Electrodes, lithium batteries and automobiles

Abstract

An electrode, a lithium battery, and a vehicle are provided. The electrode includes a current collector and an electrode active material layer disposed on at least one side of the current collector. The electrode active material layer includes at least two electrode active material sublayers. The electrode active material sublayers have a thickness of n×δ i ≦10000, n≧2 and δ i ≦5000 and H i-1 <H i The first electrode active material sublayer is in contact with the current collector.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to and the benefit of Chinese Patent Application No. 202210296429.4, entitled "Electrode, Lithium Battery and Automobile," filed on March 24, 2022. The entire contents of the above application are incorporated herein by reference.

[0002] Field The present disclosure relates to the field of lithium battery technology, and in particular to electrodes, lithium batteries, and automobiles. [Background technology]

[0003] With the development of new energy industries, market demands for the energy density of lithium batteries are increasing. Increasing the packing density of electrodes is one of the key methods for increasing the energy density of lithium batteries. However, when electrodes are rolled during electrode fabrication, the force applied to the electrode active material supported on the current collector in the thickness direction of the electrode becomes uneven, which makes it more likely for cracking to occur on the surface of the electrode active material particles and affects the stability of the electrode active material. Furthermore, cracked electrode active material consumes more electrolyte, affects the porosity of the electrode, increases the internal resistance of the battery, hinders battery capacity, and may even shorten the battery life. Summary of the Invention [Means for solving the problem]

[0004] A first aspect of the present disclosure provides an electrode comprising a current collector and an electrode active material layer disposed on at least one side of the current collector, the electrode active material layer comprising at least two electrode active material sublayers, the electrode active material sublayers satisfying the following relationship: n×δ i ≦10000, n≧2 and δ i ≦5000, and H i-1 <H i Meet the following.

[0005] n represents the total amount of the electrode active material sublayer, and i is an integer value between 2 and n. i represents the hardness of the i-th electrode active material sub-layer, and H1 represents the hardness of the first electrode active material sub-layer, both in MPa. The first electrode active material sub-layer is in contact with the current collector. δ i represents the absolute value of the difference in hardness between the ith electrode active material sub-layer and the (i-1)th electrode active material sub-layer, and is expressed in MPa.

[0006] Optionally, δ i ≦1200.

[0007] Optionally, n, δ i , and the maximum compressed density α of the electrode has the following quantitative relationship: 1.4 g / cm 3 ≦α<1.7g / cm 3 If n ≥ 2 and δ i Satisfy ≦1000.

[0008] Optionally, n, δ i , and the maximum compressed density α of the electrode has the following quantitative relationship: 2.5 g / cm 3 ≦α<2.75g / cm 3 If n ≥ 2 and δ i Meets ≦700.

[0009] Optionally, n, δ i , and the maximum compressed density α of the electrode has the following quantitative relationship: 3.3 g / cm 3 ≦α<3.75g / cm 3 If n ≥ 2 and δ i Meets ≦600.

[0010] Optionally, δ i ≦100.

[0011] Optionally, δ i ≦50.

[0012] Optionally, the maximum packed density α of the electrode is 0 g / cm 3 <α<10g / cm 3 Meet the following.

[0013] Optionally, the maximum packed density α of the electrode is 0 g / cm 3 <α<5g / cm 3 Meet the following.

[0014] Optionally, n, δ i , and the maximum compressed density α of the electrode has the following quantitative relationship: 1.3 g / cm 3 ≦α<1.8g / cm 3 , or 2.6 g / cm 3 ≦α<2.8g / cm 3 , or 3.65 g / cm 3 ≦α<5g / cm 3 If n ≥ 10 and δ i Satisfies ≦5.

[0015] Optionally, in the electrode, the absolute value of the hardness difference between any two adjacent electrode active material sub-layers is equal.

[0016] Optionally, the electrode is a positive electrode, and the positive electrode is filled with an active positive electrode material including at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium cobalt oxide, lithium manganate, lithium nickel manganate, lithium nickel cobalt manganese oxygen ternary material, lithium nickel cobalt aluminum oxygen ternary material, and lithium nickel manganese cobalt aluminum oxygen quaternary material.

[0017] Optionally, the electrode is a negative electrode, and the negative electrode is filled with an active negative electrode material, the active negative electrode material comprising at least one of graphite, natural graphite, mesocarbon microbeads, or silicon-carbon anode material.

[0018] Optionally, the electrode is a positive electrode, the positive electrode being loaded with an active positive electrode material, the active positive electrode material comprising a multi-element nickel-containing active material doped with magnesium, the multi-element nickel-containing active material comprising at least one of a lithium nickel cobalt manganese oxygen ternary material, a lithium nickel cobalt aluminum oxygen ternary material, and a lithium nickel manganese cobalt aluminum oxygen quaternary material.

[0019] Optionally, the mass content of elemental magnesium in the magnesium-doped multi-element nickel-containing active material is greater than 0 and less than 4000 ppm.

[0020] Optionally, the general structural formula of the lithium nickel cobalt manganese oxygen ternary material is Li 1+m Ni x Co y Mn 1-x-y O2, where x≧0.33, 0≦y≦0.4, and 0≦m≦0.1.

[0021] Optionally, the general structural formula of the lithium nickel cobalt aluminum oxygen ternary material is Li 1+m Ni x Co y Al 1-x-y O2, where x≧0.33, 0≦y≦0.4, and 0≦m≦0.1.

[0022] Optionally, the general structural formula of the lithium nickel manganese cobalt aluminum oxygen quaternary material is Li 1+m Ni x Co y Mn z Al 1-x-y-z O2, where x≧0.33, 0≦y≦0.4, 0≦z≦0.4, and 0≦m≦0.1.

