A positive electrode material with a hierarchical structure, a preparation method and application thereof

Abstract

The application discloses a kind of positive electrode material with hierarchical structure and its preparation method and application, belong to new energy material technical field.The positive electrode material provided by the application includes matrix material and first coating layer;The matrix material is ultra-high nickel material, and has secondary ball structure and core-shell structure;M2 is doped in bulk phase, and M3 is infiltrated in the gap between primary particles;M is doped in the core, and M1 is doped in the shell;The first coating layer includes fast ionic conductor material;Wherein, M includes at least one of Co, Mn and Al;M1 includes at least one of Zr, Nb, W, Sr, B, Y, Te and Sn;M2 includes at least one of Zr, Sr, Al, Mg, Ca and Ba;M3 includes at least one of Nb, Ti, Y, Sb, Mo, W, Te, Ta and In.The positive electrode material provided by the application has excellent comprehensive performance.The application also provides a preparation method and application of the above positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, and in particular to a cathode material with a hierarchical structure, its preparation method, and its application. Background Technology

[0002] The application of ultra-high nickel cathode materials (nickel content > 85%) is of great significance for improving the energy density of lithium-ion batteries, especially in the power fields of electric vehicles, power tools and aircraft, where there are higher requirements for range or volumetric energy density.

[0003] However, ultra-high nickel materials exhibit severe side reactions during charge and discharge, particularly under full charge conditions where oxidation is extremely strong. Electrolyte side reactions cause problems such as interfacial phase transitions, film deposition, and electrolyte gas generation. Simultaneously, the high delithiation state leads to significant cell volume expansion and contraction, and the anisotropy amplifies and disrupts the effects of these volume changes. The combination of these issues causes cracking in ultra-high nickel cathode materials during application, leading to poor contact. When coupled with the lithium insertion / deintercalation process of the anode, this results in a "breathing effect," making it difficult for the battery to meet performance requirements.

[0004] Currently, the main methods for improving the performance of ultra-high nickel materials focus on multi-element doping or multi-component coating with conventional elements. These strategies can improve the cycle stability and high-temperature stability of the materials to some extent, but bulk reaction and phase transformation reactions are inevitable in ultra-high nickel materials. For example, as charging and discharging proceed, some lithium sites are gradually replaced by nickel, especially the near-surface layer of ultra-high nickel materials transforms into spinel or even rock salt phases. At the same time, electrolyte side reactions and the deepening of cracks also increase the difficulty of charge transfer processes and increase SEI impedance. Therefore, compared with low- and medium-nickel, single-crystal materials or commercially available 811 series materials, the overall performance of ultra-high nickel cathode materials still has a significant gap.

[0005] Therefore, there is a need to provide an ultra-high nickel cathode material with excellent overall performance. Summary of the Invention

[0006] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a cathode material with a hierarchical structure, which can effectively improve the cycle performance of cathode materials, suppress the growth of DCR, and improve high-temperature storage performance.

[0007] The present invention also provides a method for preparing the above-mentioned cathode material.

[0008] The present invention also provides a lithium-ion battery comprising the above-described positive electrode material.

[0009] According to an embodiment of a first aspect of the present invention, a cathode material having a layered structure is provided, the cathode material comprising a matrix material and a first coating layer covering the matrix material;

[0010] The matrix material has a secondary spherical structure and a core-shell structure; it is doped with element M2, and element M3 is infiltrated into the gaps between the primary particles;

[0011] The core of the matrix material has the chemical formula Li[(Ni x M 1-x )] 1-a-b M2 a M3 b O2; the chemical formula of the outer shell of the matrix material is Li[(Ni x M 1-x ) 1-y M1 y ] 1-a-b M2 a M3 b O2;

[0012] The first coating layer comprises a fast ion conductor material;

[0013] Wherein, M includes at least one of Co, Mn and Al; M1 includes at least one of Zr, Nb, W, Sr, B, Y, Te and Sn; M2 includes at least one of Zr, Sr, Al, Mg, Ca and Ba; M3 includes at least one of Nb, Ti, Y, Sb, Mo, W, Te, Ta and In;

[0014] 0.88≤x≤0.98;0.35≤y≤0.60;0.0025≤a≤0.015;0.0025≤b≤0.015;

[0015] The cathode material according to embodiments of the present invention has at least the following beneficial effects:

[0016] The cathode material provided by this invention has a multi-level structure. Specifically: the first level structure is a core-shell structure of the matrix material; the second level structure is M3 elements melt-infiltrated and coated within the gaps of the primary particles of the matrix material, which is essentially equivalent to edging the primary particles; the third level structure is the first coating layer structure. This simultaneously achieves the control of the cell structure (doping elements) and the near-surface composition and structure.

[0017] In the cathode material provided by this invention, the value of y is limited. When the value of y is too large, the control over subsequent synthesis is too great, which can easily cause core-shell separation. When the value of y is too small, it is difficult to maintain the core-shell structure.

[0018] In the cathode material provided by this invention, the doped M2 element plays a role in regulating cell parameters, thereby improving structural stability at the cell level; the melt-infiltrated M3 element inhibits primary particle growth, buffers stress, and enhances interfacial kinetics, thus improving structural stability at the primary particle level. M2 and M3 synergistically enhance ion diffusion kinetics during solid-state reactions, accelerate the reaction rate, and regulate the crystal growth barrier, thereby enabling the directional design of the grain morphology of the doped material.

[0019] The cathode material provided by this invention, through multi-level design and composition, can significantly suppress the side reaction activity of the interface layer, maintain the stability of the coating structure during the reaction process, and ultimately significantly improve the cycling stability of the cathode material, suppress the increase in DCR during use, and have excellent high-temperature storage performance.

[0020] According to some embodiments of the present invention, in the positive electrode material, 0.90 ≤ x ≤ 0.95. Preferably, 0.92 ≤ x ≤ 0.94.

[0021] According to some embodiments of the present invention, in the positive electrode material, 0.35≤y≤0.60.

[0022] According to some embodiments of the present invention, in the positive electrode material, 0.50 ≤ y ≤ 0.60. For example, it can specifically be 0.5, 0.55, 0.6; or a range of values ​​consisting of any two of the above points.

