A secondary battery and an electronic device

Abstract

The application provides a secondary battery and an electronic device. The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material comprises a silicon-oxygen composite material; the peak-to-peak intensity of the thermogravimetric first derivative curve of the negative electrode sheet at 500 DEG C to 700 DEG C is Y1, the peak-to-peak intensity of the thermogravimetric first derivative curve of the negative electrode sheet at 350 DEG C to 450 DEG C is Y2, and Y1 / Y2 satisfies 0.1 <= Y1 / Y2 <= 4. The negative electrode sheet of the secondary battery provided by the application comprises a silicon-oxygen composite material and Y1 / Y2 satisfies the above relationship, which can reduce the side reaction and consumption of electrolyte in the first lithium intercalation process of the secondary battery, improve the first coulomb efficiency of the secondary battery, and improve the rate performance, cycle performance and swelling performance of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, have the characteristics of high operating voltage, high energy density, long cycle life, and wide operating temperature range. These excellent characteristics have enabled lithium-ion batteries to be widely used in three major fields: consumer electronics, power batteries, and energy storage.

[0003] Silicon materials have high theoretical specific capacity and are promising for applications in lithium-ion batteries. However, during charge-discharge cycles, silicon materials undergo volume expansion and contraction as lithium ions are inserted and extracted, leading to increased electrolyte consumption and affecting the cycle performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device to improve the cycle performance of the secondary battery. The specific technical solution is as follows:

[0005] The first aspect of this application provides a secondary battery comprising a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer including a negative active material, the negative active material including a silicon-oxygen composite material; the peak intensity of the first differential thermogravimetric curve of the negative electrode sheet at 500℃ to 700℃ is Y1, the peak intensity of the first differential thermogravimetric curve of the negative electrode sheet at 350℃ to 450℃ is Y2, and Y1 / Y2 satisfies 0.1≤Y1 / Y2≤4. The secondary battery provided by this application, including a silicon-oxygen composite material and adjusting Y1 / Y2 to satisfy the above relationship, can reduce side reactions and electrolyte consumption during the initial lithium insertion process of the secondary battery, improve the initial coulombic efficiency of the secondary battery, and improve the rate performance, cycle performance, and expansion performance of the secondary battery.

[0006] In some embodiments of this application, 0.5 ≤ Y1 / Y2 ≤ 2.5. By adjusting the value of Y1 / Y2 within the above range, it is beneficial to further reduce side reactions and electrolyte consumption during the initial lithium insertion process of the secondary battery, improve the initial coulombic efficiency of the secondary battery, and improve the rate performance, cycle performance, and expansion performance of the secondary battery.

[0007] In some embodiments of this application, the Raman spectrum of the negative electrode is at 1200 cm⁻¹. -1 Up to 1500cm -1 The peak intensity is I1, and the Raman spectrum of the negative electrode is at 300 cm⁻¹. -1 Up to 600cm -1The peak intensity is I2, and I1 / I2 satisfies 2≤I1 / I2≤15. By adjusting the value of I1 / I2 within the above range, it is beneficial to further improve the rate performance, cycle performance, and expansion performance of the secondary battery.

[0008] In some embodiments of this application, the Dv50 of the silicon-oxygen composite material is 3 μm to 15 μm; the specific surface area of ​​the silicon-oxygen composite material is 0.2 m². 2 / g to 8m 2 / g. By adjusting the Dv50 and specific surface area of ​​the silicon-oxygen composite material within the above range, it is beneficial to improve the cycle performance, expansion performance, and fast charge / discharge performance of the secondary battery.

[0009] In some embodiments of this application, the silicon-oxygen composite material has a core-shell structure, comprising a core and a first shell and a second shell disposed on at least a portion of the surface of the core; the core comprises silicon grains and lithium silicate, the first shell comprises amorphous carbon, and the second shell comprises metal oxide and lithium-modified metal oxide; the metal oxide comprises at least one of aluminum oxide, titanium dioxide, or niobium pentoxide. The negative electrode sheet comprising the silicon-oxygen composite material with the above characteristics can reduce the possibility of silicon contacting the electrolyte, reduce side reactions during the initial lithium intercalation process of the secondary battery and electrolyte consumption, improve the initial coulombic efficiency of the secondary battery, and improve the rate performance, cycle performance, and expansion performance of the secondary battery.

[0010] In some embodiments of this application, based on the mass of the silicon-oxygen composite material, the mass percentage of amorphous carbon is 1% to 5%, the sum of the mass percentages of metal oxides and lithium-ionized metal oxides is 1% to 5%, and the sum of the mass percentages of silicon grains and lithium silicates is 92% to 98%. By adjusting the mass percentages of amorphous carbon, the sum of the mass percentages of metal oxides and lithium-ionized metal oxides, and the sum of the mass percentages of silicon grains and lithium silicates to the above ranges, it is beneficial to further improve the initial coulombic efficiency of the secondary battery and improve its rate performance, cycle performance, and expansion performance.

[0011] In some embodiments of this application, the size of the silicon grains is from 0.5 nm to 10 nm. By adjusting the size of the silicon grains within the above range, the secondary battery can have a high energy density while improving its rate performance, cycle performance, and expansion performance.

[0012] In some embodiments of this application, the second shell of the silicon-oxygen composite material includes a metal element, including at least one of aluminum, titanium, or niobium, and the mass percentage of the metal element is 0.1% to 1% based on the mass of the second shell of the silicon-oxygen composite material. The negative electrode sheet, comprising the silicon-oxygen composite material with the above characteristics, can reduce the possibility of silicon contacting the electrolyte, reduce side reactions and electrolyte consumption during the initial lithium insertion process of the secondary battery, improve the initial coulombic efficiency of the secondary battery, and improve the rate performance, cycle performance, and expansion performance of the secondary battery.

[0013] In some embodiments of this application, the negative electrode active material further includes graphite, and the mass percentage of the silicon-oxygen composite material is 1% to 15% based on the mass of the silicon-oxygen composite material and the graphite. By including graphite as the negative electrode active material and adjusting the mass percentage of the silicon-oxygen composite material within the above range, the secondary battery can have high energy density while also exhibiting good cycle performance and expansion performance.

[0014] In some embodiments of this application, during charge-discharge cycle tests at 25±1℃ using a 3C charge and 0.5C discharge stage, when the secondary battery completes 800 or more cycles, the ratio of the expansion rate of the negative electrode to the expansion rate of the secondary battery is 0.5 to 4. This indicates that the expansion of the negative electrode is relatively small during cycling, thus improving the expansion of the negative electrode active material, meaning the secondary battery exhibits good expansion performance.

[0015] The second aspect of this application provides an electronic device that includes the secondary battery provided in the first aspect of this application. The secondary battery provided in the first aspect of this application has good rate performance, cycle performance, and expansion performance, thereby giving the electronic device of this application a long service life.

