A battery

Abstract

The present invention provides a battery. In the AC impedance EIS test of the battery, the charge transfer resistance Rct of the second semicircle in the intermediate frequency region satisfies: Rct < 15 mΩ; the ray slope k in the low frequency region satisfies: 1.03 < k < 57.29. The battery has a low charge transfer resistance and a low lithium ion diffusion impedance during charge and discharge. The battery has excellent lithium ion conductivity performance on the premise of having excellent cycle performance, and is a battery with both excellent cycle performance and improved capacity and rate performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries. Specifically, it relates to a battery, and more specifically, to a battery with excellent lithium-ion conductivity performance. Background Art

[0002] Improving the capacity and rate performance of batteries to meet the ever-expanding demand for batteries is one of the main research and development directions. Taking single crystal materials among the cathode materials for lithium-ion batteries on the current market as an example, they have characteristics such as good cycling performance, high tap density, and excellent high-voltage resistance performance, and are widely used in soft-pack lithium-ion batteries. However, they also have the disadvantages of relatively low specific capacity and poor rate performance. Developing batteries with both excellent cycling performance and improved capacity and rate performance will have more application prospects. Summary of the Invention

[0003] To improve the deficiencies of the prior art, the purpose of the present invention is to provide a battery that has both excellent cycling performance and improved capacity and rate performance. It has been found through research that when the battery has a low charge transfer resistance and lithium-ion diffusion resistance during the charge and discharge process, the battery not only has excellent cycling performance but also has excellent lithium-ion conductivity performance, thereby obtaining a battery with both excellent cycling performance and improved capacity and rate performance.

[0004] The purpose of the present invention is achieved through the following technical solutions:

[0005] A battery, in the AC impedance EIS test of the battery, the charge transfer resistance Rct of the second semicircle in the intermediate frequency region satisfies: Rct < 15 mΩ; the ray slope k in the low frequency region satisfies: 1.03 < k < 57.29.

[0006] According to an embodiment of the present invention, the frequency of the intermediate frequency region is 150 Hz to 500 Hz.

[0007] According to an embodiment of the present invention, the frequency of the low frequency region is 0.01 Hz to 150 Hz.

[0008] According to an embodiment of the present invention, the second semicircle in the intermediate frequency region refers to the second semicircle of the ray close to the low frequency region in the AC impedance EIS diagram.

[0009] According to an embodiment of the present invention, the ray slope in the low frequency region refers to the slope of an oblique line that appears in the low frequency region and intersects the horizontal axis.

[0010] According to an embodiment of the present invention, the charge transfer resistance Rct of the second semicircle in the intermediate frequency region satisfies: 1 mΩ ≤ Rct < 15 mΩ, preferably, 2 mΩ ≤ Rct ≤ 14 mΩ, such as Rct being approximately 2 mΩ, 3 mΩ, 4 mΩ, 5 mΩ, 6 mΩ, 7 mΩ, 7.1 mΩ, 7.2 mΩ, 7.3 mΩ, 7.4 mΩ, 7.5 mΩ, 7.6 mΩ, 7.7 mΩ, 7.8 mΩ, 7.9 mΩ, 8 mΩ, 8.1 mΩ, 8.2 mΩ, 8.3 mΩ, 8.4 mΩ, 8.5 mΩ, 8.6 mΩ, 8.7 mΩ, 8.8 mΩ, 8.9 mΩ, 9 mΩ, 9.1 mΩ, 9.2 mΩ, 9.3 mΩ, 9.4 mΩ, 9.5 mΩ, 9.6 mΩ, 9.7 mΩ, 9.8 mΩ, 9.9 mΩ, 10 mΩ, 11 mΩ, 12 mΩ, 13 mΩ or 14 mΩ.

[0011] According to an embodiment of the present invention, the ray slope k in the low frequency region satisfies: 1.05 ≤ k ≤ 56, preferably, 1.06 ≤ k ≤ 50, such as k being 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.2, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 5, 8, 10, 12, 15, 18, 20, 25, 30, 35, 40, 45 or 50.

[0012] According to an embodiment of the present invention, the conditions for the alternating current impedance EIS test are: highest frequency: 50 kHz to 5 kHz; starting frequency: consistent with the highest frequency value; lowest frequency: 0.01 Hz; scanning mode: scanning from high frequency to low frequency; test mode: POTENTIOSTAT mode, AMPLITUDE is 5 mV.

[0013] According to an embodiment of the present invention, an electrochemical impedance spectrum will be obtained in the alternating current impedance EIS test. This electrochemical impedance spectrum is obtained by applying a small amplitude alternating current excitation signal according to a sine law when the electrochemical cell is in an equilibrium state (open circuit state) or under a certain stable direct current polarization condition, and studying the variation relationship of the alternating current impedance of electrochemistry with frequency, which is called the frequency domain impedance analysis method. Since the alternating current impedance EIS records the impedance of the electrochemical cell at different response frequencies and generally measures over a wide frequency range (μHz level to MHz level), it can analyze different electrode processes with different reaction time constants.

