Negative electrode material and preparation method thereof, electrochemical device and electronic device

Abstract

The application provides a negative electrode material and a preparation method thereof, an electrochemical device and an electronic device. The negative electrode material comprises an active material and a carbon layer on the surface of the active material, and the active material comprises nitrogen-doped porous carbon and a silicon-containing material layer. The mass percentage content of silicon in the negative electrode material is 30% to 80%. The thickness D0 of the silicon-containing material layer ranges from 1 nm to 10 nm, and the ratio of the thickness D0 of the silicon-containing material layer to the pore diameter D1 of the nitrogen-doped porous carbon ranges from 0.2 to 0.8, and the ratio of the thickness D0 of the silicon-containing material layer to the thickness D2 of the carbon layer ranges from 0.05 to 10. The negative electrode material provided by the application can effectively alleviate the expansion of the negative electrode caused by the expansion of the silicon-based and graphite, thereby improving the cycle performance of the negative electrode material.

Description

[0001] This application is a divisional application of application No. 202180004023.8, titled "Negative electrode material and preparation method thereof, electrochemical device and electronic device", filed on March 16, 2021. TECHNICAL FIELD

[0002] The present application relates to the technical field of negative electrode materials, in particular to a negative electrode material and a preparation method thereof, an electrochemical device and an electronic device. BACKGROUND

[0003] At present, silicon-based negative electrode materials have a specific capacity of up to 1500-4200 mAh / g and are considered to be the most promising next-generation lithium ion negative electrode materials. However, the low electrical conductivity of silicon (>108Ω·cm) and the volume expansion of about 300% and the formation of unstable solid electrolyte interface film (SEI) during the charging and discharging process, the silicon negative electrode material will be pulverized and fall off from the current collector during the charging and discharging process, resulting in the loss of electrical contact between the active material and the current collector, leading to poor electrochemical performance, capacity decay and decreased cycle stability, which to some extent hinders its further application. Nanocrystallization of silicon-based negative electrode materials and dispersion in a carbon matrix can effectively improve the cycle performance of silicon-based negative electrode materials. For example, silicon can be ball milled to about 100 nm by wet grinding, and then granulated with pitch, polymer, etc. and carbonized to obtain the currently mainly used silicon-carbon composite material. However, the cycle performance of this negative electrode material is low and the expansion rate is relatively large. SUMMARY

[0004] In view of this, the present application provides a negative electrode material and a preparation method thereof, an electrochemical device and an electronic device. The negative electrode material can effectively alleviate the expansion of the negative electrode caused by the expansion of silicon-based and graphite, thereby improving the cycle performance of the negative electrode material.

[0005] In a first aspect, the present application provides a negative electrode material, which comprises an active material and a carbon layer on the surface of the active material, the active material comprising a nitrogen-doped porous carbon and a silicon-containing material layer; the mass percentage content of silicon in the negative electrode material is 30% to 80%.

[0006] In combination with the first aspect, in a feasible implementation manner, the silicon-containing material layer is located on the pore wall of the nitrogen-doped porous carbon.

[0007] In combination with the first aspect, in a feasible implementation manner, the negative electrode material satisfies at least one of the following conditions (1) to (4):

[0008] (1) the thickness D0 of the silicon-containing material layer is in the range of 1 nm to 10 nm;

[0009] (2) the ratio of the thickness D0 of the silicon-containing material layer to the pore size D1 of the nitrogen-doped porous carbon satisfies: 0.2≤D0 / D1<0.8;

[0010] (3) the ratio of the thickness D0 of the silicon-containing material layer to the thickness D2 of the carbon layer satisfies: 0.05≤D0 / D2≤10;

[0011] (4) the wall thickness of the porous carbon in the nitrogen-doped porous carbon is 5nm to 30nm.

[0012] In combination with the first aspect, in a feasible implementation manner, the nitrogen-doped porous carbon satisfies at least one of the following conditions (1) to (3): (1) the specific surface area of the nitrogen-doped porous carbon is 2000m 2 / g to 3500m 2 / g;

[0013] (2) the pore volume of the nitrogen-doped porous carbon is 1cm 2 / g to 10cm 2 / g;

[0014] (3) the average pore size of the pores in the nitrogen-doped porous carbon is 1nm to 20nm.

[0015] In combination with the first aspect, in a feasible implementation manner, the negative electrode material satisfies at least one of the following conditions (1) to (7):

[0016] (1) the specific surface area of the negative electrode material is 1m 2 / g to 50m 2 / g;

[0017] (2) the pore volume of the negative electrode material is 0.001cm 2 / g to 0.1cm 2 / g;

[0018] (3) the particle size range of the negative electrode material is 1μm to 100μm, and / or, the average particle size of the negative electrode material is 2.5μm to 50μm;

[0019] (4) the powder conductivity of the negative electrode material is 2.0S / cm to 30S / cm;

[0020] (5) the thickness of the carbon layer of the negative electrode material is 2nm to 20nm;

[0021] (6) the mass percentage content of the carbon layer in the negative electrode material is 3% to 10%;

[0022] (7) the mass percentage content of the nitrogen-doped porous carbon in the negative electrode material is 10% to 67%.

[0023] In combination with the first aspect, in a feasible implementation, the negative electrode material has a peak intensity ID at 1350 cm -1 and a peak intensity IG at 1580 cm -1 , and a ratio ID / IG of the peak intensity ID to the peak intensity IG ranges from 1.2 to 2.2.

[0024] In combination with the first aspect, in a feasible implementation, the nitrogen-doped porous carbon satisfies at least one of the following conditions (1) to (3):

[0025] (1) the nitrogen element in the nitrogen-doped porous carbon is doped in a carbon phase in a C-N bond form;

[0026] (2) a mass percentage content of the nitrogen in the nitrogen-doped porous carbon ranges from 0.5% to 10%;

[0027] (3) through XPS analysis, a configuration of the nitrogen in the nitrogen-doped porous carbon includes at least one of pyridine-type nitrogen, pyrrole-type nitrogen, graphite-type nitrogen, graphitized nitrogen, and oxidized nitrogen, and the mass percentage of the graphitized nitrogen in all the nitrogen ranges from 30% to 70%.

[0028] The second aspect provides a preparation method of the negative electrode material of the first aspect.

[0029] The antibiotic residue is subjected to high-temperature carbonization treatment and acid washing treatment by using a metal salt to obtain nitrogen-doped porous carbon;

[0030] The nitrogen-doped porous carbon is subjected to gas-phase deposition by using silane gas to obtain active material;

[0031] The active material is mixed with a carbon source and then subjected to high-temperature treatment to obtain the negative electrode material.

[0032] In combination with the second aspect, in a feasible implementation, the method satisfies at least one of the following conditions (1) to (3):

[0033] (1) the carbon source includes at least one of resin, pitch, and high-molecular polymer;

[0034] (2) the metal salt includes at least one of sodium chloride, potassium chloride, sodium carbonate, or potassium carbonate;

[0035] (3) the acid used in the acid washing treatment includes at least one of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, hydrofluoric acid, or phosphoric acid.

[0036] In a third aspect, the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode material of the first aspect or the negative electrode material prepared by the preparation method of the second aspect.

[0037] In combination with the third aspect, in a feasible implementation manner, the negative electrode sheet satisfies at least one of the following conditions (1) to (4):

[0038] (1) The porosity of the negative electrode active material layer is 20% to 40%;

[0039] (2) The electrical resistance of the negative electrode active material layer is 0.2 Ω to 2 Ω;

[0040] (3) The compaction density of the negative electrode active material layer is 1.5 g / cm 3 to 2.0 g / cm 3 under a pressure of 5T;

[0041] (4) The OI value of the negative electrode active material layer is 1 to 20.