[0023] According to some embodiments of the present invention, in the positive electrode material, 0.004≤a≤0.013; preferably 0.005≤a≤0.007; and preferably 0.011≤a≤0.013.

[0024] According to some embodiments of the present invention, in the positive electrode material, 0.004≤b≤0.013; preferably 0.005≤b≤0.007; and more preferably 0.011≤b≤0.013.

[0025] According to some embodiments of the present invention, in the positive electrode material, a = b.

[0026] In the positive electrode material, the a in the core and the a in the outer shell can be equal or unequal; similarly, the b in the core and the b in the outer shell can be equal or unequal.

[0027] According to some embodiments of the present invention, in the positive electrode material, M includes at least two of Co, Mn, and Al.

[0028] According to some embodiments of the present invention, in the positive electrode material, M is a combination of Co and Mn. The molar ratio of Co to Mn is 1.8 to 2.2:1; preferably 2:1.

[0029] According to some embodiments of the present invention, in the positive electrode material, M is a combination of Co and Al.

[0030] According to some embodiments of the present invention, in the positive electrode material, M1 is at least one selected from Zr, Sr, Al, Mg, and Ca. According to some embodiments of the present invention, in the positive electrode material, M1 is at least one selected from W, Nb, and Zr.

[0031] According to some embodiments of the present invention, in the cathode material, M1 is a combination of W, Nb, and Zr. The molar ratio of W, Nb, and Zr is 0.8~1.2:0.8~1.2:1; preferably 1:1:1. This further improves the stability of the resulting cathode material.

[0032] According to some embodiments of the present invention, in the positive electrode material, M1 is a combination of W and Nb. The molar ratio of W to Nb is 1:1 to 2; preferably 1:1.5.

[0033] According to some embodiments of the present invention, in the positive electrode material, M2 is at least one of Zr, Sr, Al, Mg and Ca.

[0034] According to some embodiments of the present invention, in the cathode material, M2 is a combination of Zr, Sr and Al. The molar ratio of Zr, Sr and Al is 1.8~2.2:0.8~1.2:1; preferably 2:1:1.

[0035] According to some embodiments of the present invention, in the cathode material, M3 is at least one of Ti, Y, Sb, W, Ta and Te.

[0036] According to some embodiments of the present invention, in the cathode material, M3 is a combination of Ta and Sb. The molar ratio of Ta to Sb is 1:3.5 to 4.5; preferably 1:4. These elements are not easily fluxed or doped, and therefore tend to exist in the intergranular spaces of primary particles. Furthermore, they can increase the crystal growth barrier, thus constraining the growth of primary particles. With similar amounts of added elements, the synergistic effect of Li-Ta-O and Li-Sb-O (or multi-element combinations such as Ta / Te / Sb / Y) is more pronounced.

[0037] According to some embodiments of the present invention, in the cathode material, M3 is a combination of Ti and Sb.

[0038] According to some embodiments of the present invention, in the cathode material, M3 is a combination of Ti and Te.

[0039] According to some embodiments of the present invention, in the positive electrode material, M3 is a combination of Ta and Y. The molar ratio of Ta to Y is 1:3.5 to 4.5; preferably 1:4.

[0040] According to some embodiments of the present invention, in the cathode material, M3 is a combination of Te and Sb.

[0041] According to some embodiments of the present invention, in the cathode material, M3 is a combination of Te and Y.

[0042] According to some embodiments of the present invention, in the positive electrode material, M3 is a combination of Ta, Y, and Sb. The molar ratio of Ta, Y, and Sb is 1:0.8~1.2:3.5~4.5; preferably 1:1:4.

[0043] According to some embodiments of the present invention, in the cathode material, M3 is a combination of Ti, Ta, Y and Sb.

[0044] According to some embodiments of the present invention, the ratio of the thickness l of the outer shell of the matrix material to the radius d of the inner core of the matrix material satisfies 1 / 90 ≤ l / d ≤ 1 / 6, where l ≤ 500 nm.

[0045] According to some embodiments of the present invention, the ratio of the thickness l of the outer shell of the matrix material to the radius d of the inner core of the matrix material satisfies 1 / 50 ≤ l / d ≤ 1 / 10.

[0046] According to some embodiments of the present invention, the porosity of the outer shell of the matrix material is greater than the porosity of the inner core of the matrix material. Wherein,

[0047] The porosity of the outer shell of the matrix material is 0.5–15.0%; the porosity of the positive electrode material is 0.2–5.0%.

[0048] According to some embodiments of the present invention, the fast ion conductor material of the first coating layer is a Li-M4-O type fast ion conductor material; wherein, M4 includes at least one of Co, Al, Ti, W, Sr, Ce, Mg, Ba, Ca, B and Si.

[0049] According to some embodiments of the present invention, M4 includes at least one of Co, Al, Ti, W and Sr.

[0050] According to some embodiments of the present invention, M4 is a combination of Co and Sr.

[0051] According to some embodiments of the present invention, M4 is a combination of Co and Al.

[0052] According to some embodiments of the present invention, M4 is a combination of Co and Ti.

[0053] According to some embodiments of the present invention, M4 is a combination of Co and W.

[0054] According to some embodiments of the present invention, the positive electrode material further includes a second coating layer covering the first coating layer; the second coating layer includes a Li-BO type material, and at least one of Li-M5-O and M5-O type materials;

[0055] M5 includes at least one of Al, Ti, Mg, Ce, Zr, Sn, Sb, W, and Si.

[0056] Preferably, M5 includes at least one of Al, Ce, Ti, W, Sn, and Sb.

[0057] Preferably, M5 is a combination of Al and Ti.

[0058] According to some embodiments of the present invention, the D50 particle size of the positive electrode material is 6~18μm.

[0059] According to some embodiments of the present invention, the D50 particle size of the positive electrode material is 9~15μm. For example, it can be 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm; or a range of values ​​composed of any two of the above points.

[0060] According to some embodiments of the present invention, the specific surface area of ​​the positive electrode material is 0.3~1.3m². 2 / g. For example, it could be 0.3 m. 2 / g, 0.5 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g、1.1 m 2 / g, 1.3 m 2 / g; or the range of values ​​formed by any two of the above point values.

