Lithium ion battery, preparation method thereof and power utilization device

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a lithium ion battery, a preparation method thereof and a power utilization device. The lithium ion battery comprises: a negative plate, which comprises a negative current collector and a negative coating coated on at least one surface of the negative current collector, the negative coating comprises a negative active material, and the negative active material comprises a carbon material and a silicon material; wherein the carbon material and the silicon material are respectively subjected to amorphous carbon coating treatment and meet the following conditions: h / a + H / A is more than 10 and less than or equal to 13.6; wherein h is the average thickness of the coating layer of the silicon material, and a is the intensity ratio of a D peak to a G peak in a Raman spectrum of the coating layer of the silicon material; h is the average thickness of the coating layer of the carbon material, and A is the intensity ratio of a D peak to a G peak in a Raman spectrum of the coating layer of the carbon material. Therefore, by adjusting the average thickness of the coating layers of the carbon material and the silicon material and the intensity ratio of the D peak to the G peak in the Raman spectrum, the rate capability and the cycle performance of the lithium ion battery in a low-temperature environment can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and particularly relates to a lithium-ion battery, a preparation method thereof, and an electrical device using the same. Background Art

[0002] Currently, with the development of battery technology, its application scenarios have been continuously increasing. For example, it can be applied to fields such as power grid storage, national defense, space, and deep-sea operations, and can also be widely used in daily electronic products. Among them, lithium-ion batteries have many advantages such as high energy density, no memory effect, low self-discharge, and long service life, and have become relatively ideal electrochemical energy storage devices.

[0003] Related technologies have put forward higher requirements for the low-temperature performance of lithium-ion batteries. Among them, the electrolyte plays a crucial role in the low-temperature performance of lithium-ion batteries. However, most lithium-ion batteries based on ethylene carbonate (EC) electrolytes may have problems such as a significant decrease in ionic conductivity, slow interfacial charge transfer kinetics, slow lithium-ion transport in the solid electrolyte interface (SEI) and internal electrodes, etc. at low temperatures, thereby affecting the capacity, energy, and power loss of the battery.

[0004] In the process of implementing the embodiments of the present disclosure, it is found that there are at least the following problems in the related technologies:

[0005] In the related technologies, although the battery under low-temperature conditions can be heated through a thermal management system so that the battery can operate within a suitable temperature range, the heating method using the thermal management system has low heating efficiency, and will also increase additional costs and energy consumption. In addition, uneven heating will also damage the battery.

[0006] It should be noted that the information disclosed in the above background art section is only used to enhance the understanding of the background of the present application, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0007] To have a basic understanding of some aspects of the disclosed embodiments, a simple summary is given below. The summary is not a general review, nor is it intended to identify key / important constituent elements or delineate the protection scope of these embodiments, but rather serves as a preface to the subsequent detailed description.

[0008] The embodiments of the present disclosure provide a lithium-ion battery, a preparation method thereof, and an electrical device using the same. By adjusting the average thickness of the coating layer of the carbon material and the silicon material and the intensity ratio of the D peak and the G peak in the Raman spectrum, the rate performance and cycle performance of the lithium-ion battery at low temperatures can be improved.

[0009] In some embodiments, the lithium-ion battery includes: a negative electrode sheet including a negative electrode current collector and a negative electrode coating coated on at least one surface of the negative electrode current collector, the negative electrode coating including a negative electrode active material, and the negative electrode active material including a carbon material and a silicon material; wherein, the carbon material and the silicon material are respectively treated with amorphous carbon coating and satisfy the following conditions:

[0010] 10 < h / a + H / A ≤ 13.6;

[0011] wherein, h is the average thickness of the coating layer of the silicon material in nm, a is the intensity ratio of the D peak to the G peak in the Raman spectrum of the coating layer of the silicon material; H is the average thickness of the coating layer of the carbon material in nm, and A is the intensity ratio of the D peak to the G peak in the Raman spectrum of the coating layer of the carbon material.

[0012] Optionally, the carbon material includes one or more mixtures of artificial graphite, natural graphite, hard carbon, and soft carbon; wherein, the average thickness of the coating layer of the carbon material ranges from 0.5 nm to 15 nm; and the intensity ratio of the D peak to the G peak in the Raman spectrum of the coating layer of the carbon material is from 0.152 to 0.872.

[0013] Optionally, the silicon material includes one or more mixtures of silicon-carbon materials, silicon oxides, lithiated silicon, and pure silicon; wherein, the average thickness of the coating layer of the silicon material ranges from 0.4 nm to 12 nm, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the coating layer of the silicon material is from 0.533 to 1.212.

[0014] Optionally, the percentage of the silicon material in the negative electrode active material is 3 wt% to 50 wt%.

[0015] Optionally, the average thickness of the coating layer of the silicon material and the average thickness of the coating layer of the carbon material are determined by a transmission electron microscope; wherein, the average thickness of the coating layer is determined by the following method:

[0016] The negative electrode active material is dispersed in an organic solution to form a suspension; the suspension is diluted and coated on a carbon-coated copper mesh; and the average thickness of the coating layer on the carbon-coated copper mesh is determined by transmission electron microscope analysis.

[0017] Optionally, the intensity ratio of the D peak to the G peak in the Raman spectrum of the coating layer of the carbon material and the intensity ratio of the D peak to the G peak in the Raman spectrum of the coating layer of the silicon material are determined by a Raman spectrometer; wherein, the test wavelength of the Raman spectrometer is 514 nm.

[0018] Optionally, the lithium-ion battery further includes: a positive electrode sheet including a positive electrode current collector and a positive electrode coating containing a positive electrode active material coated on at least one surface of the positive electrode current collector; wherein, the positive electrode active material includes a composite lithium metal oxide, and the composite lithium metal oxide includes one or two active substances with different crystal phases.

