Negative electrode active material, secondary battery, and electronic device

Abstract

The present invention belongs to the technical field of batteries, and provides a negative electrode active material, a secondary battery, and an electronic device. The negative electrode active material comprises a silicon-based material and an outer layer material, wherein the outer layer material comprises a conductive agent and a nitrile polymer. The infrared spectrum of the negative electrode active material comprises infrared characteristic peaks of a cyano group. The negative electrode active material comprises nitrogen and silicon; and based on the mass of the negative electrode active material, the mass content of nitrogen is D1%, the mass content of silicon is G%, and 0.02≤D1 / G≤0.5. By forming the outer layer material comprising the conductive agent and the nitrile polymer on the surface of the silicon-based material, the conductivity and the stability of the negative electrode active material can be improved, such that the secondary battery has an excellent cycle capacity retention rate and expansion inhibition performance, and the high-temperature storage performance of the secondary battery can be further improved.

Description

Negative electrode active material, secondary battery and electronic device TECHNICAL FIELD

[0001] The present application belongs to the technical field of batteries, and particularly relates to a negative electrode active material, a secondary battery and an electronic device. BACKGROUND

[0002] With the increasing demand for large-scale storage, electric vehicles and portable electronic devices, it is a top priority to develop energy storage devices with higher energy density. Secondary batteries are widely used in various fields due to their long cycle life and environmental protection characteristics. However, as a traditional negative electrode active material of secondary batteries, graphite is limited in further application due to its low capacity (372 mAh / g) and safety hazards such as active material precipitation. Therefore, the development of negative electrode active materials with high energy density and high safety has become the key to the development of current secondary battery technology.

[0003] Compared with carbon-based materials such as graphite, elemental silicon has an ultra-high theoretical specific capacity (Li 15 Si4, 3579 mAh / g) and a suitable working voltage (<0.5 V vs. Li / Li + ), and is considered to be the most promising negative electrode active material to replace graphite. However, the huge volume expansion and low conductivity of elemental silicon during alloying / de-alloying process seriously limit its large-scale application in secondary batteries.

[0004] To solve the above problems, the prior art mainly adopts methods such as nanosizing silicon, constructing porous silicon or silicon-carbon negative electrode active materials, and introducing transition metal oxides. Although silicon nanosizing and porous silicon can alleviate the volume expansion problem of elemental silicon to some extent, the high specific surface area and low tap density limit their large-scale application. Silicon-carbon composite and the introduction of transition metal oxides can reduce the volume expansion of silicon, but due to the poor mechanical properties and chemical stability of carbon and metal oxides, they also cannot achieve the ideal buffering effect. SUMMARY

[0005] To solve the above problems, the present application provides a negative electrode active material, a secondary battery and an electronic device, which can improve the conductivity of the negative electrode active material and reduce the volume expansion during charging and discharging, improve the first coulomb efficiency, inhibit the expansion performance, cycle performance and high-temperature storage performance of the secondary battery.

[0006] In a first aspect, the present application provides a negative electrode active material, comprising a silicon-based material and an outer layer material; the outer layer material is located on at least part of the surface of the silicon-based material; the outer layer material comprises a conductive agent and a nitrile polymer; the negative electrode active material includes an infrared characteristic peak of a cyano group in its infrared spectrum, and the infrared characteristic peak of the cyano group is located at 2250 cm -1 2400 cm-1 The negative active material comprises nitrogen and silicon elements; the mass content of the nitrogen element is D1%, and the mass content of the silicon element is G%, based on the mass of the negative active material, and 0.02≤D1 / G≤0.5. The present application utilizes the conductive agent and the nitrile-based polymer containing a cyano group to form a first shell. The conductive network formed on the surface of the silicon-based material by the conductive agent can improve the overall conductivity of the negative active material, reduce the negative resistance, and improve the initial coulomb efficiency of the secondary battery. When the mass content of the nitrogen element and the silicon element in the negative active material meets the above range, the conductive agent and the nitrile-based polymer can form a high-flexibility and tightly interwoven outer material on the surface of the silicon-based material, and can also promote the formation of a stable solid electrolyte interface film (SEI film) on the surface of the negative active material, which helps to buffer the volume expansion and stress of the silicon-based material under high-temperature conditions and during the cycle process, improves the interface stability of the negative active material, reduces the structural damage of the negative active material and the decomposition of the electrolyte, improves the expansion problem of the secondary battery with a silicon-containing system, and improves the high-temperature storage performance and cycle stability of the secondary battery.

[0007] In some embodiments, the negative active material satisfies at least one of the following conditions:

[0008] (1) 1.1≤D1≤18.4; controlling the content of the nitrogen element in the negative active material in this range can improve the quality of the SEI film, reduce the decomposition of the electrolyte and the generation of by-products, and make the secondary battery exhibit higher cycle performance and initial coulomb efficiency.

[0009] (2) 36.8≤G≤68.3; controlling the content of the silicon element in the negative active material in this range can make the negative active material have a higher specific capacity, and after cooperating with the conductive agent and the nitrile-based polymer in the outer material, it can significantly improve the expansion inhibition performance and cycle performance of the secondary battery.

[0010] (3) 0.04≤D1 / G≤0.37. Controlling the mass ratio of the nitrogen element and the silicon element in this range can further improve the film formation quality of the SEI film, make the negative active material maintain higher cycle stability, and optimize the flexible conductive network structure of the outer material, absorb the volume change of the silicon-based material, improve the expansion inhibition performance of the secondary battery, and optimize the cycle performance and high-temperature storage performance of the secondary battery.

[0011] In some more preferred embodiments, the negative active material satisfies at least one of the following conditions:

[0012] (1) 2.3≤D1≤9.2; the nitrile-based polymer with the nitrogen element in this content range can further improve the initial coulomb efficiency and cycle performance of the secondary battery.

[0013] (2) 43.2≤G≤51.3; the content range of silicon element can make the secondary battery exhibit more excellent expansion inhibition performance and cycle performance.

[0014] (3) 0.06≤D1 / G≤0.19. Controlling the mass ratio of nitrogen element and silicon element in the negative electrode active material to meet the range can further improve the expansion inhibition performance, cycle performance and high-temperature storage performance of the secondary battery.

[0015] In some embodiments, the sphericity of the negative electrode active material is S, and 0.8≤S≤1.0; when the sphericity of the negative electrode active material is regulated to meet this condition, it can cooperate with the outer layer material including the conductive agent and the nitrile-based polymer to more uniformly release the stress of the negative electrode active material under high-temperature conditions or during the cycle process, buffer the volume expansion and reduce the structural damage of the negative electrode active material, and improve the expansion inhibition performance, cycle performance and high-temperature storage performance of the secondary battery.