[0042] In a fourth aspect, the present application provides an electrochemical device, comprising a negative electrode active material layer, wherein the negative electrode active material layer comprises the negative electrode material of the first aspect or the negative electrode material prepared by the preparation method of the second aspect.

[0043] In combination with the fourth aspect, in a feasible implementation manner, the electrochemical device is a lithium ion battery.

[0044] In a fifth aspect, the present application provides an electronic device, comprising the electrochemical device of the fourth aspect.

[0045] Compared with the prior art, the present application has at least the following beneficial effects:

[0046] The negative electrode material provided by the present application can effectively alleviate the expansion of the negative electrode caused by the expansion of the silicon material and graphite, thereby improving the cycle performance of the negative electrode active material and reducing the expansion efficiency of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 The structure schematic diagram of the negative electrode material provided by the present application is shown in the figure. DETAILED DESCRIPTION

[0048] The following describes preferred embodiments of the present application. It should be noted that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which are also considered within the scope of protection of the present application.

[0049] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, as can any upper limit with any other upper limit. Furthermore, although not explicitly recited, every point or individual number within a range is included in that range. Thus, every midpoint or individual number can be combined as its own lower limit or upper limit with any other point or individual number or with other lower or upper limits to form a range not explicitly recited.

[0050] In the description herein, it should be noted that, unless otherwise specified, "above", "below" are inclusive of the number, and "more than one" means more than two.

[0051] The foregoing summary of the application is not intended to describe each disclosed embodiment or implementation of the present application. The following description more specifically illustrates example embodiments. Throughout this application, guidance is provided by a series of examples, which can be used in various combinations. In each instance, the list is merely representative of a group, and should not be interpreted as exhaustive.

[0052] In a first aspect, the embodiments of the present application provide a negative electrode material, such as Figure 1 As shown, the negative electrode material includes an active material 10 and a carbon layer 20 on the surface of the active material, the active material 10 includes a nitrogen-doped porous carbon and a silicon-containing material layer 11; the mass percentage content of silicon in the negative electrode material is 30% to 80%.

[0053] The negative electrode material provided by the present application can effectively alleviate the expansion of the negative electrode caused by the expansion of the silicon material and graphite, by depositing the silicon material on the pore wall of the nitrogen-doped porous carbon, using the nitrogen-doped porous carbon as a support framework of the negative electrode material, and using the internal pores 12 of the nitrogen-doped porous carbon to alleviate the volume expansion to some extent, thereby improving the cycle performance of the negative electrode active material.

[0054] In the present embodiment, the silicon-containing material layer is located on the pore wall of the nitrogen-doped porous carbon. And the nitrogen-doped porous carbon is used as the framework structure of the negative electrode material, so that the negative electrode material can provide more active sites for the attachment of lithium ions, thereby making the lithium ion battery have better charge and discharge cycle performance.

[0055] The mass percentage content of silicon in the negative electrode material is 30% to 80%, specifically, 30%, 32.4%, 44.3%, 52.5%, 60%, 65%, 70%, or 80%, and the like, and of course, other values in the above range are also possible, which are not limited herein. It can be understood that when the content of silicon in the negative electrode material is too high, the expansion rate of the negative electrode material will be significantly increased, which is easy to cause the destruction of the structure of the negative electrode material, resulting in the decline of the cycle performance of the battery; when the content of silicon in the negative electrode material is too low, the specific capacity of the negative electrode material will be reduced, which affects the power density of the negative electrode material. Preferably, the mass percentage content of silicon in the negative electrode material is 32.4% to 52.5%.

[0056] The thickness D0 of the silicon-containing material layer is 1 nm to 10 nm, specifically, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm, and the like, and of course, other values in the above range are also possible, which are not limited herein. If the thickness of the silicon-containing material layer is too small, the electrochemical performance of the material will be reduced, and the capacity of the battery will be reduced; if the thickness of the silicon-containing material layer is too large, the volume expansion effect of silicon will be more obvious, which is easy to destroy the pore structure of the nitrogen-doped porous carbon and the carbon layer, resulting in the decline of the cycle performance of the battery. Preferably, the thickness D0 of the silicon-containing material layer is 5 nm to 10 nm.

[0057] As an optional technical solution of the present application, the average pore diameter D1 of the pores in the nitrogen-doped porous carbon is 1 nm to 20 nm, specifically, 1 nm, 2 nm, 3 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, or 20 nm, and the like, but is not limited to the listed values, and other values not listed in this range are also applicable. Preferably, the average pore diameter D1 of the pores in the nitrogen-doped porous carbon is 12 nm to 20 nm.

[0058] The ratio of the thickness D0 of the silicon-containing material layer to the pore diameter D1 of the nitrogen-doped porous carbon satisfies 0.2≤D0 / D1<0.8, specifically, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, or 0.7, and the like, and of course, other values in the above range are also possible, which are not limited herein.

[0059] As an optional technical solution of the present application, the thickness D2 of the carbon layer of the negative electrode material is 2 nm to 20 nm, specifically, it can be 2 nm, 3 nm, 4 nm, 5 nm, 7 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm or 20 nm, etc., and of course it can also be other values within the above range, which is not limited here. Understandably, if the carbon layer is too thick, the lithium ion transmission efficiency will be reduced, which is not conducive to the large-rate charging and discharging of the material, and reduces the comprehensive performance of the negative electrode material; if the carbon layer is too thin, it is not conducive to increasing the conductivity of the negative electrode material and the volume expansion inhibition performance of the material is weak, resulting in poor long cycle performance.

[0060] The ratio of the thickness D0 of the silicon-containing material layer to the thickness D2 of the carbon layer satisfies the range: 0.05≤D0 / D2≤10, specifically, it can be 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, etc., and of course it can also be other values within the above range, which is not limited here.

[0061] Understandably, by controlling the ratio of the thickness of the silicon-containing material layer to the pore size of the nitrogen-doped porous carbon, and the ratio of the thickness of the silicon-containing material layer to the thickness of the carbon layer, the expansion of the silicon-containing material layer is avoided. The pore structure of the nitrogen-doped porous carbon and the carbon layer are destroyed, thereby improving the cycle capacity of the battery and reducing the expansion efficiency of the battery.

[0062] As an optional technical solution of the present application, the specific surface area of the nitrogen-doped porous carbon is 2000 m 2 / g to 3500 m 2 / g; specifically, it can be 2000 m 2 / g, 2200 m 2 / g, 2500 m 2 / g, 2800 m 2 / g, 3000 m 2 / g or 3500 m 2 / g, etc., but is not limited to the listed values, and other unlisted values within this range are also applicable.

[0063] The pore volume of the nitrogen-doped porous carbon is 1 cm 2 / g to 10 cm 2 / g; specifically, it can be 1 cm 2 / g, 2 cm 2 / g, 3 cm 2 / g, 4 cm 2 / g, 5 cm 2 / g, 6 cm 2 / g, 8 cm 2 / g, 9 cm 2 / g or 10 cm 2etc., but are not limited to the listed numerical values, and other numerical values not listed in the range are also applicable.

[0064] It can be understood that the nitrogen-doped porous carbon has a large specific surface area and pore volume, which can be beneficial for the deposition of the silicon-containing material layer in the pore structure of the nitrogen-doped porous carbon, and the internal pores of the nitrogen-doped porous carbon can relieve a certain volume expansion.

