A lithium ion secondary battery

Abstract

This application relates to the field of secondary battery technology and discloses a lithium-ion secondary battery. The positive electrode active layer comprises lithium aluminum titanium phosphate, and the negative electrode active layer comprises lithium lanthanum titanate. The mass content p of La in the positive electrode active layer is greater than the mass content q of La in the negative electrode active layer. The lithium aluminum titanium phosphate comprises at least one element selected from La, Sc, and Y, and at least one element selected from Si, Zr, and Ce. The lithium lanthanum titanate comprises at least one element selected from Al, Sc, and Y, and at least one element selected from Si, Zr, and Ce. This application introduces a titanium-containing solid electrolyte with specific elements into the active layer of the lithium-ion secondary battery, and controls the La content in the positive electrode active layer to be higher than the La content in the negative electrode active layer, thereby achieving excellent coulombic efficiency, cycle stability, safety, and rate performance of the secondary battery during high-voltage operation.

Description

Technical Field

[0001] This application relates to the field of secondary batteries, specifically to a lithium-ion secondary battery. Background Technology

[0002] Increasing the voltage window of the positive electrode material and introducing high-capacity silicon materials into the negative electrode material of lithium-ion rechargeable batteries can significantly improve the energy density of lithium batteries, and these are currently the mainstream methods for improving battery energy density. However, at high voltages (4.5V and above), lithium-containing materials are prone to irreversible phase transitions, transition metal dissolution, and lattice oxygen release, leading to a decrease in the cycle life of the rechargeable battery. Simultaneously, during the charge and discharge process of the rechargeable battery at high voltages, the positive electrode material and electrolyte are prone to side reactions, with increased exothermic reactions that can easily trigger thermal runaway, requiring more stringent safety designs. Introducing silicon anode materials into the negative electrode sheet, however, causes repeated expansion and contraction of silicon particles during the charge and discharge process, leading to pulverization and shedding of the active material, rapid capacity decay, and repeated rupture and regeneration of the solid electrolyte interphase (SEI) film during battery operation, continuously consuming electrolyte and lithium source, and reducing coulombic efficiency. Therefore, current lithium-ion rechargeable battery technology struggles to simultaneously improve battery energy density, cycle performance, and safety. Summary of the Invention

[0003] In view of this, this application provides a lithium-ion secondary battery to solve the problem that existing lithium-ion secondary batteries cannot simultaneously meet the requirements of high energy density, excellent cycle performance and safety.

[0004] According to an embodiment of this application, in a first aspect, this application provides a lithium-ion secondary battery, including a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet includes a positive current collector and a positive active layer on at least one side surface of the positive current collector, and the negative electrode sheet includes a negative current collector and a negative active layer on at least one side surface of the negative current collector. The positive electrode active layer includes a positive electrode active material and a first solid electrolyte, the first solid electrolyte including lithium aluminum titanium phosphate, the positive electrode active layer also includes La element, and the mass content of La element in the positive electrode active layer is p; The negative electrode active layer includes a negative electrode active material and a second solid electrolyte; the second solid electrolyte includes lithium lanthanum titanate, and the mass content of La element in the negative electrode active layer is q, satisfying: p > q; The lithium aluminum titanium phosphate further includes a first element and a second element, wherein the first element includes at least one of La, Sc, and Y, and the second element includes at least one of Si, Zr, and Ce; and / or, the lithium lanthanum titanate further includes a third element and a fourth element, wherein the third element includes at least one of Al, Sc, and Y, and the fourth element includes at least one of Si, Zr, and Ce.

[0005] In an optional embodiment, the mass content p of La element in the positive electrode active layer satisfies: 0.015% ≤ p ≤ 4.2%.

[0006] Furthermore, in an optional embodiment, the mass content p of La element in the positive electrode active layer satisfies: 0.02% ≤ p ≤ 4%.

[0007] In an optional embodiment, the mass content of Ti element in the positive electrode active layer is s, which satisfies: 0.07%≤s≤2%.

[0008] Furthermore, in an optional embodiment, the ratio of the mass content s of Ti element in the positive electrode active layer to the mass content p of La element in the positive electrode active layer satisfies: 0.1≤s / p≤4.5.

[0009] In an optional embodiment, the mass content q of La element in the negative electrode active layer satisfies: 0.009% ≤ q ≤ 3.3%.

[0010] Furthermore, in an optional embodiment, the mass content q of La element in the negative electrode active layer satisfies: 0.01% ≤ q ≤ 3%.

[0011] In one optional embodiment, the mass content of Ti element in the negative electrode active layer is t, which satisfies: 0.01%≤t≤2%.

[0012] Furthermore, in an optional embodiment, the ratio of the mass content t of Ti element in the negative electrode active layer to the mass content q of La element in the negative electrode active layer satisfies: 0.5≤t / q≤1.8.

[0013] In an optional embodiment, the average particle size of the first solid electrolyte is denoted as D1, and the average particle size of the second solid electrolyte is denoted as D2, satisfying: 100 nm ≤ D1 ≤ 2000 nm, 150 nm ≤ D2 ≤ 1000 nm, and 0.2 ≤ D1 / D2 ≤ 5.

[0014] Further, in an optional embodiment, the average particle size of the positive electrode active material is denoted as Z, which satisfies: 0.005≤D1 / Z≤0.1, 1000 nm≤Z≤50000 nm.

[0015] Furthermore, in an alternative implementation, the following condition is satisfied: 0.02 < D1 / Z < 0.06.

[0016] Further, in an optional embodiment, the average particle size of the negative electrode active material is denoted as F, satisfying: 0.002≤D2 / F≤0.6, 1000 nm≤F≤100000 nm.

[0017] Furthermore, in an alternative implementation, the following condition is satisfied: 0.04 < D2 / F < 0.1.

[0018] In an optional embodiment, the positive electrode active material includes a positive electrode active matrix material and a coating layer covering at least a portion of the surface of the positive electrode active matrix material, the coating layer including a third solid electrolyte, the third solid electrolyte including lithium aluminum titanium phosphate; The average particle size of the third solid electrolyte is denoted as D3, which satisfies the following conditions: 2 nm ≤ D3 < 100 nm, and D3 < D1.

[0019] Furthermore, in an optional embodiment, the positive electrode active substrate material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based material, and lithium iron phosphate material.

[0020] Furthermore, in an optional embodiment, the positive electrode active matrix material further includes La element, and the mass content of La element is 0.01% to 3% based on the total mass of the positive electrode active matrix material.

[0021] In one optional embodiment, the total mass content of lithium aluminum titanium phosphate is 0.05% to 15% based on the total mass of the positive electrode active layer.

[0022] Optionally, in one optional embodiment, the mass ratio of the first solid electrolyte to the third solid electrolyte is (0.75~80):1.

[0023] Furthermore, in an optional embodiment, the mass ratio of the first solid electrolyte to the third solid electrolyte is (1~60):1.

[0024] In one optional embodiment, the mass content of lithium lanthanum titanate is 0.04% to 7.5% based on the total mass of the negative electrode active layer.

[0025] In an optional embodiment, the X-ray diffraction pattern of the lithium aluminum titanium phosphate in the first solid electrolyte independently includes a (104) characteristic peak, a (113) characteristic peak, and a (024) characteristic peak, with the diffraction angle 2θ of each characteristic peak ranging from 20°≤2θ(104)≤22°, 23°≤2θ(113)≤25°, and 28.5°≤2θ(024)≤30.5°.

[0026] Further, in an optional embodiment, the peak intensity of the (104) characteristic peak is K1, the peak intensity of the (113) characteristic peak is K2, and the peak intensity of the (024) characteristic peak is K3, satisfying: 0.45≤K1 / K2≤0.75, 1.2≤K2 / K3≤3.5, K2>K1>K3.

[0027] In an optional embodiment, the X-ray diffraction pattern of the lithium lanthanum titanate in the negative electrode active layer independently includes a (102) characteristic peak, a (004) characteristic peak, and a (114) characteristic peak, with the diffraction angle 2θ of each characteristic peak ranging from 31.5°≤2θ(102)≤33.5°, 46.5°≤2θ(004)≤48.5°, and 57.5°≤2θ(114)≤59.5°.

[0028] Further, in an optional embodiment, the peak intensity of the (102) characteristic peak is K4, the peak intensity of the (004) characteristic peak is K5, and the peak intensity of the (114) characteristic peak is K6, satisfying: 2.5 < K4 / K5 < 4, 1 < K5 / K6 < 1.5, K4 > K5 > K6.

