Negative electrode sheet, method for producing the same, and use thereof

Abstract

This application provides a negative electrode sheet, its preparation method, and its application. The negative electrode sheet includes a current collector and a negative electrode active layer disposed on the surface of the current collector. The negative electrode active layer includes negative electrode active material particles and a modified inorganic ionic conductor. The modified inorganic ionic conductor includes an inorganic ionic conductor body and a carbon coating layer covering the surface of the inorganic ionic conductor body. The modified inorganic ionic conductor includes one or more of one-dimensional modified inorganic ionic conductor nanowires and two-dimensional modified inorganic ionic conductor nanosheets. The ionic conductivity of the negative electrode active layer gradually increases along the direction from the current collector to the negative electrode active layer. This negative electrode sheet possesses excellent ionic conductivity, electronic conductivity, and high energy density.

Description

Technical Field

[0001] This application relates to the field of batteries, and in particular to a negative electrode sheet, its preparation method, and its application. Background Technology

[0002] With the widespread application of lithium-ion batteries in various fields, the requirements for their electrochemical performance, such as energy density and rate performance, are becoming increasingly stringent. However, some negative electrode active materials, such as graphite, have low lithium-ion diffusion coefficients. Especially under high-rate charge and discharge conditions, slow ion transport can easily lead to increased electrode polarization, rapid capacity decay, and increased risk of lithium plating. To improve the energy density of lithium-ion batteries, the thickness of the active layer of the battery electrode is usually increased. However, as the thickness of the active layer increases, the lithium-ion transport path is also lengthened, resulting in a further significant reduction in ion transport rate and efficiency, thereby further reducing the battery's rate performance. Therefore, there is an urgent need to provide a battery negative electrode that combines excellent ionic conductivity, electronic conductivity, and high energy density. Summary of the Invention

[0003] In view of this, this application provides a negative electrode sheet, its preparation method and application. The negative electrode sheet introduces one-dimensional modified inorganic ion conductor nanowires and / or two-dimensional modified inorganic ion conductor nanosheets into the negative electrode active layer, and sets a gradient ion conductivity in the thickness direction of the negative electrode sheet. This allows the negative electrode sheet to build an efficient and continuous three-dimensional ion transport network inside the negative electrode sheet while ensuring good electronic conductivity and high energy density, thereby significantly improving the rate performance and cycle performance of the negative electrode sheet.

[0004] A first aspect of this application provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active layer disposed on the surface of the current collector, the negative electrode active layer comprising negative electrode active material particles and a modified inorganic ion conductor; the modified inorganic ion conductor comprising an inorganic ion conductor body and a carbon coating layer covering the surface of the inorganic ion conductor body; the modified inorganic ion conductor comprising one or more of one-dimensional modified inorganic ion conductor nanowires and two-dimensional modified inorganic ion conductor nanosheets; the ionic conductivity of the negative electrode active layer gradually increases along the direction from the current collector toward the negative electrode active layer.

[0005] In some embodiments of this application, the ionic conductivity of the negative electrode active layer is 10. -6 S / cm-10 -3 S / cm.

[0006] In some embodiments of this application, the mass percentage of the modified inorganic ion conductor in the negative electrode active layer is 0.5%-15%.

[0007] In some embodiments of this application, the negative electrode active layer includes at least two active sub-layers sequentially stacked on the surface of the current collector; the ratio of the ionic conductivity of the active sub-layer furthest from the current collector to the ionic conductivity of the active sub-layer closest to the current collector is greater than or equal to 10.

[0008] In some embodiments of this application, along the direction from the current collector to the negative electrode active layer, the ionic conductivity of the negative electrode active layer ranges from 10... -6 S / cm-10 -5 S / cm increases to 10 -4 S / cm-10 -3 S / cm.

[0009] In some embodiments of this application, the ratio of the mass percentage of the modified inorganic ion conductor in the active sublayer furthest from the current collector to the mass percentage of the modified inorganic ion conductor in the active sublayer closest to the current collector is (1.02-3):1.

[0010] In some embodiments of this application, along the direction from the current collector to the negative electrode active layer, the mass percentage of the modified inorganic ion conductor in the negative electrode active layer increases from 0.1%-0.7% to 0.9%-2%.

[0011] In some embodiments of this application, the absolute value of the difference in ionic conductivity between any two adjacent active sublayers is 1 × 10⁻⁶. -4 S / cm - 8.9 × 10 -3 S / cm.

[0012] In some embodiments of this application, the absolute value of the difference in the mass percentage of the modified inorganic ionic conductor in any two adjacent active sublayers is 0.1%-1.2%.

[0013] In some embodiments of this application, the inorganic ionic conductor body includes one or more of LLZO, LATP, LAGP, LGPS, LLTO, Li3YCl3Br3, Li3YCl6, and Li3YBr6.

[0014] In some embodiments of this application, the aspect ratio of the one-dimensional modified inorganic ionic conductor nanowire is greater than or equal to 20.

[0015] In some embodiments of this application, the diameter of the one-dimensional modified inorganic ion conductor nanowire is 5 nm-1000 nm, and the length of the one-dimensional modified inorganic ion conductor nanowire is 1 μm-50 μm.

[0016] In some embodiments of this application, the thickness of the two-dimensional modified inorganic ionic conductor nanosheet is 5 nm-1000 nm.

[0017] The second aspect of this application provides a method for preparing the negative electrode sheet provided in the first aspect, comprising: A negative electrode active layer is formed by coating a negative electrode slurry onto the surface of the current collector, thus obtaining a negative electrode sheet.

[0018] In some embodiments of this application, the step of coating the current collector surface with negative electrode slurry to form a negative electrode active layer includes: The negative electrode slurry includes at least two composite negative electrode slurries, each of which includes the negative electrode active material particles and the modified inorganic ion conductor, and the mass percentage of the modified inorganic ion conductor in the at least two composite negative electrode slurries is different. The negative electrode active layer includes at least two active sub-layers that are sequentially stacked on the surface of the current collector; Along the direction from the current collector to the negative electrode active layer, the mass percentage of the modified inorganic ion conductor in the negative electrode active layer gradually increases.

[0019] In some embodiments of this application, the preparation of the composite negative electrode slurry includes: The modified inorganic ionic conductor is added to the first solvent to obtain a mixed solution of the modified inorganic ionic conductor; Anode active material particles are added to a second solvent to obtain anode active slurry; The composite negative electrode slurry is obtained by mixing the modified inorganic ionic conductor mixed solution and the negative electrode active slurry.

[0020] In some embodiments of this application, the negative electrode active material particles include graphite.

[0021] In some embodiments of this application, the composite negative electrode slurry further includes a conductive agent, which includes one or more of SuperP, acetylene black, Ketjen black, and carbon nanotubes.

[0022] In some embodiments of this application, the adhesive includes one or more of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.

[0023] A third aspect of this application provides a battery comprising a negative electrode sheet prepared by the method of preparing the negative electrode sheet provided in the first aspect or the method of preparing the negative electrode sheet provided in the second aspect.

[0024] The fourth aspect of this application provides an electrical device, which includes the battery provided in the third aspect. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a negative electrode sheet provided in an embodiment of this application.

[0026] Figure 2 This is a schematic diagram of the cross-sectional structure of the modified inorganic ion conductor in the negative electrode sheet provided in an embodiment of this application.