[0019] Optionally, when the composite lithium metal oxide includes two active substances with different crystal phases, the first crystal phase is a layered lithium nickel cobalt manganese oxide (LiNi x Co y Mn z O 2 ), where 0.6 ≤ x ≤ 0.9, 0.1 ≤ y ≤ 0.4, z = 1 - x - y; the second crystal phase is a spinel-structured lithium manganese oxide (LiMn _2 O _4 ) or an olivine-structured lithium iron phosphate / lithium manganese iron phosphate; wherein, the weight percentage of the first active substance is 40% to 100%, and the weight percentage of the second active substance is 20% to 30%.

[0020] Optionally, the lithium-ion battery further includes: an electrolyte including a lithium salt and an organic solvent mixture;

[0021] wherein, the lithium salt includes lithium hexafluorophosphate;

[0022] The organic solvent mixture includes ethylene carbonate (EC), dimethyl carbonate (DMC), difluoroethylene carbonate (DFEC), dimethyl sulfite (DMS), or diethyl sulfite (DES).

[0023] Optionally, when the ambient temperature T satisfies -40°C ≤ T ≤ 0°C, the discharge rate C ≥ 8; wherein, the discharge rate C is determined by the following method:

[0024] At an ambient temperature of 25°C, charge and discharge the lithium-ion battery at a rate of 0.1C for formation and aging; charge at an ambient temperature of -40 to 0°C; wherein, charge at a constant current of 0.1C to 4.2V, then charge at a constant voltage to 0.01C, and stand for 10 min; then discharge at a rate of 0.1C to 2.5V, and record the discharge capacity at this time as Q 1 ; continue to charge in the above manner and perform cyclic discharge with an increase of 0.5C in the rate each time; when the discharge rate is RC, record the discharge capacity at this time as Q R ; at the first Q R / Q 1 ≤ 0.8, RC is the discharge rate C supported by the battery.

[0025] In some embodiments, the method for preparing the lithium-ion battery includes:

[0026] Preparing a positive electrode sheet: Mixing a positive electrode coating material, coating it on at least one surface of an aluminum foil, and obtaining the positive electrode sheet after drying and cold pressing;

[0027] Preparing a negative electrode sheet: Mixing a negative electrode coating material, coating it on at least one surface of an aluminum foil, and obtaining the negative electrode sheet after drying and cold pressing;

[0028] Preparing a battery core: After rolling and slitting the positive electrode sheet and the negative electrode sheet respectively, winding them together with a separator to obtain a battery core;

[0029] Assembling a lithium-ion battery: Welding the tabs of the battery core to an electrical connection sheet, installing it into a battery case, and performing electrolyte injection, sealing, and formation processes to obtain a lithium-ion battery.

[0030] In some embodiments, the electrical device includes the lithium-ion battery as described in this application.

[0031] The lithium-ion battery, its preparation method, and the electrical device provided by the embodiments of the present disclosure can achieve the following technical effects:

[0032] By limiting the average thickness of the coating layer of the silicon material and the carbon material and the intensity ratio of the D peak and the G peak in the Raman spectrum of the coating layer, the relational expression 10 < h / a + H / A ≤ 13.6 can be used as a mathematical model, and the average thickness of the coating layer of the silicon material and the carbon material and the optimal design range of the coating layer can be obtained. It can well protect the silicon core from direct contact with the electrolyte and reduce the occurrence of side reactions. At the same time, with the change of the average thickness of the coating layer, a higher discharge rate can be satisfied. In this way, the working performance (such as discharge capacity, rate performance, low-temperature performance, etc.) and cycle life of the lithium-ion battery are improved. In addition, the amorphous carbon coating layer has good electrical conductivity, can improve the electronic conductivity of the silicon material and the carbon material, reduce the impedance, and improve the kinetics. Thus, the problem of the performance decline of the lithium-ion battery in a low-temperature environment is solved, and the working performance of the lithium-ion battery in an extreme environment can be further improved at a deeper level, which has significant technical advantages and application prospects.

[0033] The above general description and the following description are only exemplary and explanatory, and are not used to limit this application. Description of the Drawings

[0034] One or more embodiments are exemplarily illustrated by corresponding drawings. These exemplary illustrations and the drawings do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are shown as similar elements. The drawings do not constitute a scale limitation, and among them:

[0035] Figure 1It is a schematic structural diagram of a lithium-ion battery provided by an embodiment of the present disclosure;

[0036] Figure 2 It is a schematic structural diagram of a battery core provided by an embodiment of the present disclosure;

[0037] Figure 3 It is an unfolded schematic diagram of a battery core provided by an embodiment of the present disclosure;

[0038] Figure 4 It is a flowchart of a preparation method of a lithium-ion battery provided by an embodiment of the present disclosure;

[0039] Figure 5 It is a line graph of the intensity ratio of the D peak and the G peak in the Raman spectrum provided by an embodiment of the present disclosure;

[0040] Figure 6 It is a test comparison graph of the capacity retention rate and the number of cycles provided by an embodiment of the present disclosure.

[0041] Reference numerals:

[0042] 1 - Positive electrode end; 10 - Battery core; 11 - Positive electrode post; 12 - Negative electrode end; 2 - Housing; 3 - Negative electrode sheet; 4 - Separator; 5 - Positive electrode sheet. Detailed implementation manners

[0043] In order to be able to understand the features and technical content of the embodiments of the present disclosure in more detail, the implementation of the embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. The accompanying drawings are only for reference and illustration purposes and are not used to limit the embodiments of the present disclosure. In the following technical description, for the sake of explanation, multiple details are provided to provide a full understanding of the disclosed embodiments. However, one or more embodiments can still be implemented without these details. In other cases, well-known structures and devices can be shown in a simplified manner.

[0044] The terms "first", "second", etc. in the specification, claims and above-mentioned drawings of the embodiments of the present disclosure are used to distinguish similar objects and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances so as to implement the embodiments of the present disclosure described here. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion.

[0045] In the embodiments of the present disclosure, the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", "middle", "outer", "front", "rear", etc. is based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the embodiments of the present disclosure and their embodiments, and are not used to limit that the indicated devices, elements, or components must have a specific orientation, or be constructed and operated in a specific orientation. Moreover, in addition to being able to represent the orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the embodiments of the present disclosure can be understood according to specific circumstances.

