Positive electrode material, positive electrode, preparation method, method for suppressing cation leaching, and lithium-ion battery

Abstract

The present invention discloses a cathode material, a cathode, a preparation method, a method for inhibiting cation dissolution, and a lithium-ion battery. The cathode material includes a cathode active material and an additive, the additive includes a nano-TiO2 / carbon composite material, the nano-TiO2 / carbon composite material includes a carbon carrier and nano-TiO2 loaded on the carbon carrier, and the nano-TiO2 has mesopores. By adopting the nano-TiO2 / carbon composite material and adding a small amount of the composite material into the cathode, the present invention can significantly inhibit the dissolution of cations in the cathode and improve the cycle performance and safety performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and relates to a cathode material, a cathode, a preparation method, a method for inhibiting cation dissolution, and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries have advantages such as high energy density, long cycle life, no memory effect, good safety performance, and environmental friendliness. Currently, they are applied to 3C digital products, large-scale energy storage power stations, new energy vehicles, ships, etc. Especially in the field of new energy vehicles, major automobile companies have put forward the agenda of stopping the sale of fuel vehicles. As an important core component of new energy vehicles, while the driving range of the battery cell is continuously improved, higher requirements are also put forward for its life and safety performance.

[0003] As the most important component of the battery, the performance of the ternary cathode material directly affects the use of the entire battery. With the continuous increase of the number of cycles, elements such as Ni, Mn, and W in the cathode material will dissolve in the cathode in the form of cations and precipitate on the anode through the electrolyte. On the one hand, the deposition of cations leads to an increase in the interface impedance of the anode. On the other hand, the dissolution of cations leads to the destruction of the cathode coating layer, resulting in poor cycle and safety performance.

[0004] CN111200128A discloses a preparation method of a cathode material for inhibiting the dissolution of transition metal ions in a lithium-ion battery cathode material with high performance, which specifically includes steps such as preparing a porous conductive polyamic acid dispersion containing an imidazole structure by in-situ polymerization, preparing a lithium-ion cathode material coated with polyamic acid with a porous conductive structure, and preparing a lithium-ion cathode material coated with porous conductive polyimide containing an imidazole structure. The cathode material prepared by this method is composed of a porous conductive polyimide material containing an imidazole structure and a lithium-ion cathode material. The porous conductive polyimide material containing an imidazole structure not only has the advantages of good high / low temperature resistance, high tensile strength, small linear expansion coefficient, low thermal shrinkage rate, excellent chemical stability, and corrosion resistance of polyimide itself, but also has a large specific surface area, high porosity, good electrical conductivity, and the ability to easily complex free transition metal ions, so as to effectively improve the cycle stability and high-temperature energy storage performance of lithium-ion batteries. However, polyamic acid itself has high insulation performance, with a dielectric constant of 4.0 at 10 3 Hz and a dielectric loss of only 0.004 - 0.007, belonging to class F to H insulation. Even if the material coated on the surface of the cathode material has a porous structure, overall, it will increase the interface impedance between the active material and the electrolyte, reduce the reaction kinetics of the cathode. Nowadays, the new energy industry is accelerating the replacement of the traditional fuel industry, putting forward higher requirements for the battery. Super fast charging and high safety performance have become important indicators of the battery. However, the increase in impedance will undoubtedly inhibit high-power fast charging and increase battery heat generation.

[0005] CN110148784A discloses an electrolyte and a lithium-ion battery using the electrolyte. By adding a positive electrode film-forming additive to the electrolyte, the oxidation and decomposition of the electrolyte on the surface of the positive electrode are inhibited, and the dissolution of metal ions in the positive electrode active material is inhibited. Although adding a positive electrode film-forming additive to the electrolyte has a certain effect on inhibiting the dissolution of metal ions in the positive electrode active material, the effect is limited. Moreover, as the cycle life of the battery increases, the positive electrode film formation fails, and the inhibitory effect on the dissolution of metal ions in the positive electrode active material is further weakened. Summary of the Invention

[0006] In view of the above problems existing in the prior art, the object of the present invention is to provide a positive electrode material, a positive electrode, a preparation method, a method for inhibiting cation dissolution, and a lithium-ion battery. By using a nano-TiO2 / carbon composite material and adding a small amount of the composite material to the positive electrode, the dissolution of cations in the positive electrode can be significantly inhibited, and the cycle performance and safety performance of the battery can be improved. The nano-TiO2 / carbon composite material uses a carbon carrier (such as a carbon nanotube) as a skeleton, which not only plays a supporting role but also constitutes a conductive network to reduce impedance. Nano-TiO2 grows uniformly on the carbon carrier. As a polar material, TiO2 has a chemical adsorption effect on the cations dissolved from the positive electrode. The TiO2 nanoparticles have a mesoporous structure, which not only has a physical confinement effect on the cations dissolved from the positive electrode but also has a very high specific surface area, can store more electrolytes, and can make the positive electrode plate have better wettability.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a positive electrode material, the positive electrode material includes a positive electrode active material and an additive, the additive includes a nano-TiO2 / carbon composite material, the nano-TiO2 / carbon composite material includes a carbon carrier and nano-TiO2 loaded on the carbon carrier, and the nano-TiO2 has mesopores.

