CN114270568A

CN114270568A - Lithium supplement additive, electrochemical device comprising same, and electronic device

Info

Publication number: CN114270568A
Application number: CN202180004900.1A
Authority: CN
Inventors: 刘小浪; 周墨林
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2021-03-16
Filing date: 2021-03-16
Publication date: 2022-04-01
Also published as: WO2022193122A1

Abstract

The application relates to the technical field of energy storage, in particular to a lithium supplement additive, an electrochemical device comprising the same and electronic equipment. The application provides a lithium supplement additive which comprises aLi2S bZ cZmSn, wherein a/(b + cm) >1, a is more than 0 and less than or equal to 1, b is more than 0 and less than or equal to 1, c is more than or equal to 0, m is more than 0, n is more than 0, and Z comprises transition metal. The lithium supplement additive has good stability, higher specific capacity and a suitable decomposition voltage platform, and can provide an additional lithium source in the first charging process so as to make up the irreversible loss of lithium ions, improve the utilization rate of active materials and improve the cycle performance and capacity retention rate of an electrochemical device containing the lithium supplement additive.

Description

Lithium supplement additive, electrochemical device comprising same, and electronic device

Technical Field

The application relates to the technical field of energy storage, in particular to a lithium supplement additive, an electrochemical device comprising the same and electronic equipment.

Background

In recent years, electrochemical devices (e.g., lithium ion batteries) have been widely used in the fields of portable electronic devices, electric vehicles, power grid energy storage, and the like. For a conventional lithium ion battery, lithium ions are mainly derived from a positive active material and are transferred to a negative electrode during a first charge, while a stable solid electrolyte film (SEI) is formed on the surface of the negative electrode. The formation of the SEI film requires irreversible consumption of a portion of active lithium, resulting in a decrease in battery capacity and energy density. Lithium supplement is a common technology for improving the performance of the lithium ion battery, and the loss of active lithium in the first charging process can be compensated by introducing additional lithium ions into the battery, so that the energy density of the lithium ion battery is increased, and the lithium ion battery has a great application prospect.

At present, lithium ion batteries are mainly divided into a negative electrode lithium supplement mode and a positive electrode lithium supplement mode. The lithium supplement of the negative electrode usually uses high-activity lithium metal, the lithium metal needs to be carried out in severe environments such as a drying room, the investment of a factory building and equipment is huge, in addition, the compatibility of the lithium metal with the existing electrolyte and electrode binder materials is poor, more side reactions exist, great safety risks exist, and the popularization and the application of the lithium supplement of the negative electrode are restricted. In contrast, the lithium of the positive electrode is supplemented without directly using metallic lithium, so that the lithium-supplementing lithium-ion battery has higher safety and operability. The key point of the anode lithium supplement lies in the selection of lithium supplement additive materials, generally, the anode lithium supplement additive has good stability and high gram volume, and a decomposition voltage platform is matched with the existing battery system. The existing common positive electrode lithium supplement additive materials mainly comprise lithium-rich transition metal oxides and organic sacrificial lithium salts with Li-C-O composition. The lithium-rich transition metal oxides such as Li2NiO2 and Li5FeO4 have poor physical and chemical properties, often contain a large amount of residual alkali in the material and cannot be effectively eliminated, and the pole piece manufacturing process has a large gel risk. Although the materials are relatively stable, the organic sacrificial lithium salt such as Li2C2O4, Li2CO3, etc., has relatively low specific capacity, and the decomposition voltage is much higher than the charge cut-off voltage of the existing positive electrode material, and the decomposition can be effectively carried out only by overcharging, and a large amount of gas is generated by decomposition, which easily causes the high-temperature storage and the cyclic gas expansion failure of the battery.

Disclosure of Invention

An object of the present application is to provide a lithium supplement additive, and an electrochemical device and an electronic apparatus including the same, in an attempt to solve at least one of the problems existing in the related art to at least some extent.

According to a first aspect of the present application, there is provided a lithium replenishment additive comprising aLi2S bZ cZmSn, wherein a/(b + cm) >1, 0 < a ≦ 1, 0 < b ≦ 1, c ≧ 0, m >0, n >0, Z comprising a transition metal.

