Electrochemical device and electronic device

Abstract

The invention relates to an electrochemical device and an electronic device. The electrochemical device comprises a positive electrode, a negative electrode and an electrolyte, the electrolyte comprises an additive, the additive comprises a first additive M, and the first additive M is selected from at least one of a fluorocarbonate compound or a compound containing sulfur and oxygen double bonds; wherein the negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises a hard carbon material. The electrochemical device disclosed by the invention has improved high-temperature cycle performance, low-temperature performance and rate capability, and meanwhile, the gram volume of the negative electrode active material is considered.

Description

Electrochemical device and electronic device Technical Field

[0001] The present application relates to the field of energy storage, and in particular to an electrochemical device and an electronic device. Background Art

[0002] With the widespread application of electrochemical devices, various types of batteries have been developed. Sodium-ion batteries are a new type of rechargeable energy storage device, operating on a similar principle to lithium-ion batteries. Compared to traditional lithium-ion batteries, they offer advantages in cost, rate capability, low-temperature performance, and cycle life. Furthermore, sodium-ion batteries offer high safety. Currently, sodium-ion batteries have garnered widespread attention and hold broad application prospects in areas such as electric vehicles and energy storage systems.

[0003] Graphite materials are widely used negative electrode active materials in lithium-ion batteries. However, due to the thermodynamic instability of the compounds formed by graphite materials and sodium, and the large ionic radius of sodium ions, which cannot be reversibly embedded / extracted between graphite layers, traditional graphite cannot be used as negative electrode active materials for sodium-ion batteries. Among the many negative electrode active materials for sodium-ion batteries that have yet to be developed, hard carbon materials have received great attention due to their advantages such as high specific capacity, good rate performance, low temperature performance and good cycle performance. In addition, the precursors of hard carbon materials are widely available. Common biomass materials, coal-based materials, asphalt-based materials and resin materials can all be used as precursors of hard carbon materials, and they are inexpensive. At the same time, the energy consumption of the heat treatment process of hard carbon materials is also lower than that of graphite materials. The cost advantages of raw materials and processing processes help to further enhance the cost advantage of sodium-ion batteries.

[0004] Hard carbon materials have a large interlayer spacing, which facilitates the insertion and extraction of sodium ions and increases the sodium ion diffusion rate. Furthermore, the numerous pore defects within hard carbon materials allow for high sodium storage capacity, making them the most ideal anode materials for sodium-ion batteries. From a sodium storage mechanism perspective, most of hard carbon's sodium storage capacity is filled at low potentials, which are close to the sodium precipitation potential and can easily induce sodium precipitation, leading not only to irreversible capacity decay but also to potential gassing and safety issues in electrochemical devices.

[0005] Therefore, there is a real need to provide an improved electrochemical device using hard carbon as a negative electrode active material.

[0006] Summary of the Invention

[0007] The purpose of this application is to provide an electrochemical device and an electronic device. The electrochemical device of this application has improved high-temperature cycle performance, low-temperature performance, and rate performance, while taking into account the gram capacity of the negative electrode active material. The specific technical solution is as follows:

[0008] In one embodiment, the present application provides an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte comprises an additive, the additive comprising a first additive M, the first additive M being selected from at least one of a fluorocarbonate compound or a compound containing a sulfur-oxygen double bond, wherein the mass percentage of the first additive M based on the mass of the electrolyte is m%; wherein the negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material comprises a hard carbon material, wherein the hard carbon material is tested by Raman spectroscopy at 1300 cm -1 to 1400cm - 1 The peak intensity at 1550 cm is ID, and the peak intensity at 1550 cm is ID. -1 to 1650cm -1 The peak intensity at IG is IG, the ratio of ID / IG is d, d is 1.0 to 1.6, and m / d is in the range of 0.01 to 4.5. In some embodiments, the electrochemical device satisfies at least one of the following conditions: (1) m / d is in the range of 1.6 to 3.6; or (2) d is in the range of 1.2 to 1.4.

[0009] In some embodiments, the interplanar spacing d002 of the hard carbon material is measured by X-ray diffraction and is in a range of 0.37 nm to 0.41 nm. In some embodiments, the interplanar spacing d002 is in a range of 0.38 nm to 0.40 nm.

[0010] In some embodiments, the electrochemical device satisfies at least one of the following conditions:

[0011] (1) The mass percentage of the fluorinated carbonate compound is 0.05% to 5% based on the mass of the electrolyte; or

[0012] (2) Based on the mass of the electrolyte, the mass percentage of the compound containing sulfur-oxygen double bonds is 0.05% to 4%.

[0013] In some embodiments, the compound containing a sulfur-oxygen double bond includes at least one of 1,3-propane sultone, propenyl-1,3-sultone, 1,2-propane sultone, 1,4-butane sultone, or vinyl sulfate, and / or the fluorocarbonate compound includes at least one of fluoroethylene carbonate or bisfluoroethylene carbonate.

[0014] In some embodiments, the hard carbon material has pores therein, the pores have a pore diameter ranging from 0.6 nm to 2.0 nm, and the pore volume is less than 0.05 cc / g as determined by nitrogen adsorption testing.

[0015] In some embodiments, the hard carbon material satisfies at least one of the following conditions:

[0016] (1) The specific surface area of ​​hard carbon material is 0.5m 2 / g to 10m 2 / g;

[0017] (2) The compacted density of the hard carbon material at 5t decompression is 0.8g / cc to 1.6g / cc;

[0018] (3) wherein the hard carbon material has a diffraction peak in the range of 18° to 30° as tested by X-ray diffraction method, and the half-peak width of the diffraction peak is 4° to 12°;

[0019] (4) The Dv50 of the hard carbon material is 2 μm to 10 μm, and the Dv50 and Dv90 of the hard carbon material satisfy the following: 2≤Dv90 / Dv50≤5.

[0020] In some embodiments, the negative electrode active material layer satisfies at least one of the following conditions:

[0021] (1) The porosity of the negative electrode active material layer is in the range of 30% to 60%;

[0022] (2) The compaction density of the negative electrode active material layer is in the range of 0.8 g / cc to 1.5 g / cc.

[0023] In some embodiments, the capacity of the negative electrode active material layer per unit area of ​​the positive electrode is V1, the positive electrode includes a positive electrode active material layer, the capacity of the positive electrode active material layer per unit area of ​​the positive electrode is V2, and the range of V1 / V2 is 1.1 to 1.5.

[0024] In some embodiments, the electrochemical device is a sodium ion battery.

[0025] In another embodiment, the present application provides an electronic device comprising the electrochemical device according to the embodiment of the present application.

[0026] The present application significantly improves the high-temperature cycle performance, low-temperature performance and rate performance of electrochemical devices (especially sodium-ion batteries) by using hard carbon in combination with a specific electrolyte and controlling their ratio.

[0027] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the following description through implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0028] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the present application.

[0029] As used in this application, the term "about" is used to describe and illustrate small variations. When used in conjunction with an event or circumstance, the term can refer to instances in which the event or circumstance occurred exactly as well as instances in which the event or circumstance occurred very approximately. For example, when used in conjunction with a numerical value, the term can refer to a range of variation of less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.