[0009] In the present invention, the positive electrode active material and the additive may form a mixture or a composite.

[0010] In the prior art, in order to inhibit the dissolution of cations in the positive electrode, each manufacturer increases the sintering temperature and the coating temperature to improve the crystallinity of the material and the depth of the coating layer (or the bonding strength with the substrate). However, simply changing the temperature will sacrifice the capacity, DCR, cycle gas generation and other performance of the material. Each manufacturer will comprehensively consider the comprehensive indicators of each performance to determine the optimal sintering and coating temperature. However, the dissolution of cations in the positive electrode is not really inhibited, and they will still precipitate on the negative electrode.

[0011] The present invention provides a novel cathode material. By adding a nano-TiO2 / carbon composite material thereto, the dissolution of cations in the cathode of a lithium-ion battery can be inhibited, preventing deposition on the anode, thereby improving the cycling performance of the material. At the same time, due to the addition of titanium dioxide nanoparticles, the thermal stability of the battery can be improved. The carbon carrier not only serves as the growth framework of nano-TiO2 but also has high electrical conductivity, which can accelerate electron transfer and enhance the performance of the battery.

[0012] Among them, nano-TiO2 grows uniformly on the carbon carrier. As a polar material, TiO2 has a chemical adsorption effect on the cations dissolved from the cathode. The TiO2 nanoparticles have a mesoporous structure, which not only has a physical confinement effect on the cations dissolved from the cathode but also has an extremely high specific surface area, storing more electrolyte, and enabling better wettability of the cathode electrode sheet.

[0013] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0014] Preferably, the nano-TiO2 is TiO2 nanospheres, the major axis radius of the TiO2 nanospheres is R T1 , and the minor axis radius is R T2 . The distance between two adjacent TiO2 nanospheres loaded on the carbon carrier is L C , 1.5 ≤ R T1 / R T2 ≤ 8.2, 0.25 ≤ R T1 / (R T1 +L C ) ≤ 1. Exemplarily, R T1 / R T2 can be 1.5, 1.7, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0 or 8.2, etc.; R T1 / (R T1 +L C ) can be 0.25, 0.3, 0.35, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc.

[0015] Optionally, the weight of the nano-TiO2 / carbon composite material is W TC , and the weight of the TiO2 nanospheres is W T , 0.50 ≤ W T / W TC≤0.95, for example, it can be 0.50, 0.52, 0.55, 0.57, 0.57, 0.62, 0.67, 0.68, 0.72, 0.75, 0.80, 0.83, 0.85, 0.86, 0.88, 0.90, 0.93 or 0.95, etc.

[0016] Preferably, the true density of the nano-TiO₂ / carbon composite is ρ T , the compacted volume of TiO₂ is V T , satisfying: 1.9 ≤ (ρ T ·V T ) / 2 ≤ 3.5. Exemplarily, (ρ T ·V T ) / 2 can be 1.9, 2.0, 2.1, 2.2, 2.3, 2.5, 2.7, 3.0, 3.3 or 3.5, etc.

[0017] The present invention does not specifically limit the test conditions for the true density and the compacted volume. For example, the test conditions for the true density can be: the true density after heating in a pure oxygen atmosphere at 500 °C for 2 h. The test conditions for the compacted volume can be: testing the compacted volume of 2 g of TiO₂ material under a pressure of 2 T.

[0018] Preferably, the nano-TiO₂ grows on the carbon carrier.

[0019] Preferably, the major axis radius of the nano-TiO₂ is 120 - 250 nm, such as 120 nm, 135 nm, 150 nm, 155 nm, 170 nm, 180 nm, 200 nm, 215 nm, 230 nm, 240 nm or 250 nm, etc.; the minor axis radius is 60 - 90 nm, such as 60 nm, 65 nm, 70 nm, 80 nm or 90 nm, etc.

[0020] When the TiO₂ nanospheres satisfy the above size and content relationship, the cation dissolution in the positive electrode can be more effectively inhibited, and the cycle performance and safety performance of the battery can be improved.

[0021] As a preferred technical solution of the positive electrode material of the present invention, the carbon carrier in the nano-TiO₂ / carbon composite is a carbon nanotube, the nano-TiO₂ / carbon composite is a TiO₂ / carbon nanotube composite, and the TiO₂ / carbon nanotube composite is prepared by the following method, and the method includes the following steps:

[0022] After dispersing the carbon nanotubes in an acid solution, a titanium source is added, and heating reaction is carried out to obtain the TiO₂ / carbon nanotube composite.