[0023] Optionally, the value of x is in the range 0.70≦x≦0.98.

[0024] A second aspect of the present disclosure provides a lithium battery, the lithium battery comprising an electrode according to the first aspect of the present disclosure.

[0025] A third aspect of the present disclosure provides a motor vehicle, the motor vehicle including a lithium battery according to the second aspect of the present disclosure. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 2 is a schematic diagram of a cross-sectional structure of an electrode according to one embodiment of the present disclosure. [Figure 2] FIG. 1 is a schematic diagram of a lithium battery according to one embodiment of the present disclosure. [Figure 3] 1 is a schematic diagram of a vehicle according to one embodiment of the present disclosure.

[0027] The symbols are as follows: 100—electrode, 10—electrode active material layer, 11—current collector, 101—first electrode active material sublayer, 102—second electrode active material sublayer, 10n—nth electrode active material sublayer, 200—lithium battery, 300—automobile. DETAILED DESCRIPTION OF THE INVENTION

[0028] The technical solutions of the present disclosure are described in detail below with reference to specific embodiments.

[0029] Generally, the packing density achievable by each electrode active material is limited to a certain range. A single electrode active material cannot achieve the maximum packing density of the electrode while ensuring the particle integrity of the electrode active material. Fabricating an electrode with a hardness gradient can effectively solve this problem.

[0030] One embodiment of the present disclosure provides an electrode. The electrode includes a current collector and an electrode active material layer disposed on at least one side of the current collector. The electrode active material layer includes at least two electrode active material sublayers. The electrode active material sublayers satisfy the following relationship: n×δ i ≦10000, n≧2 and δ i ≦5000, and H i-1 <H i (Relationship 1) is satisfied.

[0031] n represents the total amount of the electrode active material sublayer, and i is an integer value between 2 and n. i represents the hardness of the i-th electrode active material sub-layer, and H1 represents the hardness of the first electrode active material sub-layer, both in MPa. The first electrode active material sub-layer is in contact with the current collector. δ i represents the absolute value of the difference in hardness between the ith electrode active material sub-layer and the (i-1)th electrode active material sub-layer, and is expressed in MPa.

[0032] The electrode has multiple electrode active material sublayers. The electrode active material sublayer in contact with the current collector is defined as the first electrode active material sublayer. In the thickness direction of the electrode, the sublayers from the current collector side to the surface of the electrode are called the second electrode active material sublayer, the third electrode active material sublayer, the fourth electrode active material sublayer, the fifth electrode active material sublayer, ..., the nth electrode active material sublayer. The hardness of the first electrode active material sublayer to the nth electrode active material sublayer increases gradually (as shown in FIG. 1 , an electrode 100 includes a current collector 11 and an electrode active material layer 10 disposed on the current collector 11. The electrode active material layer 10 is formed by a first electrode active material sublayer 101, a second electrode active material sublayer 102, ..., and an nth electrode active material sublayer 10n). By satisfying the absolute value of the hardness difference between the electrode active material sublayers in Relational Formula 1, it is possible to ensure that the hardness difference between two adjacent electrode active material sublayers falls within a tolerable range. During the electrode rolling process, the surface electrode active material sublayers receive the greatest pressure. When the pressure is transmitted to the current collector side, the pressure on the electrode active material sublayers decreases with each layer. Because the pressure on each sublayer matches the hardness of the sublayer, the electrode active material in each sublayer is less susceptible to cracking. In this way, the entire electrode can have a high maximum compaction density while ensuring the particle integrity of the electrode active material, thereby improving the energy density and extending the cycle life of the battery. If the hardness difference between the electrode active material sublayers is too large (does not satisfy the above Relational Formula 1), the i-th sublayer can withstand a large amount of pressure during the electrode rolling process. However, when pressure is applied to the (i-1)th electrode active material sub-layer, the pressure received by the (i-1)th electrode active material sub-layer is greater than the hardness of the (i-1)th electrode active material sub-layer, and as a result, it is impossible to avoid cracking of the electrode active material in the (i-1)th electrode active material sub-layer from affecting the performance of the lithium battery.

[0033] In this disclosure, the term "electrode active material" generally refers to electrode active material particles, and "cracking of the electrode active material" generally refers to the cracking of the electrode active material particles. The hardness of each electrode active material sub-layer can be considered as the hardness of the electrode active material particles. Specifically, the method for testing the hardness of the electrode active material sub-layers (i.e., the hardness of the electrode active material particles) is as follows.

[0034] (1) Starting from the outermost layer of the electrode, the electrode active material particles of each electrode active material sub-layer are individually collected.

[0035] (2) A field emission scanning electron microscope (FESEM) is used to perform a hardness test on a single electrode active material particle. Specifically, a pointer equipped with a pressure sensor is used to apply a linearly increasing pressure to a single electrode active material particle until the electrode active material particle cracks. In this case, the pressure at the tip of the pointer changes suddenly, creating an inflection point in the force curve of the electrode active material particle, which is fed back by the pressure sensor. In this case, the pressure on the electrode active material particle is stopped, and the cracking state of the electrode active material particle is observed.

[0036] (3) The pressure value at the inflection point of the force curve is recorded as the cracking pressure of the electrode active material particles. To determine the hardness value H0 of the electrode active material particles, calculation is performed according to the following formula: H0 = 2.8P(πr) where P is the particle cracking pressure in N and r is the particle diameter in μm. 2 ) where H0 is in units of MPa.

