Gradient composite pole piece, preparation method and secondary battery

Abstract

The invention relates to the technical field of secondary batteries, in particular to a gradient composite pole piece, a preparation method and a secondary battery. The gradient composite pole piece comprises a current collector and composite active layers which are sequentially arranged in a stacked mode and contain n sub-active layers, n is larger than or equal to 2, the sub-active layer close to the current collector is the first layer, and the sub-active layer far away from the current collector is the nth layer; each sub active layer independently contains an active material, an electrolyte material and a functional additive; wherein the functional additive is a heat-conducting and electric-conducting composite material; in each sub active layer, the mass ratio A of the electrolyte material satisfies An-1 / Angt; 1, the mass ratio G of the functional additive meets Gn-1 / Gnlt; 1. According to the gradient composite pole piece, on the basis of avoiding influence on intrinsic performance, an internal conductive / ionic network is optimized, diffusion kinetics is enhanced, a rapid heat conduction network is constructed, and heat accumulation is reduced, so that the rate capability and the cycle performance are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a gradient composite electrode, a method for preparing the gradient composite electrode, and a secondary battery containing the above-mentioned gradient composite electrode. Background Technology

[0002] Rechargeable batteries possess advantages such as high energy density, high operating voltage, long cycle life, and low self-discharge rate, and have been widely used in numerous fields in recent years, including consumer electronics, vehicle and marine power, and new energy storage. With the rapid iteration and upgrading of rechargeable batteries, the industry believes that hybrid solid-liquid batteries and all-solid-state batteries, which offer higher safety and higher energy density, represent the future development direction for large-capacity rechargeable batteries. However, how to improve fast-charging performance while maintaining energy density has become one of the key research areas in this type of battery.

[0003] Using thick electrodes with high areal capacity is generally an effective way to improve battery energy density. However, this results in long ion / electron diffusion paths within the electrode, which can easily lead to an imbalance between the charging rate and the alkali metal ion insertion rate during charging. This further causes alkali metal ions to tend to be reduced on the negative electrode surface, ultimately leading to dendrite growth. Furthermore, rapid charging of the battery generates significant heat, while the electrode's own heat dissipation capacity is limited, and heat accumulation can easily trigger serious side reactions. These problems severely restrict the improvement of battery electrochemical and safety performance.

[0004] To address the aforementioned technical problems, most existing technologies attempt to alleviate them through strategies that regulate the composition within the electrode. For example, CN110581253A simply adjusts the ratio of active material to electrolyte content in the electrode; that is, along the thickness direction away from the current collector, the content gradient of the active material decreases while the content gradient of the solid electrolyte increases, aiming to improve the ionic conductivity and reduce interfacial impedance. However, relying solely on this composition regulation strategy not only has limited effect on improving electrochemical performance, but the significant reduction in the active material content also substantially lowers the battery's energy density.

[0005] Therefore, there is an urgent need to develop a composite electrode suitable for hybrid solid-liquid batteries and all-solid-state batteries, as well as a method for its preparation. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of uneven reaction and slow thermal diffusion in existing thick electrodes, which severely restrict electrochemical and safety performance. This invention provides a gradient composite electrode, a method for preparing the gradient composite electrode, and a secondary battery containing the aforementioned gradient composite electrode. This gradient composite electrode, without affecting its intrinsic performance, optimizes the internal conductive electron / ion network, enhances diffusion kinetics, constructs a fast thermally conductive network, reduces heat accumulation, and thus significantly improves rate performance and cycle performance.

[0007] To achieve the above objectives, the first aspect of the present invention provides a gradient composite electrode, the gradient composite electrode comprising a current collector and a composite active layer containing n sub-active layers stacked sequentially, wherein n≥2, the sub-active layer closer to the current collector is the first layer, and the sub-active layer farther from the current collector is the nth layer; each sub-active layer independently contains an active material, an electrolyte material, and a functional additive. The functional additive is a composite material with thermal conductivity and electrical conductivity. In each sub-active layer, the mass percentage A of the electrolyte material satisfies: A n-1 / A n >1, the mass percentage G of functional additives satisfies: G n-1 / G n <1, where A n-1 and A n Represent the mass percentage of electrolyte material in the (n-1)th layer and the nth layer, respectively, wt%, G n-1 and G n wt% represents the mass percentage of functional additives in the (n-1)th and nth layers, respectively.

[0008] The inventors of this invention have discovered that by regulating the internal components of the electrode, an electrolyte material with high compatibility with the electrode active material and high ionic conductivity can be introduced to construct a rapid ion transport pathway. This significantly reduces battery polarization and impedance problems caused by the lack of liquid electrolyte wetting in hybrid solid-liquid and all-solid-state batteries, thereby improving battery rate performance.

[0009] Meanwhile, composite materials with thermal and electrical conductivity are introduced as functional additives. In particular, their structure and composition are controlled to help build a fast thermal and electrical conductivity network inside the entire electrode. This not only facilitates the rapid conduction of heat generated inside the battery during charging and discharging, but also facilitates the rapid conduction of electrons within the electrode. This helps to reduce the problem of aggravated side reactions caused by heat accumulation and improves the battery's rate (fast charging) and cycle performance.

[0010] Furthermore, by designing a gradient structure for the electrode, the electrolyte material gradually decreases in the direction away from the current collector, while the functional additives gradually increase in the direction away from the current collector. This effectively alleviates the imbalance between the charging rate and the alkali metal ion insertion rate during charging and discharging, which is prone to occur due to the long ion / electron diffusion paths within the electrode. This significantly reduces battery polarization, thereby optimizing the electron / ion transport network channels in the entire electrode, enhancing diffusion kinetics, constructing a fast heat conduction network, reducing heat accumulation, and ultimately achieving a significant improvement in the cycle stability and rate performance of hybrid solid-liquid batteries and all-solid-state batteries.

[0011] Therefore, this invention, through the synergistic effect of internal component regulation and gradient structure, determines the transport medium of ions / electrons / heat by internal component regulation, and realizes the construction of a rapid conduction network by gradient structure design, effectively solving the problems of poor uniformity of internal electrode reaction and heat accumulation, and effectively improving the electrochemical performance and safety performance of the battery.

[0012] A second aspect of the present invention provides a method for preparing the above-mentioned gradient composite electrode, comprising the following steps: S1. The active material, electrolyte material and functional additive are dry-mixed to obtain a mixed dry material; S2. The mixed dry material is coated on the surface of the current collector to form a film, thereby forming a composite active layer containing the first sub-active layer to the nth sub-active layer, and obtaining a gradient composite electrode. or, S1': The active material, electrolyte material and functional additives are wet-mixed to obtain a mixed slurry; S2' The mixed slurry is coated on the surface of the current collector and dried to form a composite active layer containing the first sub-active layer to the nth sub-active layer in sequence, thus obtaining a gradient composite electrode.

[0013] A third aspect of the present invention provides a secondary battery comprising a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode and the negative electrode are each independently selected from the above-mentioned gradient composite electrode.

[0014] Compared with the prior art, the present invention has the following advantages: (1) The gradient composite electrode provided by the present invention introduces electrolyte materials and functional additives through the synergistic effect of internal component regulation and gradient structure, and regulates the specific gradient change trend of their mass ratio to construct a dual gradient distribution structure from the near current collector side to the far current collector side, thereby optimizing the electron / ion transport network channel in the entire electrode, enhancing diffusion dynamics, and through the fast heat conduction network constructed by functional additives, the heat generated in the electrode can be transferred to the outside in time to reduce heat accumulation, and finally achieve a significant improvement in the cycle stability and rate performance of hybrid solid-liquid batteries and all-solid batteries.

