Ternary positive electrode material with surface gradient doping and coating composite modification, preparation method of ternary positive electrode material and sulfide all-solid-state battery

Abstract

The invention belongs to the technical field of batteries, and discloses a surface gradient doping and coating composite modified ternary positive electrode material, the surface of a ternary positive electrode material matrix is provided with a gradient doping region doped with an M1 element, and the surface of the gradient doping region is provided with a coating containing an M2 element; and in the gradient doped region, the content of the doped M1 element is gradually reduced in a gradient manner from outside to inside. The ternary positive electrode material can inhibit the space charge layer effect and interface side reaction of a positive electrode material / sulfide solid electrolyte interface, so that the interface compatibility and the lithium ion migration rate are improved. According to the preparation method, surface gradient doping and surface coating composite modification are synchronously realized through a one-step synthesis method, the interfacial compatibility between the ternary material and the sulfide solid electrolyte is improved, the space charge layer effect is inhibited, and the interfacial lithium ion conduction performance is improved. And a composite modified positive electrode material which can be suitable for an all-solid-state battery system and is easy for large-scale industrial production is developed.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of power batteries, and in particular to a ternary positive electrode material applied to a full-solid-state battery and a preparation method thereof. BACKGROUND

[0002] With the development of new energy vehicles, the market has higher requirements for the energy density, charging speed, safety and other indicators of power batteries. The full-solid-state battery uses a solid-state electrolyte to transfer lithium ions between the positive electrode and the negative electrode, replacing the flammable and volatile liquid organic electrolyte, thereby improving the safety of the power battery. In addition, the solid-state electrolyte has more excellent mechanical properties and can hinder the growth of lithium dendrites, so as to be expected to use a lithium metal negative electrode in the future, thereby greatly improving the energy density of the battery.

[0003] The sulfide solid-state electrolyte has an ion conductivity comparable to that of an electrolyte and is one of the most promising solid-state electrolytes. However, there are problems such as a space charge layer, chemical / electrochemical side reactions, and contact failure between the sulfide solid-state electrolyte and the ternary positive electrode material.

[0004] The so-called space charge layer is that when the sulfide solid-state electrolyte is in contact with the ternary positive electrode material, due to the difference in chemical potential of lithium ions between the two, part of the lithium ions at the interface will migrate from the surface of the electrolyte to the oxide positive electrode material side, causing the lithium ion concentration to be different between the bulk phase of the electrolyte and the interface, thereby hindering the transfer of lithium ions. Since the ternary positive electrode material is an ion and electron composite conductor, its electronic conductivity can balance the lithium ion concentration gradient on the positive electrode material side, so that more lithium ions migrate to the positive electrode material side, forming a lithium ion “loss zone” at the interface, greatly reducing the migration rate of lithium ions at the interface between the electrolyte and the positive electrode material, and further reducing the electrochemical performance of the material. Therefore, the interface compatibility between the ternary positive electrode material and the sulfide solid-state electrolyte is poor, and the unique space charge layer effect will seriously hinder the transport of lithium ions between the interfaces, limiting the electrochemical performance of the positive electrode material in the full-solid-state battery.

[0005] The patent with the application publication number CN113745497A prepares an X and Y doped precursor by co-precipitating soluble X metal salt, Y metal salt and nickel salt, cobalt salt and manganese salt, and then mixes and calcines the precursor with lithium salt to obtain a single crystal high-nickel positive electrode material doped with X bulk phase and Y in-situ gradient. The patent with the application publication number CN118173763A obtains a modified ternary positive electrode material doped with cobalt by mixing and sintering a cobalt-containing compound and a metal compound, mixing and sintering the cobalt-doped material with a precursor and lithium salt, and performing secondary sintering and coating. The above technical solutions can improve the performance of the ternary positive electrode material in the electrolyte system to a certain extent, but cannot effectively address the interface problems faced by the ternary positive electrode material in the full-solid-state battery system. SUMMARY

[0006] To address the inherent space charge layer problem between ternary cathode materials and sulfide solid electrolytes, this invention provides a ternary cathode material and its preparation method that are modified by surface gradient doping and coating. Through the synergistic effect of gradient doping elements, transition metal elements within the ternary cathode material lattice, and oxygen, the chemical potential of lithium ions on both sides of the interface is balanced. Furthermore, the introduction of a new interface through surface coating avoids direct contact, suppressing the space charge layer effect between the electrode material and the solid electrolyte, improving interface stability and lithium ion migration rate, and enhancing the performance of the ternary cathode material in all-solid-state batteries.

