A composite cathode material for lithium-ion batteries, its preparation method, and the battery itself.

Abstract

This invention provides a composite cathode material, its preparation method, and the battery for lithium-ion batteries, belonging to the field of lithium-ion battery technology. The method includes the following steps: weighing and mixing cathode material powder and solid electrolyte powder to obtain mixture A, wherein the cathode material and solid electrolyte material are designed to be oxides with a lithium-ion concentration difference of not less than 0.012 mol / ml; adding a sacrificial agent to mixture A and mixing to obtain mixture B, wherein the amount of sacrificial agent added is 5%-15% of the mass of mixture A; and sintering mixture B to obtain the final product. By adding a sacrificial agent, byproducts are avoided between the cathode material and the solid electrolyte material during sintering, especially when the lithium-ion concentration difference between the cathode material and the solid electrolyte material is not less than 5%, as element diffusion during sintering has become a significant factor that reduces the electrochemical performance of the material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and specifically relates to a composite cathode material for lithium-ion batteries, its preparation method, and the battery itself. Background Technology

[0002] To reduce reliance on fossil fuels like petroleum, the market for battery-powered electric vehicles is expanding. Replacing non-renewable fuel-powered vehicles with electric cars is undoubtedly a future trend. Currently, most electric vehicles on the market use traditional liquid lithium-ion batteries. However, the liquid electrolyte in liquid lithium-ion batteries is a flammable organic solvent, which can easily react with the electrodes, leading to serious safety hazards such as battery fires or explosions. This undoubtedly poses a challenge to the application of lithium-ion batteries. Replacing the liquid electrolyte in traditional lithium-ion batteries with a non-flammable solid electrolyte can significantly improve battery safety. On the other hand, because lithium dendrites can pierce the separator, causing a short circuit between the positive and negative electrodes, traditional liquid lithium-ion batteries cannot use lithium metal as the negative electrode and can only use graphite, which has a lower volumetric and gravimetric energy density than lithium metal. Solid electrolytes, due to their higher mechanical strength, are less susceptible to piercing by lithium dendrites, preventing short circuits between the positive and negative electrodes. This makes it possible to use metallic lithium as the negative electrode in solid-state lithium-ion batteries, thereby increasing the energy density of lithium-ion batteries. Solid-state lithium-ion batteries are being widely studied as the next stage of development for lithium-ion batteries because the use of solid-state electrolytes can improve the safety and energy density of lithium-ion batteries.

[0003] The development of solid-state lithium-ion batteries faces two major bottlenecks. The first bottleneck is the relatively low ionic conductivity of solid-state electrolytes, which is several orders of magnitude lower than that of liquid electrolytes at room temperature. Over the past few decades, researchers have focused on designing higher-performance solid-state electrolytes, continuously improving their ionic conductivity, with some solid-state electrolytes even achieving lithium-ion conductivity comparable to liquid electrolytes. However, in traditional liquid lithium-ion batteries, the electrolyte can penetrate the pores of the electrodes, forming a tight solid-liquid interface. For solid-state lithium-ion batteries, due to the high mechanical strength and resistance to deformation of solid-state electrolytes, it is difficult to form a tight solid-solid contact with the electrodes, resulting in higher interfacial impedance, which is another bottleneck limiting the development of all-solid-state lithium-ion batteries. To improve the interfacial contact between the solid-state electrolyte and the positive electrode, it is usually necessary to fabricate a composite positive electrode together with the positive electrode active material. The smaller solid-state electrolyte can fill the gaps between the positive electrode active material particles, increasing the interfacial contact area while also playing a role in lithium-ion transport and reducing interfacial impedance.

[0004] For oxide solid electrolytes, due to their high hardness and rigidity, they are not easily deformed. Therefore, high-temperature co-firing of the composite cathode is necessary to further promote solid-solid contact at the interface. Although high-temperature co-firing can promote solid-solid contact, it can easily trigger side reactions between the cathode active material and the solid electrolyte during the co-firing process, leading to the collapse of the composite cathode structure and significantly reducing the electrochemical performance of the composite cathode. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a composite cathode material for lithium-ion batteries, a preparation method, and a battery. By adding a sacrificial agent, byproducts are avoided from forming between the cathode material and the solid electrolyte material during sintering. Especially when the difference in lithium-ion solubility between the cathode material and the solid electrolyte material is not less than 5%, element diffusion during sintering has become an important factor that cannot be ignored in reducing the electrochemical performance of the material.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] On one hand, the present invention provides a method for preparing a composite cathode material for lithium-ion batteries, comprising the following steps: weighing cathode material powder and solid electrolyte powder and mixing them to obtain mixture A, wherein the designed cathode material and solid electrolyte material are oxides and the difference in lithium-ion concentration is not less than 0.012 mol / ml; adding a sacrificial agent to mixture A and mixing it to obtain mixture B, wherein the amount of the sacrificial agent added is 5%-15% of the mass of mixture A; and sintering mixture B to obtain the final product.