[0037] (4) At least 500 electrode active material particle samples are collected from each electrode active material sublayer. The hardness of each of the at least 500 electrode active material particle samples is tested according to the above steps. The arithmetic mean of the hardness of the at least 500 electrode active material particles is taken. The arithmetic mean is used to refer to the hardness of the corresponding electrode active material sublayer. In particular, when an electrode active material sublayer is a mixture of different electrode active material particles, the hardness of the sublayer is the mass-weighted average hardness value of the electrode active material particles.

[0038] In the present disclosure, δ i represents the absolute value of the difference in hardness between the i-th electrode active material sub-layer and the (i-1)-th electrode active material sub-layer. Specifically, δ2=|H2-H1|, δ3=|H3-H2|, ..., δ n =|H n -H n-1 | etc. δ i The values ​​of may be the same or different.

[0039] In the present disclosure, each electrode active material sublayer may be formed of a single electrode active material or a mixture of different electrode active materials. The electrode active materials in the electrode active material sublayers may be different or the same. For some specific electrode active materials, the hardness of the electrode active material can be changed by changing the manufacturing process of the electrode active material or by doping or cladding the electrode active material. Therefore, an electrode containing a single type of electrode active material and having a hardness gradient can be fabricated.

[0040] In some embodiments of the present disclosure, δ i In some embodiments of the present disclosure, δ i ≦100. In some embodiments of the present disclosure, δ i ≦50. In this case, the difference in hardness between two adjacent electrode active material sub-layers becomes small, making it easier to ensure the particle integrity of the electrode active material.

[0041] In some embodiments of the present disclosure, n, δ i , and the maximum compressed density α of the electrode has the following quantitative relationship: 1.4 g / cm 3 ≦α<1.7g / cm 3 If n ≥ 2 and δ i ≦1000; 2.5g / cm 3 ≦α<2.75g / cm 3 If n ≥ 2 and δ i ≦700; 3.3g / cm 3 ≦α<3.75g / cm 3 If n ≥ 2 and δ i Meets ≦600.

[0042] In the same case, the greater the total amount n of the electrode active material sublayers and / or the smaller the absolute value of the difference in hardness between two adjacent layers, the smaller the hardness gradient in the thickness direction of the electrode active material layer. It can be understood that the maximum compressed density α of the electrode is related to the specific type of electrode active material used. When several electrode active materials are selected, the maximum compressed density of the produced electrode falls within the aforementioned specific range (e.g., 1.4 g / cm 3 ≦α<1.7g / cm 3 , or 2.5 g / cm 3 ≦α<2.75g / cm 3 , or 3.3 g / cm 3 ≦α<3.75g / cm 3 ) in n and δ i The values ​​of n and δ i The values ​​of the corresponding ranges (e.g., 1.4 g / cm 3 ≦α<1.7g / cm 3 If n ≥ 2 and δ i ≦1000 and 2.5g / cm 3 ≦α<2.75g / cm 3 If n ≥ 2 and δ i ≦700 and 3.3g / cm 3 ≦α<3.75g / cm 3 If n ≥ 2 and δ i ≦600) according to the properties of the electrode active material, which makes the electrode easier to fabricate.

[0043] In this embodiment of the present disclosure, the maximum packed density α of the electrode has a value of 0 g / cm 3 <α<10g / cm 3 In some specific embodiments of the present disclosure, the value of α is 0 g / cm 3 <α<5g / cm 3 Meet the following.

[0044] In some other embodiments of the present disclosure, n, δ, and α have the following quantitative relationship: 1.3 g / cm 3 ≦α<1.8g / cm 3 , or 2.6 g / cm 3 ≦α<2.8g / cm 3 , or 3.65 g / cm3 ≦α<5g / cm 3 If n ≥ 10 and δ i In some other embodiments of the present disclosure, 5 g / cm 3 ≦α<10g / cm 3 If n≧15 and δ i ≦2. If n, δ, and α satisfy the following quantitative relationship, a high-performance battery may be more easily obtained.

[0045] In some other embodiments of the present disclosure, the absolute value of the hardness difference between any two adjacent electrode active material sublayers in the electrode is equal. Specifically, |H2-H1|=|H3-H2|=...=|H n -H n-1 In this case, the uniformity of the hardness gradient of the electrode can be further improved, and the electrode design can be simplified.

[0046] In some embodiments of the present disclosure, the electrode active material includes a positive electrode active material or a negative electrode active material. When the electrode is a positive electrode, the electrode active material can be understood to be a positive electrode active material. When the electrode is a negative electrode, the electrode active material can be understood to be a negative electrode active material. The positive electrode active material and the negative electrode active material are materials commonly used in the battery field.

[0047] The positive electrode active material may include, but is not limited to, at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium cobalt oxide, lithium manganate, lithium nickel manganate, lithium nickel cobalt manganese oxygen ternary material, lithium nickel cobalt aluminum oxygen ternary material, or lithium nickel manganese cobalt aluminum oxygen quaternary material. The negative electrode active material may include, but is not limited to, at least one of graphite, natural graphite, mesocarbon microbeads, or silicon-carbon anode material. The positive or negative electrode active material may be an undoped or unclad electrode active material, or a doped or clad electrode active material.