[0023] In one embodiment, the acid solution is sulfuric acid.

[0024] Preferably, the concentration of the acid solution is 0.01 - 10 mol / L, such as 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.7 mol / L, 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, 6.5 mol / L, 7 mol / L, 7.5 mol / L, 8 mol / L, 8.5 mol / L, 9 mol / L or 10 mol / L, etc., and preferably 0.05 - 1 mol / L.

[0025] The present invention does not specifically limit the dispersion method, which can be ultrasonic dispersion, stirring dispersion or a combination of ultrasonic and stirring.

[0026] Preferably, the dispersion is first ultrasonic dispersion, and then stirred until evenly dispersed, so that the titanium source is dissolved in the acid solution to obtain a homogeneous solution.

[0027] Preferably, the titanium source includes at least one of titanium sulfate, titanium oxide, titanium chloride and titanium carbonate.

[0028] In one embodiment, after the heating reaction, the reaction product is filtered and washed.

[0029] Preferably, the temperature of the heating reaction is 50 - 300 °C, such as 50 °C, 60 °C, 70 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 115 °C, 120 °C, 135 °C, 150 °C, 160 °C, 180 °C, 190 °C, 200 °C, 215 °C, 230 °C, 245 °C, 260 °C, 280 °C or 300 °C, etc., and preferably 90 - 150 °C.

[0030] Preferably, the heat preservation time of the heating reaction is 30 - 300 min, such as 30 min, 45 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 145 min, 150 min, 160 min, 170 min, 180 min, 190 min, 200 min, 215 min, 230 min, 240 min, 255 min, 270 min, 280 min or 300 min, etc., and preferably 120 - 200 min.

[0031] The present invention does not specifically limit the type of the positive electrode active material, including but not limited to ternary materials. It can be a doped and / or coated positive electrode active material, or an undoped and uncoated positive electrode active material.

[0032] Preferably, the main element chemical formula of the positive electrode active material is Li n Ni x Co y Mn 1-x-y O2, and the doping or coating elements include one or more of elements such as B, Mg, Al, Ca, Ti, Cr, Zr, Nb, Mo, W, Sr, Y, etc., where 0.90 ≤ n ≤ 1.10, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1. Exemplarily, n can be 0.90, 0.92, 0.95, 0.98, 1.05 or 1.10, etc.; x can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc.; y can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc.

[0033] In a second aspect, the present invention provides a positive electrode, and the preparation raw materials of the positive electrode include the positive electrode material described in the first aspect.

[0034] Preferably, the preparation raw materials of the positive electrode further include a conductive agent and / or a binder.

[0035] In a third aspect, the present invention provides a method for preparing a positive electrode as described in the second aspect, and the method includes the following steps:

[0036] Homogenize using the preparation raw materials of the positive electrode to obtain a positive electrode slurry, and coat and roll the obtained positive electrode slurry to obtain the positive electrode;

[0037] Among them, the preparation raw materials of the positive electrode include the positive electrode material described in the first aspect.

[0038] In one embodiment, after rolling, cut into pieces to obtain a positive electrode sheet.

[0039] As a preferred technical solution of the preparation method of the positive electrode described in the present invention, the positive electrode active material and the nano-TiO₂ / carbon composite material in the positive electrode material are added separately during the preparation of the positive electrode slurry, or,

[0040] after the positive electrode active material and the nano-TiO₂ / carbon composite material are mixed, they are added in the form of a mixture during the preparation of the positive electrode slurry, or,

[0041] after the positive electrode active material and the nano-TiO₂ / carbon composite material are compounded, they are added in the form of a complex during the preparation of the positive electrode slurry.

[0042] Preferably, the mass of the nano-TiO₂ / carbon composite material accounts for 0.1-10% of the solid content of the entire positive electrode slurry, such as 0.1, 0.3, 0.5, 1, 1.5, 2, 2.5, 3, 4, 4.5, 5, 5.5, 6, 7, 8, 8.5, 9 or 10, etc., preferably 0.2-5%, and further preferably 0.5-2%.

[0043] Preferably, in the positive electrode slurry, based on the total mass of the positive electrode active material, nano-TiO₂ / carbon composite material, conductive agent, binder, and additive being 100%, the mass ratio of the positive electrode active material, nano-TiO₂ / carbon composite material, conductive agent, binder, and additive is (70-98%):(0.1-10%):(0.1-10%):(0.1-5%):(0-5%). Among them, the selection range of the positive electrode active material of 70-98% can be, for example, 70%, 72%, 75%, 78%, 80%, 85%, 88%, 92% or 96%, etc.; the selection range of the nano-TiO₂ / carbon composite material of 0.1-10% can be, for example, 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.; the selection range of the conductive agent of 0.1-10% can be, for example, 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.; the selection range of the binder of 0.1-5% can be, for example, 0.1%, 0.2%, 0.3%, 0.5%, 1%, 2%, 3%, 4% or 5%, etc.; the selection range of the additive of 0-5% can be, for example, 0%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or 5%, etc. Preferably, it is (90-98%):(0.2-5%):(0.1-2.5%):(0.1-2%):(0-5%).

