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 electrode plate, which comprises a negative electrode current collector and a negative electrode coating coated on at least one surface of the negative electrode current collector, and the negative electrode coating comprises a negative electrode active material and a solid electrolyte interface film covering the surface of the negative electrode active material; wherein in an X-ray photoelectron spectroscopy of the solid electrolyte interfacial film, an F1s characteristic peak exists between a binding energy of 690.0 eV to 682.0 eV, an S2p characteristic peak exists between a binding energy of 162.0 eV to 158.0 eV, and the characteristic peak intensity IF of the F1s characteristic peak and the characteristic peak intensity IS of the S2p characteristic peak satisfy 0.1 < = IF / IS < = 25.0.

Description

Technical Field

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

[0002] At present, with the increasing application of electric vehicles and grid energy storage systems in high-latitude areas, as well as the increasing demand in extreme environments such as polar and deep space exploration, higher requirements are placed on the low-temperature performance of batteries in related technologies. Among them, applied to the field of lithium-ion battery technology, the electrolyte plays a vital role in the low-temperature performance of the battery. The electrolyte is usually composed of solvents, lithium salts and additives. To ensure that the battery performs well in a low-temperature environment, the electrolyte needs to have the following key characteristics: First, the electrolyte should maintain a high lithium ion conductivity at low temperatures, because low temperatures will increase the viscosity of the electrolyte, thereby reducing the migration rate of lithium ions. Secondly, the electrolyte should promote the formation of a stable and conductive solid electrolyte interface (Solid Electrolyte Interface, SEI) film. A good SEI film can effectively conduct lithium ions under low temperature conditions to reduce internal resistance and improve battery performance. Finally, the electrolyte needs to have a fast charge transfer capability between the electrolyte and the electrode surface to reduce polarization at low temperatures and ensure that the lithium-ion battery can respond quickly to load changes.

[0003] 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 art:

[0004] In the related art, the performance of lithium batteries in low temperature environments is generally improved by optimizing the electrolyte ratio, for example, using a solvent system with good low temperature fluidity (for example, ethylene carbonate: dimethyl carbonate, 50 / 50, vol%) and selecting lithium salts with low melting points and good solubility (for example, lithium hexafluorophosphate LiPF6 and lithium tetrafluoroborate LiBF4). However, the methods used in the related art only focus on optimizing the electrolyte itself, which is often limited by the selection of solvents, lithium salts and additives, and cannot fully improve the working performance of lithium-ion batteries in low temperature environments.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present application, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] In order to provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. The summary is not an extensive review, nor is it intended to identify key / critical components or delineate the scope of protection of these embodiments, but rather serves as a prelude to the detailed description that follows.

[0007] The embodiments of the present disclosure provide a lithium-ion battery and a preparation method thereof, and an electrical device, which circumvent the limitations on the selection of electrolyte components by adjusting the proportion of inorganic components in the SEI film, and comprehensively optimize and improve the performance of the lithium-ion battery in a low temperature environment.

[0008] In some embodiments, the lithium-ion battery comprises: a negative electrode sheet, comprising 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 a solid electrolyte interface film covering the surface of the negative electrode active material;

[0009] Among them, in the X-ray photoelectron spectrum of the solid electrolyte interface film, there is an F1s characteristic peak between the binding energy of 690.0eV and 682.0eV, and an S2p characteristic peak between the binding energy of 162.0eV and 158.0eV, wherein the characteristic peak intensity I of the F1s characteristic peak is F and the characteristic peak intensity I of the S2p characteristic peak S Satisfy 0.1≤I F / I S ≤25.0.

[0010] Optionally, the elements in the solid electrolyte interface film on the surface of the negative electrode active material include: one or more of fluorine (F), oxygen (O), carbon (C) and sulfur (S).

[0011] Optionally, the resonance signal in the solid nuclear magnetic spectrum corresponding to the negative electrode active material includes: 19 F (~203.0ppm), 33 S (~-7ppm to ~-10ppm) and 7 One or more of Li (~1.0ppm).

[0012] Optionally, the negative electrode active material includes at least two of silicon, silicon oxide, artificial graphite, natural graphite, soft carbon or hard carbon.

[0013] Optionally, the discharge characteristics of the lithium-ion battery are: after the lithium-ion battery with a 100% charge rate is left at 25°C for 6 hours, it is discharged to 2.5V at a rate of 0.5C at 25°C, and the corresponding discharge capacity is Q 25 ; A lithium-ion battery with a charge rate of 100% is left at an ambient temperature T for 6 hours, and at the ambient temperature T, it is discharged at a discharge rate C to a voltage of 1.5V or the temperature of the electrochemical device is raised to 65°C. The discharge capacity of the electrochemical device in a constant current discharge operation is Q T ;

[0014] Among them, the ambient temperature T satisfies -40℃≤T≤0℃, the discharge rate C≥10, and the retention rate of the discharge capacity QT / Q 25 ≥60%.

