sheet for lithium batteries that combines high safety, high capacity and long cycle life, its preparation method, a method for improving the safety of lithium batteries, the corresponding positive electrode sheet, and a lithium battery.

[0011] In the "positive electrode sheet with high safety, high capacity and long cycle life" described in this invention, "long cycle life" means that the lithium battery prepared using this positive electrode sheet can achieve a capacity retention rate of over 80% after 1000 1C / 1C cycle life; "high capacity" means that the areal capacity is ≥4mAh / cm². 2 High safety indicates that the battery can pass the needle penetration and 180°C hot box tests, and it will not catch fire, explode, or emit smoke in either test.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] In a first aspect, the present invention provides a ternary cathode sheet for lithium batteries, the cathode sheet comprising a current collector and a cathode material layer located on the surface of the current collector, the cathode material layer comprising ternary cathode active material particles, a conductive agent, a binder and oxide solid electrolyte particles capable of conducting lithium ions;

[0014] The areal capacity of the positive electrode is ≥4mAh / cm². 2 The particle size D50 of the oxide solid electrolyte particles is 0.1-3 μm.

[0015] In this invention, the areal capacity of the positive electrode is ≥4mAh / cm². 2 For example, 4mAh / cm 2 6mAh / cm 2 8mAh / cm 2 10mAh / cm 2 12mAh / cm 2 Or 15mAh / cm 2 wait.

[0016] In the cathode sheet of this invention, ternary cathode active material particles serve as the main active component. To obtain a high areal capacity ternary cathode, existing technologies generally use high-specific-capacity, high-nickel ternary cathode materials or increase the electrode thickness. On the one hand, ternary cathode materials have poor high-temperature stability, and the higher the nickel content in the ternary cathode material, the worse the thermal stability. On the other hand, increasing the electrode thickness prolongs the electron and lithium-ion transport path, increasing battery impedance and Joule heat during charging and discharging. For high areal capacity ternary cathode materials, the energy stored per unit area of ​​cathode material is also higher. Once a short circuit or overheating occurs, the energy that can be released per unit area of ​​cathode material is also higher, thus causing serious safety hazards. Therefore, a solution that combines high safety and high capacity is needed.

[0017] This invention achieves a positive electrode sheet areal capacity ≥4 mAh / cm² by incorporating an oxide solid electrolyte with a particle size D50 of 0.1-3 μm, along with a conductive agent and a binder. 2The positive electrode sheet, without affecting high capacity and long cycle performance, improves the thermal stability of the positive electrode sheet, ensuring battery safety. Its technical principle is as follows: First, the oxide solid electrolyte particles have a certain ion transport capability and can effectively block contact between ternary positive electrode active material particles, improving thermal stability while ensuring ion transport. Second, the oxide solid electrolyte itself has an endothermic effect, absorbing some heat and alleviating overheating of the positive electrode. Third, the oxide solid electrolyte has high chemical stability, allowing it to maintain the current mainstream manufacturing processes for positive electrode sheets, separators, and batteries, offering advantages of high stability and low cost, making it suitable for large-scale applications. Because the oxide solid electrolyte particles themselves have a certain ion conductivity, within the solid electrolyte content range described in this invention, the introduction of the oxide solid electrolyte will not significantly hinder the ion transport capability in the positive electrode. Furthermore, the endothermic effect of the oxide solid electrolyte reduces the average temperature of the positive electrode active material during charge and discharge, reducing side reactions of the ternary positive electrode active material at high temperatures, thus contributing to ensuring the battery's long cycle performance.

[0018] In this invention, the particle size D50 of the oxide solid electrolyte particles is 0.1-3 μm, such as 0.1 μm, 0.5 μm, 1 μm, 2 μm, 2.5 μm, or 3 μm. If the oxide solid electrolyte particle size is too small, its interface resistance will increase significantly, hindering electron transport, reducing the positive electrode capacity, and lowering the battery's energy density. If the particle size is too large, the oxide solid electrolyte's effect on blocking contact between positive electrode particles is not significant, resulting in only a minor improvement in safety.

[0019] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0020] Preferably, the particle size D50 of the oxide solid electrolyte particles is 0.5-2 μm.

[0021] Preferably, the content of the ternary cathode active material particles is 80-98% based on the total mass of the ternary cathode active material particles, conductive agent, binder, and oxide solid electrolyte particles, which is 100%.

[0022] Preferably, based on the total mass of ternary cathode active material particles, conductive agent, binder, and oxide solid electrolyte particles as 100%, the content of the oxide solid electrolyte is 0.1-10%, for example, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 7.5%, 8%, 8.5%, 9%, or 10%. If the content of oxide solid electrolyte is less than 0.1%, it is difficult to effectively block the contact between ternary cathode active material particles, and the improvement in safety is not significant. If the content of oxide solid electrolyte is greater than 10%, it will affect ion transport, reduce lithium-ion conductivity, affect battery capacity, and reduce battery energy density and cycle performance. Therefore, the above range is preferred, and more preferably 1-5%.

[0023] Preferably, the content of the conductive agent is 0.1-8% based on the total mass of the ternary positive electrode active material particles, conductive agent, binder and oxide solid electrolyte particles as 100%, for example 0.1%, 0.5%, 1%, 1.5%, 2%, 3%, 3.5%, 4%, 5%, 6%, 7% or 8%.