[0016] In some embodiments, the thickness of the outer layer material in the negative electrode active material is T nm, and 0.5≤T≤200.0. The present application regulates the thickness of the outer layer material to meet this range, which can make the negative electrode active material have a higher specific capacity, improve the electrical conductivity of the negative electrode active material, and also be beneficial to improving the interface stability of the negative electrode active material, and optimize the expansion inhibition performance, cycle performance and high-temperature storage performance of the secondary battery.

[0017] In some embodiments, the negative electrode active material meets at least one of the following conditions:

[0018] (1) 0.9≤S≤1.0; when the sphericity of the secondary battery is further regulated to meet this range, the secondary battery can have higher expansion inhibition performance, cycle performance and high-temperature storage performance.

[0019] (2) 0.5≤T≤100.0; regulating the thickness T of the outer layer material to meet this range can more significantly improve the expansion inhibition performance, cycle performance and high-temperature storage performance of the secondary battery.

[0020] (3) 0.5≤S×T≤90.0; preferably, 10.4≤S×T≤67.8; controlling the value of S×T to meet this range can promote the close cooperation of each component in the negative electrode active material, uniformly release the stress in the negative electrode active material, and improve the initial coulomb efficiency, expansion inhibition performance, high-temperature storage performance and cycle performance of the secondary battery.

[0021] (4) The average particle size of the negative active material is R pm; 5.6≤R≤10.3. Controlling the average particle size of the negative active material in the range can make the negative active material achieve a suitable specific surface area, reduce the consumption of electrolyte, and also be beneficial to improving the tap density of the negative active material, so that the secondary battery has higher energy density and cycle performance.

[0022] In some embodiments, the negative active material satisfies at least one of the following conditions:

[0023] (1) The conductive agent comprises single-walled carbon nanotubes and / or multi-walled carbon nanotubes; the use of these carbon nanotubes as conductive agents can achieve long-range conductivity, further improve the electrical conductivity of the negative active material, and enable the secondary battery to exhibit higher initial coulombic efficiency and cycle performance when combined with the nitrile-based polymer of the present application.

[0024] (2) The nitrile-based polymer comprises at least one of polyacrylonitrile, polycyanoacrylate, and polycyanobenzene; these nitrile-based polymers can promote the improvement of the stability of the interface during the cycle process, thereby improving the cycle performance and anti-swelling performance of the secondary battery. Preferably, the nitrile-based polymer is polyacrylonitrile, which can use polyacrylonitrile to rivet the outer material on the silicon-carbon material, form a good coating on the silicon-based material, improve the interface stability of the negative active material and reduce the generation of interface byproducts, thereby improving the cycle stability, high-temperature storage performance, and swelling inhibition performance of the secondary battery.

[0025] (3) The silicon-based material comprises a porous carbon skeleton and a silicon material; the silicon material is located on the surface and / or inside the porous carbon skeleton. This type of silicon-based material can better cooperate with the outer material to improve the cycle performance, high-temperature storage performance, and swelling inhibition performance of the secondary battery.

[0026] In the second aspect, the present application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte; the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer arranged on at least part of the surface of the negative electrode current collector, and the negative electrode mixture layer comprises any one of the negative active materials provided in the first aspect of the present application.

[0027] In some embodiments, the negative electrode mixture layer comprises sodium elements, and the mass content of nitrogen elements is D2% and the mass content of sodium elements is N% based on the mass of the negative electrode mixture layer; the negative electrode mixture layer satisfies at least one of the following conditions:

[0028] (1) 0.58≤N≤1.74; preferably, 0.81≤N≤1.04; controlling the content of sodium elements in the negative electrode mixture layer in the above range can enable the dispersant to cooperate with the negative active material of the present application, and fully play a role in improving the initial coulombic efficiency of the secondary battery.

[0029] (2) 1.6≤D2≤8.1; preferably, 5.0≤D2≤7.8; by controlling the mass content of nitrogen element in the negative electrode active material layer to satisfy the above range, the specific capacity and the conductivity of the secondary battery can be improved, and the cycle performance and the swelling inhibition performance can be improved.

[0030] (3) 2.35≤D2 / N≤11.74; preferably, 4.81≤D2 / N≤9.63; by controlling the mass ratio of the nitrogen element and the sodium element in the negative electrode active material layer to satisfy the above range, the energy density of the secondary battery can be improved, and the initial coulombic efficiency, the cycle performance and the swelling inhibition performance of the secondary battery can be improved.

[0031] (4) the sodium element is from at least one of sodium alginate, sodium carboxymethyl cellulose, sodium hydroxymethyl cellulose or sodium hydroxyethyl carboxymethyl cellulose.

[0032] In some embodiments, the electrolyte comprises at least one of fluorobenzene or fluoroethylene carbonate; the electrolyte satisfies at least one of the following conditions based on the mass of the electrolyte:

[0033] (1) the mass content of fluorobenzene is F1%, 0.9≤F1≤5.2; preferably, 2.1≤F1≤3.1; when the electrolyte of the secondary battery contains fluorobenzene, and the mass content of fluorobenzene in the electrolyte is regulated to satisfy the above range, the high-temperature storage performance of the secondary battery can be further optimized, and the initial coulombic efficiency, the cycle performance and the swelling inhibition performance can be improved.

[0034] (2) the mass content of fluoroethylene carbonate is F2%, 3.8≤F2≤7.4; by regulating the mass content of fluoroethylene carbonate (FEC) in the electrolyte to satisfy the above range, the secondary battery can achieve more excellent high-temperature storage performance, cycle performance and swelling inhibition performance.

[0035] In a third aspect, the present application provides an electronic device comprising the secondary battery provided in the second aspect of the present application.

[0036] Based on the above negative electrode active material, secondary battery and electronic device of the present application, by forming an outer layer material comprising a conductive agent and a nitrile-based polymer on the surface of the silicon-based material, the conductivity, the interface and the structural stability of the negative electrode active material can be improved at the same time, so that the secondary battery can still have excellent cycle capacity retention rate and swelling inhibition performance under high energy density, and a more stable SEI film can be formed, and the cycle performance and the high-temperature storage performance of the secondary battery can be further improved. BRIEF DESCRIPTION OF DRAWINGS

[0037] FIG. 1 is an infrared spectrum of the negative electrode active material provided in Example 1-1 of the present application;

[0038] FIG. 2 is a partial enlarged view of the infrared spectrum of the negative electrode active material provided by Example 1-1. DETAILED DESCRIPTION

[0039] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to examples. It should be understood that the specific examples described herein are only used to explain the present application and not used to limit the present application.