[0016] The beneficial effects of this application are:

[0017] This application provides a secondary battery and an electronic device. The secondary battery includes a negative electrode sheet, which includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative active material layer includes a negative active material, which is a silicon-oxygen composite material. The peak intensity of the first differential thermogravimetric curve of the negative electrode sheet at 500℃ to 700℃ is Y1, and the peak intensity of the first differential thermogravimetric curve of the negative electrode sheet at 350℃ to 450℃ is Y2, where Y1 / Y2 satisfies 0.1≤Y1 / Y2≤4. The secondary battery provided by this application, including a silicon-oxygen composite material and adjusting Y1 / Y2 to satisfy the above relationship, can reduce side reactions and electrolyte consumption during the initial lithium insertion process of the secondary battery, improve the initial coulombic efficiency of the secondary battery, and improve the rate performance, cycle performance, and expansion performance of the secondary battery.

[0018] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0020] Figure 1 The thermogravimetric (TG) curves and thermogravimetric first derivative (DTG) curves of the negative electrode sheets in Examples 1-8 are shown.

[0021] Figure 2 The TG and DTG curves are for the negative electrode of Comparative Example 1.

[0022] Figure 3 The TG and DTG curves of the negative electrode sheets in Examples 2-5 are shown.

[0023] Figure 4 The Raman spectra of the negative electrode plates in Examples 1-8;

[0024] Figure 5 The Raman spectra of the negative electrode sheets in Examples 2-5 are shown. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0026] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0027] The first aspect of this application provides a secondary battery, which includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer including a negative active material, the negative active material including a silicon-oxygen composite material; the peak intensity of the first differential thermogravimetric curve of the negative electrode sheet at 500℃ to 700℃ is Y1, the peak intensity of the first differential thermogravimetric curve of the negative electrode sheet at 350℃ to 450℃ is Y2, Y1 / Y2 satisfies 0.1≤Y1 / Y2≤4, for example, the value of Y1 / Y2 can be 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.9, 2.5, 3, 3.5, 4 or a range of any two values ​​therein.

[0028] The peaks in the thermogravimetric first differential curve of the aforementioned negative electrode between 500℃ and 700℃ correspond to the decomposition of silicon-containing organic lithium salts (such as LixSiOy / ROCO2Li composite lithium salts, where 0 < x ≤ 2, 0 < y ≤ 3, and R represents methyl, ethyl, etc.), while the peaks between 350℃ and 450℃ correspond to the decomposition of silicon-free lithium salts (such as LiF, Li2O, etc.). The Y1 / Y2 value reflects the ratio of silicon-containing organic lithium salts to silicon-free lithium salts; the higher the peak intensity, the higher the content of the corresponding lithium salt. When the Y1 / Y2 value is too small, it is not conducive to improving the energy density of the secondary battery; when the Y1 / Y2 value is too large, it will affect the kinetic performance, cycle performance, and expansion performance of the secondary battery. The secondary battery provided in this application includes a silicon-oxygen composite material, and by controlling the Y1 / Y2 value within the scope of this application, it is possible to reduce side reactions and electrolyte consumption during the initial lithium intercalation process of the secondary battery, improve the initial coulombic efficiency and energy density of the secondary battery, and improve the rate performance, cycle performance, and expansion performance of the secondary battery.

[0029] In some embodiments of this application, 0.5 ≤ Y1 / Y2 ≤ 2.5. For example, the value of Y1 / Y2 can be 0.5, 0.7, 0.9, 1.0, 1.2, 1.5, 1.9, 2.2, 2.5, or a range consisting of any two of these values. By adjusting the value of Y1 / Y2 within the above range, it is beneficial to reduce side reactions and electrolyte consumption during the initial lithium insertion process of the secondary battery, improve the initial coulombic efficiency and energy density of the secondary battery, and improve the rate performance, cycle performance, and expansion performance of the secondary battery.

[0030] In some embodiments of this application, the Raman spectrum of the negative electrode is at 1200 cm⁻¹. -1 Up to 1500cm -1 The peak intensity is I1, and the Raman spectrum of the negative electrode is at 300 cm⁻¹. -1 Up to 600cm -1The peak intensity is I2, and I1 / I2 satisfies 2 ≤ I1 / I2 ≤ 15. For example, the value of I1 / I2 can be 2, 3, 5, 7, 9, 10, 12, 14, 15, or any range of two of these values. The Raman spectrum of the above negative electrode is at 1200 cm⁻¹. -1 Up to 1500cm -1 The peak corresponds to the characteristic D peak of graphite at 300 cm⁻¹. -1 Up to 600cm -1 The peak corresponds to the characteristic peak of amorphous silicon. The value of I1 / I2 reflects the ratio of graphite to silicon content in the negative electrode sheet. The higher the peak intensity, the higher the content of the substance corresponding to that peak. By adjusting the value of I1 / I2 within the above range, it is beneficial to further improve the rate performance, cycle performance, and expansion performance of the secondary battery.

[0031] In some embodiments of this application, the Dv50 of the silicon-oxygen composite material is 3 μm to 15 μm, preferably 5 μm to 11 μm; the specific surface area of ​​the silicon-oxygen composite material is 0.2 m². 2 / g to 8m 2 / g, preferably 0.5m 2 / g to 3m 2 / g. For example, the Dv50 of a silicon-oxygen composite material can be 3μm, 5μm, 6μm, 6.5μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 14μm, 15μm, or a range of any two of these values, and the specific surface area of ​​the silicon-oxygen composite material can be 0.2m². 2 / g, 0.5m 2 / g、1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g、2m 2 / g、3m 2 / g、5m 2 / g、7m 2 / g、8m 2 / g or a range consisting of any two of these values. During secondary battery cycling, HF in the electrolyte reaction byproducts etches the silicon-oxygen composite material, leading to the growth and erosion of the solid electrolyte interphase (SEI) film into the particles. By controlling the Dv50 of the silicon-oxygen composite material within the above range, the proportion of silicon-oxygen particles eroded by the SEI film is reduced, which is beneficial to improving the cycle performance and expansion performance of the secondary battery. By controlling the specific surface area of ​​the silicon-oxygen composite material within the above range, the silicon-oxygen composite material has a larger specific surface area and a larger contact area with the electrolyte, which is beneficial to active ions (such as Li). + This improves the dynamic performance and fast charging / discharging performance of the secondary battery by transmitting energy.

[0032] In some embodiments of this application, the silicon-oxygen composite material has a core-shell structure, comprising a core and a first shell and a second shell disposed on at least a portion of the surface of the core. The core comprises silicon grains and lithium silicate, the first shell comprises amorphous carbon, and the second shell comprises metal oxide and lithium-modified metal oxide. The metal oxide comprises at least one of aluminum oxide, titanium dioxide, or niobium pentoxide. In this silicon-oxygen composite material with the above characteristics, the silicon grains in the core are dispersed in lithium silicate, which can improve silicon expansion; the first shell comprises amorphous carbon, which can reduce the possibility of silicon contacting the electrolyte; the second shell comprises metal oxide and lithium-modified metal oxide, which can reduce electrolyte erosion of silicon, reduce side reactions during the initial lithium intercalation process, and reduce electrolyte consumption. The aforementioned first and second shells protect silicon, thereby reducing the content of silicon-containing organolithium salts in the solid electrolyte interface film, which is beneficial for improving the energy density of the secondary battery and improving its kinetic and cycle performance. The negative electrode sheet includes a silicon-oxygen composite material with the above characteristics, which can reduce side reactions and electrolyte consumption during the first lithium insertion process of the secondary battery, improve the first coulombic efficiency of the secondary battery, and improve the rate performance, cycle performance and expansion performance of the secondary battery.