[0008] Furthermore, the designed cathode material is one or more of NCM, lithium cobalt oxide, or lithium iron phosphate.

[0009] Furthermore, the NCM is LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2 or LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0010] Furthermore, the designed solid electrolyte material is lithium titanium aluminum phosphate.

[0011] Furthermore, the designed mass ratio of positive electrode material to solid electrolyte material is 7:(2.8-3.2). Weigh out the positive electrode material powder and solid electrolyte powder.

[0012] Furthermore, the sacrificial agent is lithium hydroxide, lithium carbonate, or lithium oxalate.

[0013] Furthermore, the average particle size of the sacrificial agent does not exceed 0.8 μm.

[0014] Furthermore, the sintering process is as follows: in an oxidizing atmosphere, the temperature is maintained at 600-700℃ for 0.5-1.0h.

[0015] On the other hand, the present invention provides a composite cathode material, which is prepared by the above-described preparation method.

[0016] On the other hand, the present invention provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery is made of the above-mentioned composite positive electrode material.

[0017] The beneficial effects of the technical solutions provided by the embodiments of the present invention include:

[0018] This invention prepares a lithium-ion battery with high electrochemical activity using the above-described preparation method. Specifically, the oxide-type solid electrolyte material includes various types, such as LLTO, LLZO, and LATP. In comparison, LATP has a lower cost because it does not use rare earth metals, but LATP has poor stability. Furthermore, since the difference in lithium-ion concentration between the cathode material and the solid electrolyte material is not less than 0.012 mol / ml, element diffusion is severe, and by-products such as Co3O4 and NiO are easily generated at the interface. Based on the above problems, this application proposes adding 5%-15% of a sacrificial agent by mass of mixture A. First, it prevents the interdiffusion between the cathode material and the solid electrolyte material, which would lead to the formation of byproducts. Second, the sacrificial agent has a high lithium content, which can compensate for the lithium loss during sintering. Third, the sacrificial agent can act as a modifier at the interface between the cathode material and the solid electrolyte material, improving the wettability of the interface during sintering, thereby comprehensively improving the electrochemical activity of the prepared lithium-ion battery. Finally, the sacrificial agent needs to be completely decomposed or absorbed during subsequent sintering processes; otherwise, the residual sacrificial agent will reduce the electrochemical activity of the lithium-ion battery. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The images show the XRD patterns of the dual-phase composite cathode materials prepared in Examples 1-3 and Comparative Example 1 of this invention.

[0021] Figure 2The first charge-discharge curves of the lithium-ion batteries prepared in Examples 1-3 and Comparative Example 1 of this invention at 0.1C are shown.

[0022] Figure 3 The lithium-ion batteries prepared in Examples 1-3 and Comparative Example 1 of this invention are shown in long-cycle diagrams at 1C.

[0023] Figure 4 The images show the XRD patterns of the dual-phase composite cathode materials prepared in Example 8 and Comparative Example 2 of this invention.

[0024] Figure 5 The first charge-discharge curves of the lithium-ion batteries prepared in Example 8 and Comparative Example 2 of this invention at 0.1C are shown.

[0025] Figure 6 The lithium-ion batteries prepared in Example 8 and Comparative Example 2 of this invention are shown in long-cycle diagrams at 1C.

[0026] Figure 7 The images show the XRD patterns of the dual-phase composite cathode materials prepared in Example 9 and Comparative Example 3 of this invention.

[0027] Figure 8 The first charge-discharge curves of the lithium-ion batteries prepared in Example 9 and Comparative Example 3 of this invention at 0.1C are shown.

[0028] Figure 9 This is a long-cycle diagram of the lithium-ion batteries prepared in Example 9 and Comparative Example 3 of the present invention at 1C. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] This invention provides a method for preparing a composite cathode material for lithium-ion batteries, comprising the following steps:

[0031] S1 Weigh out the positive electrode material powder and the solid electrolyte powder and mix them to obtain mixture A. The designed positive electrode material and solid electrolyte material are oxides and the difference in lithium ion concentration is not less than 0.012 mol / ml.

[0032] S2 adds a sacrificial agent to mixture A and mixes to obtain mixture B, wherein the amount of sacrificial agent added is 5%-15% of the mass of mixture A;

[0033] S3 sintersulates the mixture B to obtain the final product.