[0061] According to an embodiment of a second aspect of the present invention, a method for preparing the cathode material described in the first aspect of the present invention is provided, the method comprising the following steps:

[0062] S1. A precursor is provided, the precursor having a core-shell structure, wherein the core of the precursor has the chemical formula Ni. x M 1-x (OH)2; the chemical formula of the shell of the precursor is (Ni x M 1-x ) 1-y M1 y (OH)2;

[0063] S2. The precursor, lithium source, M2 compound and M3 compound are mixed and then subjected to a first sintering.

[0064] The highest temperature for the first sintering is 650~880℃;

[0065] S3. Coat the surface of the substrate material obtained in step S2 with a first coating layer containing fast ion conductor material.

[0066] Since the preparation method employs all the technical solutions of the cathode materials described in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments. Furthermore,

[0067] If the highest temperature of the first sintering is lower than the above range, it may lead to insufficient sintering, failure to form the target pure phase material, or incomplete reaction of raw materials such as lithium source; if it is higher than the above range, it may lead to over-burning, forming large single crystals and producing a high proportion of impurity phases.

[0068] Within the temperature range of the first sintering, M2 tends to be doped, potentially entering the transition metal layer or lithium layer; M3 forms a Li-M3-O solid solution phase, creating a "bordering" effect on the surface of the primary particles, thus protecting the primary particle interface, buffering stress, and improving interface dynamics. Simultaneously, since neither the melting infiltration of M3 nor the doping of M2 can be 100%, a melting infiltration-doping transition zone exists on the front surface region of the primary particles.

[0069] As can be seen from the chemical formula of the precursor in step S1, the Ni content in the shell of the precursor is low. Therefore, if the shell is to be fully sintered, the sintering temperature required for the shell is higher. However, the temperature of the first sintering in this invention is lower than the temperature required for the shell. Therefore, the shell cannot be fully sintered. As a result, the porosity of the shell is higher after sintering, which is more conducive to the entry of M2 and M3 elements in step S2 and the improvement of the primary particle strength. It is also more conducive to the subsequent wetting of the electrolyte.

[0070] According to some embodiments of the present invention, in step S1, the ratio of the radius of the outer shell of the precursor to the radius of the core of the precursor is 1 / 90 to 1 / 6. Preferably, it is 1 / 50 to 1 / 10; preferably 1 / 40 to 1 / 20; preferably 1 / 15 to 1 / 12; preferably 1 / 11 to 1 / 9.

[0071] Therefore, the outer shell of the precursor corresponds to the outer shell of the subsequent matrix material, and the core of the precursor corresponds to the core of the matrix material. Furthermore, due to the composition design, the outer shell of the precursor or the matrix material has high stability, effectively protecting the core and improving the structural stability of the resulting cathode material.

[0072] According to some embodiments of the present invention, in step S1, the D50 particle size of the precursor satisfies: 5.0 μm ≤ D50 ≤ 19.0 μm. For example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm; or a range of values ​​composed of any two of the above points.

[0073] According to some embodiments of the present invention, in step S1, the method for synthesizing the precursor includes the following steps:

[0074] S1a. Preparation of the precursor core: A first mixed salt solution, a precipitant, and a complexing agent are introduced concurrently into the substrate; wherein the first mixed salt solution includes a nickel salt and an M salt; the pH is controlled at 10.5–10.70 during the reaction.

[0075] S1b. Preparation of the shell of the precursor: A second mixed salt solution, a precipitant and a complexing agent are introduced concurrently into the mixture obtained in step S1a; wherein the second mixed salt solution includes nickel salt, M salt and M1 salt; during the reaction, the pH is controlled to be 9.8 to 10.2.

[0076] According to some embodiments of the present invention, the precipitant is an aqueous solution of sodium hydroxide. Its concentration is 10-30 wt%; preferably 30-32 wt%.

[0077] According to some embodiments of the present invention, the complexing agent is an aqueous ammonia solution. Its concentration is 2~10 mol / L; preferably 5~7 mol / L.

[0078] According to some embodiments of the present invention, in step S1a, the pH of the base solution is 10.0~12.2; preferably 10.5~11.5.

[0079] According to some embodiments of the present invention, in step S1a, the ammonia value in the bottom liquid is 2~4 g / L; preferably 3.5~3.5 g / L.

[0080] According to some embodiments of the present invention, in step S1a, the base liquid is a mixture of water, a precipitant, and a complexing agent.

[0081] According to some embodiments of the present invention, in step S1a, the concentration of the first mixed salt solution is 1~2.4 mol / L. Preferably, it is 1.8~2.2 mol / L.

[0082] According to some embodiments of the present invention, in step S1a, the flow rate of the first mixed salt solution is 220-250 mL / min, preferably 230-240 mL / min.

[0083] According to some embodiments of the present invention, in step S1a, the ammonia value is controlled to be 2~4 g / L during the reaction process; preferably 3.5~3.5 g / L.

[0084] According to some embodiments of the present invention, in step S1a, the reaction is carried out under stirring; the stirring speed is 250~300 rpm; preferably 260~270 rpm.

[0085] According to some embodiments of the present invention, in step S1a, the reaction temperature is 55~65°C, preferably 60°C.

[0086] According to some embodiments of the present invention, in step S1b, the M1 salt includes at least one selected from the following: sulfate, nitrate, halide, oxalate, and metal oxoate of M1. Preferably, it is at least one selected from the following: niobium oxalate, ammonium metatungstate, and zirconium nitrate.

[0087] According to some embodiments of the present invention, in step S1b, the nickel salt includes at least one of nickel sulfate, nickel chloride, and nickel oxalate.

[0088] According to some embodiments of the present invention, in step S1b, the M salt includes at least one of manganese sulfate, manganese chloride, manganese nitrate, aluminum nitrate, and aluminum sulfate.

[0089] According to some embodiments of the present invention, in step S1b, the reaction is carried out under stirring; the stirring speed is 150~200 rpm; preferably 2170~180 rpm.