[0046] In addition, the terms "arranged", "connected", and "fixed" should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or there can be internal communication between two devices, elements, or components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present disclosure can be understood according to specific circumstances.

[0047] Unless otherwise specified, the term "plurality" means two or more.

[0048] In the embodiments of the present disclosure, the character " / " indicates that the objects before and after are in an "or" relationship. For example, A / B means: A or B.

[0049] The term "and / or" is a description of the association relationship of an object, indicating that there can be three relationships. For example, A and / or B means: A or B, or, A and B these three relationships.

[0050] It should be noted that, without conflict, the embodiments in the embodiments of the present disclosure and the features in the embodiments can be combined with each other.

[0051] Combined Figure 1 As shown, the embodiments of the present disclosure provide a lithium-ion battery, including a cylindrical housing 2, the interior of which is used to accommodate a battery core, the top is the positive electrode end 1, the bottom is the negative electrode end 12, and a positive electrode post 11 is arranged on the positive electrode end 1. Specifically, Figure 2 shows a schematic structural diagram of the battery core in the present application, Figure 3 shows a schematic unfolded diagram of the battery core in the present application. Among them, the positive electrode sheet 5, the negative electrode sheet 3, and the separator 4 are stacked as Figure 3 shown, and then wound to form Figure 2The cylindrical battery core 10 shown has, at the initial stage of winding, the end of the electrode tab at the axis of the cylinder, and at the end of winding, the end of the electrode tab on the outer surface of the cylinder. Among them, the positive electrode tab 5 includes a strip-shaped positive electrode foil, a positive electrode coating and a first empty foil area coated on the surface of the strip-shaped positive electrode foil. The negative electrode tab 3 includes a strip-shaped negative electrode foil, a negative electrode coating and a second empty foil area coated on the surface of the strip-shaped negative electrode foil. The first empty foil area and the second empty foil area are perpendicular to the winding direction and form the top end face or the bottom end face of the lithium-ion battery by means such as flattening or cutting and laminating.

[0052] To further improve the rate performance and cycle performance of lithium-ion batteries in low-temperature environments, the embodiments of the present disclosure provide a lithium-ion battery, including: a negative electrode tab, including a negative electrode current collector and a negative electrode coating coated on at least one surface of the negative electrode current collector, the negative electrode coating including a negative electrode active material, and the negative electrode active material including a carbon material and a silicon material; wherein, the carbon material and the silicon material are respectively subjected to amorphous carbon coating treatment and satisfy the following conditions:

[0053] 10 < h / a + H / A ≤ 13.6;

[0054] wherein, h is the average thickness of the coating layer of the silicon material in nm, a is the ratio of the intensity of the D peak to the G peak in the Raman spectrum of the coating layer of the silicon material; H is the average thickness of the coating layer of the carbon material in nm, and A is the ratio of the intensity of the D peak to the G peak in the Raman spectrum of the coating layer of the carbon material.

[0055] By using the lithium-ion battery provided by the embodiments of the present disclosure, by limiting the average thickness of the coating layers of the silicon material and the carbon material and the ratio of the intensity of the D peak to the G peak in the Raman spectrum of the coating layer, the direct contact between the silicon core and the electrolyte can be well protected, and the occurrence of side reactions can be reduced. At the same time, with the change of the average thickness of the coating layer, a higher discharge rate can be satisfied. In this way, the working performance (such as discharge capacity, rate performance, low-temperature performance, etc.) and cycle life of the lithium-ion battery are improved. In addition, the amorphous carbon coating layer has good electrical conductivity, can improve the electronic conductivity of the silicon material and the carbon material, reduce the impedance, and improve the kinetics. On this basis, the amorphous carbon coating layer also has high structural stability, can adapt to the stress change caused by volume expansion, and has a certain ductility, can inhibit the volume expansion effect of the silicon material, thereby improving the cycle performance. Therefore, this application not only solves the problem of the performance decline of lithium-ion batteries in low-temperature environments, but also can improve the working performance of lithium-ion batteries in extreme environments at a deeper level, and has significant technical advantages and application prospects.

[0056] Optionally, the carbon material of this application includes one or more mixtures of artificial graphite, natural graphite, hard carbon, soft carbon, etc.; wherein, the value range of the average thickness of the coating layer of the carbon material is 0.5 nm to 15 nm; the ratio of the intensity of the D peak to the G peak in the Raman spectrum of the coating layer of the carbon material is 0.152 to 0.872.

[0057] In the embodiments of the present disclosure, if the thickness of the coating layer of the carbon material is too low, the graphite particles can directly contact the electrolyte, the amount of SEI film formation increases during the first cycle and subsequent cycles, and the cycle stability deteriorates. If the thickness of the coating layer of the carbon material is too high, the electron impedance increases, and the true density of the overall graphite material decreases. The risk of interlayer slip and particle breakage of the graphite layer increases under high compaction, the pore impedance of the electrode increases, and the low-temperature rate performance deteriorates. Therefore, the average thickness of the coating layer of the carbon material is controlled to be 0.5 nm to 15 nm.

[0058] In the embodiments of the present disclosure, if the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the coating layer of the carbon material is too low, the graphitization degree of the coating layer is low, which affects the overall conductivity of the silicon material, and the increase in defects reduces the charge-discharge efficiency. If the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the coating layer of the carbon material is too high, the graphitization degree of the coating layer is low, the number of defects is small, the lithium-ion diffusion kinetics deteriorates, the diffusion impedance increases, and the low-temperature rate performance decreases. Therefore, the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the coating layer of the carbon material is 0.152 to 0.872.

[0059] Optionally, the silicon material of the present application includes one or more mixtures of silicon-carbon materials, silicon oxides, lithiated silicon, and pure silicon; wherein, the average thickness of the coating layer of the silicon material ranges from 0.4 nm to 12 nm, and the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the coating layer of the silicon material is 0.533 to 1.212.