According to some embodiments of the present application, the Z comprises at least one of Fe, Co, Ni, Mn, Cu, Cr, or Mo; and/or the ZmSn comprises at least one of FeS, FeS2, CoS2, NiS2, MoS2, CuS or CuS 2.

According to some embodiments of the present application, the lithium supplement additive has a particle size of 1000 nm or less.

According to a second aspect of the present application, there is provided a method for preparing a lithium supplement additive, for preparing the lithium supplement additive according to any one of the above embodiments, comprising the steps of: mixing Li2S, a transition metal simple substance and a transition metal sulfide according to a metering ratio, and carrying out high-energy ball milling in a protective atmosphere to obtain the lithium supplement additive.

According to some embodiments of the present application, the high energy ball milling satisfies at least one of the following conditions: a) the rotating speed of the high-energy ball mill is 3000r/min to 6000 r/min; b) the high-energy ball milling time is 12h to 48 h; c) the mass ratio of the ball materials of the high-energy ball mill is 10: 1 to 50: 1.

according to a second aspect of the present application, there is also provided a method for preparing a lithium supplement additive, for preparing the lithium supplement additive according to any one of the above embodiments, comprising the steps of: mixing transition metal sulfide and metal lithium according to a metering ratio, and sintering in a protective atmosphere to enable the transition metal sulfide and the metal lithium to generate an oxidation-reduction reaction, thereby obtaining the lithium supplement additive.

According to some embodiments of the application, the temperature of the sintering is from 180 ℃ to 250 ℃.

According to a third aspect of the present application, there is provided an electrochemical device comprising a cathode, an anode, an electrolyte and a separator, at least one of the cathode, the anode and the separator comprising the lithium supplement additive according to any one of the above embodiments or the lithium supplement additive prepared by the preparation method according to any one of the above embodiments.

According to some embodiments of the application, the positive electrode comprises: a positive current collector; and a positive active material layer disposed on the positive current collector, the positive active material layer including a positive active material and the lithium supplement additive.

According to some embodiments of the application, the positive electrode comprises: a positive current collector; the positive electrode lithium supplement layer comprises the lithium supplement additive; and a positive electrode active material layer including a positive electrode active material; wherein the positive electrode lithium supplement layer is disposed between the positive electrode current collector and the positive electrode active material layer.

According to some embodiments of the application, the positive electrode comprises: a positive current collector; a positive electrode active material layer including a positive electrode active material; and a positive lithium supplement layer, wherein the positive lithium supplement layer comprises the lithium supplement additive; wherein the positive active material layer is disposed between the positive current collector and the positive lithium supplement layer.

According to some embodiments of the present application, the isolation film comprises: a porous substrate; and a positive lithium supplement layer disposed on the porous substrate, the positive lithium supplement layer comprising the lithium supplement additive; wherein the positive electrode lithium supplement layer is interposed between the porous substrate and the positive electrode.

According to some embodiments of the present application, the lithium supplement additive is present in an amount of 0.1 to 5% by mass, based on the mass of the positive electrode active material in the positive electrode.

According to a fourth aspect of the present application, there is provided an electronic device comprising the electrochemical device according to any one of the above embodiments.

The technical scheme of the application has at least the following beneficial effects: the lithium supplement additive has the advantages of high specific capacity, good stability, low decomposition voltage platform and the like, and therefore, the lithium supplement additive can be applied as a lithium supplement additive material with high efficiency and excellent performance. In the application process, the lithium supplement additive can release lithium ions to provide an additional lithium source, make up for irreversible capacity loss in the charge-discharge process of the electrochemical device, and optimize the first charge-discharge efficiency of the electrochemical device, so that the aim of improving the electrochemical performance of the electrochemical device is fulfilled. In addition, the lithium supplement additive can be compatible with the existing electrochemical device production process, is convenient to use and is convenient for large-scale popularization and application. The preparation method of the lithium supplement additive provided by the application is simple in condition, convenient to operate, strong in operability and suitable for industrial mass production. Additional aspects and advantages of embodiments of the present application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the present application.

Drawings

Drawings necessary for describing embodiments of the present application or the prior art will be briefly described below in order to describe the embodiments of the present application. It is to be understood that the drawings in the following description are only some of the embodiments of the present application. It will be apparent to those skilled in the art that other embodiments of the figures can be obtained from the structures illustrated in these figures.

