Lithium ion battery and electric device

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a lithium ion battery and a power utilization device. The lithium ion battery comprises a positive plate, the positive plate comprises a positive current collector and a positive coating, at least one surface of the positive current collector is coated with the positive coating, and in an X-ray photoelectron spectroscopy of a positive active substance, a Fe2p characteristic peak corresponding to lithium iron phosphate intrinsic exists in a binding energy interval of 710.0 eV to 730.0 eV, a corresponding N1s characteristic peak after modification of lithium iron phosphate doped with an N element exists in a binding energy interval of 395.0 eV-405.0 eV, a corresponding S2p characteristic peak after modification of lithium iron phosphate doped with an S element exists in a binding energy interval of 163.0 eV-169.0 eV, and the peak intensity of the characteristic peaks meets the following relational expressions: IN / IFe is greater than or equal to 0.01 and less than or equal to 4.0, and IS / IFe is greater than or equal to 0.01 and less than or equal to 3.0; wherein IFe is the peak value intensity of the Fe2p characteristic peak, IN is the peak value intensity of the N1s characteristic peak, IS is the peak value intensity of the S2p characteristic peak, and the intensity of the peak values represents the doping amount of the N element and the S element.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion batteries, and particularly to a lithium-ion battery and an electrical device. Background Art

[0002] Currently, lithium iron phosphate (LiFePO4), as a main representative of the cathode material of lithium-ion batteries, has become the main cathode material of commercial lithium-ion batteries with its unique advantages and is widely used in fields such as smart phones, computers, and electric vehicles. It has a relatively high theoretical specific capacity (170 mAh g -1 ), a relatively stable discharge voltage platform (about 3.4 V vs. Li / Li + ), long cycle life, excellent thermal stability, high safety, and good environmental friendliness.

[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] Due to the poor electronic conductivity of lithium iron phosphate (~10 -8 -10 -10 S cm -1 ) and the low ion diffusion rate (~10 -18 cm 2 s -1 ), the performance of lithium iron phosphate is poor under high-rate charge and discharge and low-temperature environments, thus limiting its application in high-power devices.

[0005] 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 this 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

[0006] 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 elements or delineate the protection scope of these embodiments, but rather serves as a preface to the subsequent detailed description.

[0007] The embodiments of the present disclosure provide a lithium-ion battery and an electrical device, which improve the electronic conductivity and ion diffusion rate of lithium iron phosphate through nitrogen-sulfur co-doping, thereby improving the rate performance and low-temperature adaptability of the battery, so as to play the application of the battery in high-power devices.

[0008] In some embodiments, the lithium-ion battery 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, the positive electrode coating including a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder;

[0009] In the X-ray photoelectron spectrum of the positive electrode active material, there is an Fe2p characteristic peak corresponding to the intrinsic lithium iron phosphate in the binding energy range of 710.0 eV to 730.0 eV, an N1s characteristic peak corresponding to the modified lithium iron phosphate doped with N element in the binding energy range of 395.0 eV to 405.0 eV, and an S2p characteristic peak corresponding to the modified lithium iron phosphate doped with S element in the binding energy range of 163.0 eV to 169.0 eV. Moreover, the peak intensities of the characteristic peaks satisfy the following relational expressions:

[0010] 0.01 ≤ I N / I Fe ≤ 4.0, 0.01 ≤ I S / I Fe ≤ 3.0;

[0011] Wherein, I Fe is the peak intensity of the Fe2p characteristic peak, I N is the peak intensity of the N1s characteristic peak, I S is the peak intensity of the S2p characteristic peak, and the strength of the peak represents the doping amounts of N element and S element.

[0012] Optionally, in the Raman spectrum corresponding to the positive electrode sheet active material, a target characteristic peak appears at 940 - 970 cm -1 , and the target characteristic peak corresponds to the symmetric stretching vibration of PO4 3- in lithium iron phosphate.

[0013] Optionally, the particle size D 50 corresponding to the positive electrode active material when the cumulative particle size distribution percentage reaches 50% is 500 nm - 10.0 μm, and the compaction is 2.0 - 2.8 g / cm 3 .

[0014] Optionally, the discharge characteristics of the lithium ion battery are as follows: After a lithium ion battery with a 100% charging rate is left standing at an ambient temperature of 25 °C for 6 hours, it is discharged at a rate of 0.1C to 2.5V, and the corresponding discharge capacity is Q1. The discharge capacity when discharged at 10C to 2.5V is Q2, and the retention rate of the discharge capacity Q2 / Q1 ≥ 50%.

[0015] Optionally, the discharge characteristics of the lithium ion battery are as follows: After a lithium ion battery with a 100% charging rate is left standing at an ambient temperature of 25 °C for 6 hours, at an ambient temperature of 25 °C, it is discharged at a rate of 0.5C to 2.5V, and the corresponding discharge capacity is Q 25, a lithium-ion battery with a 100% charge rate is left standing at an ambient temperature of -40°C for 6 hours, and at an ambient temperature of -40°C, it is discharged at a discharge rate of 5C until the voltage reaches 1.5V or the temperature of the electrochemical device rises to 65°C. The discharge capacity of the electrochemical device during the constant-current discharge operation is Q -40 , and the retention rate Q -40 / Q 25 ≥50%.