[0015] (2) The gradient composite electrode provided by the present invention also effectively improves the ionic conductivity and thermal conductivity of the gradient composite electrode by optimizing the changing trend of the mass ratio of electrolyte material and functional additives, the type of electrolyte material, and the structure and type of functional additives. This alleviates the problems of increased polarization and uneven internal reaction caused by high ion transport tortuosity, as well as the problem of aggravated side reactions caused by heat accumulation inside the electrode, thereby achieving the purpose of optimizing battery performance.

[0016] (3) The preparation method provided by the present invention is highly compatible with existing manufacturing processes, and can achieve rapid product introduction without increasing costs, which is convenient for industrial production. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the cross-sectional structure of a gradient composite electrode provided by the present invention.

[0018] Explanation of reference numerals in the attached figures 1. Current collector; 2. First sub-active layer; 3. Second sub-active layer; 4. Third sub-active layer. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] The first aspect of the present invention provides a gradient composite electrode, the gradient composite electrode comprising a current collector and a composite active layer containing n sub-active layers stacked sequentially, wherein n≥2, the sub-active layer closer to the current collector is the first layer, and the sub-active layer farther from the current collector is the nth layer; each sub-active layer independently contains an active material, an electrolyte material, and a functional additive. The functional additive is a composite material with thermal conductivity and electrical conductivity. In each sub-active layer, the mass percentage A of the electrolyte material satisfies: A n-1 / A n >1, the mass percentage G of functional additives satisfies: G n-1 / G n <1, where A n-1 and A n Represent the mass percentage of electrolyte material in the (n-1)th layer and the nth layer, respectively, wt%, G n-1 and G n wt% represents the mass percentage of functional additives in the (n-1)th and nth layers, respectively.

[0021] In this invention, unless otherwise specified, the gradient composite electrode includes a current collector and a composite active layer, and the composite active layer contains n sub-active layers stacked together, that is, on the current collector, the first sub-active layer... the (n-1)th sub-active layer, and the nth sub-active layer are sequentially disposed.

[0022] A schematic diagram of the cross-sectional structure of a gradient composite electrode provided by this invention is shown below. Figure 1 As shown, a first sub-active layer 2, a second sub-active layer 3, and a third sub-active layer 4 are sequentially stacked on the current collector 1 to form a composite active layer; in the direction away from the current collector 1, the mass percentage A of the electrolyte material decreases sequentially, while the mass percentage G of the functional additives increases sequentially.

[0023] In this invention, unless otherwise specified, A n-1 / A n >1 indicates that, in the direction away from the current collector, the mass percentage of electrolyte material in any two adjacent sub-active layers decreases sequentially (i.e., the mass percentage of electrolyte material in the (n-1)th active layer is A). n-1 The mass percentage of electrolyte material in the nth sub-active layer, A n Similarly, G n-1 / G n <1 indicates that, in the direction away from the current collector, the mass percentage of functional additives in any two adjacent sub-active layers shows an increasing trend (i.e., the mass percentage of electrolyte material in the (n-1)th active layer is G). n-1 <Mass percentage of electrolyte material in the nth sub-active layer G n ).

[0024] In this invention, unless otherwise specified, the rate of decrease in the mass percentage of electrolyte material in each sub-active layer can be the same or different; that is, the mass percentage of A in each sub-active layer can be... n-1 / A n Selected from the same or different.

[0025] In some embodiments of the present invention, preferably, the mass percentage A of the electrolyte material in each sub-active layer satisfies: 1.01 ≤ A n-1 / A n ≤1.21, for example, 1.01, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, 1.21, and any value within a range of any two values, preferably 1.05≤A. n-1 / A n ≤1.15.

[0026] In this invention, the mass ratio A of the electrolyte material satisfies the above trend, effectively shortening the ion transport path inside the electrode, constructing a fast ion transport network, reducing interface impedance, and improving rate performance.

[0027] In this invention, when A n-1 / A nWhen A < 1, the gradient change trend of the electrolyte material contradicts the design concept of this invention. That is, the mass ratio of the electrolyte material gradually decreases near the current collector side, while the ion transport path of the electrode near the current collector side is longer in the thickness direction, lacking more ion transport network constructed by the electrolyte material. This will inevitably cause a large alkali metal ion concentration gradient, increasing battery polarization and leading to a deterioration in rate and cycle performance. n-1 / A n >1.21, the electrolyte mass ratio on the side furthest from the current collector is too low, resulting in fewer ion pathways and hindering rate performance.

[0028] In this invention, unless otherwise specified, the rate of increase in the mass percentage of functional additives in each sub-active layer can be the same or different; that is, the mass percentage of G in each sub-active layer can be the same. n-1 / G n Selected from the same or different.

[0029] In some embodiments of the present invention, preferably, the mass percentage G of the functional additive in each sub-active layer satisfies: 0.8 ≤ G n-1 / G n ≤0.99, for example, 0.8, 0.82, 0.85, 0.88, 0.9, 0.92, 0.95, 0.96, 0.99, and any value within the range of any two values, preferably 0.85≤G. n-1 / G n ≤0.95.

[0030] In this invention, the mass ratio G of the functional additives meets the above trend, which is beneficial to the construction of the thermal and electrical conduction network inside the entire electrode, facilitates the rapid conduction of heat, and significantly reduces the aggravation of side reactions caused by heat accumulation.

[0031] In this invention, when G n-1 / G n <0.8, the content of functional additives near the current collector is relatively low, which is not conducive to the rapid dissipation of heat accumulated on the inner side of the electrode to the current collector, reducing heat transfer efficiency, causing temperature rise, increasing side reactions, and affecting battery cycle performance. When G n-1 / G n >1. The gradient change trend of functional additive materials is contrary to the design concept of this invention. That is, the material gradually decreases away from the current collector. On the one hand, the electron transport path is longer on the side of the electrode away from the current collector in the thickness direction, and there is a lack of electron transport network constructed by more functional additive materials. This will inevitably increase the battery impedance and lead to a deterioration in rate performance. On the other hand, it is not conducive to the rapid outward dissipation of heat accumulated in the electrode, which will aggravate the side reaction.

[0032] In some embodiments of the present invention, preferably, based on the total mass of the composite active layer, the total mass percentage of the electrolyte material is 0.05-35 wt%, for example, 0.05 wt%, 0.08 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 12 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, and any value within any range of any two values, preferably 0.06-30 wt%.

[0033] In this invention, the total mass percentage of the electrolyte material refers to the ratio of the sum of the masses of the electrolyte materials in the n sub-active layers to the total mass of the composite active layer; similarly, the total mass percentage of the functional additives refers to the ratio of the sum of the masses of the functional additives in the n sub-active layers to the total mass of the composite active layer; similarly, the total mass percentage of the active material refers to the ratio of the sum of the masses of the active materials in the n sub-active layers to the total mass of the composite active layer.

[0034] In this invention, preferably, the ionic conductivity of the electrolyte material is ≥10. -6 S / cm, for example, 1×10 -6 S / cm, 5×10 -6 S / cm, 8×10 -6 S / cm, 1×10 -5 S / cm, 5×10 -5 S / cm, 8×10 -5 S / cm, 1×10 -4 S / cm, 5×10 - 4 S / cm, 8×10 -4 S / cm, 1×10 -3 S / cm, 5×10 -3 S / cm, 8×10 -3 S / cm, 1×10 -2 S / cm, and any value within a range consisting of any two values.