[0090] According to some embodiments of the present invention, in step S1b, the reaction temperature is 55~65°C, preferably 60°C.

[0091] According to some embodiments of the present invention, in step S1b, the concentration of the second mixed salt solution is 1~2.4 mol / L. Preferably, it is 1.8~2.2 mol / L.

[0092] According to some embodiments of the present invention, in step S1b, the flow rate of the second mixed salt solution is 70-90 mL / min, preferably 80 mL / min.

[0093] According to some embodiments of the present invention, in step S1b, the ammonia value is controlled to be 2~4 g / L during the reaction process; preferably 3.5~3.5 g / L.

[0094] According to some embodiments of the present invention, in step S2, the M2 compound includes at least one selected from the following: oxide, hydroxide, carbonate, acetate, and oxalate of M2. Preferably, it is at least one selected from the following: zirconium dioxide, strontium oxide, and aluminum oxide.

[0095] According to some embodiments of the present invention, in step S2, the M3 compound includes at least one selected from the oxide, hydroxide, carbonate, acetate, and oxalate of M3. Preferably, it is at least one selected from antimony oxide, tantalum oxide, and yttrium oxide.

[0096] According to some embodiments of the present invention, in step S2, the lithium source includes lithium hydroxide.

[0097] According to some embodiments of the present invention, in step S2, the molar ratio of lithium in the lithium source to the transition metal in the precursor is 1.02~1.08:1; preferably 1.03~1.05:1.

[0098] According to some embodiments of the present invention, in step S2, the first sintering includes a first heat preservation platform and a second heat preservation platform performed sequentially.

[0099] According to some embodiments of the present invention, the temperature of the first insulation platform is 450~550℃, preferably 500~520℃.

[0100] According to some embodiments of the present invention, the temperature holding time of the first insulation platform is 3 to 5 hours, preferably 4 to 4.5 hours.

[0101] According to some embodiments of the present invention, the temperature of the second heat-insulating platform is 650~880℃. That is, the highest temperature of the first sintering is the temperature of the second heat-insulating platform.

[0102] According to some embodiments of the present invention, the temperature of the second insulation platform is 700~850℃, preferably 720~750℃.

[0103] According to some embodiments of the present invention, in step S2, the holding time at the highest temperature during the first sintering is 6-30 hours. Preferably, it is 10-15 hours; more preferably, it is 12-13 hours. That is, the holding time at the highest temperature during the first sintering is the holding time of the second holding platform.

[0104] According to some embodiments of the present invention, in step S3, the coating method includes mixing the matrix material and the M4 compound and then performing a second sintering.

[0105] According to some embodiments of the present invention, the temperature of the second sintering is 400~700℃. If the temperature is too high, the formed first coating layer is not conducive to lithium-ion transport and affects the capacity of the cathode material; if the temperature is too low, the stability of the obtained first coating layer is poor and it cannot play a good protective role.

[0106] According to some embodiments of the present invention, the temperature of the second sintering is 450~700℃, preferably 600~700℃.

[0107] According to some embodiments of the present invention, the duration of the second sintering is 4 to 12 hours, preferably 8 to 10 hours.

[0108] According to some embodiments of the present invention, the mass ratio of the matrix material to the M4 compound is 1:0.005~0.050, preferably 1:0.002~0.03. If the amount of M4 compound is too high, the resulting first coating layer will be too thick, which is not conducive to the transport of lithium ions and affects the capacity of the resulting cathode material. If the amount of M4 compound is too high, a uniform first coating layer cannot be formed, and thus cannot provide good protection.

[0109] According to some embodiments of the present invention, the M4 compound comprises at least one of an oxide of M4, a hydroxyl oxide, and a carbonate. Preferably, it comprises cobalt hydroxyl oxide and strontium oxide. Preferably, the mass ratio of cobalt hydroxyl oxide to strontium oxide is 5-7:1; more preferably, it is 6:1.

[0110] Under the combined influence of the type of M4 compound and the second sintering mechanism, the resulting first coating layer is an island-like coating and / or a uniform coating; and can achieve uniform co-coating of two or more elements.

[0111] The M4 compound and the Li-M3-O solid solution structure that is infiltrated on the surface of the primary particles are compatible, so better M4 coating and bonding can be achieved in step S3, thereby improving the conductivity of the obtained cathode material.

[0112] According to some embodiments of the present invention, the preparation method further includes the following steps after step S3:

[0113] S4. Wash and dry the product obtained in step S3;

[0114] S5. The product obtained in step S4, boric acid, and compound M5 are mixed and then subjected to a third sintering.

[0115] According to some embodiments of the present invention, in step S4, the temperature of the water washing is 15~25°C.

[0116] According to some embodiments of the present invention, in step S4, the duration of the water washing is 3 to 5 minutes.

[0117] According to some embodiments of the present invention, in step S4, the mass ratio of water to the product obtained in step S3 during the water washing is 0.5~0.8:1. Preferably, it is 0.6~0.7:1.

[0118] According to some embodiments of the present invention, in step S4, the drying temperature is 110~130°C.

[0119] According to some embodiments of the present invention, in step S4, the drying time is 4 to 6 hours.

[0120] According to some embodiments of the present invention, in step S5, the third sintering is carried out in an oxygen-containing atmosphere, wherein the oxygen content is ≥50%.

[0121] According to some embodiments of the present invention, in step S5, the heating rate of the third sintering is 5~15℃ / min. Preferably, it is 8~12℃ / min.

[0122] According to some embodiments of the present invention, in step S5, the temperature of the third sintering is 200~500℃. Preferably, it is 250~350℃; more preferably, it is 300~320℃.

[0123] According to some embodiments of the present invention, in step S5, the duration of the third sintering is 4 to 12 hours, preferably 8 to 10 hours.

[0124] According to some embodiments of the present invention, in step S5, the mass ratio of the product obtained in step S4 to boric acid is 1:0.001~0.008. Preferably, it is 1:0.002~0.005; more preferably, it is 1:0.002~0.003.

[0125] According to some embodiments of the present invention, in step S5, the mass ratio of the product obtained in step S4 to compound M5 is 1:0.003~0.020. Preferably, it is 1:0.005~0.01. More preferably, it is 1:0.005~0.007.