[0007] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A ternary cathode material with surface gradient doping and coating composite modification, comprising a gradient doped region of element M1 on the surface of a ternary cathode material matrix, and a coating containing element M2 on the surface of the gradient doped region; wherein the ionic radius R of element M1 is... M1 With nickel ion radius R Ni3+ The relationship between R Ni3+ <R M1 ≤1.3R Ni3+ The ionic radius R of the M2 element M2 With nickel ion radius R Ni3+ The relationship between R M2 ≥1.3R Ni3+ And R M2 - R M1 ≥ 0.3Å; The depth of the gradient doping region is within 1000 nm. Within the gradient doping region, the content of doped M1 element gradually decreases from the outside to the inside, and the proportion of M1 element content within 100 nm of the surface of the gradient doping region to the total amount of M1 element is Wt. surface % meets 30wt% <Wt surface % < 70wt%.

[0008] In the above-mentioned ternary cathode material with surface gradient doping and coating composite modification, preferably, the mass percentage of the M1 element in the ternary cathode material is 0.01~2wt%, and the mass percentage of the M2 element in the ternary cathode material is 0.01~1wt%.

[0009] Preferably, the M1 element includes one or more of Mg, Ti, Co, Ga, Zr, Nb, Mo, Sn, Sb, Ta, and W, and the M2 element includes one or more of Na, K, Ca, Zn, Sr, Y, Ba, La, and Ce.

[0010] Preferably, the nickel ion radius R Ni3+is 0.56 Å.

[0011] Preferably, the ternary cathode material has a single crystal morphology, and the particle D 50 is 2 to 7 μm.

[0012] Preferably, the coating is island-shaped coated particles, and the particle size of the coated particles is 50 to 500 nm. The coated particles are coatings with lithium ion conductivity formed by the reaction of M2 element with residual lithium on the surface.

[0013] Preferably, the chemical formula of the ternary cathode material matrix is LiNi 1-x-y-z Co x Mn y Z z O2, where 0.5 ≤ 1 - x - y - z < 1, 0 < x ≤ 0.3, 0 < y ≤ 0.3, 0 < z ≤ 0.01, and the Z element includes one or more of Mg, Al, Ca, Ti, Sr, Zr, Ba, La, and W.

[0014] Preferably, the doping depth and content of the M1 element and the content of the M2 element are obtained by EPMA analysis.

[0015] Based on a general inventive concept, the present invention also provides a preparation method for a surface gradient doping and coating composite modified ternary cathode material, including the following steps: 1) Weigh the ternary cathode material matrix and mix it with an additive containing M1 and M2 elements to obtain a mixture; 2) Perform staged calcination on the mixture to obtain a calcined product; 3) The calcined product is pulverized and sieved to obtain a surface gradient doping and coating composite modified ternary cathode material.

[0016] For the above preparation method, preferably, in step 1), the additive containing M1 and M2 elements is one or more of oxides, hydroxides, carbonates, nitrates, acids, and ammonium salts; the rotation speed of the mixer used for mixing is 500 to 2000 rpm, and the mixing time is 10 to 60 min.

[0017] Preferably, in step 2), the staged calcination includes a first stage and a second stage. The calcination temperature T1 in the first stage and the ionic radius R of the M1 element M1 satisfy 800 °C Å -1 ≤ T1 / R M1 ≤ 1300 °C Å -1 , and the calcination time is 1 to 5 h; the calcination temperature T2 in the second stage and the ionic radius R of the M1 element M1 satisfy 500 °C Å -1 ≤ T2 / R M1<800℃ Å -1 The calcination time is 1-8 hours, the heating / cooling rate is 1-10℃ / min, and the calcination atmosphere is oxygen or air. The purpose of this segmented calcination process is to first calcine at a higher temperature T1 to promote the thermal diffusion of the M1 element with a small ionic radius into the material lattice, forming a surface gradient doping; then cool down to a lower temperature T2 to prevent excessive diffusion of the M1 element and the formation of uniform bulk doping, while allowing the M2 element with a larger ionic radius to continue reacting with residual lithium to form a surface coating.