[0014] According to an embodiment of the present invention, the ionic conductivity of the battery during charge and discharge is mainly measured by performing electrochemical impedance spectroscopy (EIS) on it. Among them, the charge transfer impedance Rct and the lithium ion diffusion impedance (which can also be called the concentration polarization impedance and the Warburg diffusion impedance) are respectively represented by the second semicircle in the intermediate frequency region and the ray in the low frequency region. Specifically, the smaller the area of the second semicircle in the intermediate frequency region, the smaller the charge transfer impedance of the battery; the larger the slope of the ray in the low frequency region, the smaller the lithium ion diffusion impedance of the battery. When, in the AC impedance EIS test of the battery, the charge transfer impedance Rct of the second semicircle in the intermediate frequency region satisfies: Rct < 15 mΩ, and the slope k of the ray in the low frequency region satisfies 1.03 < k < 57.29, it indicates that the battery of the present invention has excellent ionic conductivity; at the same time, it also shows that the positive electrode material of the battery has good ionic conductivity, and the resulting effect will be that the overall conductivity of the electrode is stronger.

[0015] According to an embodiment of the present invention, the battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material, and the positive electrode material includes a plurality of particles having a polycrystalline morphology. The particles having a polycrystalline morphology are formed by nesting a plurality of primary particles.

[0016] The positive electrode material satisfies the relational expression shown in Equation 1 below:

[0017] D 50 3 = K × n × d 50 3 Equation 1

[0018] Wherein, K is a coefficient, and its range is: 0.2 ≤ K ≤ 2; n is the number of primary particles, and its range is: 2 ≤ n ≤ 500; D 50 is the median particle size of the positive electrode material, with the unit of μm; d 50 is the median particle size of the primary particles, with the unit of μm.

[0019] According to an embodiment of the present invention, the battery includes a non-aqueous electrolyte, and the non-aqueous electrolyte includes an additive; the additive is selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfate (DTD), 1,3-propane sultone (1,3-PS), or 1,4-butane sultone (1,4-BS).

[0020] Advantages of the present invention:

[0021] The present invention provides a battery, which has a low charge transfer impedance and lithium ion diffusion impedance during charge and discharge, that is, excellent lithium ion conductivity performance, thereby improving the capacity and rate performance of the battery.

[0022] Research findings show that under the same conditions, the kinetic behavior of the battery is a key factor affecting the specific capacity and rate performance of the battery. During the charge and discharge process of the battery, there are transports of lithium ions and electrons inside the battery electrode. Among them, the lithium ions inside the particles are transported through the electrolyte filled in the pores of the electrode, while the electrons are mainly conducted through the solid particles, especially the three-dimensional network composed of conductive agents, to the active material particle / electrolyte interface to participate in the electrode reaction. In electrode materials, generally speaking, when the particle size of the primary particles of the active material decreases, it often improves the ionic conductivity of the electrode material, thereby enhancing the overall conductivity of the electrode and improving the capacity and rate performance of the battery. This is mainly because when the particle size of the primary particles of the active material decreases, the diffusion path of Li+ in the electrode material is shortened, which is beneficial to the transport of Li + to proceed.

[0023] The positive electrode material in the battery of the present invention has a polycrystalline single crystal morphology. The specific surface area of the positive electrode material with a polycrystalline single crystal morphology is 5%-40% larger than that of the dispersed single crystal morphology positive electrode material, enabling the positive electrode material with a polycrystalline single crystal morphology to be well infiltrated by the electrolyte, thereby improving the ionic conductivity of the battery electrode, that is, the added positive electrode material with a polycrystalline single crystal structure morphology can improve the ionic conductivity of the positive electrode sheet. During the charge and discharge process of the battery, lithium ions inside the battery electrode are transported through the electrolyte filled in the pores of the electrode. Compared with the active material in the positive electrode sheet, the contact area between the electrolyte and the active material particles and the degree of infiltration of the electrolyte will directly affect the migration rate of lithium ions, thereby weakening the ionic conductivity. In addition, the particle morphology of the active material will also have a profound impact on the migration rate of lithium ions. The polycrystalline single crystal positive electrode material used in the present invention has a significantly increased specific surface area compared with the more dispersed single crystal active positive electrode material, which can enable the electrolyte to fully infiltrate it. On the other hand, since the positive electrode material with a polycrystalline single crystal morphology is formed by nesting several primary particles, it is different from the secondary spherical ternary material formed by stacking countless tiny particles. The formation method of the polycrystalline single crystal will significantly reduce the number of primary particles compared with the secondary spherical ternary material, weakening the occurrence of stress from different directions between different particles and avoiding the phenomenon of large-area particle breakage caused by rolling, further stabilizing the morphological structure of the polycrystalline single crystal particles; while for the dispersed single crystal morphology, due to the relatively large primary particles, they are relatively dispersed from each other and have a relatively small specific surface area. On the one hand, the contact range with the electrolyte is relatively narrow compared with the polycrystalline single crystal, and it cannot be fully infiltrated by the electrolyte, so the migration rate of lithium ions will slow down and its ionic conductivity will also weaken; on the other hand, since the dispersed single crystal primary particles are relatively larger than the polycrystalline single crystal, it will lead to a longer migration path of lithium ions and its ionic conductivity will also become very poor. Correspondingly, the charge transfer impedance and lithium ion diffusion impedance in the electrochemical AC impedance test are also relatively large.