[0126] If the amount of M5 compound and boric acid is too large, the formed second coating layer will affect the migration of lithium ions, and the capacity and impedance performance of the cathode material will deteriorate; if the amount of M5 compound or boric acid is too small, the side reaction cannot be effectively mitigated, and the contribution of the second coating layer to the stability of the cathode material will be smaller.

[0127] According to some embodiments of the present invention, the M5 compound is at least one selected from oxides, hydroxides, carbonates, and fluorides of M5. Preferably, it is alumina and titanium oxide. The molar ratio between alumina and titanium oxide is 1:0.8 to 1.2, preferably 1:1.

[0128] Due to the combined effects of the third sintering mechanism, the type of M5 compound, and boric acid, the resulting second coating layer is an island-like coating and / or a uniform coating.

[0129] Although the same elements may be used in steps S3 and S5, the products formed are different due to the different sintering mechanisms, and therefore play different roles. For example, Al in step S3 tends to form Li-Al-O, while Al in step S5 tends to remain in the state of alumina.

[0130] According to some embodiments of the present invention, the heating rates of the first sintering, the second sintering, and the third sintering are independently selected from any value of 3 to 10 °C / min. Preferably, it is 5 to 8 °C / min.

[0131] According to some embodiments of the present invention, the first sintering, the second sintering, and the third sintering are carried out in an oxygen atmosphere.

[0132] According to an embodiment of a third aspect of the present invention, a lithium-ion battery is provided, wherein the raw materials for preparing the lithium-ion battery include the positive electrode material described in the first aspect of the present invention, or the positive electrode material prepared by the preparation method described in the second aspect of the present invention.

[0133] Since the lithium-ion battery adopts all the technical solutions of the cathode material in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments.

[0134] According to some embodiments of the present invention, the lithium-ion battery includes at least one of button cells, pouch cells, prismatic cells, and cylindrical cells.

[0135] According to some embodiments of the present invention, the lithium-ion battery includes at least one of a symmetrical battery, a half-cell, and a full-cell.

[0136] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0137] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0138] Figure 1 This is a partial flowchart of Embodiment 1 of the present invention.

[0139] Figure 2 This is a partial flowchart of Comparative Example 1 of the present invention.

[0140] Figure 3 This is a cross-sectional EDS spectrum of the cathode material obtained in Example 1 of the present invention.

[0141] Figure 4 The images show the cross-sectional morphology and EDS spectrum of the cathode material obtained in Example 1 of this invention.

[0142] Figure 5 These are TEM images of the cross-sectional morphology of the cathode materials obtained in Embodiment 1 (a, b) and Comparative Example 1 (c, d) of the present invention.

[0143] Figure 6 This is a partial cross-sectional SEM image of the cathode material obtained in Embodiment 1 of the present invention.

[0144] Figure 7 yes Figure 6 EDS plot in the direction indicated by the middle arrow.

[0145] Figure 8 This is a partial cross-sectional SEM image of the cathode material obtained in Comparative Example 1 of this invention;

[0146] Figure 9 yes Figure 8 EDS plot in the direction indicated by the middle arrow.

[0147] Figure 10 This is a SEM image of the cathode material obtained in Example 1 of the present invention.

[0148] Figure 11 This is a SEM image of the cathode material obtained in Comparative Example 3 of this invention. Detailed Implementation

[0149] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0150] Example 1

[0151] refer to Figure 1 Following the process described in this example, a cathode material with a hierarchical structure was prepared. The specific steps are as follows:

[0152] S1. Preparation of precursors

[0153] S1a. Preparation of the precursor kernel:

[0154] Pure water, complexing agent solution (ammonia solution), and precipitant solution (sodium hydroxide solution) were added to the reactor to prepare a reactor bottom solution with a pH of 11.0. The ammonia content in the bottom solution was 3 g / L.

[0155] According to the chemical formula Ni of the precursor core 0.94 Co 0.04 Mn 0.02Prepare a mixed salt solution of nickel sulfate, cobalt sulfate, and manganese sulfate (total metal concentration approximately 2M) using (OH)2; use sodium hydroxide aqueous solution (32wt%) as a precipitant and ammonia aqueous solution (6mol / L) as a complexing agent.

[0156] The above three solutions were injected into the bottom liquid in parallel to prepare the precursor matrix material. The flow rate of the mixed salt was controlled at 240 ml / min, and the flow rates of the other two solutions were adjusted to control the growth pH value at 10.5-10.70 and the ammonia value at 3 g / L. The stirring speed was adjusted to 270 rpm, and the reaction temperature was controlled at 60℃. After the particle size grew to 13.05 μm (D50), the feeding was stopped to obtain a slurry with a solid content of about 460 g / L.

[0157] S1b. Preparation of the precursor shell:

[0158] According to the chemical formula (Ni) 0.94 Co 0.04 Mn 0.02 ) 0.5 W 0.2 Nb 0.3 (OH)2, prepare a mixed salt solution (concentration 2 mol / L) of nickel sulfate, cobalt sulfate, manganese sulfate, niobium oxalate and ammonium metatungstate, using sodium hydroxide aqueous solution as precipitant and ammonia aqueous solution as complexing agent (concentration of precipitant and complexing agent is the same as in step S1a).

[0159] The newly prepared mixed salt was introduced into the reactor at a flow rate of 80 ml / min, with the pH value controlled between 9.8 and 10.2, the ammonia value controlled at 3 g / L, the stirring speed adjusted to 180 rpm, and the temperature maintained at 60℃ to grow the outer shell layer of the precursor. After the particle size grew to 13.51 μm (D50), the feed was stopped, and the precursor was aged, filtered, washed, and dried to obtain an ultra-high nickel precursor with a core-shell structure.

[0160] Based on the above discussion, in this example, the matrix materials are x=0.94, y=0.5, M is Co and Mn, and the molar ratio of Co to Mn is 2:1; M1 is W and Nb, and the molar ratio of W to Nb is 2:3.

[0161] S2. First sintering

[0162] The precursor obtained in step S1, the lithium source, compound M2, and compound M3 are mixed and then subjected to a first sintering; wherein...