[0048] In some embodiments of the present disclosure, the positive electrode active material includes, but is not limited to, a multi-element nickel-containing active material doped with magnesium. The multi-element nickel-containing active material includes, but is not limited to, at least one of a lithium nickel cobalt manganese oxygen ternary material, a lithium nickel cobalt aluminum oxygen ternary material, and a lithium nickel manganese cobalt aluminum oxygen quaternary material. In this disclosure, a multi-element nickel-containing active material refers to a nickel-containing active material that is ternary or higher (generally, ternary or quaternary). NCM stands for lithium nickel cobalt manganese oxygen ternary material. In some embodiments, the general structural formula of NCM is Li 1+m Ni x Co y Mn 1-x-y O2 (x≧0.33, 0≦y≦0.4, and 0≦m≦0.1). NCA represents a lithium nickel cobalt aluminum oxygen ternary material. In some embodiments, the general structure of NCA is Li 1+m Ni x Co y Al 1-x-y O2 (x≧0.33, 0≦y≦0.4, and 0≦m≦0.1). NCMA represents a lithium nickel manganese cobalt aluminum oxygen quaternary material. In some embodiments, the general structure of NCMA is Li 1+m Ni x Co y Mn z Al 1-x-y-z It can be expressed as O2(x≧0.33, 0≦y≦0.4, 0≦z≦0.4, and 0≦m≦0.1).

[0049] In some embodiments of the present disclosure, the value of x is in the range of 0.70≦x≦0.98. When the value of x is high, the multi-element nickel-containing material may also be referred to as a "multi-element high-nickel material."

[0050] In some embodiments of the present disclosure, when the electrode active material used is a Mg-doped multi-element nickel-containing active material, the mass content of magnesium element in the magnesium-doped multi-element nickel-containing active material is greater than 0 and less than 4000 ppm.

[0051] Generally, a higher Mg doping amount indicates a higher hardness of the Mg-doped multi-element nickel-containing active material. In the electrodes of the present disclosure, the Mg doping amount in the electrode active material sublayers increases continuously from the first electrode active material sublayer to the nth electrode active material sublayer. In this way, the hardness increases sequentially from the first electrode active material sublayer to the nth electrode active material sublayer. Therefore, by simply adjusting the Mg doping amount in the multi-element nickel-containing active material, the hardness of the multi-element nickel-containing active material can be precisely controlled, allowing for the precise fabrication of electrodes containing only a single type of active material and having a hardness gradient. Similarly, electrodes containing only a single electrode active material can also be fabricated by doping with other metal elements or by other methods, such as cladding or modifying the electrode active material fabrication process.

[0052] During electrode fabrication, the electrode active material layer may be formed by coating on the surface of a current collector. Coating methods include drip coating, brushing, spraying, dipping, knife coating, and spin coating. The specific coating method may be determined depending on the raw materials of the electrode active material sublayer. The raw materials include an electrode active material, a binder, and an optional conductive agent. The raw materials may be liquid or solid.

[0053] In some embodiments of the present disclosure, the feedstock is a liquid feedstock containing a solvent. The liquid feedstock can be formed on the current collector by drip coating, brushing, spraying, dipping, knife coating, spin coating, or the like. Specifically, the electrode active material sublayers can be applied layer by layer to the surface of the current collector, or can be applied layer by layer and dried to form the electrode active material layer. Alternatively, multiple electrode active material sublayers can be applied at once using a multi-layer coating die and then dried to form the electrode active material layer. In some other embodiments, when the feedstock is a solid feedstock, the solid feedstock can be formed on the current collector by powder spraying, or the like (i.e., the electrode active material layer is produced by a dry method).

[0054] Referring to Figure 2, one embodiment of the present disclosure further provides a lithium battery 200. The lithium battery 200 comprises an electrode 100 according to an embodiment of the present disclosure. In some implementations, the positive electrode of the lithium battery 200 is the electrode 100 according to the present disclosure, and the negative electrode is a conventional pole piece. In some implementations, the negative electrode of the lithium battery 200 is the electrode 100 according to the present disclosure, and the positive electrode is a conventional pole piece. In some implementations, both the positive and negative electrodes in the lithium battery 200 are electrodes 100 according to the present disclosure.

[0055] This battery has excellent energy density and long cycle life.

[0056] 3 , an embodiment of the present disclosure further provides an automobile 300. The automobile 300 includes a lithium battery 200 according to an embodiment of the present disclosure. The lithium battery 200 includes an electrode 100 according to an embodiment of the present disclosure. The automobile 300 has a high endurance mileage.

[0057] The examples provided in this disclosure are specifically described below.

[0058] First, a series of ternary nickel-containing materials (LiNi 0.8 Co 0.1 Mn 0.1O2 and NCM811) were prepared and the hardness of the doped NCM811 was measured. When the Mg doping amount was 400 ppm, the hardness of NCM811 was approximately 100 MPa. When the Mg doping amount was approximately 700 ppm, the hardness of NCM811 was 125 MPa. When the Mg doping amount was 1000 ppm, the hardness of NCM811 was approximately 150 MPa. When the Mg doping amount was 1500 ppm, the hardness of NCM811 was approximately 175 MPa.

[0059] Example 1

[0060] (1) Preparation of the positive electrode: 100 g of NCM811, 1 g of the conductive agent Super P, and 0.5 g of the binder PVDF5130 were added to N-methylpyrrolidone (NMP) and mixed uniformly to obtain a positive electrode paste. The maximum pre-set compressed density of the electrode was 3.6 g / cm. 3 The positive electrode paste is applied to the surface of the positive electrode current collector—aluminum foil—through a three-layer coating die. After drying, rolling, and cutting, a positive electrode with three electrode active material sublayers is obtained. The average particle hardness of the first electrode active material sublayer in the positive electrode is 175 MPa, the average particle hardness of the second electrode active material sublayer is 200 MPa, and the average particle hardness of the third electrode active material sublayer is 225 MPa.