[0035] In this invention, the above-mentioned ionic conductivity parameters can be measured using conventional testing methods for those skilled in the art, such as electrochemical impedance spectroscopy, at a test temperature of 25±2℃.

[0036] In this invention, preferably, the D of the electrolyte material 50 The value is 0.1-3μm, for example, 0.1μm, 0.2μm, 0.5μm, 0.8μm, 1μm, 2μm, 3μm, and any value within the range of any two values, preferably 0.2-1μm.

[0037] In the present invention, D 50 parameters can be measured by conventional testing methods for those skilled in the art, such as by using laser particle size analysis (PSD) / scanning electron microscopy (SEM).

[0038] In the present invention, there is a wide selection range for the types of the electrolyte materials, as long as the above limitations are satisfied. Preferably, the electrolyte materials are selected from at least one of sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, borohydride solid electrolytes, and polymer electrolytes.

[0039] In a specific embodiment of the present invention, the sulfide solid electrolyte is selected from (100-x)Li2S·xP2S5, Li3PS4, Li7P3S 11 , Li6PS5X m , Li 10 GeP2S 12 , Li 10 SnP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, Li4GeS4, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li 11 Sn2PS 12 , Na3PS4, Na 11 Sn2PS 12 and Na7P3S 11 and at least one of them, where 0 < x < 100, X is selected from at least one of Cl, Br, and I, and 1 ≤ m ≤ 1.6.

[0040] In a specific embodiment of the present invention, the halide solid electrolyte is selected from at least one of Li3InCl6, LiYCl6, Li4GeI6, Li3YBr6, Li3InBr6, Li4GeCl6, Li3InI6, Li3YI6, Li7Ge3Cl 12 , Li5InCl 12 , NaAlCl4, Na2ZrCl6, and NaAlCl 2.5 O 0.75 and at least one of them.

[0041] In a specific embodiment of the present invention, the oxide solid electrolyte is selected from Li 3y La 2 / 3-y TiO3, Li 1+z Al z Ti2-z (PO4)3, Li7La3Zr2O 12 , Li3PO4, LiAlO2, Li2ZrO3, Li4Ti5O 12 β″-Al2O3 and Na3Zr2Si2PO 12 At least one of them, wherein 0 <y≤2 / 3,0≤z≤0.5。

[0042] In one specific embodiment of the present invention, the borohydride solid electrolyte is selected from Na2B. 12 H 12 Na2B 10 H 10 NaCB9H 10 At least one of Na3OBH4.

[0043] In one specific embodiment of the present invention, the polymer electrolyte is selected from at least one of PEO-based polymer electrolyte, PAN-based polymer electrolyte, PVDF-based polymer electrolyte, PVDF-HFP-based polymer electrolyte, PDMA-based polymer electrolyte, and PDOL-based polymer electrolyte.

[0044] In some embodiments of the present invention, preferably, based on the total mass of the composite active layer, the total mass percentage of the functional additive is 0.01-10 wt%, for example, 0.01 wt%, 0.02 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 10 wt%, and any value within any range of any two values, preferably 0.02-7 wt%.

[0045] In some embodiments of the present invention, preferably, the electronic conductivity of the functional additive is ≥1 S / cm, for example, 1 S / cm, 10 S / cm, 1×10 2 S / cm, 1×10 3 S / cm, 5×10 5 S / cm, 1×10 4 S / cm, 5×10 4 S / cm, 1×10 5 S / cm, 5×10 5 S / cm, 8×10 5 S / cm, 1×10 6 S / cm, 5×10 6 S / cm, 8×10 6 S / cm, 1×10 7 S / cm, 5×10 7 S / cm, 8×107 S / cm, 1×10 8 S / cm, and any value within a range consisting of any two values.

[0046] In this invention, the above-mentioned electronic conductivity parameters can be measured using conventional testing methods for those skilled in the art, such as using a powder resistivity meter at a test temperature of 25±2℃.

[0047] In some embodiments of the present invention, preferably, the thermal conductivity of the functional additive is ≥10 W / (m·K), for example, 10 W / (m·K), 25 W / (m·K), 50 W / (m·K), 80 W / (m·K), 100 W / (m·K), 300 W / (m·K), 500 W / (m·K), 800 W / (m·K), 1000 W / (m·K), 1500 W / (m·K), 2000 W / (m·K), 2500 W / (m·K), 3000 W / (m·K), and any value within a range of any two values, preferably 25-2000 W / (m·K).

[0048] In this invention, the above-mentioned thermal conductivity parameters can be measured using conventional testing methods for those skilled in the art, such as using a laser thermal conductivity meter with a test temperature of 25±2℃; thermal conductivity represents the heat flow rate within a unit length of 1m with a temperature difference of 1K.

[0049] In some embodiments of the present invention, preferably, the functional additive has a D 50 The range is 50-500nm, for example, 50nm, 80nm, 100nm, 200nm, 300nm, 400nm, 500nm, and any value within the range of any two values, preferably 100-300nm.

[0050] In some embodiments of the present invention, preferably, the functional additive has a core-shell structure, wherein the core layer is a thermally conductive material and the shell layer is a electrically conductive material.

[0051] In this invention, as a preferred embodiment, the functional additive is designed with a core-shell structure. This is mainly because some thermally conductive materials have poor intrinsic conductivity. Direct addition would not only affect internal electron transport, but also cause small thermally conductive material particles to interact with the binder, leading to adhesion and agglomeration. This results in uneven dispersion within the electrode, increasing electrode resistance and reducing battery performance. However, by adopting a core-shell structure design, with a high thermal conductivity material as the core and a high conductivity material coated on the surface, the conductivity of the material itself is increased, which is beneficial for the construction of the conductive network. Furthermore, the compatibility between the additive and the active material is increased, making it easier to disperse and thus improving battery performance.

[0052] In some embodiments of the present invention, preferably, the thermally conductive material D 50 The wavelength is 45-500 nm, and the thickness of the shell layer is 2-5 nm.

[0053] In some embodiments of the present invention, preferably, the thermally conductive material is selected from at least one of nitride ceramic materials, boride ceramic materials and zirconium-silicon intermetallic compounds, and more preferably from at least one of aluminum nitride, titanium nitride, boron nitride, zirconium diboride, zirconium disilicide and hafnium diboride.

[0054] In some embodiments of the present invention, preferably, the conductive material is selected from at least one of amorphous carbon, carbon black, graphene, carbon fiber and carbon nanotubes.

[0055] In some embodiments of the present invention, preferably, based on the total mass of the composite active layer, the total mass percentage of the active material is 45-98.94 wt%, for example, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 78 wt%, 80 wt%, 82 wt%, 85 wt%, 88 wt%, 90 wt%, 92 wt%, 95 wt%, 98.94 wt%, and any value within any range of any two values, preferably 60-95 wt%.

[0056] In some embodiments of the present invention, preferably, the active material D 50 The value is 0.2-18μm, for example, 0.2μm, 1μm, 2μm, 3μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, and any value within the range of any two values, preferably 3-12μm.

[0057] In this invention, the gradient composite electrode can be either a positive electrode or a negative electrode, depending mainly on the type of active material.

[0058] In some embodiments of the present invention, preferably, when the active material is a negative electrode active material, it is selected from at least one of hard carbon, soft carbon, graphene, artificial graphite, natural graphite, lithium titanate, silicon suboxide, silicon carbon, nano silicon, micron silicon, sodium titanate, sodium iron sulfate, sodium-transition metal phosphates, disodium terephthalate, and disodium 2,5-hydroxy-1,4-benzoquinone.