[0044] Among them, the content of the additive being 0% means that this substance is not added in the battery system. Those skilled in the art can add or not add it depending on different battery systems.

[0045] In one embodiment, the method for preparing the positive electrode paste includes: mixing a positive electrode active material, a nano-TiO2 / carbon composite material, a conductive agent, a binder, and a solvent NMP to prepare a homogeneous and stable paste.

[0046] In one embodiment, the mixing of the positive electrode active material, the nano-TiO2 / carbon composite material, the conductive agent, the binder, and the solvent NMP is carried out as follows:

[0047] The positive electrode active material, the nano-TiO2 / carbon composite material, the conductive agent, and the binder are added to a homogenizing tank and mixed at a speed of 500 - 4000 rpm (such as 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1200 rpm, 1350 rpm, 1500 rpm, 1700 rpm, 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, 3000 rpm, 3250 rpm, 3500 rpm, 3800 rpm, or 4000 rpm, etc.) for 5 - 60 min (such as 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min, etc.). After mixing evenly, 30 - 90% (such as 30%, 40%, 50%, 60%, 70%, 80%, or 90%, etc.) of NMP is added for paste mixing, and it is mixed at a speed of 500 - 4000 rpm (such as 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1200 rpm, 1350 rpm, 1500 rpm, 1700 rpm, 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, 3000 rpm, 3250 rpm, 3500 rpm, 3800 rpm, or 4000 rpm, etc.) for 5 - 60 min (such as 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min, etc.). Then the remaining NMP is added, and it is mixed at a speed of 500 - 4000 rpm (such as 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1200 rpm, 1350 rpm, 1500 rpm, 1700 rpm, 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, 3000 rpm, 3250 rpm, 3500 rpm, 3800 rpm, or 4000 rpm, etc.) for 3 - 60 min (such as 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min, etc.) to finally obtain a paste with appropriate solid content and viscosity.

[0048] The present invention does not limit the preparation method of the positive electrode active material. Exemplarily and non - restrictively, the preparation method of the positive electrode active material includes the following steps:

[0049] Using a positive electrode precursor, a lithium source, and an additive containing a doping element as raw materials, mixing them evenly and performing a one - time sintering under a suitable sintering process to synthesize a one - time sintered material. After pulverization, it is mixed evenly with an additive containing a coating element and then subjected to a second - time sintering under a suitable sintering process. The obtained second - time sintered material is pulverized, sieved, and de - ironed to obtain a ternary positive electrode material.

[0050] In one embodiment, the chemical formula of the positive electrode precursor is Ni x Co y Mn 1-x-y (OH)2 (where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1).

[0051] In one embodiment, the lithium source is lithium hydroxide and / or lithium carbonate.

[0052] In one embodiment, the positive electrode precursor, the lithium source, the additive containing a doping element, and the additive containing a coating element are all of battery grade.

[0053] In one embodiment, the atmosphere for the one - time sintering and the second - time sintering is an oxygen - containing atmosphere, which can be, for example, oxygen, air, or an air - oxygen mixed gas.

[0054] In one embodiment, the cycle of the one - time sintering is 10 - 30 h, such as 10 h, 11 h, 12 h, 13 h, 15 h, 16 h, 18 h, 19 h, 20 h, 22 h, 23 h, 25 h, 27 h, or 30 h, etc.; the sintering temperature is 700 - 1100 °C, such as 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, or 1100 °C, etc.; the cycle of the second - time sintering is 10 - 25 h, such as 10 h, 11 h, 12 h, 13 h, 15 h, 16 h, 18 h, 19 h, 20 h, 22 h, 23 h, or 25 h, etc.; the sintering temperature is 200 - 800 °C, such as 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, 750 °C, or 800 °C, etc.

[0055] Fourthly, the present invention provides a method for suppressing cation dissolution, and the method uses the method of the third aspect to prepare the positive electrode.

[0056] Fifthly, the present invention provides a lithium - ion battery, and the lithium - ion battery includes the positive electrode described in the second aspect.

[0057] The present invention does not specifically limit the preparation method of the lithium-ion battery, and those skilled in the art can use the methods disclosed in the prior art to prepare the battery. Among them, the negative electrode can use a graphite negative electrode, the separator can use a conventional separator prepared by the methods of the prior art, and the electrolyte can be prepared with a known formulation in the prior art.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] The present invention provides a novel cathode material. By adding a nano-TiO2 / carbon composite material therein, it can inhibit the dissolution of cations in the cathode of the lithium-ion battery and prevent deposition on the negative electrode, thereby improving the cycling performance of the material. At the same time, due to the addition of titanium dioxide nanoparticles, the thermal stability of the battery can be improved. The carbon carrier not only serves as the growth skeleton of nano-TiO2 but also has high conductivity, which can accelerate electron transfer and enhance the performance of the battery. Specific Embodiments

[0060] The technical solutions of the present invention will be further described below through specific embodiments.