[0034] This invention prepares a lithium-ion battery with high electrochemical activity using the above-described preparation method. Specifically, the oxide-type solid electrolyte material includes various types, such as LLTO, LLZO, ZZATO, and LATP. In comparison, LATP, i.e., lithium titanium aluminum phosphate, has a lower cost because it does not use rare earth metals. However, LATP has poor stability, and because the difference in lithium-ion concentration between the cathode material and the solid electrolyte material is not less than 0.012 mol / ml, element diffusion is severe, and by-products such as Co3O4, NiO, and Fe2O3 are easily generated at the interface. Based on the above problems, this application proposes adding 5%-15% of a sacrificial agent by mass of mixture A. First, it prevents the interdiffusion between the cathode material and the solid electrolyte material, which would lead to the formation of byproducts. Second, the sacrificial agent has a high lithium content, which can compensate for the lithium loss during sintering. Third, the sacrificial agent can act as a modifier at the interface between the cathode material and the solid electrolyte material, improving the wettability of the interface during sintering, thereby comprehensively improving the electrochemical activity of the prepared lithium-ion battery. Finally, the sacrificial agent needs to be completely decomposed or absorbed during subsequent sintering processes; otherwise, the residual sacrificial agent will reduce the electrochemical activity of the lithium-ion battery.

[0035] Preferably, the difference in lithium-ion concentration between the positive electrode material and the solid electrolyte material is not less than 0.025 mol / ml, 0.030 mol / ml, 0.035 mol / ml, and 0.040 mol / ml.

[0036] It should be noted that the cathode material powder and solid electrolyte powder in this application, as well as the designed cathode material and solid electrolyte material, can be the same or different. Specifically, if the cathode material powder or solid electrolyte powder uses the same material as the powder after final firing, then the cathode material powder and solid electrolyte powder, as well as the designed cathode material and solid electrolyte material, are the same; otherwise, they are different. Taking the cathode material as an example, if the designed cathode material is LiNi... 0.8 Co 0.1 Mn 0.1 O2, while the added cathode material powder is LiNi. 0.8 Co 0.1 Mn 0.1 If O2 is present, then both are the same. If the added cathode material powder is of the hydroxyl-oxygen type or other components, it can be sintered to prepare LiNi. 0.8 Co 0.1 Mn 0.1 For O2 materials, the cathode material powder differs from the designed cathode material. For illustrative purposes, in subsequent embodiments of the invention, the cathode material powder and solid electrolyte powder used are the same as the designed cathode material and solid electrolyte material.

[0037] The molar concentration of lithium ions is calculated as follows: nLi / V, in units of mol / L, where n Li denoted as the number of moles of lithium ions, and V as the volume of the solid material.

[0038] The mixing process is to use ball milling or grinding to improve the uniformity of the mixture. In this embodiment of the invention, ball milling is preferred. The mixing process is as follows: the material-to-ball ratio is 0.9-1.1, the rotation speed is 200-300 r / min, and the ball milling time is at least 30 h.

[0039] Specifically, the designed cathode material is one or more of NCM, lithium cobalt oxide, or lithium iron phosphate. Preferably, the NCM is LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2 or LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0040] Specifically, the designed solid electrolyte material is LATP, preferably Li. 1.3 Al 0.3 Ti 1.7 (PO3)4, compared with other oxide-type solid electrolyte materials, does not require the addition of rare earth metals, thus the cost of preparing solid-state lithium-ion batteries is lower. However, the material has poor stability and is prone to decomposition during sintering. In addition, the lithium content of the material is low, with a lithium molar concentration difference of up to 0.042 mol / ml between it and the cathode material. Therefore, it is more likely to cause element diffusion and generate byproducts, resulting in low chemical activity of the prepared battery. For the purpose of illustration, LATP is used in the embodiments of the present invention.

[0041] Specifically, the designed mass ratio of cathode material to solid electrolyte material is 7:(2.8-3.2). Cathode material powder and solid electrolyte powder are weighed out. This mass ratio affects chemical activity. Solid electrolyte material is a fast ion conductor; if a fast ion conductor forms a pathway in the cathode material, the electrochemical activity will be higher. Therefore, it is necessary to strictly control the ratio of cathode material to solid electrolyte material to increase the probability of pathway formation.