[0015] Optionally, the lithium-ion battery further comprises: an electrolyte comprising a lithium salt, an organic solvent, a first type of additive, a second type of additive and a third type of additive;

[0016] Wherein, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate and lithium bis(trifluoromethylsulfonyl)imide;

[0017] The organic solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate and ethyl methyl carbonate;

[0018] The first type of additives includes fluoroethylene carbonate (FEC) and / or bisfluoroethylene carbonate (DFEC);

[0019] The second type of additives includes diethyl sulfate (DTD) and / or diethyl sulfite (ES);

[0020] The third type of additives includes vinylene carbonate (VC) and / or ethylene carbonate (EVC).

[0021] Optionally, the mass percentage of the first type of additive in the electrolyte is M a , and M a Satisfy 0.5%≤M a ≤10.0%; the mass percentage of the second type of additive in the electrolyte is M b , and M b Satisfy 0.5%≤M b ≤10.0%; the mass percentage of the third type of additive in the electrolyte is M c , and M c Satisfy 0.1%≤M c ≤10.0%.

[0022] Optionally, the lithium-ion battery further comprises: a positive electrode sheet, comprising a positive electrode current collector and a positive electrode coating coated with at least one layer containing a positive electrode active material;

[0023] Wherein, the positive electrode active material comprises lithium nickel cobalt manganese oxide (Li1Ni x Co y Mn z M bO2), wherein 0.75≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1, and the element M includes one or more of zirconium (Zr), tungsten (W), titanium (Ti), aluminum (Al), strontium (Sr), boron (B) and neodymium (Nd).

[0024] Optionally, a ratio N / P of the capacity N of the negative electrode sheet to the capacity P of the positive electrode sheet is between 1.02 and 1.2.

[0025] Optionally, the lithium-ion battery further comprises: a shell, in which a battery core is contained, wherein the battery core is wound by a positive electrode sheet, a negative electrode sheet and a separator therebetween;

[0026] The positive electrode sheet comprises a strip-shaped positive electrode foil, a positive electrode coating coated on the surface of the strip-shaped positive electrode foil, and a first empty foil area; the negative electrode sheet comprises a strip-shaped negative electrode foil, a negative electrode coating coated on the surface of the strip-shaped negative electrode foil, and a second empty foil area; the first empty foil area and the second empty foil area are perpendicular to the winding direction, and form the top end face or bottom end face of the lithium-ion battery by flattening or cutting and stacking.

[0027] In some embodiments, the method for preparing the lithium-ion battery comprises:

[0028] 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;

[0029] 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;

[0030] 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;

[0031] 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.

[0032] In some embodiments, the electrical device comprises a lithium-ion battery as described in the present application.

[0033] The lithium-ion battery, its preparation method, and the power-using device provided in the embodiments of the present disclosure can achieve the following technical effects:

[0034] The present invention defines the characteristic peak intensity I of the F1s characteristic peak of the solid electrolyte interface film of the lithium ion battery in the X-ray photoelectron spectrum. F The characteristic peak intensity I SThe ratio range of , thereby achieving precise regulation of the inorganic components in the solid electrolyte interface film. In this way, the electron and lithium ion conductivity of the solid electrolyte interface film is further optimized, thereby effectively reducing the internal resistance of the lithium-ion battery in a low temperature environment, and improving the working performance (for example, discharge capacity, rate performance, temperature rise performance and safety performance, etc.) and cycle life of the lithium-ion battery. At the same time, the present application not only solves the problem of lithium-ion battery performance degradation in a low temperature environment, 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.

[0035] The above general description and the following description are exemplary and explanatory only and are not intended to limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] One or more embodiments are exemplarily described by corresponding drawings, which do not limit the embodiments. Elements with the same reference numerals in the drawings are shown as similar elements, and the drawings do not constitute a scale limitation, and wherein:

[0037] Figure 1 is a schematic structural diagram of a lithium-ion battery provided by an embodiment of the present disclosure;

[0038] Figure 2 is a schematic structural diagram of a battery roll core provided by an embodiment of the present disclosure;

[0039] Figure 3 is a schematic diagram of unfolding a battery roll core provided by an embodiment of the present disclosure;

[0040] Figure 4 is an X-ray photoelectron spectrum of the SEI film provided by the embodiment of the present disclosure;

[0041] Figure 5 It is a flow chart of a method for preparing a lithium-ion battery provided in an embodiment of the present disclosure.

[0042] Reference numerals:

[0043] 1-positive terminal; 10-battery coil core; 11-positive electrode column; 12-negative terminal; 2-shell; 3-negative electrode sheet; 4-diaphragm; 5-positive electrode sheet. DETAILED DESCRIPTION

[0044] In order to be able to understand the features and technical contents of the embodiments of the present disclosure in more detail, the implementation of the embodiments of the present disclosure is described in detail below in conjunction with the accompanying drawings. The attached drawings are for reference only and are not used to limit the embodiments of the present disclosure. In the following technical description, for the convenience of explanation, a full understanding of the disclosed embodiments is provided through multiple details. However, one or more embodiments can still be implemented without these details. In other cases, to simplify the drawings, well-known structures and devices can be simplified for display.