[0027] Explanation of icon numbers 100 - Negative electrode sheet; 10 - Current collector; 20 - Negative electrode active layer; 21 - First active sublayer; 22 - Second active sublayer; 23 - Third active sublayer; 201 - Negative electrode active material particles; 202 - Modified inorganic ionic conductor; 2021 - Inorganic ionic conductor body; 2022 - Carbon coating layer. Detailed Implementation

[0028] The present application will be further described in detail below with reference to preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0029] In this application, all technical terms have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this application.

[0030] With the widespread application of lithium-ion batteries in various fields, the requirements for their electrochemical performance, such as energy density and rate performance, are becoming increasingly stringent. However, some negative electrode active materials, such as graphite, have low lithium-ion diffusion coefficients. Especially under high-rate charge and discharge conditions, slow ion transport can easily lead to increased electrode polarization, rapid capacity decay, and increased risk of lithium plating. To improve the energy density of lithium-ion batteries, the thickness of the negative electrode active layer is usually increased. However, as the thickness of the negative electrode active layer increases, the lithium-ion transport path is also lengthened, resulting in a further significant reduction in ion transport rate and efficiency, thereby further reducing the battery's rate performance.

[0031] Currently, to improve the rate performance of negative electrode sheets, existing technologies employ a method of coating the surface of the negative electrode active material particles with an inorganic ion conductor to construct a rapid surface ion transport channel. However, this method only provides a two-dimensional ion transport channel on the surface of the negative electrode active material particles. The path for lithium ions to enter the interior of the negative electrode active material particles from the electrolyte remains relatively long, resulting in slow ion transport speeds and making it difficult to provide good ion transport capabilities in the thickness direction of the negative electrode sheet. Furthermore, the preparation of a uniform and dense inorganic ion conductor coating layer requires complex processes and precise process control, increasing the difficulty and cost of fabrication. Therefore, there is an urgent need to provide a battery negative electrode sheet that combines excellent ionic conductivity, electronic conductivity, and high energy density.

[0032] See Figure 1 and Figure 2This application provides a negative electrode 100, which includes a current collector 10 and a negative electrode active layer 20 disposed on the surface of the current collector 10. The negative electrode active layer 20 includes negative electrode active material particles 201 and modified inorganic ion conductors 202. The modified inorganic ion conductors 202 include an inorganic ion conductor body 2021 and a carbon coating layer 2022 covering the surface of the inorganic ion conductor body 2021. The modified inorganic ion conductors 202 include one or more of one-dimensional modified inorganic ion conductor nanowires and two-dimensional modified inorganic ion conductor nanosheets. The ionic conductivity of the negative electrode active layer 20 gradually increases along the direction from the current collector 10 to the negative electrode active layer 20. This application introduces modified inorganic ionic conductors into the negative electrode active layer of the negative electrode sheet and sets a gradient ionic conductivity in the thickness direction of the negative electrode sheet. The one-dimensional nanowire and / or two-dimensional nanosheet modified inorganic ionic conductors overlap and cross each other in the negative electrode active layer, jointly constructing a continuous three-dimensional ion conduction network that runs through the negative electrode active layer. Lithium ions can bypass the slow diffusion path inside the battery active material and migrate rapidly inside the negative electrode active layer through this three-dimensional ion conduction network, reducing impedance and significantly improving the ion transport efficiency and ion transport speed of the negative electrode sheet in the thickness direction, thereby significantly improving the rate performance and cycle stability of the negative electrode sheet.

[0033] In this embodiment, along the thickness direction of the negative electrode sheet 100, the ionic conductivity of the negative electrode active layer 20 gradually increases from the side closer to the current collector 10 to the side farther away from the current collector 10. This application controls the gradient ionic conductivity along the thickness direction of the negative electrode sheet, resulting in a lower ionic conductivity on the side of the negative electrode active layer closer to the current collector and a higher ionic conductivity on the side closer to the current collector (closer to the separator and electrolyte). The side of the negative electrode active layer closer to the current collector mainly serves as an interface stabilization region, ensuring sufficient ionic conductivity for the negative electrode active material particles in the portion of the negative electrode active layer closer to the current collector while providing good electronic conduction efficiency and interfacial bonding performance. The side of the negative electrode active layer farther from the current collector mainly serves as an ion trapping region, which can quickly receive and trap ions from the electrolyte. The higher ionic conductivity maintains efficient ion transport, rapidly transferring lithium ions to the interior of the negative electrode sheet, reducing impedance, and improving rate performance. Through the aforementioned special gradient ion conductivity design, the ion conductivity of the negative electrode provided in this application is significantly improved and it has excellent interface stability, thereby improving the rate performance and cycle life of the battery.

[0034] In some embodiments of this application, the modified inorganic ion conductor 202 includes one or more of one-dimensional modified inorganic ion conductor nanowires and two-dimensional modified inorganic ion conductor nanosheets. In some embodiments of this application, the modified inorganic ion conductor in the negative electrode active layer is a one-dimensional modified inorganic ion conductor nanowire. In this application, one-dimensional modified inorganic ion conductor nanowires refer to modified inorganic ion conductors with a nanoscale one-dimensional morphology, including but not limited to nanowires, nanofilaments, and nanorods. In some embodiments of this application, the modified inorganic ion conductor in the negative electrode active layer is a two-dimensional modified inorganic ion conductor nanosheet. In this application, two-dimensional modified inorganic ion conductor nanosheets refer to modified inorganic ion conductors with a nanoscale two-dimensional morphology, including but not limited to layered and sheet-like structures; the shape of the two-dimensional modified inorganic ion conductor nanosheet is not specifically limited. In some embodiments of this application, the modified inorganic ion conductor in the negative electrode active layer is both one-dimensional modified inorganic ion conductor nanowires and two-dimensional modified inorganic ion conductor nanosheets.

[0035] This application selects one-dimensional nanowires and / or two-dimensional nanosheets as modified inorganic ionic conductors. Compared with spherical particles, these modified inorganic ionic conductors have lower surface energy, are less prone to agglomeration due to van der Waals forces, have better dispersibility, and are easier to disperse uniformly in the negative electrode active layer, thereby constructing a more continuous three-dimensional ion conduction network.

[0036] In this application, the modified inorganic ionic conductor 202 includes an inorganic ionic conductor body 2021 and a carbon coating layer 2022 covering the surface of the inorganic ionic conductor body 2021. In this application, the carbon coating layer 2022 can completely or partially cover the inorganic ionic conductor body 2021. In some embodiments of this application, the carbon coating layer 2022 completely covers the inorganic ionic conductor body 2021. In this application, the carbon coating layer 2022 can continuously or discontinuously cover the inorganic ionic conductor body 2021. In some embodiments of this application, the carbon coating layer 2022 continuously covers the inorganic ionic conductor body 2021. By selecting a carbon coating layer on the surface of the inorganic ionic conductor, this application serves two purposes: firstly, it acts as an "electron bridge," ensuring the integrity of the electron conduction network in the thickness direction of the negative electrode; secondly, it effectively isolates the inorganic ionic conductor body from contact with water, air, electrolyte, etc., thus avoiding side reactions to a certain extent.