FIG. 1 shows a graph comparing the first charge and discharge curves of the cells of example 4 of the present application with those of comparative example 1;

FIG. 2 shows XRD patterns of the positive electrode plate of the cell in the fully discharged state of the cells of the example 4 and the comparative example 1;

fig. 3 is a graph showing the capacity retention rate of the batteries of example 4 and comparative example 1 according to the cycle number.

Detailed Description

Embodiments of the present application will be described in detail below. The embodiments of the present application should not be construed as limiting the present application.

In the detailed description and claims, a list of items linked by the term "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if item A, B is listed, the phrase "at least one of A, B" means only a; only B; or A and B. In another example, if item A, B, C is listed, the phrase "at least one of A, B, C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.

It should be noted that the term "and/or"/"used herein is only one kind of association relationship describing associated objects, and means that there may be three relationships, for example, a and/or B, and may mean: a exists alone, A and B exist simultaneously, and B exists alone.

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

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the present application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

Generally, in an electrochemical device such as a lithium ion battery, during a first charging process, a negative electrode reacts with lithium ions to generate an SEI film, so that irreversible loss of the lithium ions is caused, and finally, active lithium in the lithium ion battery is reduced, and the energy density of the battery is reduced. The lithium supplement of the positive electrode is one of important technical means for improving the prior battery ED in a short time. In recent years, metal sulfides have been frequently used as high energy density positive electrode materials. Taking pyrite FeS2 as an example, the crystal structure is cubic, Pa3 space group, and Fe and 6S are bonded in octahedral coordination. When FeS2 is used as a positive electrode material, the discharge process is subjected to two-step reaction of FeS2+2Li + +2e- → Li2FeS2 and Li2FeS2+2Li + +2e- → 2Li2S + Fe in sequence, and the final product is a Li2S/Fe nano homogeneous phase compound. On the contrary, in the charging process of Li2S/Fe, the reactions sequentially occur as 2Li2S + Fe → Li2FeS2+2Li + +2e-, Li2FeS2 → Li2-xFeS2+ xLi + + xe- (0 ≤ x ≤ 0.8) and Li2-xFeS2 → FeSy + (2-y) S + (2-x) Li + + (2-x) e- (x >0.8), and when 4mol of Li + is extracted, the theoretical specific capacity can reach 725 mAh/g. Therefore, Li2S/Fe has higher specific capacity and lower decomposition voltage, and can be used as a positive electrode lithium supplement material with application potential. In the first charging process, due to the nucleation of the phase of polysulfide ions, Li2S/Fe has a larger overpotential, but the overpotential is generally less than 3.5V, namely the lithium removal potential is lower than the charge cut-off potential of the traditional lithium ion battery, so that the complete lithium removal of Li2S/Fe can be ensured, and meanwhile, the lithium insertion potential of a lithium removal product S is generally less than 2.4V, so that active lithium generated by the decomposition of Li2S/Fe during charging cannot be re-inserted back in the working range of the lithium ion battery, and the part of active lithium can be used for compensating the irreversible capacity loss of the lithium ion battery, thereby improving the capacity of the lithium ion battery. In addition, in addition to Li2S/Fe, the compound formed by Li2S and other nano-metals has the potential of being used as a lithium supplement additive of the positive electrode. Although Li2S is also characterized by high specific capacity, low decomposition voltage plateau, etc., it is not suitable for use alone as a positive electrode lithium supplement additive. The reason is that first of all Li2S has a very low conductivity, close to an insulator, and cannot be fully delithiated by itself; secondly, the stability of Li2S is poor, the Li2S is easy to react with water and oxygen in the air, and after being compounded with nano metal particles, the Li2S can reduce the contact area with the air and improve the air stability of the material; in addition, the elemental sulfur generated after the lithium is removed by the single Li2S has poorer conductivity, and is easy to form polysulfide Li2Sx, which is dissolved in the electrolyte, thereby causing the performance of the battery to be reduced.

Based on this, the inventor of the present application has made a great deal of research, aiming at improving the traditional positive electrode lithium supplement material, and by adopting the positive electrode lithium supplement additive material compounded by lithium sulfide, metal simple substance and metal sulfide, the positive electrode lithium supplement additive material has the advantages of high specific capacity, good stability, low decomposition voltage platform and the like, so that the positive electrode lithium supplement additive material can be used as the positive electrode lithium supplement additive to make up the irreversible capacity loss in the charging and discharging processes of the battery, and the electrochemical performance of the battery is improved.