[0045] The terms "first", "second", etc. in the specification and claims of the embodiments of the present disclosure and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged where appropriate, so that the embodiments of the embodiments of the present disclosure described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0046] In the embodiments of the present disclosure, the terms "upper", "lower", "inside", "middle", "outside", "front", "back" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. These terms are mainly intended to better describe the embodiments of the present disclosure and their embodiments, and are not intended to limit the indicated devices, elements or components to have a specific direction, or to be constructed and operated in a specific direction. Moreover, in addition to being used to indicate directions or positional relationships, some of the above terms may also be used to indicate other meanings. For example, the term "upper" may also be used to indicate a certain dependency or connection relationship in certain circumstances. 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.

[0047] In addition, the terms "disposed", "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 a direct connection, or an indirect connection through an intermediate medium, or it can be an internal connection 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.

[0048] Unless otherwise stated, the term "plurality" means two or more.

[0049] In the embodiment of the present disclosure, the character " / " indicates that the preceding and following objects are in an "or" relationship. For example, A / B indicates: A or B.

[0050] The term "and / or" is a description of the association relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or, A and B.

[0051] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present disclosure may be combined with each other.

[0052] Combination Figure 1 As shown, the embodiment of the present disclosure provides a lithium-ion battery, including a cylindrical shell 2, the interior of which is used to accommodate a battery coil core, the top is a positive terminal 1, the bottom is a negative terminal 12, and a positive pole 11 is arranged on the positive terminal 1. Specifically, Figure 2 The schematic diagram of the structure of the battery roll core in this application is shown. Figure 3 FIG. 1 shows a schematic diagram of the unfolding of the battery roll core in the present application. In which, the positive electrode sheet 5, the negative electrode sheet 3 and the separator 4 are as shown in FIG. Figure 3 As shown in the stacking, and then winding to form Figure 2 The cylindrical battery winding core 10 shown has the pole piece end at the cylindrical axis at the beginning of winding, and the pole piece end at the outer surface of the cylinder at the end of winding. The positive electrode sheet 5 includes a strip positive electrode foil, a positive electrode coating coated on the surface of the strip positive electrode foil, and a first empty foil area, and the negative electrode sheet 3 includes a strip negative electrode foil, a negative electrode coating coated on the surface of the strip negative electrode foil, and a second empty foil area. The first empty foil area and the second empty foil area are perpendicular to the winding direction, and are formed into the top end face or bottom end face of the lithium-ion battery by flattening or cutting and stacking.

[0053] In this regard, in order to circumvent the limitation of electrolyte component selection and comprehensively optimize and improve the performance of lithium-ion batteries in low temperature environments, the present disclosure provides a lithium-ion battery, including a negative electrode sheet, 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 a solid electrolyte interface (SEI) film covering the surface of the negative electrode active material. Figure 4 As shown, in the X-ray photoelectron spectrum XPS of the solid electrolyte interface film, there is an F1s characteristic peak between the binding energy of 690.0eV and 682.0eV, and an S2p characteristic peak between the binding energy of 162.0eV and 158.0eV, wherein the characteristic peak intensity I F and the characteristic peak intensity I of the S2p characteristic peak S Satisfy 0.1≤I F / I S ≤25.0.

[0054] The lithium-ion battery provided by the embodiment of the present disclosure is used to limit the characteristic peak intensity I of the F1s characteristic peak of the solid electrolyte interface film of the lithium-ion battery in the X-ray photoelectron spectrum. F The characteristic peak intensity I SThe ratio range of , thereby achieving precise regulation of the inorganic components in the solid electrolyte interface film. In this way, the electron and lithium ion conductivity of the solid electrolyte interface film is further optimized, thereby effectively reducing the internal resistance of the lithium-ion battery in a low temperature environment, and improving the working performance (for example, discharge capacity, rate performance, temperature rise performance and safety performance, etc.) and cycle life of the lithium-ion battery. At the same time, the present application not only solves the problem of lithium-ion battery performance degradation in a low temperature environment, 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.

[0055] Optionally, the elements in the solid electrolyte interface film on the surface of the negative electrode active material of the present application include: one or more of fluorine (F), oxygen (O), carbon (C) and sulfur (S), and the element types are determined by XPS.

[0056] Optionally, the resonance signals in the solid nuclear magnetic spectrum (ssNMR) corresponding to the negative electrode active material of the present application include: 19 F (~203.0ppm), 33 S (~-7ppm to ~-10ppm) and 7 One or more of Li (~1.0ppm).