[0065] As an optional technical solution of the present application, the wall thickness of the porous carbon in the nitrogen-doped porous carbon is 5 nm to 30 nm; specifically, it can be 5 nm, 8 nm, 10 nm, 15 nm, 18 nm, 20 nm, 22 nm, 25 nm, 28 nm, or 30 nm, etc., and of course it can also be other values within the above range, which are not limited herein. It can be understood that controlling the wall thickness of the porous carbon in the nitrogen-doped porous carbon within the above range can effectively improve the rigidity of the skeleton structure of the nitrogen-doped porous carbon as the negative electrode material, which is beneficial to improve the cycle performance of the material.

[0066] As an optional technical solution of the present application, the nitrogen element in the nitrogen-doped porous carbon is doped in the carbon phase in the form of C-N bond. Specifically, the mass percentage content of nitrogen in the nitrogen-doped porous carbon is 0.5% to 10%, specifically it can be 0.5%, 0.8%, 1%, 2%, 3%, 5%, 7%, 9% or 10% etc., and of course it can also be other values within the above range, which are not limited herein.

[0067] As an optional technical solution of the present application, through XPS analysis, the configuration of nitrogen in the nitrogen-doped porous carbon includes at least one of pyridine nitrogen, pyrrole nitrogen, graphite nitrogen, graphitized nitrogen and oxidized nitrogen, and the mass percentage of the graphitized nitrogen in all nitrogen is 30% to 70%, specifically it can be 30%, 40%, 50%, 60% or 70% etc.

[0068] As an optional technical solution of the present application, the mass percentage content of the nitrogen-doped porous carbon in the negative electrode material is 10% to 67%, specifically it can be 10%, 20%, 25%, 30%, 35%, 40%, 50% or 67% etc., and of course it can also be other values within the above range, which are not limited herein.

[0069] As an optional technical solution of the present application, the mass percentage content of the carbon layer in the negative electrode material is 3% to 10%, specifically it can be 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10% etc., and of course it can also be other values within the above range, which are not limited herein.

[0070] As an optional technical solution of the present application, the specific surface area of the negative electrode material is 1 m 2 / g to 50 m 2 / g, specifically 1 m 2 / g, 5 m 2 / g, 10 m 2 / g, 15 m 2 / g, 20 m 2 / g, 25 m 2 / g, 30 m 2 / g, 40 m 2 / g, 49 m 2 / g or 50 m 2 / g, etc., but not only limited to the listed values, other values not listed in the range are also applicable. The specific surface area of the negative electrode material in the above range ensures the processing performance of the material, which is conducive to improving the initial efficiency of the lithium battery made of the negative electrode material and improving the cycle performance of the negative electrode material. Preferably, the specific surface area of the negative electrode material is 2.1 m 2 / g to 5.2 m 2 / g.

[0071] As an optional technical solution of the present application, the pore volume of the negative electrode material is 0.001 cm 2 / g to 0.1 cm 2 / g; specifically 0.001 cm 2 / g, 0.005 cm 2 / g, 0.01 cm 2 / g, 0.03 cm 2 / g, 0.05 cm 2 / g, 0.06 cm 2 / g, 0.08 cm 2 / g, 0.09 cm 2 / g or 0.1 cm 2 / g, etc., but not only limited to the listed values, other values not listed in the range are also applicable. It can be understood that the smaller pore volume of the negative electrode material indicates that the outer carbon layer has fewer pore structures, which is better for the combination of the inner core active material, is conducive to isolating the inner core active material from the electrolyte, forming a stable SEI film, and providing stable cycle performance.

[0072] As an optional technical solution of the present application, the particle size of the negative electrode material ranges from 1 μm to 100 μm, specifically 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm, etc., but not only limited to the listed values, other values not listed in the range are also applicable. Optionally, the average particle size D 50 of the negative electrode material is 2.5 μm to 50 μm.

[0073] As an optional technical solution of the present application, the powder conductivity of the negative electrode material is 2.0 S / cm to 30 S / cm, and can be 2.0 S / cm, 2.5 S / cm, 3.0 S / cm, 5.0 S / cm, 8.0 S / cm, 10 S / cm, 15 S / cm, 20 S / cm, 25 S / cm or 30 S / cm, etc., but is not limited to the listed values, and other values not listed in the range are also applicable.

[0074] As an optional technical solution of the present application, the peak intensity I of the negative electrode material at 1350 cm -1 -1 of the Raman spectrum is 1.2 to 2.2 times the peak intensity I of the negative electrode material at 1580 cm D -1 of the Raman spectrum. -1 G The ratio I D / I G of the peak intensity I of the negative electrode material at 1350 cm D -1 of the Raman spectrum to the peak intensity I of the negative electrode material at 1580 cm G -1 of the Raman spectrum is 1.2 to 2.2; the ratio I G / I G of the peak intensity I of the negative electrode material at 1350 cm G -1 of the Raman spectrum to the peak intensity I of the negative electrode material at 1580 cm G -1 of the Raman spectrum can be 1.2, 1.4, 1.5, 1.8, 1.9, 2.0 or 2.2, etc., but is not limited to the listed values, and other values not listed in the range are also applicable. When the ratio is too high, the surface defect degree of the negative electrode material is high, which increases the formation of the solid electrolyte (SEI) film, consumes more lithium ions, and reduces the first efficiency of the battery. When the ratio is too low, the kinetic performance of the negative electrode material decreases.

[0075] In a second aspect, the present application provides a preparation method of a negative electrode material, which comprises the following steps:

[0076] Step S10: obtaining nitrogen-doped porous carbon by high-temperature carbonization treatment and acid washing treatment of antibiotic bacterial residue.

[0077] Step S20: performing gas phase deposition on the nitrogen-doped porous carbon by using silane gas to obtain an active material.

[0078] Step S30: mixing the active material with a carbon source and then performing high-temperature treatment to obtain a negative electrode material. In the above scheme, the silicon is deposited into the nitrogen-doped porous carbon by using the way of thermal decomposition of silicon source gas, which can effectively alleviate the expansion of the negative electrode due to the expansion of silicon-based and graphite, and can effectively improve the cycle performance of the negative electrode active material.

[0079] The preparation method is specifically described below in combination with examples:

[0080] Step S10: obtaining nitrogen-doped porous carbon by high-temperature carbonization treatment and acid washing treatment of antibiotic bacterial residue.

[0081] Optionally, the mass ratio of the antibiotic residue to the metal salt is (0.1-2):1, which can be 0.1:1, 0.3:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1 or 2:1, or other values within the above range.

[0082] Before the high-temperature carbonization treatment, the antibiotic residue and the metal salt are put into deionized water, stirred uniformly, and then dried in an oven at 110°C.

[0083] Optionally, the metal salt includes at least one of sodium chloride, potassium chloride, sodium carbonate or potassium carbonate.

[0084] Optionally, the high-temperature carbonization treatment is performed at a temperature of 600-1000°C, which can be 600°C, 700°C, 800°C, 900°C, 950°C or 1000°C, or other values within the above range. The temperature increasing rate is controlled to be 1-10°C / min, which can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min or 10°C / min, or other values within the above range.

[0085] The holding time of the high-temperature carbonization treatment is 1-3h, which can be 1h, 1.5h, 2h, 2.5h or 3h, or other values within the above range.

[0086] It can be understood that the nitrogen-doped carbon material containing metal elements can be obtained through the high-temperature carbonization treatment.

[0087] Further, the metal elements in the nitrogen-doped carbon material are subjected to acid pickling treatment, so that the metal elements are dissolved in an acid solution, and the nitrogen-doped carbon material forms a porous structure.