[0059] In this invention, the sodium-transition metal phosphates mentioned above include, but are not limited to, sodium titanium phosphate.

[0060] In some embodiments of the present invention, preferably, when the active material is a positive electrode active material, it is selected from at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based positive electrode material, sodium ion oxide positive electrode material, sodium ion polyanionic positive electrode material, and sodium ion Prussian blue type positive electrode material.

[0061] In this invention, lithium nickel cobalt manganese oxide includes, but is not limited to, LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (abbreviated as NCM523), Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 (abbreviated as LRM), LiNi 0.5 Co 0.25 Mn 0.25 O2 (abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (abbreviated as NCM811), etc.

[0062] In this invention, each sub-active layer contains an electrolyte material, a functional conductive agent, and an active material, as well as an independent conductive agent and a binder.

[0063] In this invention, preferably, based on the total mass of the composite active layer, the total mass percentage of the conductive agent is 0-5 wt%, and the total mass percentage of the binder is 1-5 wt%.

[0064] In this invention, the conductive agent includes, but is not limited to, acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, Ketjen black, vapor-grown carbon fiber (VGCF), etc.; the binder includes, but is not limited to, acrylonitrile copolymer (LA133), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), polyamide-imide (PAI), polyethyleneimine (PEI), polyimide (PI), tert-butyl polyacrylate-triethoxyvinylsilane (TBATEVS), etc.

[0065] In some embodiments of the present invention, when the active material is a positive electrode active material, the current collector is a positive electrode current collector, including but not limited to aluminum foil, carbon-coated aluminum foil, and aluminum composite current collector; or, when the active material is a negative electrode active material, the current collector is a negative electrode current collector, including but not limited to copper foil, carbon-coated copper foil, and copper composite current collector.

[0066] In this invention, the aluminum composite current collector is typically a "sandwich structure" with a polymer layer in the middle and aluminum layers on both sides; similarly, the copper composite current collector is typically a "sandwich structure" with a polymer layer in the middle and copper layers on both sides.

[0067] In this invention, preferably, the alkali metal ion concentration C of the gradient composite electrode in the charged state satisfies: 0 ≤ (C0 ≤ C ... n -C1) / C n ×100%≤5%, for example, 0%, 0.1%, 0.2%, 0.4%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, and any value within a range of any two values, preferably satisfying: 0≤(C n -C1) / C n ×100%≤3%; where C n C1 and C2 represent the concentrations of alkali metal ions in the nth and 1st layers, respectively, in mol / g.

[0068] In this invention, the alkali metal ion concentration C of the gradient composite electrode in the charged state can be measured using conventional testing methods for those skilled in the art, such as time-of-flight secondary ion mass spectrometry.

[0069] Meeting the above range indicates that the gradient composite electrode provided by the present invention has strong ion transport capability, uniform distribution of alkali metal ions inside the electrode, and reduced concentration difference, thereby exhibiting high reaction uniformity.

[0070] In this invention, preferably, the ionic conductivity of the gradient composite electrode is ≥10. -8 S / cm.

[0071] In this invention, preferably, the gradient composite electrode has a thermal conductivity of 3-200 W / (m·K) in the vertical direction, for example, 3W / (m·K), 5W / (m·K), 10W / (m·K), 20W / (m·K), 50W / (m·K), 60W / (m·K), 80W / (m·K), 100W / (m·K), 120W / (m·K), 150W / (m·K), 200W / (m·K), and any value within the range of any two values, preferably 5-100W / (m·K), where the vertical direction refers to the thickness direction of the gradient composite electrode.

[0072] In this invention, preferably, the surface resistivity of the gradient composite electrode is 0.01-0.95 Ω / cm. 2 For example, 0.01Ω / cm 2 0.05Ω / cm 2 0.1Ω / cm 2 0.2Ω / cm 2 0.3Ω / cm 2 0.4Ω / cm 2 0.5Ω / cm 2 0.6Ω / cm 2 0.7Ω / cm 2 0.8Ω / cm 2 0.95Ω / cm 2 , and any value within a range consisting of any two values.

[0073] In this invention, the above-mentioned surface resistivity parameters can be measured using conventional testing methods for those skilled in the art, such as using a four-probe resistivity meter at a test temperature of 25±2℃.

[0074] In this invention, preferably, the compaction density of the gradient composite electrode is 1-3.7 g / cm³. 3 For example, 1g / cm 3 1.05g / cm 3 1.1g / cm 3 1.5g / cm 3 1.8g / cm 3 2g / cm 3 2.5g / cm 3 3g / cm 3 3.2g / cm 3 3.5g / cm 3 3.65g / cm 3 3.7g / cm 3 And any value within the range of any two values, preferably 1.05-3.65 g / cm³. 3 .

[0075] In this invention, the above-mentioned compaction density parameters can be measured using conventional testing methods for those skilled in the art, such as using a compaction density meter.

[0076] In this invention, preferably, the average areal density of the gradient composite electrode is 10-60 mg / cm³. 2 For example, 10 mg / cm 2 12mg / cm 2 15mg / cm 2 20mg / cm 230mg / cm 2 40mg / cm 2 50mg / cm 2 60mg / cm 2 And any value within the range of any two values, preferably 12-50 mg / cm³. 2 .

[0077] In this invention, the above-mentioned average areal density parameter is calculated using the electrode areal density calculation formula, that is, average areal density = mass of electrode coating ÷ effective area of ​​electrode.

[0078] In this invention, areal density refers to the mass of all materials per unit area. Therefore, the average areal density of the gradient composite electrode is actually the sum of the densities of all sub-active layers. The greater the areal density of each sub-active layer, the more material per unit area, the thicker the layer, the longer the ion / electron transport path, the greater the polarization, the more obvious the heat accumulation effect, and the easier it is for the electrochemical performance to decline.

[0079] In this invention, preferably, the areal density of each sub-active layer is 4-12 mg / cm³. 2 For example, 4 mg / cm 2 5mg / cm 2 6mg / cm 2 7mg / cm 2 8mg / cm 2 10mg / cm 2 12mg / cm 2 And any value within the range of any two values, preferably 5-8 mg / cm³. 2 .

[0080] In this invention, preferably, the thickness of each sub-active layer is independently 10-100 μm, for example, 10 μm, 20 μm, 30 μm, 50 μm, 60 μm, 80 μm, 100 μm, and any value in the range of any two values, preferably 20-80 μm.

[0081] In this invention, the above-mentioned thickness parameters can be measured using conventional testing methods for those skilled in the art, such as using a thickness gauge.

[0082] In this invention, unless otherwise specified, the thickness of the composite active layer is equal to the sum of the thicknesses of the n sub-active layers.

[0083] A second aspect of the present invention provides a method for preparing the above-mentioned gradient composite electrode, comprising the following steps: S1. The active material, electrolyte material and functional additive are dry-mixed to obtain a mixed dry material; S2. The mixed dry material is coated on the surface of the current collector to form a film, thereby forming a composite active layer containing the first sub-active layer to the nth sub-active layer, and obtaining a gradient composite electrode. or, S1': The active material, electrolyte material and functional additives are wet-mixed to obtain a mixed slurry; S2' The mixed slurry is coated on the surface of the current collector and dried to form a composite active layer containing the first sub-active layer to the nth sub-active layer in sequence, thus obtaining a gradient composite electrode.