[0029] In an optional embodiment, the positive electrode active layer further includes a positive electrode conductive agent, which includes multi-walled carbon nanotubes.

[0030] In one optional embodiment, the negative electrode active material includes a silicon-based material, which includes at least one of silicon-oxygen materials, silicon nanoparticles, and silicon-carbon materials.

[0031] In an optional embodiment, the negative electrode active layer further includes a negative electrode conductive agent, which includes single-walled carbon nanotubes.

[0032] In one optional embodiment, the charging cutoff voltage of the lithium-ion secondary battery is ≥4.5V.

[0033] The technical solution of this application has the following advantages: 1. This application provides a lithium-ion secondary battery, comprising a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive active layer on at least one side of the surface of the positive current collector. The negative electrode includes a negative current collector and a negative active layer on at least one side of the surface of the negative current collector. The positive active layer includes a positive active material and a first solid electrolyte, wherein the first solid electrolyte includes lithium aluminum titanium phosphate. The positive active layer further includes La element, and the mass content of La element in the positive active layer is p. The negative active layer includes a negative active material and a second solid electrolyte, wherein the second solid electrolyte includes lithium lanthanum titanate. The mass content of La element in the negative active layer is q, satisfying: p > q. The lithium aluminum titanium phosphate further includes a first element and a second element, wherein the first element includes at least one of La, Sc, and Y, and the second element includes at least one of Si, Zr, and Ce. And / or, the lithium lanthanum titanate further includes a third element and a fourth element, wherein the third element includes at least one of Al, Sc, and Y, and the fourth element includes at least one of Si, Zr, and Ce. This application introduces titanium-containing solid electrolytes with doped elements into the positive and negative active layers, respectively. On one hand, the structural stability of the titanium-containing solid electrolyte can be effectively improved by doping with different types of dopants. Specifically, lithium aluminum titanium phosphate is simultaneously doped with a first dopant element (La, Sc, or Y) and a second dopant element (Si, Zr, or Ce), while lithium lanthanum titanate is simultaneously doped with a third dopant element (Al, Sc, or Y) and a fourth dopant element (Si, Zr, or Ce). Both titanium-containing solid electrolytes employ a dual-site co-doping strategy. Al, La, Sc, or Y, as dopants, can stabilize the crystal framework of the titanium-containing solid electrolyte due to their large ionic radius or strong bonding ability. Si, Zr, or Ce, as dopants, can optimize the grain boundaries of the titanium-containing solid electrolyte and significantly suppress the reduction of titanium ions, thereby improving the structural stability of the titanium-containing solid electrolyte.The introduction of lithium aluminum titanium phosphate, a titanium-containing solid electrolyte with excellent structural stability, into the positive electrode active layer can suppress the dissolution of transition metals in the titanium-containing solid electrolyte during high-voltage operation of the secondary battery. This prevents side reactions between the dissolved transition metals and the electrolyte, which could lead to gas generation, and also prevents the deposition of dissolved transition metals on the negative electrode side, which could induce dendrite formation. Furthermore, the titanium-containing solid electrolyte with excellent structural stability can uniformly distribute around the positive electrode active material to form a protective layer, which can suppress side reactions between the positive electrode active material and the electrolyte to a certain extent, thereby improving the cycle stability and safety of the secondary battery under high-voltage cycling. Similarly, the introduction of lithium lanthanum titanate, a titanium-containing solid electrolyte with excellent structural stability, into the negative electrode active layer can also uniformly distribute around the negative electrode active material, effectively suppressing side reactions between the positive electrode active material and the electrolyte. It can also suppress irreversible lithium-ion insertion and titanium-ion reduction on the negative electrode side, thereby reducing irreversible capacity loss during cycling and improving the coulombic efficiency of the secondary battery.

[0034] This application also emphasizes the introduction of La into the positive and negative electrode active layers. Materials containing La exhibit excellent oxidation resistance under high voltage, enabling them to withstand the high-voltage working environment of the positive electrode. Furthermore, La can form high-energy La-O bonds in the active layer, possessing strong bonding capabilities. Combined with La's large ionic radius, this stabilizes the crystal framework of La-containing materials (such as active materials and solid electrolytes) in the active layer, effectively improving the structural stability of the positive and negative electrode active layers. Secondly, the introduction of La can significantly suppress Ti through lattice stabilization and electron cloud modulation. 4+ Reduced to Ti by lithium metal 3+ / Ti 2+ The behavior of La further stabilizes the structural stability of the active layer; moreover, the introduction of La can also effectively improve the formation of the solid electrolyte interphase (SEI) film, which is conducive to the formation of a uniform, stable and dense SEI film, thereby improving the cycle stability and safety of the secondary battery.

[0035] However, this study found that the relative content of La in the positive and negative electrode active layers also affects the electrochemical performance of the secondary battery. Therefore, this application further controls the mass content p of La in the positive electrode active layer to be higher than the mass content q of La in the negative electrode active layer, achieving a match between the La content in the positive and negative electrode active layers. This stabilizes the stability of the positive and negative electrode active materials and inhibits Ti... 4+The reduction promotes the formation of a uniform, stable and dense SEI film, enabling the secondary battery to have the advantages of excellent cycle stability and safety. At the same time, it can also avoid the excessive content of La element in the negative electrode active layer compared with the positive electrode active layer, which would limit the energy density of the secondary battery, reduce the conductivity of the active layer, and deteriorate the rate performance of the secondary battery. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0037] Figure 1 This is the X-ray diffraction pattern (XRD pattern) of the first solid electrolyte - lithium aluminum titanium phosphate - in Example 1 of this application.

[0038] Figure 2 This is the X-ray diffraction pattern (XRD pattern) of the second solid electrolyte, lithium lanthanum titanate, in Example 1 of this application.

[0039] Figure 3 This is a scanning electron microscope (SEM) image of the lithium cobalt oxide positive electrode active matrix material coated with the third solid electrolyte in Example 1 of this application.

[0040] Figure 4 This is a scanning electron microscope (SEM) image of the single-sided positive electrode active layer of Embodiment 1 of this application.

[0041] Figure 5 This is a scanning electron microscope (SEM) image of the single-sided negative electrode active layer of Embodiment 1 of this application. Detailed Implementation

[0042] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0043] It should be noted in the description of this application that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, the technical features involved in the different embodiments of this application described below may be combined with each other as long as they do not conflict with each other.

[0044] This study found that existing technologies typically introduce titanium-containing solid electrolytes into the positive and negative active layers, respectively. These electrolytes are uniformly distributed around the positive and negative active materials, forming a protective layer that can suppress side reactions between the positive and negative materials and the electrolyte to some extent. However, when the operating voltage of the secondary battery exceeds 4.5V, some lithium ions in the titanium-containing solid electrolyte in the positive active layer irreversibly escape from the crystal lattice, causing structural damage to the titanium-containing solid electrolyte. This leads to the dissolution of transition metal ions (e.g., titanium ions), which continue to react with the electrolyte and generate gas. Furthermore, the transition metal ions dissolved from the positive side are reduced on the negative side and deposited on the surface of the negative electrode, inducing dendrite formation. Consequently, the cycle performance and safety of the secondary battery at high voltages remain unimproved. On the other hand, the titanium-containing solid electrolyte introduced into the negative active layer is irreversibly intercalated with lithium ions, affecting the capacity performance and coulombic efficiency of the secondary battery. Moreover, the formation stability and capacity decay rate of the SEI film on the negative side still need improvement.

[0045] To address the challenge that secondary batteries in related technologies cannot simultaneously achieve high energy density, excellent cycle performance, and safety, this application proposes the following solution.

[0046] In a first aspect, this application provides a lithium-ion secondary battery, including a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive active layer on at least one side of the surface of the positive current collector, and the negative electrode includes a negative current collector and a negative active layer on at least one side of the surface of the negative current collector. The positive electrode active layer includes a positive electrode active material and a first solid electrolyte, wherein the first solid electrolyte includes lithium aluminum titanium phosphate; the positive electrode active layer also includes La element, and the mass content of La element in the positive electrode active layer is p; The negative electrode active layer includes a negative electrode active material and a second solid electrolyte; the second solid electrolyte includes lithium lanthanum titanate, and the mass content of La element in the negative electrode active layer is q, satisfying: p > q; The lithium aluminum titanium phosphate further includes a first element and a second element, wherein the first element includes at least one of La, Sc, and Y, and the second element includes at least one of Si, Zr, and Ce; and / or, the lithium lanthanum titanate further includes a third element and a fourth element, wherein the third element includes at least one of Al, Sc, and Y, and the fourth element includes at least one of Si, Zr, and Ce.