[0163] Li[(Ni x M 1-x )] 1-a-b M2 a M3 b O2 and Li[(Ni x M1-x )] 1-a-b M2 a M3 b In O2, a=b=0.005; M2 compound is zirconium dioxide, strontium oxide and aluminum oxide, wherein the molar ratio of zirconium, strontium and aluminum is 2:1:1; M3 compound is antimony oxide and tantalum oxide, and the molar ratio of antimony to tantalum is 4:1; the lithium source is lithium hydroxide, and the molar ratio of lithium hydroxide to the precursor is 1.03:1.

[0164] The gas atmosphere for the first sintering is an oxygen atmosphere; the sintering mechanism is to raise the temperature to 520℃ at 5℃ / min, hold for 4h, then raise the temperature to the target sintering temperature of 740℃ at 5℃ / min, hold for 12h, and then crush and sieve to obtain the first sintering product (i.e., the matrix material).

[0165] It should be noted that, due to the fact that the diffusion rates of M2 and M3 in the shell and core are not exactly the same during the first sintering process, the a and b values ​​of the shell and core may not be the same in the actual matrix material obtained. The chemical formula provided in this step is calculated based on the ideal case of uniform diffusion of compounds M2 and M3.

[0166] S3. Second sintering

[0167] The matrix material obtained in step S1 and compound M4 were mixed, sintered a second time, and then sieved.

[0168] The mass ratio of the matrix material to the M4 compound is 1:0.025; the M4 compound is cobalt hydroxyoxide and strontium oxide, with a mass ratio of 6:1.

[0169] The second sintering was carried out in an oxygen atmosphere, and the sintering mechanism was to raise the temperature to 650℃ at a rate of 5℃ / min and hold it for 8 hours.

[0170] S4. Washing and drying

[0171] The product obtained by washing with pure water in step S3, wherein the mass ratio of pure water to dicalcined product is 0.6:1, the washing temperature is 25℃ and the washing time is 5min; then it is dried at 120℃ for 5h to obtain the washed and dried product.

[0172] S5. Third sintering

[0173] The product obtained in step S4, compound M5, and boric acid were mixed and subjected to a third sintering, then cooled to room temperature, and finally pulverized, sieved, and demagnetized.

[0174] The mass ratio of the product obtained in step S4, compound M5, and boric acid is 1:0.006:0.002; compound M5 is aluminum oxide and titanium dioxide, with a mass ratio of 1:1.

[0175] The third sintering is carried out in an oxygen-containing atmosphere; the sintering mechanism for the third sintering is to raise the temperature to 310℃ and hold it for 8 hours; in this step, the oxygen content in the oxygen-containing atmosphere is ≥50%, and within this range, it has basically no effect on the results.

[0176] The flowchart for this example is as follows: Figure 1 As shown; the left figure is the precursor obtained in step S1, and the right figure is the cathode material obtained in this example.

[0177] Example 2

[0178] This example prepares a cathode material with a hierarchical structure, which differs from Example 1 in that:

[0179] In step S2, a=b=0.0125.

[0180] Example 3

[0181] This example prepares a cathode material with a hierarchical structure, which differs from Example 1 in that:

[0182] In step S1a, feeding is stopped after the D50 particle size of the precursor core grows to 12.21.

[0183] Example 4

[0184] This example prepares a cathode material with a hierarchical structure, which differs from Example 1 in that:

[0185] In step S1b, y = 0.6.

[0186] Example 5

[0187] This example prepares a cathode material with a hierarchical structure, which differs from Example 1 in that:

[0188] In step S2, the temperature of the second heat preservation platform during the first sintering is 870℃.

[0189] Example 6

[0190] This example prepares a cathode material with a hierarchical structure, which differs from Example 1 in that:

[0191] In step S2, the temperature of the second heat preservation platform during the first sintering is 660℃.

[0192] Example 7

[0193] This example prepares a cathode material with a hierarchical structure, which differs from Example 1 in that:

[0194] In step S1, M1 consists of W (ammonium metatungstate), Nb (niobium oxalate), and Zr (zirconium nitrate), with a molar ratio of W, Nb, and Zr of 1:1:1.

[0195] Example 8

[0196] This example prepares a cathode material with a hierarchical structure, which differs from Example 1 in that:

[0197] In step S2, compound M3 is tantalum oxide and yttrium oxide; and the molar ratio of Ta to Y is 1:4.

[0198] Example 9

[0199] This example prepares a cathode material with a hierarchical structure, which differs from Example 1 in that:

[0200] In step S2, compound M3 consists of tantalum oxide, yttrium oxide, and antimony oxide; and the molar ratio of Ta, Y, and Sb is 1:1:4.

[0201] Comparative Example 1

[0202] This example prepares a cathode material, which differs from Example 1 in that:

[0203] Step S1b is excluded, and in step S1a, the D50 particle size is directly grown to 13.51 μm.

[0204] The flowchart for this example is as follows: Figure 2 As shown, the left figure is the precursor obtained in step S1 of this example, and the right figure is the cathode material obtained in this example.

[0205] Comparative Example 2

[0206] This example prepares a cathode material, which differs from Example 1 in that:

[0207] M3 compound is not included in step S2.

[0208] Comparative Example 3

[0209] This example prepares a cathode material, which differs from Example 1 in that:

[0210] Step S3 is not included.

[0211] Comparative Example 4

[0212] This example prepares a cathode material, which differs from Example 1 in that:

[0213] In step S2, the second stage of constant temperature during the first sintering is 900℃.

[0214] Comparative Example 5

[0215] This example prepares a cathode material, which differs from Example 1 in that:

[0216] In step S1b, y = 0.3.

[0217] Comparative Example 6

[0218] This example prepares a cathode material, which differs from Example 1 in that:

[0219] In step S2, a=b=0.17.

[0220] Application examples

[0221] This example demonstrates the fabrication of a lithium-ion battery, as detailed below.