[0084] In this invention, unless otherwise specified, the types of active materials, electrolyte materials, functional additives and current collectors are all as defined above, and will not be elaborated upon here.

[0085] In this invention, preferably, in step S1, the mixed dry material further contains a conductive agent and a binder; in step S1', the mixed slurry further contains a conductive agent and a binder.

[0086] In this invention, in step S1', the solvent in the mixed slurry is selected from water and / or organic solvents, including but not limited to deionized water, ethanol, DMF, etc. Preferably, the solid content of the mixed slurry is 10-65 wt%.

[0087] In this invention, in steps S2 and S2', the coating is intended to apply the mixed dry material or mixed slurry to the surface of the current collector. Preferably, the coating method includes, but is not limited to, blade coating, microgravure coating, slot extrusion coating, spraying, dip coating, transfer printing, electrospinning, etc.

[0088] In this invention, preferably, in step S2, the conditions for the film-forming treatment include: calendering the mixture using a roller press, controlling the roller pressure to be ≥1MPa, preferably 25-50MPa; and the temperature to be ≥25℃, preferably 60-120℃.

[0089] In this invention, preferably, in step S2', the drying temperature is ≥25℃, and more preferably 60-120℃.

[0090] One specific embodiment of the present invention provides a method for preparing the above-mentioned gradient composite electrode, comprising: (1) The active material, electrolyte material, functional additive, conductive agent and binder are dry mixed to obtain mixed dry material 1; By adjusting the mass of each of the above components, a mixed dry material (n-1) is obtained; By adjusting the mass of each of the above components, a mixed dry material n is obtained; (2) The above-mentioned mixed dry material 1 is coated on the surface of the current collector and film-forming treatment is performed to form a first sub-active layer on the surface of the current collector; Repeat the above operation to coat the mixed dry material (n-1) onto the surface of the (n-2)th sub-active layer to form the (n-1)th sub-active layer; Repeat the above operation to coat the mixed dry material n on the surface of the (n-1)th sub-active layer to form the nth sub-active layer, thus obtaining a gradient composite electrode.

[0091] Another specific embodiment of the present invention provides a method for preparing the above-mentioned gradient composite electrode, comprising: (1) The active material, electrolyte material, functional additive, conductive agent and binder are mixed by dry or wet method to obtain mixed slurry 1; By adjusting the mass of each of the above components, a mixed slurry (n-1) is obtained; By adjusting the mass of each of the above components, a mixed slurry n is obtained; (2) The above-mentioned mixed slurry 1 is coated on the surface of the current collector and dried to form a first sub-active layer on the surface of the current collector; Repeat the above operation to coat the mixed slurry (n-1) onto the surface of the (n-2)th sub-active layer to form the (n-1)th sub-active layer; Repeat the above operation to coat the mixed slurry n onto the surface of the (n-1)th sub-active layer to form the nth sub-active layer, thus obtaining a gradient composite electrode.

[0092] A third aspect of the present invention provides a secondary battery comprising a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode and the negative electrode are each independently selected from the above-mentioned gradient composite electrode.

[0093] According to a particularly preferred embodiment of the present invention, a gradient composite electrode includes a current collector and a composite active layer containing n sub-active layers stacked sequentially, wherein n≥2, the sub-active layer closer to the current collector is the first layer, and the sub-active layer farther from the current collector is the nth layer; each sub-active layer independently contains an active material, an electrolyte material, and a functional additive. The functional additive is a composite material with thermal conductivity and electrical conductivity. In each sub-active layer, the mass percentage A of the electrolyte material satisfies: 1.05 ≤ A n-1 / A n ≤1.15, the mass percentage G of functional additives satisfies: 0.85≤G n-1 / G n ≤0.95, where A n-1 and A nRepresent the mass percentage of electrolyte material in the (n-1)th layer and the nth layer, respectively, wt%, G n-1 and G n These represent the mass percentages of functional additives in the (n-1)th and nth layers, respectively, in wt% The functional additive has a core-shell structure, with the core layer being a thermally conductive material and the shell layer being a electrically conductive material; the electronic conductivity of the functional additive is ≥1 S / cm, and the thermal conductivity is ≥10 W / (m·K).

[0094] The present invention will be described in detail below through embodiments.

[0095] Example 1 (1) The active material (silicon-carbon, D) 50 (8μm), electrolyte material (Li) 1.3 Al 0.3 Ti 1.7 (PO4)3,D 50 It has a diameter of 0.5 μm and an ionic conductivity of 10. -4 S / cm), functional additives (amorphous carbon-coated titanium nitride, D 50 The wavelength is 200 nm, the coating thickness is 5 nm, and the electronic conductivity is 10. 5 S / cm, thermal conductivity 29W / (m·K)), conductive carbon black and binder LA133 are mixed in a mass ratio of 80:10:3:2:5 and dispersed in deionized water to obtain a mixed slurry 1 with a solid content of 50wt%; The mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 was adjusted to 80:9.09:3.33:2.58:5 to obtain a mixed slurry 2 with a solid content of 50wt%; The mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 was adjusted to 80:8.26:3.7:3.04:5 to obtain a mixed slurry 3 with a solid content of 50wt%; (2) The above mixed slurry 1 is coated on copper foil and dried at 80°C for 4 hours to form a first sub-active layer with a thickness of 45 μm; the above mixed slurry 2 is coated on the surface of the first sub-active layer and dried at 80°C for 4 hours to form a second sub-active layer with a thickness of 45 μm; the above mixed slurry 3 is coated on the surface of the second sub-active layer and dried at 80°C for 4 hours to form a third sub-active layer with a thickness of 60 μm. After rolling, a gradient composite electrode P1 is obtained.

[0096] Example 2 The method is the same as in Example 1, except that... In step (1), the type of electrolyte material is replaced with Li7La3Zr2O.12 , its D 50 It has a diameter of 0.5 μm and an ionic conductivity of 10. -4 S / cm; Under the same conditions, the gradient composite electrode P2 was obtained.

[0097] Example 3 The method is the same as in Example 1, except that... In step (1), the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 in the mixed slurry 2 is adjusted to 80:9.52:3.33:2.15:5; In the mixed slurry 3, the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 is adjusted to 80:9.07:3.7:2.23:5; Under the same conditions, the gradient composite electrode P3 was obtained.

[0098] Example 4 The method is the same as in Example 1, except that... In step (1), the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 in the mixed slurry 2 is adjusted to 80:8.7:3.33:2.97:5; In the mixed slurry 3, the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 is adjusted to 80:7.56:3.7:3.74:5; Under the same conditions, gradient composite electrode P4 was obtained.

[0099] Example 5 The method is the same as in Example 1, except that... In step (1), the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 in the mixed slurry 2 is adjusted to 80:7.7:3.33:3.97:5; In the mixed slurry 3, the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 is adjusted to 80:5.92:3.7:5.38:5; Under the same conditions, gradient composite electrode P5 was obtained.

[0100] Example 6 The method is the same as in Example 1, except that... In step (1), the type of functional additive is amorphous carbon-coated boron nitride, D 50 The wavelength is 200 nm, the coating thickness is 5 nm, and the electronic conductivity is 10. 3S / cm, thermal conductivity 1700W / (m·K); Under the same conditions, gradient composite electrode P6 was obtained.