[0016] Optionally, the positive electrode active material includes lithium iron phosphate and / or lithium iron manganese phosphate.

[0017] Optionally, the lithium-ion battery further 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, and the negative electrode coating includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0018] Optionally, the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon; the negative electrode conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black; the negative electrode binder includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid, and styrene-butadiene rubber.

[0019] Optionally, 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.

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

[0021] wherein the solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and ethyl methyl carbonate; the additive includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, ethylene sulfate, ethylene sulfite, vinylene carbonate, and vinyl carbonate.

[0022] In some embodiments, the electrical device includes the lithium-ion battery as described in this application.

[0023] The lithium-ion battery and the electrical device provided by the embodiments of the present disclosure can achieve the following technical effects:

[0024] By precisely defining the ratio range of the peak intensities of the characteristic peaks of lithium iron phosphate intrinsic, lithium iron phosphate doped with N element, and lithium iron phosphate doped with S element in the positive electrode active material in the X-ray photoelectron spectroscopy, the precise regulation of the nitrogen-sulfur co-doping in the positive electrode active material is achieved.

[0025] In this way, on the one hand, nitrogen doping improves the conductivity of intrinsic electrons by regulating the electronic structure of the material. Its higher electronegativity can evenly distribute the charge density inside the crystal, reduce the polarization effect, and introduce additional carriers, thereby enhancing the semiconductor properties of the material. In addition, nitrogen doping can also cause local perturbations to the crystal lattice, making the lithium-ion diffusion channels more unobstructed, which helps to improve the lithium-ion migration rate in a low-temperature environment.

[0026] On the other hand, sulfur doping can effectively optimize the electrode / electrolyte interface, improve the interface stability, reduce the interface impedance, and thus improve the charge transfer kinetics. In addition, due to the relatively large atomic radius of sulfur, doping can cause a certain lattice distortion, making the structure of LiFePO4 more stable. At the same time, it broadens the lithium-ion diffusion channels and improves the lithium-ion migration rate. More importantly, under low-temperature conditions, sulfur doping can reduce the polarization phenomenon of the electrode material, improve the electrochemistry reaction kinetics, and ensure efficient charge and discharge performance can still be achieved in a low-temperature environment.

[0027] In summary, the lithium-ion battery of this application not only solves the problem of the decline in battery performance under low-temperature conditions, but also can improve the working performance of the battery in extreme environments at a deeper level, with significant technical advantages and application prospects.

[0028] The above general description and the following description are only exemplary and explanatory, and are not used to limit this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] One or more embodiments are exemplarily illustrated by the 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:

[0030] Figure 1 is a schematic structural diagram of a lithium-ion battery provided by an embodiment of the present disclosure;

[0031] Figure 2 is a schematic structural diagram of a battery core provided by an embodiment of the present disclosure;

[0032] Figure 3 is a developed schematic diagram of a battery core provided by an embodiment of the present disclosure;

[0033] Figure 4 is an X-ray photoelectron spectroscopy diagram of a lithium-ion battery provided by an embodiment of the present disclosure.

[0034] Reference Signs:

[0035] 1 - positive extreme; 10 - battery core; 11 - positive terminal; 12 - negative extreme; 2 - housing; 3 - negative electrode sheet; 4 - separator; 5 - positive electrode sheet. Detailed implementation

[0036] In order to more comprehensively understand the features and technical content of the embodiments of the present disclosure, 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 for reference and illustration purposes only 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 to simplify the drawings.

[0037] In the embodiments of the present disclosure, terms such as "first", "second", etc. in the specification, claims and the above-mentioned drawings are used to distinguish similar objects and do not necessarily describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so as to implement the embodiments of the present disclosure described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion.

[0038] 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. And, in addition to being able to represent an 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.

[0039] In addition, the terms "arrange", "connect", "fix" should be understood in a broad sense. For example, "connect" 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.

[0040] Unless otherwise specified, the term "plurality" means two or more.

[0041] In the embodiments of the present disclosure, the character " / " indicates an "or" relationship between the preceding and following objects. For example, A / B means: A or B.

[0042] The term "and / or" is an associative relationship describing 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.

[0043] 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.

[0044] Combined with Figure 1 As shown, the embodiments of the present disclosure provide a lithium-ion battery, including a cylindrical housing 2, which is used to accommodate a battery core inside, with the positive electrode end 1 at the top and the negative electrode end 12 at the bottom, and a positive electrode post 11 is provided on the positive electrode end 1. Specifically, Figure 2 The structural schematic diagram of the battery core in the present application is shown, Figure 3 The unfolded schematic diagram of the battery core in the present application is shown. 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 2 the cylindrical battery core 10 as shown. The end of the electrode sheet at the initial winding is the end of the electrode sheet at the axis of the cylinder, and the end of the electrode sheet at the end of the winding is the end of the electrode sheet on the outer surface of the cylinder. Among them, the positive electrode sheet 5 includes a positive electrode current collector and a positive electrode coating coated on at least one surface of the positive electrode current collector. The positive electrode coating includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The negative electrode sheet 3 includes a negative electrode current collector and a positive electrode coating coated on at least one surface of the negative electrode current collector. The negative electrode coating includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0045] In the related art, due to the poor electronic conductivity of lithium iron phosphate (~10 -8 -10 -10 Scm -1 ) and the low ion diffusion rate (~10 -18 cm 2 s -1 ), the performance of lithium iron phosphate is poor under high-rate charge and discharge and low-temperature environments, thus limiting its application in high-power devices.

