Composite positive electrode material and preparation method and application thereof

Abstract

The invention provides a composite positive electrode material and a preparation method and application thereof, and belongs to the field of lithium ion batteries. The composite positive electrode material comprises phase structure gradient lithium-rich positive electrode material particles, a solid electrolyte additive and a conductive agent, and the chemical general formula of the composite positive electrode material is xLi2MnO3. (1-x) LiTMO2 (at) A (at) B, 0lt, xlt; tM is selected from any one or a combination of at least two of Ni, Co or Mn, A comprises a solid electrolyte additive, and B comprises a conductive agent; the phase structure gradient lithium-rich positive electrode material particle comprises a monoclinic Li2MnO3 phase and a rhombic LiTMO2 phase, the content of the monoclinic Li2MnO3 phase is sequentially reduced from inside to outside, and the content of the rhombic LiTMO2 phase is sequentially increased from inside to outside. The composite positive electrode material prepared by the invention has the advantages of high compactness, high cycle performance, high thermal stability and high energy density.

Description

Technical Field

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

[0002] Climate change and energy security issues are becoming increasingly serious, urgently requiring the development of an efficient and safe energy system. Lithium-ion batteries, as an efficient, safe, and environmentally friendly energy conversion system, have come into focus. Building upon existing lithium-ion batteries, researchers are further improving the energy density of rechargeable lithium-ion batteries to meet the needs of large-scale grid storage. Furthermore, it has been discovered that lithium-rich layered transition metal oxides possess high specific capacity (>250 mAh g⁻¹). -1 ) and high energy density (>900Wh / kg) -1 While lithium-rich layered transition metal oxides offer advantages, their high first-cycle irreversible capacity, voltage decay, and capacity decay significantly hinder their practical application.

[0003] CN115064682A discloses a method for preparing and applying a lithium-rich manganese-based layered oxide with both surface and bulk modification. A lithium-rich layered oxide carbonate or hydroxide precursor is dispersed in anhydrous ethanol, and a compound of electrochemically inert metal nitrate and titanium is added. Ammonia solution with a concentration of 0.1–1 is added dropwise until the pH reaches 8.0–10.0. After stirring for 30–240 minutes, the mixture is washed and dried at 100–150°C to obtain the treated lithium-rich manganese-based layered oxide precursor. The precursor is sintered at 500–800°C for 2–6 hours, then lithium salt is added and mixed, followed by sintering at 800–1000°C for 10–16 hours to obtain the target product. However, the prepared cathode material, when assembled into a coin cell, only achieves a maximum initial discharge specific capacity of 259.4 mAh g⁻¹ at a 1C current density. -1 Furthermore, the preparation method of this patent is complex and the sintering time is long.

[0004] CN112234176A discloses a lithium-rich manganese-based precursor and its preparation method, a lithium-rich manganese-based cathode material and its preparation method, and a lithium-ion battery. A fluorine- and magnesium-doped lithium-rich manganese-based precursor is prepared via a dual-system co-precipitation method. The precursor is then lithium-containing and sintered at high temperature in an air and oxygen atmosphere to obtain the lithium-rich manganese-based cathode material. However, this patented preparation method requires additional elemental doping, increasing costs, and does not significantly improve the performance of the cathode material without elemental doping.

[0005] Therefore, how to prepare a cathode material with excellent electrochemical properties such as high energy density and cycle performance through a simple preparation method is an important research direction in this field. Summary of the Invention

[0006] The purpose of the present invention is to provide a composite cathode material with high energy density and excellent cycle performance, its preparation method and application.

[0007] To achieve the purpose of this invention, the following technical solutions are adopted:

[0008] One of the purposes of the present invention is to provide a composite cathode material, which includes phase structure gradient rich lithium cathode material particles, a solid electrolyte additive and a conductive agent. The chemical general formula of the composite cathode material is xLi2MnO3·(1 - x)LiTMO2@A@B, 0 < x < 1, TM is selected from any one or at least two combinations of Ni, Co or Mn, A includes a solid electrolyte additive, and B includes a conductive agent;

[0009] The phase structure gradient rich lithium cathode material particles include a monoclinic Li2MnO3 phase and a rhombic LiTMO2 phase. The content of the monoclinic Li2MnO3 phase decreases sequentially from the inside to the outside, and the content of the rhombic LiTMO2 phase increases sequentially from the inside to the outside.

[0010] The phase structure gradient rich lithium cathode material particles, the solid electrolyte additive and the conductive agent in the composite cathode material of the present invention are in a uniformly dispersed form.

[0011] The phase structure gradient rich lithium cathode material of the present invention can regulate the cycle stability, discharge specific capacity, safety and other performances of the composite cathode material in a lithium ion battery, effectively improving the electrochemical performance of the composite cathode material.