[0088] Optionally, the acid used in the acid pickling treatment includes at least one of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, hydrofluoric acid or phosphoric acid.

[0089] In step S20, the nitrogen-doped porous carbon is subjected to gas-phase deposition using silane gas to obtain an active material.

[0090] Optionally, the temperature of the gas-phase deposition is 400-600°C, which can be 400°C, 450°C, 500°C, 550°C or 600°C, or other values within the above range.

[0091] As an optional technical solution of the present application, the deposition time of the vapor deposition is 0.5 h to 3 h, and specifically can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, and of course can also be other values within the above range.

[0092] In the present embodiment, silane gas is used for vapor deposition of nitrogen-doped porous carbon under the protection of inert gas. Specifically, the volume fraction of silane gas in the inert gas is 2% to 6%, and specifically can be 2%, 3%, 4%, 5% or 6%, and of course can also be other values within the above range.

[0093] In step S30, the active material is mixed with the carbon source and then subjected to carbon composite treatment to obtain a negative electrode material.

[0094] As an optional technical solution of the present application, the carbon source includes at least one of resin, pitch, and high molecular polymer.

[0095] Before the carbon composite treatment, the active material and the carbon source can be dispersed in a liquid phase system (such as water), stirred to mix them thoroughly, and then dried, and the dried mixture is subjected to carbon composite treatment.

[0096] As an optional technical solution of the present application, the temperature of the carbon composite treatment is 500°C to 1200°C, and specifically can be 500°C, 550°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C, and of course can also be other values within the above range. The heating rate is controlled to be 1°C / min to 10°C / min, and specifically can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min or 10°C / min, and of course can also be other values within the above range.

[0097] As an optional technical solution of the present application, the time of the carbon composite treatment is 1 h to 24 h; specifically can be 1 h, 2 h, 6 h, 12 h, 18 h or 24 h, and of course can also be other values within the above range.

[0098] As an optional technical solution of the present application, the carbon composite treatment is carried out under the protection of inert gas, which can be at least one of nitrogen, argon, helium, krypton, etc.

[0099] In a third aspect, the present application provides a negative electrode tab, which includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector, and the negative electrode active material layer includes the negative electrode material according to the first aspect of the present application.

[0100] As an optional technical solution of the present application, the negative active material layer comprises a binder, and the binder comprises polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene rubber, acrylic butadiene rubber, epoxy resin, or nylon, etc., which are not limited herein.

[0101] As an optional technical solution of the present application, the negative active material layer further comprises a conductive material, and the conductive material comprises natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, metal fiber, copper, nickel, aluminum, silver, or polyphenylene derivative, etc., which are not limited herein.

[0102] As an optional technical solution of the present application, the negative current collector comprises, but is not limited to, a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper, or a polymer substrate coated with a conductive metal.

[0103] As an optional technical solution of the present application, the porosity of the negative active material layer is 20% to 40%, and specifically can be 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, or 40%, etc., and of course can also be other values within the above range.

[0104] As an optional technical solution of the present application, the resistance of the negative active material layer is 0.2Ω to 2Ω, and specifically can be 0.2Ω, 0.5Ω, 0.8Ω, 1Ω, 1.2Ω, 1.5Ω, 1.8Ω, or 2Ω, etc., and of course can also be other values within the above range.

[0105] As an optional technical solution of the present application, the compaction density of the negative active material layer is 1.5g / cm 3 to 2.0g / cm 3 , and specifically can be 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 , or 2.0g / cm 3 , etc., and of course can also be other values within the above range.

[0106] As an optional technical solution of the present application, the OI value of the negative active material layer is 1 to 20, and specifically can be 1, 3, 5, 8, 10, 13, 15, 18, or 20, etc., and of course can also be other values within the above range.

[0107] In a fourth aspect, the present application provides an electrochemical device comprising a negative active material layer, wherein the negative active material layer comprises the negative active material of the first aspect or the negative active material prepared by the method of the second aspect.

[0108] As an optional technical solution of the present application, the electrochemical device further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive current collector and a positive active material layer on the positive current collector.

[0109] As an optional technical solution of the present application, the positive active material comprises at least one of lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material, lithium iron phosphate, lithium manganese iron phosphate, and lithium manganate.

[0110] As an optional technical solution of the present application, the positive active material layer further comprises a binder and a conductive material. It can be understood that the binder improves the binding between the positive active material particles and also improves the binding between the positive active material and the current collector.

[0111] Specifically, the binder comprises at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resin, or nylon.

[0112] Specifically, the conductive material comprises carbon-based material, metal-based material, conductive polymer, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0113] As an optional technical solution of the present application, the positive current collector comprises, but is not limited to, an aluminum foil.

[0114] As an optional technical solution of the present application, the electrochemical device further comprises an electrolyte, wherein the electrolyte comprises an organic solvent, a lithium salt, and an additive.

[0115] The organic solvent of the electrolyte according to the present application can be any organic solvent known in the art as a solvent for an electrolyte. The electrolyte used in the electrolyte according to the present application is not limited and can be any electrolyte known in the art. The additive of the electrolyte according to the present application can be any additive known in the art as an additive for an electrolyte.

[0116] In specific embodiments, the organic solvent includes, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate.

[0117] In specific embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.

[0118] In specific embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis-trifluoromethanesulfonimide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalato)borate LiB(C2O4)2 (LiBOB), or lithium difluoro(oxalato)borate LiBF2(C2O4) (LiDFOB).

[0119] In specific embodiments, the concentration of the lithium salt in the electrolyte can be 0.5 mol / L to 3 mol / L.

[0120] As an optional technical solution of the present application, the electrochemical device includes, but is not limited to, all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors.

[0121] In specific embodiments, the electrochemical device is a lithium secondary battery, wherein the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

[0122] In a fifth aspect, the embodiments of the present application further provide an electronic device, which includes the electrochemical device of the fourth aspect.

[0123] As an optional technical solution of the present application, the electronic device includes, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, an illuminating appliance, a toy, a game machine, a clock, an electric tool, a flash, a camera, a household large storage battery or a lithium ion capacitor, etc.

[0124] The preparation of lithium ion batteries is described below by way of example and in conjunction with specific examples. Those skilled in the art will understand that the preparation methods described in the present application are merely examples, and any other suitable preparation method is within the scope of the present application.

[0125] I. Preparation of the negative electrode material

[0126] Take 100 g of dry antibiotic bacterial residue and grind it into powder. Add the bacterial residue to 500 ml of deionized water at a mass ratio of (0.1-2) : 1, mix well, and then dry in an oven at 110°C. Then carbonize the residue at 600-1000°C under an inert atmosphere for 1-3 h at a heating rate of 1-10°C / min to obtain a solid material.

[0127] Put the solid material into an acid solution with a concentration of 1-3 mol / L, and perform acid washing. After stirring for 1-24 h, remove the metal impurities by filtration to obtain nitrogen-doped porous carbon.

[0128] Put the nitrogen-doped porous carbon into a tube furnace and perform silane vapor deposition at 400-600°C under an inert atmosphere. The deposition time is 0.5-3 h, and the silane concentration is 2-6%. The active material is obtained.

[0129] Disperse the active material and an appropriate amount of carbon source in a liquid phase system, and mix well in a shearing mixer for 0.5-12 h. After drying, perform sintering under an inert atmosphere. The sintering temperature is 500-1200°C, the heating rate is 1-10°C / min, and the holding time is 1-24 h.

[0130] Examples 1-9 were prepared according to the above method. The specific parameters of Examples 1-9 are shown in Table 1 below.