[0061] (2) Preparation of negative electrode: 100g of graphite negative electrode active material, 1g of thickener, and 1g of emulsion are added to water in a specific order and mixed uniformly to obtain a negative electrode active material paste. The negative electrode active material is evenly applied to the surface of the negative electrode current collector - copper foil. After drying, it is pressed with a roll press machine to obtain a negative electrode.

[0062] (3) Battery fabrication: A battery is fabricated by alternately stacking the positive electrodes obtained in step (1), the negative electrodes obtained in step (2), and separators. The positive and negative electrodes are arranged alternately, and adjacent positive and negative electrodes are separated by a separator to obtain a dry battery core. The dry battery core is placed in an aluminum-plastic film exterior, an electrolyte is injected, and the aluminum-plastic film exterior is vacuum sealed and left at 60°C for 48 hours. The battery is then pressurized at 60°C for secondary packaging, ventilated, and liquid separation to obtain a laminated pouch-full battery with a capacity of 2.2 Ah. The fabricated battery is designated S1.

[0063] Example 2

[0064] The difference from Example 1 is that the average particle hardness of the first electrode active material sub-layer in the positive electrode is 175 MPa, the average particle hardness of the second electrode active material sub-layer is 200 MPa, and the average particle hardness of the third electrode active material sub-layer is 250 MPa. The fabricated battery is designated as S2.

[0065] Example 3

[0066] The difference from Example 1 is that the average particle hardness of the first electrode active material sub-layer in the positive electrode is 175 MPa, the average particle hardness of the second electrode active material sub-layer is 225 MPa, and the average particle hardness of the third electrode active material sub-layer is 250 MPa. The fabricated battery is designated as S3.

[0067] Example 4

[0068] The difference from Example 1 is that the average particle hardness of the first electrode active material sub-layer in the positive electrode is 100 MPa, and the average particle hardness of the second electrode active material sub-layer is 5100 MPa. The fabricated battery is designated as S4.

[0069] Example 5

[0070] The difference from Example 1 is that the average particle hardness of the first electrode active material sub-layer in the positive electrode is 175 MPa, the average particle hardness of the second electrode active material sub-layer is 275 MPa, and the average particle hardness of the third electrode active material sub-layer is 375 MPa. The fabricated battery is designated as S5.

[0071] Example 6

[0072] 100 g of NCM811, 1 g of conductive agent Super P, and 0.5 g of binder PVDF5130 were added to the NMP and mixed uniformly to obtain a positive electrode paste. The maximum preset compressed density of the electrode was 3.6 g / cm. 3 The positive electrode paste is applied to the surface of the positive electrode current collector (aluminum foil) through a single-layer coating die, then dried and wound for secondary coating until three coating layers are reached. After drying, rolling, and cutting, a positive electrode with three electrode active material sublayers is obtained. The average particle hardness of the first electrode active material sublayer in the positive electrode is 175 MPa, the average particle hardness of the second electrode active material sublayer is 200 MPa, and the average particle hardness of the third electrode active material sublayer is 225 MPa. The fabricated battery is designated S6.

[0073] Example 7

[0074] NCM811, the conductive agent Super P, and the binder PVDF5130 were mixed by jet milling, the mixture was heated and electrospun to form fibers, and the electrospun fibers were hot-pressed to obtain electrode active material sublayers with different hardness. The mass ratio of NCM811 to Super P to PVDF5130 in the mixture was 100:1:0.5. The maximum preset pressed density of the electrode was 3.6 g / cm. 3 The electrode active material sublayers are laminated on the surface of the positive electrode current collector-aluminum foil in order according to hardness, followed by hot pressing, fusion bonding, rolling, and cutting to obtain a positive electrode containing three electrode active material sublayers. The average particle hardness of the first electrode active material sublayer in the positive electrode is 175 MPa, the average particle hardness of the second electrode active material sublayer is 200 MPa, and the average particle hardness of the third electrode active material sublayer is 225 MPa. The battery thus fabricated is designated S7.

[0075] Example 8

[0076] Add 100g of NCM811, 1g of conductive agent Super P, and 0.5g of binder PVDF5130 to NMP and mix evenly to obtain a positive electrode paste. The maximum preset compressed density of the electrode is 3.6g / cm. 3 The positive electrode paste is applied to the surface of an aluminum foil through a two-layer coating die. After drying, rolling, and cutting, a positive electrode with two electrode active material sublayers is obtained. The average particle hardness of the first electrode active material sublayer in the positive electrode is 175 MPa, and the average particle hardness of the second electrode active material sublayer is 225 MPa. The fabricated battery is designated S8.

[0077] Example 9

[0078] NCM811, the conductive agent Super P, and the binder PVDF5130 were mixed by jet milling, the mixture was heated and electrospun to form fibers, and the electrospun fibers were hot-pressed to obtain electrode active material sublayers with different hardness. The mass ratio of NCM811 to Super P to PVDF5130 in the mixture was 100:1:0.5. The maximum preset pressed density of the electrode was 3.65 g / cm. 3 The electrode active material sublayers are stacked on the surface of the positive electrode current collector-aluminum foil in order according to hardness, followed by hot pressing, fusion bonding, rolling, and cutting to obtain a positive electrode containing 10 electrode active material sublayers. The average particle hardness of each electrode active material sublayer from the first to the tenth electrode active material sublayer is 175 MPa, 180 MPa, 185 MPa, ..., 220 MPa, in that order. The fabricated battery is designated S9.