[0018] The technical principle of this invention is as follows: This invention utilizes the different thermal diffusion rates of metal ions with different radii and employs a segmented calcination process to control the diffusion process of elements from the particle surface to the interior, achieving one-step synthesis of composite modified cathode materials with gradient doping and surface coating: Among them, the ionic radius of element M1 is greater than that of element Ni. 3+ Slightly larger, it is easier for M1 to enter the ternary material lattice through thermal diffusion during the calcination process, forming surface gradient doping. If the ionic radius of element M1 is larger than that of Ni... 3+ If the doping density is too low, the M1 element will diffuse entirely into the particle interior during calcination, forming uniform doping. This prevents the M1 from accumulating on the surface and forming a surface gradient doping, thus hindering targeted improvement of the material's surface structure. Therefore, this invention selects gradient-doped M1 elements to precisely regulate the chemical potential of lithium ions on the surface of the ternary material particles, balancing the lithium ion concentration on both sides of the interface, suppressing the space charge layer effect, improving near-surface lattice stability, reducing oxygen vacancies, decreasing near-surface volume changes, and suppressing contact failure between the cathode material and the solid electrolyte.

[0019] Meanwhile, the ionic radius of element M2 is greater than that of element Ni. 3+ Much larger, these lithium-ion conductors are difficult to diffuse into the crystal lattice during calcination and tend to react with residual lithium on the particle surface to form a lithium-ion conductive coating. Introducing a lithium-ion conductive coating at the interface between the cathode material particles and the sulfide solid electrolyte transforms the original cathode / electrolyte interface into a cathode / coating and coating / electrolyte interface. The formation of this new interface not only hinders direct contact between the cathode material and the solid electrolyte, thereby reducing side reactions, but also balances the chemical potentials on both sides, suppresses the formation of a space charge layer, improves the migration rate of lithium ions at the interface, and enhances the performance of ternary cathode materials in all-solid-state batteries.

[0020] In summary, this invention, based on the differences in diffusion properties of elements with different ionic radii in the crystal lattice during calcination, combines modifying elements with different ionic radii and controls the calcination temperature according to the ionic radius. It adopts a segmented calcination process to control the diffusion process of elements from the particle surface to the interior. Surface gradient doping and surface coating composite modification can be achieved simultaneously in one calcination step, which has the advantages of simple process, low cost and easy control.

[0021] Based on a general inventive concept, the present invention also provides a sulfide all-solid-state battery, which includes the ternary cathode material that has been surface-gradient doped and coated with composite modification. In addition, the sulfide all-solid-state battery also includes a sulfide solid electrolyte and a negative electrode active material.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The ternary cathode material of this invention is modified by gradient doping and coating of the substrate surface with modifying elements of different ionic radii. Surface gradient doping focuses on adjusting the chemical potential of lithium ions on the surface of the ternary material particles, balancing the lithium ion concentration on both sides of the interface, suppressing the space charge layer effect, and improving the stability of the near-surface lattice, reducing the generation of oxygen vacancies, reducing the volume change of the near-surface, and suppressing contact failure between the cathode material and the solid electrolyte. Synergistic surface coating can suppress the space charge layer effect and interfacial side reactions at the cathode material / sulfide solid electrolyte interface, thereby improving interfacial compatibility and lithium ion migration rate. Developing a composite modified cathode material suitable for all-solid-state battery systems and easy for large-scale industrial production is of great significance.

[0023] 2. The preparation method of the present invention simplifies the process and reduces production costs through a one-step synthesis method, simultaneously achieving surface gradient doping and surface coating composite modification, improving the interfacial compatibility between ternary materials and sulfide solid electrolytes, suppressing the space charge layer effect, and improving the interfacial lithium-ion conductivity. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of the ternary cathode material of the present invention.

[0026] Figure 2 This is a SEM image of the ternary cathode material of Embodiment 1 of the present invention.

[0027] Figure 3 This is an EPMA mapping and line scan image of the ternary cathode material in Embodiment 1 of the present invention (the horizontal axis is in mm; the vertical axis is the signal strength).

[0028] Figure 4 This is a SEM image of the ternary cathode material in Example 2 of the present invention.

[0029] Figure 5 This is the EPMA mapping and line scan image of the ternary cathode material in Embodiment 2 of the present invention (the horizontal axis is in mm; the vertical axis is the signal strength).

[0030] Figure 6 This is a SEM image of the ternary cathode material of Comparative Example 1 of the present invention.

[0031] Figure 7 The image shows the EPMA mapping and line scan of the ternary cathode material in Comparative Example 1 of this invention (the horizontal axis is in mm; the vertical axis is the signal strength).

[0032] Figure 8 This is a SEM image of the ternary cathode material of Comparative Example 2 of the present invention.