[0037] In some embodiments of this application, the thickness of the carbon coating layer 2022 is 2 nm-10 nm. In some embodiments of this application, the thickness of the carbon coating layer 2022 can be, for example, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm. By controlling the thickness of the carbon coating layer on the surface of the inorganic ionic conductor within a suitable range, while ensuring that the modified inorganic ionic conductor provides a high ionic conductivity for the negative electrode active layer, it is possible to further improve the electronic contact at the interface, reduce the additional impedance generated by lithium-ion transport, and thus further improve the electronic conductivity of the negative electrode active layer.

[0038] In some embodiments of this application, the modified inorganic ionic conductor 202 can be prepared by, but is not limited to, chemical vapor deposition or liquid-phase coating-carbonization to form a carbon coating layer 2022 on the surface of the inorganic ionic conductor body 2021. In some embodiments of this application, the modified inorganic ionic conductor 202 is prepared by chemical vapor deposition. Specifically, for example, the inorganic ionic conductor body can be placed in a tube furnace, heated to 550°C-650°C under the protection of an inert gas (e.g., Ar), and then a carbon source gas (e.g., one or more of methane, acetylene, and ethylene) can be introduced. Finally, the mixture is cooled under an inert atmosphere to obtain the modified inorganic ionic conductor. In some embodiments of this application, the modified inorganic ionic conductor 202 is prepared by a liquid-phase coating-carbonization method. Specifically, for example, the inorganic ionic conductor bulk is dispersed in an aqueous or ethanol solution containing a carbon source (e.g., one or more of glucose, sucrose, polydopamine, and citric acid), mixed, evaporated and dried, and then subjected to heat treatment under an inert atmosphere to achieve carbonization, thereby obtaining the modified inorganic ionic conductor. In some embodiments, the heat treatment time is 600℃-700℃ for 1 h-2 h. In some specific embodiments, operations including but not limited to stirring and ultrasonic treatment can be used when dispersing the inorganic ionic conductor bulk to further improve the dispersion uniformity of the inorganic ionic conductor bulk in the solution and avoid agglomeration as much as possible, and further improve the coating uniformity of the carbon coating layer.

[0039] In some embodiments of this application, the modified inorganic ion conductors 202 in the negative electrode active layer 20 form a three-dimensional ion conduction network, and the negative electrode active material particles 201 are distributed in the pores of this three-dimensional ion conduction network. The linear or filamentous modified inorganic ion conductors in the negative electrode active layer interweave between the negative electrode active particles and overlap to form a three-dimensional ion conduction network penetrating the interior of the negative electrode sheet. This enables three-dimensional ion transport within the negative electrode sheet, significantly improving ion conductivity and reducing the battery's internal resistance, thereby reducing the polarization voltage and lithium plating risk of the negative electrode sheet during fast charging. Furthermore, the distribution of the negative electrode active material particles in the pores of this three-dimensional ion conduction network allows the modified inorganic ion conductors to physically separate the negative electrode active material particles, preventing excessively dense stacking of the particles and providing sufficient space for electrolyte wetting and ion migration.

[0040] In some embodiments of this application, the ionic conductivity of the negative electrode active layer 20 is 10. -6 S / cm-10 -3 S / cm. In some specific embodiments, the ionic conductivity of the negative electrode active layer 20 may be, for example, 10. -6 S / cm, 2×10 -6 S / cm, 4×10 -6 S / cm, 5×110 -6 S / cm, 6×10 -6 S / cm, 8×10 -6 S / cm, 10 -5 S / cm, 2×10 -5 S / cm, 4×10 -5 S / cm, 5×10 -5 S / cm, 6×10 -5 S / cm, 8×10 -5 S / cm, 10 -4 S / cm, 2×10 -4 S / cm, 4×10 -4 S / cm, 5×10 -4 S / cm, 6×10 -4 S / cm, 8×10 -4 S / cm, 10 -3 S / cm. By controlling the ionic conductivity of the negative electrode active layer within the above range, good ionic conductivity can be provided for the negative electrode active layer.

[0041] In some embodiments of this application, along the direction from the current collector 10 to the negative electrode active layer 20, the ionic conductivity of the negative electrode active layer 20 increases from 10... -6 S / cm-10 -5 S / cm increases to 10 -4 S / cm-10 -3S / cm. That is to say, the minimum ionic conductivity of the negative electrode active layer 20 is 10. -6 S / cm-10 -5 S / cm, the maximum ionic conductivity is 10. -4 S / cm-10 -3 S / cm, along the thickness direction of the negative electrode, the ionic conductivity of the active sublayer shows an increase from 10. -6 S / cm-10 -5 S / cm increases to 10 -4 S / cm-10 -3 The trend of S / cm. By further limiting the above parameters, the gradient change of ionic conductivity of the negative electrode active layer can be further controlled, the electronic conductivity and interfacial bonding stability of the active sublayer near the current collector can be further improved, and the capture and transport effect of lithium ions on the active sublayer away from the current collector can be further improved.

[0042] In some embodiments of this application, the mass percentage of the modified inorganic ionic conductor 202 in the negative electrode active layer 20 is 0.5%-15%. In some specific embodiments, the mass percentage of the modified inorganic ionic conductor 202 in the negative electrode active layer 20 can be, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, 12%, 13%, 14%, or 15%. By controlling the mass percentage of the modified inorganic ionic conductor in the negative electrode active layer, the ionic conductivity and electronic conductivity of the negative electrode sheet can be further controlled.

[0043] In some embodiments of this application, the negative electrode active layer 20 includes at least two active sublayers sequentially stacked on the surface of the current collector 10. In some specific embodiments, the number of active sublayers in the negative electrode active layer 20 may be, for example, 2, 3, 4, or 5.

[0044] In some embodiments of this application, along the direction from the current collector 10 to the negative electrode active layer 20, the mass percentage of the modified inorganic ion conductor 202 in the negative electrode active layer 20 increases from 0.1%-0.7% to 0.9%-2%. In other words, the minimum mass percentage of modified inorganic ionic conductors 202 in any active sublayer of the negative electrode active layer 20 is 0.1%-0.7%, specifically, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or 0.7%; the maximum mass percentage of modified inorganic ionic conductors 202 in any active sublayer of the negative electrode active layer 20 is 0.9%-2%, specifically, for example, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%. Along the thickness direction of the negative electrode sheet 100, the mass percentage of modified inorganic ionic conductors 202 in the negative electrode active layer 20 shows a trend of increasing from 0.1%-0.7% to 0.9%-2%. By further adjusting the content of modified inorganic ionic conductors in the negative electrode active layer, the ionic conductivity gradient of the negative electrode active layer can be further controlled.

[0045] In some embodiments of this application, the negative electrode active layer 20 includes at least two active sublayers sequentially stacked on the surface of the current collector 10, wherein the ionic conductivity of the active sublayer closest to the current collector 10 is 10. -6 S / cm-10 -5 The ionic conductivity of the active sublayer 10 Ω / cm, located 10 Ω from the current collector, is 10 Ω / cm. -4 S / cm-10 -3 S / cm.

[0046] In some embodiments of this application, the ratio of the ionic conductivity of the active sublayer farthest from the current collector 10 to the ionic conductivity of the active sublayer closest to the current collector 10 is greater than or equal to 10. In some embodiments, the ratio of the ionic conductivity of the active sublayer farthest from the current collector 10 to the ionic conductivity of the active sublayer closest to the current collector 10 is 20-100. In some specific embodiments, the ratio of the ionic conductivity of the active sublayer farthest from the current collector 10 to the ionic conductivity of the active sublayer closest to the current collector 10 can be, for example, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100. By controlling the ratio of the ionic conductivity of the active material layer closest to the current collector and the active sublayer closest to the separator within a suitable range, the gradient change of the ionic conductivity of the negative electrode active layer can be further regulated as a whole, and a stronger driving force can be provided for ion transport.