[0222] The above-prepared positive electrode material, conductive agent SuperP, and binder polyvinylidene fluoride (PVDF) were mixed with N-methylpyrrolidone (NMP) at a mass ratio of 90:5:5 and stirred evenly to form a positive electrode slurry (solid content approximately 40%). This slurry was coated onto current collector aluminum foil, dried at 105°C, and then rolled at room temperature until the areal density reached 2.8~3.3 g / cm³. 3 Then, the material is punched and cut into φ14mm round sheets to form the positive electrode sheet; wherein the positive electrode material is from the examples or comparative examples.

[0223] Assemble the button cells inside the glove box. The assembly sequence is: negative electrode shell - nickel foam - lithium sheet (φ18mm) - 8 drops of electrolyte - separator (φ22mm, 16μm thick) - 8 drops of electrolyte - positive electrode sheet - positive electrode shell. The electrolyte is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC:EMC:DMC volume ratio = 1:1:1), containing 1.0M LiPF6. The battery casing (positive and negative electrode shells) is 24mm in size. Place the assembled button cells in the mold of a hydraulic sealing machine (purchased from Shenzhen Kejing Zhida Technology Co., Ltd.), lock them in place, and apply pressure >450kg / cm². 2 Then unlock it and take out the sealed button cell battery, which is the lithium secondary battery obtained in this example.

[0224] Test Example 1

[0225] This example tested the particle size, overall morphology, cross-sectional morphology, EDS energy dispersive spectroscopy, porosity, and specific surface area of ​​the cathode materials obtained in the examples and comparative examples. The cross-sectional performance was tested by performing SEM (scanning electron microscopy) or TEM (transmission electron microscopy) measurements after sectioning, simultaneously acquiring EDS energy dispersive spectroscopy. Particle size was measured using a laser particle size analyzer. Specific surface area was measured using BET (beta-internal emission testing). Porosity was characterized by obtaining high-resolution SEM images of the cathode material, using image recognition software to capture the area of ​​"voids" within a selected region, and calculating the area ratio of voids in the selected region. The test results show:

[0226] Particle size testing results show that the particle size distribution of the cathode material obtained in the embodiments of the present invention is between 0.3 and 1.3 μm. 2 Within the range of / g; more commonly distributed in the range of 0.9~1.1 m 2 Within the range of / g, and the specific surface area of ​​the cathode materials obtained in different embodiments is very small.

[0227] The D50 particle size of the cathode materials prepared in the embodiments and comparative examples of this invention is 11~14μm, with most distributed around 12.4μm. Different preparation methods have little effect on the particle size. Furthermore, although the cathode material inherits some characteristics such as particle size from the precursor during sintering, the fusion of small particles during sintering means that the overall D50 particle size of the cathode material obtained in the test may be 1.5μm smaller or 0.5μm larger than that of the precursor.

[0228] The cathode materials prepared in the embodiments and comparative examples of this invention have a secondary spherical morphology. Furthermore, the materials prepared in the embodiments exhibit a distinct core-shell structure (due to the thinness of the first and second coating layers, the core-shell structure here mainly reflects the core-shell structure of the matrix material), and the porosity of the shell layer is higher than that of the core layer; specifically, the porosity of the shell layer is approximately 8%, while the porosity of the core layer is approximately 3%. In contrast, Comparative Example 1 did not incorporate a core-shell structure in the precursor, and Comparative Example 4's structure was damaged due to the excessively high sintering temperature during the first sintering. Therefore, neither Comparative Example 1 nor Comparative Example 4 exhibits a distinct core-shell structure or a significant difference in porosity.

[0229] In the cathode material prepared according to the embodiments of the present invention, there are obvious differences in elemental distribution. Specifically, M4 and M5 are mainly distributed in the very surface layer of the cathode material, forming a coating. Since the first and second coating layers are very thin, M2 is basically uniformly distributed in the bulk phase of the cathode material, according to the test results. M3 is mainly distributed on the surface of the primary particles, i.e., at the contact position between adjacent primary particles. M1 is mainly distributed in the shell layer, with a deeper distribution depth than M4 or M5. The content of Ni and Mn is high at the core and low at the outer layer. Co, due to its presence in the first coating layer, shows a trend of first decreasing, then increasing, and then decreasing again from the center to the edge. This indicates that the cathode material prepared according to the present invention does indeed possess a multi-level structure, including a core-shell structure, a double-layer coating structure, bulk doping, and intergranular infiltration of primary particles.

[0230] From ordinary SEM images, the morphology of the cathode materials obtained in the examples and comparative examples is not significantly different. Whether or not they are coated, how many times they are coated, and whether or not they undergo melting and infiltration have little impact on their overall morphology. To distinguish them, cross-sectional characterization is usually required.

[0231] Specific test results are as follows: Figures 3-11 As shown.

[0232] Test Example 2

[0233] This example tests the electrochemical performance of the lithium-ion battery obtained from the application example, specifically its cycle performance, DCR values ​​before and after cycling, rate performance, and high-temperature storage performance.

[0234] The testing method for room temperature and high temperature cycling performance is as follows: At 25℃ (room temperature) or 45℃ (high temperature), the charge-discharge cycle characteristics of the coin cells are tested using a Blue Electric test cabinet, with 1C = 200mAh / g set. In the first week, activation is performed using 0.1C / 0.1C; from week 2 to week 51, cycling is performed using 1C / 1C. Specifically, charging and discharging are performed at a 1C charge-discharge rate within a voltage range of 2.8V to 4.25V. Specifically, the cells are charged at a constant current of 1C to 4.25V, then charged at a constant voltage of 4.25V to a cutoff current of 0.02C, rested for 5 minutes, and then discharged at 1C to 2.8V, rested for 5 minutes. The charge-discharge capacity at the first 1C and the 50th week at 1C is recorded.

[0235] Cycle capacity retention (%) = (50th cycle discharge capacity / 1st cycle discharge capacity) × 100%.

[0236] The DCR test method before and after cycling is as follows: The lithium-ion battery obtained in the application example is tested in a room temperature chamber (25℃). The test format is as follows: Week 1: 0.1C / 0.1C; Week 2: 0.1C full charge to 4.25V constant voltage state (cutoff condition 30μA and ≥1h) → rest for 5min → 0.1C discharge (to 2.8V). Take the voltage value V1 at the cutoff point after 5min rest, and accurately control the sampling interval time 60s to discharge the first point V2. According to the 1C current I1, calculate the ratio of the voltage difference (V2-V1) before and after 60s of discharge to the current I1 to obtain the corresponding DCR level.