[0042] Specifically, the sacrificial agent is lithium hydroxide, lithium carbonate, or lithium oxalate. Specifically, lithium hydroxide (LiOH), lithium carbonate (Li2CO3), and lithium oxalate (Li2C2O4) are used. It should be noted that when using LiOH·H2O as the sacrificial agent, the mass of bound water needs to be added to the calculated mass of LiOH. For example, if the calculated mass of LiOH is 75 mg, then the mass of LiOH·H2O to be added is 131.3 mg. The average particle size of the sacrificial agent does not exceed 0.8 μm. First, the particle size of the sacrificial agent affects its interfacial energy, thus affecting its activity during sintering. Second, using this particle size and corresponding ratio ensures that the sacrificial agent is completely decomposed or absorbed in subsequent preparation processes, and there is no independent sacrificial agent phase. The sacrificial agent has a high lithium concentration, which results in higher costs. This invention, by adding less sacrificial agent and considering the particle size and sintering process, prepares a composite cathode material that meets the objectives of this invention. To further improve the electrochemical activity of the prepared composite cathode material, the average particle size of the cathode material is preferably 4-20 μm, the average particle size of the solid electrolyte material is 1-5 μm, and the average particle size of the sacrificial agent is not less than 0.2 and not more than 0.8 μm. When the particle size is too small, agglomeration is more serious and the cost is higher, while when the particle size is too large, the suppression performance is poor.

[0043] Specifically, the sintering process is as follows: In an oxidizing atmosphere, the temperature is held at 600-700℃ for 0.5-1.0 h. Cooling is then performed, such as natural cooling or furnace cooling. Preferably, the temperature is increased to 600-700℃ at a rate not exceeding 10℃ / min.

[0044] This invention also provides a composite cathode material, which is prepared using the above-described preparation method.

[0045] This invention also provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery is prepared using the above-mentioned composite positive electrode material.

[0046] In the following embodiments:

[0047] XRD testing: Rigaku Ultima IV-185 X-ray powder diffractometer (Japan) was used.

[0048] Half-cell assembly: The composite cathode material prepared in the embodiments and comparative examples of the present invention was slurried and coated with Super P and PVDF at a mass ratio of 80:10:10, and then cut into electrode sheets with a diameter of 10 mm. Using lithium metal as the negative electrode and LB-363 electrolyte from Suzhou Duoduo Chemical Technology Co., Ltd. as the electrolyte, the half-cell was assembled in an argon glove box.

[0049] Lithium-ion battery charge / discharge test: LiNi 0.8Co 0.1 Mn 0.1 O2 / Li 1.3 Al 0.3 Ti 1.7 The battery prepared using (PO3)4 composite cathode material has a charge / discharge voltage range of 2.8-4.5V. (LiCoO2 / Li) 1.3 Al 0.3 Ti 1.7 The battery prepared with (PO3)4 composite cathode material has a charge / discharge voltage range of 3.0-4.5V. (LiFePO4 / Li) 1.3 Al 0.3 Ti 1.7 The battery prepared by the (PO3)4 composite cathode material has a charge-discharge voltage range of 2.5-4.0V. Before the cycle test, it is activated at 0.1C for three cycles, and then the charge-discharge cycle test is carried out at 1C with the same voltage range. All electrochemical performance tests are carried out at room temperature.

[0050] To better illustrate the embodiments of the present invention, the present invention will be further described in detail below through specific examples.

[0051] Example 1

[0052] This invention provides a composite cathode material for lithium-ion batteries and its preparation method, comprising:

[0053] S1 weighs LiNi at a mass ratio of 7:3 0.8 Co 0.1 Mn 0.1 O2 powder and Li 1.3 Al 0.3 Ti 1.7 (PO3)4 powder was mixed to obtain mixture A, LiNi 0.8 Co 0.1 Mn 0.1 O2 and Li 1.3 Al 0.3 Ti 1.7 The difference in lithium ion concentration in (PO3)4 was 0.039 mol / ml.

[0054] S2 adds LiOH·H2O to mixture A and mixes to obtain mixture B, wherein the mass of the added LiOH·H2O is 15% of that in mixture A.

[0055] S3 placed the mixture B in an air atmosphere at 700°C for 0.5 h and then naturally cooled it to room temperature to finally obtain a two-phase composite cathode material, denoted as NCM811 / LATP-1.

[0056] The prepared NCM811 / LATP-1 was analyzed by XRD, such as... Figure 1 As shown, the peak intensity and position of NCM811 remain unchanged, indicating that the addition of the sacrificial agent suppressed the side reactions of the biphase composite cathode during high-temperature co-firing, stabilized the structure of the biphase composite cathode, and there is no sacrificial agent phase.

[0057] like Figure 2 As shown, the lithium-ion battery prepared in this embodiment has a specific capacity of 225 mAh / g during the first charge-discharge cycle at 0.1C. (As indicated...) Figure 3 At 1C, the cycle efficiency is 83.53% over 100 cycles.

[0058] Example 2

[0059] This invention provides a composite cathode material for lithium-ion batteries and its preparation method, comprising:

[0060] S1 weighs LiNi at a mass ratio of 7:3 0.8 Co 0.1 Mn 0.1 O2 powder and Li 1.3 Al 0.3 Ti 1.7 (PO3)4 powder was mixed to obtain mixture A, LiNi 0.8 Co 0.1 Mn 0.1 O2 and Li 1.3 Al 0.3 Ti 1.7 The difference in lithium ion concentration in (PO3)4 was 0.039 mol / ml.