[0101] Example 7 The method is the same as in Example 1, except that... In step (1), the type of functional additive is amorphous carbon-coated aluminum nitride, D 50 The wavelength is 200 nm, the coating thickness is 5 nm, and the electronic conductivity is 10. 3 S / cm, thermal conductivity is 320W / (m·K); Under the same conditions, gradient composite electrode P7 was obtained.

[0102] Example 8 The method is the same as in Example 1, except that... In step (1), the type of functional additive is a mixture of amorphous carbon and titanium nitride, D 50 It is 200nm and has an electronic conductivity of 10. 5 S / cm, thermal conductivity 10.7 W / (m·K); Under the same conditions, gradient composite electrode P8 was obtained.

[0103] Example 9 The method is the same as in Example 1, except that... In step (1), the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 in the mixed slurry 2 is adjusted to 80:9.09:3.53:2.38:5; In the mixed slurry 3, the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 is adjusted to 80:8.26:4.15:2.59:5; Under the same conditions, gradient composite electrode P9 was obtained.

[0104] Example 10 The method is the same as in Example 1, except that... In step (1), the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 in the mixed slurry 2 is adjusted to 80:9.09:3.16:2.75:5; In the mixed slurry 3, the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 is adjusted to 80:8.26:3.22:3.52:5; Under the same conditions, gradient composite electrode P10 was obtained.

[0105] Example 11 The method is the same as in Example 1, except that... In step (1), the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 in the mixed slurry 2 is adjusted to 80:9.09:4:1.91:5; In the mixed slurry 3, the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 is adjusted to 80:8.26:5.33:1.41:5; Under the same conditions, the gradient composite electrode P11 was obtained.

[0106] Example 12 The method is the same as in Example 1, except that... In step (1), the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 in the mixed slurry 2 is adjusted to 80:8.33:3.75:2.92:5; In the mixed slurry 3, the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 is adjusted to 80:6.94:4.69:3.37:5; Under the same conditions, gradient composite electrode P12 was obtained.

[0107] Example 13 The method is the same as in Example 1, except that... In step (1), Li 1.3 Al 0.3 Ti 1.7 (PO4)3 of D 50 Replace with 0.2μm; Under the same conditions, gradient composite electrode P13 was obtained.

[0108] Example 14 The method is the same as in Example 1, except that... In step (1), Li 1.3 Al 0.3 Ti 1.7 (PO4)3 of D 50 Replace with 1μm; Under the same conditions, the gradient composite electrode P14 was obtained.

[0109] Example 15 The method is the same as in Example 1, except that... In step (1), the amorphous carbon-coated titanium nitride D 50 Replace with 100nm; Under the same conditions, the gradient composite electrode P15 was obtained.

[0110] Example 16 The method is the same as in Example 1, except that... In step (1), the amorphous carbon-coated titanium nitride D 50 Replace with 400nm; Under the same conditions, gradient composite electrode P16 was obtained.

[0111] Example 17 The method is the same as in Example 1, except that... In step (1), the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 is adjusted to 85:5:2.43:2.57:5 to obtain mixed slurry 1; The mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 was adjusted to 85:4.55:2.56:2.89:5 to obtain mixed slurry 2; The mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 was adjusted to 85:4.13:2.69:3.18:5 to obtain mixed slurry 3; Under the same conditions, gradient composite electrode P17 was obtained.

[0112] Example 18 The method is the same as in Example 1, except that... In step (1), the mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 in the mixed slurry 2 is adjusted to 80:8.33:3.16:3.51:5; In step (2), the above mixed slurry 1 is coated on copper foil and dried at 80°C for 4 hours to form a first sub-active layer with a thickness of 75 μm; the above mixed slurry 2 is coated on the surface of the first sub-active layer and dried at 80°C for 4 hours to form a second sub-active layer with a thickness of 75 μm. After rolling, a gradient composite electrode P18 is obtained.

[0113] Example 19 (1) The active material (LiNi) 0.9 Co 0.05 Mn 0.05 O2, D 50 (9μm), electrolyte material (Li6PS5Cl, D) 50 It has a diameter of 1 μm and an ionic conductivity of 10. -2 S / cm), functional additives (amorphous carbon-coated titanium nitride, D 50 The wavelength is 200 nm, the coating thickness is 5 nm, and the electronic conductivity is 10. 5Dry pulp 1 was obtained by mixing and dispersing conductive carbon black and binder PTFE in a mass ratio of 80:13:3:2:2 and then fiberizing them; The mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder PTFE was adjusted to 80:11.82:3.33:2.85:2 to obtain dry slurry 2; The mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder PTFE was adjusted to 80:10.74:3.7:3.56:2 to obtain dry slurry 3; (2) Using a roller press, dry slurry 1, dry slurry 2 and dry slurry 3 are sequentially stacked and rolled onto aluminum foil. The pressure of the roller is controlled at 30MPa and the temperature is 100℃ to obtain gradient composite electrode P19.

[0114] Example 20 The method is the same as in Example 1, except that... The mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 was adjusted to 80:9.52:3.48:2:5 to obtain mixed slurry 2; The mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 was adjusted to 80:8.66:4.34:2:5 to obtain mixed slurry 3; Under the same conditions, gradient composite electrode P20 was obtained.

[0115] Comparative Example 1 (1) The active material (silicon-carbon, D) 50 (8μm), electrolyte material (Li) 1.3 Al 0.3 Ti 1.7 (PO4)3,D 50 It has a diameter of 0.5 μm and an ionic conductivity of 10. -4 S / cm), functional additives (amorphous carbon-coated titanium nitride, D 50 The wavelength is 200 nm, the coating thickness is 5 nm, and the electronic conductivity is 10. 5 S / cm, thermal conductivity 29W / (m·K)), conductive carbon black and binder LA133 are mixed in a mass ratio of 80:9.12:3.35:2.53:5 and dispersed in deionized water to obtain a mixed slurry with a solid content of 50wt%. (2) The mixed slurry is coated on copper foil and dried at 80°C for 4 hours to obtain composite electrode DP1.

[0116] Comparative Example 2 The method is the same as in Example 1, except that no functional additives are added. In step (1), the mass ratio of the above active material, electrolyte material, conductive carbon black and binder LA133 is 80:10:5:5, to obtain mixed slurry 1; The mass ratio of the above active material, electrolyte material, conductive carbon black and binder LA133 was adjusted to 80:9.09:5.91:5 to obtain mixed slurry 2; The mass ratio of the above-mentioned active material, electrolyte material, conductive carbon black and binder LA133 was adjusted to 80:8.26:6.74:5 to obtain mixed slurry 3; Under the same conditions, the composite gradient pole piece DP2 is obtained.

[0117] Comparative Example 3 The method is the same as in Example 1, except that no electrolyte material is added. In step (1), the mass ratio of the above active material, functional additive, conductive carbon black and binder LA133 is 80:3:12:5, to obtain mixed slurry 1; The mass ratio of the above active material, functional additive, conductive carbon black and binder LA133 was adjusted to 80:3.33:11.67:5 to obtain mixed slurry 2; The mass ratio of the above active material, functional additive, conductive carbon black and binder LA133 was adjusted to 80:3.7:11.3:5 to obtain mixed slurry 3; Under the same conditions, the composite gradient pole piece DP3 was obtained.

[0118] Comparative Example 4 The method is the same as in Example 1, except that... In step (1), the mass ratio of the above active material, electrolyte material, functional additive, conductive carbon black and binder LA133 is 80:8.26:3.7:3.04:5, to obtain mixed slurry 1; The mass ratio of the above-mentioned active material, electrolyte material, functional additive, conductive carbon black and binder LA133 was adjusted to 80:9.09:3.33:2.58:5 to obtain mixed slurry 2; The mass ratio of the above-mentioned active material, electrolyte material, functional additive and binder LA133 was adjusted to 80:10:3:2:5 to obtain mixed slurry 3; Under the same conditions, the composite gradient pole piece DP4 was obtained.