[0040] In a first aspect, the present application provides a negative electrode active material, comprising a silicon-based material and an outer layer material; the outer layer material is located on at least part of the surface of the silicon-based material; the outer layer material comprises a conductive agent and a nitrile-based polymer; the infrared spectrum of the negative electrode active material comprises an infrared characteristic peak of a cyano group, and the infrared characteristic peak of the cyano group is located between 2250 cm -1 and 2400 cm -1 ; the negative electrode active material comprises nitrogen and silicon elements; the mass content of the nitrogen element is D1%, and the mass content of the silicon element is G%, based on the mass of the negative electrode active material, and 0.02≤D1 / G≤0.5. The present application forms an outer layer material comprising a conductive agent and a nitrile-based polymer on the surface of the silicon-based material, which can form a conductive network structure of the conductive agent on the surface of the negative electrode active material, improve the electrical conductivity of the negative electrode active material, improve the electronic conduction performance, and cooperate with the silicon-based material to improve the energy density of the secondary battery, while promoting the ion transmission rate of the secondary battery during the charging and discharging process, and improving the first coulomb efficiency. On this basis, controlling the mass ratio of the silicon element and the nitrogen element in the negative electrode active material to meet the above relationship can improve the flexibility and structural stability of the outer layer material, and promote the formation of a stable SEI film on the surface of the negative electrode active material, which helps to buffer the volume expansion and stress of the silicon-based material under high temperature conditions and during the cycle process, reduces the structural damage of the negative electrode active material and the decomposition of the electrolyte, and improves the expansion inhibition performance, high-temperature storage performance and cycle stability of the secondary battery.

[0041] In the present application, the mass content of the silicon element and the nitrogen element in the negative electrode active material satisfies 0.02≤D1 / G≤0.5, preferably 0.04≤D1 / G≤0.37, and more preferably 0.06≤D1 / G≤0.19. For example, the value of D1 / G is 0.02, 0.04, 0.06, 0.09, 0.12, 0.14, 0.16, 0.19, 0.20, 0.23, 0.26, 0.30, 0.31, 0.33, 0.36, 0.37, 0.42, 0.43, 0.46, 0.48, 0.5 or a value within a range consisting of any two of these values. Controlling the content ratio of the silicon element and the nitrogen element within the above range can improve the cooperation effect of the nitrile-based polymer and the silicon-based material, and further improve the cycle performance and high-temperature storage performance of the secondary battery during the cycle process.

[0042] In some embodiments, 1.1≤D1≤18.4; preferably 2.3≤D1≤9.2. Exemplarily, D1 is 1.1, 1.3, 2.3, 3.8, 4.6, 6.8, 7.1, 9.2, 11.2, 11.8, 13.6, 14.9, 15.7, 17.3, 18.4 or a value within a range consisting of any two of these values. Controlling the content of nitrogen element in the negative active material in the above range can improve the stability of SEI film, reduce the side reaction of silicon-based material with electrolyte, improve the volume stability of silicon-based material, and further improve the high-temperature storage performance, cycle performance and swelling inhibition performance of the secondary battery.

[0043] In some embodiments, 36.8≤G≤68.3, preferably 43.2≤G≤51.3, for example G can be 36.8, 38.8, 40.0, 43.2, 44.3, 47.0, 49.2, 51.3, 53.4, 55.4, 58.1, 59.8, 62.5, 65.2, 67.1, 68.3 or a value within a range consisting of any two of these values. Controlling the content of silicon element in the negative active material in the above range and cooperating with the nitrile-based polymer can improve the gravimetric capacity of the negative active material, reduce the volume expansion effect, improve the volume stability of the negative active material during the cycle process, and thus improve the swelling inhibition performance and cycle performance of the secondary battery.

[0044] The method for controlling the mass content of silicon element and nitrogen element in the negative active material in the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the mass content of silicon element can be controlled by controlling the content of silicon element in the silicon-based material or changing the addition ratio of the silicon-based material, and the mass content of nitrogen element can be controlled by controlling the addition ratio of the nitrile-based compound.

[0045] The element content (silicon element, nitrogen element, etc.) of the negative active material in the present application can be tested by a method known in the art, for example, the element content of the negative active material sample can be quantitatively tested by Shimadzu / Kratos X-ray photoelectron spectrometer AXIS SUPRA+.

[0046] In some embodiments, the sphericity of the negative active material is S, 0.8≤S≤1.0; preferably 0.9≤S≤1.0; for example, S is 0.8, 0.81, 0.82, 0.84, 0.85, 0.87, 0.89, 0.91, 0.92, 0.93, 0.94, 0.96, 0.97, 0.99, 1.0, or a value within a range defined by any two of these values. Controlling the sphericity of the negative active material to meet the above range, in combination with the outer layer material comprising a conductive agent and a nitrile-based polymer, can more uniformly release the stress of the negative active material under high temperature conditions or during cycling, buffer volume expansion and reduce structural damage to the negative active material, and improve the expansion inhibition performance, cycle performance, and high-temperature storage performance of the secondary battery.

[0047] In the present application, the sphericity S of the negative active material can be tested using methods known in the art, for example, the sphericity of the negative active material can be tested using the equivalent diameter method, which includes: using a ZEISS-SEM (sigma-02-33) scanning electron microscope to observe a particle sample of the negative active material, randomly selecting 20 negative active material particles, and calculating the perimeter equivalent diameter and the area equivalent diameter of each; or cutting a negative electrode sheet to obtain a test surface, performing argon ion polishing treatment on the test surface to obtain a test sample, then using a scanning electron microscope to observe the negative active material in the test sample, randomly selecting 20 negative active material particles, and calculating the perimeter equivalent diameter and the area equivalent diameter of the negative active material particles. The sphericity of each negative active material particle = perimeter equivalent diameter / area equivalent diameter, and the arithmetic mean of the sphericity of the 20 negative active material particles is calculated to obtain the sphericity of the negative active material.

[0048] In some embodiments, the thickness of the outer layer material in the negative active material is T nm, 0.5≤T≤200.0; preferably 0.5≤T≤100.0. For example, T is 0.5, 4.7, 17.6, 27.2, 37.5, 50.5, 54.4, 67.9, 76.2, 92.5, 100.0, 104.7, 111.3, 125.7, 129.8, 143.3, 150.1, 160.9, 171.7, 185.6, 189.9, 200, or a value within a range defined by any two of these values. Controlling the thickness of the outer layer material to meet the above range can enable the negative active material to have a higher gravimetric capacity, improve the electrical conductivity of the negative active material, and also be beneficial to improving the interface stability of the negative active material, and optimizing the expansion inhibition performance, cycle performance, and high-temperature storage performance of the secondary battery.