[0024] Preferably, the content of the binder is 0.1-10%, for example, 0.1%, 0.8%, 1.2%, 3%, 5%, 6%, 7%, 8% or 10%, etc., based on the total mass of the ternary positive electrode active material particles, conductive agent, binder and oxide solid electrolyte particles as 100%.

[0025] Preferably, the oxide solid electrolyte particles comprise any one or a combination of at least two of the following compounds: Li with a NASICON structure. 1+x1 Al x1 Ge 2-x1 (PO4)3(LAGP) or its isomorphous heteroatomic doped compounds, Li 1+ x2 Al x2 Ti 2-x2 (PO4)3(LATP) or its isomorphous heteroatom-doped compounds, perovskite-structured Li x3 La 2 / 3-x3 TiO3 (LLTO) or its isomorphous heteroatomic doped compounds, Li 3 / 8 Sr 7 / 16 Ta 3 / 4 Hf 1 / 4 O3(LSTH) or its isomorphous heteroatomic doped compounds, Li 2x4-y1 Sr 1-x4 Ta y1 Zr 1-y1O₃(LSTZ) or its isomorphous heteroatom-doped compound, anti-perovskite structure Li 3-2x5 M x5 HalO, Li₃OCl or their isomorphous heteroatom-doped compounds, LISICON structure Li 4-x6 Si 1-x6 P x6 O₄ or its isomorphous heteroatom-doped compound, Li 14 ZnGe₄O 16 (LZGO) or its isomorphous heteroatom-doped compound, garnet structure Li 7-x7 La₃Zr 2-x7 O 12 (LLZO) or its isomorphous heteroatom-doped compound, wherein 0<x1≤0.75, 0<x2≤0.5, 0.06≤x3≤0.14, 0.25≤y1≤1, x4=0.75y1, 0≤x5≤0.01, 0.5≤x6≤0.6; 0≤x7<1; M includes but is not limited to Mg 2+ , Ca 2+ , Sr 2+ or Ba 2+ any one or a combination of at least two of the above, other high-valent cations commonly used in the art are also applicable to the present invention, and Hal is the element Cl or I.

[0026] Preferably, the oxide solid electrolyte particles include Li 1+x2 Al x2 Ti 2-x2 (PO₄)₃ and / or Li 7- x7 La₃Zr 2-x7 O 12 , preferably Li 1+x2 Al x2 Ti 2-x2 (PO₄)₃.

[0027] The ternary positive electrode active material particles include lithium nickel cobalt manganese oxide (NCM) and / or lithium nickel cobalt aluminum oxide (NCA).

[0028] Preferably, the chemical composition of the ternary positive electrode active material particles is LiNi x Co y M 1-x-yO2, M is at least one of Mn or Al, x≥0.6, for example 0.6, 0.65, 0.7, 0.8 or 0.88, etc. The ternary cathode active material of this preferred technical solution is a high-nickel ternary cathode material, which has high specific energy but poor thermal stability. This invention improves it by using an oxide solid electrolyte combined with a conductive agent and a binder, which can solve its safety problem and give full play to its high energy density advantage.

[0029] Preferably, the conductive agent comprises any one or a combination of at least two of Super-P, KS-6, carbon black, carbon nanotubes, CNTs, acetylene black, or graphene. Typical but non-limiting examples of such combinations include: combinations of Super-P and KS-6, combinations of Super-P and carbon black, combinations of Super-P and carbon nanotubes, combinations of carbon black and CNTs, combinations of KS-6, carbon black, and CNTs, etc., with a preferred combination being carbon nanotubes and Super-P.

[0030] Preferably, the adhesive comprises any one or a combination of at least two of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), or polytetrafluoroethylene (PTFE). Typical limiting examples of such combinations include combinations of PVDF and PEO, combinations of PVDF and PTFE, and combinations of PVDF and PVDF-HFP.

[0031] Preferably, the ratio of the particle size D50 of the ternary cathode active material particles to the particle size D50 of the oxide solid electrolyte particles is ≥5, for example, 5, 6, 8, 10, 12, 13, or 15. If the particle sizes are close, due to the limitation of the solid electrolyte content, under this particle size condition, its content is insufficient to prevent contact between the ternary cathode active material particles, resulting in poor material safety performance.

[0032] In a second aspect, the present invention provides a method for preparing a positive electrode sheet as described in the first aspect, the method comprising the following steps:

[0033] S1: Premix the positive electrode active material particles and oxide solid electrolyte particles to obtain a premixed material, wherein the positive electrode active material particles include ternary positive electrode active material particles;

[0034] S2: Add the adhesive solution of the binder to the premixed material, mix, and obtain a primary slurry;

[0035] S3: Add a conductive agent to the primary slurry and mix to obtain a secondary slurry;

[0036] S4: Coat the secondary slurry onto the current collector, controlling the electrode surface capacity to be ≥4mAh / cm².2 After baking and rolling, the positive electrode sheet is obtained.

[0037] In the method of the present invention, steps S2 and S3 can each be added at once or in stages.