[0030] In addition, amounts, ratios, and other numerical values ​​are sometimes presented herein in a range format. It should be understood that such a range format is used for convenience and brevity and should be interpreted flexibly to include not only the values ​​explicitly specified as limits of the range, but also all individual values ​​or sub-ranges encompassed within the range, as if each value and sub-range were explicitly specified.

[0031] In the detailed description and claims, a list of items linked by the terms "one of," "one of," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, the phrase "one of A, B, and C" means only A; only B; or only C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0032] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0033] 1. Electrochemical Device

[0034] In some embodiments, the present application provides an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte.

[0035] In some embodiments, the electrolyte includes an additive, the additive includes a first additive M, the first additive M is selected from at least one of a fluorinated carbonate compound or a compound containing a sulfur-oxygen double bond, wherein the mass percentage of the first additive M based on the mass of the electrolyte is m%; wherein the negative electrode includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a hard carbon material, wherein the hard carbon material is tested by Raman spectroscopy at 1300 cm -1 to 1400cm -1 The peak intensity at 1550 cm is ID, and the peak intensity at 1550 cm is ID. -1 to 1650cm -1 The peak intensity at is IG, the ratio of ID / IG is d, d is 1.0 to 1.6, and the range of m / d is 0.01 to 4.5.

[0036] In some embodiments, m / d ranges from 0.01 to 4.5. In some embodiments, m / d ranges from 1.6 to 3.6. In some embodiments, m / d is 0.01, 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 4.5, or a range consisting of any two of these values.

[0037] In some embodiments, m is 1 to 10. In some embodiments, m is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range consisting of any two of these values.

[0038] In some embodiments, d is 1.2 to 1.4. In some embodiments, d is 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or a range consisting of any two of these values.

[0039] On the one hand, when the ID / IG ratio d of the hard carbon material is within the above range, the hard carbon material has a high defect content. These defects may be caused by the disordered microcrystalline structure of the hard carbon material or by micropore defects within the hard carbon material. A high defect content can provide the hard carbon material with more sodium ion adsorption sites, thereby improving the material's rapid charge and discharge capabilities. Therefore, the hard carbon material of the present application, when used as a negative electrode active material in an electrochemical device, can enable the electrochemical device to have excellent kinetic performance.

[0040] On the other hand, an embodiment of the present application provides an electrolyte that matches the above-mentioned high-kinetic hard carbon material. The electrolyte contains a first additive M, and the first additive M is selected from at least one of a fluorocarbonate compound or a compound containing a sulfur-oxygen double bond. During the first charge and discharge process, a solid electrolyte interface film (i.e., SEI film) is formed on the surface of the negative electrode active material of the sodium ion battery. The SEI film with a stable structure is the key to the stable circulation of sodium ions. By selecting the composition and content of the additives in the electrolyte system, the SEI film can be controlled to make its structure uniform, dense and thin, which can isolate the electrolyte from further decomposition and broaden the actual electrochemical window of the electrolyte. The strong electron-withdrawing effect of the fluorine atoms in the fluorocarbonate compounds can enhance the electronic ability of the central atom, and can be reduced on the negative electrode surface at a higher potential (~0.7V) to form a stable SEI film, and further prevent the decomposition of carbonate compounds on the surface of the active material. Compound additives containing sulfur-oxygen double bonds also have a similar effect. Since the electronegativity of sulfur atoms is higher than that of carbon atoms, they are reduced on the negative electrode surface before carbonate compounds with similar structures, forming a stable SEI film rich in sulfur elements, which can improve the high and low temperature performance of electrochemical devices and reduce interface impedance.

[0041] Furthermore, the inventors of the present application have found that the surface defects and defect content of the hard carbon active material will also affect the formation and structural stability of the SEI film. Since the defect reaction activity is higher, it can induce the formation of the SEI film and affect its stability. Therefore, the selection of the content of the electrolyte additive in the sodium ion battery system needs to further consider the surface defect content of the hard carbon active material. The inventors of the present application have found that when the ratio d of ID / IG in the Raman spectrum of the hard carbon material and the mass percentage m% of the first additive M satisfy the m / d range within the above range, the SEI film formed at this time can effectively improve the sodium ion transfer rate, thereby improving the kinetics, low temperature performance and cycle performance of the sodium ion battery, while taking into account the gram capacity of the negative electrode active material.

[0042] In some embodiments, the interplanar spacing d002 of the hard carbon material is measured by X-ray diffraction and is in the range of 0.37 nm to 0.41 nm. In some embodiments, the interplanar spacing d002 of the hard carbon material is in the range of 0.38 nm to 0.40 nm. In some embodiments, the interplanar spacing d002 of the hard carbon material is 0.37 nm, 0.38 nm, 0.39 nm, 0.40 nm, 0.41 nm, or a value within the range of any two of these values. When the interplanar spacing d002 of the hard carbon material is within the above range, the larger 002 interplanar spacing facilitates the rapid transport of sodium ions within the hard carbon material, thereby improving the reversible capacity and kinetic performance of the hard carbon material when applied to negative electrode active materials. In some embodiments, the interplanar spacing d002 is in the range of 0.38 nm to 0.40 nm, which can further improve the kinetic performance of the hard carbon material.

[0043] In some embodiments, the weight percentage of the fluorinated carbonate compound is 0.05% to 5% based on the weight of the electrolyte. In some embodiments, the weight percentage of the fluorinated carbonate compound is 0.05%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, or a range consisting of any two of these values.

[0044] In some embodiments, the weight percentage of the compound containing sulfur-oxygen double bonds is 0.05% to 4% based on the weight of the electrolyte. In some embodiments, the weight percentage of the compound containing sulfur-oxygen double bonds is 0.05%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or a range consisting of any two of these values.

[0045] The inventors of the present application have discovered that when the mass percentage of the fluorinated carbonate compound additive in the electrolyte system is in the range of 0.05% to 5%, and / or the mass percentage of the compound additive containing sulfur-oxygen double bonds is in the range of 0.05% to 4%, the SEI film formed at this time has an appropriate thickness and a stable structure.

[0046] In some embodiments, the compound containing a sulfur-oxygen double bond includes at least one of 1,3-propane sultone, propenyl-1,3-sultone, 1,2-propane sultone, 1,4-butane sultone, or vinyl sulfate.

[0047] In some embodiments, the fluorocarbonate compound includes at least one of fluoroethylene carbonate or bisfluoroethylene carbonate.

[0048] In some embodiments, the hard carbon material has pores therein, the pores have a pore diameter ranging from 0.6 nm to 2.0 nm, and the pore volume is less than 0.05 cc / g as determined by nitrogen adsorption testing.

[0049] In some embodiments, the pores have a pore size range of 0.6 nm, 0.8 nm, 1.0 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm, 2.0 nm, or a range consisting of any two of these values.

[0050] In some embodiments, the pore volume of the pores is 0.01 cc / g, 0.02 cc / g, 0.03 cc / g, 0.04 cc / g, 0.05 cc / g, or a range consisting of any two of these values.