[0024] The battery electrode sheet containing a polycrystalline single-crystal active cathode material provided by the present invention is not easily broken during rolling, the electrolyte infiltration is sufficient, and the diffusion path in the electrode material during the charge and discharge process of the lithium-ion battery is short. As a result, the lithium-ion battery containing the polycrystalline single-crystal active cathode material has a low charge transfer resistance and lithium-ion diffusion resistance during the charge and discharge process, that is, the lithium-ion conductivity performance is excellent, thereby improving the capacity and rate performance of the battery. Description of the Drawings

[0025] Figure 1 SEM electron micrograph of the ternary material in Example 1 (polycrystalline single crystal).

[0026] Figure 2 SEM electron micrograph of the ternary material in Comparative Example 1 (single crystal).

[0027] Figure 3 AC battery impedance EIS spectra of Example 1 and Comparative Example 1. Detailed Description of the Invention

[0028] [Cathode Material]

[0029] As described above, the battery of the present invention includes a cathode material, and the cathode material includes a plurality of particles having a polycrystalline single-crystal morphology, and the particles having a polycrystalline single-crystal morphology are formed by nesting a plurality of primary particles; the cathode material satisfies the relational expression shown in Formula 1 below:

[0030] D 50 3 = K × n × d 50 3 Formula 1

[0031] Wherein, K is a coefficient, and its range is: 0.2 ≤ K ≤ 2; n is the number of primary particles, and its range is: 2 ≤ n ≤ 500; D 50 is the median particle size of the cathode material, with the unit of μm; d 50 is the median particle size of the primary particle, with the unit of μm.

[0032] In one embodiment, K is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2.0.

[0033] In one embodiment, n is 2, 5, 10, 20, 50, 80, 90, 100, 120, 130, 150, 180, 200, 220, 230, 240, 250, 260, 280, 300, 320, 340, 350, 380, 400, 420, 430, 450, 480, 490 or 500.

[0034] In one embodiment, the particles with a polycrystalline single-crystal morphology in the positive electrode material are formed by nesting a number of primary particles. The nesting in the present invention is not a core-shell structure. The core-shell structure has obvious core and shell structures, while the particles with a polycrystalline single-crystal morphology in the present invention are formed by nested aggregation of a number of primary particles, that is, a surrounding structure is formed by fusion connection and mutual nesting of one primary particle and multiple primary particles in the particles with a polycrystalline single-crystal morphology through internal driving forces. For example, refer to Figure 1 .

[0035] In one embodiment, the number of "a number of" means one or more than two.

[0036] In one embodiment, the particles with a polycrystalline single-crystal morphology are formed by nesting 2 - 500 (such as 5 - 100) primary particles.

[0037] In one embodiment, the surface of the particles with a polycrystalline single-crystal morphology is relatively smooth.

[0038] In one embodiment, the polycrystalline single-crystal morphology structure of the particles is different from the single-crystal structure in the prior art and also different from the secondary sphere structure. The secondary sphere structure generally exists in ternary materials and needs to be synthesized with a precursor of D 50 > 7μm. Moreover, the spherical particles formed by the secondary sphere particles known in the field of ternary materials are very regular. Secondary sphere particles, also called polycrystalline materials, have great differences between the primary particles of secondary sphere particles and single crystals, quasi-single crystals, and the polycrystalline single crystals of the present invention, and the growth modes are also different. The particles with a polycrystalline single-crystal morphology of the present invention are prepared using a precursor of ternary material with D 50 < 7μm (D 50 such as 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 6.5μm or a range composed of two of the above two-point values); the growth of its primary particles tends to grow in the direction of single crystallization. In order to prevent it from completely forming a single-crystallized dispersed structure, the present invention controls the calcination temperature, etc. to form a polycrystalline single-crystal morphology structure by selecting a precursor with a specific particle size and a doping modifier.

[0039] In one embodiment, the median particle size d of the primary particles 50is from 0.1 μm to 3 μm, such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm or 3 μm.

[0040] In one embodiment, the median particle size D of the positive electrode material 50 is from 0.2 μm to 20 μm, such as 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, 3.5 μm, 4 μm, 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 20 μm.