[0061] The "doping amount" and "coating amount" mentioned in the embodiments of the present invention are both based on the final finished cathode active material with doping and coating.

[0062] Example 1

[0063] This example provides a method for inhibiting the dissolution of cations in the cathode, including the following steps:

[0064] Step 1: Preparation of the cathode active material:

[0065] The cathode precursor, lithium source, and additive are all battery-grade. The cathode precursor is Ni 0.6 Co 0.1 Mn 0.3 (OH)2, the lithium source is lithium carbonate, the doping element for the first sintering is Al, the doping amount is 1000 ppm, in an air atmosphere, the sintering temperature is 950 °C, and the cycle is 20 h. After powder making, secondary sintering is carried out. The coating element for the secondary sintering is W, the coating amount is 1000 ppm, in an air atmosphere, the sintering temperature is 450 °C, and the cycle is 12 h. After dispersion, sieving, and iron removal, a ternary cathode active material is obtained.

[0066] Step 2: Preparation of the polar nano-TiO2 / CNT composite material:

[0067] Carbon nanotubes (CNT) were first dispersed by ultrasonic and then dispersed by stirring in a sulfuric acid solution (concentration of 0.1M), and titanium sulfate was added to dissolve the titanium source. The solution was heated to 110°C and kept warm for 180 minutes. Finally, the solution was filtered and washed to obtain a polar nano-TiO2 / CNT composite material. In the composite material, the long axis R of the nano-TiO2 particles T1 180nm, R T2 The short axis is 75nm, and the distance between two adjacent TiO2 nanospheres is L C 60~165nm, R T1 / R T2 =2.4,0.52≤R T1 / (R T1 +L C )≤0.75, TG test TiO2 particle mass accounts for the composite material W T / W TC =92%, the nano-TiO2 / carbon composite material was heated at 500℃ in pure oxygen atmosphere for 2h, and the true density of the nano-TiO2 / carbon composite material was tested to be ρ T , 2g of TiO2 particles are tested for compaction volume V under a pressure of 2T T , where (ρ T ·V T ) / 2=2.8.

[0068] Step 3: Preparation of positive electrode slurry:

[0069] The synthesized positive electrode active material, TiO2 / CNT composite material, conductive carbon black and binder were added to a homogenization tank in a mass ratio of 95%:1%:2%:2%, mixed at 800 rpm for 10 min, and after uniform mixing, 80% of NMP was added and mixed at 3000 rpm for 60 min, and the remaining NMP was added and mixed at 4000 rpm for 3 min to finally obtain a slurry with suitable solid content and viscosity.

[0070] The prepared positive electrode slurry is coated, rolled and cut into pieces to obtain positive electrode sheets.

[0071] Step 4: Preparation of the battery:

[0072] A soft-pack battery is assembled using natural graphite as the negative electrode (gram capacity 350 mAh / g), a separator (composed of a base film with a thickness of 9 μm, a ceramic film with a thickness of 3 μm, a first glue layer with a thickness of 1 μm and a second glue layer with a thickness of 1 μm stacked in sequence), the above-mentioned positive electrode sheet and an electrolyte (purchased from Xinzhoubang Electrolyte, model TM1R049).

[0073] Example 2

[0074] This embodiment provides a method for suppressing cation dissolution in the positive electrode, including the following steps:

[0075] Step 1: Preparation of the positive electrode active material:

[0076] The positive electrode precursor, lithium source, and additive are all of battery grade. The positive electrode precursor is Ni 0.6 Co 0.1 Mn 0.3 (OH)2, the lithium source is lithium carbonate, the doping element for the first sintering is Al, the doping amount is 1000 ppm, in an air atmosphere, the sintering temperature is 950 °C, the cycle is 20 h. After powder making, secondary sintering is carried out. The coating element for the secondary sintering is W, the coating amount is 1000 ppm, in an air atmosphere, the sintering temperature is 450 °C, the cycle is 12 h. After dispersion, sieving, and iron removal, the ternary positive electrode active material is obtained.