[0047] like Figure 1As shown, taking the negative electrode 100 as an example, the negative electrode active layer 20 includes three active sublayers sequentially stacked on the surface of the current collector 10, namely, the first active sublayer 21, the second active sublayer 22, and the third active sublayer 23. Among them, the first active sublayer 21 has the lowest ionic conductivity, the third active sublayer 23 has the highest ionic conductivity, and the ratio of the ionic conductivity of the third active sublayer 23 to that of the first active sublayer 21 is greater than or equal to 10.

[0048] In some embodiments of this application, the absolute value of the difference in ionic conductivity between any two adjacent active sublayers is 1 × 10⁻⁶. -4 S / cm - 8.9 × 10 -3 S / cm. In some specific embodiments, the absolute value of the difference in ionic conductivity between any two adjacent active sublayers can be, for example, 1 × 10⁻⁶. -4 S / cm, 2×10 -4 S / cm, 3×10 -4 S / cm, 4×10 -4 S / cm, 5×10 -4 S / cm, 6×10 -4 S / cm, 7×10 -4 S / cm, 8×10 -4 S / cm, 9×10 -4 S / cm, 1×10 -3 S / cm, 2×10 -3 S / cm, 3×10 -3 S / cm, 4×10 -3 S / cm, 5×10 -3 S / cm, 6×10 -3 S / cm, 7×10 -3 S / cm, 8×10 -3 S / cm, 8.9×10 -3 S / cm. By further controlling the difference in ionic conductivity between adjacent active sublayers, the ion transport efficiency and continuity in the thickness direction of the negative electrode can be further improved.

[0049] In some embodiments of this application, the mass percentage of modified inorganic ion conductor 202 in the active sublayer farthest from the current collector 10 is (1.02-3):1 to the mass percentage of modified inorganic ion conductor 202 in the active sublayer closest to the current collector 10. In some specific embodiments, the mass percentage of modified inorganic ion conductor 202 in the active sublayer farthest from the current collector 10 is, for example, 1.02:1, 1.1:1, 1.2:1, 1.4:1, 1.5:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, or 3:1. By further controlling the content of modified inorganic ionic conductors in different active sublayers, the gradient change of ionic conductivity of the negative electrode active layer can be further regulated.

[0050] In some embodiments of this application, the absolute value of the difference in the mass percentage content of modified inorganic ionic conductors in any two adjacent active sublayers is 0.1%-1.2%. In some specific embodiments, the absolute value of the difference in the mass percentage content of modified inorganic ionic conductors in any two adjacent active sublayers can be, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, or 1.2%. By further controlling the difference in the content of modified inorganic ionic conductors in adjacent active sublayers, the difference in electronic conductivity between adjacent active sublayers can be further controlled.

[0051] In some embodiments of this application, the inorganic ionic conductor body includes one or more of LLZO, LATP, LAGP, LGPS, LLTO, Li3YCl3Br3, Li3YCl6, and Li3YBr6. In these embodiments, the negative electrode active layer may include only one modified inorganic ionic conductor, or it may include two or more different modified inorganic ionic conductors. In some specific embodiments of this application, the inorganic ionic conductor body may be, for example, one or more of LLZO, Li3YCl3Br3, Li3YCl6, and Li3YBr6. By further selecting the above-mentioned inorganic ionic conductor body that is compatible with low potential, the possibility of its reduction can be avoided to a certain extent, thereby further improving the stability of the modified inorganic ionic conductor body.

[0052] In this application, LLZO specifically refers to lithium lanthanum zirconate, with the chemical formula Li7La3Zr2O. 12 LATP specifically refers to lithium titanium aluminum phosphate, with the chemical formula Li. 1+x Al x Ti 2-x(PO4)3, where 0 < x ≤ 0.5; LAGP specifically refers to lithium aluminum germanium phosphate, with the chemical formula Li 1+ x Al x Ge 2-x (PO4)3, where 0 < x ≤ 0.8; LGPS specifically refers to lithium germanium phosphorus sulfide, with the chemical formula Li 10 GeP2S 12 ; LLTO specifically refers to lithium lanthanum titanate, with the chemical formula Li 3x La 2 / 3-x TiO3, where x ≈ 0.1. By selecting the above-mentioned inorganic ion conductor body with higher ionic conductivity, the ionic conductivity of the negative electrode sheet can be further improved.

[0053] In some embodiments of the present application, the aspect ratio of the one-dimensional modified inorganic ion conductor nanowire is greater than or equal to 20. In some embodiments, the aspect ratio of the one-dimensional modified inorganic ion conductor nanowire is 20 - 200. In some specific embodiments, the aspect ratio of the one-dimensional modified inorganic ion conductor nanowire can be, for example, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200. By further controlling the aspect ratio of the one-dimensional modified inorganic ion conductor nanowire, the contact between the modified inorganic ion conductors can be further improved, thereby further improving the density and continuity of the three-dimensional ionic conduction network and the three-dimensional electronic conduction network, further improving the ionic conductivity and electronic conductivity of the negative electrode sheet, and further improving the rate performance and cycle life of the battery.

[0054] In some embodiments of this application, the diameter of the one-dimensional modified inorganic ionic conductor nanowire is 5 nm-1000 nm. In some specific embodiments, the diameter of the one-dimensional modified inorganic ionic conductor nanowire can be, for example, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 60 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, or 1000 nm. In some embodiments of this application, the thickness of the two-dimensional modified inorganic ionic conductor nanosheet is 5 nm-1000 nm. In some specific embodiments, the thickness of the two-dimensional modified inorganic ion conductor nanosheets can be, for example, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 60 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, or 1000 nm. By further limiting the diameter of the two-dimensional modified inorganic ion conductor nanowires or the thickness of the two-dimensional modified inorganic ion conductor nanosheets, on the one hand, the decrease in ionic conductivity caused by the quantum confinement effect can be effectively avoided, while ensuring sufficient mechanical strength; on the other hand, the modified inorganic ion conductors can also have a large specific surface area, providing abundant ion transport interfaces for three-dimensional ion transport networks.

[0055] In some embodiments of this application, the length of the one-dimensional modified inorganic ion conductor nanowire is 1 μm-50 μm. In some specific embodiments, the length of the one-dimensional modified inorganic ion conductor nanowire can be, for example, 1 μm, 2 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm. By setting the length of the one-dimensional modified inorganic ion conductor nanowire within the above-mentioned suitable range, a single one-dimensional modified inorganic ion conductor nanowire can simultaneously connect multiple negative electrode active particles, further improving the integrity and continuity of the ion transport network and further reducing the tortuosity of the ion transport network.

[0056] In some embodiments of this application, the negative electrode active material particles include graphite. By selecting graphite, which has excellent conductivity, as the active material of the negative electrode sheet, the negative electrode active material particles themselves can serve as a good electron transport network substrate for the negative electrode sheet. This eliminates the need for an additional electron transport network to occupy space that would otherwise be used for the ion transport network, thus providing sufficient space for electrolyte wetting and ion migration. In other embodiments of this application, the negative electrode active material particles also include silicon material.