[0051] The hard carbon material described in the present application has a rich pore structure inside. When the hard carbon material has a pore structure in the above-mentioned pore size range, during the sodium storage process, sodium ions can be stored in the micropores, thereby providing a higher reversible capacity. In some embodiments, in an electrochemical device used with metallic sodium as a counter electrode, the gram capacity of the hard carbon material is 200mAh / g to 1000mAh / g. Therefore, when the hard carbon material of the present application is applied to the negative active material of a sodium ion battery, the sodium ion battery can have a high energy density. When the pore volume of the pores is within the above-mentioned range, the open pore structure on the surface of the material or the content of external connecting pores is low.

[0052] In some embodiments, the specific surface area of ​​the hard carbon material is 0.5 m 2 / g to 10m 2 In some embodiments, the specific surface area of ​​the hard carbon material is 0.5 m 2 / g、1m 2 / g, 1.5m 2 / g, 2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g、5m 2 / g, 5.5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g、10m 2 / g or a value within a range consisting of any two of these values.

[0053] When the specific surface area of ​​the hard carbon material is within the above range, it can not only ensure that the SEI film formed during the first charging process of the electrochemical device has an area of ​​appropriate size, but also reduce the amount of binder in the negative electrode active material layer, reduce the loss of active ions and the internal resistance of the negative electrode active material layer, thereby improving the first coulombic efficiency, cycle performance and safety performance of the electrochemical device.

[0054] In some embodiments, the compaction density of the hard carbon material at 5t is 0.8g / cc to 1.6g / cc. In some embodiments, the compaction density of the hard carbon material at 5t is 0.8g / cc, 1.0g / cc, 1.2g / cc, 1.4g / cc, 1.6g / cc or a value within the range of any two of these values. It is foreseeable that a suitable particle size distribution of the active material helps to improve the powder compaction density of the material. From the perspective of the active material itself, the density of the active material is mainly due to the disordered arrangement of the microcrystalline layers inside the material and a large number of pore defects. Since the above-mentioned hard carbon material has abundant pore defects for sodium storage, the powder compaction density of the hard carbon material is much lower than that of the graphite material. When the compaction density of the hard carbon material at 5 tons of pressure is within the above-mentioned range, the hard carbon material has a higher powder compaction density.

[0055] In some embodiments, the hard carbon material has a diffraction peak in the range of 18° to 30°, and a half-value width of the diffraction peak is 4° to 12°, as measured by X-ray diffraction. In some embodiments, the half-value width of the diffraction peak is 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, or a range consisting of any two of these values.

[0056] In some embodiments, the hard carbon material has a Dv50 of 2 μm to 10 μm. In some embodiments, the hard carbon material has a Dv50 of 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range consisting of any two of these values. When the volume average particle size of the hard carbon material is within this range, the hard carbon material can have good electrolyte wettability and a small specific surface area, thereby reducing the consumption of active ions due to the formation of the SEI film on the hard carbon material surface during the initial charge. Therefore, the hard carbon material of the present application, when used as a negative electrode active material in an electrochemical device, can enable the electrochemical device to have both good kinetic performance and a high initial coulombic efficiency. In some embodiments, the Dv50 and Dv90 of the hard carbon material satisfy the following: 2 ≤ Dv90 / Dv50 ≤ 5. In some embodiments, the ratio of the Dv50 to Dv90 (Dv90 / Dv50) of the hard carbon material is 2, 3, 4, 5, or a range consisting of any two of these values. When the ratio of Dv50 to Dv90 of the hard carbon material is within the above range, a suitable particle size distribution helps to improve the compaction density of the active material layer. After cold pressing of the active material layer, the particles are in closer contact with each other, and the porosity of the active material layer can be effectively improved. At the same time, the close contact between particles helps to reduce the electrode impedance and improve the kinetic performance of the electrochemical device. Furthermore, a suitable particle size distribution also helps to improve the processing performance of the active material layer, and the thickness of the active material layer can be effectively increased, further improving the mass density of the electrochemical device.

[0057] In some embodiments, the hard carbon material has a Dv90 of 5 to 50 μm. In some embodiments, the hard carbon material has a Dv90 of 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or a range consisting of any two of these values.

[0058] In some embodiments, the porosity of the negative electrode active material layer ranges from 30% to 60%. In some embodiments, the porosity of the negative electrode active material layer is 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range consisting of any two of these values.

[0059] In some embodiments, the negative electrode active material layer has a compaction density ranging from 0.8 g / cc to 1.5 g / cc. In some embodiments, the negative electrode active material layer has a compaction density of 0.8 g / cc, 0.9 g / cc, 1.0 g / cc, 1.1 g / cc, 1.2 g / cc, 1.3 g / cc, 1.4 g / cc, 1.5 g / cc, or a range consisting of any two of these values.

[0060] In some embodiments, the thickness of the single-sided negative electrode active material layer is in the range of 50 μm to 120 μm. In some embodiments, the thickness of the negative electrode active material layer is in the range of 50 μm, 80 μm, 100 μm, 120 μm, or a range consisting of any two of these values.

[0061] In some embodiments, the capacity of the negative electrode active material layer per unit area of ​​active sheet is V1, the positive electrode includes a positive electrode active material layer, the capacity of the positive electrode active material layer per unit area of ​​active sheet is V2, and the range of V1 / V2 is 1.1 to 1.5. In some embodiments, the range of V1 / V2 is 1.1 to 1.2. In some embodiments, V1 / V2 is 1.1, 1.2, 1.3, 1.4, 1.5 or a value within the range of any two of these values. The sodium storage platform potential of the hard carbon material is close to the sodium precipitation potential. A slight increase in polarization during the cycle may lead to sodium precipitation, which in turn leads to capacity loss, gas production or safety issues. In order to further reduce the possibility of sodium precipitation, the capacity of the negative electrode active material layer per unit area of ​​active sheet needs to be slightly higher than the capacity of the corresponding positive electrode active material layer per unit area of ​​active sheet. When the ratio of the capacity of the negative electrode active material layer per unit area of ​​active sheet to the capacity of the positive electrode active material layer per unit area of ​​active sheet is within the above range, the present application can reduce safety issues and effectively ensure the energy density of the electrochemical device.

[0062] In some embodiments, the negative electrode of the present application includes a negative electrode current collector. In some embodiments, the negative electrode current collector of the present application is not particularly limited, and a metal foil, a porous metal plate or a composite current collector may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). As an example, the negative electrode pole piece is the negative electrode pole piece of a lithium ion battery, and the negative electrode current collector may be copper foil. As another example, the negative electrode pole piece is the negative electrode pole piece of a sodium ion battery, and the negative electrode current collector may be copper foil or aluminum foil.

[0063] In some embodiments, the negative electrode current collector has two surfaces that are opposite to each other in the thickness direction of the negative electrode current collector, and the negative electrode active material layer may be disposed on one surface of the negative electrode current collector or on both surfaces of the negative electrode current collector. For example, the negative electrode current collector has two surfaces that are opposite to each other in the thickness direction of the negative electrode current collector, and the negative electrode active material layer may be disposed on either one or both of the two opposite surfaces of the negative electrode current collector.