[0047] In this application, the first element (La, Sc, or Y) and the second element (Si, Zr, or Ce) in the lithium aluminum titanium phosphate are introduced as doping elements; the third element (Al, Sc, or Y) and the fourth element (Si, Zr, or Ce) in the lithium lanthanum titanate are also introduced as doping elements.

[0048] This application introduces titanium-containing solid electrolytes with doped elements into the positive and negative active layers, respectively. On one hand, the structural stability of the titanium-containing solid electrolyte can be effectively improved by doping with different types of dopants. Specifically, lithium aluminum titanium phosphate is simultaneously doped with a first dopant element (La, Sc, or Y) and a second dopant element (Si, Zr, or Ce), while lithium lanthanum titanate is simultaneously doped with a third dopant element (Al, Sc, or Y) and a fourth dopant element (Si, Zr, or Ce). Both titanium-containing solid electrolytes employ a dual-site co-doping strategy. Al, La, Sc, or Y, as dopants, can stabilize the crystal framework of the titanium-containing solid electrolyte due to their large ionic radius or strong bonding ability. Si, Zr, or Ce, as dopants, can optimize the grain boundaries of the titanium-containing solid electrolyte and significantly suppress the reduction of titanium ions, thereby improving the structural stability of the titanium-containing solid electrolyte. The introduction of lithium aluminum titanium phosphate, a titanium-containing solid electrolyte with excellent structural stability, into the positive electrode active layer can suppress the dissolution of transition metals in the titanium-containing solid electrolyte during high-voltage operation of the secondary battery. This prevents side reactions between the dissolved transition metals and the electrolyte, which could lead to gas generation, and also prevents the deposition of dissolved transition metals on the negative electrode side, which could induce dendrite formation. Furthermore, the titanium-containing solid electrolyte with excellent structural stability can uniformly distribute around the positive electrode active material to form a protective layer, which can suppress side reactions between the positive electrode active material and the electrolyte to a certain extent, thereby improving the cycle stability and safety of the secondary battery under high-voltage cycling. Similarly, the introduction of lithium lanthanum titanate, a titanium-containing solid electrolyte with excellent structural stability, into the negative electrode active layer can also uniformly distribute around the negative electrode active material, effectively suppressing side reactions between the positive electrode active material and the electrolyte. It can also suppress irreversible lithium-ion insertion and titanium-ion reduction on the negative electrode side, thereby reducing irreversible capacity loss during cycling and improving the coulombic efficiency of the secondary battery.

[0049] This application also emphasizes the introduction of La into the positive and negative electrode active layers. Materials containing La exhibit excellent oxidation resistance under high voltage, enabling them to withstand the high-voltage working environment of the positive electrode. Furthermore, La can form high-energy La-O bonds in the active layer, possessing strong bonding capabilities. Combined with La's large ionic radius, this stabilizes the crystal framework of La-containing materials (such as active materials and solid electrolytes) in the active layer, effectively improving the structural stability of the positive and negative electrode active layers. Secondly, the introduction of La can significantly suppress Ti through lattice stabilization and electron cloud modulation. 4+ Reduced to Ti by lithium metal 3+ / Ti 2+ The behavior of La further stabilizes the structural stability of the active layer; moreover, the introduction of La can also effectively improve the formation of the solid electrolyte interphase (SEI) film, which is conducive to the formation of a uniform, stable and dense SEI film, thereby improving the cycle stability and safety of the secondary battery.

[0050] However, this study found that the relative content of La in the positive and negative electrode active layers also affects the electrochemical performance of the secondary battery. Therefore, this application further controls the mass content p of La in the positive electrode active layer to be higher than the mass content q of La in the negative electrode active layer, achieving a match between the La content in the positive and negative electrode active layers. This stabilizes the stability of the positive and negative electrode active materials and inhibits Ti... 4+ The reduction promotes the formation of a uniform, stable and dense SEI film, enabling the secondary battery to have the advantages of excellent cycle stability and safety. At the same time, it can also avoid the excessive content of La element in the negative electrode active layer compared with the positive electrode active layer, which would limit the energy density of the secondary battery, reduce the conductivity of the active layer, and deteriorate the rate performance of the secondary battery.

[0051] This study found that if the mass content p of La in the positive electrode active layer is lower than or equal to the mass content q of La in the negative electrode active layer, the mass content p of La in the positive electrode active layer will be too low, or the mass content q of La in the negative electrode active layer will be too high, and the mass content p of La in the positive electrode active layer will be too low. In such cases, the structural stability of the titanium-containing solid electrolyte and the positive electrode material cannot be guaranteed. When the secondary battery is cycled at high voltage, the structure is easily damaged, leading to the dissolution of transition metal elements and side reactions with the electrolyte, resulting in gas generation. At the same time, the dissolved transition metal elements will also reduce and precipitate on the negative electrode side, inducing dendrite formation, which is not conducive to improving the cycle stability and safety of the secondary battery. On the other hand, if the mass content q of La in the negative electrode active layer is too high or even higher than that in the positive electrode active layer, the content of other substances in the negative electrode active layer will decrease, affecting the energy density of the battery. Furthermore, too much La on the negative electrode side will also lead to a decrease in the conductivity of the negative electrode sheet, affecting the rate performance of the secondary battery.

[0052] It should be noted that the mass content p of La element in the positive electrode active layer can be obtained by ICP-OES (inductively coupled plasma optical emission spectrometry); the mass content q of La element in the negative electrode active layer can be obtained by ICP-OES (inductively coupled plasma optical emission spectrometry).

[0053] It is understood that the La element in the positive electrode active layer of this application may be derived from the positive electrode active material, and / or the La element may also be derived from the first solid electrolyte.

[0054] Optionally, in this application, the first solid electrolyte further includes lithium lanthanum titanate.

[0055] Optionally, in this application, the chemical formula of the lithium aluminum titanium phosphate all satisfies: Li 1+x M a Al x-a Ti 2-b-x Q b (PO4)3, 0.1≤x≤0.4, 0.001≤a≤0.3, 0.001≤b≤0.3, M includes at least one element from La, Sc, and Y, and Q includes at least one element from Si, Zr, and Ce.

[0056] Optionally, in this application, the chemical formula of the lithium lanthanum titanate all satisfies: Li 3y La 2 / 3-y-m A m Ti 1-n D nO3, 0.1≤y≤0.15, 0.001≤m≤0.2, 0.001≤n≤0.3, A includes at least one element from Al, Sc, and Y, and D includes at least one element from Si, Zr, and Ce.

[0057] In some embodiments, the mass content p of La element in the positive electrode active layer satisfies: 0.015% ≤ p ≤ 4.2%, preferably 0.02% ≤ p ≤ 4%. This ensures sufficient La element is provided in the positive electrode active layer, more effectively improving the stability of the crystal lattice framework of the material in the positive electrode active layer, further enhancing the structural stability of the positive electrode active layer, thereby improving the cycle stability and safety of the secondary battery. Simultaneously, it effectively avoids the negative impact of excessive La element in the positive electrode active layer on the crystal structure and ion transport, thereby further improving the cycle performance and rate performance of the secondary battery.

[0058] This study found that if the mass content p of La in the positive electrode active layer is lower than a certain value, it will result in insufficient La in the positive electrode active layer, leading to a decrease in the stability of the crystal framework of the material in the positive electrode active layer and a decrease in the structural stability of the positive electrode active layer, which is detrimental to improving the cycle stability and safety of the secondary battery. Conversely, if the mass content p of La in the positive electrode active layer is higher than a certain value, it will lead to local enrichment of La in the positive electrode active layer, making the La-containing material prone to crystal distortion, which will reduce the cycle stability and safety of the secondary battery. Furthermore, excessive La in the positive electrode active layer will also affect the transport of lithium ions, resulting in a decrease in the rate performance of the secondary battery.

[0059] For example, the mass content p of La element in the positive electrode active layer can be, for example, 0.015%, 0.019%, 0.02%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.1%, 4.2%, or a value within the range of any two of the above values.

[0060] In some embodiments, the mass content of Ti element in the positive electrode active layer is s, satisfying: 0.07% ≤ s ≤ 2%. Thus, the mass content s of Ti element in the positive electrode active layer is in the range of 0.07% to 2%, which can improve the lattice stability of the titanium-containing solid electrolyte, preventing the dissolution of transition metals caused by structural collapse of the titanium-containing solid electrolyte during high-voltage operation of the secondary battery. Furthermore, an appropriate amount of Ti element can promote more effective suppression of direct contact between the positive electrode active material and the electrolyte, avoiding the occurrence of side reactions and further improving the cycle stability and safety of the secondary battery under high-voltage operating conditions. On the other hand, a specific mass content of Ti element can also improve the electronic conductivity and ionic conductivity of the positive electrode active layer, thereby improving the rate performance of the secondary battery.