[0057] In some embodiments of this application, the mass percentage of negative electrode active material particles in the negative electrode active layer is 92%-98%. In some specific embodiments, the mass percentage of negative electrode active material particles in the negative electrode active layer may be, for example, 92%, 93%, 94%, 95%, 96%, 97%, or 98%. By further controlling the content of negative electrode active material particles in the negative electrode active layer within the above-mentioned suitable range, the energy density of the negative electrode sheet can be further improved.

[0058] This application involves a special design of the modified inorganic ionic conductor in the negative electrode and the setting of a gradient ionic conductivity along the thickness direction of the negative electrode. The ion transport network and electron transport network in the negative electrode do not interfere with each other, and the "ion-electron" synergistic effect of the negative electrode is achieved. This allows the negative electrode to significantly improve its ionic conductivity and overall stability while ensuring good electronic conductivity and high energy density. Its application in batteries can significantly improve the rate performance and cycle life of the battery.

[0059] This application also provides a method for preparing the negative electrode sheet described above, comprising: A negative electrode active layer is formed by coating a negative electrode slurry onto the surface of the current collector, thus obtaining a negative electrode sheet.

[0060] In some embodiments of this application, the method for preparing the negative electrode sheet includes: S101. A negative electrode slurry is coated on the surface of the current collector to obtain a negative electrode precursor. S102. The negative electrode precursor is dried and rolled to obtain a negative electrode sheet. The negative electrode sheet includes a current collector and a negative electrode active layer disposed on the surface of the current collector. The ionic conductivity of the negative electrode active layer gradually increases along the direction from the current collector to the negative electrode active layer.

[0061] In step S101, the negative electrode slurry includes negative electrode active material particles and modified inorganic ion conductors; the modified inorganic ion conductor includes an inorganic ion conductor body and a carbon coating layer covering the surface of the inorganic ion conductor body, and the modified inorganic ion conductor includes one or more of one-dimensional modified inorganic ion conductor nanowires and two-dimensional modified inorganic ion conductor nanosheets.

[0062] In some embodiments of this application, coating the current collector surface with a negative electrode slurry to form a negative electrode active layer may include: S201. The negative electrode slurry includes at least two composite negative electrode slurries. Each composite negative electrode slurry includes negative electrode active material particles and modified inorganic ion conductors. The mass percentage of modified inorganic ion conductors in the at least two composite negative electrode slurries is different. S202. At least two composite negative electrode slurries are sequentially layered and coated on the surface of the current collector in order of increasing mass percentage of modified inorganic ionic conductors.

[0063] In some embodiments of this application, the types of composite negative electrode slurry can be, for example, two, three, four, or five. In some embodiments of this application, the selection of modified inorganic ion conductors in different composite negative electrode slurries can be the same or different. In some specific embodiments of this application, there are three types of composite negative electrode slurry: a first composite negative electrode slurry, a second active negative electrode slurry, and a third active negative electrode slurry. Specifically, the first composite negative electrode slurry contains a modified inorganic ion conductor with a mass percentage greater than 0 and less than or equal to 2%; the second composite negative electrode slurry contains a modified inorganic ion conductor with a mass percentage greater than 2 and less than or equal to 5%; and the third composite negative electrode slurry contains a modified inorganic ion conductor with a mass percentage greater than 5 and less than or equal to 10%.

[0064] In step S202, at least two composite negative electrode slurries are sequentially layered and coated on the surface of the current collector in order of increasing mass percentage of modified inorganic ionic conductors. This can be done by coating the composite negative electrode slurries one by one, baking them to a semi-dry state (non-flowing and non-sticky), and then coating the next layer and baking it to a semi-dry state until all composite negative electrode slurries are coated.

[0065] In some embodiments of this application, the preparation of each composite negative electrode slurry includes: S301. Add the modified inorganic ionic conductor to the first solvent to obtain a mixed solution of the modified inorganic ionic conductor; S302. Add the negative electrode active material particles to the second solvent to obtain the negative electrode active slurry; S303. A composite negative electrode slurry is obtained by mixing a modified inorganic ionic conductor mixed solution with a negative electrode active slurry.

[0066] In step S301, the first solvent includes, but is not limited to, water; specifically, it may be, for example, deionized water.

[0067] In some embodiments of this application, adding the inorganic ionic conductor to the first solvent further includes a stirring and dispersion treatment. In some embodiments, the stirring and dispersion treatment causes the modified inorganic ionic conductor and the first solvent to form a stable and homogeneous mixed solution of the modified inorganic ionic conductor under strong shear force. In some embodiments of this application, the stirring and dispersion treatment is carried out in a stirring tank at a speed of 300 rpm to 3500 rpm for a duration of 15 min to 120 min. In some specific embodiments, the stirring and dispersion speed can be, for example, 300 rpm, 500 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, 1800 rpm, 2000 rpm, 2400 rpm, 2500 rpm, 2800 rpm, 3000 rpm, 3200 rpm, or 3500 rpm; the stirring and dispersion time can be, for example, [missing information]. In some embodiments of this application, adding the inorganic ionic conductor to the first solvent further includes ultrasonic treatment. In some embodiments, the frequency of the ultrasonic treatment is 20 kHz to 40 kHz. In some specific embodiments, the ultrasonic treatment frequencies are 20 kHz, 22 kHz, 24 kHz, 25 kHz, 26 kHz, 28 kHz, 30 kHz, 32 kHz, 34 kHz, 35 kHz, 36 kHz, 38 kHz, and 40 kHz. In some embodiments, after every 3 minutes of ultrasonic treatment, the mixture is allowed to stand for 2 minutes, and this ultrasonic treatment is repeated multiple times until the modified inorganic ionic conductor mixture is uniformly dispersed. Further employing stirring dispersion treatment and / or ultrasonic treatment can further improve the dispersion uniformity of the modified inorganic ionic conductor in the modified inorganic ionic conductor mixture, further improve the uniformity and stability of the modified inorganic ionic conductor mixture, and effectively inhibit the aggregation of the modified inorganic ionic conductor.

[0068] In some embodiments of this application, the modified inorganic ionic conductor mixed solution further includes a surface modifier, specifically, one or more of a dispersant, surfactant, and silane coupling agent. By selecting the above-mentioned surface modifier, the surface of the modified inorganic ionic conductor can be further modified, imparting surface charge or functional groups to it and increasing its compatibility with the solvent. In some specific embodiments of this application, the surface modifier may be, for example, citric acid. Citric acid can achieve electrostatic stabilization, giving the surface of the modified inorganic ionic conductor a strong negative charge under alkaline conditions. Through its carboxylic acid complexing or ion exchange with the metal sites (e.g., La and Zr in LLZO) on the surface of the modified inorganic ionic conductor, the surface becomes negatively charged, thereby avoiding the adsorption and aggregation of the modified inorganic ionic conductor to a certain extent. In some embodiments, the modified inorganic ionic conductor mixed solution includes citric acid, and the pH value of the modified inorganic ionic conductor mixed solution is 9-10.