[0079] Example 10

[0080] NCM811, the conductive agent Super P, and the binder PVDF5130 were mixed by jet milling, the mixture was heated and electrospun to form fibers, and the electrospun fibers were hot-pressed to obtain electrode active material sublayers with different hardness. The mass ratio of NCM811 to Super P to PVDF5130 in the mixture was 100:1:0.5. The maximum preset pressed density of the electrode was 3.65 g / cm. 3 The electrode active material sublayers are sequentially stacked on the surface of the positive electrode current collector-aluminum foil in order of hardness, followed by hot pressing, fusion bonding, rolling, and cutting to obtain a positive electrode comprising 10 electrode active material sublayers. The average particle hardness of each of the electrode active material sublayers from the first to the tenth electrode active material sublayers is 120 MPa, 140 MPa, 160 MPa, ..., 300 MPa, in that order. The fabricated battery is designated S10.

[0081] Example 11

[0082] The difference from Example 8 is that the preset maximum compressed density of the electrode is 3.65 g / cm 3 and the number of electrode active material sub-layers in the electrode is six. The average particle hardness of each electrode active material sub-layer from the first electrode active material sub-layer to the sixth electrode active material sub-layer is 175 MPa, 195 MPa, 215 MPa, ..., 275 MPa, in that order. The fabricated battery is designated S11.

[0083] Example 12

[0084] Lithium iron phosphate (LFP), conductive agent Super P, and binder PVDF5130 were mixed by jet milling, the mixture was heated and electrospun to form fibers, and the electrospun material was hot-pressed to obtain electrode active material sublayers with different hardness. The mass ratio of LFP to conductive agent to binder was 90:5:5. The maximum preset pressed density of the electrode was 2.65 g / cm. 3The electrode active material sublayers are sequentially stacked on the surface of the positive electrode current collector-aluminum foil in order of hardness, followed by hot pressing, fusion bonding, rolling, and cutting to obtain a positive electrode containing 10 electrode active material sublayers. The average particle hardness of each electrode active material sublayer from the first to the tenth electrode active material sublayer is 175 MPa, 180 MPa, 185 MPa, ..., 220 MPa, in that order. The fabricated battery is designated S12.

[0085] Example 13

[0086] The difference from Example 12 is that the preset maximum compressed density of the electrode is 2.5 g / cm 3 The number of electrode active material sub-layers of the prepared positive electrode is three. The absolute value δ of the hardness difference between any two adjacent electrode active material sub-layers is i The pressure was 25 MPa in both cases. The battery thus fabricated was designated S13.

[0087] Example 14

[0088] (1) Preparation of negative electrode: 100 g of graphite negative electrode active material, 1 g of thickener, and 1 g of emulsion are added to water in a specific order and mixed uniformly to obtain a negative electrode active material paste. The maximum preset compressed density of the electrode is 1.65 g / cm. 3 The positive electrode paste is applied to the surface of the negative electrode current collector (aluminum foil) through a three-layer coating die. After drying, rolling, and cutting, a negative electrode with 10 electrode active material sublayers is obtained. The average particle hardness of the electrode active material sublayers is 300 MPa, 305 MPa, ..., 345 MPa, respectively.

[0089] (2) Preparation of the positive electrode: 100 g of NCM811, 1 g of the conductive agent Super P, and 0.5 g of the binder PVDF5130 were added to N-methylpyrrolidone (NMP) and mixed uniformly to obtain a positive electrode paste. The positive electrode paste was then uniformly applied to the surface of the positive electrode current collector (aluminum foil).

[0090] (3) Battery fabrication: A battery is fabricated by alternately stacking the negative electrodes obtained in step (1), the positive electrodes obtained in step (2), and separators. The positive and negative electrodes are arranged alternately, and adjacent positive and negative electrodes are separated by a separator to obtain a dry battery core. The dry battery core is placed in an aluminum-plastic film exterior, an electrolyte is injected, and the aluminum-plastic film exterior is vacuum sealed and left at 60°C for 48 hours. The battery is then pressurized at 60°C for secondary packaging, ventilated, and liquid separation to obtain a laminated pouch-full battery with a capacity of 2.2 Ah. The fabricated battery is designated S14.

[0091] Example 15

[0092] The difference from Example 14 is that the maximum compressed density of the resulting negative electrode is 1.2 g / cm 3 The number of electrode active material sublayers is three, and the absolute value of the hardness difference between any two adjacent electrode active material sublayers is δ i The pressures were all 25 MPa. The battery thus fabricated was designated S15.

[0093] Example 16

[0094] The positive electrode prepared in Example 7 and the negative electrode prepared in Example 14 are assembled into a battery S16.

[0095] Example 17

[0096] The difference from Example 15 is that the maximum compressed density of the resulting negative electrode is 1.63 g / cm 3 The number of electrode active material sublayers is two, and the absolute value of the hardness difference between any two adjacent electrode active material sublayers is δ i The obtained battery is designated as S17.

[0097] To highlight the beneficial effects of the embodiments of the present disclosure, the following comparisons are set out.

[0098] Comparison 1

[0099] NCM811, conductive agent Super P, and binder PVDF5130 were mixed by jet milling, the mixture was heated and electrospun to form fibers, and the electrospun fibers were then hot-pressed to obtain the active material layer. The maximum pre-set compressed density of the electrode was 3.65 g / cm. 3 The mass ratio of NCM811 to Super P to PVDF5130 was 100:1:0.5. The active material layer was placed on the positive electrode current collector - aluminum foil, and rolled to obtain a positive electrode with one electrode active material sublayer and an average particle hardness of 220 MPa. The fabricated battery was designated DS1.