[0061] This study found that if the mass content of Ti element s in the positive electrode active layer is less than 0.07%, the lattice stability of the titanium-containing solid electrolyte decreases. During high-voltage cycling, the secondary battery is prone to structural collapse, leading to the dissolution of transition metals and hindering the suppression of side reactions between the positive electrode active material and the electrolyte. This negatively impacts the cycle stability and safety of the secondary battery under high voltage operation. Furthermore, an excessively low Ti element mass content s also affects the transport of electrons and ions in the positive electrode active layer, resulting in significant electrode polarization and a decrease in the rate performance and discharge capacity of the secondary battery. Conversely, if the mass content of Ti element s in the positive electrode active layer is greater than 2%, the Ti element is easily unevenly distributed, leading to lattice distortion and increased internal stress in the titanium-containing solid electrolyte. During secondary battery cycling, particles are prone to cracking, pulverization, and structural collapse, resulting in poor positive electrode structural stability. Transition metals are easily dissolved, causing severe side reactions with the electrolyte and inducing gas generation. Excessive titanium ions concentrate on the negative electrode side, making them more susceptible to reduction and dendrite formation, thus affecting the cycle stability and safety of the secondary battery.

[0062] It should be noted that the mass content s of Ti element in the positive electrode active layer can be obtained by ICP-OES (inductively coupled plasma optical emission spectrometry). For example, the mass content s of Ti element in the positive electrode active layer can be 0.07%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, or a value within any two of the above ranges.

[0063] Furthermore, in some embodiments, the ratio of the mass content s of Ti element in the positive electrode active layer to the mass content p of La element in the positive electrode active layer satisfies: 0.1 ≤ s / p ≤ 4.5. This achieves a match between Ti and La elements in the positive electrode active layer, resulting in an optimal balance between interfacial impedance, structural stability, and ion transport in the positive electrode active material. An appropriate amount of Ti element in the positive electrode active layer can improve the ionic conductivity of the positive electrode, which is beneficial for constructing lithium-ion channels, reducing impedance, and further improving rate performance. An appropriate amount of La element can stabilize the crystal structure, improving the cycle stability and safety of the secondary battery. The combined effect of both elements can improve lithium-ion transport while ensuring the stability of the positive electrode structure.

[0064] For example, the ratio of the mass content s of Ti element in the positive electrode active layer to the mass content p of La element in the positive electrode active layer can be, for example, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.5, or a value within the range of any two of the above values.

[0065] In some embodiments, the mass content q of La element in the negative electrode active layer satisfies: 0.009% ≤ q ≤ 3.3%, preferably 0.01% ≤ q ≤ 3%. This has several advantages: First, the strong bonding ability and large ionic radius of La element can further improve the stability of the solid electrolyte crystal structure in the negative electrode, making it easier to avoid side reactions between the negative electrode active material and the electrolyte. Second, it can more effectively suppress the oxidation of titanium ions, and the presence of an appropriate amount of La element in the negative electrode active layer can better improve the formation of the SEI film, further promoting the stability, uniformity, and density of the SEI, thereby improving the cycle stability and safety of the secondary battery. Third, an appropriate amount of La element can also avoid the negative impact of excessive La element in the negative electrode active layer on its conductivity and energy density, thus better ensuring that the secondary battery has high energy density and excellent rate performance.

[0066] This study found that if the mass content q of La element in the negative electrode active layer is lower than a certain value, it cannot effectively improve the structural stability of the solid electrolyte and is not conducive to suppressing the occurrence of side reactions between the active material and the electrolyte. The stability of the negative electrode structure cannot be effectively improved, which is not conducive to improving the cycle stability and safety of the secondary battery. If the mass content q of La element in the negative electrode active layer is higher than a certain value, the mass ratio of the negative electrode active material in the negative electrode active layer decreases, resulting in a decrease in the energy density of the secondary battery. Moreover, if the La element content in the negative electrode active layer is too high, it will also lead to a decrease in the conductivity of the negative electrode sheet and a deterioration in the rate performance.

[0067] For example, the mass content q of La element in the negative electrode active layer can be, for example, 0.009%, 0.01%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.1%, 3.2%, 3.3%, or a value within the range of any two of the above values.

[0068] In some embodiments, the mass content of Ti element in the negative electrode active layer is t, satisfying: 0.01% ≤ t ≤ 2%. This provides a lithium-ion conductive channel, improving lithium-ion transport, ensuring good interface and structural stability of the negative electrode, reducing side reactions, and preventing excessive reduction of titanium ions and impaired electron conduction due to excessive Ti element. This further improves the structural stability and kinetic performance of the negative electrode active layer, thus enhancing the cycle stability, safety, and rate capability of the secondary battery.

[0069] This study found that if the mass content t of Ti element in the negative electrode active layer is less than 0.01%, it will lead to a decrease in the ionic conductivity of the negative electrode, a deterioration in the lithium ion transport effect, and an inability to effectively improve the structural stability of the negative electrode, thus hindering the improvement of the cycle stability, safety, and rate performance of the secondary battery. Conversely, if the mass content t of Ti element in the negative electrode active layer is greater than 2%, it will lead to an inability of La element in the negative electrode to effectively suppress the reduction of excess titanium ions, resulting in a decrease in the structural stability of the negative electrode, which in turn leads to a decrease in the cycle stability of the secondary battery and an inability to effectively improve its capacity. Furthermore, excessive Ti content will also lead to an excessive amount of electronic insulating phase in the negative electrode, hindering electron conduction and thus deteriorating the rate performance of the secondary battery.

[0070] It should be noted that the mass content t of Ti element in the negative electrode active layer can be obtained by ICP-OES (inductively coupled plasma optical emission spectrometry). For example, the mass content t of Ti element in the negative electrode active layer can be 0.01%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, or a value within any two of the above ranges.

[0071] Furthermore, in some embodiments, the ratio of the mass content t of Ti element in the negative electrode active layer to the mass content q of La element in the negative electrode active layer satisfies: 0.5 ≤ t / q ≤ 1.8. This achieves better matching between Ti and La elements in the negative electrode active layer, enabling synergistic regulation of lithium-ion transport kinetics, electron conductivity, interface stability, and structural stability in the negative electrode. Simultaneously, the appropriate ratio of their contents further facilitates the influence of La element on Ti. 4+ The reduction suppression effect is more conducive to improving the cycle stability, rate performance, and safety of secondary batteries.

[0072] For example, the ratio of the mass content t of Ti element in the negative electrode active layer to the mass content q of La element in the negative electrode active layer can be, for example, 0.5, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, etc., or a value within the range of any two of the above values.

[0073] In some embodiments, the average particle size of the first solid electrolyte is denoted as D1, and the average particle size of the second solid electrolyte is denoted as D2, satisfying the following conditions: 100 nm ≤ D1 ≤ 2000 nm, 150 nm ≤ D2 ≤ 1000 nm, and 0.2 ≤ D1 / D2 ≤ 5. This helps the first and second solid electrolytes to achieve better performance in the positive and negative electrode active layers, respectively.

[0074] Among them, the average particle size D1 of the first solid electrolyte is in the range of 100 nm to 2000 nm. Its dispersion in the positive electrode active layer is more uniform, which is more conducive to improving the stability of the positive electrode structure and can match the positive electrode active material to construct a continuous and uniform ion-conducting framework, ensuring that the electrode porosity is appropriate, which is more conducive to the transport of lithium ions. This can further improve the cycle stability, rate performance and safety performance of the secondary battery under high voltage.

[0075] The average particle size D2 of the second solid electrolyte is between 150 nm and 1000 nm, which makes it more uniformly dispersed in the negative electrode active layer, further ensuring the stability of the negative electrode structure. The moderate average particle size of the second solid electrolyte in the negative electrode active layer is also more conducive to constructing a stable, uniform, and moderately thick SEI film, as well as ensuring moderate electrode porosity and improving lithium-ion transport. This is more conducive to improving the cycle stability, rate performance, and safety of the secondary battery when operating at high voltage.