[0033] In some embodiments of this application, the silicon-oxygen composite material includes a core and a first shell and a second shell sequentially disposed on at least a portion of the surface of the core. In other embodiments, the silicon-oxygen composite material includes a core and a second shell and a first shell sequentially disposed on at least a portion of the surface of the core. This application does not impose any particular limitation on these embodiments, as long as the purpose of this application is achieved.

[0034] In some embodiments of this application, based on the mass of the silicon-oxygen composite material, the mass percentage of amorphous carbon is 1% to 5%, the sum of the mass percentages of metal oxides and lithium-ionized metal oxides is 1% to 5%, and the sum of the mass percentages of silicon grains and lithium silicates is 92% to 98%. For example, the mass percentage of amorphous carbon can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range of two such values; the sum of the mass percentages of metal oxides and lithium-ionized metal oxides can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range of two such values; and the sum of the mass percentages of silicon grains and lithium silicates can be 92%, 92.5%, 93%, 94%, 95%, 96%, 97%, 98%, or any range of two such values. By adjusting the mass percentage of amorphous carbon, the sum of the mass percentages of metal oxides and lithium-ionized metal oxides, and the sum of the mass percentages of silicon grains and lithium silicates within the above ranges, it is beneficial to better leverage the protective functions of the first and second shells, thereby further improving the initial coulombic efficiency and energy density of the secondary battery, and enhancing its rate performance, cycle performance, and expansion performance.

[0035] This application does not impose a particular limitation on the mass ratio of metal oxide to lithiated metal oxide, as long as the purpose of this application is achieved. For example, the mass ratio of metal oxide to lithiated metal oxide can be 1:5 to 5:1. This application also does not impose a particular limitation on the mass ratio of silicon grains to lithium silicate, as long as the purpose of this application is achieved. For example, the mass ratio of silicon grains to lithium silicate can be 2:3 to 3.5:1. In this application, the core particle size is 3 μm to 15 μm, preferably 4.5 μm to 8 μm.

[0036] In some embodiments of this application, the size of the silicon grains is from 0.5 nm to 10 nm. For example, the size of the silicon grains can be 0.5 nm, 1 nm, 2.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 9 nm, 10 nm, or a range of any two values ​​therein. By adjusting the size of the silicon grains within the above range, the secondary battery can have a high energy density while improving its rate performance, cycle performance, and expansion performance.

[0037] In some embodiments of this application, the second shell of the silicon-oxygen composite material includes a metal element, including at least one selected from aluminum, titanium, or niobium. Based on the mass of the second shell of the silicon-oxygen composite material, the mass percentage of the metal element is from 0.1% to 1%, for example, the mass percentage of the metal element can be 0.1%, 0.3%, 0.4%, 0.5%, 0.7%, 0.8%, 0.9%, 1%, or a range consisting of any two of these values. The negative electrode sheet, comprising the silicon-oxygen composite material with the above characteristics, can reduce the possibility of silicon contacting the electrolyte, reduce side reactions and electrolyte consumption during the initial lithium insertion process of the secondary battery, improve the initial coulombic efficiency of the secondary battery, and improve the cycle performance and expansion performance of the secondary battery.

[0038] This application does not impose any particular limitation on the preparation method of silicon-oxygen composite materials, as long as the purpose of this application can be achieved. For example, it can be prepared by the following method: Elemental silicon and silicon dioxide are mixed uniformly and placed in the evaporation chamber of a deposition furnace. The mixture is heated to 1100℃ to 1300℃ for the first deposition. The deposited SiO blocks are then collected in the deposition chamber and processed by crushing and grading to obtain the silicon-oxygen material. The silicon-oxygen material is then subjected to a second deposition in an acetylene atmosphere, depositing amorphous carbon on the surface of the silicon-oxygen material, resulting in a silicon-oxygen material with a first layer of amorphous carbon on the surface, denoted as C@SiO material. The C@SiO material is placed in an ethanol solution, and a salt containing a metal element (e.g., aluminum isopropoxide) and polyvinylpyrrolidone (PVP) are added. After stirring evenly, the mixture is spray-dried and then calcined for the first time under an inert atmosphere to obtain a C@SiO silicon-oxygen material with Al2O3 on the surface, denoted as Al2O3@C@SiO material. Al2O3@C@SiO material is uniformly mixed with lithium nitride (Li3N), and then calcined a second time under an inert atmosphere. During calcination, Li3N decomposes into lithium and nitrogen gas. The lithium at the calcination temperature is in a molten state and can react with the Al2O3 on the surface of the Al2O3@C@SiO material to form lithiated Al2O3. It can also react with the internal silicon-oxygen material, ultimately obtaining a silicon-oxygen composite material comprising a first shell and a second shell. The core is the product of the reaction between molten lithium and silicon-oxygen material, including lithium silicate and silicon grains, with the silicon grains dispersed in the lithium silicate. The first shell comprises amorphous carbon, and the second shell comprises Al2O3 and lithiated Al2O3. In the above preparation method, the molar ratio of elemental silicon to silicon dioxide is 1:(0.5 to 2), the molar ratio of aluminum isopropoxide to polyvinylpyrrolidone (PVP) is 1:(0.5 to 2), and the total mass of aluminum isopropoxide and PVP to the mass ratio of C@SiO material is 2% to 8%. The mass ratio of Al2O3@C@SiO material to lithium nitride (Li3N) was (85:15) to (95:5). The second deposition temperature was 500℃ to 700℃, and the time was 2h to 4h; the first calcination temperature was 500℃ to 700℃, and the time was 4h to 6h; the second calcination temperature was 600℃ to 800℃, and the time was 4h to 6h.

[0039] This application does not impose any particular limitation on the classification method described above, as long as it achieves the purpose of this application. For example, the crushed silicon-oxygen material can be classified by methods such as sieving or air classification. This application does not impose any particular limitation on the flow rate of acetylene gas, which can be selected according to conventional operations in the art, as long as it achieves the purpose of this application. For example, the flow rate of acetylene gas can be from 2 L / min to 10 L / min. This application does not impose any particular limitation on the inert atmosphere gas, as long as it achieves the purpose of this application. For example, it can include, but is not limited to, at least one of helium or argon.