[0057] In this way, the F, S and O / C elements in the solid electrolyte interface film correspond to inorganic salts such as LiF, Li2S and Li2CO3 respectively. By adjusting the composition of inorganic salts, the conduction of lithium ions can be improved, the interface stability can be enhanced, and the battery rate and cycle performance can be improved.

[0058] Optionally, the negative electrode active material of the present application includes at least two of silicon, silicon oxide, artificial graphite, natural graphite, soft carbon or hard carbon. Among them, the carbon material is selected from a mixture of one or more of artificial graphite, natural graphite, hard carbon and soft carbon. Silicon has a higher theoretical specific capacity and specific energy density, and can achieve a higher ability to embed and de-embed lithium ions, but embedding causes volume expansion, and de-embedding causes volume contraction.

[0059] It can be seen that materials such as silicon and silicon oxide have higher theoretical specific capacity, while materials such as graphite, soft carbon and hard carbon provide better conductivity and good cycle stability. In this way, the application can give full play to the advantages of various materials through reasonable material matching, reduce the problems of negative electrode expansion and capacity attenuation, and improve the comprehensive performance, life and safety of the battery.

[0060] Optionally, the discharge characteristics of the lithium-ion battery of the present application are: after the lithium-ion battery with a charge rate SOC of 100% is left at 25°C for 6 hours, it is discharged to 2.5V at a rate of 0.5C at 25°C, and the corresponding discharge capacity is Q 25The lithium-ion battery with a 100% charge rate is left at ambient temperature T for 6 hours, and discharged at a discharge rate C to a voltage of 1.5V at ambient temperature T or the temperature of the electrochemical device is raised to 65°C. The discharge capacity of the electrochemical device in the constant current discharge operation is Q T .

[0061] Among them, the ambient temperature T satisfies -40℃≤T≤0℃, the discharge rate C satisfies C≥10, and the retention rate of the discharge capacity satisfies Q T / Q 25 ≥60%.

[0062] In this way, the lithium-ion battery of the present application can still maintain good energy output performance and cycle stability under low temperature and high rate discharge, and is particularly suitable for application scenarios in low temperature environments or high power requirements.

[0063] Optionally, the lithium ion battery of the present application also includes an electrolyte, wherein the electrolyte includes a lithium salt, an organic solvent, a first type of additive, a second type of additive, and a third type of additive. Wherein, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, and lithium bis(trifluoromethylsulfonyl)imide. The organic solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and ethyl methyl carbonate. The first type of additive includes fluoroethylene carbonate (FEC) and / or bis(fluoroethylene carbonate) (DFEC). The second type of additive includes vinyl sulfate (DTD) and / or vinyl sulfite (ES). The third type of additive includes vinylene carbonate (VC) and / or vinyl carbonate (EVC).

[0064] It can be seen that the first type of additives mainly generate inorganic salts mainly composed of LiF during the reduction and decomposition process; the second type of additives mainly generate inorganic salts mainly composed of LiS after reduction and decomposition; and the third type of additives mainly generate inorganic salts mainly composed of Li2CO3. In this way, the present application optimizes the composition of the solid electrolyte interface film by adjusting the ratio of the above three types of additives, thereby effectively improving the rate performance of the battery under low temperature conditions.

[0065] Specifically, based on the mass of the electrolyte, the mass percentage of the first type of additive in the electrolyte is M a , and M a Satisfy 0.5%≤M a ≤10.0%; the mass percentage of the second type of additive in the electrolyte is M b , and M b Satisfy 0.5%≤M b ≤10.0%; the mass percentage of the third type of additive in the electrolyte is M c , and M c Satisfy 0.1%≤Mc ≤10.0%.

[0066] In this way, by adjusting the appropriate ratio of the first type of additives, the second type of additives and the third type of additives, it is helpful to improve the cycle stability, rate performance and low temperature performance of lithium-ion batteries. In addition, the above ratio adjustment can significantly improve the safety of the battery, reduce adverse reactions, and improve the overall performance of the battery under different working conditions.

[0067] In this way, the present application can better optimize the discharge capacity and cycle performance of lithium-ion batteries in low temperature environments through the combination of the first type of binder, the second type of binder and the third type of binder.

[0068] Optionally, the lithium-ion battery of the present application further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode coating coated with at least one layer of positive electrode active material. The positive electrode active material comprises lithium nickel cobalt manganese oxide (Li1Ni x Co y Mn z M w O2), wherein 0.75≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1, and the element M includes one or more of zirconium (Zr), tungsten (W), titanium (Ti), aluminum (Al), strontium (Sr), boron (B) and neodymium (Nd).

[0069] In this way, the lithium-ion battery of the present application forms a high energy density combination system of the battery by adopting a positive electrode ternary high nickel material and a negative electrode graphite doped silicon system.

[0070] Optionally, the ratio N / P of the capacity N of the negative electrode sheet to the capacity P of the positive electrode sheet of the present application is between 1.02 and 1.2.