[0038] Preferably, the premixing is vacuum premixing or premixing under conditions where the dew point is ≤-30℃ (e.g., -30℃, -35℃, -40℃, -45℃, or -50℃, etc.). In this preferred technical solution, the positive electrode active material particles and oxide solid electrolyte particles are first vacuum premixed or premixed under conditions where the dew point is ≤-30℃. The purpose is to ensure that the two are uniformly dispersed and to guarantee the stability of the ternary positive electrode active material and the oxide solid electrolyte. For example, under conditions where the dew point is ≥0℃, Li 7-x7 La3Zr 2-x7 O 12 (0≤x7<1) It is prone to side reactions with water, which can lead to product structure damage and performance degradation.

[0039] Preferably, the premixing and mixing processes are carried out in a ball mill or a mixer.

[0040] Preferably, the premixing and mixing are carried out using a rotary mixer with a rotation speed ≥20 rpm, such as 20 rpm, 30 rpm, 40 rpm, 50 rpm, 60 rpm, 70 rpm, 80 rpm, 85 rpm or 100 rpm, etc., and preferably 30-90 rpm; and a rotation speed ≥200 rpm, such as 200 rpm, 300 rpm, 400 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1300 rpm, 1500 rpm, 1750 rpm, 2000 rpm, 2200 rpm, 2500 rpm or 3000 rpm, etc., and preferably 500-2000 rpm.

[0041] Preferably, the premixing time is 0.5-4h, such as 0.5h, 1h, 1.5h, 2h, 3h or 4h, and preferably 1-2h.

[0042] Preferably, the dew point is ≤-45℃, and more preferably ≤-60℃.

[0043] To ensure good dispersibility and structural stability of the oxide solid electrolyte, effectively block contact between ternary cathode active material particles, and improve the thermal stability of the cathode sheet, the above-mentioned revolution speed, rotation speed, and dew point conditions are preferred.

[0044] As a further preferred embodiment of the method described in this invention, the method includes the following steps:

[0045] S1: The ternary positive electrode active material particles and oxide solid electrolyte particles are vacuum premixed in a rotary mixer with a rotation speed of 30-90 rpm and a rotation speed of 500-2000 rpm. The premixing time is 0.5-4 h to obtain a uniformly mixed premixed material.

[0046] S2: Gradually add the uniformly mixed adhesive to the uniformly mixed premixed material described in S1, with a revolution speed of 30-90 rpm and a rotation speed of 500-2000 rpm, to obtain a uniformly mixed slurry.

[0047] S3: Gradually add conductive agent to the uniformly mixed slurry described in S2, with an orbital speed of 30-90 rpm and a rotational speed of 500-2000 rpm, and finally obtain a uniformly mixed ternary cathode slurry;

[0048] S4: Coat the slurry described in S3 onto the current collector, controlling the electrode surface capacity to be ≥4mAh / cm². 2 After drying, rolling, and die-cutting, high-safety, high-capacity ternary cathode electrode sheets are obtained.

[0049] Thirdly, the present invention provides a method for improving the safety of lithium batteries, the method comprising, during the preparation of the positive electrode sheet, adding oxide solid electrolyte particles with a particle size D50 of 0.1-3 μm and dispersing them among the positive electrode active material particles, wherein the areal capacity of the positive electrode sheet is ≥4 mAh / cm². 2 .

[0050] The present invention also provides a positive electrode obtained by a third aspect of the method.

[0051] Fourthly, the present invention provides a lithium battery, the lithium battery comprising the positive electrode sheet described in the first aspect.

[0052] Preferably, the lithium battery includes a liquid lithium battery or a semi-solid lithium battery.

[0053] Preferably, the liquid lithium battery includes the positive electrode, negative electrode, and liquid electrolyte (also known as electrolyte solution) described in the first aspect.

[0054] Preferably, the semi-solid lithium battery includes the positive electrode, the negative electrode, and the electrolyte layer containing liquid electrolyte as described in the first aspect.

[0055] Compared with existing technologies, the present invention has the following beneficial effects:

[0056] This invention achieves a positive electrode sheet with an areal capacity ≥4 mAh / cm² by adding an oxide solid electrolyte with a particle size D50 of 0.1-3 μm, in combination with a conductive agent and a binder.2 The positive electrode sheet of this invention can significantly improve battery safety while ensuring high electrode capacity and long cycle performance. Its technical principle is as follows: First, oxide solid electrolyte particles have a certain ion transport capability and can effectively block contact between ternary positive electrode active material particles, thus improving the thermal stability of the positive electrode while ensuring ion transport. Second, oxide solid electrolyte itself has a certain heat capacity, which can absorb some of the heat generated by the positive electrode and alleviate overheating. Third, the oxide solid electrolyte is directly mixed into the positive electrode material without affecting the electrochemical performance of the positive electrode active particles themselves. In contrast, if the positive electrode active particles are modified by coating them with oxide electrolyte, the coating layer will hinder the ion and electron transport of the positive electrode active particles, affecting the overall performance of the battery. Furthermore, the oxide solid electrolyte has high chemical stability and can be directly mixed into the positive electrode active material before electrode preparation. The positive electrode sheet provided by this invention is compatible with the mainstream preparation process of existing lithium-ion battery positive electrode sheets, does not affect the preparation process of the positive electrode and the battery cell, has low cost for large-scale production, and is suitable for large-scale applications.