[0100] Comparison 2

[0101] NCM811, the conductive agent Super P, and the binder PVDF5130 were mixed by jet milling, the mixture was heated and electrospun to form fibers, and the electrospun fibers were hot-pressed to obtain electrode active material sublayers with different hardness. The mass ratio of NCM811 to Super P to PVDF5130 was 100:1:0.5. The maximum preset pressed density of the electrode was 3.65 g / cm. 3 The electrode active material sublayers are stacked on the positive electrode current collector-aluminum foil in order according to hardness, followed by hot pressing, fusion bonding, rolling, and cutting to obtain a positive electrode containing two electrode active material sublayers. The average particle hardness of the first electrode active material sublayer is 10 MPa, and the average particle hardness of the second electrode active material sublayer is 6010 MPa. The battery thus fabricated is designated DS2.

[0102] Comparison 3

[0103] LFP, conductive agent Super P, and binder PVDF5130 are mixed by jet milling. The maximum pre-set pressed density of the electrode is 2.65 g / cm. 3 The mixture is heated and electrospun to form fibers, and the electrospun material is hot-pressed to obtain pole pieces. A single layer of positive electrode with an average particle hardness of 220 MPa is obtained. The battery thus fabricated is designated DS3.

[0104] Comparison 4

[0105] LFP, conductive agent Super P, and binder PVDF5130 are mixed by jet milling, the mixture is heated and electrospun to form fibers, and the electrospun material is hot-pressed to obtain pole pieces. The maximum pre-set compressed density of the electrode is 2.65 g / cm. 3 These are stacked in two layers, hot-pressed, fused, and rolled to obtain a two-layer positive electrode. The average particle hardness of the first electrode active material sublayer is 10 MPa. The average particle hardness of the second electrode active material sublayer is 6010 MPa. The battery thus fabricated is designated DS4.

[0106] The parameters of the electrodes prepared in the above examples and comparative examples are summarized in Table 1. [Table 1]

[0107] Electrochemical performance tests are conducted on the electrodes and batteries fabricated in the foregoing Examples and Comparative Examples, including the following test methods.

[0108] (1) The fabricated electrode was rolled while gradually increasing the pressure, and the cracking of the electrode active material particles in the electrode was observed and the compressed density of the electrode was measured. The rolling was stopped when the electrode active material particles cracked, and the compressed density measured in the previous experiment was taken as the maximum compressed density α of the electrode. The results are summarized in Table 2.

[0109] (2) Battery cycle performance test: 2.2 Ah at 1C. 1) Charge: Charge at a constant current and voltage of 1 / 3C to 4.25 V / cell, set the cutoff current to 0.05C, and leave for 30 minutes. (2) Discharge: Discharge at a constant current of 1 / 3C to 2.5 V / cell and leave for 30 minutes. 3) Perform three cycles and record the third discharge capacity as the battery's actual capacity C0. 4) Charge: Set the battery's actual capacity C0 to 1C, charge at a constant current and voltage of 1C to 4.25 V, and set the cutoff current to 0.05C. 5) Leave for 30 minutes. (6) Discharge: Set the battery's actual capacity C0 to 1C, and discharge at a constant current of 1C to 2.5 V. 7) Leave for 30 minutes. 8) Repeat steps 4) to 7) a total of 500 times. (Note that, since the positive electrode active material used in Examples 12 and 13 and Comparative Examples 3 and 4 was LFP, the upper limit voltage during the test was set to 3.8 V and the lower limit voltage was set to 2.0 V.) The measurement results of the capacity retention rate and the direct current resistance under load (DCIR) of the battery after 500 cycles are summarized in Table 3.

[0110] (3) The fully charged batteries S1 to S12 and DS1 to DS4 are disassembled to obtain the positive electrodes of the batteries S1 to S17 and DS1 to DS4. A specific amount of electrolyte is added to the positive electrodes. After the electrolyte has completely permeated the electrodes, the samples are prepared and subjected to differential scanning calorimetry (DSC) testing. The specific test conditions are as follows: in an air atmosphere, the temperature is raised from room temperature at a rate of 5°C / min, and the thermal decomposition temperature of the electrodes is measured. The results are summarized in Table 4.

[0111] [Table 2]

[0112] [Table 3]

[0113] [Table 4]

[0114] The data in Tables 2 and 3 show that while the particle integrity of the electrode active material is maintained, the maximum compressed density of the electrode active material in the electrodes provided in Examples 1 to 17 of the present disclosure is close to the predetermined maximum compressed density. For the same materials, the maximum compressed density of the electrodes in the Examples is significantly higher than that of the Controls. The greater the number of electrode active material sublayers in an electrode and the smaller the hardness difference between adjacent sublayers, the greater the maximum compressed density of the electrode (see Examples 9 and 11). If the maximum compressed density of an electrode is within an appropriate range, a higher maximum compressed density indicates a higher energy density of the corresponding battery. However, for the same electrode active material in the pole pieces of the batteries, the battery capacity retention rates of the Example batteries S1 to S17 are higher than those of the Controls, and the DC internal resistance of the Example batteries is relatively low. The thermal decomposition temperatures of the positive electrodes were measured, and it was found that the thermal decomposition temperatures of the positive electrodes prepared in the Examples were higher than those of the Controls when the same electrode active material was used. (For the case where the electrode active material is NCM811, see Examples S1 to S11 and S16, and Comparative Examples DS1 and DS2. For the case where the electrode active material is LFP, see Examples S12 and S13, and Comparative Examples DS3 and DS4.) This indicates that the positive electrodes provided in the Examples of the present disclosure have better thermal stability and can provide batteries with more stable high-temperature performance and higher safety performance. In particular, although the positive electrodes used in S16 and S7 are the same, there is a difference in thermal decomposition temperature, which is due to normal experimental error.