[0119] Comparative Example 5 The method is the same as in Example 1, except that... In step (1), the type of functional additive is replaced with titanium nitride (D). 50The wavelength is 200 nm, and the thermal conductivity is 29 W / (m·K). Under the same conditions, the composite gradient pole piece DP5 was obtained.

[0120] Comparative Example 6 The method is the same as in Example 1, except that... In step (1), the type of functional additive is replaced with amorphous carbon (D). 50 It is 50nm and has an electronic conductivity of 10. 4 S / cm); Under the same conditions, the composite gradient pole piece DP6 was obtained.

[0121] Table 1

[0122] Continued from Table 1

[0123] As can be seen from the results in Table 1, compared with Comparative Examples 1-6, Examples 1-20, employing the dual-gradient variation design of the solid electrolyte and functional additives within the electrode of this invention, exhibit faster transport speed of alkali metal ions to the current collector side, reducing internal polarization of the electrode and alleviating the problem of uneven alkali metal ion concentration distribution within the electrode (i.e., (C)). n -C1) / C n (This indicator value is even smaller). At the same time, the rapid heat conduction network constructed by functional additives with thermal conductivity helps to quickly remove heat to the current collector side, reducing heat accumulation inside the electrode and effectively reducing the consumption of side reactions.

[0124] Test case The composite electrodes (P1-P20 and DP1-DP6) prepared in Examples 1-20 and Comparative Examples 1-6 were assembled into solid-state batteries.

[0125] Solid electrolyte is coated onto the surface of the composite electrodes (P1-P20 and DP1-DP6) described in the above technical solution using a coating equipment. After drying, the electrodes are cut into 50×50mm plates and welded with tabs to serve as working electrodes. A lithium-indium composite foil with tabs is used as the counter electrode and stacked on the surface of the working electrode, ensuring that the solid electrolyte film layer is located between the composite electrode and the lithium-indium composite foil, thus obtaining a bare cell. The bare cell is then hot-pressed using a hot-pressing equipment at a temperature of 80℃ and a holding pressure of 400MPa for 10 minutes. Finally, it is vacuum-sealed with an aluminum-plastic film to obtain a solid-state battery.

[0126] The above-mentioned batteries were subjected to performance tests under a certain external pressure at a temperature of 25°C. The test results are shown in Table 2.

[0127] 1) Cyclic test: The charge / discharge regime is 0.5C / 1C, and the voltage range is -0.61V to 1.5V (P1-P18, P20 and DP1-DP6) or 2.0-3.8V (P19). After 100 cycles, the cycle capacity retention rate is calculated based on the reversible specific capacity of the first cycle. 2) Rate test: Keep the voltage range constant and set the charge and discharge rates to 0.1C, 0.33C, 0.5C and 1C in sequence. The rate performance is expressed as the capacity retention rate relative to the reversible specific capacity at 0.1C.

[0128] Table 2

[0129] As can be seen from the data in Table 2, compared with Comparative Examples 1-6, the composite electrodes of Examples 1-20 using the dual gradient strategy of the present invention have higher specific capacity, rate performance and cycle stability.

[0130] (1) The impact of the dual-gradient strategy design of solid electrolyte and functional additives on battery performance As can be seen from the data of Examples 1-2 and Comparative Example 1, compared with the strategy of uniform distribution of each component in the electrode in Comparative Example 1, it is impossible to achieve rapid ion transport in the electrode near the current collector and rapid heat conduction to the outside of the electrode. However, Examples 1-2 construct a fast conductive network based on the transport characteristics of ions / electrons in the electrode to effectively reduce polarization and improve rate performance. At the same time, a high-efficiency thermal conductive network is built to reduce heat accumulation inside the electrode, reduce side reactions, and improve cycle performance.

[0131] (2) Effect of solid electrolyte gradient change rate on battery performance As shown by the data from Examples 1 and 3-5, the gradient rate of change of the solid electrolyte reflects, on the one hand, the content and distribution of the solid electrolyte in each sub-active layer, and on the other hand, affects the construction of the ion-conducting network. Solid electrolytes have high ion conductivity but poor electronic conductivity; therefore, it is necessary to control its gradient rate within the range of this invention to ensure the construction of a highly efficient ion-conducting network within the electrode without affecting its electron transport capability, thereby achieving the goal of improving rate performance.

[0132] (3) The influence of the structure of functional additives on electrical properties As can be seen from the data of Examples 1 and 8, the electrical performance of the functional additive with a core-shell structure in Example 1 is better than that of the mixture of carbon and thermally conductive material directly added in Example 8. Example 1 uses a functional additive with a core-shell structure, with a core of high thermal conductivity and a shell of high electrical conductivity. This structure not only facilitates the uniform dispersion of small-particle-size functional additives, but also avoids the interaction between thermally conductive material particles and binder, which leads to adhesion and agglomeration, thus improving electrical conductivity and exhibiting superior rate performance and cycle performance.

[0133] (4) Effect of the gradient change rate of functional additives on battery performance As shown by the data from Examples 1 and 9-11, the gradient change rate of the functional additive reflects both the content and distribution of the functional additive in each sub-active layer and its influence on the construction of the thermally conductive network. The functional additive has high thermal conductivity but relatively poor ionic conductivity; therefore, its change rate needs to be controlled within the range of this invention to ensure the construction of a highly efficient thermally conductive network within the electrode without affecting its ion / electron transport capability, thereby improving cycle performance.

[0134] (5) Effect of solid electrolyte / functional additive particle size on battery performance Data from Examples 1, 13-14, and 15-16 show that battery electrical performance can be controlled by adjusting the particle size of the solid electrolyte and functional additives. The particle size must be controlled within the range specified in this invention to ensure the construction of a highly efficient thermally conductive network within the electrode without affecting its ion / electron transport capability, thereby improving cycle performance.

[0135] (6) The synergistic effect of solid electrolyte and functional additive component regulation and gradient design strategy on battery performance As can be seen from the data of Comparative Examples 1-6 and Example 1, compared with the average distribution of each component in Comparative Example 1, the introduction of a solid electrolyte in Comparative Example 2, the introduction of a functional additive in Comparative Example 3, the reverse gradient design in Comparative Example 4, the use of only thermally conductive materials as functional additives in Comparative Example 5, and the use of only conductive materials as functional additives in Comparative Example 6, Example 1 introduces both a solid electrolyte and a specific functional additive to complete a dual gradient design. The solid electrolyte can construct a fast alkali metal ion transport network, enabling alkali metal ions to be rapidly transported to the current collector side, thereby reducing polarization. The functional additive can improve electron transport within the electrode and construct a thermally conductive network to reduce heat accumulation within the electrode and the resulting side reactions. Therefore, the best capacity utilization, rate capability, and cycle performance are obtained.

[0136] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A gradient composite electrode, characterized in that, The gradient composite electrode includes a current collector and a composite active layer containing n sub-active layers stacked sequentially, wherein n≥2, the sub-active layer closer to the current collector is the first layer, and the sub-active layer farther from the current collector is the nth layer; each sub-active layer independently contains active material, electrolyte material and functional additives. The functional additive is a composite material with thermal conductivity and electrical conductivity. In each sub-active layer, the mass percentage A of the electrolyte material satisfies: A n-1 / A n >1, the mass percentage G of functional additives satisfies: G n-1 / G n <1, where A n-1 and A n Represent the mass percentage of electrolyte material in the (n-1)th layer and the nth layer, respectively, wt%, G n-1 and G n wt% represents the mass percentage of functional additives in the (n-1)th and nth layers, respectively.