[0057] The lithium battery assembled based on the positive electrode sheet described in this invention has the characteristics of high capacity, high safety, and long cycle life, and the battery can successfully pass the nail penetration test. A preferred embodiment of the positive electrode sheet of this invention can also achieve high specific energy (generally referring to a battery mass specific energy ≥ 260Wh / Kg) while possessing the above-mentioned effects. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the internal structure of the positive electrode material layer in the ternary electrode sheet of the present invention, which is doped with oxide solid electrolyte, wherein 1-oxide solid electrolyte, 2-ternary positive electrode active material, and 3-conductive agent;

[0059] Figure 2 Image of the battery after the nail penetration test (Comparative Example 1);

[0060] Figure 3 The image shows the battery after the needle penetration test in Example 1. Detailed Implementation

[0061] To further illustrate the present invention, the positive electrode sheet provided by the present invention will be described in detail below with reference to the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0062] I. Preparation of ternary electrode sheets for oxide-doped solid electrolytes

[0063] The ternary cathode active material, oxide solid electrolyte, conductive agent, and binder are weighed according to the proportions listed in Table 1 for C1-C22 and C25-C30. First, the ternary cathode active material and oxide solid electrolyte are premixed under vacuum to obtain a uniformly dispersed premixed material. PVDF NMP adhesive is gradually added to the uniformly dispersed premixed material. After mixing evenly, conductive agents Super-P and CNT are gradually added and mixed evenly to obtain a ternary cathode slurry with a certain fluidity. Then, it is coated on aluminum foil, dried by blowing air, and rolled to obtain cathode sheets named C1, C2...C22, and C25-C30, respectively.

[0064] The conductive agent is carbon nanotubes and conductive carbon black (CNT+Super-P, with a mass ratio of carbon nanotubes to conductive carbon black of 1:2), and the binder is polyvinylidene fluoride (PVDF).

[0065] See the schematic diagram of the internal structure of the positive electrode material layer in the ternary electrode sheet of the oxide-doped solid electrolyte. Figure 1 .

[0066] II. Preparation of Ternary Electrode Sheets for Undoped Oxide Solid Electrolytes

[0067] The ternary cathode active material, conductive agent, and binder were weighed according to the proportions listed in Table 1 for C23 and C24. PVDF NMP adhesive was gradually added to the ternary cathode active material. After thorough mixing, conductive agent Super-P and CNT (CNT and conductive carbon black Super-P in a mass ratio of 1:2) were gradually added and mixed thoroughly to obtain a ternary cathode slurry with a certain fluidity. Then, it was coated onto aluminum foil, dried by blowing air, and rolled to obtain cathode sheets named C23 and C24, respectively.

[0068] The types of conductive agents and binders are the same as in Example 1, except that the pre-vacuum premixing step is not performed, and the other operations are the same as in Example 1.

[0069] Table 1. Parameters of high-safety, high-capacity ternary electrode sheets

[0070]

[0071]

[0072] Note: α is the ratio of D50 of the ternary cathode material to D50 of the oxide solid electrolyte.

[0073] The ratio is the mass ratio of ternary cathode active material, oxide solid electrolyte, conductive agent, and binder.

[0074] The oxide solid electrolyte is Li 1.4Al 0.4 Ti 1.6 (PO4)3 (abbreviated as LATP-1), Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (abbreviated as LATP-2), Li 1.5 Al 0.5 Ti 1.5 (PO4)3 (abbreviated as LATP-3), Li 6.4 La3Zr 1.6 Ta 0.6 O 12 (abbreviated as LLZO-1), Li7La3Zr2O 12 (abbreviated as LLZO-2), Li 1.5 Al 0.5 Ge 1.5 (PO4)3 (abbreviated as LAGP-1), Li 1.3 Al 0.3 Ge 1.7 (PO4)3 (abbreviated as LAGP-2), Li 0.5 La 0.5 TiO3 (abbreviated as LLTO-1), Li 0.34 La 0.56 TiO3 (abbreviated as LLTO-2), Li3OCl (abbreviated as LOC), Li 3 / 8 Sr 7 / 16 Ta 3 / 4 Zr 1 / 4 O3 (abbreviated as LSTZ), Li 14 ZnGe4O 16 (abbreviated as LZGO).

[0075] The ternary cathode material is LiNi. 0.8 Co 0.1 Mn 0.1 O2 (abbreviated as Ni80), LiNi 0.83 Co 0.12 Mn 0.05 O2 (abbreviated as Ni83), LiNi 0.88 Co 0.09 Mn 0.03 O2 (abbreviated as Ni88), LiNi 0.8 Co 0.15 Al 0.05 O2 (abbreviated as NCA).

[0076] III. Preparation of the negative electrode

[0077] In this invention, the negative electrode is commonly made of graphite, silicon-carbon, silicon-oxygen-carbon, soft / hard carbon, mesophase carbon microspheres, or composite lithium metal. This invention does not impose requirements on the negative electrode; the areal capacity only needs to match the positive electrode when preparing the battery cell.

[0078] More specifically, the active material, conductive agent, and binder of the negative electrode are added to deionized water at a mass ratio of 96:2:2 and mixed evenly to obtain a negative electrode slurry with a certain fluidity. This slurry is then coated onto copper foil, dried by blowing air, and rolled to obtain negative electrode sheets, named A1, A2, ... A5. The conductive agent is a mixture of carbon nanotubes (CNTs) and conductive carbon black Super-P at a mass ratio of 1:2, and the binder is a mixture of CMC and SBR at a mass ratio of 1:1.