[0060] In the embodiments of the present disclosure, if the thickness of the coating layer of the silicon material is too low, the silicon particles directly contact the electrolyte, the amount of SEI film formation increases during the first cycle and subsequent cycles, and the cycle stability deteriorates; and if the thickness of the coating layer of the silicon material is too low, the carbon conductive network is discontinuous, the electron impedance increases, and the low-temperature rate performance deteriorates. In addition, if the thickness of the coating layer of the silicon material is too low, it cannot play a role in buffering the volume expansion of the silicon material; if the thickness of the coating layer of the silicon material is too high, the weight proportion of silicon in the silicon material decreases, and the reversible capacity decreases. Therefore, the average thickness of the coating layer of the silicon material ranges from 0.4 nm to 12 nm.

[0061] In the embodiments of the present disclosure, if the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the coating layer of the silicon material is too low, the graphitization degree of the coating layer is low, which affects the overall conductivity of the silicon material and excellent low-temperature rate performance cannot be obtained. If the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the coating layer of silicon is too high, the graphitization degree of the coating layer is high, the interlayer spacing of the coating layer is small, the lithium-ion diffusion kinetics decreases, and there is a risk of forming Si / C. Therefore, the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the coating layer of the silicon material is 0.533 to 1.212.

[0062] Optionally, the percentage of the silicon material in the negative electrode active material of the present application is 3 wt% to 50 wt%.

[0063] Optionally, the average thickness of the coating layer of the silicon material and the average thickness of the coating layer of the carbon material are determined by a transmission electron microscope; wherein, the average thickness of the coating layer is determined by the following method:

[0064] Disperse the negative electrode active material in an organic solution to form a suspension; dilute the suspension and coat it on a copper foil with carbon coating; analyze the average thickness of the coating layer on the copper foil with carbon coating by a transmission electron microscope.

[0065] Optionally, the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the coating layer of the carbon material and the ratio of the intensity of the D peak to the intensity of the G peak in the Raman spectrum of the coating layer of the silicon material are determined by a Raman spectrometer; wherein, the test wavelength of the Raman spectrometer is 514 nm.

[0066] Optionally, the degree of graphitization of the carbon coating can be determined by a Raman spectrometer to obtain the ratio of the intensity of the D peak to the intensity of the G peak.

[0067] Optionally, the lithium ion battery further includes: a positive electrode sheet, including a positive electrode current collector and a positive electrode coating coated on at least one surface of the positive electrode current collector and containing a positive electrode active material; wherein, the positive electrode active material includes a composite lithium metal oxide, and the composite lithium metal oxide includes one or two active substances with different crystal phases.

[0068] Optionally, when the composite lithium metal oxide includes two active substances with different crystal phases, the first crystal phase is a layered lithium nickel cobalt manganese oxide (LiNi x Co y Mn z O 2 ), where 0.6 ≤ x ≤ 0.9, 0.1 ≤ y ≤ 0.4, z = 1 - x - y; the second crystal phase is a spinel structured lithium manganese oxide (LiMn _2 O _4 ) or an olivine structured lithium iron phosphate / lithium manganese iron phosphate; wherein, the weight percentage of the first active substance is 40% to 100%, and the weight percentage of the second active substance is 20% to 30%.

[0069] Optionally, the positive electrode active material of the present application further includes a small amount of doping elements, such as any one of aluminum (Al), strontium (Sr), titanium (Ti), zirconium (Zr), and niobium (Nb), so as to improve the battery energy density and cycle life.

[0070] Optionally, the lithium-ion battery of the present application further includes: an electrolyte solution, including a lithium salt and an organic solvent mixture; wherein, the lithium salt includes lithium hexafluorophosphate; the organic solvent mixture includes ethylene carbonate (EC), dimethyl carbonate (DMC), difluoroethylene carbonate (DFEC), dimethyl sulfite (DMS), or diethyl sulfite (DES).

[0071] Specifically, based on the mass of the electrolyte solution, the molar concentration of the lithium salt is 0.5 M to 2.0 M, and the concentration of the organic solvent mixture is 0.5% to 2%.

[0072] Optionally, when the ambient temperature T satisfies -40°C ≤ T ≤ 0°C, the discharge rate C ≥ 8; wherein, the discharge rate C is determined by the following method:

[0073] When the ambient temperature is 25°C, charge and discharge the lithium-ion battery at a rate of 0.1C for formation and aging; charge at an ambient temperature of -40 to 0°C; wherein, charge at a constant current of 0.1C to 4.2V, then charge at a constant voltage to 0.01C, and let it stand for 10 min; then discharge at a rate of 0.1C to 2.5V, and record the discharge capacity at this time as Q 1 ; continue to charge in the above manner, and perform cyclic discharge each time with an increased rate of 0.5C; when the discharge rate is RC, record the discharge capacity at this time as Q R ; wherein, at the first Q R / Q 1 ≤ 0.8, RC is the discharge rate C supported by the battery.

[0074] Meanwhile, as shown in Figure 4 , the embodiments of the present disclosure provide a method for preparing a lithium-ion battery, including:

[0075] Step 401: Prepare a positive electrode sheet: Mix positive electrode coating materials, coat them on at least one surface of an aluminum foil, and obtain a positive electrode sheet after drying and cold pressing.

[0076] Step 402: Prepare a negative electrode sheet: Mix negative electrode coating materials, coat them on at least one surface of an aluminum foil, and obtain a negative electrode sheet after drying and cold pressing.

[0077] Step 403: Prepare a battery core: Roll the positive electrode sheet and the negative electrode sheet together with a separator after rolling and slitting respectively to obtain a battery core.

[0078] Step 404: Assemble a lithium-ion battery: Weld the tabs of the battery core to an electrical connection sheet, install it in a battery case, and perform electrolyte injection, sealing, and formation processes to obtain a lithium-ion battery.

[0079] In addition, an embodiment of the present disclosure provides an electrical device, including a lithium-ion battery for providing power as described in this application.

[0080] The following continues to further explain the present invention with embodiments.