[0076] Meanwhile, this application controls the ratio of the average particle size D1 of the first solid electrolyte to the average particle size D2 of the second solid electrolyte within the range of 0.2 to 5, achieving matching of the average particle size of the solid electrolytes in the positive and negative electrode active layers. On the one hand, this makes the overall ion transport impedance of the secondary battery more matched, so that the ion transport channels constructed by the first solid electrolyte and the positive electrode active material in the positive electrode are similar to the ion transport channels constructed by the second solid electrolyte and the negative electrode active material in the negative electrode, reducing the overall polarization of the battery. On the other hand, matching the average particle size of the first solid electrolyte in the positive electrode active layer and the second solid electrolyte in the negative electrode active layer also makes the structural stress of the positive and negative electrodes more balanced, and the stress coordination, cycle stability and safety of the secondary battery during charging and discharging are better.

[0077] It should be noted that the average particle size D1 of the first solid electrolyte can be obtained by uniformly selecting 50 particles from the scanning electron microscope (SEM) image of the positive electrode active layer, testing their particle size, and calculating the average value; the average particle size D2 of the second solid electrolyte can be obtained by uniformly selecting 50 particles from the scanning electron microscope (SEM) image of the negative electrode active layer, testing their particle size, and calculating the average value. For example, the average particle size D1 of the first solid electrolyte can be, for example, 100 nm, 200 nm, 400 nm, 600 nm, 800 nm, 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm, 2000 nm, etc., or a value within the range of any two of the above values; the average particle size D2 of the second solid electrolyte can be, for example, 150 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, etc., or a value within the range of any two of the above values; the ratio of the average particle size D1 of the first solid electrolyte to the average particle size D2 of the second solid electrolyte can be, for example, 0.2, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, etc., or a value within the range of any two of the above values.

[0078] Furthermore, in some embodiments, the average particle size of the positive electrode active material is denoted as Z, satisfying: 0.005 ≤ D1 / Z ≤ 0.1, 1000 nm ≤ Z ≤ 50000 nm, and particularly satisfying: 0.02 < D1 / Z < 0.06. Thus, in the positive electrode active layer, the ratio of the average particle size D1 of the first solid electrolyte to the average particle size Z of the positive electrode active material is within the aforementioned specific range. This allows for a larger contact area and better contact effect between the solid electrolyte and the active material, more effectively improving the structural stability of the titanium-containing solid electrolyte and the positive electrode active material during cycling, thereby further improving the structural stability of the positive electrode active layer. In addition, the matching of their average particle sizes allows the solid electrolyte to fill the gaps between the active materials, promoting the formation of a continuous lithium-ion transport network while further improving the peeling force of the negative electrode sheet and increasing the compaction density of the electrode sheet, thereby further improving the cycle performance of the secondary battery.

[0079] It should be noted that the average particle size Z of the positive electrode active material can be obtained by randomly selecting 50 particles of the positive electrode active material from a scanning electron microscope (SEM) image, testing their particle size, and calculating the average value. For example, the ratio of the average particle size D1 of the first solid electrolyte to the average particle size Z of the positive electrode active material can be, for example, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a value within any two of the above values; the average particle size Z of the positive electrode active material can be, for example, 1000 nm, 5000 nm, 10000 nm, 15000 nm, 20000 nm, 25000 nm, 30000 nm, 35000 nm, 40000 nm, 45000 nm, 50000 nm, or a value within any two of the above values.

[0080] Furthermore, in some embodiments, the average particle size of the negative electrode active material is denoted as F, satisfying: 0.002 ≤ D² / F ≤ 0.6, 1000 nm ≤ F ≤ 100000 nm, and particularly satisfying: 0.04 < D² / F < 0.1. This achieves a match between the average particle size of the second solid electrolyte and the negative electrode active material, which is beneficial for further improving the interfacial contact effect between the titanium-containing solid electrolyte and the negative electrode active material. It also facilitates the embedding of the second solid electrolyte into the gaps of the negative electrode active material. The uniform distribution of the solid electrolyte around the negative electrode active layer supports the active particles, which helps improve the stability of the negative electrode structure and forms continuous and interconnected ion transport channels, facilitating lithium ion transport. In addition, the appropriate average particle size ratio of the second solid electrolyte and the negative electrode active material further promotes the formation of a stable, uniform, and appropriately thick SEI film, thereby further improving the cycle stability, rate performance, and safety of the secondary battery.

[0081] It should be noted that the average particle size F of the negative electrode active material can be obtained by uniformly selecting 50 particles of the negative electrode active material from a scanning electron microscope (SEM) image, testing their particle size, and calculating the average value. For example, the ratio of the average particle size D2 of the second solid electrolyte to the average particle size F of the negative electrode active material can be, for example, 0.002, 0.005, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or a value within any two of the above values; the average particle size F of the negative electrode active material can be, for example, 1000 nm, 10000 nm, 20000 nm, 40000 nm, 60000 nm, 80000 nm, 100000 nm, or a value within any two of the above values.

[0082] In some embodiments, the positive electrode active material includes a positive electrode active matrix material and a coating layer covering at least a portion of the surface of the positive electrode active matrix material. The coating layer includes a third solid electrolyte, which includes lithium aluminum titanium phosphate. The average particle size of the third solid electrolyte is denoted as D3, satisfying: 2 nm ≤ D3 < 100 nm, and D3 < D1. Thus, this application further introduces a third solid electrolyte coating at least a portion of the surface of the positive electrode active matrix material into the positive electrode active layer. This results in good structural stability, more effectively suppressing the dissolution of transition metals from the titanium-containing solid electrolyte and the positive electrode active material during high-voltage operation of the secondary battery. It also further avoids direct contact between the electrolyte and the positive electrode active material, thereby more effectively preventing side reactions and gas generation in the battery, and more effectively preventing the deposition of dissolved transition metals from the solid electrolyte and the positive electrode active material on the negative electrode side to induce dendrite formation. This significantly improves the cycle stability and safety of the secondary battery under high-voltage cycling. Secondly, this application further limits the average particle size D3 of the third solid electrolyte to 2 nm ≤ D3 < 100 nm, which facilitates the formation of an effective coating layer on the surface of the positive electrode active matrix material, and further improves the physical isolation and material structural stability. Furthermore, this application controls the average particle size D3 of the third solid electrolyte to be smaller than the average particle size D1 of the first solid electrolyte, which is more conducive to achieving efficient interface protection while more effectively ensuring the continuity of ion channels and a reasonable pore structure inside the positive electrode, thus further contributing to obtaining a secondary battery that balances good cycle stability and excellent rate performance.

[0083] It should be noted that the average particle size D3 of the third solid electrolyte can be obtained by uniformly selecting 50 particles from a scanning electron microscope (SEM) image, testing their particle size, and calculating the average value. For example, the average particle size D3 of the third solid electrolyte can be 2 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 99 nm, or a value within any two of the above ranges.

[0084] Furthermore, in some embodiments, the positive electrode active substrate material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based material, and lithium iron phosphate material.

[0085] Furthermore, in some embodiments, the positive electrode active matrix material includes La element, and the mass content of La element is 0.01% to 3% based on the total mass of the positive electrode active matrix material. Thus, this application introduces the dopant element La into the positive electrode active matrix material. The large radius of La element can cause lattice expansion of the positive electrode active material, further improving the transport and diffusion effect of lithium ions on the positive electrode side. On the other hand, the strong bonding ability of La element can stabilize the lattice oxygen of the positive electrode active matrix material, improving the structural stability of the positive electrode active material, thereby further enhancing the cycle stability, rate performance, and safety of the secondary battery. Meanwhile, this application also controls the mass content of the doping element La in the positive electrode active matrix material to be within the range of 0.01% to 3%, which can ensure that there is enough La element in the positive electrode active matrix material to improve the lithium ion transport effect and enhance the structural stability of the positive electrode active material. It can also avoid excessive La element reducing the proportion of active material on the positive electrode side, which would lead to a decrease in the specific capacity of the secondary battery. Furthermore, it avoids excessive La element forming a second phase that blocks the lithium ion diffusion channel and causes local lattice distortion, which would instead damage the structural stability of the positive electrode active material.

[0086] It should be noted that the mass content of the dopant element La in the positive electrode active matrix material can be obtained by ICP-OES (inductively coupled plasma optical emission spectrometry). For example, the mass content of the dopant element La in the positive electrode active matrix material is 0.01%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, or a value within the range of any two of the above values.

[0087] Optionally, in some embodiments, the Ti content in the third solid electrolyte is 0.01% to 1% and the La content is 0.001% to 2%, based on the total mass of the positive electrode active layer.

[0088] In some embodiments, the total mass content of lithium aluminum titanium phosphate is 0.05% to 15% based on the total mass of the positive electrode active layer.