[0012] The use of the solid electrolyte additive in the composite cathode material of the present invention improves the compatibility between the cathode material and the solid electrolyte, helps to reduce the interfacial impedance and improve the overall performance of the battery; First, the use of the solid electrolyte additive enhances the ion conduction between the cathode material and the solid electrolyte, thereby improving the rate performance and cycle stability of the solid state battery; Second, the use of the solid electrolyte additive improves the mechanical stability of the battery, reduces the crack propagation phenomenon caused by the volume change during the charge and discharge process of the battery, thereby improving the durability and reliability of the battery; Finally, the solid electrolyte additive fills the gaps between the structure gradient rich lithium cathode material particles, improving the denseness of the composite cathode material.

[0013] The addition of the conductive agent in this invention increases the conductive contact between active materials, thereby improving electronic conductivity. The conductive agent collects current between active materials and between active materials and current collectors, thereby reducing the contact resistance of the electrodes and accelerating the movement speed of electrons.

[0014] This invention utilizes the synergistic effect of phase-structure gradient lithium-rich cathode material particles, solid electrolyte additives, and conductive agents. The phase-structure gradient lithium-rich cathode material particles provide more active sites and ion diffusion channels. Combined with the solid electrolyte additives and conductive agents, this helps to construct a more optimized battery structure, further improving the battery's discharge specific capacity and energy density, reducing volume expansion and contraction during charge and discharge, and extending the battery's cycle life. Specifically, the synergistic effect of the conductive agent and solid electrolyte additives accelerates the lithium-ion diffusion rate, enabling rapid charge and discharge; the synergistic use of the conductive agent and phase-structure gradient lithium-rich cathode material particles further enhances the battery's performance at high temperatures; and the synergistic effect of the solid electrolyte additives and phase-structure gradient lithium-rich cathode material particles further improves the battery's thermal stability and reduces the risk of thermal runaway.

[0015] As a preferred embodiment of the present invention, the solid electrolyte additive includes oxide solid electrolytes and / or halide solid electrolytes.

[0016] Preferably, the oxide solid electrolyte includes any one or a combination of at least two of the following: NASICON structure oxide solid electrolyte, LISICON structure oxide solid electrolyte, garnet solid electrolyte, or perovskite structure oxide solid electrolyte. Typical but non-limiting examples of such combinations include: a combination of NASICON structure oxide solid electrolyte and LISICON structure oxide solid electrolyte, a combination of LISICON structure oxide solid electrolyte and garnet solid electrolyte, a combination of garnet solid electrolyte and perovskite structure oxide solid electrolyte, or a combination of NASICON structure oxide solid electrolyte and garnet solid electrolyte, etc.

[0017] Preferably, the chemical formula of the halide solid electrolyte is Li3MX6, where M is selected from any one or at least two combinations of Zr, Hf, In, Sc, Y, La, Ce, Pr, Nb, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu. Typical but non-limiting examples of such combinations include: combinations of Zr and Hf, In and Sc, Y and La, Ce and Pr, Nb and Sm, Eu and Gd, Tb and Dy, Ho and Er, Tm and Yb, or Lu and Zr, etc.

[0018] X is selected from any one or at least two combinations of F, Cl, Br or I, wherein typical but non-limiting examples of such combinations include combinations of F and Cl, combinations of Cl and Br, or combinations of Br and I.

[0019] As a preferred technical solution of the present invention, the conductive agent includes any one or a combination of at least two of acetylene black, carbon nanotubes, graphene, or carbon black. Typical but non-limiting examples of such combinations include: a combination of acetylene black and carbon nanotubes, a combination of carbon nanotubes and graphene, a combination of acetylene black and graphene, or a combination of carbon nanotubes and graphene, etc.

[0020] Preferably, the mass ratio of the positive electrode active material, the solid electrolyte additive, and the conductive agent is (85-93):(5-10):(2-5), wherein the mass ratio can be 85:10:5, 87:8:5, 87:10:3, 89:9:2, 89:6:5, 90:5:5, 90:8:2, 91:5:4, 91:7:2, or 93:5:2, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0021] As a preferred embodiment of the present invention, the tap density of the lithium-rich cathode material is 2.0–4.5 g / cm³. 3 .

[0022] This invention combines phase-structure gradient lithium-rich cathode material particles, solid electrolyte additives, and conductive agents, and prepares them by sintering using a discharge plasma sintering method. The resulting lithium-rich cathode material exhibits excellent compactness, further improving the energy density of the battery.