[0041] In one embodiment, the primary particles are ternary materials.

[0042] In one embodiment, the chemical formula of the ternary material is Li a Ni 1-x-y-p Co x M 1 y M 2 p O 2 , 0.95 ≤ a < 1.08, 0.5 ≤ 1 - x - y - p < 1.0, 0 < x ≤ 0.3, 0 < y ≤ 0.2, 0 < p ≤ 0.005; M 1 is Mn or Al, M 2 is one or more of Mg, Sr, Ba, Y, W, Nb, Mo. Preferably, 0.0005 ≤ p ≤ 0.005.

[0043] In one embodiment, the positive electrode material further includes a coating layer, and the coating layer coats the surfaces of a plurality of the particles having a polycrystalline single crystal morphology.

[0044] In one embodiment, the mass of the coating layer is 500 ppm - 5000 ppm, such as 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1500 ppm, 1800 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm or 5000 ppm; that is, the mass of the coating layer accounts for 0.05 - 0.5 wt% of the total mass of the cathode material, such as 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt% or 0.5 wt%.

[0045] In one embodiment, the material for forming the coating layer is a metal compound and / or a non-metal compound.

[0046] In one embodiment, the metal compound is selected from at least one of aluminum oxide, tungsten oxide, molybdenum oxide, zirconium oxide and titanium oxide.

[0047] In one embodiment, the non-metal compound is selected from boron oxide.

[0048] In one embodiment, the coating layer includes a first coating layer and a second coating layer. The first coating layer is coated on the surface of several of the particles having a polycrystalline single crystal morphology, and the second coating layer is coated on the outer surface of the first coating layer. The first coating layer is a metal compound, and the second coating layer is a metal compound and / or a non-metal compound.

[0049] [Preparation of Cathode Material]

[0050] The present invention also provides a method for preparing the above-mentioned cathode material, and the method comprises the following steps:

[0051] Step S1: Mix a ternary precursor with a particle size of <7μm, a lithium source and a doping modifier uniformly to obtain a precursor mixture; 50 <7μm of ternary precursor, lithium source and doping modifier are mixed evenly to obtain a precursor mixture;

[0052] Step S2: Subject the above-mentioned precursor mixture to a first calcination to prepare a polycrystalline single crystal ternary cathode material.

[0053] In one embodiment, the method further comprises the following steps:

[0054] Step S3: Add a first coating agent to the above-mentioned cathode material, mix at high speed, and then perform a constant temperature heat treatment in an oxygen-containing environment to obtain a single-layer coated polycrystalline single crystal ternary cathode material;

[0055] Step S4: The second coating agent is added to the single-layer coated polycrystalline ternary cathode material obtained in the above step S3, and after high-speed mixing, it is subjected to isothermal heat treatment in an oxygen-containing environment, pulverized and separated to obtain a double-layer coated polycrystalline ternary cathode material.

[0056] In one embodiment, in step S1, the ternary precursor is Ni 1-x-y Co x M 1 y (OH) 2 , where 0.5 ≤ 1 - x - y < 1.0, 0 < x ≤ 0.3, 0 < y ≤ 0.2.

[0057] In one embodiment, in step S1, the lithium source is selected from one or more of lithium hydroxide, lithium nitrate, lithium sulfate, lithium chloride, lithium carbonate, lithium phosphate, lithium fluoride, lithium acetate, lithium oxalate, or lithium hydrogen phosphate;

[0058] In one embodiment, in step S1, the doping elements of the doping modifier are preferably one or more of Mg, Sr, Ba, Y, W, Nb, Mo, and the addition amount of the doping elements is 0 - 5000 ppm (excluding 0 ppm).

[0059] In one embodiment, in step S1, the molar ratio of the lithium source to the ternary precursor is 1.01 - 1.15:1.

[0060] In one embodiment, in step S1, the mixing is, for example, dry ball milling, the ball milling medium is zirconia balls or steel balls, the speed is 200 - 800 r / min, and the time is 3 - 6 h.

[0061] In one embodiment, in step S2, the first roasting is to raise the temperature to 400 - 600 °C at a rate of 2 - 15 °C / min and hold for 1 - 6 h, then raise the temperature to 700 - 800 °C at a rate of 2 - 15 °C / min and hold for 2 - 12 h, and finally raise the temperature to 800 - 920 °C at a rate of 2 - 15 °C / min and hold for 2 - 16 h, and then cool naturally.

[0062] In one embodiment, in step S2, the material after the first roasting is pulverized and separated to obtain a polycrystalline ternary cathode material.

[0063] In one embodiment, in step S3, the first coating agent is a metal compound. The metal compound is at least one of nanoscale oxides, hydroxides, or salts containing Al, Ti, Zr, Mo, W, preferably nanoscale oxides or hydroxides of Al, Ti, W. Among them, the mass of the first coating agent accounts for 0.05 - 0.50 wt% of the mass of the polycrystalline ternary cathode material.