[0064] In some embodiments, the negative electrode active material layer may further include a binder. The binder may be selected from at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0065] In some embodiments, the negative electrode active material layer may further optionally include a conductive agent. The conductive agent may be selected from a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. For example, the carbon-based material may be selected from at least one of natural graphite, artificial graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The metal-based material may be selected from metal powder and metal fibers. The conductive polymer may include a polyphenylene derivative.

[0066] In some embodiments, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0067] The negative electrode in this application can be prepared according to conventional methods in the art. For example, the hard carbon and optional other negative electrode active materials, a conductive agent, a binder, and a thickener are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is then coated on the negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying and cold pressing.

[0068] It should be noted that the parameters of each negative electrode active material layer provided in this application refer to the parameter range of the negative electrode active material layer on a single surface. When the negative electrode active material layer is provided on both surfaces of the negative electrode current collector, if the parameters of the negative electrode active material layer on either surface meet the protection range required by this application, it is considered to fall within the protection scope of this application.

[0069] The negative electrode plate of the present application may optionally include other additional functional layers in addition to the negative electrode active material layer. For example, in some embodiments, the negative electrode plate of the present application further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode plate of the present application further includes a protective layer covering the surface of the negative electrode active material layer.

[0070] In some embodiments, the present application provides a method for preparing hard carbon, the preparation method comprising:

[0071] (1) oxidizing the precursor material at 100-500° C. for 100-400 minutes to obtain an oxidized precursor material;

[0072] (2) pre-carbonizing, pre-pyrolyzing, and carbonizing the oxidized precursor material to obtain a carbonized material, and grading the carbonized material to obtain a precursor hard carbon material having corresponding Dv50 and Dv90 values;

[0073] (3) Maintaining the precursor hard carbon material at 500-1100° C. for 5-15 hours for surface coating.

[0074] In some embodiments, the precursor material in the above-mentioned hard carbon material preparation method can be a biomass material, a resin material, a sugar material, an asphalt material or a coal material. The biomass material includes, but is not limited to: lignin, cellulose, straw, coconut shell, walnut shell, etc. The resin material can be a phenolic resin, furfural resin, epoxy resin, amide resin, fluorine-containing or chlorine-containing resin, etc. The sugar material can be glucose, magnesium gluconate, sodium gluconate, fructose, starch, maltose and other sugar derivatives.

[0075] In some embodiments, the oxidation treatment temperature is 100° C., 200° C., 300° C., 400° C., 500° C., or a range consisting of any two of these values. In some embodiments, the oxidation treatment time is 100 min, 200 min, 300 min, 400 min, or a range consisting of any two of these values.

[0076] In some embodiments, the pre-carbonization temperature is 400-700° C., and the pre-carbonization time is 1-4 hours. In some embodiments, the pre-carbonization temperature is 400° C., 500° C., 600° C., 700° C., or a range consisting of any two of these values.

[0077] In some embodiments, the pre-carbonization time is 1 hour, 2 hours, 3 hours, 4 hours, or a range consisting of any two of these values.

[0078] In some embodiments, the pre-pyrolysis temperature is 50-200° C. In some embodiments, the pre-pyrolysis temperature is 50° C., 80° C., 100° C., 150° C., 180° C., 200° C., or a range consisting of any two of these values.

[0079] In some embodiments, the pre-pyrolysis time is 5-20 hours. In some embodiments, the pre-pyrolysis time is 5 hours, 8 hours, 10 hours, 12 hours, 14 hours, 14 hours, 20 hours, or a value within a range consisting of any two of these values.

[0080] In some embodiments, the pre-pyrolysis material is crushed, screened, and cleaned. In some embodiments, the cleanup can be performed by washing with an acidic solution, such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, or a mixture of the foregoing acids.

[0081] In some embodiments, the carbonization temperature is 800-1500° C. In some embodiments, the carbonization temperature is 800° C., 1000° C., 1200° C., 1300° C., 1400° C., 1500° C., or a value within a range consisting of any two of these values.

[0082] In some embodiments, the carbonization treatment time is 0.5-5 hours. In some embodiments, the carbonization treatment time is 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 5 hours, or a value within a range consisting of any two of these values.

[0083] In some embodiments, the pre-carbonization and carbonization treatments are performed in an inert gas, wherein the inert gas comprises nitrogen, helium, argon, or a mixture thereof.

[0084] In some embodiments, the surface coating method in the hard carbon material preparation method can include high-temperature melt coating with asphalt or molten resin, spray coating with a soluble resin, or high-temperature coating with a reducing gas. It should be noted that the asphalt, molten resin, or soluble resin coating requires further pyrolysis at a temperature ranging from 700°C to 1300°C. The reducing gas can include methane, acetylene, cyclohexane, benzene, toluene, and the like.

[0085] The material, composition and manufacturing method of the positive electrode sheet used in the electrochemical device of the present application may include any technology known in the prior art.

[0086] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0087] In some embodiments, the positive electrode active material layer includes a positive electrode active material. The specific type of the positive electrode active material is not particularly limited and can be selected according to needs.

[0088] In some embodiments, the electrochemical device is a sodium-ion battery. The positive electrode active material may be a positive electrode active material known in the art for use in sodium-ion secondary batteries. For example, the positive electrode active material may include one or more of a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound.

[0089] As an example, the sodium transition metal oxides include: Na 1-x Cu h Fe k Mn l M 1 m O 2-y , where M 1 One or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn and Ba, 0 <x≤0.33,0<h≤0.24,0≤k≤0.32,0<l≤0.68,0≤m<0.1,h+k+l+m=1,0≤y<0.2;Na 0.67 Mn 0.7 Ni z M 2 0.3-z O2, where M 2 is one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn and Ba, 0 <z≤0.1;Na a Lib Ni c Mn d Fe e O2, where 0.67 < a ≤ 1, 0 < b < 0.2, 0 < c < 0.3, 0.67 < d + e < 0.8, and b + c + d + e = 1. As an example, the above polyanionic compounds may include: A 1 f M 3 g (PO4) i O j X 1 3-j , where A 1 is Na and one or more selected from H, Li, K, and NH4, M 3 is one or more selected from Ti, Cr, Mn, Fe, Co, Ni, V, Cu, and Zn, X 1 is one or more selected from F, Cl, and Br, 0 < f ≤ 4, 0 < g ≤ 2, 1 ≤ i ≤ 3, 0 ≤ j ≤ 2; Na n M 4 PO4X 2 , where M 4 is one or more selected from Mn, Fe, Co, Ni, Cu, and Zn, X[[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Each independently is one or more of transition metal cations, 0 < u ≤ 2, 0 < v ≤ 1, 0 < w ≤ 1, 0 < x < 6. For example, A 2 is H + , Li + , Na + , K + , NH4 + , Rb + , Cs + , Fr + , Be 2+ , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ and Ra 2+ is one or more of them, M 6 and M 7 Each independently is a cation of one or more transition metal elements selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, and W. Preferably, A 2 is Li + , Na + and K + is one or more of them, M 6 is a cation of one or more transition metal elements selected from Mn, Fe, Co, Ni, and Cu, M 7 is a cation of one or more transition metal elements selected from Mn, Fe, Co, Ni, and Cu.