[0023] A second objective of this invention is to provide a method for preparing the composite cathode material as described in one objective, the method comprising the following steps:

[0024] A phase-gradient lithium-rich cathode material precursor, a lithium source, a solid electrolyte additive, and a conductive agent are mixed and then sintered by discharge plasma to obtain the composite cathode material. The phase-gradient lithium-rich cathode material precursor includes a monoclinic Li2MnO3 phase and a rhombic LiTMO2 phase. The content of the monoclinic Li2MnO3 phase decreases from the inside to the outside, while the content of the rhombic LiTMO2 phase increases from the inside to the outside.

[0025] This invention employs a method for preparing composite cathode materials using discharge plasma sintering. Under the influence of an electric field, the lithium-rich manganese-based cathode material precursor, lithium source, solid electrolyte additive, and conductivity are sintered, resulting in the accumulation of all particles and improving the density of the composite cathode material. Through discharge plasma sintering, a small amount of conductive agent enables good conductive contact to be formed between the sintered lithium-rich cathode material particles with phase structure gradients and the solid electrolyte, as well as between the lithium-rich cathode material particles themselves, significantly improving the conductivity of the composite cathode material.

[0026] As a preferred technical solution of the present invention, the molar ratio of the total number of Ni, Co and Mn moles to the number of lithium source moles in the phase structure gradient lithium-rich cathode material precursor is (1-5):1. The molar ratio can be 1:1, 2:1, 3:1, 4:1 or 5:1, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, the lithium source includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, lithium oxalate, or lithium acetate, wherein typical but non-limiting examples of the combination include: a combination of lithium hydroxide and lithium carbonate, a combination of lithium carbonate and lithium oxalate, a combination of lithium oxalate and lithium acetate, or a combination of lithium carbonate and lithium acetate, etc.

[0028] As a preferred technical solution of the present invention, the voltage of the discharge plasma sintering is 50-850V, wherein the voltage can be 50V, 100V, 150V, 200V, 250V, 300V, 350V, 400V, 450V, 500V, 550V, 600V, 650V, 700V, 750V, 800V or 850V, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0029] Preferably, the pressure of the discharge plasma sintering in step (3) is 0 to 120 MPa, wherein the pressure can be 0 MPa, 10 MPa, 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, 100 MPa, 110 MPa or 120 MPa, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the temperature of the discharge plasma sintering in step (3) is 400 to 1500°C, wherein the temperature can be 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C or 1500°C, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Preferably, the discharge plasma sintering time in step (3) is 30s to 4h, wherein the time can be 30s, 1min, 5min, 10min, 30min, 1h, 2h, 3h or 4h, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, the discharge plasma sintering rate in step (3) is 50 to 300 °C / min, wherein the rate can be 50 °C / min, 100 °C / min, 150 °C / min, 200 °C / min, 250 °C / min or 300 °C / min, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] As a preferred technical solution of the present invention, the preparation method includes:

[0034] A phase-gradient lithium-rich cathode material precursor, a lithium source, a solid electrolyte additive, and a conductive agent are mixed and then sintered under discharge plasma conditions of 50–850 V, 0–120 MPa, 400–1500 °C, 30 s–4 h, and 50–300 °C / min to obtain the composite cathode material. The phase-gradient lithium-rich cathode material precursor includes a monoclinic Li₂MnO₃ phase and a rhombic LiTMO₂ phase. The content of the monoclinic Li₂MnO₃ phase decreases from the inside to the outside, while the content of the rhombic LiTMO₂ phase increases from the inside to the outside.

[0035] A third objective of this invention is to provide an all-solid-state battery, which includes a positive electrode, a solid electrolyte, and a negative electrode, wherein the positive electrode includes a composite positive electrode material as described in one objective.

[0036] The all-solid-state battery prepared by this invention is suitable for temperature variations from high to low temperatures, supports fast charging, and has higher safety, higher energy density, longer cycle life, and better low-temperature performance.

[0037] As a preferred embodiment of the present invention, the compaction density of the positive electrode sheet is 2.6–4.0 g / cm³. 3 The compaction density may be 2.6 g / cm³. 3 2.7g / cm 3 2.8g / cm 3 2.9g / cm 3 3.0g / cm 3 3.1g / cm 3 3.2g / cm 3 3.3g / cm3 、 3.4 g / cm 3 、 3.5 g / cm 3 、 3.6 g / cm 3 、 3.7 g / cm 3 、 3.8 g / cm 3 、 3.9 g / cm 3 or 4.0 g / cm 3 etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0038] Preferably, the solid electrolyte includes an oxide solid electrolyte and / or a halide solid electrolyte.

[0039] The types of the solid electrolyte additives in the preferred solid electrolyte and the positive electrode material of the present invention are the same.