[0071] At the same time, combined Figure 5 As shown, the present disclosure provides a method for preparing a lithium-ion battery, comprising:

[0072] Step 501: Prepare a positive electrode sheet: mix a positive electrode coating material, coat it on at least one side of an aluminum foil, and obtain a positive electrode sheet after drying and cold pressing.

[0073] Step 502: preparing a negative electrode sheet: mixing a negative electrode coating material, coating it on at least one side of the aluminum foil, and drying and cold pressing to obtain a negative electrode sheet.

[0074] Step 503: preparing a 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.

[0075] Step 504: Assembling the lithium-ion battery: welding the tabs of the battery core to the electrical connection sheet, placing the battery into a battery casing, and performing electrolyte injection, sealing and formation processes to obtain a lithium-ion battery.

[0076] In addition, an embodiment of the present disclosure provides an electrical device, comprising a lithium-ion battery for providing electric power as described in the present application.

[0077] The present invention will be further explained with reference to the following examples.

[0078] Example 1

[0079] Embodiment 1 provides a lithium ion battery, which is prepared by the following method:

[0080] Preparation of positive electrode sheet: Select positive electrode active material (Li1Ni 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black, carbon nanotubes and polyvinylidene fluoride (PVDF) are thoroughly stirred and mixed in an N-methylpyrrolidone solvent system in a mass ratio of 96:1:1:2 to obtain a positive electrode coating material, and then the positive electrode coating material is coated on a 12.0 μm thick aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.

[0081] Preparation of negative electrode sheet: Calculated by mass percentage, the negative electrode coating material includes 96.0% silicon-carbon material (Si content 10.0wt%, graphite content 86.0wt%), 1.5% carbon nanotubes, 1.0% thickener sodium carboxymethyl cellulose (CMC) and 1.5% binder polyacrylic acid (PAA). The above substances are added to deionized water and stirred to form a negative electrode coating material with a solid content of 40%. The negative electrode coating material is then coated on both sides of the negative electrode collector (copper foil), and after drying and cold pressing, a negative electrode sheet is formed with a compaction density of 1.5g / cm 3 .

[0082] Preparation of electrolyte: lithium salt lithium hexafluorophosphate (LiPF6), organic solvent ethylene carbonate (EC), dimethyl carbonate (DMC), a first type of additive fluoroethylene carbonate (FEC), a second additive vinyl sulfate (DTD) and a third type of additive vinylene carbonate (VC) are mixed in a mass percentage of 10.0:20.0:55.0:2.0:8.0:5.0 to obtain an electrolyte.

[0083] Preparation of diaphragm: A high-porosity diaphragm is selected, in which the thickness of the polyethylene PE base film is 7-15 μm, preferably 9 μm. The thickness of the ceramic coating on both sides of the base film is 1.0 μm, and the thickness of the polyvinylidene fluoride PVDF coating is 1.0 μm.

[0084] Assembling lithium-ion batteries: The positive and negative electrode sheets are rolled and slit respectively, and then wound together with the separator to obtain a cylindrical battery core, which is then welded to the electrical connection sheet and loaded into the battery shell. After completing the injection, sealing and formation processes, the lithium-ion battery of this embodiment is obtained. The shell of the lithium-ion battery is a cylinder with the size parameters of diameter: 21.0 mm and length 70.0 mm.

[0085] Example 2

[0086] Example 2 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass percentage of the first type of additive fluoroethylene carbonate added is 4.0%, the mass percentage of the second additive vinyl sulfate added is 6.0%, and the rest is the same as Example 1.

[0087] Example 3

[0088] Example 3 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass percentage of the first type of additive fluoroethylene carbonate added is 5.0%, the mass percentage of the second additive vinyl sulfate added is 5.0%, and the rest is the same as Example 1.

[0089] Example 4

[0090] Example 4 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass percentage of the first type of additive fluoroethylene carbonate added is 6.0%, the mass percentage of the second additive vinyl sulfate added is 4.0%, and the rest is the same as Example 1.

[0091] Example 5

[0092] Example 5 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass percentage of the first type of additive fluoroethylene carbonate added is 8.0%, the mass percentage of the second additive vinyl sulfate added is 2.0%, and the rest is the same as Example 1.

[0093] Example 6

[0094] Example 6 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass percentage of the first type of additive fluoroethylene carbonate added is 1.8%, the mass percentage of the second additive vinyl sulfate added is 7.2%, and the mass percentage of the third additive vinylene carbonate added is 6.0%. The rest is the same as Example 1.

[0095] Example 7

[0096] Example 7 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass percentage of the first type of additive fluoroethylene carbonate added is 1.6%, the mass percentage of the second additive vinyl sulfate added is 6.4%, and the mass percentage of the third additive vinylene carbonate added is 7.0%. The rest is the same as Example 1.