[0049] The application does not make special restrictions on the test method of the thickness of the outer layer material of the negative electrode active material, and the method known in the art can be used for testing. For example, 20 negative electrode active materials can be randomly selected, 20 cross-section samples of the negative electrode active materials are prepared, a scanning electron microscope is used to observe and count the maximum thickness and minimum thickness of the outer layer material on the cross-section of each negative electrode active material, the arithmetic mean of the maximum thickness and the minimum thickness is calculated as the thickness of the outer layer material in a single negative electrode active material, and then the arithmetic mean of the 20 negative electrode active materials is calculated, which is denoted as the thickness T of the outer layer material, nm.

[0050] In some embodiments, 0.5≤S×T≤90.0; preferably, 10.4≤S×T≤67.8. Exemplarily, the value of S×T is 0.5, 2.0, 6.7, 12.6, 14.9, 22.0, 24.9, 33.1, 34.9, 40.3, 45.2, 48.0, 56.6, 60.4, 65.7, 69.6, 75.2, 77.4, 82.8, 88.6, 90.0 or a value within a range consisting of any two of these values. Controlling the value of S×T to meet the above range can promote the close cooperation of each component in the negative electrode active material, uniformly release the stress in the negative electrode active material, and improve the initial coulomb efficiency, swelling performance, high-temperature storage performance and cycle performance of the secondary battery.

[0051] In some embodiments, the average particle size of the negative electrode active material is Rμm, and 5.6≤R≤10.3. For example, R can be 5.6, 5.9, 6.2, 6.6, 7.0, 7.1, 7.7, 8.1, 8.3, 8.7, 8.9, 9.3, 9.8, 10.0, 10.3 or a value within a range consisting of any two of these values. On the basis of controlling the element content of the above negative electrode active material, the application further regulates the average particle size of the negative electrode active material in the above range, so that the negative electrode active material has a suitable specific surface area, which is beneficial to improve the synergistic effect between elements, reduce the occurrence of side reactions and the consumption of electrolyte during the cycle process, and also helps to improve the compaction density of the negative electrode active material, which is beneficial to improve the electrical conductivity of the negative electrode active material and improve the cycle performance and initial coulomb efficiency of the secondary battery.

[0052] The average particle size of the negative active material in the present application can be tested by a method known in the art, for example, a method comprising the following steps can be used: selecting a sample area on the negative electrode tab, taking a SEM photo of the sample area by scanning electron microscope, then randomly selecting 10 particles of the negative active material as samples from the SEM photo by using image analysis software, calculating the area of each of the negative active material samples, then assuming that the negative active material samples are spherical, calculating the particle size R0 (diameter) of each of the negative active material samples by the following formula: R0 = 2 x (S / π) 1 / 2 ; wherein S is the area of the negative active material sample. The particle size R0 of the above-mentioned negative active material samples is calculated for 3 SEM images, and the particle sizes of the 30 (10 x 3) negative active material samples obtained are arithmetically averaged to obtain the average particle size R of the negative active material to be tested.

[0053] In some embodiments, the conductive agent comprises single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The use of single-walled carbon nanotubes or multi-walled carbon nanotubes can further improve the electrical conductivity of the negative active material, and in combination with the nitrile-based polymer of the present application, the structural stability of the outer layer material can be optimized, further improving the cycle stability of the negative active material, and the secondary battery exhibits higher initial coulombic efficiency, cycle performance and swelling inhibition performance.

[0054] In some embodiments, the nitrile-based polymer comprises polyacrylonitrile, which, in combination with the conductive agent and silicon-based material of the present application, can further promote the improvement of the stability of the interface during the cycle process, improve the cycle stability, high-temperature storage performance and swelling inhibition performance of the secondary battery.

[0055] The silicon-based material in the present application can be a material known in the art, for example, silicon-carbon material, silicon-oxygen material and silicon. In some preferred embodiments, the silicon-based material comprises a porous carbon skeleton and a silicon material; the silicon material is located on the surface and / or inside the porous carbon skeleton. Such silicon-carbon material can better cooperate with the outer layer material, and the multiple fixation and support of silicon by the porous carbon skeleton in cooperation with the outer layer material can further limit the swelling effect during the silicon alloying process, improve the swelling inhibition performance and cycle stability of the secondary battery, and in addition, it is beneficial to improve the overall electrical conductivity of the negative active material, promote the embedding and extraction of the active material, and improve the energy density and initial coulombic efficiency of the secondary battery.

[0056] The silicon-carbon material used in the present application can be prepared by a method known in the art, which is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, it can comprise chemical vapor deposition of a silicon source and a carbon source.

[0057] In some embodiments, the negative active material is prepared by a method comprising the following steps:

[0058] S1: providing a silicon-carbon material; the silicon-based material comprises a porous carbon framework and a silicon material; the silicon material is located on the surface and inside of the porous carbon framework.

[0059] S2: performing a first dispersion treatment on the conductive agent and the nitrile-based polymer in a solvent to obtain a dispersion system; the solvent comprises at least one of water, ethanol, propanol, butanol, ethylene glycol, propylene glycol, dimethyl methanol, dimethyl sulfoxide, and ethyl acetate;

[0060] S3: adding the silicon-carbon material in S1 to the dispersion system in S2 to perform a second dispersion treatment, and then performing a drying treatment, to obtain the negative electrode active material of the present application.

[0061] The present application does not particularly limit the specific parameters of the first dispersion treatment, the second dispersion treatment, and the drying treatment in the preparation method of the negative electrode active material, as long as the purpose of the present application can be achieved. The order of adding the conductive agent and the nitrile-based polymer during the first dispersion treatment is not particularly limited, as long as the purpose of the present application can be achieved. For example, the order of adding the conductive agent and the nitrile-based polymer can be adjusted to make the two have different first dispersion treatment times, so as to control the area ratio of the conductive agent and the nitrile-based polymer in the outer layer material.

[0062] In a second aspect, the present application provides a secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte; the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer arranged on at least part of the surface of the negative electrode current collector, and the negative electrode mixture layer comprises any one of the negative electrode active materials provided in the first aspect of the present application.

[0063] The secondary battery of the present application is not particularly limited, and for example, can include but is not limited to: lithium ion secondary batteries (lithium ion batteries) and sodium ion batteries, etc.

[0064] In some embodiments, the negative electrode mixture layer comprises a sodium element, the mass content of the nitrogen element is D2%, and the mass content of the sodium element is N%, based on the mass of the negative electrode mixture layer; 2.35≤D2 / N≤11.74; preferably, 4.81≤D2 / N≤9.63; for example, the value of D2 / N is 2.35, 2.95, 3.61, 4.41, 4.81, 4.93, 5.31, 6.26, 7.09, 7.82, 8.76, 9.14, 9.63, 10.07, 11.00, 11.74, or a value within a range consisting of any two of these values. Controlling the mass ratio of the nitrogen element and the sodium element in the negative electrode mixture layer to satisfy the above range can improve the energy density of the secondary battery, and improve the first coulomb efficiency, the cycle performance, and the swelling inhibition performance of the secondary battery.