[0131] Further, Comparative Example 1 was prepared according to the above method. The aspect ratio of the porous carbon fiber framework prepared in Comparative Example 1 is 1.0. The specific parameters of Comparative Example 1 are shown in Table 1 below.

[0132] Further, Comparative Example 2 was prepared according to the above method. In the preparation process of Comparative Example 2, the mixed solution was not spun into polymeric fibers, but was made into a block-shaped polymer. The carbon framework in the prepared negative electrode material was in a spherical shape. The specific parameters of Comparative Example 2 are shown in Table 1 below.

[0133] Table 1. Performance parameters of the negative electrode material

[0134]

[0135] II. Performance test of the negative electrode material

[0136] (1) Discharge test:

[0137] The negative electrode material, conductive carbon black and polymer were mixed with deionized water in a mass ratio of 80:10:10 to form a slurry, which was coated with a doctor blade to form a coating layer with a thickness of 100 μm. The coating layer was dried in a vacuum drying oven at 85°C for 12 hours. Then, the coating layer was cut into a circular piece with a diameter of 1 cm using a punch machine in a dry environment. A coin-type battery was assembled in a glove box using a lithium sheet as a counter electrode, a ceglard composite membrane as a separator, and an electrolyte. The charge and discharge performance of the battery was tested using a LAND battery test.

[0138] (2) Specific surface area test:

[0139] Under constant temperature and low temperature, the adsorption amount of gas on the surface of a solid at different relative pressures was measured, and the monolayer adsorption amount of the sample was obtained based on the Brunauer-Emmett-Teller adsorption theory and its formula (BET formula), so as to calculate the specific surface area of the solid.

[0140] BET formula:

[0141] Wherein: W is the mass of the gas adsorbed by the solid sample at a relative pressure;

[0142] Wm is the saturated adsorption amount of a monolayer of gas;

[0143] Slope: (c-1)(WmC), intercept: 1 / WmC, total specific surface area: (Wm*N*Acs / M), specific surface area:

[0144] S = St / m, where m is the mass of the sample, Acs: the average area occupied by each N2 molecule

[0145] 1.5 g to 3.5 g of the negative electrode material powder sample was weighed and loaded into the test sample tube of the TriStar II 3020, and the test was performed after degassing at 200°C for 120 min.

[0146] (3) Particle size test:

[0147] About 0.02 g of the powder sample was added to a 50 ml clean beaker, about 20 ml of deionized water was added, and a few drops of 1% surfactant were added to make the powder completely dispersed in the water. Ultrasonic cleaning was performed in a 120 W ultrasonic cleaning machine for 5 min, and the particle size distribution was tested using a MasterSizer 2000.

[0148] (4) Test method for silicon content of the negative electrode material:

[0149] First, the carbon content of the sample was tested, and the percentage of silicon content was obtained by subtracting the test value from 100%. The carbon content test is as follows:

[0150] The negative electrode material sample is heated by a high-frequency furnace under oxygen-rich conditions to oxidize carbon and sulfur into carbon dioxide and sulfur dioxide. The gas is treated and then enters the corresponding absorption cell to absorb the corresponding infrared radiation, which is then converted into a corresponding signal by a detector. The signal is sampled by a computer, linearly corrected, and converted into a value proportional to the concentration of carbon dioxide and sulfur dioxide. The values obtained during the entire analysis process are then added, and after the analysis is complete, the cumulative value is divided by the weight value in the computer, multiplied by the correction coefficient, and subtracted from the blank to obtain the percentage of carbon and sulfur in the sample. The high-frequency infrared carbon and sulfur analyzer (Shanghai Deke HCS-140) is used for sample testing.

[0151] (5) Powder conductivity test of negative electrode material:

[0152] A resistivity tester (Suzhou Crystal Electronics ST-2255A) is used to take 5g of powder sample, which is pressed to 5000kg±2kg by an electronic press for 15-25s. The sample is placed between the electrodes of the tester, with a height h (cm), a voltage U between the two ends, a current I, and a resistance R (KΩ). The area S of the pressed sample is 3.14cm 2 . The powder electronic conductivity is calculated according to the formula δ = h / (S*R) / 1000, with the unit of S / m.

[0153] (6) Nitrogen content test of nitrogen-doped porous carbon:

[0154] The nitrogen element content is determined by a CN802 carbon and nitrogen element analyzer produced by VELP Company of Italy, with a TCD detector as the N detector, under an argon atmosphere at 1030°C, with a power of 1400W.

[0155] (7) Raman test:

[0156] The Raman spectrum is measured by a Jobin Yvon LabRAM HR spectrometer, with a light source of 532nm and a test range of 0cm -1 ~4000cm -1 . The test range is 100μm*100μm, and the average value of I D / I G is obtained by counting 100 I D / I G values.

[0157] (8) XPS test:

[0158] The XPS test equipment is an ESCLAB250Xi of Thermo Fisher Company, with Al as the target for excitation source and a power of 250w, and a vacuum degree of >10 -9 Pa. The configuration of nitrogen in the nitrogen-doped porous carbon is determined by XPS test.

[0159] (9)Porosity test:

[0160] Porosity of the negative electrode material and negative electrode sheet is tested by gas replacement method. Calculation method: percentage of sample pore volume to total area, P = (V-V0) / V*100%, V0: true volume, V: apparent volume.

[0161] (10) Cross-section test of negative electrode material:

[0162] The cross-section polisher uses an ion source to ionize inert gas to generate inert ions. After acceleration and focusing, high-speed inert ions will impact atoms or molecules on the surface of the sample to achieve ion polishing. After CP cutting, the sample is placed on a SEM special sample stage for SEM testing. The instrument model is IB-09010CP, ion acceleration voltage is 2-6kV, and argon gas is used. By cross-section test, the silicon-containing material layer thickness D0, the outer carbon layer thickness D2 and the wall thickness of the porous carbon of the silicon-carbon negative electrode material are tested after cutting.

[0163] (11) TEM test:

[0164] Transmission electron microscopy characterization is carried out on a Japan Electronics JEOL JEM-2010 transmission electron microscope with an operating voltage of 200kV, and the structure of the negative electrode material is observed, as shown in Figure 1 .

[0165] (12) Pore volume test:

[0166] 1.5g to 3.5g of powder sample is weighed and loaded into the test sample tube of TriStar II 3020, and the test is carried out after degassing at 200℃ for 120min. The pore volume is estimated from the adsorption amount (V STP , cm 3 g -1 ) at a relative pressure (P / Po) of 0.99.

[0167] (13) Pore size test method of nitrogen-doped porous carbon:

[0168] 1.5g to 3.5g of nitrogen-doped porous carbon powder sample is weighed and loaded into the test sample tube of TriStar II 3020, and the test is carried out after degassing at 200℃ for 120min. The pore size distribution is calculated by BJH method using adsorption data.

[0169] (14) Mass percentage content test method of carbon layer:

[0170] The silicon content in the silicon-carbon core not compounded with carbon is measured by test method (4), and the mathematical relationship between the mass content of silicon and the mass content of nitrogen-doped porous carbon is obtained. Then the mass percentage content of silicon in the negative electrode material is measured in the same way, and the mass percentage content of the carbon layer is obtained by combining the mass percentage content relationship between silicon and nitrogen-doped porous carbon.

[0171] (15) Test method for mass percentage content of nitrogen-doped porous carbon:

[0172] The silicon content in the silicon-carbon core not compounded with carbon is measured by test method (4), and the mathematical relationship between the mass content of silicon and the mass content of nitrogen-doped porous carbon is obtained. Then the mass percentage content of silicon in the negative electrode material is measured in the same way, and the mass percentage content of the carbon layer is obtained by combining the mass percentage content relationship between silicon and nitrogen-doped porous carbon.