[0081] Embodiment 1

[0082] Embodiment 1 provides a lithium-ion battery, which is prepared by the following method:

[0083] Prepare the positive electrode sheet: including a positive electrode current collector aluminum foil and a positive electrode coating coated on both surfaces of the aluminum foil; wherein, calculated by weight percentage, the positive electrode coating includes 97% of positive electrode active material (LiNi 0.8 Co 0.15 Al 0.05 O 2 ), 0.4% of single-walled carbon nanotube conductive agent, 1.6% of conductive agent, and 1% of polyvinylidene fluoride (PVDF) binder. Add the above substances to NMP and stir to form a positive electrode slurry with a solid content of 60%. Coating on the positive electrode current collector, drying and heat treatment to form a positive electrode sheet;

[0084] Prepare the negative electrode sheet: including a negative electrode current collector copper foil and a negative electrode coating coated on both surfaces of the copper foil. Calculated by weight percentage, the weight percentage of the negative electrode active material in the negative electrode coating is 96%. Among them, the weight percentage of graphite in the active material is 50% to 97%, and the weight percentage of silicon-carbon material is 3% to 50%. The content of conductive carbon black in the negative electrode coating is 1.5%, the content of dispersant CMC is 0.8%, the content of binder SBR is 1.2%, and the content of binder PAA is 0.5%. Add the above substances to deionized water and stir to form a negative electrode slurry with a solid content of 50%. Coating on the negative electrode current collector, drying and heat treatment to form a negative electrode sheet.

[0085] Prepare the electrolyte: Dissolve the fully dried lithium salt lithium hexafluorophosphate (LiPF 6 ) in an organic solvent containing 1% of dimethyl sulfite (DMS) to prepare an electrolyte with a concentration of 1 mol / L.

[0086] Prepare the separator: Select a separator with a high porosity. The thickness of the base film polyethylene PE in the separator is 7 μm to 15 μm, preferably 9 μm. The thickness of the ceramic coating on one side of the base film is 3 μm. Here, the porosity of the separator is 40.2%.

[0087] Assembly of a lithium-ion battery: The positive electrode sheet, negative electrode sheet, and separator are wound by a winding machine to form a battery core. The core is subjected to cutting and laminating of the positive electrode tab and negative electrode tab, and then the positive electrode current collector and negative electrode current collector are welded to the core respectively. Next, the negative electrode current collector is welded to the steel shell. An insulating sheet is placed above the positive electrode current collector, and the positive electrode current collector is welded to the cap. Then, grooving, liquid injection, and sealing are completed. The lithium-ion battery of this embodiment is obtained. The housing of the lithium-ion battery is a cylinder, and its dimensional parameters are diameter: 21.0 mm, length 70.0 mm.

[0088] The relevant parameter settings involved in this Embodiment 1 are shown in Table 1 below. Among them, in Table 1, the average thickness of the Si / C coating layer refers to the average thickness of the coating layer of the silicon material; ID / IG-a refers to the ratio of the intensities of the D peak and G peak in the Raman spectrum of the coating layer of the silicon material; the average thickness of the graphite coating layer refers to the average thickness of the coating layer of the carbon material; ID / IG-A refers to the ratio of the intensities of the D peak and G peak in the Raman spectrum of the coating layer of the carbon material.

[0089] Battery type Full-tab cylindrical battery Cathode material type <![CDATA[LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA)]]> <![CDATA[Positive electrode surface density mg / cm 2 > 13 <![CDATA[Positive electrode sheet compaction g / cm 3 > 3.5 <![CDATA[Negative electrode surface density mg / cm 2 > 6 <![CDATA[Negative electrode sheet compaction g / cm 3 > 1.45 Negative electrode Si / C content 10％ Si / C coating thickness h - nm 2.23 ID / IG - a 0.66 Graphite coating thickness H - nm 3.33 ID / IG - A 0.398 Electrolyte lithium salt concentration <![CDATA[1M LiPF 6 > Electrolyte additive type 1% Dimethyl sulfite (DMS)

[0090] Table 1

[0091] Embodiment 2

[0092] Embodiment 2 provides a lithium-ion battery. The difference between this embodiment and Embodiment 1 is that the average thickness of the Si / C coating layer is reduced to 1.23 nm, and the ratio of the intensities of the D peak and G peak in the Raman spectrum of the average thickness of the Si / C coating layer remains basically unchanged, and the others are the same as those in Embodiment 1.

[0093] Embodiment 3

[0094] Embodiment 3 provides a lithium-ion battery. The difference between this embodiment and Embodiment 1 is that the average thickness of the Si / C coating layer is reduced to 1.55 nm, and the ratio of the intensities of the D peak and G peak in the Raman spectrum of the Si / C coating layer remains basically unchanged, and the others are the same as those in Embodiment 1.

[0095] Embodiment 4

[0096] Embodiment 4 provides a lithium-ion battery. The difference between this embodiment and Embodiment 1 is that the average thickness of the Si / C coating layer is reduced to 1.92 nm, and the ratio of the intensities of the D peak and G peak in the Raman spectrum of the Si / C coating layer remains basically unchanged, and the others are the same as those in Embodiment 1.

[0097] Embodiment 5

[0098] Example 5 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the Si / C coating layer is increased to 2.56 nm, and the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the Si / C coating layer remains basically unchanged, and the others are the same as those in Example 1.

[0099] Example 6

[0100] Example 6 provides a lithium-ion battery. The difference between this example and Example 1 is that the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the Si / C coating layer is increased to 0.71, the average thickness of the Si / C coating layer remains basically unchanged, and the others are the same as those in Example 1.

[0101] Example 7

[0102] Example 7 provides a lithium-ion battery. The difference between this example and Example 1 is that the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the Si / C coating layer is increased to 0.77, the average thickness of the Si / C coating layer remains basically unchanged, and the others are the same as those in Example 1.

[0103] Example 8

[0104] Example 8 provides a lithium-ion battery. The difference between this example and Example 1 is that the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the Si / C coating layer is increased to 0.82, the average thickness of the Si / C coating layer remains basically unchanged, and the others are the same as those in Example 1.

[0105] Example 9

[0106] Example 9 provides a lithium-ion battery. The difference between this example and Example 1 is that the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the Si / C coating layer is increased to 0.85, the average thickness of the Si / C coating layer remains basically unchanged, and the others are the same as those in Example 1.