[0089] For example, the total mass content of lithium aluminum titanium phosphate in the positive electrode active layer may be 0.05%, 0.1%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 15%, or a value within the range of any two of the above values.

[0090] It is understood that in this application, the "total mass content of lithium aluminum titanium phosphate in the positive electrode active layer" refers to the total mass content of the first solid electrolyte and the third solid electrolyte, based on the total mass of the positive electrode active layer.

[0091] Optionally, in some embodiments, the mass ratio of the first solid electrolyte to the third solid electrolyte is (0.75~80):1.

[0092] Furthermore, in some embodiments, the mass ratio of the first solid electrolyte to the third solid electrolyte is (1~60):1.

[0093] In some embodiments, the mass content of lithium lanthanum titanate is 0.04% to 7.5% based on the total mass of the negative electrode active layer.

[0094] For example, the mass content of lithium lanthanum titanate in the negative electrode active layer may be, for example, 0.04%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, or a value within the range of any two of the above values.

[0095] In some embodiments, the X-ray diffraction pattern of the lithium aluminum titanium phosphate in the first solid electrolyte independently includes a (104) characteristic peak, a (113) characteristic peak and a (024) characteristic peak, with the diffraction angle 2θ of each characteristic peak ranging from 20°≤2θ(104)≤22°, 23°≤2θ(113)≤25°, and 28.5°≤2θ(024)≤30.5°.

[0096] Furthermore, in some embodiments, the peak intensity of the characteristic peak (104) is K1, the peak intensity of the characteristic peak (113) is K2, and the peak intensity of the characteristic peak (024) is K3, satisfying: 0.45≤K1 / K2≤0.75, 1.2≤K2 / K3≤3.5, K2>K1>K3.

[0097] This application controls the relative relationship between the peak intensities of the characteristic peaks (104), (113), and (024) in the X-ray diffraction pattern of lithium aluminum titanium phosphate, indicating that lithium aluminum iron phosphate has a stable crystal structure. When applied to the positive electrode active layer of a secondary battery, it can more effectively suppress the dissolution of transition metals in the positive electrode sheet, further avoid the side reaction between the dissolved transition metals and the electrolyte that causes gas generation, and further avoid the deposition of dissolved transition metal elements on the negative electrode side that induces dendrite formation. In addition, the relative relationship between the peak intensities of the specific characteristic peaks in lithium aluminum titanium phosphate satisfies the above relationship, which can also further suppress the side reaction between the positive electrode active material and the electrolyte, thereby further improving the cycle stability and safety of the secondary battery.

[0098] It should be noted that the X-ray diffraction pattern of the lithium aluminum titanium phosphate can be obtained by X-ray diffraction (XRD). For example, the ratio of the peak intensity K1 of the characteristic peak (104) to the peak intensity K2 of the characteristic peak (113) is 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, or a value within the range of any two of the above values; the ratio of the peak intensity K2 of the characteristic peak (113) to the peak intensity K3 of the characteristic peak (024) can be, for example, 1.2, 1.5, 2.0, 2.5, 3.0, 3.5, or a value within the range of any two of the above values.

[0099] In some embodiments, the X-ray diffraction pattern of the lithium lanthanum titanate in the negative electrode active layer independently includes a (102) characteristic peak, a (004) characteristic peak, and a (114) characteristic peak, with the diffraction angle 2θ of each characteristic peak ranging from 31.5°≤2θ(102)≤33.5°, 46.5°≤2θ(004)≤48.5°, and 57.5°≤2θ(114)≤59.5°.

[0100] Furthermore, in some embodiments, the peak intensity of the (102) characteristic peak is K4, the peak intensity of the (004) characteristic peak is K5, and the peak intensity of the (114) characteristic peak is K6, satisfying: 2.5 < K4 / K5 < 4, 1 < K5 / K6 < 1.5, K4 > K5 > K6.

[0101] When the relative relationship between the peak intensities of the (102), (004), and (114) characteristic peaks in the X-ray diffraction pattern of lithium lanthanum titanate controlled by this application satisfies the above-mentioned relationship, the structure stability of the active layer can be better improved when applied to the positive and negative active layers of a secondary battery. This effectively suppresses the occurrence of side reactions between the positive and negative active layers and the electrolyte, and can better solve the problems of transition metal dissolution on the positive side and lithium ion insertion and titanium ion reduction on the negative side. This is more conducive to improving the cycle stability and safety of the secondary battery, and more conducive to reducing irreversible capacity loss during the cycle of the secondary battery.

[0102] It should be noted that the X-ray diffraction pattern of the lithium lanthanum titanate can be obtained by X-ray diffraction (XRD). For example, the ratio of the peak intensity K4 of the characteristic peak (102) to the peak intensity K5 of the characteristic peak (004) is 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, or a value within the range of any two of the above values; the ratio of the peak intensity K5 of the characteristic peak (004) to the peak intensity K6 of the characteristic peak (114) can be, for example, 1.01, 1.1, 1.2, 1.3, 1.4, 1.49, or a value within the range of any two of the above values.

[0103] In some embodiments, the positive electrode active layer further includes a positive electrode conductive agent, which includes multi-walled carbon nanotubes.

[0104] In some embodiments, the negative electrode active material includes a silicon-based material, which includes at least one of silicon-oxygen materials, silicon nanoparticles, and silicon-carbon materials.

[0105] Furthermore, in some embodiments, the negative electrode active material further includes a carbon-based material, which includes graphite.

[0106] In some embodiments, the silicon-based material includes a silicon-carbon material, which comprises porous carbon and silicon particles located in the porous carbon channels, wherein the silicon content of the silicon-carbon material is 30% to 80% by mass.

[0107] In some embodiments, the average particle size of the silicon-carbon material is 1 μm to 20 μm.

[0108] In some embodiments, the negative electrode active layer further includes a negative electrode conductive agent, which includes single-walled carbon nanotubes.

[0109] In some embodiments, the charging cutoff voltage of the lithium-ion secondary battery is ≥4.5 V.

[0110] Example 1 This embodiment provides a method for preparing a lithium-ion secondary battery, which specifically includes the following steps: (1) First solid electrolyte (Li 1.3 La 0.1 Al 0.2 Ti 1.4 Si 0.3 Preparation of (PO4)3 Lithium nitrate, lanthanum nitrate, aluminum nitrate, titanium dioxide, ethyl silicate, and phosphoric acid were dispersed in ethanol at a molar ratio of Li, La, Al, Ti, Si, and P of 1.3:0.1:0.2:1.4:0.3:3. The mixture was stirred and evaporated to dryness at 60 °C. The resulting product was then thoroughly ground for 6 h and pressed into discs with a diameter of 12 mm and a thickness of 1 mm under a pressure of 300 MPa to obtain the precursor. The precursor was placed in a muffle furnace and sintered at 1000 °C at a heating rate of 5 °C / min for 12 h in an air atmosphere. Finally, the mixture was crushed and ball-milled to obtain the first solid electrolyte – lithium aluminum titanium phosphate. The average particle size D1 of the first solid electrolyte was controlled to be 300 nm through crushing and ball-milling processes. Its X-ray diffraction pattern is shown below. Figure 1 As shown, by Figure 1 As shown, in the X-ray diffraction pattern of the first solid electrolyte - lithium aluminum titanium phosphate, the diffraction angle 2θ of the characteristic peak (104) is 21.3°, the diffraction angle 2θ of the characteristic peak (113) is 24.3°, and the diffraction angle 2θ of the characteristic peak (024) is 29.4°. With the peak intensity of the characteristic peak (104) as K1, the peak intensity of the characteristic peak (113) as K2, and the peak intensity of the characteristic peak (024) as K3, the following conditions are met: K1 / K2=0.65, K2 / K3=2.23, and K2>K1>K3.