Provided are a lithium supplement additive, a method for preparing the same, and an electrochemical device and an electronic device including the same.

Lithium supplementing additive

In some embodiments, the present application provides a lithium replenishment additive comprising aLi2S bZ cZmSn, wherein a/(b + cm) >1, 0 < a ≦ 1, 0 < b ≦ 1, c ≧ 0, m >0, n >0, and Z comprises a transition metal. Further, in some embodiments, c >0.

The composition of the lithium supplement additive represented by the above formula in the embodiments of the present application contains at least lithium sulfide, a transition metal simple substance, and optionally a metal sulfide containing a transition metal. The lithium supplement additive is used as a positive electrode lithium supplement material to be applied to an electrochemical device such as a lithium ion battery, so that Li2S and transition metal Z are subjected to conversion reaction to generate sulfide ZmSn and release Li < + > in the first charging process of the lithium ion battery (> 3.5V); when the subsequent discharge reaches 2.5V or above, the metal sulfide ZmSn generated in the positive pole piece can not re-embed Li +, namely the conversion reaction process is irreversible, and the redundant Li + can be used for compensating Li + consumed in processes of forming an SEI film on the negative pole and the like. On one hand, the metal sulfide has relatively stable physicochemical properties, for example, FeS2 is the main component of natural pyrite, and the risk of gas expansion does not exist, so that the lithium supplement additive has excellent stability; on the other hand, the metal sulfide can fill up the pores generated by the decomposition of the lithium supplement material, so that the direct contact area between the electrolyte and the active material is not increased too much, the occurrence of the related side reaction of the electrolyte is reduced, and the first charge-discharge efficiency, the energy density and the cycle performance of the lithium ion battery are improved.

Therefore, the provided lithium supplement additive has high specific capacity and a suitable decomposition voltage platform, and can provide an additional lithium source in the first charging process to make up the irreversible loss of Li < + > and improve the utilization rate of the positive active material. In addition, the lithium supplement additive provides an additional lithium source in the first charging process, part of the lithium supplement additive is stored in the anode in the form of active lithium, and the active lithium is slowly released in the subsequent charging and discharging processes of the battery to make up the irreversible loss of the active lithium in the circulating process, so that the capacity retention rate of the battery in the circulating process can be improved, namely the circulating performance of the battery is improved. When the lithium supplement additive is used as a positive electrode lithium supplement material and applied to an electrochemical device such as a lithium ion battery, the lithium ion battery has high energy density, and has a wide application prospect in the fields of 3C electronic products and batteries for electric vehicles. In addition, the lithium supplement additive has the characteristics of wide raw material source, relatively simple preparation process, easiness in realizing industrial production, lower cost and the like.

In some embodiments, according to some embodiments of the present application, the Z comprises at least one of Fe, Co, Ni, Mn, Cu, Cr, or Mo. In some embodiments, the transition metal Z is Fe. In some embodiments, the transition metal Z is Co. In some embodiments, the transition metal Z is Ni. In some embodiments, the transition metal Z is Mn. In some embodiments, the transition metal Z is Cu. In some embodiments, the transition metal Z is Cr. In some embodiments, the transition metal Z is Mo. In some embodiments, the transition metal Z is any two or more of Fe, Co, Ni, Mn, Cu, Cr, or Mo.

In some embodiments, the ZmSn comprises at least one of FeS, FeS2, CoS2, NiS2, MoS2, CuS, or CuS 2. It is understood that the metal element in the metal sulfide in the lithium supplement additive described herein can be selected and collocated arbitrarily among the elements Fe, Co, Ni, Mn, Cu, Cr, or Mo, and for clarity and simplicity of description, the present application only discusses some of them, such as FeS2, CoS, or CuS2, as examples.

In some embodiments, the ZmS may be FeS 2.

In some embodiments, the ZmS can be CoS.

In some embodiments, the ZmS may be CuS 2.