[0040] Typically, the mass percentages of amorphous carbon, metal oxides, and lithium-ion silicates in silicon-oxygen composites can be controlled by altering the mass ratios of aluminum isopropoxide and PVP to silicon-oxygen materials, the mass ratio of Al2O3@C@SiO to Li3N, the temperature and time of the second deposition, and the temperature and time of the second calcination. For example, increasing the mass ratio of aluminum isopropoxide and PVP to silicon-oxygen materials increases the mass percentages of metal oxides and lithium-ion silicates; decreasing this ratio decreases the mass percentages of metal oxides and lithium-ion silicates. Increasing the mass ratio of Al2O3@C@SiO to Li3N increases the mass percentages of silicon grains and lithium-ion silicates; decreasing this ratio decreases the mass percentages of silicon grains and lithium-ion silicates. Increasing the second deposition temperature increases the mass percentage of amorphous carbon; decreasing the second deposition temperature decreases the mass percentage of amorphous carbon. Extending the second deposition time increases the mass percentage of amorphous carbon; shortening the second deposition time decreases the mass percentage of amorphous carbon. Increasing the second calcination temperature decreases the mass percentage of metal oxides and lithiated metal oxides, while increasing the mass percentage of silicon grains and lithium silicates; decreasing the second calcination temperature increases the mass percentage of metal oxides and lithiated metal oxides, while decreasing the mass percentage of silicon grains and lithium silicates. Extending the second calcination time decreases the mass percentage of metal oxides and lithiated metal oxides, while increasing the mass percentage of silicon grains and lithium silicates; shortening the second deposition time increases the mass percentage of metal oxides and lithiated metal oxides, while decreasing the mass percentage of silicon grains and lithium silicates.

[0041] In some embodiments of this application, the negative electrode active material further includes graphite. Based on the mass of the silicon-oxygen composite material and the graphite, the mass percentage of the silicon-oxygen composite material is from 1% to 15%, for example, the mass percentage of the silicon-oxygen composite material can be 1%, 3%, 4%, 5%, 7%, 8%, 9%, 10%, 12%, 15%, or a range consisting of any two of these values. By including graphite as the negative electrode active material and adjusting the mass percentage of the silicon-oxygen composite material within the above range, the secondary battery can achieve high energy density while also exhibiting good cycle performance and expansion performance.

[0042] In this application, the mass percentage of silicon element is 0.1% to 10% based on the mass of the negative electrode active material layer. A silicon element mass percentage within this range allows the secondary battery to have both high energy density and good expansion performance.

[0043] Typically, the Y1 / Y2 ratio can be controlled by altering the content of silicon-oxygen composite materials, silicon grains, and the mass percentage of lithium silicate in the negative electrode active material layer. For example, increasing the content of silicon-oxygen composite materials in the negative electrode active material layer increases the Y1 / Y2 ratio; decreasing it decreases it. Similarly, increasing the mass percentage of silicon grains and lithium silicate increases the Y1 / Y2 ratio; decreasing it decreases it.

[0044] In some embodiments of this application, during charge-discharge cycle tests at 25±1℃ using a 3C charge and 0.5C discharge stage, when the secondary battery completes 800 or more cycles, the ratio of the expansion rate of the negative electrode to the expansion rate of the secondary battery is between 0.5 and 4. For example, the ratio can be 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, or any combination of two of these values. This indicates that the expansion of the negative electrode is relatively small during cycling, improving the expansion of the negative electrode active material, meaning the secondary battery exhibits good expansion performance. In this application, the charge-discharge cycle test process of the above-mentioned 3C charge and 0.5C discharge is as follows: the secondary battery is left to stand in an environment of 45°C for 5 minutes, then charged at a constant current of 3C to 4.25V, then charged at a constant current of 2C to 4.4V, then charged at a constant current of 1C to 4.4V, then charged at a constant voltage of 4.45V to 0.05C, left to stand for 5 minutes, then discharged at a constant current of 0.5C to 3.0V, and left to stand for 5 minutes.

[0045] This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam, or copper foam, etc. In this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode active material layer is 30 μm to 130 μm. In this application, the negative electrode active material layer may be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that "surface" here can refer to the entire area of ​​the negative electrode current collector or only a portion thereof; this application does not impose any particular limitation, as long as it achieves the purpose of this application. The negative electrode active material layer of this application may also include a conductive agent and a binder.

[0046] The secondary battery of this application also includes a positive electrode sheet. This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. This application does not impose any particular limitation on the positive current collector, as long as it achieves the purpose of this application. For example, the positive current collector may include aluminum foil or aluminum alloy foil, etc. The positive active material layer of this application includes a positive active material. This application does not impose any particular limitation on the type of positive active material, as long as it achieves the purpose of this application. For example, the positive active material may include at least one of lithium nickel cobalt manganese oxide (NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate, etc. In this application, the positive electrode active material may also contain non-metallic elements, such as at least one selected from fluorine, phosphorus, boron, chlorine, silicon, and sulfur. These elements can further improve the stability of the positive electrode active material. In this application, there are no particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application is achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the single-sided positive electrode active material layer is 30 μm to 120 μm. In this application, the positive electrode active material layer can be disposed on one surface or on two surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector or only a part of it; there are no particular limitations in this application, as long as the purpose of this application is achieved. The positive electrode active material layer of this application may also contain conductive agents and binders.

[0047] The conductive agent and binder described above are not particularly limited, as long as they can achieve the purpose of this application. For example, the conductive agent may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon nanofibers, flake graphite, carbon dots, or graphene. The binder may include at least one of polyacrylamide, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamide-imide, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), waterborne acrylic resin, carboxymethyl cellulose (CMC), or sodium carboxymethyl cellulose (CMC-Na).

[0048] In this application, the secondary battery further includes an electrolyte, which comprises a lithium salt and a non-aqueous solvent. The lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the concentration of the lithium salt in the electrolyte, as long as it achieves the purpose of this application. For example, the concentration of the lithium salt in the electrolyte is from 0.9 mol / L to 1.5 mol / L. This application does not impose any particular limitation on the non-aqueous solvent, as long as it achieves the purpose of this application, such as including but not limited to at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorinated carbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0049] The secondary battery of this application also includes a separator. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the separator material can be, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) separators based on polytetrafluoroethylene, polyester membranes (e.g., polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex, or aramid membranes. The separator type can be, but is not limited to, at least one of woven membranes, nonwoven membranes (non-woven fabrics), microporous membranes, composite membranes, rolled membranes, or spun membranes. The separator of this application can have a porous structure, and the pore size is not particularly limited, as long as it achieves the purpose of this application. For example, the pore size can be from 0.01 μm to 1 μm. In this application, the separator thickness is not particularly limited, as long as it achieves the purpose of this application. For example, the thickness can be from 5 μm to 500 μm.

[0050] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0051] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, lithium-ion secondary batteries, sodium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries. The lithium-ion battery structure described in this application includes wound structures or stacked structures. This application does not particularly limit the shape of the secondary battery, as long as it achieves the purpose of this application. For example, it may include, but is not limited to, cylindrical batteries, prismatic batteries, irregularly shaped batteries, or button batteries.