[0033] Figure 9 This is the EPMA mapping diagram of the ternary cathode material in Comparative Example 2 of this invention.

[0034] Figure 10 This is a SEM image of the ternary cathode material of Comparative Example 3 of the present invention.

[0035] Figure 11 The image shows the EPMA mapping and line scan of the ternary cathode material in Comparative Example 3 of this invention (the horizontal axis is in mm; the vertical axis is the signal strength).

[0036] Figure 12 This is a SEM image of the ternary cathode material of Comparative Example 4 of the present invention.

[0037] Figure 13 The image shows the EPMA mapping and line scan of the ternary cathode material in Comparative Example 4 of this invention (the horizontal axis is in mm; the vertical axis is the signal strength).

[0038] Figure 14 The first charge-discharge curves of the ternary cathode materials in Example 1 and Comparative Example 1 of this invention are shown.

[0039] Figure 15 The diagram shows the cycle performance of solid-state mold batteries in various embodiments and comparative examples of the present invention. Detailed Implementation

[0040] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0041] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0042] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0043] The ternary cathode material of the present invention, which is modified by surface gradient doping and coating, such as... Figure 1 There is a gradient doping region of M1 element on the surface of the ternary cathode material (NCM) matrix. The content of M1 element in this region gradually decreases from the outside to the inside. There is a coating containing M2 element on the surface of the gradient doping region.

[0044] In the following examples, the nickel ion radius R Ni3+ It is 0.56 Å.

[0045] Example 1: A method for preparing a ternary cathode material with surface gradient doping and coating composite modification according to the present invention includes the following steps: 1) Weigh 10 kg of ternary cathode material matrix LiNi 0.85 Co 0.10 Mn 0.045 Al 0.005 O2, with 1 wt% TiO2 (based on Ti content, R Ti4+ =0.61Å) and 0.3wt% La2O3 (based on La content, R La3+ =1.03Å) was mixed in a high-speed mixer at a speed of 1200 rpm for 45 min; 2) The mixture was placed in a box furnace for calcination, with the temperature increased at a rate of 5℃ / min, and the calcination temperature T1 was 750℃, T1 / R Ti4+ =1230℃ Å -1 The calcination time was 4 hours; then the temperature was lowered at a rate of 3℃ / min, and the calcination temperature T2 was 470℃, T2 / R Ti4+ =770℃ Å -1 The calcination time was 5 hours, and the atmosphere was oxygen, to obtain the calcined product; 3) The calcined product is crushed and sieved to obtain a ternary cathode material with Ti gradient doping and La coating composite modification.

[0046] like Figure 2 As shown, the ternary cathode material modified by Ti surface gradient doping and La coating has a single crystal morphology, and the particle size is D. 50 The particle size is about 4μm, and the surface is covered with nanoscale island-like coatings formed by the metal element La, with the coating particle size being 150nm.

[0047] like Figure 3 As shown, EPMA analysis revealed a Ti gradient doping depth of 810 nm on the surface. The Ti content within the doped region gradually decreases from the outside to the inside. The proportion of Ti content (Wt) within a 100 nm depth range on the particle surface relative to the total Ti content is [not specified]. surface %=56%.

[0048] Example 2: A method for preparing a ternary cathode material with surface gradient doping and coating composite modification according to the present invention includes the following steps: 1) Weigh 10 kg of ternary cathode material matrix LiNi 0.90 Co 0.05 Mn 0.04 Al 0.01 O2, with 0.8 wt% ZrO2 (based on Zr content, R Zr4+ =0.72Å) and 0.2wt% Nb2O5 (based on Nb content, R Nb5+ =0.64Å) and 0.2wt% Sr(NO3)2 (based on Sr content, R Sr2+ =1.18Å) was mixed in a high-speed mixer at a speed of 1500 rpm for 35 min; 2) The mixture was placed in a box furnace for calcination, with the temperature increased at a rate of 2℃ / min. The calcination temperature T1 was 640℃, and T1 / R Zr4+ =889℃ Å -1 T1 / R Nb5+ =1000℃ Å -1 The calcination time was 5 hours; then the temperature was lowered at a rate of 2℃ / min, and the calcination temperature T2 was 450℃, T2 / R Zr4+ =703℃ Å -1 T2 / R Nb5+ =625℃ Å -1 The calcination time was 8 hours, and the atmosphere was oxygen, to obtain the calcined product; 3) The calcined product is crushed and sieved to obtain a ternary cathode material with surface Zr / Nb gradient doping and Sr coating composite modification.