[0097] Example 8

[0098] Example 8 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass percentage of the first type of additive fluoroethylene carbonate added is 1.4%, the mass percentage of the second additive vinyl sulfate added is 5.6%, and the mass percentage of the third additive vinylene carbonate added is 8.0%. The rest is the same as Example 1.

[0099] Example 9

[0100] Example 9 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass percentage of the first type of additive fluoroethylene carbonate added is 1.2%, the mass percentage of the second additive vinyl sulfate added is 4.8%, and the mass percentage of the third additive vinylene carbonate added is 9.0%. The rest is the same as Example 1.

[0101] Example 10

[0102] Example 10 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass percentage of the first type of additive fluoroethylene carbonate added is 1.0%, the mass percentage of the second additive vinyl sulfate added is 4.0%, and the mass percentage of the third additive vinylene carbonate added is 9.0%. The rest is the same as Example 1.

[0103] Embodiment 11

[0104] Example 11 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass percentage of the added third additive vinylene carbonate is 7.5%, the mass percentage of the added lithium hexafluorophosphate is 7.5%, and the rest is the same as Example 1.

[0105] Example 12

[0106] Example 12 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass percentage of the added third additive vinylene carbonate is 10.0%, the mass percentage of the added lithium hexafluorophosphate is 5.0%, and the rest is the same as Example 1.

[0107] Comparative Example 1

[0108] Comparative Example 1 provides a lithium-ion battery. The difference between this comparative example and Example 1 is that the mass percentage of the first type of additive fluoroethylene carbonate added is 0.5%, the mass percentage of the second additive vinyl sulfate added is 9.5%, and the rest is the same as Example 1.

[0109] Comparative Example 2

[0110] Comparative Example 2 provides a lithium-ion battery. The difference between this comparative example and Example 1 is that the mass percentage of the first type of additive fluoroethylene carbonate added is 9.5%, the mass percentage of the second additive vinyl sulfate added is 0.5%, and the rest is the same as Example 1.

[0111] Comparative Example 3

[0112] Comparative Example 3 provides a lithium-ion battery. The difference between this comparative example and Example 1 is that the mass percentage of the first type of additive fluoroethylene carbonate added is 2.9%, the mass percentage of the second additive vinyl sulfate added is 11.6%, and the mass percentage of the third additive vinylene carbonate added is 0.5%. The rest is the same as Example 1.

[0113] Comparative Example 4

[0114] Comparative Example 4 provides a lithium-ion battery. The difference between this comparative example and Example 1 is that the mass percentage of the added third additive vinylene carbonate is 1.3%, the mass percentage of the added lithium hexafluorophosphate is 2.0%, and the rest is the same as Example 1.

[0115] Performance evaluation:

[0116] Test 1: Test of the characteristic peak intensity (height) and element type of the SEI film corresponding to the surface of the active material of the negative electrode.

[0117] Characteristic peak intensity test: First, discharge the lithium-ion battery to 2.5V. In the glove box, carefully disassemble the battery and take out the negative electrode of the cylindrical battery cell. Next, soak the electrode in dimethyl carbonate for 30 minutes, wipe the surface after taking it out to remove the residual organic solvent, and repeat this process three times to ensure that all possible impurities and residues are removed. Subsequently, rinse the electrode with ethanol and wipe it again to remove the solvent, and finally let it stand in the glove box for 48 hours to ensure that the electrode is completely dry. After drying, scrape the material in the electrode feeding area and put it into a sealed bag, then take out the glove box and immediately perform XPS characterization. Finally, the XPS spectrum was analyzed, where the characteristic peaks in the range of 690.0eV to 682.0eV belong to F1s, and the characteristic peaks in the range of 162.0eV to 158.0eV belong to S2p, and the intensity (height) ratio of the two characteristic peaks is marked as IF / IS.

[0118] Test of element types: By analyzing the same XPS spectrum, the attribution of characteristic peaks can be determined according to the following range: the characteristic peak located in the range of 690.0eV to 682.0eV belongs to F1s, the characteristic peak located in the range of 540.0eV to 527.5eV belongs to O1s, the characteristic peak located in the range of 285.5eV to 283.5eV belongs to C1s (the corrected C1s peak in the background needs to be deducted), and the characteristic peak located in the range of 162.0eV to 158.0eV belongs to S2p, thereby determining the type of elements in the sample.

[0119] Test 2: Solid-state NMR spectrum test of the negative electrode active material.

[0120] The sample pretreatment steps are the same as 1. After drying, the active material on the electrode is scraped and placed in a sample tube suitable for solid NMR. The sample tube is sealed to avoid contact with air as much as possible. Finally, the sample tube is quickly removed from the glove box and solid nuclear magnetic resonance (ssNMR) test is performed. During the test, record 19 F (~203.0ppm), 33 S (range ~7ppm to ~10ppm) and 7 The resonance signals of characteristic peaks such as Li (~1.0ppm) are detected, and the test data are analyzed to determine the chemical state and coordination of each element in the sample.