[0061] S2 adds Li2CO3 to mixture A and mixes to obtain mixture B, wherein the mass of the added Li2CO3 is 15% of that in mixture A.

[0062] S3 placed the mixture B in an air atmosphere at 700°C for 0.5 h and then naturally cooled it to room temperature to finally obtain a two-phase composite cathode material, denoted as NCM811 / LATP-2.

[0063] The prepared NCM811 / LATP-2 was analyzed by XRD, such as... Figure 1 As shown, the peak intensity and position of NCM811 remain unchanged, indicating that the addition of the sacrificial agent suppressed the side reactions of the biphase composite cathode during high-temperature co-firing, stabilized the structure of the biphase composite cathode, and there is no sacrificial agent phase.

[0064] like Figure 2 As shown, the lithium-ion battery prepared in this embodiment has a specific capacity of 224 mAh / g during the first charge-discharge cycle at 0.1C. Figure 3At 1C, the cycle efficiency is 83.42% over 100 cycles.

[0065] Example 3

[0066] This invention provides a composite cathode material for lithium-ion batteries and its preparation method, comprising:

[0067] S1 weighs LiNi at a mass ratio of 7:3 0.8 Co 0.1 Mn 0.1 O2 powder and Li 1.3 Al 0.3 Ti 1.7 (PO3)4 powder was mixed to obtain mixture A, LiNi 0.8 Co 0.1 Mn 0.1 O2 and Li 1.3 Al 0.3 Ti 1.7 The difference in lithium ion concentration in (PO3)4 was 0.039 mol / ml.

[0068] S2 adds Li2C2O4 to mixture A and mixes to obtain mixture B, wherein the mass of the added Li2C2O4 is 15% of that in mixture A.

[0069] S3 placed the mixture B in an air atmosphere at 700°C for 0.5 h and then naturally cooled it to room temperature to finally obtain a two-phase composite cathode material, denoted as NCM811 / LATP-3.

[0070] The prepared NCM811 / LATP-3 was analyzed by XRD, such as... Figure 1 As shown, the peak intensity and position of NCM811 remain unchanged, indicating that the addition of the sacrificial agent suppressed the side reactions of the biphase composite cathode during high-temperature co-firing, stabilized the structure of the biphase composite cathode, and there is no sacrificial agent phase.

[0071] like Figure 2 As shown, the lithium-ion battery prepared in this embodiment has a specific capacity of 210 mAh / g during the first charge-discharge cycle at 0.1C. Figure 3 At 1C, the cycle efficiency is 53.95% over 100 cycles.

[0072] Example 4

[0073] This invention provides a composite cathode material for lithium-ion batteries and its preparation method, comprising:

[0074] S1 weighs LiNi at a mass ratio of 7:3 0.8 Co 0.1 Mn 0.1 O2 powder and Li 1.3Al 0.3 Ti 1.7 (PO3)4 powder was mixed to obtain mixture A, LiNi 0.8 Co 0.1 Mn 0.1 O2 and Li 1.3 Al 0.3 Ti 1.7 The difference in lithium ion concentration in (PO3)4 was 0.039 mol / ml.

[0075] S2 adds LiOH·H2O to mixture A and mixes to obtain mixture B, wherein the mass of the added LiOH·H2O is 10% of that in mixture A.

[0076] S3 placed the mixture B in an air atmosphere at 700°C for 0.5 h and then naturally cooled it to room temperature to finally obtain a two-phase composite cathode material, denoted as NCM811 / LATP-4.

[0077] XRD analysis of the prepared NCM811 / LATP-4 showed that the peak intensity and position of NCM811 remained unchanged, indicating that the addition of the sacrificial agent suppressed the side reactions of the biphase composite cathode during high-temperature co-firing, stabilized the structure of the biphase composite cathode, and that there was no sacrificial agent phase.

[0078] The lithium-ion battery prepared in this embodiment has a specific capacity of 218 mAh / g in the first charge-discharge cycle at 0.1C and a cycle efficiency of 80.13% in 100 cycles at 1C.

[0079] Example 5

[0080] This invention provides a composite cathode material for lithium-ion batteries and its preparation method, comprising:

[0081] S1 weighs LiNi at a mass ratio of 7:3 0.8 Co 0.1 Mn 0.1 O2 powder and Li 1.3 Al 0.3 Ti 1.7 (PO3)4 powder was mixed to obtain mixture A, LiNi 0.8 Co 0.1 Mn 0.1 O2 and Li 1.3 Al 0.3 Ti 1.7 The difference in lithium ion concentration in (PO3)4 was 0.039 mol / ml.