[0049] like Figure 4As shown, the ternary cathode material modified by Nb surface gradient doping and Sr coating has a single crystal morphology, and the particle size is D. 50 The particle size is about 3.5 μm, and the surface is covered with nanoscale island-like coatings formed by the metal element Sr, with the coating particle size being about 290 nm.

[0050] like Figure 5 As shown, EPMA analysis revealed that the surface Zr gradient doping depth was 530 nm, and the surface Nb gradient doping depth was 620 nm. The content of Zr and Nb elements in the doped region gradually decreased from the outside to the inside. The proportion of Zr element in the particle surface depth of 100 nm to the total Zr element content was Wt. surface %=67%, the proportion of Nb element within a depth of 100 nm on the particle surface to the total Nb element content (Wt) surface %=45%.

[0051] Example 3: A method for preparing a ternary cathode material with surface gradient doping and coating composite modification according to the present invention includes the following steps: 1) Weigh 10 kg of ternary cathode material matrix LiNi 0.75 Co 0.20 Mn 0.04 Sr 0.01 O2, with 0.35wt% SnO2 (based on Sn content, R Sn4+ =0.69Å) and 0.25wt% Sb2O5 (based on Sb content, R Sb4+ =0.60Å) and 0.6wt% BaCO3 (based on Ba content, R Ba2+ =1.35Å) and 0.4wt% Ca(OH)2 (based on Ca content, R Ca2+ =1.00Å) was mixed in a high-speed mixer at a speed of 1100 rpm for 50 min; 2) The mixture was placed in a box furnace for calcination, with the temperature increased at a rate of 5℃ / min. The calcination temperature T1 was 760℃, and T1 / R Sn4+ =1101℃ Å -1 T1 / R Sb5+ =1267℃ Å -1 The calcination time was 3 hours; then the temperature was lowered at a rate of 4℃ / min, and the calcination temperature T2 was 420℃, T2 / R Sn4+ =608℃ Å -1 T2 / R Sb5+ =700℃ Å -1 The calcination time was 6 hours, and the atmosphere was oxygen, to obtain the calcined product. 3) The calcined product is crushed and sieved to obtain a ternary cathode material with surface Sn / Sb gradient doping and Ba / Ca coating composite modification.

[0052] The ternary cathode material modified by Sn / Sb surface gradient doping and Ba coating has a single-crystal morphology, with particle D 50 The particle size is about 4.2 μm, and the surface is covered with metal elements Ba and Ca to form nanoscale island-like coatings, with the coating particle sizes being 370 nm and 280 nm, respectively.

[0053] EPMA analysis revealed that the surface Sn gradient doping depth was 440 nm, and the surface Sb gradient doping depth was 720 nm. The content of Sn and Sb elements within the doped region gradually decreased from the outside to the inside. The proportion of Sn element content (Wt) within a 100 nm depth range on the particle surface relative to the total Sn content was... surface %=64%, the proportion of Sb element within a depth of 100 nm on the particle surface to the total Sb element content (Wt) surface %=39%.

[0054] Example 4: A method for preparing a ternary cathode material with surface gradient doping and coating composite modification according to the present invention includes the following steps: 1) Weigh 10 kg of ternary cathode material matrix LiNi 0.65 Co 0.07 Mn 0.277 W 0.003 O2, with 0.75 wt% Ta2O5 (based on Ta content, R Ta5+ =0.64Å) and 0.45wt% K2CO3 (as K content, R K+ =1.38Å) was mixed in a high-speed mixer at a speed of 1800 rpm for 30 min; 2) The mixture was placed in a box furnace for calcination, with the temperature increased at a rate of 6℃ / min, and the calcination temperature T1 was 780℃, T1 / R Ta5+ =1219℃ Å -1 The calcination time was 2 hours, followed by a cooling rate of 3℃ / min. The calcination temperature T2 was 500℃, and the ratio of T2 to R was... Ta5+ =781℃ Å -1 The calcination time was 7 hours, and the atmosphere was air, to obtain the calcined product; 3) The calcined product is crushed and sieved to obtain a ternary cathode material with surface Ta gradient doping and K coating composite modification.

[0055] The ternary cathode material modified by Ta surface gradient doping and K coating has a single crystal morphology, with particles D 50The particle size is about 4.3 μm, and the surface is covered with nanoscale island-like coatings formed by the metal element K, with the coating particle size being 310 nm.