In some embodiments, 0.5 ≦ a ≦ 1, and further, 0.5 ≦ a ≦ 0.8. In some embodiments, 0.1 ≦ b ≦ 0.9, further, 0.3 ≦ b ≦ 0.8. In addition, the composition of the lithium supplement additive can obtain the expected lithium supplement capacity when the composition of the lithium supplement additive is in the range, so the composition of the specific lithium supplement additive can be adjusted according to the target requirement.

In some embodiments, the lithium supplement additive has a particle size of 1000 nm or less. The lithium supplement additive in the embodiment of the application is in a nanometer level, the particle size of the lithium supplement additive is larger than 0 and smaller than or equal to 1000 nanometers, and if the particle size of the lithium supplement additive is too large, the reaction activity of the material is not favorably improved. In some embodiments, the lithium supplement additive has a particle size of 900 nm or less. In some embodiments, the lithium supplement additive has a particle size of 800 nm or less.

Preparation method of lithium supplement additive

The lithium supplement additive can be prepared by a high-energy ball milling method or a metal melting method, and has the characteristics of wide raw material source, relatively simple preparation process, easiness in industrial production, lower cost and the like.

In some embodiments, the present application provides a method for preparing a lithium supplement additive by using a high energy ball milling method, the method comprising the steps of:

and weighing Li2S, the transition metal simple substance and the transition metal sulfide according to a metering ratio, uniformly mixing, and carrying out high-energy ball milling in a protective atmosphere to obtain the lithium supplement additive.

It should be noted that the preparation process of the high-energy ball milling of the lithium supplement additive needs to be carried out under a protective atmosphere. The kind of the protective atmosphere is not limited in the embodiments of the present application, and may be at least one of inert gases such as argon, nitrogen, neon, and the like. In some embodiments, the present application discusses argon as an exemplary protective atmosphere, but it is understood that the type of protective atmosphere is not limited thereto.

In theory, after the amolLi2S, bmolZ and cmolZmSn are subjected to the high-energy ball milling treatment, a lithium supplement additive with a chemical composition of aLi2S bZ cZmSn can be obtained, wherein a/(b + cm) >1, a is more than 0 and less than or equal to 1, b is more than 0 and less than or equal to 1, c is more than or equal to 0, m is more than 0, n is more than 0, and Z comprises transition metal.

In some embodiments, the high energy ball mill rotates at a speed of 3000r/min to 6000 r/min. In some embodiments, the high energy ball mill rotates at a speed of 3000r/min to 5000 r/min. In some embodiments, the high energy ball mill rotates at a speed of 3000r/min to 4000 r/min.

In some embodiments, the high energy ball milling time is from 12h to 48 h. In some embodiments, the high energy ball milling time is 20h to 40 h. In some embodiments, the high energy ball milling time is from 24h to 36 h.

In the high-energy ball milling process, if the ball milling time is too short, for example, the ball milling time is less than 12 hours, the raw materials are not uniformly mixed, and the particle size is too large, so that the reaction activity of the materials is not improved; when the ball milling time is too long, for example, the ball milling time exceeds 48 hours, the particle size of the material reaches the nanometer level, the ball milling time is further prolonged, the material is not beneficial to further refinement, and the efficiency is reduced.

In some embodiments, the high energy ball mill has a mass ratio of 10: 1 to 50: 1. in some embodiments, the high energy ball mill has a mass ratio of 15: 1 to 40: 1. in some embodiments, the high energy ball mill has a mass ratio of 20: 1 to 35: 1.

as an exemplary embodiment, a method for preparing a lithium supplement additive by using a high energy ball milling method comprises: under the condition of argon atmosphere, weighing Li2S, a metal simple substance and a metal sulfide raw material according to a metering ratio, uniformly mixing, and carrying out high-energy ball milling under the protection of argon atmosphere, wherein the rotating speed is 3500r/min, and the ball milling time is 24 h; and after the ball milling is finished, sieving the mixture by a 400-mesh sieve to obtain the lithium supplement additive.

In some embodiments, the present application also provides another method for preparing a lithium supplement additive by using a metal melting method, the method comprising the steps of:

weighing and mixing transition metal sulfide and metal lithium according to a metering ratio, then sintering in a protective atmosphere, and enabling the transition metal sulfide and the metal lithium to generate an oxidation-reduction reaction in the sintering process to obtain the lithium supplement additive. Further, in some embodiments, the transition metal sulfide and the lithium metal undergo a redox reaction during sintering to form a composite product of aLi2S · bZ · cZmSn, and then the ball milling is continued to obtain the lithium supplement additive.