[0077] Step 2: Preparation of the polar nano-TiO2 / CNT composite material:

[0078] Carbon nanotubes (CNT) are first ultrasonically dispersed and then stirred and dispersed in a sulfuric acid solution (concentration of 0.5 M). Then, titanium sulfate is added. After dissolving the titanium source, the solution is heated to 110 °C and kept warm for 180 min. Finally, the solution is filtered and washed to obtain the polar nano-TiO2 / CNT composite material. In this composite material, the major axis R T1 of the nano-TiO2 particles is 200 nm, the minor axis R T2 is 90 nm, the distance between two adjacent TiO2 nanospheres is L C is 50 - 85 nm, R T1 / R T2 = 2.2, 0.71 ≤ R T1 / (R T1 + L C ) ≤ 0.80, the mass of the TiO2 particles in the TG test accounts for W T / W TC = 95%, the nano-TiO2 / carbon composite material is heated in a pure oxygen atmosphere at 500 °C for 2 h, and the true density of the nano-TiO2 / carbon composite material is tested as ρ T , the compaction volume V T of 2 g of TiO2 particles is tested under a pressure of 2 T, where (ρ T· V T ) / 2 = 3.4.

[0079] Step 3: Preparation of the positive electrode slurry:

[0080] The synthesized positive electrode active material, TiO2 / CNT composite material, conductive carbon black and binder were added to a homogenization tank in a mass ratio of 95%:1%:2%:2%, mixed at 800 rpm for 10 min, and after uniform mixing, 80% of NMP was added and mixed at 3000 rpm for 60 min, and the remaining NMP was added and mixed at 4000 rpm for 3 min to finally obtain a slurry with suitable solid content and viscosity.

[0081] The prepared positive electrode slurry is coated, rolled and cut into pieces to obtain positive electrode sheets.

[0082] Step 4: Preparation of the battery:

[0083] A soft-pack battery is assembled using natural graphite as the negative electrode (gram capacity 350 mAh / g), a separator (composed of a base film with a thickness of 9 μm, a ceramic film with a thickness of 3 μm, a first glue layer with a thickness of 1 μm and a second glue layer with a thickness of 1 μm stacked in sequence), the above-mentioned positive electrode sheet and an electrolyte (purchased from Xinzhoubang Electrolyte, model TM1R049).

[0084] Example 3

[0085] This embodiment provides a method for inhibiting the dissolution of cations in a positive electrode, comprising the following steps:

[0086] Step 1: Preparation of positive electrode active material:

[0087] The cathode precursor, lithium source and additives are all battery grade. The cathode precursor is Ni 0.6 Co 0.1 Mn 0.3 (OH)2, the lithium source is lithium carbonate, the primary sintering doping element is Al, the doping amount is 1000ppm, the sintering temperature is 950℃ under air atmosphere, the cycle is 20h, and the secondary sintering is carried out after powder making. The secondary sintering coating element is W, the coating amount is 1000ppm, the sintering temperature is 450℃ under air atmosphere, the cycle is 12h. After dispersion, screening and iron removal, the ternary positive electrode active material is obtained.

[0088] Step 2: Preparation of polar nano-TiO2 / CNT composite materials:

[0089] Carbon nanotubes (CNT) were first dispersed by ultrasonic and then dispersed by stirring in a sulfuric acid solution (concentration of 0.1M), and titanium sulfate was added to dissolve the titanium source. The solution was heated to 90°C and kept warm for 200 minutes. Finally, the solution was filtered and washed to obtain a polar nano-TiO2 / CNT composite material. In the composite material, the long axis R of the nano-TiO2 particles was T1 150nm, R T2 The short axis is 80nm, and the distance between two adjacent TiO2 nanospheres is L C80~190nm, R T1 / R T2 =1.875,0.44≤R T1 / (R T1 +L C )≤0.65, the mass of TiO2 particles in the TG test accounts for 90% of the composite material, the nano-TiO2 / carbon composite material is heated at 500℃ in pure oxygen atmosphere for 2h, and the true density of the nano-TiO2 / carbon composite material is ρ T , 2g of TiO2 particles are tested for compaction volume V under a pressure of 2T T , where (ρ T ·V T ) / 2=2.1.

[0090] Step 3: Preparation of positive electrode slurry:

[0091] The synthesized positive electrode active material, TiO2 / CNT composite material, conductive carbon black and binder were added to a homogenization tank in a mass ratio of 95%:2%:1.5%:1.5%, mixed at a speed of 1000 rpm for 5 minutes, and after mixing evenly, 70% of NMP was added and mixed at a speed of 2000 rpm for 45 minutes, and then the remaining NMP was added and mixed at a speed of 2000 rpm for 5 minutes to finally obtain a slurry with suitable solid content and viscosity.

[0092] The prepared positive electrode slurry is coated, rolled and cut into pieces to obtain positive electrode sheets.

[0093] Step 4: Preparation of the battery:

[0094] A soft-pack battery is assembled using natural graphite as the negative electrode (gram capacity 350 mAh / g), a separator (composed of a base film with a thickness of 9 μm, a ceramic film with a thickness of 3 μm, a first glue layer with a thickness of 1 μm and a second glue layer with a thickness of 1 μm stacked in sequence), the above-mentioned positive electrode sheet and an electrolyte (purchased from Xinzhoubang Electrolyte, model TM1R049).