[0056] EPMA analysis revealed a surface Ta gradient doping depth of 500 nm. The Ta content within the doped region gradually decreased from the outside to the inside. The proportion of Ta within a 100 nm depth on the particle surface (Wt) was the highest among all Ta elements. surface %=42%.

[0057] Example 5: A method for preparing a ternary cathode material with surface gradient doping and coating composite modification according to the present invention includes the following steps: 1) Weigh 10 kg of ternary cathode material matrix LiNi 0.93 Co 0.4 Mn 0.025 Mg 0.005 O2, and 0.4 wt% (NH4)2MoO4 (based on Mo content, R Mo6+ =0.59Å) and 0.55wt% SrCO3 (based on Sr content, R Sr2+ =1.18Å) was mixed in a high-speed mixer at a speed of 900 rpm for 60 min; 2) The mixture was placed in a box furnace for calcination, with the temperature increased at a rate of 4℃ / min, and the calcination temperature T1 was 580℃, T1 / R Mo6+ =983℃ Å -1 The calcination time was 3 hours, followed by a cooling rate of 2℃ / min. The calcination temperature T2 was 390℃, and the ratio of T2 to R was... Mo6+ =565℃ Å -1 The calcination time was 8 hours, and the atmosphere was oxygen, to obtain the calcined product; 3) The calcined product is crushed and sieved to obtain a ternary cathode material with surface Mo gradient doping and Sr coating composite modification.

[0058] The ternary cathode material modified by Mo surface gradient doping and Sr coating has a single crystal morphology and particle D 50 The particle size is about 3.1 μm, and the surface is covered with nanoscale island-like coatings formed by the metal element Sr, with the coating particle size being 260 nm.

[0059] EPMA analysis revealed a surface Mo gradient doping depth of 350 nm. The Mo content within the doped region gradually decreased from the outside to the inside. The proportion of Mo in the total Mo content (Wt) within a 100 nm depth region on the particle surface was [not specified]. surface %=51%.

[0060] Comparative Example 1: A method for preparing a ternary cathode material includes the following steps: 1) Weigh 10 kg of ternary cathode material matrix LiNi 0.85 Co 0.10 Mn 0.045 Al 0.005 O2, with 1 wt% TiO2 (based on Ti content, R Ti4+ =0.61Å) and 0.3wt% La2O3 (based on La content, R La3+ =1.03Å) was mixed in a high-speed mixer at a speed of 1200 rpm for 45 min; 2) The mixture was placed in a box furnace for calcination, with the temperature increased at a rate of 5℃ / min, and the calcination temperature T1 was 750℃, T1 / R Ti4+ =1230℃ Å -1 The calcination time was 10 hours to obtain the calcined product; 3) The calcined product is crushed and sieved to obtain a Ti bulk doped and La coated composite modified ternary cathode material.

[0061] like Figure 6 As shown, the ternary cathode material modified by Ti bulk doping and La coating exhibits a single-crystal morphology, with particle D... 50 The particle size is about 4μm, and the surface is covered with nanoscale island-like coatings formed by the metal element La, with the coating particle size being 170nm.

[0062] like Figure 7 As shown, EPMA analysis revealed that after sintering at high temperature, Ti elements diffused into the bulk lattice through thermal diffusion and were uniformly distributed within the particles.

[0063] Comparative Example 2: A method for preparing a ternary cathode material includes the following steps: 1) Weigh 10 kg of ternary cathode material matrix LiNi 0.85 Co 0.10 Mn 0.045 Al 0.005 O2, with 1 wt% ZnO2 (based on Zn content, R Zn4+ =0.74Å) and 0.3wt% La2O3 (based on La content, R La3+ =1.03Å) was mixed in a high-speed mixer at a speed of 1200 rpm for 45 min; 2) The mixture was placed in a box furnace for calcination at a temperature of 750℃ for 10 hours, with a heating rate of 5℃ / min and an oxygen atmosphere, to obtain the calcined product. 3) The calcined product is crushed and sieved to obtain a ternary cathode material with Zn / La coating modification on the surface.

[0064] like Figure 8 As shown, the ternary cathode material modified by Zn and La coating exhibits a single-crystal morphology, with particle D... 50 The particle size is about 4μm, and the surface is covered with nanoscale island-like coatings formed by the metal elements Zn and La, with particle sizes of 430nm and 300nm, respectively.

[0065] like Figure 9 As shown, EPMA analysis revealed that Zn elements were distributed on the surface of the material particles in an island-like pattern, with no bulk doping.