[0065] In some embodiments, 0.58≤N≤1.74; preferably, 0.81≤N≤1.04; for example, N is 0.58, 0.61, 0.70, 0.76, 0.81, 0.86, 0.99, 1.04, 1.15, 1.25, 1.37, 1.40, 1.53, 1.57, 1.70, 1.74, or a value within a range between any two of these values. Controlling the content of sodium element in the negative electrode mixture layer in the above range can enable the dispersant to cooperate with the negative electrode active material of the present application, fully play the role of improving the first coulombic efficiency of the secondary battery, and be beneficial to the cycle performance and high-temperature storage performance of the secondary battery.

[0066] In some embodiments, 1.6≤D2≤8.1; preferably, 5.0≤D2≤7.8; for example, D2 is 1.6, 2.0, 2.5, 2.8, 3.4, 3.7, 4.4, 5.0, 5.2, 5.6, 6.4, 6.7, 7.2, 7.8, 8.1, or a value within a range between any two of these values. By controlling the mass content of nitrogen element in the negative electrode mixture layer to satisfy the above range, the specific capacity and conductivity of the secondary battery can be improved, and its cycle performance, high-temperature storage performance, and swelling inhibition performance can be improved.

[0067] In some embodiments, the sodium element is from at least one of sodium alginate, sodium carboxymethyl cellulose, sodium hydroxymethyl cellulose, or sodium hydroxyethyl carboxymethyl cellulose. The above dispersant can better cooperate with the negative electrode active material of the present application, and improve the first coulombic efficiency, cycle performance, high-temperature storage performance, and swelling inhibition performance of the secondary battery.

[0068] In the present application, the negative electrode active material is included in the negative electrode mixture layer of the negative electrode sheet. The negative electrode sheet of the present application also includes a negative electrode current collector. In the present application, the negative electrode mixture layer can be provided on one side of the surface in the thickness direction of the negative electrode current collector, or on both sides of the surface in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the negative electrode current collector, or a partial area of the negative electrode current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. The thickness of the negative electrode mixture layer is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided negative electrode mixture layer can be 30 μm to 160 μm.

[0069] The negative current collector is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the negative current collector can include a copper foil, an aluminum foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a composite current collector (e.g., a carbon copper composite current collector, a nickel copper composite current collector, a titanium copper composite current collector), a polymer substrate coated with a conductive metal, or any combination thereof. The thickness of the negative current collector is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the thickness of the negative current collector is 4 μm to 10 μm.

[0070] In the present application, the negative electrode active material layer can further include a negative electrode binder, which can include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid, styrene butadiene rubber, acrylated styrene butadiene rubber, an epoxy resin, or nylon.

[0071] In the present application, the negative electrode active material layer can further include a conductive agent, and the type of the conductive agent in the negative electrode active material layer is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the conductive agent can include, but is not limited to, a carbon-based material, a metal-based material, a conductive polymer, and a mixture 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 a metal powder, a metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative. The mass ratio of the negative electrode active material, the conductive agent, and the negative electrode binder in the negative electrode active material layer is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the loading amount of the negative electrode active material in the negative electrode tab is 1.0 mg / cm 2 to 1.5 mg / cm 2 .

[0072] In some embodiments, the electrolyte includes at least one of fluorobenzene or fluoroethylene carbonate; the mass content of the fluorobenzene is F1% based on the mass of the electrolyte, 0.9≤F1≤5.2; preferably, 2.1≤F1≤3.1; for example, F1 is 0.9, 1.0, 1.2, 1.5, 1.7, 2.0, 2.1, 2.5, 2.7, 2.9, 2.9, 3.3, 3.5, 3.8, 4.0, 4.2, 4.4, 4.6, 4.9, 5.0, 5.2, or a value within a range between any two of these values. When the electrolyte of the secondary battery contains fluorobenzene, and the mass content of the fluorobenzene in the electrolyte is regulated to satisfy the above range, the high-temperature storage performance of the secondary battery can be further optimized, and its first coulombic efficiency, cycle performance, and swelling suppression performance can be improved.

[0073] In some embodiments, the mass content of fluoroethylene carbonate is F2% based on the mass of the electrolyte solution, 3.8 ≤ F2 ≤ 7.4, for example, F2 is 3.8, 4.0, 4.2, 4.3, 4.4, 4.6, 4.9, 5.0, 5.3, 5.4, 5.5, 5.7, 6.0, 6.1, 6.4, 6.6, 6.7, 6.8, 7.2, 7.3, 7.4, or a value within a range defined by any two of these values. Controlling the mass content of fluoroethylene carbonate (FEC) in the electrolyte solution to be within the above range enables the secondary battery to achieve more excellent high-temperature storage performance, cycle performance, and swelling suppression performance.

[0074] According to some embodiments of the present application, the electrolyte further includes a lithium salt and a non-aqueous solvent. The lithium salt can include, but is not limited to, at least one of 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), lithium difluoro(oxalato)borate LiBF2(C2O4) (LiDFOB), LiNO3, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, Li2SiF6, lithium bis-trifluoromethanesulfonimide (LiTFSI), or lithium difluoroborate. The present application does not limit the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application does not particularly limit the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent can include, but is not limited to, at least one of a carbonate compound, a carboxylate compound, an ether compound, or another organic solvent. The above-mentioned carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluorinated carbonate compound. The above-mentioned chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or ethyl methyl carbonate (EMC). The above-mentioned cyclic carbonate can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, or vinyl ethylene carbonate. The fluorinated carbonate compound can include, but is not limited to, at least one of carbonic acid-1,2-difluoroethylene ester, carbonic acid-1,1-difluoroethylene ester, carbonic acid-1,1,2-trifluoroethylene ester, carbonic acid-1,1,2,2-tetrafluoroethylene ester, carbonic acid-1-fluoro-2-methyl ethylene ester, carbonic acid-1-fluoro-1-methyl ethylene ester, carbonic acid-1,2-difluoro-1-methyl ethylene ester, carbonic acid-1,1,2-trifluoro-2-methyl ethylene ester, or carbonic acid trifluoromethyl ethylene ester. The above-mentioned carboxylate compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, pentolactone, or hexolactone. The above-mentioned ether compound can include, but is not limited to, at least one of 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (1,2-dimethoxy ethane, DME), dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-diethoxy ethane, 1-ethoxy-1-methoxy ethane, 2-methyl tetrahydrofuran, or tetrahydrofuran.The above other organic solvents can include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0075] The positive electrode according to the present application is not particularly limited as long as the object of the present application can be achieved. For example, the positive electrode includes a positive electrode current collector and a positive electrode mixture layer on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode mixture layer on at least one surface of the positive electrode current collector" means that the positive electrode mixture layer can be on one surface of the positive electrode current collector in the thickness direction of the positive electrode current collector, or can be on both surfaces of the positive electrode current collector in the thickness direction of the positive electrode current collector. Note that the "surface" herein can be the entire area of the surface of the positive electrode current collector, or can be a part of the area of the surface of the positive electrode current collector, and the present application is not particularly limited as long as the object of the present application can be achieved.