It should be noted that the metal melting preparation process of the lithium supplement additive needs to be carried out under a protective atmosphere. The kind of the protective atmosphere is not limited in the embodiments of the present application, and may be at least one of inert gases such as argon, nitrogen, neon, and the like. In some embodiments, the present application discusses argon as an exemplary protective atmosphere, but it is understood that the type of protective atmosphere is not limited thereto.

In some embodiments, the temperature of the sintering is 180 ℃ to 250 ℃. In some embodiments, the temperature of the sintering is 190 ℃ to 220 ℃. In some embodiments, the temperature of the sintering is about 200 ℃.

The lithium supplement additive is prepared by adopting a metal melting method, metal lithium and metal sulfide are subjected to redox reaction in the sintering process, the nano metal simple substance and Li2S generated in situ can be compounded more uniformly in theory, and then the target lithium supplement additive can be obtained by ball milling and grinding.

Compared with a metal melting method, the method for preparing the lithium supplement additive by adopting the high-energy ball milling method has the advantages that the synthesis process is more controllable, and the preparation of the lithium supplement additive with required performance is more facilitated.

The lithium supplement additive prepared by the preparation method provided by the embodiment of the application has stable properties, and can be used for making up the irreversible active lithium loss caused by the SEI film formation in the first charging process of the lithium ion battery, so that the reversible capacity of the lithium ion battery is improved.

Electrochemical device

In some embodiments, the present application provides an electrochemical device comprising a cathode, an anode, an electrolyte, and a separator, at least one of the cathode, the anode, and the separator comprising a lithium supplement additive as described in any of the above embodiments or prepared by a method of making as described in any of the above embodiments.

When the provided lithium supplement additive is applied to an electrochemical device, various addition modes can be provided, and the addition modes of the additive include, but are not limited to the following modes: (1) firstly, coating a lithium supplement additive on a positive current collector in a priming mode, and then coating a positive material containing a positive active material; (2) coating a positive electrode material containing a positive electrode active material on a positive electrode current collector, and coating a lithium supplement additive layer on the surface of a positive electrode piece; (3) directly mixing the lithium supplement additive with a positive electrode material containing a positive electrode active material to prepare mixed slurry and coating the mixed slurry; (4) and spraying the lithium supplement additive on the side of the isolating membrane facing the positive electrode.

It is to be understood that the layered structure including the lithium supplement additive may be provided on one surface of the positive electrode current collector, or may also be provided on both surfaces of the positive electrode current collector, or may be provided on one surface of the separator, or may also be provided on both surfaces of the separator.

In addition, the lithium supplement additive can be added by coating, for example, by deposition. For example, the lithium supplement additive may be coated or deposited on the positive electrode current collector before the positive electrode material including the positive electrode active material is coated or deposited. Or, coating or depositing a positive electrode material containing a positive electrode active material on the positive electrode current collector, and coating or depositing a lithium supplement additive layer on the surface of the positive electrode piece.

Therefore, based on at least the above addition modes, the lithium supplement additive of the embodiment can be contained in the positive electrode or the separation film in the electrochemical device, and the specific structure of the positive electrode or the separation film can have various forms. In particular, in some embodiments, the lithium supplement additives of the embodiments of the present application can be included in a positive electrode in an electrochemical device.

In some embodiments, the positive electrode comprises:

a positive current collector; and

and the positive active material layer is arranged on the positive current collector and comprises a positive active material and the lithium supplement additive.

The positive electrode may be obtained by preparing a material including a positive electrode active material and a lithium supplement additive into a mixed positive electrode slurry, and coating or depositing the mixed positive electrode slurry on a positive electrode current collector. That is, the lithium supplement additive is added in a mixed coating manner, and the resulting mixed coating layer containing the positive electrode active material and the lithium supplement additive in the positive electrode. It is to be understood that the above mixed positive electrode slurry may further include a conductive agent, a binder, and a solvent. Therefore, the lithium ion battery is convenient to process and manufacture, and is beneficial to controlling the addition of the lithium supplement additive, thereby being beneficial to improving the relevant electrochemical performance of the electrochemical device.