[0069] In some embodiments, the dispersant may be one or more of polyvinylpyrrolidone (PVP), KH-550, KH-560, and KH-570. The dispersant can further improve the dispersibility of the modified inorganic ionic conductor in the mixed solution, thereby further improving the homogeneity and stability of the modified inorganic ionic conductor mixed solution and effectively inhibiting the aggregation of the modified inorganic ionic conductor. In some embodiments, the surfactant may be a nonionic surfactant, specifically, for example, PVP. By selecting a suitable surfactant, its steric hindrance effect can be effectively utilized, and it can be oriented and adsorbed at the solid-liquid interface, thereby further improving the homogeneity and stability of the modified inorganic ionic conductor mixed solution. In some embodiments, the silane coupling agent includes, but is not limited to, one or more of KH-560, KH-550, and KH-570. The epoxy groups of the above-mentioned silane coupling agents are relatively stable to water. One end can bond with modified inorganic ionic conductors, while the epoxy group at the other end has high reactivity and can react with carboxyl groups, amino groups, etc., or fix other components in the polymer network formed by crosslinking of silane coupling agents.

[0070] In step S302, the second solvent includes, but is not limited to, water. In some embodiments, the solid content of the negative electrode active material particles in the negative electrode active slurry is 70%-75%. In some specific embodiments, the solid content of the negative electrode active material particles in the negative electrode active slurry can be, for example, 70%, 71%, 72%, 73%, 74%, or 75%. By mixing the negative electrode active slurry with the second solvent first, pre-wetting is achieved, forming a low-solids slurry, thus avoiding hard agglomeration caused by direct mixing of the negative electrode active material particle powder with the modified inorganic ionic conductor mixed solution.

[0071] In step S303, when mixing the modified inorganic ionic conductor mixed solution and the negative electrode active slurry, the mixing operation can be one or more of the following: stirring, dispersing, etc. Through the above operations, one-dimensional nanowire and / or two-dimensional nanosheet modified inorganic ionic conductors can be inserted into and attached to the surface and gaps of the negative electrode active particles, and then dried to obtain a complete and continuous three-dimensional network structure. In some embodiments of this application, the operation of mixing the modified inorganic ionic conductor mixed solution and the negative electrode active slurry can be, for example, by slowly adding the modified inorganic ionic conductor mixed solution to the negative electrode active slurry under continuous dispersion conditions, so that the modified inorganic ionic conductors are uniformly dispersed and inserted between the negative electrode active particles.

[0072] In some embodiments of this application, the composite negative electrode slurry further includes a conductive agent. In some specific embodiments, the conductive agent may be one or more of Super P, acetylene black, Ketjen black, and carbon nanotubes. Adding a suitable conductive agent can further improve the electronic conductivity of the negative electrode sheet. In embodiments of this application, the conductive agent may be added during the mixing of the modified inorganic ionic conductor mixed solution and the negative electrode active slurry, or it may be added after the mixing of the modified inorganic ionic conductor mixed solution and the negative electrode active slurry.

[0073] In some embodiments of this application, the mass percentage of the conductive agent in the composite negative electrode slurry is 0.1%-5%. In some specific embodiments, the mass percentage of the conductive agent in the composite negative electrode slurry can be, for example, 0.1%, 0.3%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.7%, 1.9%, 2%, 2.1%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. By further controlling the content of the conductive agent in the composite negative electrode slurry within the above-mentioned suitable range, the electronic conductivity is further improved while ensuring that the negative electrode sheet has a high energy density.

[0074] In some embodiments of this application, the composite negative electrode slurry further includes a binder. In some specific embodiments, the binder may be one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA). In some specific embodiments of this application, the binder is sodium carboxymethyl cellulose and styrene-butadiene rubber. By adding a suitable binder, the components in the negative electrode active layer can be effectively connected, and the bonding force between the negative electrode active layer and the current collector can be improved, as well as the coating performance of the composite negative electrode slurry can be enhanced. In some embodiments of this application, the binder is added after the modified inorganic ion conductor mixed solution and the negative electrode active slurry are mixed. Adding the binder too early will cause the modified inorganic ion conductor to combine with the binder first. The binder will preferentially adsorb and coat the surface of the modified inorganic ion conductor, resulting in ion transport blockage. Moreover, the huge viscous resistance will severely weaken the transmission of shear force, causing a large amount of modified inorganic ion conductor to agglomerate, making it impossible to achieve uniform dispersion, which is not conducive to the subsequent construction of a three-dimensional ion conduction network.

[0075] In some embodiments of this application, the mass percentage of the binder in the composite negative electrode slurry is 1%-2%. In some specific embodiments, the mass percentage of the binder in the composite negative electrode slurry can be, for example, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%. By further controlling the content of the binder in the composite negative electrode slurry within a suitable range, the coating performance of the composite negative electrode slurry can be further improved while ensuring good bonding between the components.

[0076] The method for preparing the negative electrode provided in this application is simple, low-cost, and has controllable parameters, making it suitable for large-scale industrial production.

[0077] This application also provides a battery comprising a positive electrode, a negative electrode, a separator and an electrolyte located between the positive and negative electrodes, wherein the negative electrode is the aforementioned negative electrode. In some embodiments of this application, the battery may be a lithium-ion battery. By selecting a negative electrode containing the negative electrode provided in this application, the overall electrochemical performance and cycle life of the battery can be significantly improved.

[0078] This application also provides an electrical device that includes the battery described above. This electrical device may be, for example, an electric vehicle, a mobile phone, a tablet computer, a laptop computer, a wearable device (watch, bracelet), a digital camera, etc.

[0079] The present application will be further described below with reference to several embodiments: Example 1 (1) 80 g of one-dimensional modified inorganic ion conductor nanowires (average length 30 μm, average diameter 600 nm, aspect ratio 50) with LLZO as the main body and a carbon coating layer thickness of 5 nm were added to a binder containing 32 g of sodium carboxymethyl cellulose (CMC). After stirring and mixing evenly, the nanowires were added to 1103.4 mL of deionized water, and 16 g of polyvinylpyrrolidone (PVP) dispersant was added. The nanowires were stirred and dispersed to obtain a modified inorganic ion conductor mixed solution. 1472 g of graphite, the negative electrode active material, was added to 1103.4 mL of deionized water to obtain a negative electrode active slurry. The modified inorganic ion conductor mixed solution and the negative electrode active slurry were mixed to prepare the first composite negative electrode slurry. (2) Repeat the operation of (1), except that the mass of the one-dimensional modified inorganic ion conductor nanowire is 40 g; and the second composite negative electrode slurry is prepared. (3) Repeat the operation of (1), except that the mass of the one-dimensional modified inorganic ionic conductor nanowire is 10 g; and the third composite negative electrode slurry is prepared. (4) First, a third composite negative electrode slurry is coated on the surface of the copper foil of the negative electrode current collector, and then vacuum-baked in a 100°C oven for 3 hours to form a negative electrode. Then, a second composite negative electrode slurry is coated on the surface of the third composite negative electrode slurry, and then vacuum-baked in a 100°C oven for 3 hours. Then, a first composite negative electrode slurry is coated on the surface of the second composite negative electrode slurry, and then vacuum-baked in a 100°C oven for 3 hours. After rolling, a negative electrode sheet is obtained.

[0080] Example 2 The only difference from Example 1 is that the one-dimensional modified inorganic ionic conductor nanowires are replaced with two-dimensional modified inorganic ionic conductor nanosheets (average thickness of 600 nm, average lateral dimension of 30 μm, and aspect ratio of 50).