[0046] To address the above technical problems, the modification methods in the related art mainly focus on the following aspects: (1) Particle size regulation: By reducing the particle size of LiFePO4, the diffusion path of lithium ions is shortened, and the rate performance is improved; (2) Carbon coating modification: A conductive carbon (such as a carbon layer formed by pyrolysis of carbon sources such as glucose and citric acid) is coated on the surface of LiFePO4 to improve electronic conductivity and reduce the contact resistance between particles. However, although the above methods have improved the conductivity and rate performance of lithium iron phosphate to a certain extent, there are still limitations. For example, an overly thick carbon coating layer may affect ion transport, and too small particle size may lead to an increase in interfacial side reactions, etc.

[0047] In response, the embodiments of the present disclosure provide a lithium-ion battery, which improves the electronic conductivity and ion diffusion rate of lithium iron phosphate through nitrogen-sulfur co-doping, thereby improving its rate performance and low-temperature adaptability. The lithium-ion battery includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode current collector and a positive electrode coating coated on at least one surface of the positive electrode current collector. The positive electrode coating includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0048] Preferably, the positive electrode active material of the present application includes lithium iron phosphate and / or lithium manganese iron phosphate.

[0049] Preferably, the negative electrode active material of the present application includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon. The negative electrode conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black. The negative electrode binder includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid, and styrene-butadiene rubber.

[0050] Preferably, the ratio N / P of the capacity N of the negative electrode sheet to the capacity P of the positive electrode sheet in the present application is between 1.02 and 1.2.

[0051] Meanwhile, as shown in Figure 4 In the X-ray photoelectron spectrum of the positive electrode active material, there is an Fe2p characteristic peak corresponding to the intrinsic of lithium iron phosphate in the binding energy range of 710.0 eV to 730.0 eV, an N1s characteristic peak corresponding to the modification of lithium iron phosphate doped with N element in the binding energy range of 395.0 eV to 405.0 eV, and an S2p characteristic peak corresponding to the modification of lithium iron phosphate doped with S element in the binding energy range of 163.0 eV to 169.0 eV, and the peak intensities of the characteristic peaks satisfy the following relational expressions:

[0052] 0.01 ≤ I N / I Fe ≤ 4.0, 0.01 ≤ I S / I Fe ≤ 3.0;

[0053] Wherein, IFe is the peak intensity of the Fe2p characteristic peak, I N is the peak intensity of the N1s characteristic peak, I S is the peak intensity of the S2p characteristic peak, and the strength of the peak represents the doping amounts of N and S elements.

[0054] By using the lithium-ion battery provided by the embodiments of the present disclosure, through precisely defining the ratio range of the peak intensities of the characteristic peaks of lithium iron phosphate per se, lithium iron phosphate doped with N element, and lithium iron phosphate doped with S element in the X-ray photoelectron spectroscopy in the cathode active material, the precise regulation of the nitrogen-sulfur co-doping in the cathode active material is realized.

[0055] In this way, on the one hand, nitrogen doping improves the conductivity of intrinsic electrons by regulating the electronic structure of the material. Its higher electronegativity can evenly distribute the charge density inside the crystal, reduce the polarization effect, and introduce additional carriers, thereby enhancing the semiconductor characteristics of the material. In addition, nitrogen doping can also cause local perturbation to the crystal lattice, making the lithium-ion diffusion channels smoother, which helps to improve the lithium-ion migration rate in a low-temperature environment.

[0056] On the other hand, sulfur doping can effectively optimize the electrode / electrolyte interface, improve the interface stability, reduce the interface impedance, and thus improve the charge transfer kinetics. In addition, due to the relatively large atomic radius of sulfur, lattice distortion can be caused after doping, making the structure of LiFePO4 more stable, while broadening the lithium-ion diffusion channels and increasing the lithium-ion migration rate. More importantly, under low-temperature conditions, sulfur doping can reduce the polarization phenomenon of the electrode material, improve the electrochemistry reaction kinetics, and ensure efficient charge-discharge performance can still be achieved in a low-temperature environment.

[0057] Optionally, in the Raman spectrum corresponding to the cathode active material, a target characteristic peak appears at 940 - 970 cm -1 , and the target characteristic peak corresponds to the symmetric stretching vibration of PO4 in lithium iron phosphate 3- .

[0058] In this way, it can better characterize the crystal structure integrity and purity of lithium iron phosphate in the cathode active material, prove that the prepared cathode material has a clear phase composition and good structural stability, and thus helps to achieve excellent cycle stability and rate performance of the battery.

[0059] Optionally, the particle size D corresponding to the cumulative particle size distribution percentage reaching 50% of the cathode active material of this application 50 is 500 nm - 10.0 μm, and the compaction is 2.0 - 2.8 g / cm 3 .