[0079] Table 2 Parameters of negative electrode

[0080]

[0081] The silicon-carbon material used is the SL450A-SOC nano silicon-carbon anode material from Liyang Tianmu Pioneer Battery Materials Technology Co., Ltd., and the silicon-oxygen-carbon material is the S450-2A silicon-oxygen-carbon anode material from BTR New Energy Materials Co., Ltd.

[0082] IV. Cell Manufacturing

[0083] A 15Ah soft-pack battery cell was prepared according to the data listed in Table 3. The electrode dimensions are: positive electrode 107mm*83mm and negative electrode 109mm*85mm.

[0084] Table 3 Cell Parameters

[0085]

[0086]

[0087]

[0088] Examples 1-20 and 23-28 are liquid lithium batteries using a double-sided ceramic separator and a commercially available electrolyte. Specifically, Comparative Examples 1-4 and Examples 1-20 have an electrolyte composition of 1 mol / L LiPF6-EC / DEC (3:7, V / V) + 2 wt% VC + 1 wt% LiDFOB; Examples 23-25 ​​have an electrolyte composition of 1.2 mol / L LiPF6-EC / EMC (3:7, V / V) + 2 wt% FEC + 1 wt% LiDFOB; Examples 26-28 have an electrolyte composition of 1.2 mol / L LiPF6-EC / DEC (3:7, V / V) + 2 wt% FEC + 1 wt% LiDFOB + 1 wt% 1,3-PS; Examples 21-22 are semi-solid lithium batteries using a PVDF-HFP based gel polymer electrolyte membrane and an electrolyte composition of 1 mol / L LiPF6-EC / DEC. LiPF6-EC / DEC(3:7,V / V)+2wt%VC+1wt%LiDFOB.

[0089] V. Battery Performance Testing

[0090] The resistance, capacity retention after 100 cycles, and capacity retention after 1000 cycles of the lithium batteries prepared in Examples 1-28 and Comparative Examples 1-4 were tested, and the results are shown in Table 4. Test voltage range: 2.75-4.2V, charge / discharge current: 1C / 1C.

[0091] Table 4. Electrical performance of lithium batteries

[0092]

[0093]

[0094] This invention improves battery safety by incorporating oxide solid electrolyte into a high-nickel ternary cathode. A comparison of Comparative Examples 1-2 and Examples 1-28 shows that the battery prepared using this invention has minimal impact on battery performance. This is mainly because oxide solid electrolyte particles themselves possess a certain ionic conductivity. Within the solid electrolyte content range described in this invention, the introduction of oxide solid electrolyte does not significantly hinder ion transport in the cathode. Furthermore, the endothermic effect of oxide solid electrolyte lowers the average temperature of the cathode active material during charge and discharge, reducing side reactions of the ternary cathode active material at high temperatures, thus contributing to long-cycle performance. However, if the particle size of the incorporated oxide solid electrolyte is too small, or if the amount incorporated is too large, it will increase the battery's internal resistance and reduce its energy density.

[0095] VI. Cell Needle Penetration Safety Test

[0096] The lithium batteries prepared in Examples 1-28 and Comparative Examples 1-4 were subjected to nail penetration safety tests in accordance with the safety requirements and test methods for power batteries for electric vehicles in the standard GB / T 31485-2015.

[0097] Needle penetration test: The battery is charged at 1C constant current and constant voltage with a cutoff current of 0.05C. A φ5mm high-temperature resistant steel needle is used to penetrate the battery from a direction perpendicular to the battery plates at a speed of 25±5mm / s. The penetration position should be close to the geometric center of the punctured surface. The steel needle remains in the battery. Observe for 30 minutes and monitor the change in cell surface temperature during the process. Record whether the cell catches fire or explodes. The results are shown in Table 5.

[0098] Table 5 Record of Cell Puncture Results

[0099]

[0100]

[0101] This invention improves battery safety by incorporating an oxide solid electrolyte into a high-nickel ternary cathode material. Comparisons of Comparative Examples 1-2 and Examples 1-5, 7-11, 13-14, and 16-28 show that the battery prepared using this invention does not catch fire or explode upon needle penetration, with a cell surface temperature of 41.3-57.6°C during the penetration test, thus improving battery safety. In contrast, the cathode materials in Comparative Examples 1-2, which do not contain an oxide solid electrolyte, result in batteries that catch fire and explode upon needle penetration, experiencing thermal runaway, with a maximum cell surface temperature reaching 793.7°C. This is primarily because the addition of the oxide solid electrolyte to the ternary cathode active material effectively blocks contact between the ternary active particles, improving the material's thermal stability. Secondly, the oxide solid electrolyte of this invention itself has a certain heat capacity, which can absorb some of the heat generated by the cathode, alleviating overheating.

[0102] As shown in Comparative Examples 3-4 and Examples 1-5, although oxide solid electrolytes were added in Comparative Examples 3-4, the particle size of the oxide solid electrolytes was too small, which hindered electron transport, increased interfacial impedance, and reduced the energy density of the battery; the particle size of the oxide solid electrolytes was too large, resulting in ineffective isolation between the positive electrode particles and thus minimal improvement in safety, making it unable to pass the needle penetration test. Therefore, it can be concluded that neither too small nor too large particle size of the positive electrode mix can achieve the effect of improving safety while ensuring battery energy density.