[0081] Example 3 (1) 80 g of one-dimensional modified inorganic ion conductor nanowires (average length 30 μm, average diameter 600 nm, aspect ratio 50) with LLZO as the bulk inorganic ion conductor and a carbon coating thickness of 5 nm as the carbon coating layer were added to 32 g of binder CMC. After stirring and mixing evenly, the nanowires were added to 1103.4 mL of deionized water and 16 g of dispersant PVP were added. The nanowires were stirred and dispersed to obtain a modified inorganic ion conductor mixed solution. 1472 g of negative electrode active material graphite was added to 1103.4 mL of deionized water to obtain a negative electrode active slurry. The modified inorganic ion conductor mixed solution and the negative electrode active slurry were mixed to prepare the first composite negative electrode slurry. (2) Repeat the operation of (1), except that the mass of the one-dimensional modified inorganic ionic conductor nanowire is 10 g; and the second composite negative electrode slurry is prepared. (3) First, a second composite negative electrode slurry is coated on the surface of the copper foil of the negative electrode current collector, and then it is placed in a 100°C oven and vacuum baked for 3 hours to form a negative electrode sheet. Then, a first composite negative electrode slurry is coated on the surface of the second composite negative electrode slurry, and then it is placed in a 100°C oven and vacuum baked for 3 hours. After rolling, a negative electrode sheet is obtained.

[0082] Example 4 (1) 80 g of one-dimensional modified inorganic ion conductor nanowires (average length 30 μm, average diameter 600 nm, aspect ratio 50) with LLZO as the inorganic ion conductor body and a carbon coating layer thickness of 5 nm were added to 32 g of binder CMC. After stirring and mixing evenly, the nanowires were added to 1103.4 mL of deionized water and 16 g of dispersant PVP were added. The nanowires were stirred and dispersed to obtain a modified inorganic ion conductor mixed solution. 1472 g of negative electrode active material graphite was added to 1103.4 mL of deionized water to obtain a negative electrode active slurry. The modified inorganic ion conductor mixed solution and the negative electrode active slurry were mixed to prepare the first composite negative electrode slurry. (2) Repeat the operation of (1), except that the mass of the one-dimensional modified inorganic ion conductor nanowire is 60 g; and the second composite negative electrode slurry is prepared. (3) Repeat the operation of (1), except that the mass of the one-dimensional modified inorganic ionic conductor nanowire is 40 g; and the third composite negative electrode slurry is prepared. (3) Repeat the operation of (1), except that the mass of the one-dimensional modified inorganic ion conductor nanowire is 10 g; and the fourth composite negative electrode slurry is prepared. (5) First, a fourth composite negative electrode slurry is coated on the surface of the copper foil of the negative electrode current collector, and then vacuum-baked in a 100°C oven for 3 hours to form a negative electrode. Then, a third composite negative electrode slurry is coated on the surface of the fourth composite negative electrode slurry, and then vacuum-baked in a 100°C oven for 3 hours. Then, a second composite negative electrode slurry is coated on the surface of the third composite negative electrode slurry, and then vacuum-baked in a 100°C oven for 3 hours. Then, a first composite negative electrode slurry is coated on the surface of the second composite negative electrode slurry, and then vacuum-baked in a 100°C oven for 3 hours. After rolling, a negative electrode sheet is obtained.

[0083] Example 5 The only difference from Example 1 is that the inorganic ionic conductor body is Li. 1.5 Al 0.5 Ge 1.5 (PO4)3.

[0084] Example 6 The only difference from Example 1 is that the inorganic ionic conductor body is Li3YCl6.

[0085] Example 7 (1) 80 g of one-dimensional modified inorganic ion conductor nanowires (average length 30 μm, average diameter 600 nm, aspect ratio 50) with LLZO as the bulk inorganic ion conductor and a carbon coating thickness of 5 nm as the carbon coating layer were added to 32 g of binder CMC. After stirring and mixing evenly, the nanowires were added to 1103.4 mL of deionized water and 16 g of dispersant PVP were added. The nanowires were stirred and dispersed to obtain a modified inorganic ion conductor mixed solution. 1472 g of negative electrode active material graphite was added to 1103.4 mL of deionized water to obtain a negative electrode active slurry. The modified inorganic ion conductor mixed solution and the negative electrode active slurry were mixed to prepare the first composite negative electrode slurry. (2) Repeat the operation of (1), except that the mass of the one-dimensional modified inorganic ion conductor nanowire is 50 g; and the second composite negative electrode slurry is prepared. (3) Repeat the operation of (1), except that the mass of the one-dimensional modified inorganic ion conductor nanowire is 20 g; and the third composite negative electrode slurry is prepared. (4) First, a third composite negative electrode slurry is coated on the surface of the copper foil of the negative electrode current collector, and then vacuum-baked in a 100°C oven for 3 hours to form a negative electrode. Then, a second composite negative electrode slurry is coated on the surface of the third composite negative electrode slurry, and then vacuum-baked in a 100°C oven for 3 hours. Then, a first composite negative electrode slurry is coated on the surface of the second composite negative electrode slurry, and then vacuum-baked in a 100°C oven for 3 hours. After rolling, a negative electrode sheet is obtained.

[0086] Example 8 The only difference from Example 1 is that the one-dimensional modified inorganic ionic conductor nanowire has an average length of 30 μm, an average diameter of 200 nm, and an aspect ratio of 150.

[0087] Comparative Example 1 (1) 80 g of one-dimensional modified inorganic ion conductor nanowires (average length 30 μm, average diameter 600 nm, aspect ratio 50) with LLZO as the bulk inorganic ion conductor and a carbon coating thickness of 5 nm were added to 32 g of binder CMC. After stirring and mixing evenly, the nanowires were added to 1103.4 mL of deionized water and 16 g of dispersant PVP were added. The nanowires were stirred and dispersed to obtain a modified inorganic ion conductor mixed solution. 1472 g of negative electrode active material graphite was added to 1103.4 mL of deionized water to obtain a negative electrode active slurry. The modified inorganic ion conductor mixed solution and the negative electrode active slurry were mixed to prepare a composite negative electrode slurry. (2) A composite negative electrode slurry is coated on the surface of the copper foil of the negative electrode current collector, and then vacuum baked in an oven at 100°C for 3 hours. After rolling, a negative electrode sheet is obtained.

[0088] Comparative Example 2 (1) 80 g of one-dimensional modified inorganic ion conductor nanowires (average length 30 μm, average diameter 600 nm, aspect ratio 50) with LLZO as the bulk inorganic ion conductor and a carbon coating thickness of 5 nm as the carbon coating layer were added to 32 g of binder CMC. After stirring and mixing evenly, the nanowires were added to 1103.4 mL of deionized water and 16 g of dispersant PVP were added. The nanowires were stirred and dispersed to obtain a modified inorganic ion conductor mixed solution. 1472 g of negative electrode active material graphite was added to 1103.4 mL of deionized water to obtain a negative electrode active slurry. The modified inorganic ion conductor mixed solution and the negative electrode active slurry were mixed to prepare the first composite negative electrode slurry. (2) Repeat the operation of (1), except that the mass of the one-dimensional modified inorganic ion conductor nanowire is 40 g; and the second composite negative electrode slurry is prepared. (3) Repeat the operation of (1), except that the mass of the one-dimensional modified inorganic ionic conductor nanowire is 10 g; and the third composite negative electrode slurry is prepared. (4) First, a first composite negative electrode slurry is coated on the surface of the copper foil of the negative electrode current collector, and then vacuum-baked in a 100°C oven for 3 hours to form a negative electrode. Then, a second composite negative electrode slurry is coated on the surface of the first composite negative electrode slurry, and then vacuum-baked in a 100°C oven for 3 hours. Then, a third composite negative electrode slurry is coated on the surface of the second composite negative electrode slurry, and then vacuum-baked in a 100°C oven for 3 hours. After rolling, a negative electrode sheet is obtained.