[0107] Example 10

[0108] Example 10 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the graphite coating layer is increased to 4.35 nm, and the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the graphite coating layer is increased to 0.435, and the others are the same as those in Example 1.

[0109] Example 11

[0110] Example 11 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the graphite coating layer is increased to 5.52 nm, and the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the graphite coating layer is increased to 0.551, and the others are the same as those in Example 1.

[0111] Example 12

[0112] Example 12 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the graphite coating layer is increased to 6.11 nm, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the graphite coating layer is increased to 0.599. Other aspects are the same as those in Example 1.

[0113] Example 13

[0114] Example 13 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the graphite coating layer is reduced to 2.41 nm, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the graphite coating layer is reduced to 0.356. Other aspects are the same as those in Example 1.

[0115] Example 14

[0116] Example 14 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the graphite coating layer is reduced to 2.35 nm, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the graphite coating layer is reduced to 0.311. Other aspects are the same as those in Example 1.

[0117] Example 15

[0118] Example 15 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the coating layer of the carbon material is reduced to 2.02 nm, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the coating layer of the carbon material is reduced to 0.289. Other aspects are the same as those in Example 1.

[0119] Example 16

[0120] Example 16 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the graphite coating layer is reduced to 1.67 nm, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the graphite coating layer is reduced to 0.244. Other aspects are the same as those in Example 1.

[0121] Comparative Example 1

[0122] Comparative Example 1 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the Si / C coating layer is reduced to 0.85 nm, and the intensity ratio of the D peak to the G peak in the Raman spectrum of the Si / C coating layer remains basically unchanged. Other aspects are the same as those in Example 1.

[0123] Comparative Example 2

[0124] Comparative Example 2 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the Si / C coating layer is increased to 8.22 nm, and the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the Si / C coating layer remains basically unchanged. Others are the same as in Example 1.

[0125] Comparative Example 3

[0126] Comparative Example 3 provides a lithium-ion battery. The difference between this example and Example 1 is that the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the Si / C coating layer is increased to 1.02, and the average thickness of the Si / C coating layer remains basically unchanged. Others are the same as in Example 1.

[0127] Comparative Example 4

[0128] Comparative Example 4 provides a lithium-ion battery. The difference between this example and Example 1 is that the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the Si / C coating layer is increased to 1.11, and the average thickness of the Si / C coating layer remains basically unchanged. Others are the same as in Example 1.

[0129] Comparative Example 5

[0130] Comparative Example 5 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the carbon material coating layer is reduced to 0.67 nm, and the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the carbon material coating layer is reduced to 0.173. Others are the same as in Example 1.

[0131] Comparative Example 6

[0132] Comparative Example 6 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the graphite coating layer is increased to 8.41 nm, and the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the graphite coating layer is increased to 0.633. Others are the same as in Example 1.

[0133] Comparative Example 7

[0134] Comparative Example 7 provides a lithium-ion battery. The difference between this example and Example 1 is that the average thickness of the Si / C coating layer is reduced to 0.51 nm, the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the Si / C coating layer is increased to 1.05, the average thickness of the graphite coating layer is increased to 9.21 nm, and the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the graphite coating layer is increased to 0.661. Others are the same as in Example 1.

[0135] Among them, for the parameters of Examples 1 to 16 and Comparative Examples 1 to 7, refer to Table 2 below.

[0136]

[0137] Table 2

[0138] Here, the control groups are set as follows:

[0139] Control Group 1: Examples 1 to 5, and Comparative Examples 1 and 2, which is a control group set with the average thickness of the Si / C coating layer as a variable.

[0140] Control Group 2: Example 1, Examples 6 to 9, and Comparative Examples 3 and 4, which is a control group set with the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the Si / C coating layer as a variable.

[0141] Control Group 3: Example 1, Examples 10 to 16, and Comparative Examples 5 and 6, which is a control group set with the average thickness of the graphite coating layer and the ratio of the intensities of the D peak and the G peak I in the Raman spectrum of the graphite coating layer as variables.

[0142] The capacity retention rate tests and the maximum supported discharge rate analysis are respectively carried out on the above Examples 1 to 16 and Comparative Examples 1 to 7.

[0143] Here, the test conditions include an environmental temperature of 0 °C, and 600 cycles of constant current charge and discharge are carried out at a 2C / 8C rate. Among them, the specific test method includes:

[0144] S1. Under the condition of an environmental temperature of 25 °C, charge and discharge formation and aging are carried out at a rate of 0.1C.

[0145] S2. Under the condition of an environmental temperature of 0 °C, the battery is constantly charged at a 2C charge rate until 4.2V, and then constantly charged at a constant voltage until the current is 0.025C, and left standing for more than 15 minutes; it is constantly discharged at an 8C discharge rate until 2.5V, and the discharge capacity is recorded as the initial capacity and denoted as C 0 ;

[0146] S3. Repeat the above S2 step 600 times, and record the discharge capacity at the 600th cycle, denoted as C 600 ;

[0147] S4. Calculate the 600-cycle retention rate as C 600 / C 0 ×100%.

[0148] Here, the test method for the maximum supported discharge rate RC includes:

[0149] S5: Under the condition of an environmental temperature of 25 °C, charge and discharge formation and aging are carried out at a rate of 0.1C.

[0150] S6: Charge at an ambient temperature of -40 to 0 °C; specifically, charge at a constant current of 0.1C until 4.2V, then charge at a constant voltage until 0.01C, and let it stand for 10 min; then discharge at a rate of 0.1C to 2.5V, and record the discharge capacity at this time as Q 1 ; Continue to charge in the above manner and perform cyclic discharge each time with an increased rate of 0.5C; when the discharge rate is RC, record the discharge capacity at this time as Q R ; At the first Q R / Q 1 ≤0.8, RC is the discharge rate C supported by the battery.

[0151] Perform capacity retention rate tests and maximum supported discharge rate analyses on Examples 1 to 16 and Comparative Examples 1 to 7 respectively, and combine them as shown in Figure 5 and Figure 6 ; Among them, the test results of Control Group 1 are shown in Table 3.