[0121] Test 3: Test of discharge capacity retention rate at different temperatures.

[0122] The 100% SOC lithium-ion battery was placed in a 25°C constant temperature box for 6 hours, and then discharged at 25°C at a rate of 0.5C to 2.5V, with a discharge capacity of Q 25 ; Place the lithium-ion battery with 100% SOC in a -10℃ constant temperature box for 6 hours, then discharge it at -10℃ at a rate of 0.5C to 1.5V or the device temperature rises to 65℃, the discharge capacity is Q -10 ; Place the lithium-ion battery with 100% SOC in a -20℃ constant temperature box for 6 hours, then discharge it at a rate of 0.5C at -20℃ until it reaches 1.5V or the device temperature rises to 65℃. The discharge capacity is Q -20 ; Place the lithium-ion battery with 100% SOC in a -30℃ constant temperature box for 6 hours, then discharge it at a rate of 0.5C at -30℃ until it reaches 1.5V or the device temperature rises to 65℃. The discharge capacity is Q -30 ; Place the lithium-ion battery with 100% SOC in a -40℃ constant temperature box for 6 hours, then discharge it at a rate of 0.5C at -40℃ until it reaches 1.5V or the device temperature rises to 65℃. The discharge capacity is Q -40 , statistical discharge capacity retention rate QT / Q 25 The capacity retention rates of the batteries of Examples 1 to 12 and Comparative Examples 1 to 4 were compared, and the results are shown in Table 1.

[0123] Table 1

[0124]

[0125] Test 4: Low temperature cycle performance test.

[0126] Place the battery in a -25℃ constant temperature box for 4 hours and test it according to the following steps: Charge to 4.2V at a constant current of 1.0C, then switch to constant voltage charging until the current drops to 0.01C. After charging, let it stand for 10 minutes. Perform constant current discharge at a rate of 1.0C to 2.5V, and the released capacity is counted as Q1. After discharge, let it stand for 10 minutes. Repeat the above charging and discharging process, and count the released capacity of 50, 100 and 200 cycles, which are counted as Q respectively. 50 , Q 100 and Q 200 . Calculation method of discharge capacity retention rate: Q X / Q1,Q X Where X is 50, 100 and 200. The discharge capacity retention rates of the batteries of Examples 1 to 12 and Comparative Examples 1 to 4 are compared, and the results are shown in Table 2.

[0127] Table 2

[0128]

[0129] As shown in Table 1, comparing Examples 1 to 12, it can be seen that as I F / I S As the value increases, the discharge capacity retention rate of lithium-ion batteries in the range of -10℃ to -50℃ shows a downward trend. This phenomenon can be attributed to: (1) the Li2S and Li2SO X These S-containing inorganic components mainly come from the reduction of vinyl sulfate, while the F-containing inorganic component LiF in the SEI film mainly comes from the reduction of fluoroethylene carbonate and a small amount of lithium hexafluorophosphate. (2) Li2S and Li2SO X The lithium ion conductivity of LiF is stronger than that of LiF, so it is beneficial to improve the efficiency of lithium ion transmission through the SEI film at low temperature. (3) Reducing the transmission impedance of the SEI film can reduce the polarization effect and is beneficial to the low temperature discharge capacity. As shown in Table 2, by comparing Examples 1 to 5, it can be seen that as I F / I S The capacity retention rate of lithium-ion batteries at 50 cycles, 100 cycles, and 200 cycles all showed an upward trend. This phenomenon is attributed to the fact that LiF is superior to Li2S and Li2SOX It has stronger chemical stability and can play a certain "shielding role" to protect the negative electrode active material from being corroded or reacted by the electrolyte. Comparative Examples 6 to 10, as the amount of vinyl carbonate added increases, the capacity retention rate of the lithium-ion battery at 50 cycles, 100 cycles and 200 cycles all show an upward trend. This phenomenon is attributed to the fact that vinyl carbonate can be reduced to an organic component (polyethylene carbonate) in the SEI film, which can enhance the stability and flexibility of the SEI film and improve the cycle performance. Comparative Examples 1, 11 and 12 show that as the amount of lithium hexafluorophosphate added decreases, the capacity retention rate of the lithium-ion battery at 50 cycles, 100 cycles and 200 cycles all show a significant downward trend. This phenomenon is attributed to the fact that after the lithium salt concentration is reduced, the migration speed of lithium ions in the electrolyte in the low concentration area is significantly reduced, which will increase the internal resistance of the battery and lead to increased polarization, which is particularly obvious at low temperatures. It has been calculated that the I of the lithium-ion battery described in this application F / I S All satisfy: 0.1≤I F / I S ≤25.0.