[0091] In some embodiments, the positive electrode active material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0092] In some embodiments, the positive electrode active material layer may further optionally include a binder. As an example, the conductive agent may be selected from carbon-based materials, metal-based materials, conductive polymers, or any combination of the above substances. As an example, the carbon-based materials may be selected from at least one of natural graphite, artificial graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The metal-based materials may be selected from metal powders, metal fibers. The conductive polymer may include polyphenylene derivatives.

[0093] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used as the positive electrode current collector. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. As an example, the metal material may be selected from one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer base layer may be selected from polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, and the like.

[0094] The positive electrode sheets herein can be prepared according to conventional methods in the art. For example, the positive electrode active material layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0095] The positive electrode sheet of the present application may optionally include other additional functional layers in addition to the positive electrode active material layer. For example, in some embodiments, the positive electrode sheet of the present application further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the positive electrode current collector and the positive electrode active material layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode sheet of the present application further includes a protective layer covering the surface of the positive electrode active material layer.

[0096] The electrolyte plays a role in conducting active ions between the positive electrode and the negative electrode. The electrolyte that can be used in the electrochemical device of the present application can be an electrolyte known in the prior art.

[0097] In some embodiments, the electrolyte may include an organic solvent, an electrolyte salt, and optional additives.

[0098] In some embodiments, the electrochemical device is a sodium-ion battery, and the electrolyte salt may include a sodium salt. For example, the sodium salt may be selected from at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3. In some embodiments, the concentration of the sodium salt in the electrolyte is about 0.5-3 mol / L, about 0.5-2 mol / L, or about 0.8-1.5 mol / L.

[0099] In some embodiments, the electrochemical device is a lithium ion battery, and the electrolyte salt may include a lithium salt. In some embodiments, the electrolyte includes, but is not limited to: inorganic lithium salts, such as LiClO4, LiPF6, LiBF4, LiSbF6, LiSO3F, LiN(FSO2)2, etc.; fluorine-containing organic lithium salts, such as LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,3-hexafluoropropane disulfonyl imide lithium, cyclic 1,2-tetrafluoroethane disulfonyl imide lithium, LiN(CF3SO2)(C4F9SO2), LiC (CF3SO2)3, LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2; lithium salts containing dicarboxylic acid complexes, such as lithium bis(oxalato)borate, lithium difluorooxalatoborate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, etc. In addition, the above electrolytes can be used alone or in combination of two or more. For example, in some embodiments, the electrolyte includes a combination of LiPF6 and LiBF4. In some embodiments, the electrolyte comprises a combination of an inorganic lithium salt such as LiPF6 or LiBF4 and a fluorine-containing organic lithium salt such as LiCF3SO3, LiN(CF3SO2)2, or LiN(C2F5SO2)2. In some embodiments, the concentration of the electrolyte is in a range of 0.8 to 3 mol / L, such as 0.8 to 2.5 mol / L, 0.8 to 2 mol / L, 1 to 2 mol / L, 0.5 to 1.5 mol / L, 0.8 to 1.3 mol / L, 0.5 to 1.2 mol / L, and for example 1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L.

[0100] In some embodiments, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0101] In addition to the fluorinated carbonate compounds and compounds containing sulfur-oxygen double bonds mentioned above, as an example, the additives may also include, but are not limited to, at least one of: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE). The above-mentioned organic solvents can be used alone or in combination. Alternatively, two or more of the above-mentioned organic solvents are used in combination.

[0102] The electrolyte solution can be prepared according to conventional methods in the art. For example, an organic solvent, an electrolyte salt, and optional additives can be uniformly mixed to obtain the electrolyte solution. The order in which the materials are added is not particularly limited. For example, the electrolyte salt and optional additives can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution; alternatively, the electrolyte salt can be first added to the organic solvent, and then the optional additives can be added to the organic solvent and mixed uniformly to obtain the electrolyte solution.

[0103] Isolation film

[0104] The separator is placed between the positive and negative electrodes to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular restrictions on the type of separator; any known porous separator with good chemical and mechanical stability can be used.

[0105] In some embodiments, the material of the isolation membrane can be selected from one or more of, but not limited to, fiberglass, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. Alternatively, the isolation membrane can include polyethylene and / or polypropylene. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different. In some embodiments, the isolation membrane can also be provided with a ceramic coating or a metal oxide coating.

[0106] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly through a winding process or a lamination process.

[0107] The electrochemical device of the present application further includes an outer packaging for encapsulating the electrode assembly and the electrolyte. In some embodiments, the outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., or a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0108] This application does not particularly limit the shape of the electrochemical device; it may be cylindrical, square, or any other shape. The positive electrode sheet, negative electrode sheet, and separator may be wound or laminated to form an electrode assembly. The electrode assembly is encapsulated in the electrochemical device. The electrochemical device may contain one or more electrode assemblies, and those skilled in the art may select the desired number based on specific needs.

[0109] The preparation process of an electrochemical device is well known to those skilled in the art and is not particularly limited herein. For example, a lithium-ion battery or a sodium-ion battery can be manufactured by overlapping the positive and negative electrodes with a separator, winding and folding the electrodes as needed, and then placing the electrodes within a housing. The electrolyte is then injected into the housing and sealed. Furthermore, overcurrent protection elements, guide plates, and the like can be placed within the housing as needed to prevent pressure buildup and overcharge and discharge within the sodium-ion or lithium-ion battery.

[0110] The preparation of sodium ion batteries is described below using sodium ion batteries as an example and in combination with specific embodiments. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0111] Example

[0112] The following describes the performance evaluation of the sodium ion battery according to the embodiments and comparative examples of the present application.

[0113] 1. Preparation of sodium-ion batteries

[0114] 1. Preparation of negative electrode

[0115] A. Preparation of hard carbon materials (negative electrode active materials)

[0116] The hard carbon materials in Examples 1-1 to 1-7, Examples 1-15 to 1-20, and Comparative Example 1-1 were prepared as follows:

[0117] 100g of high-temperature asphalt, a precursor material with a softening point of about 240°C, and 10g of potassium tartrate template are added to the reactor, heated to 250°C and stirred to melt the precursor material and the template and mix them to obtain a mixed precursor material; after cooling to room temperature, the mixed precursor material is crushed to a Dv50 of 8-15μm to obtain a powder of the precursor material; then the powder of the precursor material is re-charged into the reactor, heated to 200°C and kept warm, and a mixture of oxygen and nitrogen (wherein the volume proportion of oxygen is 10%) is introduced into the reactor at a rate of 200ml / min for 180min to oxidize the precursor powder. During the oxidation treatment, the reactor needs to be kept stirred to obtain an oxidized precursor material.