[0082] S2 adds LiOH·H2O to mixture A and mixes to obtain mixture B, wherein the mass of the added LiOH·H2O is 15% of that in mixture A.

[0083] S3 placed the mixture B in an air atmosphere and co-fired it at 650°C for 0.5 h, then naturally cooled it to room temperature to finally obtain a two-phase composite cathode material, denoted as NCM811 / LATP-5.

[0084] XRD analysis of the prepared NCM811 / LATP-5 showed that the peak intensity and position of NCM811 remained unchanged, indicating that the addition of the sacrificial agent suppressed the side reactions of the biphase composite cathode during high-temperature co-firing, stabilized the structure of the biphase composite cathode, and that there was no sacrificial agent phase.

[0085] The lithium-ion battery prepared in this embodiment has a specific capacity of 223 mAh / g in the first charge-discharge cycle at 0.1C and a cycle efficiency of 85.19% in 100 cycles at 1C.

[0086] Example 6

[0087] This invention provides a composite cathode material for lithium-ion batteries and its preparation method, comprising:

[0088] S1 weighs LiNi at a mass ratio of 7:2.8 0.8 Co 0.1 Mn 0.1 O2 powder and Li 1.3 Al 0.3 Ti 1.7 (PO3)4 powder was mixed to obtain mixture A, LiNi 0.8 Co 0.1 Mn 0.1 O2 and Li 1.3 Al 0.3 Ti 1.7 The difference in lithium ion concentration in (PO3)4 was 0.039 mol / ml.

[0089] S2 adds LiOH·H2O to mixture A and mixes to obtain mixture B, wherein the mass of the added LiOH·H2O is 15% of that in mixture A.

[0090] S3 placed the mixture B in an air atmosphere at 600°C for 0.5 h and then naturally cooled it to room temperature to finally obtain a two-phase composite cathode material, denoted as NCM811 / LATP-6.

[0091] XRD analysis of the prepared NCM811 / LATP-6 showed that the peak intensity and position of NCM811 remained unchanged, indicating that the addition of the sacrificial agent suppressed the side reactions of the biphase composite cathode during high-temperature co-firing, stabilized the structure of the biphase composite cathode, and that there was no sacrificial agent phase.

[0092] The lithium-ion battery prepared in this embodiment has a specific capacity of 220 mAh / g in the first charge-discharge cycle at 0.1C and a cycle efficiency of 81.35% in 100 cycles at 1C.

[0093] Example 7

[0094] This invention provides a composite cathode material for lithium-ion batteries and its preparation method, comprising:

[0095] S1 weighs LiNi at a mass ratio of 7:3.2 0.8 Co 0.1 Mn 0.1 O2 powder and Li 1.3 Al 0.3 Ti 1.7 (PO3)4 powder was mixed to obtain mixture A, LiNi 0.8 Co 0.1 Mn 0.1 O2 and Li 1.3 Al 0.3 Ti 1.7 The difference in lithium ion concentration in (PO3)4 was 0.039 mol / ml.

[0096] S2 adds LiOH·H2O to mixture A and mixes to obtain mixture B, wherein the mass of the added LiOH·H2O is 5% of that in mixture A.

[0097] S3 placed the mixture B in an air atmosphere at 700°C for 1.0 h and then naturally cooled it to room temperature to finally obtain a two-phase composite cathode material, denoted as NCM811 / LATP-7.

[0098] XRD analysis of the prepared NCM811 / LATP-7 showed that the peak intensity and position of NCM811 remained unchanged, indicating that the addition of the sacrificial agent suppressed the side reactions of the biphase composite cathode during high-temperature co-firing, stabilized the structure of the biphase composite cathode, and that there was no sacrificial agent phase.

[0099] The lithium-ion battery prepared in this embodiment has a specific capacity of 171 mAh / g in the first charge-discharge cycle at 0.1C and a cycle efficiency of 76.38% in 100 cycles at 1C.

[0100] Example 8

[0101] This invention provides a composite cathode material for lithium-ion batteries and its preparation method, comprising:

[0102] S1 weighs LiCoO2 powder and Li at a mass ratio of 7:3. 1.3 Al 0.3 Ti 1.7(PO3)4 powder was mixed to obtain mixture A, LiCoO2 and Li 1.3 Al 0.3 Ti 1.7 The difference in lithium ion concentration in (PO3)4 is 0.042 mol / ml.

[0103] S2 adds LiOH·H2O to mixture A and mixes to obtain mixture B, wherein the mass of the added LiOH·H2O is 15% of that in mixture A.