[0060] In this way, while ensuring the density of the electrode structure, the kinetic performance and energy density of the cathode material can be taken into account, effectively maintaining the conductive contact between particles and the sufficient wetting of the electrolyte, thereby improving the diffusion efficiency of lithium ions and the reversibility of the electrode reaction, and further contributing to achieving high energy density and excellent cycle stability of the battery.

[0061] Optionally, the discharge characteristics of the lithium-ion battery are as follows: After a lithium-ion battery with a 100% charge rate is left standing at an ambient temperature of 25°C for 6 hours, it is discharged at a rate of 0.1C to 2.5V, and the corresponding discharge capacity is Q1. The discharge capacity when discharged at 10C to 2.5V is Q2, and the retention rate of the discharge capacity Q2 / Q1 ≥ 50%.

[0062] In this way, it can better characterize the capacity retention ability of the battery under high-rate discharge conditions, indicating that the cathode material has a good electron and ion transport channel structure and excellent electrode reaction kinetics performance, thus contributing to improving the output performance and stability of the lithium-ion battery in fast charging and high-power application scenarios.

[0063] Optionally, the discharge characteristics of the lithium-ion battery of the present application are as follows: After a lithium-ion battery with a 100% charge rate is left standing at an ambient temperature of 25°C for 6 hours, at an ambient temperature of 25°C, it is discharged at a rate of 0.5C to 2.5V, and the corresponding discharge capacity is Q 25 A lithium-ion battery with a 100% charge rate is left standing at an ambient temperature of -40°C for 6 hours, and at an ambient temperature of -40°C, it is discharged at a discharge rate of 5C to a voltage of 1.5V or the temperature of the electrochemical device rises to 65°C. The discharge capacity of the electrochemical device during the constant current discharge operation is Q -40 and the retention rate of the discharge capacity Q -40 / Q 25 ≥ 50%.

[0064] In this way, it can better reflect the practicality of the battery under extreme low temperature and high-rate composite operation conditions, indicating that the cathode material used has good low-temperature discharge activity and electron / ion transport ability, and the electrode still maintains low polarization and excellent electrochemical reaction reversibility in a harsh temperature range, thus significantly improving the power output ability and safe operating window of the battery in extreme environments.

[0065] Optionally, the lithium-ion battery of the present application further includes an electrolyte, where the electrolyte includes a lithium salt, a solvent, and an additive. Specifically, the lithium salt of the present application 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. Among them, the solvent of the present application includes one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and ethyl methyl carbonate. The additive of the present application includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, ethylene sulfate, ethylene sulfite, vinylene carbonate, and vinyl carbonate.

[0066] In addition, an embodiment of the present disclosure provides an electrical device including the lithium-ion battery as described in the present application.

[0067] The lithium-ion battery and the electrical device provided by the present application improve the rate performance and low-temperature performance of the lithium iron phosphate battery. By optimizing the nitrogen and sulfur co-doping, tap density, and particle size of lithium iron phosphate, a lithium iron phosphate battery with excellent high-rate discharge and low-temperature performance can be achieved.

[0068] The following continues to further explain the present application with examples.

[0069] Example 1

[0070] Example 1 provides a lithium-ion battery prepared by the following method:

[0071] 1. Method for fabricating the positive electrode sheet:

[0072] Take the positive electrode active material (nitrogen-sulfur co-doped lithium iron phosphate LiFePO4@NS-1.0%, D 50 is 4.2 μm), conductive carbon black, carbon nanotubes, and polyvinylidene fluoride (PVDF), and stir and mix them evenly in an N-methylpyrrolidone solvent system according to a mass ratio of 96:1:1:2 to obtain a positive electrode coating material. Then, coat the positive electrode coating material on an aluminum foil with a thickness of 12.0 μm, and after drying and cold pressing, obtain a positive electrode sheet with a tap density of 2.45 g / cm 3 .

[0073] Preparation of nitrogen-sulfur co-doped lithium iron phosphate (LiFePO4@NS)

[0074] (1) Preparation of the precursor

[0075] Weigh iron phosphate (FePO4), lithium carbonate (Li2CO3), and thiourea (CH4N2S, serving as both a nitrogen source and a sulfur source) according to a molar ratio of 100:100:2, put them into a ball milling tank, and perform high-energy ball milling for 4 hours to obtain a uniformly mixed precursor.

[0076] (2) Two-step sintering doping

[0077] The first stage: Low-temperature pre-sintering

[0078] Place the ball-milled precursor in a tube furnace. Under the protection of argon (Ar), pre-sinter at 350 °C for 2 hours. During this process, thiourea (CH4N2S) thermally decomposes to generate NH3 and H2S gases, promoting the preliminary embedding of nitrogen and sulfur elements into the precursor lattice.

[0079] The second stage: High-temperature solid-phase synthesis

[0080] Under the protection of argon (Ar) or nitrogen (N2), continue to heat up to 700 °C and hold for 12 hours, enabling nitrogen (N) and sulfur (S) elements to be doped into the LiFePO4 lattice, and at the same time promoting the crystallization of the material to form LiFePO4@NS-1.0% with high crystallinity, where 1.0% represents the molar percentage of thiourea in the precursor.