[0118] The oxidized precursor material prepared above was placed in a tubular furnace, heated to 600°C and kept warm for 2 hours for pre-carbonization treatment to obtain a pre-carbonized material. The treatment process was a heating rate of 2°C / min and an atmosphere of 10L / min of nitrogen. The pre-carbonized material was crushed and placed in a 1mol / L hydrochloric acid solution, heated to 100°C and stirred for 12 hours to obtain a pre-pyrolytic carbon solution. The pH value of the pre-pyrolytic carbon solution was washed to neutral by multiple water washings and filtrations, and then filtered again and dried to obtain pre-pyrolytic carbon. 50g of the pre-pyrolytic carbon was placed in a tubular furnace, heated to 1200°C and kept warm for 2 hours for carbonization treatment. The treatment process was a heating rate of 4°C / min and an atmosphere of 10L / min of nitrogen to obtain a carbonized material. The carbonized material was subjected to graded treatment to obtain a precursor hard carbon material with a Dv50 of 5.2μm and a Dv90 of 13.2μm.

[0119] Take 50g of the above-prepared precursor hard carbon material and place it in a rotary furnace with an inner volume of 1L. After heating to 750°C under a nitrogen atmosphere of 0.5L / min, change the atmosphere to a 0.5L / min ethylene-argon mixed gas (wherein the volume proportion of ethylene is 10%), and keep warm for 10 hours to coat the surface of the above-mentioned precursor hard carbon material and prepare the required hard carbon material.

[0120] The hard carbon materials in Examples 1-8 to 1-11 were prepared as follows: in the coating treatment step, the coating times were 16 h, 8 h, 4 h, and 2 h, respectively, and the remaining conditions were consistent with the preparation process in Example 1-1.

[0121] The hard carbon materials in Examples 1-12 to 1-14 were prepared as follows: the oxidation treatment time of the precursor powder was 150 min, 300 min, and 60 min, respectively, and the other conditions were consistent with the preparation process in Example 1-1.

[0122] The hard carbon material in Comparative Example 1-2 was prepared as follows: the oxidation treatment of the hard carbon material precursor powder lasted for 60 minutes, and the coating treatment lasted for 16 hours. After the coating treatment, the material was heated to 900°C in a tube furnace and held at that temperature for 2 hours for secondary carbonization. The heating rate was 4°C / min, and the atmosphere was nitrogen at a flow rate of 10 L / min. All other conditions were the same as those in Example 1-1.

[0123] The hard carbon material in Comparative Examples 1-3 was prepared as follows: During the coating step, the coating time was 16 hours. Following the coating, the material was heated to 1000°C in a tube furnace and held at that temperature for 2 hours for secondary carbonization. The heating rate was 4°C / min, and the carbonization atmosphere was nitrogen at 10 L / min. All other conditions were the same as those in Example 1-1.

[0124] The hard carbon materials in Examples 2-1 to 2-10 were prepared as follows: after carbonization, the materials were graded to obtain materials with corresponding Dv50 and Dv90, and the remaining conditions were consistent with the preparation process in Example 1-2.

[0125] B. The hard carbon material (negative electrode active material) prepared above, the binder styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC-Na) were dissolved in deionized water at a weight ratio of 97:1.5:1.5 to form a negative electrode slurry (solid content 40 wt%). A 10 μm thick aluminum foil was used as the negative electrode current collector. The negative electrode slurry was applied to the current collector of the negative electrode sheet to a thickness of 50 μm on one side. The sheet was then dried at 85°C, cold pressed, cut, and slit, and then dried under vacuum at 120°C for 12 hours to obtain the negative electrode sheet.

[0126] 2. Preparation of positive electrode

[0127] The positive electrode active material NaNi 7 / 20 Fe 7 / 20 Mn 3 / 10 O2, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:1.4:1.6, N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred evenly to obtain a positive electrode slurry; the positive electrode slurry (solid content of 72wt%) is evenly coated on the positive electrode current collector aluminum foil with a coating thickness of 80μm, dried at 85°C, and then cold pressed, cut into pieces, and slit, and dried under vacuum conditions at 85°C for 4 hours to obtain a positive electrode sheet.

[0128] 3. Preparation of electrolyte

[0129] Ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are mixed in a mass ratio of 1:1:1 to obtain an organic solvent; NaPF6 is dissolved in the organic solvent, and fluoroethylene carbonate (FEC) and / or a compound containing a sulfur-oxygen double bond are added and mixed uniformly to obtain an electrolyte. The mass percentage of NaPF6 based on the total mass of the electrolyte is 12.5%. The mass percentages of fluoroethylene carbonate (FEC) and the compound containing a sulfur-oxygen double bond are shown in Table 1. m% is the sum of the mass percentages of the fluorocarbonate compound and the compound containing a sulfur-oxygen double bond.

[0130] 4. Preparation of isolation membrane

[0131] Polyethylene (PE) with a thickness of 7 μm was used as the separator.

[0132] 5. Preparation of sodium ion batteries

[0133] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to form an electrode assembly 52. ​​The electrode assembly 52 is placed in an outer package, and the aforementioned electrolyte is added. After packaging, standing, forming, and shaping, a sodium-ion battery is obtained. The sodium-ion battery is designed for a potential range of 2.0V to 4.53V.

[0134] 2. Sodium-ion battery performance test method

[0135] 1. Test method for ID / IG value of hard carbon materials

[0136] In the present application, the ratio of ID / IG of hard carbon materials has a meaning well known in the art and can be measured by methods known in the art. For example, Raman spectroscopy is used to test the surface defectivity of the sample using a laser micro-confocal Raman spectrometer. An area of ​​100 μm × 100 μm is selected on the negative active material layer, and a laser micro-confocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instruments Division) is used to scan the particles within the area to obtain the D peak and G peak of all particles within the area. The data is processed using LabSpec software to obtain the peak intensities of the D peak and G peak of each particle, which are ID and IG, respectively. The laser wavelength of the Raman spectrometer can be in the range of 532 nm to 785 nm. The value of ID / IG in the text is the average value of the ID and IG ratios of all particles measured within the range. D peak: generally at 1350±50 cm -1 Nearby, caused by the radial breathing mode of the symmetric stretching vibration of sp2 carbon atoms in the aromatic ring (structural defect); G peak: appears at 1580±50cm -1 The ID / IG value is denoted as d in this application.

[0137] 2. Test method for interplanar spacing d002 of hard carbon materials

[0138] The X-ray diffraction patterns of hard carbon materials have the meanings known in the art and are measured using an X-ray powder diffractometer. The negative electrode active material, graphite, was tested using an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE), with a Cu Kα target; the voltage and current were 40 kV / 40 mA, the scanning angle range was 5° to 80°, the scanning step length was 0.00836°, and the time per step was 0.3 s. Furthermore, according to Bragg's law, 2dsinθ = λ (d is the interplanar spacing), so d002 = λ / (2sinθ), where θ is the angle at which the 002 peak has its maximum peak intensity.

[0139] 3. Test method for the content of each component in the electrolyte

[0140] The components and their contents in the electrolyte can be determined by conventional methods in the art. For example, the components and their contents in the electrolyte can be detected by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), etc.