[0089] Comparative Example 3 The only difference from Example 1 is that the one-dimensional modified inorganic ionic conductor nanowires do not have a carbon coating layer.

[0090] Performance testing Resistivity: The resistivity of the negative electrode sheets prepared in Examples 1-8 and Comparative Examples 1-3 was measured using a four-probe resistance meter. The results are shown in Table 1.

[0091] Ionic conductivity: The ionic conductivity of the blocked symmetric cells assembled from the negative electrode sheets prepared by Examples 1-8 and Comparative Examples 1-3 was measured using an electrochemical workstation. The results are shown in Table 1.

[0092] Electrochemical performance testing: The negative and positive electrode sheets (the positive electrode material is lithium iron phosphate), separators, and electrolytes (including ethylene carbonate, ethyl acetate, lithium hexafluorophosphate, and vinylene carbonate) prepared in Examples 1-8 and Comparative Examples 1-3 were assembled into batteries. The discharge DCR (Direct Current Resistance) of the batteries was measured under the conditions of 50% SOC, 1C, and 10s. The results are shown in Table 1. The capacity of the batteries was measured before and after 200 cycles at 25°C and 1C-1C. The capacity retention rate was calculated. The results are shown in Table 1.

[0093] Table 1

[0094] As can be seen from the data in Table 1, compared with Comparative Examples 1 and 2, Examples 1-8 of this application significantly optimized the internal ion transport path of the electrode through the design of an ion conductivity gradient in a suitable direction, thereby improving the ion conductivity of the negative electrode and enhancing the rate performance and cycle performance of the battery. Compared with Comparative Example 3, Examples 1-8 of this application significantly reduced resistivity and improved the cycle stability of the battery by carbon coating the surface of the inorganic ion conductor.

[0095] The preferred embodiments have been described in detail above, but the present invention is not limited to the specific implementation methods described above. Those skilled in the art can make various specific modifications under the guidance of this application without departing from the scope of protection of this application, and these modifications all fall within the scope of protection of the present invention.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode includes a current collector and a negative electrode active layer disposed on the surface of the current collector. The negative electrode active layer includes negative electrode active material particles and a modified inorganic ion conductor. The modified inorganic ion conductor includes an inorganic ion conductor body and a carbon coating layer covering the surface of the inorganic ion conductor body. The modified inorganic ion conductor includes one or more of one-dimensional modified inorganic ion conductor nanowires and two-dimensional modified inorganic ion conductor nanosheets. The ionic conductivity of the negative electrode active layer gradually increases along the direction from the current collector to the negative electrode active layer.

2. The negative electrode sheet as described in claim 1, characterized in that, The ionic conductivity of the negative electrode active layer is 10. -6 S / cm-10 -3 S / cm; and / or, The modified inorganic ion conductor in the negative electrode active layer has a mass percentage content of 0.5%-1.5%.

3. The negative electrode sheet as described in claim 1 or 2, characterized in that, The negative electrode active layer comprises at least two active sublayers sequentially stacked on the surface of the current collector; the ratio of the ionic conductivity of the active sublayer furthest from the current collector to the ionic conductivity of the active sublayer closest to the current collector is greater than or equal to 10; and / or, Along the direction from the current collector to the negative electrode active layer, the ionic conductivity of the negative electrode active layer increases from 10. -6 S / cm-10 -5 S / cm increases to 10 -4 S / cm-10 -3 S / cm; The ratio of the mass percentage of the modified inorganic ionic conductor in the active sublayer furthest from the current collector to the mass percentage of the modified inorganic ionic conductor in the active sublayer closest to the current collector is (1.02-3):1; and / or, Along the direction from the current collector to the negative electrode active layer, the mass percentage of the modified inorganic ionic conductor in the negative electrode active layer increases from 0.1%-0.7% to 0.9%-2%; and / or, The absolute value of the difference in ionic conductivity between any two adjacent active sublayers is 1 × 10⁻⁶. -4 S / cm - 8.9 × 10 -3 S / cm; and / or, The absolute value of the difference in the mass percentage of the modified inorganic ionic conductor in any two adjacent active sublayers is 0.1%-1.2%.

4. The negative electrode sheet according to any one of claims 1-3, characterized in that, The inorganic ionic conductor body includes one or more of LLZO, LATP, LAGP, LGPS, LLTO, Li3YCl3Br3, Li3YCl6, and Li3YBr6; and / or, The aspect ratio of the one-dimensional modified inorganic ionic conductor nanowire is greater than or equal to 20; and / or, The diameter of the one-dimensional modified inorganic ion conductor nanowire is 5 nm-1000 nm, and the length of the one-dimensional modified inorganic ion conductor nanowire is 1 μm-50 μm; and / or, The thickness of the two-dimensional modified inorganic ionic conductor nanosheets is 5 nm-1000 nm.

5. A method for preparing a negative electrode sheet as described in any one of claims 1-4, characterized in that, include: A negative electrode active layer is formed by coating a negative electrode slurry on the surface of the current collector, thereby obtaining a negative electrode sheet; the negative electrode slurry includes negative electrode active material particles and modified inorganic ionic conductors.

6. The method for preparing the negative electrode sheet as described in claim 5, characterized in that, The process of coating the current collector surface with negative electrode slurry to form a negative electrode active layer includes: The negative electrode slurry includes at least two composite negative electrode slurries, each of which includes the negative electrode active material particles and the modified inorganic ion conductor, and the mass percentage of the modified inorganic ion conductor in the at least two composite negative electrode slurries is different. The negative electrode active layer includes at least two active sub-layers that are sequentially stacked on the surface of the current collector; Along the direction from the current collector to the negative electrode active layer, the mass percentage of the modified inorganic ion conductor in the negative electrode active layer gradually increases.

7. The method for preparing the negative electrode sheet as described in claim 6, characterized in that, The preparation of the composite negative electrode slurry includes: The modified inorganic ionic conductor is added to the first solvent to obtain a mixed solution of the modified inorganic ionic conductor; Anode active material particles are added to a second solvent to obtain anode active slurry; The composite negative electrode slurry is obtained by mixing the modified inorganic ionic conductor mixed solution and the negative electrode active slurry.

8. The method for preparing the negative electrode sheet according to any one of claims 5-7, characterized in that, The negative electrode active material particles include graphite; and / or, The negative electrode slurry further includes a conductive agent, which includes one or more of Super P, acetylene black, Ketjen black, and carbon nanotubes; and / or, The negative electrode slurry also includes a binder, which includes one or more of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.

9. A battery, characterized in that, The battery includes a negative electrode sheet as described in any one of claims 1-4 or a negative electrode sheet prepared by any one of claims 5-8.

10. An electrical appliance, characterized in that, The electrical device includes the battery as described in claim 9.

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