[0081] (3) Carbon coating modification (optional)

[0082] To improve the electronic conductivity, a carbon source (such as glucose, citric acid, etc.) can be introduced during the calcination process, and a conductive carbon layer is formed on the material surface by high-temperature carbonization to further optimize the electrochemical performance.

[0083] (4) Final product

[0084] After calcination, the obtained product is crushed and screened to prepare a nitrogen and sulfur co-doped lithium iron phosphate composite material with a particle size of 1 - 8 μm, namely LiFePO4@NS-1.0%. Among them, 1.0% represents the percentage of thiourea in the total molar amount of iron phosphate, lithium carbonate, and thiourea.

[0085] 2. Method for fabricating the negative electrode:

[0086] The negative electrode sheet includes a negative electrode current collector copper foil and a negative electrode coating material coated on both surfaces of the copper foil. Calculated by mass percentage, the negative electrode coating material includes 96.0% graphite, 1.5% carbon nanotubes, 1.0% thickener sodium carboxymethyl cellulose (CMC), and 1.5% binder styrene-butadiene rubber (SBR). Add the above substances to deionized water and stir to form the negative electrode coating material with a solid content of 40%. Then coat the negative electrode coating material on both sides of the negative electrode current collector (copper foil), and after drying and cold pressing, form the negative electrode sheet with a compaction density of 1.5 g / cm 3 ;

[0087] 3. Preparation of the electrolyte:

[0088] Lithium salt lithium hexafluorophosphate (LiPF6), organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), first type of additive fluoroethylene carbonate (FEC), second additive divinyl sulfate (DTD), and third type of additive vinylene carbonate (VC)

[0089] Mix them according to the mass percentage ratio of 10.0:20.0:55.0:2.0:8.0:5.0 to obtain an electrolyte solution.

[0090] 4. Preparation of the separator:

[0091] Select a separator with a high porosity. The thickness of the base film PE in the separator is 9 μm, the thickness of the ceramic coatings on both sides of the base film is 1.0 μm, and the thickness of the PVDF coating is 1.0 μm.

[0092] 5. Assembly of the lithium-ion battery:

[0093] Roll and slit the positive electrode sheet and the negative electrode sheet respectively, and then wind them together with the separator to obtain a 4680 cylindrical battery core. Subsequently, after welding the battery core with the connecting piece, it is placed into the battery case. After completing the processes of injecting electrolyte, sealing, and forming, the lithium-ion battery of Example 1 is obtained. The case of this lithium-ion battery is cylindrical, and its dimensional parameters are diameter: 46.0 mm, length 80.0 mm.

[0094] Example 2

[0095] The difference between this example and Example 1 is that the molar percentage of thiourea (CH4N2S) in the added precursor is 2.0%, that is, LiFePO4@NS - 2.0%, and the others are the same as those in Example 1.

[0096] Example 3

[0097] The difference between this example and Example 1 is that the molar percentage of thiourea (CH4N2S) in the added precursor is 3.0%, that is, LiFePO4@NS - 3.0%, and the others are the same as those in Example 1.

[0098] Example 4

[0099] The difference between this example and Example 1 is that the molar percentage of thiourea (CH4N2S) in the added precursor is 4.0%, that is, LiFePO4@NS - 4.0%, and the others are the same as those in Example 1.

[0100] Example 5

[0101] The difference between this example and Example 1 is that the molar percentage of thiourea (CH4N2S) in the added precursor is 5.0%, that is, LiFePO4@NS - 5.0%, and the others are the same as those in Example 1.

[0102] Example 6

[0103] The difference between this example and Example 1 is that the molar percentage of thiourea (CH4N2S) in the added precursor is 6.0%, that is, LiFePO4@NS-6.0%, and the others are the same as those in Example 1.

[0104] Example 7

[0105] The difference between this example and Example 1 is that the molar percentage of thiourea (CH4N2S) in the added precursor is 7.0%, that is, LiFePO4@NS-7.0%, and the others are the same as those in Example 1.

[0106] Example 8

[0107] The difference between this example and Example 1 is that the molar percentage of thiourea (CH4N2S) in the added precursor is 8.0%, that is, LiFePO4@NS-8.0%, and the others are the same as those in Example 1.

[0108] Example 9

[0109] The difference between this example and Example 1 is that the molar percentage of thiourea (CH4N2S) in the added precursor is 9.0%, that is, LiFePO4@NS-9.0%, and the others are the same as those in Example 1.

[0110] Example 10

[0111] The difference between this example and Example 1 is that the molar percentage of thiourea (CH4N2S) in the added precursor is 10.0%, that is, LiFePO4@NS-10.0%, and the others are the same as those in Example 1.

[0112] Example 11

[0113] The difference between this example and Example 7 is that the compaction of the positive electrode sheet is 2.25 g / cm 3 , and the others are the same as those in Example 7.

[0114] Example 12

[0115] The difference between this example and Example 7 is that the compaction of the positive electrode sheet is 2.35 g / cm 3 , and the others are the same as those in Example 7.