[0103] As can be seen from Examples 3 and 6-11, although an oxide solid electrolyte was added to the positive electrode in Example 6, the amount of oxide solid electrolyte was too small, resulting in insignificant heat absorption and insulation effects, and thus little improvement in safety, failing to pass the needle penetration test. In Example 11, an oxide solid electrolyte was added to the positive electrode, and although it passed the needle penetration test, the excessive amount would reduce the battery's energy density. Therefore, it is clear that neither too little nor too much oxide electrolyte in the positive electrode can achieve the effect of ensuring battery energy density while simultaneously improving safety.

[0104] Although an oxide solid electrolyte was added in Example 12, with a particle size D50 within the preferred range of 0.1-3 μm and an addition amount within the preferred range of 0.1-10%, the ratio of D50 of the ternary cathode material to D50 of the oxide solid electrolyte was less than 5. That is, the particle sizes of the two were relatively close. As a result, within this particle size and content range, the amount of oxide solid electrolyte was insufficient to block the contact between the ternary cathode active material particles, resulting in poor safety performance and thus failing the needle penetration test. However, its surface temperature was lower than that of the cells in Comparative Examples 1-2, indicating that the oxide solid electrolyte can reduce the energy during thermal runaway to a certain extent.

[0105] Although an oxide solid electrolyte was added in Example 15, with a particle size D50 within the preferred range of 0.1-3 μm and an addition amount within the preferred range of 0.1-10%, and the ratio of D50 of the ternary cathode material to D50 of the oxide solid electrolyte was greater than 5, the premixing speed was too low, resulting in poor dispersion and easy agglomeration between particles, leading to poor safety and thus failing to pass the needle penetration test. However, its cell surface temperature was lower than that of Comparative Examples 1-2, indicating that the oxide solid electrolyte can reduce the energy during thermal runaway to a certain extent.

[0106] Examples 3, 18-20, and 23-28 show that doping with different oxide solid electrolytes improves the safety performance of the battery to a certain extent, with LATP showing the best improvement. Examples 3, 24-25, 16, 27, 17, 26, 19, and 28 show that for each electrolyte, the electrolyte composition has little impact on battery safety, and the batteries can all pass the nail penetration test smoothly.

[0107] Examples 23-28 demonstrate that the positive electrode sheet provided by the present invention, when used in conjunction with conventional commercial electrolyte, can improve the safety of the battery cell, enabling the battery cell to pass the nail penetration test smoothly.

[0108] VII. Safety Test of Battery Cells in 180℃ Hot Box

[0109] The battery was charged at a constant current and constant voltage of 1C with a cutoff current of 0.05C; heated to 180℃ for 2 hours with a heating rate of 5℃ / mm, held at 180℃ for 2 hours, and observed for 1 hour; "no fire or explosion" was recorded as passing, otherwise it failed, and the change in cell surface temperature was monitored during the process. The test results are shown in Table 6.

[0110] Table 6. Record of Safety Results of Battery Cells in 180℃ Hot Box

[0111]

[0112]

[0113] This invention improves battery safety by incorporating an oxide solid electrolyte into a high-nickel ternary cathode material. Comparative Examples 1-2 and Examples 1-5, 7-10, 13-14, and 16-28 show that batteries prepared using this invention exhibit cell surface temperatures of 181.4-188.7°C and weight loss rates of 15.1%-27.1% during 180°C hot-box testing, without ignition or explosion. In contrast, batteries prepared using the cathode material of Comparative Examples 1-2, which did not contain the oxide solid electrolyte, experienced thermal runaway, with surface temperatures reaching a maximum of 560.8°C. This is primarily because the addition of the oxide solid electrolyte to the ternary cathode active material effectively blocks contact between ternary active particles, improving material thermal stability. Secondly, the oxide solid electrolyte of this invention possesses a certain heat capacity, absorbing some of the heat generated by the cathode and mitigating overheating. Therefore, the batteries successfully pass the 180°C hot-box test.

[0114] As shown in Comparative Examples 3-4 and Examples 1-5, although oxide solid electrolytes were added in Comparative Examples 3-4, the particle size of the oxide solid electrolytes was too small, which hindered electron transport, increased interfacial impedance, and reduced the energy density of the battery; conversely, the particle size of the oxide solid electrolytes was too large, resulting in insufficient isolation between the positive electrode particles and thus only a minor improvement in safety, preventing the battery from passing the 180°C hot box test. Therefore, it can be concluded that neither excessively small nor excessively large particle size in the positive electrode mixing can achieve the effect of improving safety while maintaining battery energy density.

[0115] As can be seen from Examples 3 and 6-11, although oxide solid electrolyte was added to the positive electrode in Example 6, the amount of oxide solid electrolyte mixed in too little or too much could not achieve a good effect on improving safety. If the amount of oxide solid electrolyte mixed in too little, the heat absorption and heat insulation effect of the solid electrolyte would not be obvious, and the improvement on safety would not be significant. In Example 11, oxide solid electrolyte was added to the positive electrode, and although it passed the 180°C hot box test, the amount mixed in too much would reduce the energy density of the battery.