[0152]

[0153] Table 3

[0154] It can be seen from Table 3 that the ratio of the intensities of the D peak and the G peak in the Raman spectrum of the graphite coating layer is approximately around 0.65. An amorphous carbon coating layer with an appropriate thickness can well protect the silicon core from direct contact with the electrolyte and reduce the occurrence of side reactions. Moreover, the amorphous carbon coating layer has good electrical conductivity, which can improve the electronic conductivity of the silicon-carbon material, reduce the impedance, and enhance the kinetics.

[0155] In addition, the amorphous carbon layer has high structural stability, can adapt to the stress changes caused by volume expansion, and has certain ductility, which can inhibit the volume expansion effect of the silicon material and improve the cycle performance.

[0156] It can be seen from Examples 1 to 5 that as the average thickness of the coating layer increases, the lithium-ion battery can meet a higher discharge rate, and the capacity retention rate at 0 °C and 2C / 8C cycling for 600 cycles increases. The average thickness and design of the amorphous carbon coating layer on the Si / C and graphite outer layer both meet 10 < h / a + H / A ≤ 13.6. Therefore, excellent low-temperature rate performance and cycle performance can be obtained.

[0157] In Comparative Examples 1 and 2, the design of the average thickness of the Si / C coating layer is too low, making it difficult to resist the intrusion of the electrolyte, resulting in a large number of side reactions, and having a low electronic conductivity, causing high impedance, which does not meet 10 < h / a + H / A ≤ 13.6. Therefore, it is difficult to obtain excellent low-temperature rate performance and cycle performance.

[0158] The test results of Control Group 2 are shown in Table 4.

[0159]

[0160] Table 4

[0161] As can be seen from Table 4, the average thickness of the Si / C coating layer is about 2.2 nm. The peak intensity ratio of the D band and the G band represents the degree of disorder on the surface of the carbon material. Among them, the higher the ID / IG value, the higher the degree of disorder, the lower the graphitization degree, the lower the electronic conductivity of the coating layer, the increase in impedance, and the decrease in kinetics.

[0162] As can be seen from Example 1, Examples 6 to 9, with the increase in the peak intensity ratio of the D band and the G band of the Si / C coating layer, the maximum discharge rate of the lithium-ion battery decreases, and the capacity retention rate during 600 cycles at 2C / 8C at 0 °C also decreases. However, the average thickness and design of the coating layer of Si / C and the graphite outer layer meet 10 < h / a + H / A ≤ 13.6, and the discharge device can still support a maximum discharge rate of 8C and above. At 0 °C, the capacity retention rate during 600 cycles at 2C / 8C is still greater than 80%. For Comparative Example 3 and Comparative Example 4, the peak intensity ratio of the D band and the G band of the Si / C coating layer is too large, the graphitization degree of the coating layer is too low, the electronic conductivity is lower, the impedance increases, and the kinetics decreases, which does not meet 10 < h / a + H / A ≤ 13.6, so it is difficult to obtain excellent low-temperature rate performance and cycling performance.

[0163] The test results of Control Group 3 are shown in Table 5.

[0164]

[0165] Table 5

[0166] As can be seen from Table 5, the combinations of the Si / C and graphite coating layers and the special design of the degree of disorder in Examples 1, 10 to 16 all meet the formula 10 < h / a + H / A ≤ 13.6, and the lithium-ion battery can still support a maximum discharge rate of 8C and above. At 0 °C, the capacity retention rate during 600 cycles at 2C / 8C is greater than 80%, showing excellent low-temperature rate and cycling performance.

[0167] In Comparative Example 5, the average thickness of the graphite coating layer is too low to resist the intrusion of the electrolyte, resulting in a large number of side reactions. In Comparative Example 6, the combinations of the average thickness and the design of the degree of disorder of Si / C and graphite in the amorphous carbon coating layer do not meet 10 < h / a + H / A ≤ 13.6, and the maximum discharge rate supported by the lithium-ion battery is less than 4C. At an ambient temperature of 0 °C and during 600 cycles at 2C / 8C, the capacity retention rate is less than 50%, and it is difficult to obtain excellent low-temperature rate performance and cycling performance.

[0168] The peak intensity ratio of the D band to the G band of the coating layer of the graphite material represents the degree of disorder on the surface of the carbon material. Among them, the higher the peak intensity ratio of the D band to the G band, the higher the degree of disorder and the lower the degree of graphitization, and the electronic conductivity of the coating layer decreases. Similarly, a higher degree of disorder indicates that the material surface has more defects, which can serve as active sites for lithium ion insertion, forming a pre-insertion on the outer layer of graphite, and is beneficial to the diffusion kinetics process of lithium ions in the graphite material.

[0169] In addition, for a relatively thick amorphous carbon coating layer, more defects are generated on the material surface, the active sites for lithium ion insertion increase, which is beneficial to the diffusion kinetics process of lithium ions in the graphite material. However, the electronic impedance will decrease, the true density of the material decreases, it is more likely to be crushed, new interfaces are formed, and side reactions increase. While appropriately reducing the thickness of the amorphous carbon coating can increase the true density of graphite, making it more resistant to compression, not easily crushed during the rolling process of the negative electrode sheet, forming small particle fresh interfaces, which is more conducive to reducing the pore impedance of the electrode sheet and improving the low-temperature kinetics of the battery.

[0170] In summary, by limiting the average thickness of the coating layers of the silicon material and the carbon material and the intensity ratio of the D peak to the G peak in the Raman spectrum of the coating layer, the direct contact between the silicon core and the electrolyte can be well protected, and the occurrence of side reactions can be reduced. At the same time, with the change of the average thickness of the coating layer, a higher discharge rate can be satisfied. In this way, the working performance of the lithium-ion battery is improved. Therefore, this application not only solves the problem of the performance degradation of lithium-ion batteries in low-temperature environments, but also can improve the working performance of lithium-ion batteries in extreme environments at a deeper level, having significant technical advantages and application prospects.