[0040] Preferably, the oxide solid electrolyte includes any one or a combination of at least two of garnet-type oxide solid electrolytes, perovskite-type oxide solid electrolytes, or NASICON-type oxide solid electrolytes. Typical but non-limiting examples of the combination include: a combination of garnet-type oxide solid electrolyte and perovskite-type oxide solid electrolyte, a combination of perovskite-type oxide solid electrolyte and NASICON-type oxide solid electrolyte, or a combination of garnet-type oxide solid electrolyte and NASICON-type oxide solid electrolyte, etc.

[0041] Preferably, the garnet-type oxide solid electrolyte includes Li y C3D2O 12 , where C is selected from any one or a combination of at least two of La, Nb, Mg, Ba, Ca, or Sr. Typical but non-limiting examples of the combination include: a combination of La and Nb, a combination of Nb and Mg, a combination of Mg and Ba, a combination of Ba and Ca, or a combination of Ca and Sr, etc. D is selected from any one or a combination of at least two of Te, Ta, Nb, Zr, or In. Typical but non-limiting examples of the combination include: a combination of Te and Ta, a combination of Ta and Nb, a combination of Nb and Zr, or a combination of Zr and In, etc. 0 < y ≤ 7, where the value of y can be 1, 2, 3, 4, 5, 6, or 7, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0042] Preferably, the perovskite oxide solid electrolyte includes any one or a combination of at least two of Li3LaTiO3, LiTi2(PO4)3, or Li3PO4, wherein typical but non-limiting examples of the combination include combinations of Li3LaTiO3 and LiTi2(PO4)3, combinations of LiTi2(PO4)3 and Li3PO4, or combinations of Li3LaTiO3 and Li3PO4, etc.

[0043] Preferably, the NASICON-type oxide solid electrolyte includes Na 1+z Zr2Si z P 3-z O 12 , 0≤z≤3, where the value of z can be 0, 1, 2 or 3, etc., but is not limited to the listed values. Other unlisted values ​​within this range also apply.

[0044] Preferably, the chemical formula of the halide solid electrolyte is Li3MX6, where M is selected from any one or at least two combinations of Zr, Hf, In, Sc, Y, La, Ce, Pr, Nb, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu. Typical but non-limiting examples of such combinations include: combinations of Zr and Hf, In and Sc, Y and La, Ce and Pr, Nb and Sm, Eu and Gd, Tb and Dy, Ho and Er, Tm and Yb, or Lu and Zr, etc.

[0045] X is selected from any one or at least two combinations of F, Cl, Br or I, wherein typical but non-limiting examples of such combinations include combinations of F and Cl, combinations of Cl and Br, or combinations of Br and I.

[0046] The fourth objective of this invention is to provide an application of the composite cathode material as described in the first objective, wherein the composite cathode material is applied in the field of lithium-ion batteries.

[0047] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0048] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0049] (1) The composite cathode material prepared by the present invention includes lithium-rich cathode material particles with phase structure gradient, solid electrolyte additives and conductive agents. Under the synergistic effect of the three, the energy density, thermal stability and cycle performance of the composite cathode material are significantly improved.

[0050] (2) The preparation method of the composite cathode material of the present invention adopts the method of plasma sintering. Under the action of an electric field, the morphology of the cathode material changes along the direction of the electric field, improving the good contact between the material particles, and thus improving the conductivity of the composite cathode material; through discharge plasma sintering, the density of the composite cathode material is improved, and thus the energy density of the cathode material is improved.

[0051] (3) The present invention prepares the composite cathode material into a all-solid-state battery. Since the composite cathode material contains a solid electrolyte additive, the contact performance between the composite cathode material and the solid electrolyte is good, the interfacial impedance of the battery is low, the cycle performance is improved, and it has the advantages of high energy density, long cycle life and high safety. Description of the Drawings

[0052] Figure 1 It is a schematic diagram of the composite cathode material prepared in Example 1 of the present invention.

[0053] In the figure: 1 - phase structure gradient rich lithium cathode material particles; 2 - solid electrolyte additive; 3 - conductive agent. Detailed Embodiments

[0054] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0055] Example 1

[0056] This example provides a composite cathode material as Figure 1 shown. The composite cathode material includes phase structure gradient rich lithium cathode material particles 1, solid electrolyte additive 2 and conductive agent 3. The chemical general formula of the composite cathode material is xLi2MnO3·(1 - x)LiTMO2@A@B, 0 < x < 1. The phase structure gradient rich lithium cathode material is xLi2MnO3·(1 - x)LiTMO2 (core 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 )O2, shell 0.3Li2MnO3·0.7Li(Ni 0.42 Mn 0.42 Co 0.16 )O2). It includes a monoclinic Li2MnO3 phase and a rhombic LiTMO2 phase. The content of the monoclinic Li2MnO3 phase decreases sequentially from the inside to the outside, and the content of the rhombic LiTMO2 phase increases sequentially from the inside to the outside. A is 60LiTi2(PO4)3, and B is graphene.