[0076] The positive electrode current collector according to the present application is not particularly limited as long as the object of the present application can be achieved. For example, the positive electrode current collector can include an aluminum foil, an aluminum alloy foil, or a composite current collector (for example, an aluminum-carbon composite current collector), and the like. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, and the like) on a polymer base material.

[0077] The positive electrode mixture layer according to the present application includes a positive electrode material, and the type of the positive electrode material according to the present application is not particularly limited as long as the object of the present application can be achieved. For example, the positive electrode material can include at least one of lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2(NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type lithium manganese oxide, spinel-type lithium nickel manganese oxide, and lithium titanate. In the present application, the positive electrode material can further include a non-metal element, for example, the non-metal element includes at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In the present application, the thickness of the positive electrode current collector and the positive electrode mixture layer is not particularly limited as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode mixture layer is 30 μm to 120 μm.

[0078] In the present application, the positive electrode mixture layer can further include a positive electrode binder and a conductive agent. The present application does not particularly limit the kind of the positive electrode binder in the positive electrode mixture layer, as long as the purpose of the present application can be achieved, for example, the positive electrode binder can include, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefin, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified styrene butadiene rubber (SBR), or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0079] The present application does not particularly limit the kind of the conductive agent in the positive electrode mixture layer, as long as the purpose of the present application can be achieved, for example, the conductive agent can be the same as the kind of the conductive agent in the negative electrode mixture layer described above. In some embodiments, the conductive agent includes a carbon-based material, such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, or carbon fiber; a metal-based material, such as metal powder or metal fiber of copper, nickel, aluminum, silver, or the like; a conductive polymer, such as a polyphenylene derivative; or a mixture thereof. The present application does not particularly limit the mass ratio of the positive electrode material, the conductive agent, and the positive electrode binder in the positive electrode mixture layer, and a person skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved, for example, the loading amount of the positive electrode material in the positive electrode sheet is 4.0 mg / cm 2 to 10.0 mg / cm 2 .

[0080] The secondary battery of the present application further includes a separator film, and the material and shape of the separator film used in the secondary battery of the present application are not particularly limited, which can be any technology disclosed in the prior art. In some embodiments, the separator film includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present application, and the like.

[0081] For example, the separator film can include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0082] The surface treatment layer can be a polymer layer or an inorganic layer, or a mixed polymer and inorganic layer. The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0083] The secondary battery of the present application further includes a packaging bag for containing the positive electrode sheet, the negative electrode sheet, the separator, and the electrolyte, and other components known in the art, which are not limited by the present application. The packaging bag is not particularly limited by the present application, and can be a packaging bag known in the art, as long as the purpose of the present application can be achieved.

[0084] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and is not particularly limited by the present application, for example, can include but is not limited to the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, and winding, folding, etc. as needed to obtain an electrode assembly with a winding structure, placing the electrode assembly into the packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain the secondary battery; or stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, then fixing the four corners of the entire stack structure with adhesive tape to obtain an electrode assembly with a stack structure, placing the electrode assembly into the packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain the secondary battery. In addition, a current protection element, a guide plate, etc. can also be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0085] In a third aspect, the present application provides an electronic device comprising the secondary battery provided in the second aspect of the present application.

[0086] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the art. For example, the electronic device can include, but is not limited to, a notebook computer, a pen input type computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copier, 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 audio player, 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 timepiece, an electric power tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor.

[0087] The scheme of the present application is described below in combination with the following specific examples. Unless otherwise specified, the raw materials used in the following examples are all from ordinary commercially available products, and the devices or equipment used are all purchased from conventional market sales channels. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are mass-based.

[0088] Example 1-1

[0089] The present example provides a negative electrode active material, which comprises a silicon-based material and an outer layer material; the outer layer material is located on at least part of the surface of the silicon-based material; the outer layer material comprises multi-walled carbon nanotubes (a conductive agent) and polyacrylonitrile (a nitrile-based polymer).

[0090] Referring to the infrared spectrum of Example 1 shown in FIG. 1, the infrared spectrum of the negative electrode active material includes an infrared characteristic peak of a cyano group; as can be seen from the partial enlarged view of FIG. 2, the infrared characteristic peak of the cyano group is located between 2340 cm -1 and 2300 cm -1 ; the negative electrode active material comprises nitrogen and silicon elements; the mass content D1% of the nitrogen element is 1.11%, and the mass content G% of the silicon element is 54.2%, based on the mass of the negative electrode active material, wherein D1 / G = 0.02.

[0091] In the negative electrode active material, the sphericity S = 0.85; the thickness T nm of the outer layer material is 0.5 nm. The average particle size R μm of the negative electrode active material is 5.3 μm.

[0092] The negative electrode active material of the present example is prepared by a method comprising the following steps:

[0093] S1: providing a silicon-carbon material; the silicon-based material comprises a porous carbon skeleton and a silicon material; the silicon material is located on the surface and inside the porous carbon skeleton.

[0094] S2: the multi-walled carbon nanotubes and the polyacrylonitrile are subjected to a first dispersion treatment in a solvent for 4 hours to obtain a dispersion system; the solvent comprises ethanol and butanol (mass ratio 1:1).

[0095] S3: the silicon-carbon material in S1 is added to the dispersion system in S2 to perform a second dispersion treatment for 4 hours, and then a drying treatment at 200°C for 4 hours to obtain the negative electrode active material of the present example.

[0096] Preparation of the negative electrode: the negative electrode active material prepared above is used as the active material, acetylene black is used as the conductive agent, and sodium alginate is used as the binder. The mass ratio of the active material, acetylene black, and sodium alginate is 70:20:10. The active material and acetylene black are mixed in proportion, ground uniformly, and then added to the aqueous sodium alginate solution in proportion and stirred for 4 hours to obtain a negative electrode mixture slurry. Finally, the slurry is uniformly coated on a copper foil and vacuum dried at 70°C for 12 hours, and then cold-pressed to obtain the negative electrode. The loading amount of the active material is 1.2 mg / cm 2 The mass content of nitrogen in the negative electrode mixture layer is 0.77%, and the mass content of sodium is 1.6%.