[0171] The above description and the drawings fully illustrate the embodiments of the present disclosure so that those skilled in the art can practice them. Other embodiments may include structural and other changes. The embodiments only represent possible variations. Unless explicitly required, the individual components and functions are optional, and the order of operations can vary. Parts and features of some embodiments may be included in or substituted for parts and features of other embodiments. The embodiments of the present disclosure are not limited to the structures already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present disclosure is only limited by the appended claims.

Claims

1. A lithium ion battery, characterized in that: include: A negative electrode sheet comprises a negative electrode current collector and a negative electrode coating coated on at least one surface of the negative electrode current collector, wherein the negative electrode coating comprises a negative electrode active material, and the negative electrode active material comprises a carbon material and a silicon material; wherein the carbon material and the silicon material are respectively subjected to an amorphous carbon coating treatment and meet the following conditions: 10<h / a+H / A≤13.6; Wherein, h is the average thickness of the coating layer of the silicon material, nm, and a is the ratio of the D peak intensity to the G peak intensity in the Raman spectrum of the coating layer of the silicon material; H is the average thickness of the coating layer of the carbon material, nm, and A is the ratio of the D peak intensity to the G peak intensity in the Raman spectrum of the coating layer of the carbon material.

2. The lithium-ion battery according to claim 1, characterized in that The carbon material comprises a mixture of one or more of artificial graphite, natural graphite, hard carbon and soft carbon; wherein the average thickness of the coating layer of the carbon material ranges from 0.5 nm to 15 nm; and the ratio of the D peak and G peak intensities in the Raman spectrum of the coating layer of the carbon material ranges from 0.152 to 0.

872.

3. The lithium-ion battery according to claim 1, characterized in that The silicon material includes a mixture of one or more of silicon-carbon material, silicon oxide, lithium silicon, and pure silicon; wherein the average thickness of the coating layer of the silicon material ranges from 0.4nm to 12nm, and the ratio of the D peak and G peak intensities in the Raman spectrum of the coating layer of the silicon material is 0.533 to 1.

212.

4. The lithium-ion battery according to claim 1, characterized in that: The percentage of the silicon material in the negative electrode active material is 3wt% to 50wt%.

5. The lithium-ion battery according to claim 1, characterized in that: The average thickness of the coating layer of the silicon material and the average thickness of the coating layer of the carbon material are determined by transmission electron microscopy; wherein the average thickness of the coating layer is determined by the following method: The negative electrode active material is dispersed in an organic solution to form a suspension; the suspension is diluted and coated on a carbon-coated copper mesh; and the average thickness of the coating layer on the carbon-coated copper mesh is determined by transmission electron microscopy analysis.

6. The lithium-ion battery according to claim 1, characterized in that The intensity ratio of the D peak to the G peak in the Raman spectrum of the coating layer of the carbon material and the intensity ratio of the D peak to the G peak in the Raman spectrum of the coating layer of the silicon material are determined by a Raman spectrometer; wherein the test wavelength of the Raman spectrometer is 514nm.

7. The lithium ion battery according to any one of claims 1 to 6, characterized in that: Also includes: A positive electrode sheet comprises a positive electrode current collector and a positive electrode coating containing a positive electrode active material coated on at least one surface of the positive electrode current collector; wherein the positive electrode active material comprises a composite lithium metal oxide, and the composite lithium metal oxide comprises one or two active substances of different crystal phases.

8. The lithium-ion battery according to claim 7, characterized in that: In the case where the composite lithium metal oxide includes two active materials with different crystal phases, the first crystal phase is a layered structure of lithium nickel cobalt manganese oxide LiNi x Co y Mn z O2 wherein 0.6≤x≤0.9, 0.1≤y≤0.4, z=1-xy; the second crystal phase is a spinel structured lithium manganese oxide LiMn2O4 or an olivine structured lithium iron phosphate / lithium manganese iron phosphate; wherein the weight percentage of the first active substance is 40% to 100%, and the weight percentage of the second active substance is 20% to 30%.

9. The lithium ion battery according to any one of claims 1 to 6, characterized in that: Also includes: an electrolyte comprising a lithium salt and an organic solvent mixture; Wherein, the lithium salt includes lithium hexafluorophosphate; The organic solvent mixture includes ethylene carbonate EC, dimethyl carbonate DMC, bisfluoroethylene carbonate DFEC, dimethyl sulfite DMS or diethyl sulfite DES.

10. The lithium ion battery according to any one of claims 1 to 6, characterized in that: When the ambient temperature T satisfies -40℃≤T≤0℃, the discharge rate RC≥8; wherein the discharge rate C is determined by the following method: When the ambient temperature is 25°C, the lithium-ion battery is charged and discharged at a rate of 0.1C for formation and aging; when the ambient temperature is -40 to 0°C, the battery is charged; when the ambient temperature is -40 to 0°C, the battery is charged to 4.2V at a constant current of 0.1C, and then charged to 0.01C at a constant voltage, and left to stand for 10 minutes; then the battery is discharged to 2.5V at a rate of 0.1C, and the discharge capacity at this time is recorded as Q1; the battery is charged in the above manner, and the rate is increased by 0.5C each time for cyclic discharge; when the discharge rate is RC, the discharge capacity at this time is recorded as Q R ; In the first Q R When / Q1≤0.8, RC is the discharge rate C supported by the battery.

11. A method for preparing a lithium ion battery according to any one of claims 1 to 10, characterized in that: include: Prepare the positive electrode sheet: mix the positive electrode coating material, coat it on at least one side of the aluminum foil, and then dry and cold press it to obtain the positive electrode sheet; Preparation of negative electrode sheet: Mixing negative electrode coating materials, coating on at least one side of the aluminum foil, drying and cold pressing to obtain a negative electrode sheet; Preparation of battery roll core: rolling and slitting the positive electrode sheet and the negative electrode sheet respectively and then winding them together with the separator to obtain a battery roll core; Assembling lithium-ion batteries: Welding the tabs of the battery core to the electrical connectors, inserting them into the battery casing, and performing electrolyte injection, sealing and formation processes to obtain lithium-ion batteries.

12. An electrical device, characterized in that: Comprising a lithium ion battery as claimed in any one of claims 1 to 10.

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