[0237] The rate performance test method is as follows: The lithium-ion batteries obtained in the application example are tested in a room temperature chamber (25℃). The test format is as follows: Weeks 1-2: 0.1C / 0.1C, Weeks 3-4: 0.2C / 0.2C, Weeks 5-6: 0.5C / 0.5C, Weeks 7-8: 1C / 1C, Weeks 9-10: 2C / 2C, Weeks 11-12: 5C / 5C, Weeks 13-14: 0.1C / 0.1C. The ratio of the discharge capacity at different currents to the discharge capacity at 1~20.1C is used as the corresponding rate level. The voltage range of the rate test is 2.8~4.25V.

[0238] The test results for the above performance items are shown in Table 1.

[0239] Table 1. Electrochemical performance results of lithium-ion batteries obtained from application examples.

[0240]

[0241] Comparing the results of Example 1 and Comparative Examples 1-4, it can be seen that if the precursor obtained in step S1 does not have a core-shell structure, does not include M3, does not include the first coating layer, or exceeds the firing temperature, the high and low temperature cycling performance of the obtained cathode material will decrease significantly. Therefore, it can be seen that in the cathode material provided by the present invention, the multi-level structure jointly suppresses the side reaction activity at the interface and significantly improves its cycling performance.

[0242] Comparing the results of Example 1 and Comparative Examples 1-4, it can be seen that if the coating layer or M3 is not included, the rate performance of the obtained cathode material is slightly improved. However, if the core-shell structure is not included or the firing temperature is too high, the rate performance decreases. This shows that in the matrix material, the high porosity of the outer shell is conducive to electrolyte wetting, so the core-shell structure can improve the rate to a certain extent. On the other hand, the coating layer or the M3 melt depth in the interparticle gap will hinder electrolyte wetting to a certain extent, and thus reduce the rate performance to a certain extent.

[0243] Comparing the results of Example 1 and Comparative Examples 5-6, it can be seen that if the amount of cathode material added, especially the amount of M1, M2 and M3 added, is not within the range required by the present invention, the overall performance of the obtained cathode material will decrease slightly.

[0244] In summary, within the scope provided by this invention, a cathode material with excellent high and low temperature cycling performance and rate performance, and a relatively small DCR growth rate, can be obtained, and further, a lithium-ion battery with excellent cycling and rate performance can be obtained. Due to the above advantages, the cathode material or lithium-ion battery prepared by this invention is expected to find wide application in the fields of power batteries, energy storage technology, and 3C small household appliances.

[0245] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A cathode material having a hierarchical structure, characterized in that, The positive electrode material comprises a base material and a first coating layer covering the base material; The base material has a secondary spherical structure and a core-shell structure; wherein the base material is doped with element M2, and the interstitial space of primary particles is infiltrated with element M3; Li[(Ni x M 1-x ) 1-a-b M2 a M3 b O2; the outer shell of the base material has a chemical formula of Li[(Ni x M 1-x ) 1-y M1 y ] 1-a-b M2 a M3 b O2. The first coating layer comprises a fast ion conductor material; M comprises at least one of Co, Mn and Al; M1 comprises at least one of Zr, Nb, W, Sr, B, Y, Te and Sn; M2 comprises at least one of Zr, Sr, Al, Mg, Ca and Ba; M3 comprises at least one of Nb, Ti, Y, Sb, Mo, W, Te, Ta and In; 0.88≤x≤0.98; 0.35≤y≤0.60; 0.0025≤a≤0.015; 0.0025≤b≤0.

015.

2. The positive electrode material of claim 1, wherein, The fast ion conductor material of the first coating layer is a Li-M4-O type fast ion conductor material; wherein M4 comprises at least one of Co, Al, Ti, W, Ce, Sr, Mg, Ba, Ca, B and Si.

3. The positive electrode material of claim 1, wherein, The positive electrode material further comprises a second coating layer covering the first coating layer; the second coating layer comprises a Li-B-O type material and at least one of a Li-M5-O type material and a M5-O type material; M5 comprises at least one of Al, Ti, Mg, Ce, Zr, Sn, Sb, W and Si.

4. The positive electrode material according to any one of claims 1 to 3, characterized in that, The ratio of the thickness l of the shell of the base material to the radius d of the inner core of the base material satisfies 1 / 90≤l / d≤1 / 6.

5. A method for producing the positive electrode material according to any one of claims 1 to 4, characterized by, The preparation method comprises the following steps: S1. providing a precursor having a core-shell structure, the inner core of the precursor having a chemical formula of Ni x M 1-x (OH)2; the outer shell of the precursor having a chemical formula of (Ni x M 1-x ) 1-y M1 y (OH)2; S2. mixing the precursor, a lithium source, a M2 compound and a M3 compound, and then performing a first sintering; The highest temperature of the first sintering is 650-880℃; S3. coating the base material obtained in step S2 with a first coating layer containing a fast ion conductor material.

6. The production method according to claim 5, wherein The preparation method further comprises the following steps after step S3: S4. washing and drying the product obtained in step S3; S5. mixing the product obtained in step S4, boric acid and a M5 compound, and then performing a third sintering.

7. The production method according to claim 5 or 6, characterized by, In step S1, the porosity of the shell of the precursor is greater than the porosity of the inner core of the precursor; and / or, in step S2, the holding time at the highest temperature of the first sintering is 6-30h.

8. The production method according to claim 5 or 6, characterized by, In step S3, the coating method comprises mixing the base material and a M4 compound, and then performing a second sintering.

9. The production method according to claim 8, characterized by, The temperature of the second sintering is 400-700℃; and / or, the mass ratio of the base material to the M4 compound is 1:0.005-0.

050.

10. A lithium-ion battery, characterized by, The raw materials for preparing the lithium ion battery comprise the positive electrode material according to any one of claims 1-4, or the positive electrode material prepared by the preparation method according to any one of claims 5-9.

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