[0141] 4. Test methods for pore size and pore volume of hard carbon materials

[0142] The surface pore structure of hard carbon materials can be determined using methods known in the art. For example, it can be measured using an ASAP2460 physical adsorption analyzer. Specifically, after drying and degassing the negative electrode active material powder, the ASAP2460 physical adsorption analyzer is used with a nitrogen atmosphere and various test pressures to measure the nitrogen adsorption and plot adsorption and desorption isotherms. The pore shape is determined based on the shape of the hysteresis loop, and a DFT model is used to fit the pore size distribution curve of the active material's micropores, thereby determining the content and pore size of externally connected micropores.

[0143] 5. Particle size test method of hard carbon materials

[0144] Volume average particle size D of hard carbon material V 50. D V "90" has a well-known meaning in the art, indicating that 50% and 90% of the particles in the volume-based particle size distribution of the hard carbon material have a particle size smaller than this value. This value can be determined using methods known in the art. For example, it can be measured using a laser particle size analyzer (e.g., Malvern Mastersizer 2000E, UK) in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. Furthermore, the ratio Dv90 / Dv50 can be determined.

[0145] 6. Decompression compaction density of hard carbon material under 5t

[0146] The test standard refers to GB / T 24533-2009, "Graphite Anode Materials for Lithium-ion Batteries." The specific test method is to weigh 1.0000±0.0500g of the negative electrode active material sample and place it in a test mold (CARVER#3619 (13mm). The active material sample is then placed in the test equipment, a Sansi Zongheng UTM7305 test tonnage 5.0t tester. The pressure is increased at a rate of 10mm / min, the pressure is maintained for 30s, the pressure is released at a rate of 30mm / min, and the pressure is released for 10s. The compacted density is measured during the pressure release. The compacted density is calculated as follows: Compacted density = mass of negative electrode active material / force-bearing area of ​​negative electrode active material / thickness of negative electrode active material.

[0147] 7. Specific surface area test method of hard carbon materials

[0148] The specific surface area of ​​the hard carbon material has a well-known meaning in the art and can be measured using methods known in the art. For example, the specific surface area of ​​the negative electrode active material can be measured using a specific surface area analyzer (Tristar II 3020M) by nitrogen adsorption / desorption method.

[0149] 8. Test method for compaction density of negative electrode active material layer

[0150] The compacted density of the negative electrode active material layer has a meaning well known in the art and can be measured using methods known in the art. For example, a treated negative electrode sheet (a negative electrode current collector coated with a negative electrode active material layer on both sides) with an area of ​​S is weighed using an electronic balance, with the weight recorded as W1. The thickness of the negative electrode sheet is measured using a caliper to obtain the thickness T1 of the negative electrode sheet. The negative electrode active material layer is then washed off with a solvent, dried, and the weight of the negative electrode current collector is measured as W2. The thickness of the negative electrode current collector is also measured using a caliper to obtain the thickness T2 of the negative electrode current collector. The compacted density of the negative electrode active material layer disposed on one side of the negative electrode current collector is PD = (W1 - W2) / [(T1 - T2)·S].

[0151] 9. Test method for porosity of negative electrode active material layer

[0152] The negative electrode active material layer samples were prepared into complete discs. Five samples were tested for each example or comparative example. The volume of each sample was about 0.35 cm 3 The porosity of the negative electrode active material layer was tested according to the standard "GB / T24586-2009 Determination of Apparent Density, True Density and Porosity of Iron Ore", and the test gas was helium.

[0153] 10. Test methods for gram capacity and initial efficiency of negative electrode active materials

[0154] The gram capacity and first efficiency of the negative electrode active material have meanings well known in the art and can be measured using methods known in the art. For example, a hard carbon material can be uniformly mixed with an appropriate amount of a binder, a conductive agent, and a solvent to obtain a negative electrode slurry; the negative electrode slurry can be coated on the surface of the negative electrode current collector to obtain a negative electrode plate; a metal sodium plate is used as a counter electrode and assembled with the negative electrode plate into a button cell; the button cell is subjected to a charge and discharge cycle, and the test mode is constant current discharge-constant voltage discharge-constant current charge; the first sodium removal capacity obtained from the test is the gram capacity of the active material, and the first sodium removal capacity is divided by the first sodium storage capacity to obtain the first efficiency. Furthermore, the button cell is charged and discharged at a current density of 0.05C in a constant current discharge-constant voltage discharge-constant current charge mode, and the ratio of 0.05C constant current sodium storage capacity / total sodium storage capacity = the test capacity of the constant current discharge part / (the test capacity of the constant current discharge part + the test capacity of the constant voltage discharge part).

[0155] 11. Rate performance test method for sodium ion batteries

[0156] Take 5 sodium-ion batteries from each group, and repeatedly charge and discharge the batteries through the following steps. The capacity (average value) of each charging stage is counted, and the capacity ratio of the CC segment is calculated.

[0157] The specific steps are as follows: First, place the sodium-ion battery in a 25°C environment for 1 hour. Perform constant current charging (CC) on the battery at a charging rate of 3C. After charging to the rated voltage, switch to constant voltage charging (CV). Stop charging when the charging current is lower than 0.05C and leave it for 5 minutes. Then discharge the battery to the rated voltage at a constant current of 0.2C and leave it for 5 minutes to ensure the integrity of the subsequent charging and discharging process. The 3C charging capacity retention rate calculation formula is: 3C charging capacity retention rate = [CC segment charging capacity / (CC + CV) total charging capacity] × 100%.

[0158] 12. 45°C cycle performance test method for sodium ion batteries

[0159] The battery under test was placed at a test temperature of 45°C and left to rest for 5 minutes. The electrochemical device was charged and discharged at a current of 1.0C within the design voltage range. The first recorded discharge capacity was recorded as D0. The above charge and discharge process was repeated 1000 times, and the last recorded discharge capacity was recorded as D1. After cycling at 45°C, the capacity decay rate was D1 / D0, expressed in %.

[0160] 13. Test method for low-temperature charge and discharge performance of sodium ion batteries

[0161] At 25°C, charge the sodium ion battery to the rated voltage at 0.02C, then discharge it to the rated voltage at 0.02C, and record its discharge capacity A0. Then cool it to -20°C, keep it warm for 1 hour, and then charge the sodium ion battery to the rated voltage at 0.02C at -20°C, then discharge it to the rated voltage at 0.02C, and record its discharge capacity A1. Discharge capacity retention rate at -20°C = A1 / A0

[0162] 14. Test method for electrolyte retention (liquid capacity) of sodium ion batteries

[0163] In the present application, the electrolyte retention amount of the electrochemical device, that is, the electrolyte retention value is obtained by dividing the mass of the electrolyte in the electrochemical device by the 0.2C discharge capacity of the electrochemical device.

[0164] It should be noted that, in the present application, various parameter tests of the negative electrode active material or the negative electrode active material layer may be conducted by sampling during the battery preparation process or by sampling from a prepared electrochemical device.

[0165] When the test sample is sampled from a sodium ion battery that has been charged and discharged multiple times, as an example, the sampling can be performed according to the following steps (1) to (3).