[0116] Although an oxide solid electrolyte was added in Example 12, with a particle size D50 within the preferred range of 0.1-3 μm and an addition amount within the preferred range of 0.1-10%, the ratio of D50 of the ternary cathode material to D50 of the oxide solid electrolyte was less than 5. That is, the particle sizes of the two were relatively close. As a result, within this particle size and content range, the amount of oxide solid electrolyte was insufficient to block the contact between the ternary cathode active material particles, resulting in poor safety performance and thus failing the 180°C hot box test. However, its surface temperature was lower than that of the cells in Comparative Examples 1-2, indicating that the oxide solid electrolyte can reduce the energy during thermal runaway to a certain extent.

[0117] Although Example 15 added an oxide solid electrolyte with a particle size D50 within the preferred range of 0.1-3 μm and an addition amount within the preferred range of 0.1-10%, and the ratio of D50 of the ternary cathode material to D50 of the oxide solid electrolyte was greater than 5, the premixing speed was too low, resulting in poor dispersion and easy particle agglomeration, leading to poor safety and thus failing the 180°C hot box test. However, its cell surface temperature was lower than that of Comparative Examples 1-2, indicating that the oxide solid electrolyte can reduce the energy during thermal runaway to some extent.

[0118] In the embodiments provided by this invention, the ternary cathode material LiNi is used. x Co y M 1-x-y The nickel content x of O2 is 0.80, 0.83 or 0.88. The higher the nickel content of the high-nickel ternary cathode material, the worse its thermal stability. As can be seen from Examples 17 and 18, the cathode sheet provided by the present invention can still pass the hot box test smoothly when the nickel content is high (x = 0.88). For cathode active materials with low Ni content (x = 0.6-0.8), the cathode sheet provided by the present invention can also ensure good safety.

[0119] Examples 3, 18-20, and 23-28 show that doping different oxide solid electrolytes improves the safety performance of the battery to a certain extent, with LATP showing the best improvement. Examples 3, 24-25, 16, 27, 17, 26, 19, and 28 show that for each electrolyte, the electrolyte composition has little impact on battery safety.

[0120] Examples 23-28 demonstrate that the positive electrode sheet provided by the present invention, when used with conventional commercial electrolyte, can improve the safety of the battery cell, enabling the battery cell to pass the hot box test smoothly.

[0121] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A ternary cathode sheet for lithium batteries, characterized in that, The lithium battery includes a liquid lithium battery or a semi-solid lithium battery. The positive electrode sheet includes a current collector and a positive electrode material layer located on the surface of the current collector. The positive electrode material layer includes ternary positive electrode active material particles, a conductive agent, a binder, and oxide solid electrolyte particles capable of conducting lithium ions. The areal capacity of the positive electrode is ≥4mAh / cm². 2 The particle size D50 of the oxide solid electrolyte particles is 0.1-3 μm; Based on the total mass of ternary cathode active material particles, conductive agent, binder, and oxide solid electrolyte particles as 100%, the content of the oxide solid electrolyte is 0.1-10%; The ratio α of the ternary cathode material D50 to the oxide solid electrolyte D50 is ≥5; the ternary cathode sheet for the lithium battery is prepared by the following method: S1: Premix the positive electrode active material particles and oxide solid electrolyte particles to obtain a premixed material, wherein the positive electrode active material particles include ternary positive electrode active material particles; S2: Add the adhesive solution of the binder to the premixed material, mix, and obtain a primary slurry; S3: Add a conductive agent to the primary slurry and mix to obtain a secondary slurry; S4: Coat the secondary slurry onto the current collector, controlling the electrode surface capacity to be ≥4mAh / cm². 2 After baking and rolling, the positive electrode sheet is obtained.

2. The positive electrode sheet according to claim 1, characterized in that, The particle size D50 of the oxide solid electrolyte particles is 0.5-2 μm.

3. The positive electrode sheet according to claim 1, characterized in that, The content of the ternary cathode active material particles is 80-98%, based on the total mass of the ternary cathode active material particles, conductive agent, binder and oxide solid electrolyte particles as 100%.

4. The positive electrode sheet according to claim 1, characterized in that, The content of the oxide solid electrolyte is 1-5%, based on the total mass of the ternary cathode active material particles, conductive agent, binder and oxide solid electrolyte particles as 100%.

5. The positive electrode sheet according to claim 1, characterized in that, The content of the conductive agent is 0.1-8%, based on the total mass of the ternary positive electrode active material particles, conductive agent, binder and oxide solid electrolyte particles as 100%.

6. The positive electrode sheet according to claim 1, characterized in that, The content of the binder is 0.1-10%, based on the total mass of ternary cathode active material particles, conductive agent, binder and oxide solid electrolyte particles as 100%.