[0104] S3 placed the mixture B in an air atmosphere at 700°C for 0.5 h and then naturally cooled it to room temperature to finally obtain a two-phase composite cathode material, denoted as LiCoO2 / LATP-1.

[0105] The prepared LiCoO2 / LATP-1 was analyzed by XRD, such as... Figure 4 As shown, the peak intensity and position of LiCoO2 remain unchanged, indicating that the addition of the sacrificial agent suppressed the side reactions of the biphase composite cathode during high-temperature co-firing, stabilized the structure of the biphase composite cathode, and there is no sacrificial agent phase.

[0106] like Figure 5 The lithium-ion battery prepared in this embodiment has a specific capacity of 185 mAh / g during the first charge-discharge cycle at 0.1C. Figure 6 As shown, the cycle efficiency is 87.68% after 100 cycles at 1C.

[0107] Example 9

[0108] This invention provides a composite cathode material for lithium-ion batteries and its preparation method, comprising:

[0109] S1 weighs LiFePO4 powder and Li at a mass ratio of 7:3. 1.3 Al 0.3 Ti 1.7 (PO3)4 powder was mixed to obtain mixture A, LiFePO4 and Li 1.3 Al 0.3 Ti 1.7 The difference in lithium ion concentration in (PO3)4 is 0.013 mol / ml.

[0110] S2 adds LiOH·H2O to mixture A and mixes to obtain mixture B, wherein the mass of the added LiOH·H2O is 15% of that in mixture A.

[0111] S3 placed the mixture B in an air atmosphere at 700°C for 0.5 h and then naturally cooled it to room temperature to finally obtain a two-phase composite cathode material, denoted as LiFePO4 / LATP-1.

[0112] The prepared LiFePO4 / LATP-1 was analyzed by XRD, such as... Figure 7 The LiFePO4 peak intensity and position remained unchanged, indicating that the addition of the sacrificial agent suppressed the side reactions of the biphase composite cathode during high-temperature co-firing, stabilized the structure of the biphase composite cathode, and there was no sacrificial agent phase.

[0113] like Figure 8 The lithium-ion battery prepared in this embodiment has a specific capacity of 160 mAh / g during the first charge-discharge cycle at 0.1C. Figure 9 At 1C, the cycle efficiency is 94.66% after 100 cycles.

[0114] Comparative Example 1

[0115] Compared with Example 1, step S2 is omitted in this comparative example.

[0116] The prepared NCM811 / LATP-10 was analyzed by XRD, such as... Figure 1 As shown, after co-firing at 700℃ for 0.5h, the intensity of the strongest peak (003) and the second strongest peak (104) of NCM811 in Comparative Example 1 decreased significantly, indicating that NCM811 participated in the side reaction during the high-temperature co-firing process; the changes in the layered crack peaks (006) / (102) and (018) / (110) indicate that the layered structure of NCM811 gradually deteriorated.

[0117] like Figure 2 As shown, the lithium-ion battery prepared in this embodiment has a specific capacity of 102 mAh / g during the first charge-discharge cycle at 0.1C. Figure 3 At 1C, the cycle efficiency is 18.27% over 100 cycles.

[0118] Comparative Example 2

[0119] Compared with Example 8, step S2 is omitted in this comparative example.

[0120] The prepared LiCoO2 / LATP-10 was analyzed by XRD, such as... Figure 4 As shown, after co-firing at 700℃ for 0.5h, the intensity of the strongest peak (003) and the second strongest peak (104) of LiCoO2 decreased significantly, and a peak of Co3O4 appeared, indicating that LiCoO2 participated in the side reaction during the high-temperature co-firing process.

[0121] like Figure 5 The lithium-ion battery prepared in this embodiment has a specific capacity of 99 mAh / g during the first charge-discharge cycle at 0.1C. Figure 6 As shown, the cycle efficiency is 64.75% after 100 cycles at 1C.

[0122] Comparative Example 3

[0123] Compared with Example 9, step S2 is omitted in this comparative example.

[0124] The prepared LiFePO4 / LATP-10 was analyzed by XRD, such as... Figure 7 After co-firing at 700℃ for 0.5 h, the peak intensity of LiFePO4 decreased significantly, and a peak of Fe2O3 appeared, indicating that LiFePO4 participated in the side reaction during the high-temperature co-firing process.

[0125] like Figure 8 The lithium-ion battery prepared in this embodiment has a specific capacity of 101 mAh / g during the first charge-discharge cycle at 0.1C. Figure 9 At 1C, the cycle efficiency is 91.24% after 100 cycles.

[0126] Comparative Example 4

[0127] Compared to Example 6, in this comparative example, the mass of LiOH·H2O added is 16% of mixture A.