[0116] Example 13

[0117] The difference between this example and Example 7 is that the compaction of the positive electrode sheet is 2.55 g / cm 3 , and the others are the same as those in Example 7.

[0118] Example 14

[0119] The difference between this example and Example 7 is that the D of the positive electrode active material 50 is 0.8 μm, and the others are the same as those in Example 7.

[0120] Example 15

[0121] The difference between this example and Example 7 is that the D of the positive electrode active material 50 is 1.7 μm, and the others are the same as those in Example 7.

[0122] Example 16

[0123] The difference between this example and Example 7 is that the D of the positive electrode active material 50 is 7.6 μm, and the others are the same as those in Example 7.

[0124] Comparative Example 1

[0125] The difference between this example and Example 5 is that the lithium iron phosphate of the positive electrode active material is not subjected to nitrogen-sulfur co-doping, and the others are the same as those in Example 5.

[0126] Comparative Example 2

[0127] The difference between this example and Example 5 is that the added precursors are iron phosphate (FePO4), lithium carbonate (Li2CO3) and urea (CH4N2O), and the molar ratio is 100:100:10, that is, LiFePO4@N-5.0%, and the others are the same as those in Example 5.

[0128] Comparative Example 3

[0129] The difference between this example and Example 5 is that the added precursors are iron phosphate (FePO4), lithium carbonate (Li2CO3) and hydrogen sulfide (H2S), and the molar ratio is 100:100:10, that is, LiFePO4@S-5.0%, and the others are the same as those in Example 5.

[0130] Testing method for the lithium-ion battery of this application:

[0131] First, discharge the lithium-ion battery at a constant current to 2.5 V to ensure it is in a safe state, reducing the risk of short circuit or thermal runaway during disassembly. Inside a glove box (protected by argon or other inert atmosphere), carefully disassemble the battery and remove the positive electrode sheet of the cylindrical cell. Use tweezers or suitable tools to peel off the electrode sheet, avoiding damage to the active material layer. Then, cut the removed positive electrode sheet into appropriate sizes and soak it in an anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove the residual electrolyte and possible by-products. After taking out the electrode sheet, gently wipe the surface with dust-free wiping paper, then replace the fresh DMC solution and repeat the soaking-wiping process three times to ensure there are no residual contaminants on the electrode sheet surface. Subsequently, rinse the electrode sheet with anhydrous ethanol and wipe it again to further remove the solvent and impurities. After completing the cleaning, place the electrode sheet in the glove box and let it stand for 48 hours to ensure the electrode sheet is completely dry, preventing interference from solvent residues in subsequent tests. Gently scrape the positive active material layer of the dried electrode sheet using a plastic spatula or blade, ensuring that the collected powder is not contaminated. Transfer the scraped powder into a centrifuge tube filled with anhydrous ethanol and ultrasonically disperse it in an ultrasonic cleaner for 30 minutes to further remove possible residual electrolyte, binder, and impurities. After ultrasonic treatment, centrifuge the sample (set the rotation speed at 5000 rpm for 2 minutes), discard the supernatant, redisperse the powder with anhydrous ethanol, ultrasonically treat it for another 10 minutes, and then centrifuge again. Repeat this process three times to ensure the purity of the powder sample. Finally, collect the precipitate and transfer it to a vacuum drying oven, dry it at 80 °C for 12 hours to ensure complete removal of the residual solvent. Put the dried powder into a sealed bag or sealed sample box, immediately take it out of the glove box, and quickly perform XPS, Raman spectroscopy (Raman) characterization and active material particle D 50 testing.

[0132] Specific method for measuring the peak intensity (height) of the characteristic peaks corresponding to elements in the XPS spectrum: The XPS test uses a PHI-5000 Versa Probe device, with AlKα (1486.6 eV) as the X-ray source and the power set at 150 W (15 kV × 10 mA). The test includes a full-spectrum scan (0–1100 eV, step size 1 eV), background subtraction using Shirley background correction, and data normalization and elemental quantitative analysis using C1s (284.8 eV) as an internal standard.

[0133] Specific Raman measurement method: Use a 532 nm laser as the excitation light source. Set the laser power to 1–5 mW to avoid sample ablation. Uniformly disperse the sample on a silicon substrate. Collect Raman spectra in the range of 500 - 1500 cm-1. Set the spectral resolution to 1 cm-1 and accumulate scans 3 - 5 times to improve the signal-to-noise ratio. The instrument uses an XYZ automatic displacement platform for precise focusing and calibrates with a silicon wafer (520.7 cm-1) before testing to ensure data accuracy.

[0134] Positive electrode active material particle D 50 Specific measurement method:

[0135] Take a small amount of powder and evenly spread it on the conductive tape. Then, take clear particle images of at least 5 different regions under a scanning electron microscope (SEM). Import the images using ImageJ or Nanomeasure software. After calibrating the scale, manually or automatically measure the projected diameters of more than 200 particles. Arrange the data in ascending order and draw a cumulative distribution curve. Take the particle size value corresponding to a cumulative percentage of 50% as D 50 At the same time, it is necessary to exclude the interference data of obvious aggregates to ensure accuracy.