[0115] In conclusion, the electrodes in the embodiments of the present disclosure can be used to provide batteries with high energy density and long cycle life.

[0116] The above description is an exemplary embodiment of the present disclosure. It should be noted that those skilled in the art can make improvements and modifications without departing from the principle of the present disclosure. All such improvements and modifications shall fall within the protection scope of the present disclosure.

Claims

1. An electrode (100) comprising a current collector (11) and an electrode active material layer (10) disposed on at least one side of the current collector (11), wherein the electrode active material layer (10) comprises at least two electrode active material sublayers, and the electrode active material sublayers satisfy the following relationship: n×δ ｉ ≦10000, and H ｉ－１ <H ｉ Fulfilling In the formula, n represents the total amount of the electrode active material sublayer, i is an integer value of 2 to n, and H ｉ is the hardness of the i-th electrode active material sublayer, and H １ is the hardness of the first electrode active material sublayer (101), both in MPa, the first electrode active material sublayer (101) is in contact with the current collector (11), δ ｉ is the absolute value of the hardness difference between the i-th electrode active material sub-layer and the (i-1)-th electrode active material sub-layer, and is expressed in MPa. n, δ i and the maximum packed density α of said electrode satisfy the following quantitative relationship: n≧2 and δ i ≦1000 if 1.4 g / cm 3 ≦α<1.7 g / cm 3 ; or n, δ i and the maximum packed density α of said electrode satisfy the following quantitative relationship: n≧2 and δ i ≦700 if 2.5 g / cm 3 ≦α<2.75 g / cm 3 ; or An electrode (100), wherein n, δ i and the maximum packed density α of said electrode satisfy the following quantitative relationship: n≧2 and δ i ≦600 if 3.3 g / cm 3 ≦α<3.75 g / cm 3 .

2. δ ｉ 100. The electrode (100) of claim 1, wherein:

3. δ ｉ 10. The electrode (100) of claim 1, wherein ≦50.

4. The maximum compressed density α of the electrode (100) is 0 g / cm ３ < α < 10 g / cm ３ The electrode (100) of claim 1, wherein

5. The maximum compressed density α of the electrode is 0 g / cm ３ < α < 5 g / cm ３ The electrode (100) of claim 3, wherein

6. n, δ ｉ , and α has the following quantitative relationship: 1.3 g / cm ３ ≦α<1.8 g / cm ３ , or 2.6 g / cm ３ ≦α<2.8 g / cm ３ , or 3.65 g / cm ３ ≦α<5 g / cm ３ When n≧10 and δ ｉ 10. The electrode (100) of claim 1, wherein:

7. The electrode (100) of claim 1, wherein the absolute value of the hardness difference between any two adjacent electrode active material sublayers in the electrode (100) is equal.

8. 10. The electrode (100) of claim 1, wherein the electrode is a positive electrode and the positive electrode is loaded with an active positive electrode material, the active positive electrode material comprising at least one of lithium iron phosphate, lithium manganese phosphate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium cobalt oxide, lithium manganate, lithium nickel manganate, lithium nickel cobalt manganese oxygen ternary material, lithium nickel cobalt aluminum oxygen ternary material, and lithium nickel manganese cobalt aluminum oxygen quaternary material.

9. 10. The electrode (100) of claim 1, wherein the electrode is a negative electrode, the negative electrode being loaded with an active negative electrode material, the active negative electrode material comprising at least one of graphite, natural graphite, mesocarbon microbeads, or silicon-carbon anode material.

10. 10. The electrode (100) of claim 1, wherein the electrode is a positive electrode, the positive electrode being loaded with an active positive electrode material, the active positive electrode material comprising a multi-element nickel-containing active material doped with magnesium, the multi-element nickel-containing active material comprising at least one of a lithium nickel cobalt manganese oxygen ternary material, a lithium nickel cobalt aluminum oxygen ternary material, or a lithium nickel manganese cobalt aluminum oxygen quaternary material.

11. 11. The electrode (100) of claim 10, wherein the mass content of elemental magnesium in the magnesium-doped multi-element nickel-containing active material is greater than 0 and less than 4000 ppm.

12. The general structural formula of the lithium nickel cobalt manganese oxygen ternary material is Li １＋ｍ Ni ｘ Co ｙ Mn １－ｘ－ｙ O ２ 11. The electrode (100) of claim 8 or 10, wherein x≧0.33, 0≦y≦0.4, and 0≦m≦0.

1.

13. The general structural formula of the lithium nickel cobalt aluminum oxygen ternary material is Li １＋ｍ Ni ｘ Co ｙ Al １－ｘ－ｙ O ２ 11. The electrode (100) of claim 8 or 10, wherein x≧0.33, 0≦y≦0.4, and 0≦m≦0.

1.

14. The general structural formula of the lithium nickel manganese cobalt aluminum oxygen quaternary material is Li １＋ｍ Ni ｘ Co ｙ Mn ｚ Al １－ｘ－ｙ－ｚ O ２ 11. The electrode (100) of claim 8 or 10, wherein x≧0.33, 0≦y≦0.4, 0≦z≦0.4, and 0≦m≦0.

1.

15. 13. The electrode (100) of claim 12, wherein the value of x is in the range of 0.70≦x≦0.

98.

16. A lithium battery (200) comprising the electrode (100) of claim 1.

17. A motor vehicle (300) comprising the lithium battery (200) of claim 16.

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