[0111] (2) Second solid electrolyte (Li 0.33 La 0.54 Al 0.02 Ti 0.95 Si 0.05 Preparation of O3 Lithium nitrate, lanthanum nitrate, aluminum nitrate, tetrabutyl titanate, and ethyl silicate were dispersed in ethanol at a molar ratio of Li, La, Al, Ti, and Si of 0.33:0.54:0.02:0.95:0.05. The mixture was stirred and evaporated to dryness at 60°C. The resulting product was then thoroughly ground and pressed into discs with a diameter of 12 mm and a thickness of 1 mm under a pressure of 300 MPa to obtain a precursor. The precursor was then placed in a muffle furnace and sintered at 1000°C at a heating rate of 5°C / min for 12 h in an air atmosphere. Finally, the mixture was crushed and ball-milled to obtain the second solid electrolyte – lithium lanthanum titanate. The average particle size D2 of the second solid electrolyte was controlled to be 600 nm through crushing and ball-milling processes. Its X-ray diffraction pattern is shown below. Figure 2 As shown, by Figure 2 It can be seen that in the X-ray diffraction pattern of lithium lanthanum titanate, the diffraction angle 2θ of the characteristic peak (102) is 32.2°, the diffraction angle 2θ of the characteristic peak (004) is 47.3°, and the diffraction angle 2θ of the characteristic peak (114) is 58.6°. With the peak intensity of the characteristic peak (102) as K4, the peak intensity of the characteristic peak (004) as K5, and the peak intensity of the characteristic peak (114) as K6, the following conditions are met: K4 / K5=2.94, K5 / K6=1.15, which satisfies K4>K5>K6.

[0112] (3) Third solid electrolyte (Li 1.3 La 0.1 Al 0.2 Ti 1.4 Si 0.3 Preparation of (PO4)3 Lithium nitrate, lanthanum nitrate, aluminum nitrate, titanium dioxide, ethyl silicate, and phosphoric acid were dispersed in ethanol in a molar ratio of Li, La, Al, Ti, Si, and P of 1.3:0.1:0.2:1.4:0.3:3. The mixture was stirred and evaporated to dryness at 60 °C. The resulting product was then thoroughly ground for 12 h and pressed into discs with a diameter of 12 mm and a thickness of 1 mm under a pressure of 300 MPa to obtain a precursor. The precursor was then placed in a muffle furnace and sintered at 1000 °C at a heating rate of 5 °C / min for 12 h in an air atmosphere. Finally, the mixture was crushed and ball-milled using a crusher and a ball mill to obtain a third solid electrolyte. The average particle size D3 of the third solid electrolyte was controlled to be 30 nm through the crushing and ball-milling process.

[0113] (4) Preparation of positive electrode sheet ① The lithium cobalt oxide cathode powder (based on the total mass of the lithium cobalt oxide cathode active matrix material, which contains 0.5% by mass of doped La element) and the third solid electrolyte Li1.3 La 0.1 Al 0.2 Ti 1.4 Si 0.3 (PO4)3 powder (average particle size 30 nm) was mixed at a mass ratio of 99.8:0.2. The mixture was then added to a 1:1 volume ratio of water and ethanol and stirred until homogeneous, resulting in a slurry with a solid content of 20%. The slurry was then spray-dried at a temperature of 200 °C, a fan frequency of 30 Hz, and a feed rate of 450 mL / h. The collected powder was then dried in a vacuum oven at 90 °C. The resulting sample was then placed in an inert atmosphere and kept at 300 °C for 2 h, followed by natural cooling to obtain the positive electrode active material, which is composed of a third solid electrolyte, Li. 1.3 La 0.1 Al 0.2 Ti 1.4 Si 0.3 The structure consists of lithium cobalt oxide coated with (PO4)3, with an average particle size of 10,000 nm. Its scanning electron microscope image is shown below. Figure 3 ,Depend on Figure 3 As shown, the surface of the lithium cobalt oxide cathode material is coated with a uniformly distributed solid electrolyte.

[0114] ② Lithium cobalt oxide coated with the third solid electrolyte, the first solid electrolyte, polyvinylidene fluoride, conductive carbon black, and multi-walled carbon nanotubes were mixed in a mass ratio of 95.4:1:1.7:1:0.9. N-methylpyrrolidone solvent was added, and the mixture was stirred using a vacuum mixer to obtain a positive electrode slurry. This slurry was then coated onto both sides of a 9 μm thick aluminum foil along its thickness direction. The single-sided density of the coated positive electrode active layer was 20.5 mg / cm². 2 The aluminum foil coated with the positive electrode slurry was initially dried in a forced-air drying oven at 60 ℃ for 5 min, then baked in a vacuum oven at 100 ℃ for 10 h. The positive electrode sheet was then rolled and sliced ​​using a roller press to obtain the positive electrode sheet. The scanning electron microscope image of the single-sided positive electrode active layer is shown below. Figure 4 As shown, by Figure 4 It can be seen that solid electrolyte particles are distributed between the positive electrode active materials in the positive electrode active layer, such as... Figure 4 The substance in the box marked A is the first solid electrolyte particle.

[0115] (5) Preparation of negative electrode sheet Graphite, silicon-carbon material (average conductivity 15 S / cm, average particle size 8 μm, elemental Si content 45% in silicon-carbon material, silicon-carbon material consisting of porous carbon and silicon particles located in the porous carbon channels), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), styrene-butadiene rubber (SBR), conductive carbon black, single-walled carbon nanotubes, and a second solid electrolyte were uniformly mixed in a mass ratio of 85:10:1:1:1:0.6:0.4:1. An appropriate amount of deionized water was added as a solvent, and the mixture was stirred evenly using a vacuum mixer to obtain a negative electrode slurry. This negative electrode slurry was then coated onto both sides of a 5 μm thick carbon-coated copper foil along its thickness direction. The one-sided density of the coated negative electrode active coating was 9 mg / cm². 2 The coated electrode sheets were transferred to a vacuum drying oven and baked at 85°C for 11 hours. They were then rolled and sliced ​​using a two-roll press to obtain the negative electrode sheet. The average particle size of the mixed graphite and silicon-carbon negative electrode active material in the negative electrode sheet was 12000 nm. The scanning electron microscope (SEM) image of the single-sided negative electrode active layer showed... Figure 5 As shown, by Figure 5 It can be seen that the negative electrode active layer contains uniformly distributed silicon-carbon material and graphite material, and solid electrolyte particles are distributed between the silicon-carbon material and graphite material. Figure 5 The substance in the box labeled B is the second solid electrolyte.

[0116] (6) Assembly of lithium-ion secondary batteries The negative and positive electrode sheets prepared in the above steps, along with a commercially available separator, are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to obtain a battery cell. The battery cell is placed in an outer packaging aluminum foil, and a commercially available electrolyte is injected into the outer packaging. After vacuum sealing, settling, formation, shaping, and sorting, a lithium-ion secondary battery is obtained. The separator is a 6 μm thick porous polyethylene membrane, and the electrolyte is a mixed solution of 1 mol / L LiPF6 dissolved in ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (EMC) (volume ratio 1:1:1).

[0117] The preparation methods and parameter settings of the remaining embodiments and comparative examples are basically the same as those of Example 1. The differences are shown in Tables 1, 2 and 3. In Tables 1 to 3, D1 represents the average particle size of the first solid electrolyte, in nm; K1 represents the peak intensity of the characteristic peak (104); K2 represents the peak intensity of the characteristic peak (113); K3 represents the peak intensity of the characteristic peak (024); D3 represents the average particle size of the third solid electrolyte, in nm; Z represents the average particle size of the positive electrode active material, in nm; D1 / Z represents the ratio of the average particle size of the first solid electrolyte to the average particle size of the positive electrode active material; p represents the mass content of La element based on the total mass of the positive electrode active layer; s represents the mass content of Ti element based on the total mass of the positive electrode active layer; s / p represents the ratio of the mass content of La element to the mass content of Ti element in the positive electrode active layer; D2 represents the average particle size of the second solid electrolyte, in nm. The values ​​are: nm; D1 / D2 represents the ratio of the average particle size of the first solid electrolyte to the average particle size of the second solid electrolyte; K4 represents the peak intensity of the characteristic peak (102); K5 represents the peak intensity of the characteristic peak (004); K6 represents the peak intensity of the characteristic peak (114); q represents the mass content of La element based on the total mass of the negative electrode active layer; t represents the mass content of Ti element based on the total mass of the negative electrode active layer; q / t represents the ratio of the mass content of La element to the mass content of Ti element in the negative electrode active layer; F represents the average particle size of the negative electrode active material, in nm; D2 / F represents the ratio of the average particle size of the second solid electrolyte to the average particle size of the negative electrode active material; g represents the mass content of the second solid electrolyte based on the total mass of the negative electrode active layer; " / " represents none.

[0118] Those skilled in the art will understand that, in order to obtain first solid electrolytes, second solid electrolytes and third solid electrolytes with different chemical compositions, the types and amounts of raw materials used in the preparation of each solid electrolyte can be adjusted, and the desired average particle size of solid electrolyte materials can also be obtained by controlling the crushing and grinding conditions.