[0066] Comparative Example 3: A method for preparing a ternary cathode material includes the following steps: 1) Weigh 10 kg of ternary cathode material matrix LiNi 0.85 Co 0.10 Mn 0.045 Al 0.005 O2, with 1 wt% TiO2 (based on Ti content, R Ti4+ =0.61Å) and 0.3wt% La2O3 (based on La content, R La3+ =1.03Å) was mixed in a high-speed mixer at a speed of 1200 rpm for 45 min; 2) The mixture was placed in a box furnace for calcination, with the temperature increased at a rate of 5℃ / min, and the calcination temperature T1 was 750℃, T1 / R Ti4+ =1230℃ Å -1 The calcination time was 4 hours, followed by a cooling rate of 3℃ / min. The calcination temperature T2 was 650℃, and the ratio of T2 to R was... Ti4+ =1065℃ Å -1 The calcination time was 5 hours to obtain the calcined product; 3) The calcined product is crushed and sieved to obtain a Ti bulk doped and La coated composite modified ternary cathode material.

[0067] like Figure 10 As shown, the ternary cathode material modified by Ti surface gradient doping and La coating has a single crystal morphology, and the particle size is D. 50 The particle size is about 4μm, and the surface is covered with nanoscale island-like coatings formed by the metal element La, with the coating particle size being 170nm.

[0068] like Figure 11As shown, EPMA analysis revealed a Ti gradient doping depth of 1740 nm on the surface. The proportion of Ti element within a 100 nm depth range on the particle surface (Wt) is also shown. surface %=17%.

[0069] Comparative Example 4: A method for preparing a ternary cathode material includes the following steps: 1) Weigh 10 kg of ternary cathode material matrix LiNi 0.85 Co 0.10 Mn 0.045 Al 0.005 O2, with 1 wt% TiO2 (based on Ti content, R Ti4+ =0.61Å) and 0.3wt% La2O3 (based on La content, R La3+ =1.03Å) was mixed in a high-speed mixer at a speed of 1200 rpm for 45 min; 2) The mixture was placed in a box furnace for calcination, with the temperature increased at a rate of 5℃ / min. The calcination temperature T1 was 460℃, and T1 / R Ti4+ =754℃ Å -1 The calcination time was 4 hours, followed by a cooling rate of 3℃ / min. The calcination temperature T2 was 400℃, and the ratio of T2 to R was... Ti4+ =655℃ Å -1 The calcination time was 5 hours to obtain the calcined product; 3) The calcined product is crushed and sieved to obtain a Ti bulk doped and La coated composite modified ternary cathode material.

[0070] like Figure 12 As shown, the ternary cathode material modified by Ti surface gradient doping and La coating has a single crystal morphology, and the particle size is D. 50 The particle size is about 4μm, and the surface is covered with nanoscale island-like coatings formed by the metal element La, with the coating particle size being 140nm.

[0071] like Figure 13 As shown, EPMA analysis revealed a Ti gradient doping depth of 670 nm on the surface. The proportion of Ti element within a 100 nm depth range on the particle surface (Wt) is also shown. surface %=78%.

[0072] The assembly method for all-solid-state molded batteries is as follows: The steps for assembling an all-solid-state mold battery in a glove box protected by an argon atmosphere are as follows: 1) Place the sulfide solid electrolyte Li6PS5Cl powder in a mold and press it into a sheet under pressure; 2) Take the composite-coated ternary cathode material obtained in the above example or the single-coated ternary cathode material obtained in the comparative example, mix it with the solid electrolyte Li6PS5Cl and the conductive agent VGCF in a mass ratio of 70:29:1 to obtain a composite cathode, and then pour the composite cathode into one side of the electrolyte sheet and press it under pressure; 3) Attach the indium sheet and lithium sheet to the other side of the electrolyte sheet in sequence, and then apply pressure; 4) Assemble the mold battery and apply a constant pressure of 50MPa to test its electrochemical performance.

[0073] Electrochemical testing methods: The assembled mold battery was placed in a 30°C constant temperature chamber, and the test voltage range was 2.1~3.7V. The first four charge-discharge cycles were 0.1C, 0.2C, 0.33C, and 0.5C, respectively, followed by 50 charge-discharge cycles at a rate of 0.33C. The initial charge-discharge specific capacity, initial coulombic efficiency, and 50-cycle capacity retention of the examples and comparative examples are shown in Table 1. Figures 14-15 .