[0057] This embodiment also provides a preparation method of the above composite cathode material, and the preparation method includes the following steps:

[0058] (1) Nickel sulfate, cobalt sulfate, and manganese sulfate solutions are separately and independently configured into solution A and solution B with a concentration of 2 mol / L in deionized water. Among them, the molar ratio of Ni, Co, and Mn in solution A is 0.21:0.08:0.71, and the molar ratio of Ni, Co, and Mn in solution B is 0.343:0.1305:0.5265;

[0059] (2) 600 mL of solution B is added to 600 mL of stirred solution A through a constant current pump. At the same time, the mixed solution of solution A and solution B is added to a reaction kettle through a constant current pump. 2 mol / L Na2CO3 solution and 2 mol / L ammonia water are separately and independently added to the reaction kettle in parallel through a constant current pump, and stirred at a stirring rate of 1000 rpm to obtain a mixed solution with a pH of 8.1. The mixed solution is heated at a reaction temperature of 55 °C for 10 h to obtain a phase structure gradient rich lithium cathode material precursor;

[0060] (3) The phase structure gradient rich lithium cathode material precursor, Li2CO3, LiTi2(PO4)3, and graphene prepared in step (2) are mixed (where the mass ratio of the phase structure gradient rich lithium cathode material precursor, LiTi2(PO4)3, and graphene is 90:6:4, and the molar ratio of the total molar number of Ni, Co, and Mn in the phase structure gradient rich lithium cathode material precursor to the molar number of lithium source is 3:1), and are sintered by discharge plasma at a voltage of 450 V, a pressure of 60 MPa, a temperature of 950 °C, a time of 30 min (excluding the heating time), and a rate of 150 °C / min to obtain the composite cathode material.

[0061] This embodiment also provides a all-solid-state battery. The positive electrode sheet of the all-solid-state battery uses the above composite cathode material. The solid electrolyte of the solid-state battery is 60LiTi2(PO4)3, and the active material of the solid-state battery selects natural graphite.

[0062] Example 2

[0063] This embodiment provides a composite cathode material, which includes phase structure gradient rich lithium cathode material particles, a solid electrolyte additive, and a conductive agent. The chemical general formula of the composite cathode material is xLi2MnO3·(1 - x)LiTMO2@A@B, 0 < x < 1. Among them, the general formula of the phase structure gradient rich lithium cathode material is xLi2MnO3·(1 - x)LiTMO2 (the core is 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16O2, outer shell 0.3Li2MnO3·0.7Li(Ni) 0.42 Mn 0.42 Co 0.16 The compound contains monoclinic Li₂MnO₃ and rhombic LiTMO₂ phases, with the content of the monoclinic Li₂MnO₃ phase decreasing from the inside out, and the content of the rhombic LiTMO₂ phase increasing from the inside out. A is Li₇La₃Zr₂O. 12 B is acetylene black.

[0064] This embodiment also provides a method for preparing the above-mentioned composite cathode material, the method comprising the following steps:

[0065] (1) Dissolve nickel sulfate, cobalt sulfate, and manganese sulfate in deionized water to prepare solutions A and B with a concentration of 2 mol / L, respectively. The molar ratio of Ni, Co, and Mn in solution A is 0.21:0.08:0.71, and the molar ratio of Ni, Co, and Mn in solution B is 0.343:0.1305:0.5265.

[0066] (2) 600 mL of solution B was added to 600 mL of solution A under stirring by a constant flow pump. At the same time, the solution after mixing solution A and solution B was added to the reaction vessel by a constant flow pump. 2 mol / L Na2CO3 solution and 2 mol / L ammonia water were added to the reaction vessel separately and in parallel by constant flow pumps. The mixture was stirred at a stirring rate of 1000 rpm to obtain a mixed solution with a pH of 8.1. The mixed solution was heated at a reaction temperature of 55℃ for 20 h to obtain a lithium-rich cathode material precursor with a phase structure gradient.

[0067] (3) The lithium-rich cathode material precursor with phase structure gradient prepared in step (2), Li2CO3, Li7La3Zr2O 12 Mixed with acetylene black (wherein, phase structure gradient lithium-rich cathode material precursor, Li7La3Zr2O) 12 The composite cathode material was obtained by sintering acetylene black at a mass ratio of 85:10:5 and a molar ratio of the total molar number of Ni, Co, and Mn to the molar number of lithium source in the phase structure gradient lithium-rich cathode material precursor of 2:1. The material was sintered by discharge plasma at a voltage of 50V, a pressure of 30MPa, a temperature of 400℃, a time of 2h (excluding heating time), and a rate of 50℃ / min.