7. The positive electrode sheet according to claim 1, characterized in that, Said oxide solid electrolyte particles comprise any one or a combination of at least two of the following compounds: Li with NASICON structure 1+x1 Al x1 Ge2-x1(PO4)3 or an isomorphous heteroatom-doped compound thereof, Li 1+x2 Al x2 Ti 2-x2 (PO4)3 or an isomorphous heteroatom-doped compound thereof, Li with perovskite structure 3x3 La 2 / 3-x3 TiO3 or an isomorphous heteroatom-doped compound thereof, Li 3 / 8 Sr 7 / 16 Ta 3 / 4 Hf 1 / 4 O3 or an isomorphous heteroatom-doped compound thereof, Li 2x4-y1 Sr 1-x4 Ta y1 Zr 1-y1 O3 or an isomorphous heteroatom-doped compound thereof, Li with anti-perovskite structure 3- 2x5 M x5 HalO, Li3OCl or an isomorphous heteroatom-doped compound thereof, Li with LISICON structure 4-x6 Si 1-x6 P x6 O4 or an isomorphous heteroatom-doped compound thereof, Li 14 ZnGe4O 16 or an isomorphous heteroatom-doped compound thereof, Li with garnet structure 7- x7 La3Zr 2-x7 O 12 or an isomorphous heteroatom-doped compound thereof, wherein 0<x1≤0.75, 0<x2≤0.5, 0.06≤x3≤0.14, 0.25≤y1≤1, x4=0.75y1, 0≤x5≤0.01, 0.5≤x6≤0.6; 0≤x7<1; wherein M comprises Mg 2+ , Ca 2 + , Sr 2+ or Ba 2+ any one or a combination of at least two of the above, and Hal is the element Cl or I.

8. The positive electrode sheet according to claim 1, characterized in that, The oxide solid electrolyte particles include Li 1+ x2 Al x2 T i2-x2 (PO4)3 and / or Li 7-x7 La3Zr 2-x7 O 12 .

9. The positive electrode sheet according to claim 1, characterized in that, The oxide solid electrolyte particles are Li 1+ x2 Al x2 Ti 2-x2 (PO4)3.

10. The positive electrode sheet according to claim 1, characterized in that, The ternary cathode active material particles include lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

11. The positive electrode sheet according to claim 1, characterized in that, The chemical composition of the ternary cathode active material particles is LiNi x Co y M 1-x-y O2, M is at least one of Mn or Al, and x ≥ 0.

6.

12. The positive electrode sheet according to claim 1, characterized in that, The conductive agent includes any one or a combination of at least two of Super-P, KS-6, carbon black, carbon nanofibers, CNT, acetylene black, or graphene.

13. The positive electrode sheet according to claim 12, characterized in that, The conductive agent is a combination of carbon nanotubes and Super-P.

14. The positive electrode sheet according to claim 1, characterized in that, The adhesive includes any one or a combination of at least two of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyethylene oxide, and polytetrafluoroethylene.

15. The method for preparing the positive electrode sheet according to any one of claims 1-14, characterized in that, The method includes the following steps: S1: Premix the positive electrode active material particles and oxide solid electrolyte particles to obtain a premixed material, wherein the positive electrode active material particles include ternary positive electrode active material particles; S2: Add the adhesive solution of the binder to the premixed material, mix, and obtain a primary slurry; S3: Add a conductive agent to the primary slurry and mix to obtain a secondary slurry; S4: Coat the secondary slurry onto the current collector, controlling the electrode surface capacity to be ≥4mAh / cm². 2 After baking and rolling, the positive electrode sheet is obtained.

16. The method according to claim 15, characterized in that, The premixing is performed under vacuum premixing or under conditions where the dew point is ≤-30℃.

17. The method according to claim 15, characterized in that, The premixing and mixing processes are carried out in a ball mill or a mixer.

18. The method according to claim 15, characterized in that, The premixing and mixing are carried out using a rotary mixer with a rotation speed of ≥20 rpm.

19. The method according to claim 18, characterized in that, The premixing and mixing are carried out using a rotary mixer with a rotation speed of 30-90 rpm.

20. The method according to claim 18, characterized in that, The premixing and mixing are carried out using a rotary mixer with a rotation speed of ≥200 rpm.

21. The method according to claim 20, characterized in that, The premixing and mixing are carried out using a rotary mixer with a rotation speed of 500-2000 rpm.

22. The method according to claim 15, characterized in that, The premixing time is 0.5-4 hours.

23. The method according to claim 22, characterized in that, The premixing time is 1-2 hours.

24. The method according to claim 16, characterized in that, The dew point is ≤-45℃.

25. The method according to claim 24, characterized in that, The dew point is ≤-60℃.

26. A method for improving the safety of lithium batteries, characterized in that, The method includes adding oxide solid electrolyte particles with a particle size D50 of 0.1-3 μm during the preparation of the positive electrode sheet, and dispersing them between the positive electrode active material particles. The areal capacity of the positive electrode sheet is ≥4 mAh / cm². 2 ; The positive electrode is the positive electrode as described in any one of claims 1 to 14.

27. A lithium battery, characterized in that, The lithium battery includes the positive electrode sheet as described in any one of claims 1-14.

28. The lithium battery according to claim 27, characterized in that, The lithium battery includes liquid lithium battery or semi-solid lithium battery.

29. The lithium battery according to claim 28, characterized in that, The liquid lithium battery includes the positive electrode, negative electrode, and liquid electrolyte as described in any one of claims 1-14.

30. The lithium battery according to claim 27, characterized in that, The semi-solid lithium battery includes a positive electrode, a negative electrode, and an electrolyte layer containing liquid electrolyte as described in any one of claims 1-14.

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