[0128] XRD analysis of the prepared NCM811 / LATP-11 revealed the presence of a partial lithium oxide phase.

[0129] The lithium-ion battery prepared in this embodiment has a specific capacity of 215 mAh / g in the first charge-discharge cycle at 0.1C and a cycle efficiency of 70.20% in 100 cycles at 1C.

[0130] Comparative Example 5

[0131] Compared to Example 7, in this comparative example, the mass of LiOH·H2O added is 4% of mixture A.

[0132] XRD analysis of the prepared NCM811 / LATP-12 showed that the intensity of the strongest peak (003) and the second strongest peak (104) of NCM811 decreased slightly, indicating that some byproducts were generated in the reaction.

[0133] The lithium-ion battery prepared in this embodiment has a specific capacity of 165 mAh / g in the first charge-discharge cycle at 0.1C and a cycle efficiency of 62.3% in 100 cycles at 1C.

[0134] Comparative Example 6

[0135] Compared with Example 7, in this comparative example, in step S3, the mixture B is placed in an air atmosphere and co-fired at 700°C for 1.2 hours.

[0136] XRD analysis of the prepared NCM811 / LATP-13 showed that the intensity of the strongest peak (003) and the second strongest peak (104) of NCM811 decreased slightly, indicating that some byproducts were generated in the reaction.

[0137] The lithium-ion battery prepared in this embodiment has a specific capacity of 167 mAh / g in the first charge-discharge cycle at 0.1C and a cycle efficiency of 66.3% in 100 cycles at 1C.

[0138] Comparative Example 7

[0139] Compared with Example 6, in this comparative example, in step S3, the mixture B is placed in an air atmosphere and co-fired at 600°C for 0.4 hours.

[0140] XRD analysis of the prepared NCM811 / LATP-14 revealed the presence of a partial lithium oxide phase.

[0141] The lithium-ion battery prepared in this embodiment has a specific capacity of 211 mAh / g in the first charge-discharge cycle at 0.1C and a cycle efficiency of 71.8% in 100 cycles at 1C.

[0142] Example 8

[0143] Compared with Example 1, the average particle size of LiOH·H2O in this comparative example is 1 μm.

[0144] XRD analysis of the prepared NCM811 / LATP-15 showed that the intensity of the strongest peak (003) and the second strongest peak (104) of NCM811 decreased slightly, indicating that some byproducts were generated during the reaction.

[0145] Comparative Examples 1-9 and 1-3 show that, without the addition of a sacrificial agent, all prepared biphase composite cathode materials exhibit byproduct formation, resulting in low electrochemical activity of the prepared lithium-ion batteries. Comparative Examples 6 and 7 and 4-7 show that the amount of sacrificial agent added and the sintering process affect the battery performance. Insufficient addition leads to the formation of a small amount of byproducts, while excessive addition results in the retention of some lithium oxide phase. Both factors contribute to low electrochemical activity in the prepared lithium-ion batteries. Comparative Examples 1 and 8 show that the particle size of the sacrificial agent affects its inhibition of NCM811 and LATP; excessively large particle sizes result in weaker inhibition.

[0146] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite cathode material for lithium-ion batteries, characterized in that, Includes the following steps: Weigh out the positive electrode material powder and the solid electrolyte powder and mix them to obtain mixture A. The designed positive electrode material and solid electrolyte material are oxides and the difference in lithium ion concentration is not less than 0.012 mol / ml. Add a sacrificial agent to mixture A and mix to obtain mixture B, wherein the amount of sacrificial agent added is 5%-15% of the mass of mixture A; The mixture B is sintered to obtain the final product; The designed cathode material is one or more of NCM, lithium cobalt oxide, or lithium iron phosphate; The designed solid electrolyte material is lithium titanium aluminum phosphate; The designed mass ratio of positive electrode material to solid electrolyte material is 7:(2.8-3.2). Weigh out the positive electrode material powder and solid electrolyte powder. The sacrificial agent is lithium hydroxide, lithium carbonate, or lithium oxalate, wherein the lithium hydroxide is LiOH·H2O. The sintering process is as follows: in an oxidizing atmosphere, the temperature is maintained at 600-700℃ for 0.5-1.0h.

2. The preparation method according to claim 1, characterized in that, The NCM is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2 or LiNi 0.6 Co 0.2 Mn 0.2 O2.

3. The preparation method according to claim 1, characterized in that, The average particle size of the sacrificial agent does not exceed 0.8 μm.

4. A composite cathode material, characterized in that, The composite cathode material is prepared using any one of the preparation methods described in claims 1-3.

5. A lithium-ion battery, characterized in that, The positive electrode of the lithium-ion battery is prepared using the composite positive electrode material described in claim 4.

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