[0166] (1) The sodium ion battery is discharged (for safety reasons, the battery is generally fully discharged); the battery is disassembled and the negative electrode plate is removed, and the negative electrode plate is soaked in dimethyl carbonate (DMC) for a certain period of time (e.g., 2 to 10 hours); the negative electrode plate is then removed and dried at a certain temperature and time (e.g., 60°C for 4 hours), and the negative electrode plate is removed after drying. At this point, samples can be taken from the dried negative electrode plate to test the various parameters related to the negative electrode active material layer described above in this application.

[0167] (2) Bake the negative electrode sheet dried in step (1) at a certain temperature and time (e.g., 400°C, 2 hours), and sample the negative electrode active material from any area of ​​the baked negative electrode sheet (sampling can be done by scraping powder with a blade).

[0168] (3) The negative electrode active material collected in step (2) is sieved (for example, sieved with a 200-mesh sieve) to obtain a sample that can be used to test the parameters of the negative electrode active material mentioned above.

[0169] 3. Test Results

[0170] The parameters and test data of Examples 1-1 to 1-20 and Comparative Examples 1-1 to 1-3 are shown in Table 1. Table 1 “ / ” means that the substance was not added.

[0171] From the comparison of Examples 1-1 to 1-20 with Comparative Example 1-1, it can be seen that compared with the sodium ion battery in which the electrolyte does not contain a fluorinated carbonate compound and a compound containing a sulfur-oxygen double bond, the sodium ion battery in which the electrolyte contains a fluorinated carbonate compound and / or a compound containing a sulfur-oxygen double bond has improved high-temperature cycle performance, low-temperature performance and rate performance, while taking into account the gram capacity of the negative electrode active material.

[0172] Comparison of Examples 1-1 to 1-20 with Comparative Examples 1-2 and 1-3 also shows that when d is 1.0 to 1.6 and m / d is in the range of 0.01 to 4.5, the sodium ion battery has improved high-temperature cycle performance, low-temperature performance, and rate performance, while taking into account the gram capacity of the negative electrode active material. When m / d is in the range of 1.6 to 3.6 and / or d is 1.2 to 1.4, the effect is even more excellent.

[0173] When the interplanar spacing d002 of the hard carbon material ranges from 0.37nm to 0.41nm, it helps further improve the high-temperature cycling performance, low-temperature performance, and rate capability of sodium-ion batteries, while also taking into account the specific capacity of the negative electrode active material. When the interplanar spacing d002 of the hard carbon material ranges from 0.38nm to 0.40nm, the effect is even better.

[0174] The parameters and test data of Examples 2-1 to 2-10 are shown in Tables 2 and 3, respectively. Except for the parameters in Tables 2 and 3, the settings of Examples 2-1 to 2-10 are consistent with those of Example 1-2.

[0175] Table 2

[0176] Table 3

[0177] The results show that the appropriate particle size matching, specific surface area, compaction density, pore size, pore volume, thickness and porosity of hard carbon materials can enable sodium ion batteries to have a suitable range of liquid retention, which can further improve the initial efficiency of the negative electrode active material and further enhance the performance of the sodium ion battery while taking into account the gram capacity of the negative electrode active material.

[0178] References throughout this specification to "some embodiments," "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "a portion of an example" mean that at least one embodiment or example in this application includes the particular features, structures, materials, or characteristics described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in an example," "in a specific example," or "an example," are not necessarily references to the same embodiment or example in this application. In addition, the particular features, structures, materials, or characteristics described herein may be combined in any suitable manner in one or more embodiments or examples.

[0179] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte comprises an additive, wherein the additive comprises a first additive M, wherein the first additive M is selected from at least one of a fluorocarbonate compound or a compound containing a sulfur-oxygen double bond, wherein the mass percentage of the first additive M is m% based on the mass of the electrolyte; wherein the negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises a hard carbon material, The hard carbon material is tested by Raman spectroscopy at 1300 cm -1 Up to 1400cm -1 The peak intensity at 1550 cm is ID, and the hard carbon material has a peak intensity at 1550 cm -1 Up to 1650cm -1 The peak intensity at is IG, the ratio of ID / IG is d, d is 1.0 to 1.6, and The range of m / d is 0.01 to 4.

5.

2. The electrochemical device according to claim 1, wherein the electrochemical device satisfies at least one of the following conditions: (1) m / d is in the range of 1.6 to 3.6; or (2) d is 1.2 to 1.

4.

3. The electrochemical device according to claim 1, wherein the interplanar spacing d002 of the hard carbon material is in the range of 0.37 nm to 0.41 nm as measured by X-ray diffraction.

4. The electrochemical device according to claim 1, wherein the electrochemical device satisfies at least one of the following conditions: (1) Based on the mass of the electrolyte, the mass percentage of the fluorinated carbonate compound is 0.05% to 5%; or (2) Based on the mass of the electrolyte, the mass percentage of the compound containing sulfur-oxygen double bonds is 0.05% to 4%. The electrochemical device according to claim 3 , wherein the interplanar spacing d002 is in the range of 0.38 nm to 0.40 nm.

6. The electrochemical device according to claim 1, wherein the compound containing sulfur-oxygen double bonds comprises at least one of 1,3-propane sultone, propenyl-1,3-sultone, 1,2-propane sultone, 1,4-butane sultone or vinyl sulfate, and / or the fluorocarbonate compound comprises at least one of fluoroethylene carbonate or bisfluoroethylene carbonate.

7. The electrochemical device according to claim 1, wherein the hard carbon material has pores therein, the pores have a pore diameter ranging from 0.6 nm to 2.0 nm, and the pore volume of the pores is less than 0.05 cc / g as measured by a nitrogen adsorption test.

8. The electrochemical device according to claim 1, wherein the hard carbon material satisfies at least one of the following conditions: (1) The specific surface area of ​​the hard carbon material is 0.5 m 2 / g to 10m 2 / g; (2) the compaction density of the hard carbon material at 5 t decompression is 0.8 g / cc to 1.6 g / cc; (3) wherein the hard carbon material has a diffraction peak in the range of 18° to 30° as tested by an X-ray diffraction method, and the half-peak width of the diffraction peak is 4° to 12°; (4) The Dv50 of the hard carbon material is 2 μm to 10 μm, and the Dv50 and Dv90 of the hard carbon material satisfy the following: 2≤Dv90 / Dv50≤5.

9. The electrochemical device according to claim 1, wherein the negative electrode active material layer satisfies at least one of the following conditions: (1) The porosity of the negative electrode active material layer is in the range of 30% to 60%; (2) The compaction density of the negative electrode active material layer is in the range of 0.8 g / cc to 1.5 g / cc.

10. The electrochemical device according to claim 1, wherein: The capacity of the negative electrode active material layer per unit area is V1, The positive electrode includes a positive electrode active material layer, the positive electrode active material layer has a capacity per unit area of ​​the positive electrode sheet of V2, and V1 / V2 is in a range of 1.1 to 1.

5. The electrochemical device according to claim 1 , wherein the electrochemical device is a sodium ion battery.

12. An electronic device comprising the electrochemical device according to any one of claims 1 to 11.