[0095] Example 4

[0096] The difference from Example 1 is that the carbon nanotubes are replaced by graphene.

[0097] Example 5

[0098] The difference from Example 1 is that the mass ratio of the synthesized positive electrode active material, the TiO2 / CNT composite material, the conductive carbon black and the binder is 95%:0.2%:3.0%:1.8%.

[0099] Example 6

[0100] The difference from Example 1 is that the mass ratio of the synthesized cathode active material, TiO2 / CNT composite material, conductive carbon black, and binder is 95%:3%:0.5%:1.5%.

[0101] Example 7

[0102] The difference from the Example is that in Example 1, carbon nanotubes were not added in Step 2, and the TiO2 nanoparticles obtained by heating the washed material in an oxygen atmosphere at 500 °C for 2 h were added to the preparation of the cathode slurry together with CNT respectively. Other steps of battery preparation are the same as those in Example 1.

[0103] Comparative Example 1

[0104] The difference from Example 1 is that Step 2 was not carried out, and the TiO2 / CNT composite material was not added in the preparation of the cathode slurry. The mass ratio of the synthesized cathode active material, conductive carbon black, and binder is the same as that in Example 1.

[0105] Comparative Example 2

[0106] The difference from Example 2 is that Step 2 was not carried out, and the TiO2 / CNT composite material was not added in the preparation of the cathode slurry. The mass ratio of the synthesized cathode active material, conductive carbon black, and binder is the same as that in Example 1. Carbon nanotubes were added in the preparation of the cathode slurry, and the content is the same as that of the carbon nanotubes in the TiO2 / CNT composite material described in Example 1.

[0107] Comparative Example 3

[0108] The difference from Example 1 is that titanium sulfate in Step 2 was replaced with an equimolar amount of zirconium sulfate.

[0109] The electroperformance tests of Examples 1-7 and Comparative Examples 1-3 were carried out using a Blue-Energy test system. The batteries were charged and discharged at 25 °C in an incubator, the test voltage was 2.8-4.35 V, and the charge-discharge capacity was tested at a current density of 0.33C. The test results are shown in Table 1.

[0110] Table 1 Test Results of Soft-Pack Batteries

[0111]

[0112]

[0113] After the soft-pack test, compared with Comparative Examples 1 and 2, the discharge capacity and initial efficiency of Example 1 are comparable, but the cycle performance of Example 1 is significantly improved, while the precipitation of cations at the negative electrode is reduced, and the increase in DCR is significantly reduced. Compared with Comparative Example 3, Example 1 has better capacity, initial efficiency, and DCR growth performance.

[0114] When Example 1 is compared with Example 2 and Example 3, the discharge capacity and the initial efficiency are comparable, but the cycling performance of Example 1 is significantly improved. At the same time, the precipitation of cations on the negative electrode is reduced, and the increase in DCR is significantly decreased, which is due to the influence of the parameter change of the TiO2 / CNT composite material.

[0115] When Example 1 is compared with Example 4, the cycling DCR growth performance of Example 1 is better, because CNT can not only serve as the skeleton for the growth of TiO2, but also ensure that the TiO2 particles continuously improve the DCR growth during the cycling process.

[0116] When Example 1 is compared with Example 5 and Example 6, Example 1 has more advantages in terms of cycling retention rate and DCR growth, because in the cell preparation process, the addition amount of the TiO2 / CNT composite material will affect the performance of the cell.

[0117] When Example 1 is compared with Example 7, the performance becomes worse when only TiO2 nanoparticles and CNT are added in Example 7.

[0118] Table 2 ICP element test results of the negative electrode sheet after battery disassembly

[0119]

[0120] After disassembling the battery after 800 cycles of cycling, the metal dissolution of the negative electrode sheet was tested. The results showed that the examples could significantly inhibit the dissolution of cations in the positive electrode compared with the comparative examples, which was consistent with the electrical performance test results.