[0074] Table 1: Test Results of Examples and Comparative Examples

[0075] The results show that the ternary cathode materials prepared in Examples 1-5 of this invention have higher initial charge-discharge efficiency, capacity utilization, and cycle stability compared to Comparative Examples 1-4. This indicates that the surface gradient doping and surface coating composite modification strategy provided by this invention can effectively suppress the space charge layer effect and interfacial side reactions between the ternary cathode material and the sulfide solid electrolyte interface, thereby improving interfacial compatibility.

Claims

1. A ternary cathode material with surface gradient doping and coating composite modification, characterized in that, The surface of the ternary cathode material matrix has a gradient doped region containing element M1, and the surface of the gradient doped region has a coating containing element M2; the ionic radius R of element M1 is... M1 With respect to the nickel ion radius R Ni3+ The relationship between R Ni3+ <R M1 ≤1.3R Ni3+ The ionic radius R of the M2 element M2 With respect to the nickel ion radius R Ni3+ The relationship between R M2 ≥1.3R Ni3+ And R M2 - R M1 ≥ 0.3Å; The depth of the gradient doping region is within 1000 nm. Within this gradient doping region, the content of doped M1 element gradually decreases from the outside to the inside, and the proportion of M1 element content within 100 nm of the surface of the gradient doping region to the total amount of M1 element is Wt. surface % meets 30wt% < Wt surface % < 70wt%.

2. The ternary cathode material with surface gradient doping and coating composite modification according to claim 1, characterized in that, The mass percentage of element M1 in the ternary cathode material is 0.01~2wt%, and the mass percentage of element M2 in the ternary cathode material is 0.01~1wt%.

3. The ternary cathode material with surface gradient doping and coating composite modification according to claim 1, characterized in that, The M1 element includes one or more of Mg, Ti, Co, Ga, Zr, Nb, Mo, Sn, Sb, Ta, and W, and the M2 element includes one or more of Na, K, Ca, Zn, Sr, Y, Ba, La, and Ce.

4. The ternary cathode material with surface gradient doping and coating composite modification according to claim 1, characterized in that, The ternary cathode material is a single crystal with particle size D. 50 It is 2~7μm.

5. The ternary cathode material with surface gradient doping and coating composite modification according to claim 1, characterized in that, The coating material is island-shaped coated particles with a particle size of 50~500nm.

6. The ternary cathode material with surface gradient doping and coating composite modification according to any one of claims 1 to 5, characterized in that, The chemical formula of the ternary cathode material matrix is LiNi 1-x-y-z Co x Mn y Z z O2, where 0.5 ≤ 1 - x - y - z < 1, 0 < x ≤ 0.3, 0 < y ≤ 0.3, 0 < z ≤ 0.01, and the Z element includes one or more of Mg, Al, Ca, Ti, Sr, Zr, Ba, La, and W.

7. A method for preparing a ternary cathode material with surface gradient doping and coating composite modification as described in any one of claims 1 to 6, characterized in that, Includes the following steps: 1) Weigh out the ternary cathode material matrix and mix it with an additive containing elements M1 and M2 to obtain a mixture; 2) The mixture is subjected to segmented calcination to obtain the calcined product; 3) The calcined product is crushed and sieved to obtain a ternary cathode material with surface gradient doping and coating composite modification.

8. The method for preparing the ternary cathode material with surface gradient doping and coating composite modification according to claim 7, characterized in that, In step 1), the additive containing elements M1 and M2 is one or more of oxides, hydroxides, carbonates, nitrates, acids and ammonium salts; the mixing machine is used at a speed of 500~2000 rpm and the mixing time is 10~60 min.

9. The method for preparing the ternary cathode material with surface gradient doping and coating composite modification according to claim 7, characterized in that, In step 2), the segmented calcination includes a first stage and a second stage, wherein the calcination temperature T1 of the first stage and the ionic radius R of element M1 are... M1 Meets 800℃ Å -1 ≤T1 / R M1 ≤1300℃ Å -1 The calcination time is 1-5 hours; the calcination temperature T2 in the second stage and the ionic radius R of element M1 are also considered. M1 Meets 500℃ Å -1 ≤T2 / R M1 <800℃ Å -1 The calcination time is 1~8h, the heating / cooling rate is 1~10℃ / min, and the calcination atmosphere is oxygen or air.

10. A sulfide all-solid-state battery, characterized in that, It includes the ternary cathode material with surface gradient doping and coating composite modification as described in any one of claims 1 to 6, or the ternary cathode material with surface gradient doping and coating composite modification prepared by the preparation method described in any one of claims 7 to 9.

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