[0064] In one embodiment, in step S3, the isothermal heat treatment is to raise the temperature to 200 - 900°C at a rate of 2 - 15°C / min and hold for 3 - 16 h.

[0065] In one embodiment, in step S4, the second coating agent is at least one of a metal compound and / or a non-metal compound. Among them, the metal compound is at least one of nano-scale oxides, hydroxides or salts containing Al, Ti, Zr, Mo, W, preferably nano-scale oxides or hydroxides of Al, Ti, W. The non-metal compound is selected from boron oxide. Among them, the mass of the second coating agent accounts for 0.05 - 0.50 wt% of the mass of the polycrystalline ternary cathode material.

[0066] In one embodiment, in step S4, the isothermal heat treatment is to raise the temperature to 200 - 900°C at a rate of 2 - 15°C / min and hold for 2 - 16 h.

[0067] [Positive electrode sheet]

[0068] The battery of the present invention further includes a positive electrode sheet, and the positive electrode sheet includes the above-mentioned positive electrode material.

[0069] In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes the above-mentioned positive electrode material.

[0070] [Battery]

[0071] As described above, the present invention also provides a battery. In the AC impedance EIS test of the battery, the charge transfer resistance Rct of the second semi-circle in the middle frequency region satisfies: Rct < 15 mΩ; the ray slope k in the low frequency region satisfies: 1.03 < k < 57.29.

[0072] In one embodiment, the battery satisfies the above various limitations.

[0073] In one embodiment, the battery includes the above-mentioned positive electrode material or the above-mentioned positive electrode sheet.

[0074] [Preparation of battery]

[0075] The present invention provides a preparation method of the above battery, which includes the following steps:

[0076] Step S1: Weigh 100 g of the above-mentioned polycrystalline single-crystalline cathode material, conductive agent Super P, and binder PVDF in sequence according to a weight ratio of 96:2:2, mix them in 40 g of NMP, obtain a uniform slurry through vacuum stirring, then uniformly coat the slurry on an aluminum foil current collector, and after rolling baking in a 10 m oven at 100 °C (rolling speed 2 m / min), vacuum baking at 85 °C for 20 h, cold pressing, and slitting, obtain a positive electrode sheet;

[0077] Step S2: Weigh 100 g of artificial graphite: conductive agent Super P: CMC: SBR in sequence according to a weight ratio of 95:2:1.5:1.5, mix them in 40 g of deionized water, obtain a uniform slurry through vacuum stirring, then uniformly coat the slurry on a copper foil current collector, and after rolling baking in a 10 m oven at 100 °C (rolling speed 2 m / min), vacuum baking at 85 °C for 20 h, cold pressing, and slitting, obtain a negative electrode sheet;

[0078] Step S3: Stack the positive electrode sheet, negative electrode sheet, and separator into a lithium-ion battery cell; place the lithium-ion battery cell into a soft-pack battery package and inject an electrolyte containing 1 mol / L lithium hexafluorophosphate (LiPF 6 ) in a volume ratio of ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) = 1:1:1, and containing 2 wt% vinylene carbonate (VC) and 3 wt% 1,3-propane sultone (1,3-PS);

[0079] Step S4: After steps such as hot pressing, formation, cold pressing, aging, secondary sealing, and sorting, prepare a lithium-ion battery using the polycrystalline single-crystalline ternary cathode as the positive electrode active material.

[0080] The present invention provides another preparation method for the above battery, which includes the following steps:

[0081] Step S1: Weigh the above-mentioned polycrystalline single-crystalline cathode material, conductive agent Super P, and binder PVDF in sequence according to a weight ratio of 96:2:2, mix them in NMP, obtain a uniform slurry through vacuum stirring, then uniformly coat the slurry on an aluminum foil current collector, and after baking in an oven at 100 °C for 12 h and slitting, obtain a small positive electrode disc containing the cathode material;

[0082] Step S2: Fabricate a button cell: The positive electrode sheet is obtained from the above S1, the negative electrode is a lithium sheet, the separator is a conventional separator, and the electrolyte is a solution containing 1 mol / L lithium hexafluorophosphate (LiPF 6An electrolyte solution containing ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) = 1:1:1 (by volume), 2 wt% vinylene carbonate (VC) and 3 wt% 1,3 - propane sultone (1,3 - PS); a button cell of model 2016 was fabricated by stamping.

[0083] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only for illustrative and explanatory purposes of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0084] Unless otherwise specified, the experimental methods used in the following embodiments are all conventional methods; unless otherwise specified, the reagents, materials, etc. used in the following embodiments can all be obtained from commercial sources.

[0085] The test of the initial DC internal resistance in the following embodiments: 1. Let it stand for 10 minutes; 2. Discharge at 0.2C to the cut - off voltage of 2.75V; 3. Let it stand for 10 minutes; Place it at the corresponding test temperature and leave it for a period of time until it reaches a stable state (the standing time shall not be less than 2h), discharge with a certain pulse current for a certain time, and calculate the DCIR therefrom.