[0097] Preparation of the positive electrode: super-P is used as the conductive agent, and PVDF is used as the binder. The mass ratio of the active material (LiFePO4), super-P, and PVDF is 70:20:10. The active material and super-P are mixed in proportion, ground uniformly, and then added to the prepared 10 wt.% PVDF solution in proportion and stirred for 4 hours to obtain a positive electrode mixture slurry. Finally, the positive electrode mixture slurry is uniformly coated on an aluminum foil and vacuum dried at 70°C for 12 hours, and then cold-pressed to obtain the positive electrode. The loading amount of the active material is 8 mg / cm 2 .

[0098] Preparation of the electrolyte: ethylene carbonate and dimethyl carbonate (EC and DMC, volume ratio 1:1) are used as the base solvent, and 1 mol / L of LiPF6 is added to the base solvent to obtain the electrolyte.

[0099] Preparation of the separator: a 25 μm microporous single-layer polypropylene (PP) film is used as the separator.

[0100] Preparation of the secondary battery: the negative electrode is cut into a circular electrode sheet with a diameter of 10 mm, and a lithium metal sheet and the circular electrode sheet are used as the counter electrodes to assemble a coin-type half-battery in a glove box.

[0101] Alternatively, the above positive electrode, separator, and negative electrode are stacked in order with the separator between the positive electrode and the negative electrode to play a separating role, and then wound to obtain a bare battery cell. The bare battery cell is placed in an outer package, injected with the electrolyte, and packaged. After processes such as formation, degassing, and edge cutting, a lithium ion battery is obtained.

[0102] Test method:

[0103] Gravimetric capacity test of negative active material

[0104] The button half-cell was placed on the blue instrument tester for testing. The test procedure was as follows: first step, 0.05C discharge to 0V voltage, second step, 5min standing, third step, 50μA discharge to 0V voltage, fourth step, 5min standing, fifth step, 20μA discharge to 0V voltage, sixth step, 5min standing, seventh step, 0.1C charge to 2V voltage, eighth step, 5min standing, the first step to the eighth step was repeated twice. Then 1C discharge to 0V voltage, 5min standing, 0.1C charge to 2V voltage, and the test was ended. The cumulative capacity of the first, third, and fifth steps in the first cycle was the discharge capacity, the charge capacity was obtained by charging to 2.0V at 0.1C, the gravimetric capacity of the negative active material was obtained by dividing the charge capacity by the weight of the negative active material, and the first coulombic efficiency was obtained by dividing the charge capacity by the discharge capacity.

[0105] Cycle capacity retention rate and cycle expansion rate test:

[0106] The lithium ion battery was placed in a constant temperature oven at 25℃±1℃ for 30 minutes, charged to 4.35V at a constant current of 0.5C, then charged to 0.025C at 4.35V constant voltage, and then discharged to 3.0V at 0.5C. This was one cycle of charge and discharge process, and the first cycle discharge capacity C0and the initial thickness H 10 of the lithium ion battery were recorded. 11 After that, the above cycle process was repeated for 600 cycles. The cycle discharge capacity C1and the thickness H 11 after cycling of the 600th cycle were recorded. 10 10

[0107] 600 cycle capacity retention rate = C1 / C0×100%.

[0108] Cycle expansion rate = (H 20 -H 21 ) / H 21 ×100%.

[0109] High temperature storage expansion rate test:

[0110] The lithium ion battery was placed in a constant temperature oven at 25℃±1℃ for 30 minutes, charged to 4.35V at a constant current of 0.5C, then charged to 0.025C at 4.35V constant voltage, and then discharged to 3.0V at 0.5C. This was one cycle of charge and discharge process, and the first cycle discharge capacity C0and the initial thickness H 20 of the lithium ion battery were recorded. 21 After that, the above cycle process was repeated for 600 cycles. The cycle discharge capacity C1and the thickness H 21 after cycling of the 600th cycle were recorded. 20) / H 20 x 100%.

[0111] The negative active materials of the following examples and comparative examples differ from example 1-1 only in that the mass content of silicon element and / or nitrogen element in the negative active material is adjusted according to table 1, the sphericity, the thickness of the outer layer material and the average particle size, wherein the element content is adjusted only by changing the addition amount of silicon-based material, nitrile-based polymer and conductive agent accordingly. The addition amount of nitrogen element in the negative active material of comparative example 1-1 is 0, but the same mass of nitrile-based polymer as in example 1-1 is added to the negative mixture slurry to ensure that the mass ratio of nitrile-based polymer in the negative electrode sheet of comparative example 1-1 is the same as that of example 1-1.

[0112] Table 1

[0113] As can be seen from table 1, the negative active material of the present application forms an outer layer material composed of conductive agent and nitrile-based polymer on the surface of the silicon-based material, wherein the mass content of nitrogen element is D1% and the mass content of silicon element is G% based on the negative active material. When 0.02≤D1 / G≤0.5 is controlled, the cycle capacity retention rate of the secondary battery can be improved, the swelling performance and high-temperature storage performance can be inhibited. Preferably, when 0.04≤D1 / G≤0.37 is satisfied, the cycle capacity retention rate of the secondary battery can be further improved, the swelling performance and high-temperature storage performance can be inhibited. More preferably, when 0.06≤D1 / G≤0.19 is satisfied, the secondary battery has more excellent cycle capacity retention rate, swelling performance and high-temperature storage performance.

[0114] In particular, when 1.1≤D1≤18.4 is controlled, especially when 2.3≤D1≤9.2 is satisfied, the secondary battery exhibits higher cycle performance and high-temperature performance. When 36.8≤G≤68.3 is controlled, especially when 43.2≤G≤51.3 is satisfied, the silicon element can better cooperate with the nitrogen element, improving the swelling performance and cycle performance of the secondary battery.

[0115] In particular, when the sphericity S of the negative active material is controlled to satisfy 0.8≤S≤1.0, the swelling performance, cycle performance and high-temperature storage performance of the secondary battery can be improved. When the sphericity is further improved to 0.9≤S≤1.0, the secondary battery has higher swelling performance, cycle performance and high-temperature storage performance. In particular, when the thickness T nm of the outer layer material is controlled to satisfy 0.5≤T≤200.0, the swelling performance, cycle performance and high-temperature storage performance of the secondary battery can be optimized. Especially when the thickness T of the outer layer material satisfies 0.5≤T≤100.0, the swelling performance, cycle performance and high-temperature storage performance of the secondary battery can be more significantly improved.

[0116] In particular, when the negative active material satisfies 0.5≤S×T≤90.0, the initial coulombic efficiency, the expansion performance, the high-temperature storage performance, and the cycle performance of the secondary battery can be improved. Preferably, when 10.4≤S×T≤67.8 is satisfied, the expansion performance, the high-temperature storage performance, and the cycle performance of the secondary battery can be further improved. In particular, when the average particle diameter Rμm of the negative active material is controlled to be in the range of 5.6≤R≤10.3, the secondary battery can have higher cycle performance, expansion performance, and high-temperature storage performance.