[0173] III. Preparation of negative electrode sheet

[0174] The negative electrode material, graphite, conductive agent (conductive carbon black, ), and binder PAA of the above examples and comparative examples are mixed in a weight ratio of 70:15:5:10, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on a negative electrode current collector copper foil; the copper foil is dried, then cold-pressed under a pressure of 5t, cut into pieces, and dried under vacuum to obtain a negative electrode sheet.

[0175] IV. Performance test of negative electrode sheet:

[0176] (1) Test of compaction density of negative electrode active material layer:

[0177] The compaction density PD of the negative electrode active material layer is m / V, where m represents the weight of the negative electrode active material layer, and V represents the volume of the negative electrode active material layer. m can be measured using an electronic balance with a precision of 0.01 g or more. The product of the surface area and thickness of the negative electrode active material layer is the volume V of the negative electrode active material layer, and the thickness can be measured using a screw micrometer with a precision of 0.5 μm.

[0178] (2) Test of OI value of negative electrode active material layer:

[0179] The OI value of the negative electrode active material layer can be obtained by using an X-ray powder diffractometer (X'pert PRO). According to the general method for X-ray diffraction analysis and the method for measuring the lattice parameters of graphite JIS K0131-1996 and JB / T 4220-2011, the X-ray diffraction spectrum is obtained, and the OI value is C 004 / C 110 , where C 004 is the peak area of the 004 characteristic diffraction peak, and C110 The peak area of ​​the characteristic diffraction peak of 110.

[0180] (3) Resistance test of the negative electrode active material layer:

[0181] The resistance of the negative electrode active material layer was tested using the four-probe method. The instrument used for the four-probe method was a precision DC voltage and current source (SB118 type). Four copper plates, each 1.5cm long, 1cm wide, and 2mm thick, were fixed equidistantly on a line, with a spacing L (1-2cm) between the two middle plates. The substrate for fixing the copper plates was an insulating material. During the test, the lower surfaces of the four copper plates were pressed onto the negative electrode being tested (pressure 3000Kg) for 60s. A DC current I was applied to the two end plates, and the voltage V was measured on the two middle plates. The I and V values ​​were read three times, and the average values ​​Ia and Va were recorded. The value of Va / Ia is the resistance of the negative electrode active material layer at the test point. Twelve points were tested on each negative electrode sheet, and the average value was taken.

[0182] (4) Porosity test of the negative electrode active material layer:

[0183] The porosity of the negative electrode active material layer was tested using the gas displacement method. The calculation method was: P = (V - V0) / V * 100%, where V0 is the true volume of the material layer and V is the apparent volume.

[0184] V. Preparation of Lithium-ion Batteries

[0185] (1) Preparation of positive electrode sheet

[0186] Lithium cobalt oxide (LiCoO2), conductive carbon black, and polyvinylidene fluoride binder were mixed in a weight ratio of 95:2.5:2.5. N-methylpyrrolidone (NMP) was added and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto the positive electrode current collector aluminum foil. The aluminum foil was dried, and then cold-pressed, cut, and slit before being dried under vacuum to obtain the positive electrode sheet.

[0187] (2) Preparation of negative electrode sheet

[0188] The above embodiments and comparative examples use negative electrode materials, graphite, and conductive agents (conductive carbon black). The negative electrode slurry is obtained by mixing the negative electrode slurry and the binder PAA in a weight ratio of 70:15:5:10, adding deionized water, and stirring under vacuum. The negative electrode slurry is then uniformly coated onto the negative electrode current collector copper foil. The copper foil is dried, and then cold-pressed, cut, and slit before being dried under vacuum to obtain the negative electrode sheet.

[0189] (3) Electrolyte

[0190] In a glove box under dry argon atmosphere, LiPF6 was added into a solvent mixed from propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (weight ratio about 1:1:1) and mixed uniformly, wherein the concentration of LiPF6 was about 1.15 mol / L, and the electrolyte was obtained by uniform mixing.

[0191] (4) Separating film

[0192] The polyethylene porous polymer film was used as the separating film.

[0193] (5) Preparation of lithium ion battery The positive electrode sheet, the separating film, and the negative electrode sheet were stacked in order, and the separating film was arranged between the positive electrode sheet and the negative electrode sheet to play a separating role, and then the bare battery cell was obtained by winding. After welding the tab, the bare battery cell was placed in an outer packaging foil aluminum plastic film, the electrolyte prepared above was injected into the dried bare battery cell, and the lithium ion battery was obtained through processes such as vacuum packaging, standing, formation, shaping, and capacity testing.

[0194] VI. Performance test of lithium battery

[0195] (1) Cycle performance test of lithium ion battery

[0196] The lithium ion battery was placed in a 45°C (25°C) constant temperature box and stood for 30 minutes to make the lithium ion battery reach a constant temperature. The lithium ion battery reaching the constant temperature was charged at 0.7C constant current to a voltage of 4.4V, and then charged at 4.4V constant voltage to a current of 0.025C, and then stood for 5 minutes and discharged at 0.5C constant current to a voltage of 3.0V. The capacity obtained by the above steps was the initial capacity, and the cycle test was performed at 0.7C charge / 0.5C discharge. The capacity decay curve was obtained by comparing the capacity of each step with the initial capacity. The cycle number at which the capacity retention rate was 90% was recorded as the room temperature cycle performance of the battery at 25°C, and the cycle number at which the capacity retention rate was 80% was recorded as the high temperature cycle performance of the battery at 45°C. The cycle performance of the material was compared by comparing the cycle numbers in the above two cases.

[0197] (2) Discharge rate test

[0198] The lithium ion battery was placed in a 25°C constant temperature box and stood for 30 minutes to make the lithium ion battery reach a constant temperature. The lithium ion battery reaching the constant temperature was discharged at 0.2C constant current to a voltage of 3.0V, and then stood for 5 minutes and charged at 0.5C constant current to a voltage of 4.45V, and then charged at 4.45V constant voltage to a current of 0.05C and then stood for 5 minutes. The discharge rate was adjusted, and the discharge test was performed at 0.2C, 0.5C, 1C, 1.5C, and 2.0C, respectively, and the discharge capacities were obtained. The capacity obtained at each rate was compared with the capacity obtained at 0.2C, and the rate performance was compared by comparing the ratio of the capacities at 2C and 0.2C.

[0199] (3) Battery full charge expansion rate test:

[0200] The thickness of the fresh battery at half charge (50% SOC) is tested by using a screw micrometer, and the battery is cycled to 400 cycles at full charge (100% SOC), and then the thickness of the battery at this time is tested by using a screw micrometer. The expansion rate of the battery at full charge (100% SOC) at this time is obtained by comparing the thickness of the fresh battery at half charge (50% SOC) with the thickness of the battery at this time.

[0201] The performance parameters of the negative electrode materials of Examples 1 to 9 and Comparative Examples 1 to 4 prepared according to the above method are shown in Table 1, and the performance test results of the lithium batteries prepared are shown in Table 2.

[0202] Table 2

[0203]

[0204] As can be seen from the test results of Examples 1 to 3, under the premise that the pore size of the nitrogen-doped porous carbon, the thickness of the carbon layer and the nitrogen content are consistent, as the content of silicon deposited on the nitrogen-doped porous carbon increases, the specific capacity of the negative electrode material of Examples 1 to 3 also gradually increases. However, the increase in the thickness of the nano-silicon-containing material layer will increase the expansion rate of the battery, until the silicon expansion destroys the pore structure and the outer carbon layer, causing rapid decay of the cycle. As shown in Example 3, when the thickness of the silicon-containing material layer increases to 10 nm, the cycle performance, expansion rate and rate performance will all be deteriorated. Comparative Example 1 directly shows that when the high silicon content reaches 75.9%, the silicon particle expansion is easy to cause the destruction of the structure of the negative electrode material, and thus causes the cycle performance to decay seriously. Preferably, the mass percentage content of silicon in the negative electrode material is 32.4% to 52.5%.