[0086] Example 1

[0087] (1) According to Li 2 CO 3 and D 50 Ni with a particle size of 3 - 7 μm (excluding 7 μm) 0.65 Co 0.15 Mn 0.25 (OH) 2 High - speed mixing was carried out at a molar ratio of Li / (Ni + Co + Mn) of 1.05:1 under the condition of 400 r / min, and then a certain amount of nano - MoO 3 and WO 3 were added, and high - speed mixing was continued at a rotation speed of 400 r / min. The addition amount of Mo 2 O 3 was 0.2% of the molar ratio of Ni 0.65 Co 0.15 Mn 0.25 (OH) 2 , and the addition amount of WO 3 was 0.2% of the molar ratio of Ni 0.65 Co 0.15 Mn 0.25 (OH) 2The molar ratio is 0.3%; the mixture is loaded into a sagger and sintered for the first time in a box furnace, with oxygen introduced as the sintering atmosphere. The synthesis mainly has three constant-temperature sections, and the heating rate between each section is 2 °C / min: the low-temperature section is kept at 400 °C for 1 h; the medium-temperature section is kept at 700 °C for 2 h; the high-temperature section is kept at 900 °C for 12 h; then, after the box furnace is naturally cooled, the material is taken out, pulverized by air flow and sieved through a 300-mesh sieve to obtain the multi-polycrystalline ternary material;

[0088] In the multi-polycrystalline ternary material, the number of primary particles n is 5 - 100, and the median particle size D 50 of the cathode material is 4.08 μm; the median particle size d 50 of the primary particles is 0.2 - 1.5 μm;

[0089] It satisfies the relational expression shown in Equation 1 below:

[0090] D 50 3 = K × n × d 50 3 Equation 1

[0091] where K is 0.3 - 2.

[0092] The above-obtained multi-polycrystalline ternary material is mixed evenly with nano-scale Al 2 O 3 , where the mass ratio of Al 2 O 3 to the multi-polycrystalline ternary material is designed as 1000 ppm, and then the second sintering is carried out. It is heated to 600 °C at a rate of 2 °C / min in an oxygen atmosphere and kept for 10 h. After cooling, a multi-polycrystalline ternary material with a single-layer coating is obtained. The above-obtained multi-polycrystalline ternary material with a single-layer coating is mixed evenly with nano-scale WO 3 , where the mass ratio of WO 3 to the multi-polycrystalline ternary material with a single-layer coating is designed as 2000 ppm, and the third sintering is carried out. It is heated to 500 °C at a rate of 2 °C / min in an oxygen atmosphere and kept for 10 h. After cooling, a multi-polycrystalline ternary material with a double-layer coating is obtained. Its scanning electron microscope image is as shown in Figure 1 shown.

[0093] (2) Weigh the above multi-polycrystalline cathode material, conductive agent Super P, and binder PVDF in a weight ratio of 96:2:2 in sequence, mix them in NMP, and obtain a uniform slurry through vacuum stirring. Then, the slurry is evenly coated on an aluminum foil current collector and baked in an oven at 100 °C for 12 h and then slit to obtain a small circular cathode sheet containing the cathode material;

[0094] Making button cells: Place the positive electrode case, positive electrode wafer, separator, negative lithium sheet, gasket, shrapnel, and negative electrode case in sequence, and add electrolyte (ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) = 1:1:1 (volume ratio) containing 1 mol / L lithium hexafluorophosphate (LiPF 6 ) and an electrolyte containing 2 wt% vinylene carbonate (VC) and 3 wt% 1,3 - propane sultone (1,3 - PS)), and then make 2016 - type button cells after stamping.

[0095] Electrical performance test: All tests are carried out in the voltage range of 4.4V - 3V; The test conditions for specific capacity: charge at 0.1C and discharge at 0.1C; The test conditions for rate performance: Step 1: charge at 0.5C / discharge at 0.1C, Step 2: charge at 0.5C / discharge at 0.2C, Step 3: charge at 0.5C / discharge at 0.5C, Step 4: charge at 0.5C / discharge at 1C; EIS test: 1. Stand still for 30 min; 2. Discharge at 0.5C to the lower limit voltage; 3. Stand still for 30 min; 4. Charge at 1C constant current to the upper limit voltage; 5. Stand still for 2 h, test the voltage and internal resistance at full charge state at 25℃ ± 5℃; 6. Then conduct AC impedance EIS test, with the following parameters: highest frequency: 50 kHz - 5 kHz, starting frequency: consistent with the highest frequency value; lowest frequency: about 0.01 Hz; scanning mode: scan from high frequency to low frequency; test mode: POTENTIOSTAT mode, AMPLITUDE is 5 mV.