[0068] This embodiment also provides an all-solid-state battery, wherein the positive electrode of the all-solid-state battery adopts the above-mentioned composite positive electrode material, and the solid electrolyte of the solid-state battery is Li7La3Zr2O. 12 The active material of the negative electrode sheet of the solid-state battery is natural graphite.

[0069] Example 3

[0070] This example provides a composite cathode material, which includes phase structure gradient lithium-rich cathode material particles, a solid electrolyte additive, and a conductive agent. The chemical general formula of the composite cathode material is xLi2MnO3·(1 - x)LiTMO2@A@B, where 0 < x < 1, 0 < x < 1. Among them, the phase structure gradient lithium-rich cathode material has a general formula of xLi2MnO3·(1 - x)LiTMO2 (the core is 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 )O2, and the shell is 0.3Li2MnO3·0.7Li(Ni 0.42 Mn 0.42 Co 0.16 )O2), including a monoclinic Li2MnO3 phase and a rhombic LiTMO2 phase. The content of the monoclinic Li2MnO3 phase decreases sequentially from the inside to the outside, and the content of the rhombic LiTMO2 phase increases sequentially from the inside to the outside. A is Li3ZrCl6, and B is carbon nanotubes.

[0071] This example also provides a preparation method for the above composite cathode material. The preparation method includes the following steps:

[0072] (1) Nickel sulfate, cobalt sulfate, and manganese sulfate solutions are independently prepared into solution A and solution B with a concentration of 2 mol / L in deionized water. Among them, the molar ratio of Ni, Co, and Mn in solution A is 0.21:0.08:0.71, and the molar ratio of Ni, Co, and Mn in solution B is 0.343:0.1305:0.5265;

[0073] (2) 600 mL of solution B is added to 600 mL of stirred solution A through a constant flow pump. At the same time, the mixed solution of solution A and solution B is added to a reaction kettle through a constant flow pump. 2 mol / L Na2CO3 solution and 2 mol / L ammonia water are independently added to the reaction kettle through a constant flow pump in a co-current manner, and stirred at a stirring rate of 1000 rpm to obtain a mixed solution with a pH of 8.1. The mixed solution is heated at a reaction temperature of 55 °C for 40 h to obtain a phase structure gradient lithium-rich cathode material precursor;

[0074] (3) The phase structure gradient lithium-rich cathode material precursor, Li2CO3, Li3ZrCl6 and carbon nanotubes prepared in step (2) are mixed (wherein, the mass ratio of the phase structure gradient lithium-rich cathode material precursor, Li3ZrCl6 and carbon nanotubes is 93:5:2, and the molar ratio of the total molar number of Ni, Co and Mn in the phase structure gradient lithium-rich cathode material precursor to the molar number of lithium source is 5:1), and sintered by discharge plasma at a voltage of 850V, a pressure of 120MPa, a temperature of 1500℃, a time of 30s (excluding the heating time) and a rate of 300℃ / min to obtain the composite cathode material.

[0075] This embodiment also provides an all-solid-state battery, wherein the positive electrode of the all-solid-state battery adopts the above-mentioned composite positive electrode material, the solid electrolyte of the solid-state battery is Li3ZrCl6, and the active material of the negative electrode of the solid-state battery is natural graphite.

[0076] Example 4

[0077] In this embodiment, all conditions are the same as in Example 1, except that the pressure of the discharge plasma sintering is replaced with 0 MPa.

[0078] Example 5

[0079] In this embodiment, the solid electrolyte in the all-solid-state battery is replaced with Li7La3Zr2O. 12 Except for the above, all other conditions are the same as in Example 1.

[0080] Comparative Example 1

[0081] In this comparative example, step (3) is replaced by: filtering, washing, and drying the lithium-rich cathode material precursor with phase structure gradient prepared in step (2), uniformly mixing it with Li2CO3 at a ratio of lithium molar to Ni, Co, and Mn molar to 1.6:1, pre-calcining it at 500°C for 5 hours in air atmosphere, and then heating it to 900°C and holding it for 10 hours to obtain a lithium-rich manganese-based cathode material with a phase structure ratio gradient. All other conditions are the same as in Example 1.

[0082] Comparative Example 2

[0083] In this comparative example, except that steps (1) and (2) were replaced with the traditional coprecipitation method to prepare a precursor without a phase structure gradient, all other conditions were the same as in Example 1.

[0084] Comparative Example 3

[0085] In this comparative example, except that steps (1) and (2) are replaced with the traditional coprecipitation method to prepare a precursor without phase structure gradient, all other conditions are the same as in comparative example 1.

[0086] Comparative Example 4

[0087] Except for step (3) where 60LiTi2(PO4)3 is not added, all other conditions in this comparative example are the same as in Example 1.

[0088] Comparative Example 5

[0089] Except for step (3) where graphene is not added, all other conditions in this comparative example are the same as in Example 1.