[0205] As can be seen from the test results of Examples 3 to 5, under the premise that the silicon content, the thickness of the silicon-containing material layer D0, the thickness of the carbon layer D2 and the nitrogen content of the negative electrode material are consistent, the pore size D1 of the nitrogen-doped porous carbon of Examples 3 to 5 gradually increases, which can reserve more sufficient space for silicon expansion to obtain a more stable structure, and thus exhibit better cycle performance. As shown in Example 5, when the pore size increases to 20 nm, the cycle performance, expansion rate and rate performance of the battery are all improved. Comparative Example 2 directly deposits silicon particles on a carbon matrix without pores, and the expansion of the silicon particles will cause rapid decay of the cycle performance. Therefore, the use of nitrogen-doped porous carbon with a porous structure can effectively alleviate the decay of the cycle performance caused by the expansion of the silicon particles.

[0206] As can be seen from the test results of Examples 2, 6 and 7, under the premise that the silicon content of the negative electrode material, the thickness D0 of the silicon-containing material layer, the pore size D1 of the nitrogen-doped porous carbon and the nitrogen content are consistent, the thickness D2 of the carbon layer of Examples 6, 2 and 7 gradually increases. It can be seen that increasing the thickness of the carbon layer can effectively alleviate the stress caused by the expansion of the internal silicon particles, maintain the stability of the structure during the charging and discharging process, and effectively isolate the electrolyte to avoid side reactions between the silicon particles and the electrolyte. However, excessively increasing the thickness of the outer carbon layer increases the transmission distance of ions and electrons, which is not conducive to the performance of the rate capability, and is also not conducive to the performance of the high energy of silicon. As shown in Examples 6 and 7, when the thickness of the carbon layer is reduced to 2 nm and increased to 20 nm, the cycle performance, expansion rate and rate capability of the battery all decrease. In Comparative Example 3, the outer layer of the nitrogen-doped porous carbon has no carbon layer, and the stress generated by the expansion of the internal silicon particles during the cycle process can destroy the structure, and the side reactions between silicon and electrolyte can also cause rapid attenuation of the cycle.

[0207] As can be seen from the test results of Examples 2, 8 and 9, under the premise that the silicon content of the negative electrode material, the thickness D0 of the silicon-containing material layer, the pore size D1 of the nitrogen-doped porous carbon and the thickness of the outer carbon layer are consistent, the nitrogen content of Examples 8, 2 and 9 gradually increases. Increasing the nitrogen content is beneficial to improving the interaction force between nitrogen atoms in the porous carbon and silicon particles, improving the adhesion of silicon, avoiding the loss of electrical contact due to the volume expansion of silicon particles from the carbon matrix during the charging and discharging process of the silicon negative electrode, and disturbing the conjugated electron system of carbon atoms by doping nitrogen to provide larger electrochemical active area and active sites, and synergistically promote the charge transfer between carbon atoms and heteroatoms to improve the conductivity and specific capacity of carbon materials. However, a higher nitrogen content can destroy the ordered structure of the carbon matrix and reduce the structural stability of the carbon matrix. As shown in Examples 8 and 9, when the nitrogen content is reduced to 3% and increased to 8%, the cycle performance, expansion rate and rate capability of the battery all decrease. In Comparative Example 4, the porous carbon is not doped with nitrogen, and the capacity, rate and cycle performance of the negative electrode material are greatly reduced.

[0208] The negative electrode materials of Examples 10 to 15 prepared according to the above method, wherein the mass percentage content of silicon in the negative electrode material is 50%, the thickness D0 of the silicon-containing material layer is 10 nm, and the ratio D0 / D1 of the thickness D0 of the silicon-containing material layer to the pore size D1 of the nitrogen-doped porous carbon is 0.7. The other performance parameters are shown in Table 3-1, and the performance test results of the lithium battery prepared are shown in Table 3-2.

[0209] Table 3-1

[0210]

[0211] Table 3-2

[0212]

[0213] From the test results of examples 10 to 12, it can be seen that, under the premise of keeping the average particle size and other conditions unchanged, the powder conductivity of the negative electrode material is improved by increasing the thickness of the outer carbon layer. The overall I D / I G value of the negative electrode material is reduced due to the influence of the increased thickness of the carbon layer. After increasing the thickness of the carbon layer, the combination with the active material in the core is better, the pore volume of the negative electrode material is reduced, the reduction of the surface pore volume of the outer carbon layer is beneficial to the isolation of the electrolyte and the formation of a stable SEI film. The increase of the thickness of the carbon layer is beneficial to the strengthening of the constraint on the expansion stress of the silicon-carbon core. When the thickness of the carbon layer is 15 nm in example 12, the battery shows good electrochemical performance. However, the thickness of the carbon layer cannot be increased blindly, otherwise the silicon content of the negative electrode material will be reduced and the energy density of the negative electrode material will be reduced.

[0214] From the test results of examples 11, 13, 14 and 15, it can be seen that, under the premise of keeping the thickness of the carbon layer and other conditions unchanged, the average particle size of the particles is increased. Larger particles will cause larger expansion, which is easy to cause the problem of powdering of the electrode sheet, causing the negative electrode material to fall off from the negative electrode sheet and causing rapid decay of the electrochemical performance. Example 15 directly shows that when the average particle size of the negative electrode material is increased to 60 pm, the battery shows poor electrochemical performance.

[0215] The performance test results of the lithium batteries prepared from the negative electrode materials of examples 16 to 25 prepared according to the above method are shown in the table.

[0216] Table 4-1

[0217]

[0218] Table 4-2

[0219]

[0220]

[0221] From the test results of examples 16 to 19, it can be seen that, under the premise of keeping the nitrogen-doped porous carbon pore volume, wall thickness and other conditions unchanged, the pore size of the nitrogen-doped porous carbon is increased. The specific surface area of the porous carbon will be reduced. The appropriate increase of the pore size is beneficial to reserving more sufficient space for the expansion of silicon to obtain a more stable structure, thereby showing better cycle performance. However, when the pore size is too large, under the premise of keeping the pore volume, pore wall thickness and silicon content unchanged, the thickness of the silicon-containing material layer will also increase accordingly. The larger expansion stress will destroy the pore structure, causing the structure to collapse, thereby causing the breakage of the overall particles and causing the deterioration of the cycle performance. Example 19 proves that when the pore size is increased to 30 nm, the battery shows poor electrochemical performance.

[0222] From the test results of Examples 17, 20, 21 and 22, it can be seen that, under the premise of keeping the pore size and other conditions unchanged, increasing the pore volume increases the specific surface area, and since the carbon content is unchanged, the corresponding porous carbon wall thickness is increased. A larger pore volume means that the thickness of the silicon-containing material layer deposited on the pore surface is smaller, and the expansion stress caused in the lithium intercalation reaction is also smaller. The increase in the thickness of the porous carbon wall is more conducive to buffering the expansion stress. However, further increasing the pore volume and the number of pores will reduce the stability of the overall structure. Example 22 directly shows that when the pore volume is increased to 15 cm 2 / g, the negative electrode material collapses after lithium intercalation, and the battery shows rapid capacity decay and increased swelling.