[0096] (3) Weigh 100 g of the above - mentioned polycrystalline single - crystal cathode material, conductive agent Super P, and binder PVDF in a weight ratio of 96:2:2 in sequence, mix them in 40 g of NMP, obtain a uniform slurry through vacuum stirring, then evenly coat the slurry on the aluminum foil current collector, and after rolling baking in a 10 m oven at 100℃ (rolling belt speed 2 m / min), vacuum baking at 85℃ for 20 h, cold pressing, and slitting, obtain a positive electrode sheet with a double - layer coating containing polycrystalline single - crystal ternary cathode material; Weigh 100 g of artificial graphite: conductive agent Super P: CMC: SBR in a weight ratio of 95:2:1.5:1.5 in sequence, mix them in 40 g of deionized water, obtain a uniform slurry through vacuum stirring, then evenly coat the slurry on the copper foil current collector, and after rolling baking in a 10 m oven at 100℃ (rolling belt speed 2 m / min), vacuum baking at 85℃ for 20 h, cold pressing, and slitting, obtain a negative electrode sheet;

[0097] Making lithium - ion batteries: Stack the positive electrode sheet, negative electrode sheet, and separator into a lithium - ion battery cell; Place the lithium - ion battery cell into a soft - pack battery package and inject an electrolyte containing 1 mol / L lithium hexafluorophosphate (LiPF 6Ethylene carbonate (EC): Ethyl methyl carbonate (EMC): Diethyl carbonate (DEC) = 1:1:1 (by volume), an electrolyte containing 2 wt% vinylene carbonate (VC) and 3 wt% 1,3 - propane sultone (1,3 - PS); After steps such as hot pressing, forming, cold pressing, aging, secondary sealing, and sorting, a lithium - ion battery is prepared using a multi - crystal ternary cathode material with double - layer coating as the cathode active material.

[0098] Electrical performance test: After the lithium - ion battery is left standing at 25 °C in a normal - temperature environment for 24 h, it is charged to 4.3 V at a current rate of 0.1C of the sorted capacity, and after standing for 10 min, it is discharged at a current rate of 0.1C of the designed capacity until the voltage reaches 3.0 V. Taking the discharge capacity of this time as the benchmark, after standing for 10 min, it is charged to 4.3 V at 0.1C, 0.2C, 0.5C, 1.0C, 2.0C, 5C, and 10C respectively, and then discharged at the charging current rate until the discharge voltage reaches 3.0 V. There is a 10 - min interval between each charge - discharge, and each charge - discharge cycle is repeated 5 times, and the discharge rate is calculated. The test results are shown in Table 3.

[0099] After the lithium - ion battery is left standing at 45 °C in a constant - temperature environment for 24 h, it is charged to 4.3 V at the above - mentioned 1C current rate, and charged at a constant voltage of 4.3 V with a cut - off current of 0.05C. Then, after standing for 10 min, it is discharged at the same current until the voltage reaches 3.0 V, forming a charge - discharge cycle. After standing for 10 min, the next cycle is carried out. The entire cycle test is carried out at 45 °C, and the test results are shown in Table 3.

[0100] Comparative Example 1

[0101] (1) According to Li 2 CO 3 and D 50 Ni with a particle size less than 10 μm 0.65 Co 0.15 Mn 0.25 (OH) 2 Mix at a high speed at 400 r / min according to the molar ratio of Li / (Ni + Co + Mn) of 1.05:1.0. The mixed material is loaded into a crucible and sintered for the first time in a box furnace, with oxygen introduced as the sintering atmosphere. It is calcined at 930 °C for 24 h; then, after the box furnace cools naturally, the material is taken out, crushed, and passed through a 300 - mesh sieve; then, after the muffle furnace cools naturally, the material is taken out, pulverized by air flow, and passed through a 300 - mesh sieve to obtain a single - crystal - type ternary material.

[0102] Mix the single - crystal - type ternary material obtained above evenly with nano - scale Al 2 O 3 where Al 2 O3 With Li 1.05 Ni 0.65 Co 0.15 Mn 0.25 O 2 Designed according to a molar ratio of 1000 ppm, the second sintering is carried out, and it is calcined at 600 °C for 10 h in an oxygen atmosphere. After cooling, a single-crystalline ternary material with a single-layer coating is obtained.

[0103] In the single-crystalline ternary material, the number of primary particles n is 1, and the median particle size D of the cathode material 50 is 3.56 μm; the median particle size d of the primary particles 50 is 3.56 μm.

[0104] (2) Weigh the above single-crystalline ternary material with a single-layer coating, conductive agent Super P, and binder PVDF in a weight ratio of 96:2:2 in sequence, mix them in NMP, and obtain a uniform slurry through vacuum stirring. Then, coat the slurry evenly on an aluminum foil current collector, bake it in an oven at 100 °C for 12 h, and cut it to obtain a small circular cathode sheet containing the cathode material;

[0105] (3) Fabricate 2016-type button cells and lithium-ion batteries, and conduct corresponding performance tests: same as Example 1.