[0130] The above description and the accompanying drawings sufficiently illustrate the embodiments of the present disclosure to enable those skilled in the art to practice them. Other embodiments may include structural and other changes. The embodiments represent only possible variations. Unless explicitly required, individual components and functions are optional, and the order of operations may vary. Portions and features of some embodiments may be included in or replace portions and features of other embodiments. The embodiments of the present disclosure are not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes may be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A lithium ion battery, characterized in that: include: A negative electrode sheet, comprising 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 a solid electrolyte interface film covering the surface of the negative electrode active material; Among them, in the X-ray photoelectron spectrum of the solid electrolyte interface film, there is an F1s characteristic peak between the binding energy of 690.0eV and 682.0eV, and an S2p characteristic peak between the binding energy of 162.0eV and 158.0eV, wherein the characteristic peak intensity I of the F1s characteristic peak is F and the characteristic peak intensity I of the S2p characteristic peak S Satisfy 0.1≤I F / I S ≤25.

0.

2. The lithium-ion battery according to claim 1, characterized in that The elements in the solid electrolyte interface film on the surface of the negative electrode active material include: one or more of fluorine (F), oxygen (O), carbon (C) and sulfur (S).

3. The lithium-ion battery according to claim 1, characterized in that The resonance signals in the solid nuclear magnetic spectrum corresponding to the negative electrode active material include: 19 F (~203.0ppm), 33 S (~-7ppm to ~-10ppm) and 7 One or more of Li (~1.0ppm).

4. The lithium-ion battery according to claim 1, characterized in that: The negative electrode active material includes at least two of silicon, silicon oxide, artificial graphite, natural graphite, soft carbon or hard carbon.

5. The lithium-ion battery according to claim 1, characterized in that: The discharge characteristics of the lithium-ion battery are as follows: after the lithium-ion battery with a 100% charge rate is left at 25°C for 6 hours, it is discharged to 2.5V at a rate of 0.5C at 25°C, and the corresponding discharge capacity is Q 25 ; A lithium-ion battery with a charge rate of 100% is left at an ambient temperature T for 6 hours, and at the ambient temperature T, it is discharged at a discharge rate C to a voltage of 1.5V or the temperature of the electrochemical device is raised to 65°C. The discharge capacity of the electrochemical device in a constant current discharge operation is Q T ; Among them, the ambient temperature T satisfies -40℃≤T≤0℃, the discharge rate C≥10, and the retention rate of the discharge capacity Q T / Q 25 ≥60%.

6. The lithium ion battery according to any one of claims 1 to 5, characterized in that: Also includes: An electrolyte, comprising a lithium salt, an organic solvent, a first additive, a second additive, and a third additive; Wherein, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate and lithium bis(trifluoromethylsulfonyl)imide; The organic solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate and ethyl methyl carbonate; The first type of additives includes fluoroethylene carbonate (FEC) and / or bisfluoroethylene carbonate (DFEC); The second type of additives includes diethyl sulfate (DTD) and / or diethyl sulfite (ES); The third type of additives includes vinylene carbonate (VC) and / or ethylene carbonate (EVC).

7. The lithium-ion battery according to claim 6, characterized in that: The mass percentage of the first type of additive in the electrolyte is M a , and M a Satisfy 0.5%≤M a ≤10.0%; the mass percentage of the second type of additive in the electrolyte is M b , and M b Satisfy 0.5%≤M b ≤10.0%; the mass percentage of the third type of additive in the electrolyte is M c , and M c Satisfy 0.1%≤M c ≤10.0%.

8. The lithium ion battery according to any one of claims 1 to 5, characterized in that: Also includes: A positive electrode sheet, comprising a positive electrode current collector and a positive electrode coating coated with at least one layer containing a positive electrode active material; Wherein, the positive electrode active material comprises lithium nickel cobalt manganese oxide (Li1Ni x Co y Mn z M b O2), wherein 0.75≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1, and the element M includes one or more of zirconium (Zr), tungsten (W), titanium (Ti), aluminum (Al), strontium (Sr), boron (B) and neodymium (Nd).

9. The lithium-ion battery according to claim 8, characterized in that: The ratio N / P of the capacity N of the negative electrode sheet to the capacity P of the positive electrode sheet is between 1.02 and 1.

2.

10. The lithium ion battery according to claim 1, characterized in that: Also includes: A shell, in which a battery core is accommodated, wherein the battery core is wound by a positive electrode sheet, a negative electrode sheet and a separator therebetween; The positive electrode sheet comprises a strip-shaped positive electrode foil, a positive electrode coating coated on the surface of the strip-shaped positive electrode foil, and a first empty foil area; the negative electrode sheet comprises a strip-shaped negative electrode foil, a negative electrode coating coated on the surface of the strip-shaped negative electrode foil, and a second empty foil area; the first empty foil area and the second empty foil area are perpendicular to the winding direction, and form the top end face or bottom end face of the lithium-ion battery by flattening or cutting and stacking.

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.

Images