[0119] Table 1

[0120] Table 2

[0121] Table 3

[0122] Test example: The lithium-ion secondary batteries provided in the above embodiments and comparative examples were tested as follows: (1) Test method for initial coulomb efficiency: First, at room temperature (25°C), the lithium-ion secondary batteries provided in the above embodiments and comparative examples were charged to 4.55V using 0.1C, and then charged at a constant voltage of 4.55V to 0.05C cutoff to obtain the initial charge capacity of the material. After resting for 5 minutes, the material was discharged to 2.8V using 0.1C to obtain the initial discharge capacity of the material. Finally, the percentage of the initial discharge capacity to the initial charge capacity is the initial coulombic efficiency of the secondary battery.

[0123] (2) Test method for cycle capacity retention: After standing at 25℃±2℃ for 10 minutes, the lithium-ion secondary batteries provided in the above embodiments and comparative examples were charged at 1C to the upper limit of the cutoff voltage of 4.55V, cut off at 0.05C, and left to stand for 10 minutes; then discharged at 1C to 2.5V, and left to stand for 10 minutes to obtain the initial capacity C0; the above charge and discharge process was repeated until the 500th cycle of constant voltage charging was completed and left to stand for 10 minutes, then discharged again at a current density of 1C to 2.5V, and left to stand for 10 minutes. The discharge capacity of the battery at this time was recorded as the capacity C1 after the cycle. Then the capacity retention rate after 500 cycles = C1 / C0 × 100%.

[0124] (3) Furnace temperature test The lithium-ion secondary batteries provided in the above embodiments and comparative examples were charged to 4.55V at 0.7C and then charged at a constant voltage to 0.025C. The fully charged cells were placed in a test chamber and subjected to a temperature rise rate of 5℃ / min. The highest furnace temperature at which the cells did not catch fire or explode within 60 minutes of constant temperature was recorded.

[0125] (4) Ratio performance The lithium-ion secondary batteries provided in the above embodiments and comparative examples were charged to 4.55V at a constant current density of 0.7C, and then charged at a constant voltage of 4.55V with a cutoff current of 0.05C. After standing for 10 minutes, they were discharged to 2.5V at current densities of 0.2C and 2C, respectively. The percentage of the discharge specific capacity at 2C to the discharge specific capacity at 0.2C is the battery's rate discharge capability, which is its rate performance.

[0126] The test results are shown in Table 4.

[0127] Table 4

[0128] As can be seen from Tables 1-4, this application introduces titanium-containing solid electrolytes with doped elements into the positive and negative active layers, respectively. Through dual-site co-doping, the structural stability of the titanium-containing solid electrolyte can be improved. At the same time, by introducing La elements into the positive and negative active layers and controlling the mass content p of La elements in the positive active layer to be higher than the mass content q of La elements in the negative active layer, the cycle stability, coulombic efficiency and safety of the secondary battery under high voltage cycling are improved.

[0129] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A lithium-ion secondary battery, comprising a positive electrode and a negative electrode, wherein the positive electrode comprises a positive current collector and a positive active layer on at least one side surface of the positive current collector, and the negative electrode comprises a negative current collector and a negative active layer on at least one side surface of the negative current collector, characterized in that, The positive electrode active layer includes a positive electrode active material and a first solid electrolyte, wherein the first solid electrolyte includes lithium aluminum titanium phosphate; the positive electrode active layer also includes La element, and the mass content of La element in the positive electrode active layer is p; The negative electrode active layer includes a negative electrode active material and a second solid electrolyte. The second solid electrolyte includes lithium lanthanum titanate. The mass content of La element in the negative electrode active layer is q, satisfying: p > q. The lithium aluminum titanium phosphate further includes a first element and a second element, wherein the first element includes at least one of La, Sc, and Y, and the second element includes at least one of Si, Zr, and Ce; and / or, the lithium lanthanum titanate further includes a third element and a fourth element, wherein the third element includes at least one of Al, Sc, and Y, and the fourth element includes at least one of Si, Zr, and Ce.

2. The lithium-ion secondary battery according to claim 1, characterized in that, The mass content of Ti element in the positive electrode active layer is s, and the positive electrode active layer satisfies at least one of the following conditions: (A) 0.015% ≤ p ≤ 4.2%; preferably, 0.02% ≤ p ≤ 4%; (B) 0.07% ≤ s ≤ 2%; (C) 0.1≤s / p≤4.

5.

3. The lithium-ion secondary battery according to claim 1, characterized in that, The mass content of Ti element in the negative electrode active layer is t, and the negative electrode active layer satisfies at least one of the following conditions: (a) 0.009% ≤ q ≤ 3.3%; preferably, 0.01% ≤ q ≤ 3%; (b) 0.01% ≤ t ≤ 2%; (c) 0.5≤t / q≤1.

8.

4. The lithium-ion secondary battery according to claim 1, characterized in that, Let the average particle size of the first solid electrolyte be denoted as D1, and the average particle size of the second solid electrolyte be denoted as D2, satisfying the following conditions: 100 nm ≤ D1 ≤ 2000 nm, 150 nm ≤ D2 ≤ 1000 nm, and 0.2 ≤ D1 / D2 ≤ 5.

5. The lithium-ion secondary battery according to claim 4, characterized in that, The average particle size of the positive electrode active material is denoted as Z, which satisfies the following conditions: 0.005≤D1 / Z≤0.1, 1000 nm≤Z≤50000 nm, preferably 0.02<D1 / Z<0.06; And / or, the average particle size of the negative electrode active material is denoted as F, which satisfies: 0.002≤D2 / F≤0.6, 1000 nm≤F≤100000 nm, preferably 0.04<D2 / F<0.

1.

6. The lithium-ion secondary battery according to claim 4, characterized in that, The positive electrode active material includes a positive electrode active matrix material and a coating layer covering at least a portion of the surface of the positive electrode active matrix material, the coating layer including a third solid electrolyte, the third solid electrolyte including lithium aluminum titanium phosphate; The average particle size of the third solid electrolyte is denoted as D3, which satisfies the following conditions: 2 nm ≤ D3 < 100 nm, and D3 < D1; and / or, the positive electrode active matrix material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based material, and lithium iron phosphate material. Preferably, the positive electrode active matrix material further includes La element, and the mass content of La element is 0.01% to 3% based on the total mass of the positive electrode active matrix material.

7. The lithium-ion secondary battery according to claim 6, characterized in that, Based on the total mass of the positive electrode active layer, the total mass content of lithium aluminum titanium phosphate is 0.05%~15%; And / or, based on the total mass of the negative electrode active layer, the mass content of the lithium lanthanum titanate is 0.04% to 7.5%.

8. The lithium-ion secondary battery according to any one of claims 1 to 7, characterized in that, The X-ray diffraction pattern of the lithium aluminum titanium phosphate in the first solid electrolyte independently includes a (104) characteristic peak, a (113) characteristic peak and a (024) characteristic peak, and the diffraction angle 2θ of each characteristic peak ranges as follows: 20°≤2θ(104)≤22°, 23°≤2θ(113)≤25°, 28.5°≤2θ(024)≤30.5°; And / or, the X-ray diffraction pattern of the lithium lanthanum titanate in the negative electrode active layer independently includes a (102) characteristic peak, a (004) characteristic peak and a (114) characteristic peak, with the diffraction angle 2θ of each characteristic peak ranging from 31.5°≤2θ(102)≤33.5°, 46.5°≤2θ(004)≤48.5°, and 57.5°≤2θ(114)≤59.5°.

9. The lithium-ion secondary battery according to claim 8, characterized in that, The peak intensity of the characteristic peak (104) is K1, the peak intensity of the characteristic peak (113) is K2, and the peak intensity of the characteristic peak (024) is K3, satisfying: 0.45≤K1 / K2≤0.75, 1.2≤K2 / K3≤3.5, K2>K1>K3; And / or, the peak intensity of the characteristic peak of (102) is K4, the peak intensity of the characteristic peak of (004) is K5, and the peak intensity of the characteristic peak of (114) is K6, satisfying: 2.5 < K4 / K5 < 4, 1 < K5 / K6 < 1.5, K4 > K5 > K6.

10. The lithium-ion secondary battery according to any one of claims 1 to 7, characterized in that, The positive electrode active layer further includes a positive electrode conductive agent, which includes multi-walled carbon nanotubes. And / or, the negative electrode active material includes a silicon-based material, which includes at least one of silicon-oxygen materials, silicon nanoparticles, and silicon-carbon materials; And / or, the negative electrode active layer further includes a negative electrode conductive agent, the negative electrode conductive agent including single-walled carbon nanotubes; And / or, the charging cut-off voltage of the lithium-ion secondary battery is ≥4.5V.

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