[0090] Comparative Example 6

[0091] Except for step (3), which did not add 60LiTi2(PO4)3 and graphene, the conditions in this comparative example were the same as in Example 1.

[0092] Comparative Example 7

[0093] The only difference between this comparative example and Example 1 is that the solid electrolyte was replaced with a membrane and the electrolyte was LiPF6 / EC+DEC (Klud).

[0094] After drying and rolling, the composite cathode materials prepared in Examples 1-5 and Comparative Examples 1-7 were tested for compaction density. The all-solid-state batteries prepared in Examples 1-5 and Comparative Examples 1-7 were tested for cycle retention rate and nail penetration. The test results are shown in Table 1.

[0095] The test method for cycle retention rate is as follows: at room temperature (25℃), the battery is activated for 3 cycles under the conditions of voltage range 2.0-4.8V and current density of 0.1C, and then the charge-discharge cycle test is carried out under the conditions of voltage range 2.0-4.8V and current density of 0.1C to test the capacity retention rate within 100 cycles.

[0096] The needle penetration test is performed as follows: When the battery is fully charged (100% SOC), a 5mm diameter steel needle (with a 60° conical angle at the tip, and a smooth surface free of rust, oxide layer, and oil) is inserted perpendicularly to the battery at a speed of 25mm / s. The needle remains inside the pouch cell, and the battery is observed for 1 hour. The battery passes the needle penetration test if it does not smoke, catch fire, or explode; otherwise, it fails.

[0097] Table 1

[0098]

[0099]

[0100] As can be seen from the table above, and from Examples 1-3 of the present invention, the all-solid-state battery prepared by the present invention has good density, capacity retention and safety performance.

[0101] As can be seen from Example 4, the positive electrode material prepared by the present invention is subjected to discharge plasma sintering under pressureless conditions. After being rolled into a positive electrode sheet, the compaction density decreases slightly, while the cycle performance and safety performance of the battery remain almost unchanged.

[0102] As can be seen from Example 5, the solid electrolyte of the present invention is replaced with Li7La3Zr2O. 12 Subsequently, the cycle performance of the prepared all-solid-state battery decreased significantly.

[0103] As shown in Comparative Example 1, after sintering the solid electrolyte, conductive agent, and lithium-rich cathode material particles with phase structure gradient by discharge plasma, the cycle performance, compaction density, and safety performance of the all-solid-state battery all decrease.

[0104] As shown in Comparative Example 2, when a precursor without phase structure gradient is prepared, both the cycle performance and safety performance of the battery decrease.

[0105] As can be seen from Comparative Example 3, when a precursor without phase structure gradient is prepared and is not co-sintered with solid electrolyte and conductive agent in step (3), the cycle performance, compaction density and safety performance of the all-solid-state battery all decrease.

[0106] As can be seen from Comparative Example 4, without adding solid electrolyte additives to the cathode material, the interfacial performance between the cathode material and the solid electrolyte in the prepared all-solid-state battery deteriorates, the cycle performance of the battery decreases, and the compaction density decreases compared with Example 1 under the same conditions.

[0107] As shown in Comparative Example 5, without adding a conductive agent to the cathode material, the electronic conductivity of the prepared all-solid-state battery decreases, and the cycle performance of the battery also decreases.

[0108] As shown in Comparative Example 6, the absence of solid electrolyte additives and conductive agents in the cathode material disrupts the original phase structure gradient of the lithium-rich cathode material, solid electrolyte additives, and conductive agents, resulting in decreased battery cycle performance, reduced compaction density, and decreased safety performance.

[0109] As can be seen from Comparative Example 7, replacing the battery with a lithium-ion battery using liquid electrolyte as the medium improves the battery's cycle performance. This shows that the positive electrode material prepared by this invention is also suitable for lithium-ion batteries with liquid electrolyte. However, compared to the all-solid-state battery, the safety performance of Comparative Example 7 is significantly reduced.

[0110] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A composite cathode material, characterized in that, The composite cathode material includes phase structure gradient lithium-rich cathode material particles, a solid electrolyte additive, and a conductive agent. The chemical general formula of the composite cathode material is xLi2MnO3·(1-x)LiTMO2@A@B, where 0 < x < 1, TM is selected from any one or at least two combinations of Ni, Co, or Mn, A includes a solid electrolyte additive, and B includes a conductive agent; The phase structure gradient lithium-rich cathode material particles include a monoclinic Li2MnO3 phase and a rhombic LiTMO2 phase. The content of the monoclinic Li2MnO3 phase decreases sequentially from the inside to the outside, and the content of the rhombic LiTMO2 phase increases sequentially from the inside to the outside.