[0223] From the test results of Examples 17, 23, 24 and 25, it can be seen that, under the premise of keeping the pore size and other conditions unchanged, increasing the thickness of the porous carbon wall reduces the pore volume and the specific surface area, since the carbon content is unchanged. At the initial stage of increasing the wall thickness, it is beneficial to increase the buffering of the silicon expansion stress, but continuing to increase the wall thickness will reduce the pore volume. Under the same silicon content, the thickness of the silicon deposition will increase, and the increase in the thickness of the silicon-containing material layer will increase the expansion stress, which will dominate the electrochemical performance. Example 25 directly shows that when the wall thickness is increased to 40 nm, the buffering effect of the wall thickness on the expansion is insufficient to support the substantial increase in the expansion stress, and the battery shows poor electrochemical performance.

[0224] The performance test results of the lithium batteries prepared from the negative electrode materials of Examples 26 to 32 prepared according to the above method are shown in the table.

[0225] Table 5

[0226]

[0227] From the test results of Examples 26 to 30, it can be seen that, under the premise of keeping the OI value of the electrode sheet and other conditions unchanged, when the porosity of the silicon-carbon negative electrode material is increased, as shown in Example 28, when the porosity is increased to 33%, the composite has a good expansion space, which is conducive to improving the expansion performance, but too many pores deteriorate the electrical contact, which is not conducive to the rate performance. When the porosity is reduced to 22%, as shown in Example 26, the low porosity is not conducive to buffering the expansion stress generated during lithium intercalation, resulting in poor expansion performance in the cycle. Examples 29 and 30 respectively reduce the porosity to 10% and increase it to 50%, which greatly deteriorates the expansion performance and rate performance of the material, respectively.

[0228] From the test results of Examples 27, 31 to 32, it can be seen that, under the premise of keeping the porosity of the pole piece and other conditions unchanged, increasing the pole piece OI value is conducive to improving the lithium ion transmission rate and improving the rate performance of the battery.

[0229] Although the present application is disclosed with the preferred embodiments, it is not intended to limit the claims, any person skilled in the art can make several possible changes and modifications without departing from the concept of the present application, therefore the protection scope of the present application should be defined by the scope of the claims of the present application.

Claims

1. A negative electrode material, characterized by, The negative electrode material comprises an active material and a carbon layer on the surface of the active material, the active material comprises a nitrogen-doped porous carbon and a silicon-containing material layer; the powder conductivity of the negative electrode material is 2.0 S / cm to 30 S / cm; by Raman spectroscopy, the ratio ID / IG of the peak intensity ID at 1350 cm -1 to the peak intensity IG at 1580 cm -1 of the negative electrode material ranges from 1.2 to 2.2; the mass percentage content of silicon in the negative electrode material is 30% to 80%. The nitrogen-doped porous carbon satisfies at least one of conditions (1) to (3) below: (1) the specific surface area of the nitrogen-doped porous carbon is 2000 m 2 / g to 3500 m 2 / g; (2) the nitrogen-doped porous carbon has a pore volume of 1 cm 2 / g to 10 cm 2 / g; (3) The average pore size of the pores in the nitrogen-doped porous carbon is 1 nm to 20 nm.

2. The negative electrode material according to claim 1, characterized in that, The silicon-containing material layer is located on the pore wall of the nitrogen-doped porous carbon.

3. The negative electrode material according to claim 1 or 2, characterized in that, The negative electrode material satisfies at least one of conditions (1) to (4) below: (1) The thickness D0 of the silicon-containing material layer is in the range of 1 nm to 10 nm; (2) The ratio of the thickness D0 of the silicon-containing material layer to the pore size D1 of the nitrogen-doped porous carbon satisfies: 0.2≤D0 / D1<0.8; (3) The ratio of the thickness D0 of the silicon-containing material layer to the thickness D2 of the carbon layer satisfies: 0.05≤D0 / D2≤10; (4) The wall thickness of the porous carbon in the nitrogen-doped porous carbon is 5 nm to 30 nm.

4. The negative electrode material of claim 1, wherein, The negative electrode material satisfies at least one of conditions (1) to (7) below: (1) the specific surface area of the negative electrode material is 1 m 2 / g to 50 m 2 / g; (2) the pore volume of the negative electrode material is 0.001 cm 2 / g to 0.1 cm 2 / g; (3) The particle size of the negative electrode material is in the range of 1 µm to 100 µm, and / or the average particle size of the negative electrode material is 2.5 µm to 50 µm; (4) The thickness of the carbon layer of the negative electrode material is 2 nm to 20 nm; (5) The mass percentage content of the carbon layer in the negative electrode material is 3% to 10%; (6) The mass percentage content of the nitrogen-doped porous carbon in the negative electrode material is 10% to 67%.

5. The negative electrode material of claim 1, wherein, The nitrogen-doped porous carbon satisfies at least one of conditions (1) to (3) below: (1) The nitrogen element in the nitrogen-doped porous carbon is doped in the carbon phase in the form of C-N bond; (2) The mass percentage content of nitrogen in the nitrogen-doped porous carbon is 0.5% to 10%; (3) Through XPS analysis, the configuration of nitrogen in the nitrogen-doped porous carbon includes at least one of pyridine nitrogen, pyrrole nitrogen, graphite nitrogen, graphitized nitrogen, and oxidized nitrogen, and the mass percentage of the graphitized nitrogen in all nitrogen is 30% to 70%.

6. A method for producing the negative electrode material according to any one of claims 1 to 5, characterized by, The method comprises the following steps: carrying out high-temperature carbonization treatment and acid washing treatment on the antibiotic bacterial residue by using a metal salt to obtain nitrogen-doped porous carbon; carrying out gas phase deposition on the nitrogen-doped porous carbon by using silane gas to obtain an active material; mixing the active material with a carbon source and then carrying out carbon composite treatment to obtain a negative electrode material.

7. The preparation method according to claim 6, characterized in that, The method satisfies at least one of conditions (1) to (3) below: (1) The carbon source includes at least one of resin, pitch, and high molecular polymer; (2) The metal salt includes at least one of sodium chloride, potassium chloride, sodium carbonate, or potassium carbonate; (3) The acid used in the acid washing treatment includes at least one of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, hydrofluoric acid, or phosphoric acid.

8. A negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided on a surface of the negative electrode current collector, characterized by The negative electrode active material layer comprises the negative electrode material of any one of claims 1 to 5 or the negative electrode material prepared by the preparation method of any one of claims 6 to 7.

9. The negative electrode sheet according to claim 8, characterized by, The negative electrode tab satisfies at least one of conditions (1) to (4) below: (1) The porosity of the negative electrode active material layer is 20% to 40%; (2) The electrical resistance of the negative electrode active material layer is in the range of 0.2 Ω to 2 Ω; (3) the compacted density of the negative electrode active material layer is 1.5 g / cm3or more and 2.0 g / cm3or less under a pressure of 5T 3 . (3) the compacted density of the negative electrode active material layer is 1.5 g / cm3or more and 2.0 g / cm3or less under a pressure of 5T 3 . (4) The OI value of the negative electrode active material layer is in the range of 1 to 20.

10. An electrochemical device comprising a negative electrode active material layer, characterized by, The negative active material layer comprises the negative electrode material of any one of claims 1 to 5 or the negative electrode material prepared by the preparation method of any one of claims 6 to 7.

11. The electrochemical device of claim 10, wherein, The electrochemical device is a lithium ion battery.

12. An electronic device, comprising: The electronic device comprises the electrochemical device of claim 10.

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