[0136] Test method for the compaction density of the positive electrode sheet:

[0137] First, cut the negative electrode sheet that has been rinsed with dimethyl carbonate and vacuum dried into 6 square samples of standard size (2.0 cm × 2.0 cm). Then, wipe off the active material on the front and back of 3 of the square samples, rinse with ethanol, dry, weigh, and calculate to obtain the average mass M1. At the same time, use a micrometer to measure the average thickness L1 of the samples. Then, weigh the mass of the other 3 square samples and calculate to obtain the average mass M2. At the same time, measure the average thickness L2 of the samples, and calculate the thickness of the electrode sheet: L2 - L1, in cm. Provide the following formula to calculate the compaction density of the electrode sheet (unit g / cm 3 )

[0138]

[0139] Test method for the discharge performance at a rate of 25 °C ambient temperature:

[0140] Place the battery in an incubator at 25 °C ambient temperature for 4 h and perform the test according to the following steps:

[0141] (1) Constant current and constant voltage charge to 3.65 V at 0.1 C, with a cut-off current of 0.01 C, and let it stand for 30 min;

[0142] (2) Constant current discharge to 2.5 V cut-off at 0.1 C, with the capacity meter reading Q1, and let it stand for 30 min;

[0143] (3) Constant current and constant voltage charge to 3.65 V under the condition of 0.1 C, with the cut-off current of 0.01 C, and stand for 30 min;

[0144] (4) Constant current discharge to 2.5 V cut-off under the condition of 10 C, with the capacity meter as Q2, and stand for 30 min;

[0145] The calculation method of the 10 C capacity retention rate is: Q2 / Q1×100.

[0146] Low temperature rate performance test method:

[0147] Place the lithium-ion battery with 100% SOC in a constant temperature oven at 25 °C for 6 h, and then discharge at a rate of 0.5 C to 2.5 V at 25 °C, with the discharge capacity as Q 25 ; Place the lithium-ion battery with 100% SOC in a constant temperature oven at -40 °C for 6 h, and then discharge at a rate of 5 C to 1.5 V or until the device temperature rises to 65 °C at -40 °C, with the discharge capacity as Q -40 , and count the discharge capacity retention rate Q 25 / Q -40 ×100.

[0148] Cycle performance test method:

[0149] Place the battery in a constant temperature oven at 25 °C for 4 h and conduct the test according to the following steps:

[0150] First cycle constant current and constant voltage charge: Constant current charge to 3.65 V at 0.1 C, and then switch to constant voltage charge until the current drops to 0.01 C.

[0151] After charging is completed, stand for 10 minutes.

[0152] Conduct constant current discharge, and discharge to 2.5 V at a rate of 0.1 C.

[0153] Repeat the above charging and discharging process: Constant current charge to 3.65 V at a rate of 1 C. Stand for 30 minutes again.

[0154] Constant current discharge to 2.5 V at a rate of 1 C.

[0155] Repeat the above charging and discharging process for a total of 1000 cycles.

[0156] Count the discharge capacities Q1 and Q of the battery after 1 cycle and 1000 cycles of cycling 1000 , and count the capacity attenuation rate of the battery (Q1 - Q 1000 ) / Q1×100.

[0157] Table 1

[0158]

[0159] As shown in Table 1, by comparing Examples 1 to 10, it can be seen that the lithium-ion battery of Example 7 has the most excellent room-temperature rate performance and low-temperature rate performance. At this time, I N / I Fe and I S / I Fe have values of 0.62 and 0.45. Deviating from this ratio will lead to a decline in the kinetic performance of the lithium-ion battery. In addition, as I N / I Fe > 0.62 and I S / I Fe > 0.45, the sequential performance of the lithium-ion battery shows a significant downward trend. This is attributed to the fact that there is an optimal threshold for the synergistic effect of co-doping nitrogen (N) and sulfur (S) in the lattice of lithium iron phosphate (LiFePO4). Specifically, in Examples 1-7 (increasing N / S ratio): as the doping amounts of N and S increase, N atoms replace some O sites to form the LiFeP(O,N)4 structure, and sulfur (S 2- ) then enters the lattice interstitial or replaces some P sites. This dual doping optimizes the electronic conduction network of LiFePO4 (N provides an electron transport path) and expands the lithium-ion diffusion channels (the larger ionic radius of S reduces the Li + migration barrier). When I N / I Fe = 0.62 and I S / I Fe = 0.45, the doping ratios of N and S reach the critical balance, forming both a continuous electronic conduction and ion diffusion network. Excessive N and S lead to increased lattice distortion, poorer lattice stability, and after N doping exceeds the threshold, local polarization of the Fe-N bond is triggered, hindering Li + diffusion and affecting the battery kinetic performance. By comparing Examples 7, 11 to 13, it can be seen that as the compaction gradually increases, the kinetic performance of the lithium battery also shows a trend of first increasing and then decreasing, which is attributed to the fact that the compaction density of the lithium iron phosphate positive electrode sheet also needs to be balanced between enhanced electron conduction and hindered ion transport. Moderate compaction improves the kinetic performance by optimizing particle contact and shortening the diffusion path, while excessive compaction leads to performance decline due to structural damage and insufficient electrolyte penetration. By comparing Examples 7, 14 to 16, it can be seen that as the active material D 50 of the positive electrode sheet gradually increases, there is a trend of decreasing kinetic performance and increasing cycle performance, which is attributed to the lithium iron phosphate active material D 50The increase reduces the kinetic performance by decreasing the reaction interface / extending the diffusion path, but improves the cycling stability by reducing the volume expansion / suppressing side reactions. Comparing Example 7 with Comparative Examples 1 to 3, it can be seen that whether nitrogen and sulfur doping are not carried out, or only nitrogen or sulfur is doped, the kinetic performance of the lithium battery is lower than that of the nitrogen-sulfur co-doping case. This is mainly attributed to the synergistic effect between the promotion of electron conductivity by nitrogen doping (N contribution) and the promotion of the optimization of lithium ion diffusion channels by sulfur doping (S contribution), effectively overcoming the limitations of single element doping, thereby significantly improving the rate performance and kinetic characteristics of the electrode material. As shown above, by optimizing the nitrogen-sulfur co-doping and the tap density and particle size of lithium iron phosphate, the rate performance and low temperature adaptability of lithium iron phosphate can be improved.