2. The composite cathode material according to claim 1, characterized in that, The solid electrolyte additive includes an oxide solid electrolyte and / or a halide solid electrolyte; Preferably, the oxide solid electrolyte includes any one or at least two combinations of garnet-type oxide solid electrolytes, perovskite-type oxide solid electrolytes, or NASICON-type oxide solid electrolytes; Preferably, the garnet-type oxide solid electrolyte comprises Li y C3D2O 12 Wherein, C is selected from any one or at least two of La, Nb, Mg, Ba, Ca, or Sr, and D is selected from any one or at least two of Te, Ta, Nb, Zr, or In. <y≤7; Preferably, the perovskite-type oxide solid electrolyte includes any one or at least two combinations of Li3LaTiO3, LiTi2(PO4)3, or Li3PO4; Preferably, the NASICON-type oxide solid electrolyte includes Na 1+z Zr2Si z P 3-z O 12 , 0≤z≤3; Preferably, the chemical formula of the halide solid electrolyte is Li3MX6, M is selected from any one or at least two combinations of Zr, Hf, In, Sc, Y, La, Ce, Pr, Nb, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu, and X is selected from any one or at least two combinations of F, Cl, Br, or I; Preferably, the conductive agent includes any one or at least two combinations of acetylene black, carbon nanotubes, graphene, or carbon black; Preferably, the mass ratio of the cathode active material, the solid electrolyte additive, and the conductive agent is (85~93):(5~10):(2~5).

3. The lithium-rich cathode material according to claim 1 or 2, characterized in that, The tap density of the lithium-rich cathode material is 2.0–4.5 g / cm³. 3 .

4. A method for preparing a composite cathode material as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: Mix a phase structure gradient lithium-rich cathode material precursor, a lithium source, a solid electrolyte additive, and a conductive agent, and perform spark plasma sintering to obtain the composite cathode material. Among them, the phase structure gradient lithium-rich cathode material precursor includes a monoclinic Li2MnO3 phase and a rhombic LiTMO2 phase. The content of the monoclinic Li2MnO3 phase decreases sequentially from the inside to the outside, and the content of the rhombic LiTMO2 phase increases sequentially from the inside to the outside.

5. The preparation method according to claim 4, characterized in that, The molar ratio of the total molar number of Ni, Co, and Mn in the phase structure gradient lithium-rich cathode material precursor to the molar number of the lithium source is (1~5):1; Preferably, the lithium source includes any one or at least two combinations of lithium hydroxide, lithium carbonate, lithium oxalate, or lithium acetate; 6. The preparation method according to claim 4 or 5, characterized in that, The voltage of the spark plasma sintering is 50~850V; Preferably, the pressure of the spark plasma sintering in step (3) is 0~120MPa; Preferably, the temperature of the spark plasma sintering in step (3) is 400~1500℃; Preferably, the time of the spark plasma sintering in step (3) is 30s~4h; Preferably, the rate of discharge plasma sintering in step (3) is 50 to 300 °C / min.

7. The preparation method according to any one of claims 4-6, characterized in that, The preparation method includes: A phase-gradient lithium-rich cathode material precursor, a lithium source, a solid electrolyte additive, and a conductive agent are mixed and then sintered under discharge plasma conditions of 50–850 V, 0–120 MPa, 400–1500 °C, 30 s–4 h, and 50–300 °C / min to obtain the composite cathode material. The phase-gradient lithium-rich cathode material precursor includes a monoclinic Li₂MnO₃ phase and a rhombic LiTMO₂ phase. The content of the monoclinic Li₂MnO₃ phase decreases from the inside to the outside, while the content of the rhombic LiTMO₂ phase increases from the inside to the outside.

8. An all-solid-state battery, characterized in that, The all-solid-state battery includes a positive electrode, a solid electrolyte, and a negative electrode, wherein the positive electrode includes a composite positive electrode material as described in any one of claims 1-3.

9. The all-solid-state battery according to claim 8, characterized in that, The compaction density of the positive electrode sheet is 3.5–5.0 g / cm³. 3 ; Preferably, the solid electrolyte includes an oxide solid electrolyte and / or a halide solid electrolyte; Preferably, the oxide solid electrolyte includes any one or a combination of at least two of the following: NASICON structure oxide solid electrolyte, LISICON structure oxide solid electrolyte, garnet solid electrolyte, or perovskite structure oxide solid electrolyte. Preferably, the chemical formula of the halide solid electrolyte is Li3MX6, where M is selected from any one or at least two combinations of Zr, Hf, In, Sc, Y, La, Ce, Pr, Nb, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu, and X is selected from any one or at least two combinations of F, Cl, Br, or I.

10. An application of the composite cathode material as described in any one of claims 1-3, characterized in that, The composite cathode material is used in the field of lithium-ion batteries.

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