[0052] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application has no particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0053] The second aspect of this application provides an electronic device that includes the secondary battery provided in the first aspect of this application. The secondary battery provided in the first aspect of this application has good rate performance, cycle performance, and expansion performance, thereby giving the electronic device of this application a long service life.

[0054] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries or lithium-ion capacitors, etc.

[0055] Example

[0056] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0057] Test methods and equipment

[0058] Thermogravimetric (TG) curve test:

[0059] A fully discharged lithium-ion battery was disassembled, and the negative electrode sheet was removed and soaked in dimethyl carbonate (DMC) for 20 minutes to remove the electrolyte. Then, the negative electrode sheet was placed in an oven and baked at 80°C for 12 hours to obtain the treated negative electrode sheet. Using N2 as the purge gas, the temperature was increased at a rate of 10°C / min within the range of 35°C to 800°C. Thermogravimetric analysis (TG) tests were performed on the TG curve and the first derivative thermogravimetric (DTG) curve of the negative electrode sheet.

[0060] Raman spectroscopy test:

[0061] A fully discharged lithium-ion battery was disassembled, and the negative electrode sheet was removed and immersed in dimethyl carbonate (DMC) for 20 minutes to remove the electrolyte. The negative electrode sheet was then placed in an oven and baked at 80°C for 12 hours to obtain the treated negative electrode sheet. Raman spectroscopy was performed on the prepared sample using a Jobin Yvon LabRAM HR instrument with a 532 nm light source and a measurement range of 0 cm⁻¹. -1 Up to 4000cm-1 The area of ​​the test sample was 100μm×100μm.

[0062] Content testing of each component in silicon-oxygen composite materials:

[0063] The mass percentage of amorphous carbon in silicon-oxygen composite materials was determined using a high-frequency infrared carbon-sulfur analyzer (Shanghai Dekai HCS-140). The silicon-oxygen composite sample was heated at high temperature in a high-frequency furnace under oxygen-enriched conditions to oxidize the amorphous carbon into carbon dioxide. This gas was then processed and entered a corresponding absorption cell, where it absorbed the corresponding infrared radiation, which was then converted into a corresponding signal by a detector. This signal was sampled by a computer, and after analysis and processing, the mass percentage of amorphous carbon in the silicon-oxygen composite material could be output.

[0064] Immersing the silicon-oxygen composite material in a 0.5 mol / L acetic acid solution for 30 minutes can dissolve the lithium-modified metal oxides (such as LiAlO2) coating the surface of the silicon-oxygen composite material without dissolving Al2O3. Then, the content of metal elements (non-lithium elements) in the solution can be tested using an inductively coupled plasma optical emission spectrometer (ICP-OES (PE Avio 200)) to obtain the content of lithium-modified metal oxides.

[0065] Immersing the silicon-oxygen composite material in a 1 mol / L nitric acid solution for 30 minutes dissolves both the metal oxide and lithium-ion oxide coatings on the surface of the composite material. The content of non-lithium metal elements in the solution is then measured using the same method (the percentage of aluminum by mass if aluminum is the metal). This yields the sum of the mass percentages of the metal oxide and lithium-ion oxides. Subtracting the measured lithium-ion oxide content from the sum of the mass percentages of the metal oxide and lithium-ion oxides gives the mass percentage of the metal oxide. Dividing the mass percentage of the metal oxide by the mass percentage of the lithium-ion oxide gives the mass ratio of the two.

[0066] After measuring the silicon and lithium content in the silicon-oxygen composite material using an ICP-OES (PE Avio 200) instrument, the lithium content in the lithium silicate is obtained by subtracting the lithium content in the aforementioned lithiated metal oxide. The mass percentage of lithium silicate can then be calculated. Dividing the silicon content in the lithium silicate by the silicon content yields the mass percentage of silicon grains. The sum of the mass percentages of silicon grains and lithium silicate can then be calculated. Dividing the mass percentage of silicon grains by the mass percentage of lithium silicate gives the mass ratio of the two.

[0067] Particle size test:

[0068] The particle size distribution of the silicon-oxygen composite material was tested using a laser particle size analyzer (MasterSizer 2000). In the volumetric particle size distribution of the material, starting from the smallest particle size, the particle size reaching 50% of the volumetric accumulation is defined as Dv50.

[0069] Specific surface area test:

[0070] The nitrogen adsorption-desorption curve of the silicon-oxygen composite material was tested using a specific surface area analyzer (TriStar3020), and the specific surface area of ​​the silicon-oxygen composite material was calculated using the BET calculation method.

[0071] Silicon grain size testing:

[0072] The material was XRD tested using an X-ray powder diffractometer (POWDIX 600 / 300), and the size of the silicon grains was calculated using the Scherrer formula for the peak near 28.5°.

[0073] Gram capacity and first coulomb efficiency test:

[0074] The silicon-oxygen composite material, conductive carbon black, and styrene-butadiene rubber binder of the embodiment were mixed in a mass ratio of 8:1:1, and then deionized water was added as a solvent to prepare a negative electrode slurry with a solid content of 25 wt%, which was stirred evenly. The negative electrode slurry was uniformly coated on one surface of a 10 μm thick copper foil negative electrode current collector using a 50 μm doctor blade and dried at 70°C to obtain a negative electrode sheet with a single-sided coating of a 45 μm thick negative electrode active material layer. After drying and rolling, it was punched into small round pieces with a diameter of 14 mm using a punching machine as the working electrode. After weighing and recording the mass of the small round pieces, a circular lithium sheet with a diameter of 15 mm was used as the counter electrode. The separator and electrolyte were prepared according to the method in Example 1-1. The separator was cut into round pieces with a diameter of 16 mm and assembled into a CR2032 type coin cell in a dry argon atmosphere glove box. The above-mentioned coin cell was placed at a test temperature of 25°C for 5 minutes, then discharged at a constant current of 0.1C to 0.005V, and then charged at a constant voltage of 0.005V to 0.005C. The lithium insertion capacity C0 was recorded. After placing it at a constant current of 5 minutes, it was charged at a constant current of 0.1C to 0.8V, and the lithium extraction capacity C1 was recorded. The specific capacity of the silicon-oxygen composite material is obtained by dividing C1 by the mass of the silicon-oxygen composite material, in mAh / g. The mass of the silicon-oxygen composite material = (mass of small discs - mass of copper foil) × 0.8; the initial coulombic efficiency = C1 / C0 × 100%.

[0075] The specific capacity and initial coulombic efficiency testing methods for the graphite / ordinary silicon oxide material / pre-lithiated silicon oxide material in the comparative examples are the same as those for the specific capacity and initial coulombic efficiency testing of the silicon oxide composite material, except that the aforementioned materials are used to replace the silicon oxide composite material.