[0160] The above description and the drawings sufficiently 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 represent only possible variations. Unless explicitly required, the individual components and functions are optional, and the order of operations may 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 described above 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 limited only by the appended claims.

Claims

1. A lithium-ion battery, characterized in that, Comprising: a positive electrode sheet, comprising a positive electrode current collector and a positive electrode coating coated on at least one surface of the positive electrode current collector, the positive electrode coating comprising a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder; In the X-ray photoelectron spectrum of the positive electrode active material, there is an Fe2p characteristic peak corresponding to the intrinsic lithium iron phosphate in the binding energy range of 710.0 eV to 730.0 eV, an N1s characteristic peak corresponding to the lithium iron phosphate doped with N element modification in the binding energy range of 395.0 eV to 405.0 eV, an S2p characteristic peak corresponding to the lithium iron phosphate doped with S element modification in the binding energy range of 163.0 eV to 169.0 eV, and the peak intensity of the characteristic peak satisfies the following relationship: 0.01 ≤ I N / I Fe ≤ 4.0, 0.01 ≤ I S / I Fe ≤ 3.0; Among them, I Fe is the peak intensity of the Fe2p characteristic peak, I N is the peak intensity of the N1s characteristic peak, I S is the peak intensity of the S2p characteristic peak, and the strength of the peak indicates the doping amounts of N element and S element.

2. The lithium-ion battery according to claim 1, wherein, In the Raman spectrum corresponding to the active material of the positive electrode sheet, a target characteristic peak appears at 940-970 cm -1 where the target characteristic peak corresponds to the symmetric stretching vibration of PO4 3- in lithium iron phosphate.

3. The lithium-ion battery according to claim 1, characterized in that, The particle size D corresponding to when the cumulative particle size distribution percentage of the positive electrode active material reaches 50% 50 is 500 nm - 10.0 μm, and the tap density is 2.0 - 2.8 g / cm 3 .

4. 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 standing at an ambient temperature of 25°C for 6 hours, it is discharged at a rate of 0.1C to 2.5V, and the corresponding discharge capacity is Q1. The discharge capacity when discharged at 10C to 2.5V is Q2, and the retention rate of the discharge capacity Q2 / Q1 ≥ 50%.

5. The lithium ion battery according to claim 1, characterized in that, The discharge characteristics of the lithium-ion battery are as follows: After a lithium-ion battery with a 100% charge rate is left standing at an ambient temperature of 25°C for 6 hours, it is discharged at a rate of 0.5C to 2.5V at an ambient temperature of 25°C, and the corresponding discharge capacity is Q 25 , a lithium-ion battery with a 100% charge rate is left standing at an ambient temperature of -40°C for 6 hours, and at an ambient temperature of -40°C, it is discharged at a discharge rate of 5C to a voltage of 1.5V or the temperature of the electrochemical device rises to 65°C. The discharge capacity of the electrochemical device in the constant current discharge operation is Q -40 , and the retention rate of the discharge capacity is Q -40 / Q 25 ≥50%.

6. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material includes lithium iron phosphate and / or lithium manganese iron phosphate.

7. The lithium-ion battery according to any one of claims 1 to 6, characterized in that, Further comprising: a negative electrode sheet, comprising a negative electrode current collector and a positive electrode coating coated on at least one surface of the negative electrode current collector, the negative electrode coating comprising a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

8. The lithium-ion battery according to claim 7, wherein The negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon; The negative electrode conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black; The negative electrode binder includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid, and styrene-butadiene rubber.

9. The lithium-ion battery according to claim 7, wherein, 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 any one of claims 1 to 6, characterized in that, Further comprising: an electrolyte, comprising a lithium salt, a solvent, and an additive, wherein the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluoro(oxalato)borate, and lithium bis(trifluoromethylsulfonyl)imide; wherein the solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and ethyl methyl carbonate; The additive includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, ethylene sulfate, ethylene sulfite, vinylene carbonate, and vinyl carbonate.

11. An electrical device, characterized in that, Comprising the lithium ion battery according to any one of claims 1 to 10.

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