2. The gradient composite electrode according to claim 1, wherein, In each sub-active layer, the mass percentage A of the electrolyte material satisfies: 1.01 ≤ A n-1 / A n ≤1.21, preferably 1.05≤A n-1 / A n ≤1.15; And / or, in each sub-active layer, the mass percentage G of the functional additive satisfies: 0.8 ≤ G n-1 / G n ≤0.99, preferably 0.85≤G n-1 / G n ≤0.

95.

3. The gradient composite electrode according to claim 1 or 2, wherein, Based on the total mass of the composite active layer, the total mass percentage of the electrolyte material is 0.05-35 wt%, preferably 0.06-30 wt%. And / or, the ionic conductivity of the electrolyte material is ≥10. -6 S / cm; And / or, the D of the electrolyte material 50 The thickness is 0.1-3 μm, preferably 0.2-1 μm.

4. The gradient composite electrode according to any one of claims 1-3, wherein, The electrolyte material is selected from at least one of sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, borohydride solid electrolytes, and polymer electrolytes; And / or, the sulfide solid electrolyte is selected from (100 - x)Li2S·xP2S5, Li3PS4, Li7P3S 11 , Li6PS5X m , Li 10 GeP2S 12 , Li 10 SnP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4, Li4GeS4, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li 11 Sn2PS 12 , Na3PS4, Na 11 Sn2PS 12 and Na7P3S 11 and at least one of the above, where 0 < x < 100, X is selected from at least one of Cl, Br, and I, and 1 ≤ m ≤ 1.6; And / or, the halide solid electrolyte is selected from Li3InCl6, LiYCl6, Li4GeI6, Li3YBr6, Li3InBr6, Li4GeCl6, Li3InI6, Li3YI6, Li7Ge3Cl 12 ,Li5InCl 12 NaAlCl4, Na2ZrCl6 and NaAlCl 2.5 O 0.75 At least one of them; And / or, the oxide solid electrolyte is selected from Li 3y La 2 / 3-y TiO3, Li 1+z Al z Ti 2-z (PO4)3, Li7La3Zr2O 12 , Li3PO4, LiAlO2, Li2ZrO3, Li4Ti5O 12 β″-Al2O3 and Na3Zr2Si2PO 12 At least one of them, wherein 0 <y≤2 / 3,0≤z≤0.5; And / or, the borohydride solid electrolyte is selected from Na2B. 12 H 12 Na2B 10 H 10 NaCB9H 10 and at least one of Na3OBH4; And / or, the polymer electrolyte is selected from at least one of PEO-based polymer electrolytes, PAN-based polymer electrolytes, PVDF-based polymer electrolytes, PVDF-HFP-based polymer electrolytes, PDMA-based polymer electrolytes, and PDOL-based polymer electrolytes.

5. The gradient composite electrode according to any one of claims 1-4, wherein, Based on the total mass of the composite active layer, the total mass percentage of the functional additives is 0.01-10 wt%, preferably 0.02-7 wt%. And / or, the functional additive has an electronic conductivity ≥1 S / cm and a thermal conductivity ≥10 W / (m·K); And / or, the D of the functional additive 50 The wavelength range is 50-500nm, preferably 100-300nm.

6. The gradient composite electrode according to any one of claims 1-5, wherein, The functional additive has a core-shell structure, with the core layer being a thermally conductive material and the shell layer being a electrically conductive material; And / or, the thickness of the shell layer is 2-5 nm; And / or, the thermally conductive material is selected from at least one of nitride ceramic materials, boride ceramic materials and zirconium-silicon intermetallic compounds, preferably from at least one of aluminum nitride, titanium nitride, boron nitride, zirconium diboride, zirconium disilicide and hafnium diboride; And / or, the conductive material is selected from at least one of amorphous carbon, carbon black, graphene, carbon fiber and carbon nanotubes.

7. The gradient composite electrode according to any one of claims 1-6, wherein, Based on the total mass of the composite active layer, the total mass percentage of the active material is 45-98.94 wt%, preferably 60-95 wt%. And / or, the D of the active material 50 The micrometer size is 0.2-18 μm, preferably 3-12 μm; And / or, when the active material is a negative electrode active material, it is selected from at least one of hard carbon, soft carbon, graphene, artificial graphite, natural graphite, lithium titanate, silicon suboxide, silicon carbide, nano silicon, micron silicon, sodium titanate, sodium iron sulfate, sodium-transition metal phosphates, disodium terephthalate and disodium 2,5-hydroxy-1,4-benzoquinone. And / or, when the active material is a positive electrode active material, it is selected from at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based positive electrode material, sodium ion oxide positive electrode material, sodium ion polyanion type positive electrode material, and sodium ion Prussian blue type positive electrode material, as well as modified compounds obtained by doping and modifying the above materials; And / or, each sub-active layer also independently contains a conductive agent and a binder; And / or, based on the total mass of the composite active layer, the total mass percentage of the conductive agent is 0-5 wt%, and the total mass percentage of the binder is 1-5 wt%.

8. The gradient composite electrode according to any one of claims 1-7, wherein, When the gradient composite electrode is in the charged state, its alkali metal ion concentration C satisfies: 0% ≤ (C n -C1) / C n ×100%≤5%, where C n C1 and C2 represent the concentrations of alkali metal ions in the nth and 1st layers, respectively, in mol / g; And / or, the ionic conductivity of the gradient composite electrode is ≥10. -8 S / cm; And / or, the gradient composite electrode has a thermal conductivity of 3-200 W / (m·K) in the vertical direction, preferably 5-100 W / (m·K), where the vertical direction refers to the thickness direction of the gradient composite electrode; And / or, the sheet resistivity of the gradient composite electrode is 0.01-0.95 Ω / cm. 2 .

9. A method for preparing a gradient composite electrode according to any one of claims 1-8, characterized in that, Includes the following steps: S1. The active material, electrolyte material and functional additive are dry-mixed to obtain a mixed dry material; S2. The mixed dry material is coated on the surface of the current collector to form a film, thereby forming a composite active layer containing the first sub-active layer to the nth sub-active layer, and obtaining a gradient composite electrode. or, S1': The active material, electrolyte material and functional additives are wet-mixed to obtain a mixed slurry; S2' The mixed slurry is coated on the surface of the current collector and dried to form a composite active layer containing the first sub-active layer to the nth sub-active layer in sequence, thus obtaining a gradient composite electrode.

10. The preparation method according to claim 9, wherein, In step S1, the mixed dry material also contains a conductive agent and a binder; In step S1', the mixed slurry also contains a conductive agent and a binder; And / or, in step S1', the solid content of the mixed slurry is 10-65 wt%; And / or, in step S2, the conditions for the film-forming treatment include: calendering the mixed dry material using a roller press, controlling the roller pressure to be ≥1MPa and the temperature to be ≥25℃; And / or, in step S2', the drying temperature is ≥25°C.

11. A secondary battery, characterized in that, It includes a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode and the negative electrode are each independently selected from the gradient composite electrode described in any one of claims 1-8, or from the gradient composite electrode obtained by the preparation method described in claim 9 or 10.

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