[0121] The applicant declares that the present invention uses the above-mentioned examples to illustrate the detailed method of the present invention, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A cathode material, characterized in that, The positive electrode material includes a positive electrode active material, a nano-TiO₂ / carbon composite material, a conductive agent, a binder, and an additive; Based on the total mass of the positive electrode active material, nano-TiO₂ / carbon composite material, conductive agent, binder, and additive being 100%, the mass ratio of the positive electrode active material, nano-TiO₂ / carbon composite material, conductive agent, binder, and additive is (70 - 98%):(0.1 - 10%):(0.1 - 10%):(0.1 - 5%):(0 - 5%); The nano-TiO₂ / carbon composite material includes a carbon carrier and nano-TiO₂ supported on the carbon carrier, and the nano-TiO₂ has mesopores; The major axis radius of the nano-TiO₂ is 120 - 250 nm, and the minor axis radius is 60 - 90 nm; The nano-TiO₂ is a TiO₂ nano-sphere, and the major axis radius of the TiO₂ nano-sphere is R T1 , and the minor axis radius is R T2 . The distance between two adjacent TiO₂ nano-spheres supported on the carbon carrier is L C , 1.5 ≤ R T1 / R T2 ≤ 8.2, 0.25 ≤ R T1 / (R T1 +L C ) ≤ 1; The weight of the nano-TiO₂ / carbon composite is W TC The weight of the TiO₂ nanospheres is W T 0.50 ≤ W T / W TC ≤ 0.95; The true density of the nano-TiO2 / carbon composite is ρ T , the compacted volume of TiO2 is V T , satisfying: 1.9 ≤ (ρ T ·V T ) / 2 ≤ 3.

5.

2. The cathode material according to claim 1, characterized in that, The nano-TiO₂ grows on the carbon carrier.

3. The cathode material according to claim 1, characterized in that, The carbon carrier in the nano-TiO₂ / carbon composite material is a carbon nanotube, the nano-TiO₂ / carbon composite material is a TiO₂ / carbon nanotube composite material, and the TiO₂ / carbon nanotube composite material is prepared by the following method, and the method includes the following steps: After dispersing the carbon nanotubes in an acid solution, a titanium source is added, and a heating reaction is carried out to obtain the TiO₂ / carbon nanotube composite material.

4. The cathode material according to claim 3, wherein, The concentration of the acid solution is 0.01 - 10 mol / L.

5. The cathode material according to claim 4, characterized in that, The concentration of the acid solution is 0.05 - 1 mol / L.

6. The cathode material according to claim 3, characterized in that, The dispersion is first ultrasonic dispersion and then stirred to be uniformly dispersed.

7. The cathode material according to claim 3, characterized in that, The titanium source includes at least one of titanium sulfate, titanium oxide, titanium chloride, and titanium carbonate.

8. The cathode material according to claim 3, wherein The temperature of the heating reaction is 50 - 300 °C.

9. The cathode material according to claim 8, characterized in that, The temperature of the heating reaction is 90 - 150 °C.

10. The cathode material according to claim 3, characterized in that, The heat preservation time of the heating reaction is 30 - 300 min.

11. The cathode material according to claim 10, characterized in that, The heat preservation time of the heating reaction is 120 - 200 min.

12. The cathode material according to claim 1, wherein The main element chemical formula of the positive electrode active material is Li n Ni x Co y Mn 1-x-y O2, and the doping or coating elements include one or more of B, Mg, Al, Ca, Ti, Cr, Zr, Nb, Mo, W, Sr or Y, where 0.90 ≤ n ≤ 1.10, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1.

13. A positive electrode, characterized in that, The preparation raw materials of the positive electrode include the positive electrode material according to any one of claims 1 - 12.

14. A method for preparing a positive electrode as described in claim 13, characterized in that, The method includes the following steps: Using the preparation raw materials of the positive electrode for homogenization to obtain a positive electrode slurry, and using the positive electrode slurry for coating and rolling to obtain the positive electrode; Among them, the preparation raw materials of the positive electrode include the positive electrode material according to any one of claims 1 - 12.

15. The method for preparing the positive electrode according to claim 14, characterized in that, The positive electrode active material and the nano-TiO₂ / carbon composite material in the positive electrode material are respectively added during the preparation of the positive electrode slurry; or, After the positive electrode active material and the nano-TiO₂ / carbon composite material are mixed, they are added in the form of a mixture during the preparation of the positive electrode slurry, or, After the positive electrode active material and the nano-TiO₂ / carbon composite material are compounded, they are added in the form of a composite during the preparation of the positive electrode slurry.

16. A method for preparing a positive electrode as described in claim 15, characterized in that, The mass of the nano-TiO₂ / carbon composite material accounts for 0.2 - 5% of the solid content of the entire positive electrode slurry.

17. A method for preparing a positive electrode as described in claim 16, characterized in that, The mass of the nano-TiO₂ / carbon composite material accounts for 0.5 - 2% of the solid content of the entire positive electrode slurry.

18. A method for preparing a positive electrode as described in claim 15, characterized in that, In the positive electrode paste, based on the total mass of the positive electrode active material, nano-TiO2 / carbon composite material, conductive agent, binder, and additive being 100%, the mass ratio of the positive electrode active material, nano-TiO2 / carbon composite material, conductive agent, binder, and additive is (90-98%):(0.2-5%):(0.1-2.5%):(0.1-2%):(0-5%).

19. A method for suppressing cation elution, characterized in that, The positive electrode is prepared by the method according to any one of claims 14-18.

20. A lithium-ion battery, characterized in that, The lithium ion battery includes the positive electrode according to claim 13.

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