[0076] AC impedance test:

[0077] A lithium-ion battery from the example / comparative case to be tested was used. A copper wire was connected to the battery as a reference electrode to obtain a three-electrode battery. Lithium was deposited onto the copper wire of the reference electrode at a current of 20 μA for 6 hours. After lithium deposition, the electrochemical impedance spectroscopy (EIS) of the three-electrode battery was measured. The lithium-deposited three-electrode battery was connected to an electrochemical workstation (Bio-Logic VMP3B, Biologic, France) to test its EIS. The test frequency range was 30 mHz to 50 kHz, and the amplitude was 5 mV. After data acquisition, the data was analyzed using impedance complex plane plots to obtain the AC impedance Rct of the lithium-ion battery, in mΩ.

[0078] Ratio performance test:

[0079] The lithium-ion batteries used in the examples / comparative examples to be tested were placed at a test temperature of 25°C and allowed to stand for 5 minutes. Then, they were charged at a constant current of 0.7C to 4.45V, followed by constant voltage charging at 4.45V to 0.05C. After standing for 5 minutes, they were discharged at a constant current of 0.2C to 3.0V, and the 0.2C discharge capacity was recorded. This process was repeated for 5 minutes, followed by constant current discharge at 2C, and the 2C discharge capacity was recorded. Rate performance = 2C discharge capacity / 0.2C discharge capacity × 100%.

[0080] Cyclic performance and expansion performance testing:

[0081] At a test temperature of 45℃, the lithium-ion battery under test was left to stand for 5 minutes, and the initial thickness MMC0 of the lithium-ion battery was recorded. The lithium-ion battery was then charged at a constant current of 3C to 4.25V, then at 2C to 4.4V, then at 1C to 4.45V, and finally charged at a constant voltage of 4.45V to 0.05C, and the discharge capacity C4 of the lithium-ion battery was recorded. After standing for 5 minutes, it was discharged at a constant current of 0.5C to 3.0V, and then stood for 5 minutes. After 400 cycles of the above 3C charge / 0.5C discharge cycle, the thickness MMC1 and discharge capacity C5 of the lithium-ion battery were recorded. The capacity retention rate (%) after 400 cycles = C5 / C1 × 100%, and the expansion rate (%) after 400 cycles = (MMC1 - MMC0) / MMC0 × 100%.

[0082] Test of the expansion ratio of the negative electrode sheet and the lithium-ion battery after 800 cycles:

[0083] The lithium-ion batteries under test were divided into two groups. One group was cycled 800 times according to the steps described above for cycle performance and expansion performance testing. The initial thickness of the lithium-ion battery was MMC0, and the thickness after 800 cycles was MMC2. Then, the lithium-ion batteries that had been fully discharged after 800 cycles were disassembled, and the thickness H1 of the negative electrode was measured. The other group was directly disassembled, and the initial thickness H0 of the negative electrode was measured. The expansion ratio of the negative electrode to the lithium-ion battery after 800 cycles was calculated as (MMC2 - MMC0) / (H1 - H0).

[0084] Energy density test:

[0085] In an environment of 25°C, the lithium-ion battery of the embodiment was charged and then discharged according to the following procedure to obtain the discharge capacity of the lithium-ion battery: The lithium-ion battery was charged at a constant current of 0.7C to 4.45V, then charged at a constant voltage of 4.45V to 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.2C to 3.0V, left to stand for 5 minutes to obtain the discharge capacity D. After the above lithium-ion battery was charged at a constant current of 0.7C to 3.85V, it was then charged at a constant voltage of 3.85V to 0.05C. The length L, width W, and height H of the lithium-ion battery were measured using a laser thickness gauge to obtain the volume V of the lithium-ion battery = L × W × H. Its energy density (E D = D / V, with units of Wh / L.

[0086] Example 1-1

[0087] <Preparation of Silicon-Oxide Composite Materials>

[0088] Step 1: Mix elemental silicon and silicon dioxide in a 1:1 molar ratio and place them in the evaporation chamber of the deposition furnace. Heat to 1200℃ and evaporate. Collect the deposited SiO blocks (first deposition) in the deposition chamber. After crushing, grading and other treatments, obtain silicon-oxygen material with a Dv50 of 7μm.

[0089] Step 2: Place the material obtained in Step 1 in a vapor deposition furnace, introduce acetylene gas at a flow rate of 3 L / min, and deposit at 600℃ for 3 hours (second deposition) to deposit the first layer of amorphous carbon on the surface of the silicon-oxygen material, thus obtaining a silicon-oxygen material with amorphous carbon on the surface, denoted as C@SiO material.

[0090] Step 3: The C@SiO material was placed in an ethanol solution, and aluminum isopropoxide and polyvinylpyrrolidone (PVP) were added at a molar ratio of 1:1. After stirring evenly, the mixture was spray-dried and then calcined for the first time under an argon atmosphere to obtain C@SiO material with Al2O3 on its surface, denoted as Al2O3@C@SiO material. The first calcination temperature was 600℃ and the time was 5 hours; the total mass ratio of aluminum isopropoxide and PVP to the mass ratio of C@SiO material was A%, and A% was 2%.

[0091] Step 4: The Al2O3@C@SiO material and lithium nitride (Li3N) are mixed uniformly at a mass ratio of 95:5, and then calcined a second time under an argon atmosphere to obtain a silicon-oxygen composite material with a first shell and a second shell on the surface. The second calcination temperature is 700℃ and the time is 5h. The core of the silicon-oxygen composite material includes silicon grains and lithium silicate, the first shell includes amorphous carbon, and the second shell includes Al2O3 and lithium-modified Al2O3.

[0092] <Preparation of Negative Electrode Sheets>

[0093] The silicon-oxygen composite material prepared above was uniformly mixed with graphite to obtain the negative electrode active material. The silicon-oxygen composite material had a mass percentage content of 3%, based on the mass of the silicon-oxygen composite material and graphite. The graphite particle size Dv50 was 14.2 μm, and the specific surface area was 1.02 m². 2 / g.

[0094] A negative electrode active material, conductive carbon black (conductive agent), styrene-butadiene rubber (binder), and sodium carboxymethyl cellulose (thickener) were mixed in a mass ratio of 97:0.5:0.4:2.1. Deionized water was then added as a solvent to prepare a negative electrode slurry with a solid content of 46 wt%, and the mixture was stirred evenly. The negative electrode slurry was uniformly coated onto one surface of a 12 μm thick copper foil current collector. The copper foil was dried at 85°C for 4 hours to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer, with a coating thickness of 60 μm. The above steps were repeated on the other surface of the aluminum foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After drying under vacuum at 85°C for 4 hours, the sheet was cold-pressed, cut, and slit to obtain a negative electrode sheet with a size of 76.6 mm × 875 mm.