[0117] The secondary batteries of the following examples differ from Example 1-1 only in that the mass content of nitrogen element and / or sodium element in the negative electrode mixture layer is adjusted according to Table 2 (wherein the mass content of nitrogen element and sodium element in the negative electrode mixture layer is adjusted by adjusting the type of negative active material and the ratio of negative active material and sodium alginate according to Table 2, and the remainder is multi-walled carbon nanotubes), and / or the mass content of fluorobenzene and / or fluoroethylene carbonate in the electrolyte is adjusted (the adjustment method is to add the corresponding mass of fluorobenzene and / or fluoroethylene carbonate to the base solvent).

[0118] Table 2

[0119] As can be seen from Table 2, when the mass content D2% of nitrogen element and the mass content N% of sodium element in the negative electrode mixture layer satisfy 2.35≤D2 / N≤11.74, the cycle performance and the expansion performance of the secondary battery can be improved. In particular, when 4.81≤D2 / N≤9.63, the cycle performance and the expansion performance of the secondary battery can be further improved.

[0120] In particular, when the content of sodium element in the negative electrode mixture layer is controlled to be in the range of 0.58≤N≤1.74, the cycle performance and the high-temperature storage performance of the secondary battery are improved. In particular, when 0.81≤N≤1.04, the cycle performance and the high-temperature storage performance of the secondary battery are more excellent. In particular, when the secondary battery satisfies 1.6≤D2≤8.1, the cycle performance and the expansion performance of the secondary battery can be improved, and in particular, when 5.0≤D2≤7.8, the cycle performance and the expansion performance of the secondary battery are significantly improved.

[0121] Particularly, the addition of fluorobenzene and / or fluoroethylene carbonate to the electrolyte is matched with the negative electrode system of the application, which can optimize the high-temperature storage performance of the secondary battery and improve its first coulombic efficiency, cycle performance and swelling inhibition performance. Preferably, when the mass content F1% of fluorobenzene in the electrolyte is regulated to meet 0.9≤F1≤5.2, the high-temperature storage performance, cycle performance and swelling inhibition performance of the secondary battery can be further optimized; preferably, when 2.1≤F1≤3.1, the high-temperature storage performance, cycle performance and swelling inhibition performance of the secondary battery can be significantly improved.

[0122] Particularly, the mass content F2% of fluoroethylene carbonate in the electrolyte is regulated to meet 3.8≤F2≤7.4, which can make the secondary battery achieve more excellent high-temperature storage performance, cycle performance and swelling inhibition performance. In particular, when the electrolyte contains both fluorobenzene and fluoroethylene carbonate and meets the above preferred range, the secondary battery has extremely excellent high-temperature storage performance, cycle performance and swelling inhibition performance.

[0123] The above is only a preferred embodiment of the application and is not intended to limit the application. Any modification, equivalent replacement and improvement made within the principles of the application shall be included in the protection scope of the application.

Claims

1. A negative electrode active material, characterized by, The silicon-based material and the outer layer material; the outer layer material is located on at least part of the surface of the silicon-based material; the outer layer material comprises a conductive agent and a nitrile-based polymer; The negative active material includes an infrared characteristic peak of a cyano group in an infrared spectrum of the negative active material, the infrared characteristic peak of the cyano group being located between 2250 cm -1 and 2400 cm -1 . The negative electrode active material comprises nitrogen and silicon; the mass content of the nitrogen is D1%, and the mass content of the silicon is G%, based on the mass of the negative electrode active material, and 0.02≤D1 / G≤0.

5.

2. The negative electrode active material according to claim 1, characterized by The negative electrode active material satisfies at least one of the following conditions: (1)1.1≤D1≤18.4； (2)36.8≤G≤68.3； (3) 0.04≤D1 / G≤0.

37.

3. The negative electrode active material according to claim 2, characterized by The negative electrode active material satisfies at least one of the following conditions: (1)2.3≤D1≤9.2； (2)43.2≤G≤51.3； (3) 0.06≤D1 / G≤0.

19.

4. The negative electrode active material according to any one of claims 1 to 3, characterized by, The sphericity of the negative electrode active material is S, and 0.8≤S≤1.0; and / or, The thickness of the outer layer material in the negative electrode active material is T nm, and 0.5≤T≤200.

0.

5. The negative electrode active material according to claim 4, characterized by The negative electrode active material satisfies at least one of the following conditions: (1)0.9≤S≤1.0； (2)0.5≤T≤100.0； (3) 0.5≤S×T≤90.0; preferably, 10.4≤S×T≤67.8; (4) the average particle size of the negative electrode active material is R μm; 5.6≤R≤10.3。 6. The negative electrode active material according to any one of claims 1 to 3, characterized by, The negative electrode active material satisfies at least one of the following conditions: (1) the conductive agent comprises single-walled carbon nanotubes and / or multi-walled carbon nanotubes; (2) the nitrile-based polymer comprises at least one of polyacrylonitrile, polycyanoacrylate, and polycyanobenzene; (3) the silicon-based material comprises a porous carbon skeleton and a silicon material; the silicon material is located on the surface and / or inside of the porous carbon skeleton.

7. A secondary battery characterized by comprising: The secondary battery comprises a positive electrode, a negative electrode, and an electrolyte. The negative electrode comprises a negative electrode current collector and a negative electrode mixture layer disposed on at least part of the surface of the negative electrode current collector, and the negative electrode mixture layer comprises the negative electrode active material of any one of claims 1 to 6.

8. The secondary battery according to claim 7, characterized by The negative electrode mixture layer comprises sodium, and the mass content of the nitrogen is D2% and the mass content of the sodium is N%, based on the mass of the negative electrode mixture layer. The negative electrode mixture layer satisfies at least one of the following conditions: (1) 0.58≤N≤1.74; preferably, 0.81≤N≤1.04; (2) 1.6≤D2≤8.1; preferably, 5.0≤D2≤7.8; (3) 2.35≤D2 / N≤11.74; preferably, 4.81≤D2 / N≤9.63; (4) the sodium is derived from at least one of sodium alginate, sodium carboxymethyl cellulose, sodium hydroxymethyl cellulose, or sodium hydroxyethyl carboxymethyl cellulose.

9. The secondary battery of claim 7, wherein the electrolyte comprises at least one of fluorobenzene or fluoroethylene carbonate; and the electrolyte satisfies at least one of the following conditions based on the mass of the electrolyte: (1) the mass content of the fluorobenzene is F1%, and 0.9≤F1≤5.2; preferably, 2.1≤F1≤3.1; (2) the mass content of the fluoroethylene carbonate is F2%, and 3.8≤F2≤7.

4.

10. An electronic device, comprising: The secondary battery of any one of claims 7 to 9.

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