[0106] Table 1 Specific capacity and rate performance data of 2016-type button cells in Example 1 and Comparative Example 1

[0107]

[0108] Table 2 EIS test data of 2016-type button cells in Example 1 and Comparative Example 1

[0109] Charge transfer resistance Rct / mΩ Warburg impedance ray slope k Example 1 8.137 1.19 Comparative Example 1 25.233 0.23

[0110] The test results in Table 1 show that the polycrystalline single crystal of the present invention has a higher specific capacity at 0.1C discharge than the single crystal and also has an advantage in rate performance. Especially when the rate is increased to 0.5C and 1C, the advantage of the discharge specific capacity is obvious; the test results in Table 2 show that the polycrystalline single crystal has a great advantage in charge transfer impedance and lithium ion diffusion impedance compared with the single crystal, which can fully illustrate that the polycrystalline single crystal material of the present invention has excellent ionic conductivity, excellent charge and discharge capacity, and rate performance when applied to lithium-ion batteries.

[0111] Table 3 Performance test results of lithium-ion batteries in Example 1 and Comparative Example 1

[0112]

[0113] It can be seen from the data in Table 3 that in Example 1, when discharging from the upper limit voltage of 4.3V to 3.0V, a capacity of 180.1mAh / g can be achieved, and after 1200 cycles at this voltage and 45°C, the capacity retention rate is still 89.42%. In Example 1 and Comparative Example 1, the particle size of the precursor was regulated, and substances containing Mo and W were added during synthesis to regulate the growth mode of primary particles and control the calcination temperature, resulting in the formation of polycrystalline single crystal and single crystal morphologies respectively. It can be clearly seen from Table 3 that at high voltage and high rate cycling up to 4.3V, its rate performance is much higher than that of single crystal materials, making the battery have excellent cycle performance and improved capacity and rate performance.

[0114] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A battery, characterized in that, in the AC impedance EIS test of the battery, the charge transfer resistance Rct of the second semicircle in the intermediate frequency region satisfies: Rct < 15 mΩ; the ray slope k in the low frequency region satisfies: 1.03 < k < 57.29; the battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material, the positive electrode material includes a plurality of particles with a polycrystalline single crystal morphology, and the particles with a polycrystalline single crystal morphology are formed by nesting a plurality of primary particles, that is, one primary particle in the formed particles with a polycrystalline single crystal morphology is fused and connected with multiple primary particles through an internal driving force to form a surrounding structure of mutual nesting; the positive electrode material satisfies the relational expression shown in Formula 1 below: D 50 3 =K×n×d 50 3 Equation 1 Among them, K is a coefficient, and its range is: 0.2 ≤ K ≤ 2; n is the number of primary particles, and its range is: 2 ≤ n ≤ 500; D 50 is the median particle size of the positive electrode material, with the unit of μm; d 50 is the median particle size of the primary particle, with the unit of μm; The median particle size d of the primary particles 50 is 0.1 μm - 2 μm; the frequency of the intermediate frequency region is 150 Hz to 500 Hz, and the frequency of the low frequency region is 0.01 Hz to 150 Hz; The primary particles are ternary materials, and the chemical formula of the ternary materials is Li a Ni 1-x-y-p Co x M 1 y M 2 p O 2 , 0.95 ≤ a < 1.08, 0.5 ≤ 1 - x - y - p < 1.0, 0 < x ≤ 0.3, 0 < y ≤ 0.2, 0 < p ≤ 0.005; M 1 is Mn or Al, and M 2 is one or more of Mg, Sr, Ba, Y, W, Nb, and Mo.

2. The battery according to claim 1, characterized in that, Particles with a polycrystalline morphology are prepared using the precursor of a ternary material with a size of 50 50 less than 7 μm.

3. The battery according to claim 1, characterized in that, The median particle size D of the positive electrode material 50 is 0.2 μm to 20 μm.

4. The battery according to claim 1, characterized in that, the positive electrode material further includes a coating layer, and the coating layer coats the surfaces of a plurality of the particles with a polycrystalline single crystal morphology; the mass of the coating layer accounts for 0.05 - 0.5 wt% of the total mass of the positive electrode material.

5. The battery according to claim 4, characterized in that, the coating layer includes a first coating layer and a second coating layer, the first coating layer coats the surfaces of a plurality of the particles with a polycrystalline single crystal morphology, the second coating layer coats the outer surface of the first coating layer, the first coating layer is a metal compound, and the second coating layer is a metal compound and / or a non-metal compound.

6. The battery according to claim 1, characterized in that, the battery includes a non-aqueous electrolyte, and the non-aqueous electrolyte includes an additive; the additive is selected from at least one of fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, ethylene sulfate, 1,3 - propane sultone or 1,4 - butane sultone.

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