[0095] <Preparation of the positive electrode>

[0096] Lithium cobalt oxide (positive electrode active material), conductive carbon black (conductive agent), and PVDF (binder) were mixed in a mass ratio of 96:2:2. NMP was added as a solvent, and the mixture was stirred until homogeneous, resulting in a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was uniformly coated onto one surface of a 13 μm thick aluminum foil used as a positive electrode current collector. The foil was then dried at 90°C to obtain a single-sided positive electrode sheet with a 50 μm thick positive electrode active material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a double-sided positive electrode sheet. After drying under vacuum at 90°C for 4 hours, the sheet was cold-pressed, cut, and slit to obtain a positive electrode sheet with a size of 74 mm × 867 mm.

[0097] <Preparation of Electrolyte>

[0098] In a dry argon atmosphere glove box, lithium salt LiPF6 was added to a mixed solvent of basic organic solvent DMC:DEC:EC = 1:1:1 to dissolve and mix evenly to obtain an electrolyte. Ethylene carbonate was added as an additive. Based on the mass of the electrolyte, the mass percentage of lithium salt was 12.5%, the mass percentage of vinylene carbonate was 2%, and the remainder was the basic organic solvent.

[0099] <Preparation of the diaphragm>

[0100] PVDF and alumina were mixed at a mass ratio of 9:1, and NMP was added as a solvent to prepare a slurry with a solid content of 12wt%. The slurry was stirred evenly and then uniformly coated on one surface of a 7μm thick PP film substrate. After drying, a diaphragm with a 2μm coating on one side was obtained.

[0101] <Preparation of Lithium-ion Batteries>

[0102] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. The electrodes are then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 85°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, and shaping processes.

[0103] Examples 1-2 to Examples 1-10

[0104] Except for adjusting the preparation parameters in Table 1 <Preparation of Silicon-Oxide Composite Materials>, the rest are the same as in Examples 1-1 and 1-11.

[0105] Except for the silicon-oxygen composite material prepared by the following <Preparation of Silicon-Oxide Composite Material> process, the rest is the same as in Examples 1-1.

[0106] <Preparation of Silicon-Oxide Composite Materials>

[0107] Step 1: Mix elemental silicon and silicon dioxide in a 1:1 molar ratio and place them in the evaporation chamber of the deposition furnace. Heat to 1200℃ and evaporate. Collect the deposited SiO blocks (first deposition) in the deposition chamber. After crushing, grading and other treatments, obtain silicon-oxygen material with a Dv50 of 7μm.

[0108] Step 2: The above-mentioned silicon-oxygen material was placed in an ethanol solution, and aluminum isopropoxide and polyvinylpyrrolidone (PVP) were added at a molar ratio of 1:1. After stirring evenly, the mixture was spray-dried and then calcined for the first time under an argon atmosphere to obtain a silicon-oxygen material with Al2O3 on its surface, denoted as Al2O3@SiO material. The first calcination temperature was 600℃ and the time was 5 hours; the mass ratio of the total mass of aluminum isopropoxide and PVP to the mass of silicon-oxygen material was A%, and A% was 4%.

[0109] Step 3: Place the Al2O3@SiO material obtained in Step 2 into a vapor deposition furnace, introduce acetylene gas at a flow rate of 3 L / min, and deposit at 600℃ for 5 h (second deposition). The first layer of amorphous carbon is deposited on the surface of the Al2O3@SiO material, resulting in an Al2O3@SiO material with amorphous carbon on the surface, denoted as C@Al2O3@SiO material.

[0110] Step 4: Mix C@Al2O3@SiO materials with Li3N at a mass ratio of 90:10 until homogeneous, then calcine a second time under an argon atmosphere to obtain a silicon-oxygen composite material with a first and second shell on the surface. The second calcination temperature is 600℃ and the time is 5 hours. The core of the silicon-oxygen composite material consists of silicon grains and lithium silicate, the first shell consists of amorphous carbon, and the second shell consists of Al2O3 and lithium-modified Al2O3.

[0111] Example 2-1

[0112] Except for adjusting the mass percentage of the silicon-oxygen composite material according to Table 3, the rest is the same as in Examples 1-8.

[0113] Examples 2-2 to 2-6

[0114] Except for adjusting the mass percentage of the silicon-oxygen composite material according to Table 3, the rest is the same as in Example 2-1.

[0115] Comparative Example 1

[0116] Except for replacing the silicon-oxygen composite material with purchased artificial graphite material (Aladdin, G434784), the rest is the same as in Examples 1-1.

[0117] Comparative Example 2

[0118] Except for replacing the silicon-oxygen composite material with a purchased ordinary silicon-oxygen material (Aladdin, S431223), the rest is the same as in Examples 1-1.

[0119] Comparative Example 3

[0120] Except for replacing the silicon-oxygen composite material with the pre-lithiated silicon-oxygen material prepared by the following <Preparation of Pre-lithiated Silicon-Oxide Material> process, the rest is the same as in Examples 1-1.

[0121] <Preparation of Pre-lithiated Silicon Oxide Material> Step 1: Mix elemental silicon and silicon dioxide in a molar ratio of 1:1 and place them in the evaporation chamber of the deposition furnace. Heat to 1200℃ and evaporate. Collect the deposited SiO block in the deposition chamber (first deposition). After crushing, grading and other treatments, obtain silicon oxide material with a Dv50 of 7μm.

[0122] Step 2: Place the material obtained in Step 1 in a vapor deposition furnace, introduce acetylene gas at a flow rate of 3 L / min, and deposit at 600℃ for 3 h (second deposition) to deposit amorphous carbon on the surface of the silicon-oxygen material, thus obtaining a silicon-oxygen material with a first layer of amorphous carbon on the surface, denoted as C@SiO material.

[0123] Step 3: The C@SiO material and lithium nitride (Li3N) are mixed uniformly at a mass ratio of 95:5, and then calcined a second time under an argon atmosphere to obtain a pre-lithiated silicon-oxygen material with a first shell on the surface. The second calcination temperature is 700℃ and the time is 5h; the first shell consists of amorphous carbon.

[0124] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0125] Table 1

[0126]

[0127]

[0128] As can be seen from Examples 1-1 to 1-11 and Comparative Examples 1 to 3, when the value of Y1 / Y2 is too small, the specific capacity of the corresponding negative electrode active material is low, which is not conducive to improving the capacity of the lithium-ion battery. For example, compared with Comparative Example 1, the specific capacity of the negative electrode active material in this application embodiment is more than three times that of the artificial graphite material in Comparative Example 1, that is, the lithium-ion battery in this application embodiment has a higher capacity. Although the lithium-ion battery of Comparative Example 1 has better rate performance, cycle performance and expansion performance, it cannot achieve high capacity. When the value of Y1 / Y2 is too large, the AC impedance of the lithium-ion battery is large, the rate performance and cycle capacity retention rate are low, and the expansion ratio of the negative electrode sheet to the battery is high after 800 cycles. For example, compared with Comparative Examples 2 and 3, the lithium-ion battery in this application embodiment has lower AC impedance, higher rate performance and cycle capacity retention rate, and its expansion ratio of the negative electrode sheet to the battery is lower after 800 cycles. The negative electrode of the lithium-ion battery in this embodiment includes a silicon-oxygen composite material, and when Y1 / Y2 satisfies 0.1≤Y1 / Y2≤4, the lithium-ion battery simultaneously has lower AC impedance, higher capacity, rate performance and cycle capacity retention. Furthermore, the ratio of the expansion rate of the negative electrode to the battery is lower after 800 cycles, indicating that the lithium-ion battery provided in this application can simultaneously have better rate performance, cycle performance and expansion performance.

[0129] As can be seen from Examples 1-1 to 1-11, the lithium-ion batteries within the scope of this application have lower AC impedance, higher rate performance, and better cycle capacity retention, and the ratio of the negative electrode sheet to the battery expansion rate is lower after 800 cycles. This indicates that the lithium-ion batteries provided by this application have lower AC impedance, better rate performance, better cycle performance, and better expansion performance.

[0130] Table 3

[0131]

[0132] The I1 / I2 ratio and the mass percentage of silicon-oxygen composite material typically affect the performance of lithium-ion batteries, such as energy density, rate performance, cycle performance, and expansion performance. As can be seen from Examples 1-8 and Examples 2-1 to 2-6, the lithium-ion batteries within the scope of this application, with their I1 / I2 ratio and silicon-oxygen composite material content, exhibit high energy density, rate performance, and cycle capacity retention, as well as low cycle expansion rate. This demonstrates that the lithium-ion batteries provided in this application possess high energy density while also exhibiting good rate performance, cycle performance, and expansion performance.

[0133] Figure 1 and Figure 2 The thermogravimetric (TG) curves and first derivative thermogravimetric (DTG) curves of the negative electrode sheets of Examples 1-8 and Comparative Example 1 are shown respectively. From Figure 1 It can be seen that the peak intensity Y1 of the negative electrode sheet of Examples 1-8 of this application is -0.13% min at 587.9℃ and the peak intensity Y2 is -0.15% min at 427.3℃. The calculated value of Y1 / Y2 is 0.87. Figure 1 In the graph, the peaks between 500℃ and 700℃ correspond to the decomposition of silicon-containing organolithium salts, while the peaks between 350℃ and 450℃ correspond to the decomposition of silicon-free lithium salts. The Y1 / Y2 ratio reflects the ratio of silicon-containing organolithium salts to silicon-free lithium salts; the higher the peak intensity, the higher the content of the corresponding lithium salt. Figure 2 It can be seen that the DTG curve of the negative electrode of Comparative Example 1 does not show an endothermic peak between 500℃ and 700℃, indicating that the negative electrode of Comparative Example 1 does not contain silicon-containing organic lithium salt, i.e., Y1 is 0%min. The peak intensity Y2 at 391.8℃ between 350℃ and 450℃ is -0.24%min, which corresponds to the decomposition without silicon lithium salt. The calculated value of Y1 / Y2 is 0.

[0134] Figure 3 The TG and DTG curves of the negative electrode sheets in Examples 2-5 are shown. From Figure 3 It can be seen that the peak intensity Y1 of the negative electrode sheet of Examples 2-5 is -0.36%min at 594.8℃ and the peak intensity Y2 is -0.10%min at 401.8℃, so the value of Y1 / Y2 is 3.6.

[0135] Figure 4 The Raman spectra of the negative electrode sheets of Examples 1-8 are shown. The Raman spectra of the negative electrode sheets of Examples 1-8 are at 1342.1 cm⁻¹. -1 The peak intensity I1 at 421.9 cm⁻¹ is 632.9. -1 The peak intensity I2 at the point is 111.2, and the calculated value of I1 / I2 is 5.69.

[0136] Figure 5 The Raman spectra of the negative electrode sheets of Examples 2-5 are shown. The Raman spectra of the negative electrode sheets of Examples 2-5 are at 1345.4 cm⁻¹. -1 The peak intensity I1 is 459.3, and it is at 429.2 cm⁻¹. -1 The peak intensity I2 is 116.3, and the calculated value of I1 / I2 is 3.95.

[0137] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0138] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0139] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A secondary battery, comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer comprising a negative active material, the negative active material comprising a silicon-oxygen composite material; The silicon-oxygen composite material has a core-shell structure, comprising a core and a first shell and a second shell disposed on at least a portion of the surface of the core; the core comprises silicon grains and lithium silicate, the first shell comprises amorphous carbon, and the second shell comprises metal oxide and lithium-modified metal oxide; the metal oxide comprises at least one of aluminum oxide, titanium dioxide, or niobium pentoxide. The peak intensity of the first differential thermogravimetric curve of the negative electrode sheet at 500℃ to 700℃ is Y1, and the peak intensity of the first differential thermogravimetric curve of the negative electrode sheet at 350℃ to 450℃ is Y2. Y1 / Y2 satisfies 0.1 ≤ Y1 / Y2 ≤ 4. The thermogravimetric first differential curve of the negative electrode sheet was obtained by using N2 as the purge gas and heating at a rate of 10℃ / min within the range of 35℃ to 800℃.

2. The secondary battery according to claim 1, wherein, 0.5≤Y1 / Y2≤2.

5.

3. The secondary battery according to claim 1, wherein, The Raman spectrum of the negative electrode is at 1200 cm⁻¹. -1 Up to 1500cm -1 The peak intensity is I1, and the Raman spectrum of the negative electrode is at 300 cm⁻¹. -1 Up to 600cm -1 The peak intensity is I2, and I1 / I2 satisfies 2≤I1 / I2≤15.

4. The secondary battery according to claim 1, wherein, The silicon-oxygen composite material has a Dv50 of 3 μm to 15 μm; the specific surface area of ​​the silicon-oxygen composite material is 0.2 m². 2 / g to 8m 2 / g.

5. The secondary battery according to claim 1, wherein, Based on the mass of the silicon-oxygen composite material, the mass percentage of amorphous carbon is 1% to 5%, the mass percentage of the metal oxide and the lithium-ionized metal oxide is 1% to 5%, and the sum of the mass percentages of the silicon grains and the lithium silicate is 92% to 98%.

6. The secondary battery according to claim 1, wherein, The size of the silicon grains is from 0.5 nm to 10 nm.

7. The secondary battery according to claim 1, wherein, The second shell comprises a metallic element, including at least one of aluminum, titanium, or niobium, and the mass percentage of the metallic element is 0.1% to 1% based on the mass of the second shell of the silicon-oxygen composite material.

8. The secondary battery according to claim 1, wherein, The negative electrode active material also includes graphite, and the mass percentage of the silicon-oxygen composite material is 1% to 15% based on the mass of the silicon-oxygen composite material and the graphite.

9. The secondary battery according to claim 1, wherein, In a charge-discharge cycle test at 25±1℃ using a 3C charge and 0.5C discharge cycle, when the secondary battery has 800 or more cycles, the ratio of the expansion rate of the negative electrode to the expansion rate of the secondary battery is 0.5 to 4.

10. An electronic device comprising a secondary battery according to any one of claims 1 to 9.

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