In some embodiments, the positive electrode comprises:

a positive current collector;

the positive electrode lithium supplement layer comprises the lithium supplement additive; and

a positive electrode active material layer including a positive electrode active material;

wherein the positive electrode lithium supplement layer is disposed between the positive electrode current collector and the positive electrode active material layer.

The method comprises the steps of coating a first slurry containing a lithium supplement additive on a positive electrode current collector, drying to form a positive electrode lithium supplement layer, and coating a second slurry containing a positive electrode active material on the positive electrode lithium supplement layer to form a positive electrode active material layer on the surface of the positive electrode lithium supplement layer. That is, the lithium supplement additive is added in a manner of priming. Generally, the first paste may further include a conductive agent and a binder, and the second paste may further include a conductive agent, a binder, and a solvent.

In some embodiments, the positive electrode comprises:

a positive current collector;

a positive electrode active material layer including a positive electrode active material; and

the positive electrode lithium supplement layer comprises the lithium supplement additive;

wherein the positive active material layer is disposed between the positive current collector and the positive lithium supplement layer.

And coating the second slurry containing the positive electrode active material on a positive electrode current collector, drying to form a positive electrode active material layer, and coating the first slurry containing the lithium supplement additive on the positive electrode active material layer to form a positive electrode lithium supplement layer on the surface of the positive electrode active material layer. That is, the lithium supplement additive is added in a top coating manner. Generally, the first paste may further include a conductive agent and a binder, and the second paste may further include a conductive agent, a binder, and a solvent.

In some embodiments, the isolation film comprises:

a porous substrate; and

a positive lithium supplement layer disposed on the porous substrate, the positive lithium supplement layer comprising the lithium supplement additive;

wherein the positive electrode lithium supplement layer is interposed between the porous substrate and the positive electrode. The anode lithium supplement layer is arranged on the isolating membrane and is positioned on one side of the isolating membrane facing the anode.

In order to ensure the lithium supplement effect, in some embodiments, the lithium supplement additive is included in an amount of 0.1 to 5% by mass based on the mass of the positive electrode active material in the positive electrode. In some embodiments, the lithium supplement additive is present in an amount of 0.5 to 4% by mass, based on the mass of the positive electrode active material in the positive electrode. In some embodiments, the lithium supplement additive is present in an amount of 1 to 3% by mass, based on the mass of the positive electrode active material in the positive electrode. In some embodiments, the mass percent of the lithium replenishment additive is about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.8%, about 1%, about 1.5%, about 2%, about 2.5%, about 2.8%, about 3%, about 3.2%, about 3.5%, about 4%, about 4.5%, about 5%, etc., based on the mass of the positive electrode active material in the positive electrode. By controlling the adding content of the lithium supplement additive within the proper range, the negative effects possibly brought by adding excessive lithium supplement additive, such as increased thickness of the positive pole piece, incomplete decomposition, increased side reactions and the like, can be avoided; the problem of unobvious improvement of battery efficiency and cycle performance caused by adding too little lithium supplement additive can also be avoided.

In some embodiments, the positive electrode active material layer of the positive electrode further includes a conductive agent to impart conductivity to the electrode. The conductive agent may include any conductive material commonly used in the art as long as it does not cause a chemical change. As an example, the conductive agent may be selected from one or more of graphite, conductive carbon black, superconducting carbon, acetylene black, ketjen black, carbon dots, graphene, carbon nanotubes, or carbon nanofibers.

In some embodiments, the positive electrode active material layer of the positive electrode further includes a binder, and the binder may improve the binding of the positive electrode active material particles to each other and the binding of the positive electrode active material to the positive electrode current collector. The binder may be any binder commonly used in the art. As an example, the binder may be selected from one or more of polyethylene, polypropylene, polyvinyl chloride, styrene-butadiene rubber (SBR), water-based acrylic resin (water-based acrylic resin), carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

In addition, the conductive agent and the binder included in the lithium supplement layer of the positive electrode may also be selected from at least one of the conductive agents and the binders listed above, and will not be described in detail herein.

In some embodiments, the positive electrode current collector may employ a positive electrode current collector commonly used in the art. As an example, the positive current collector is a metal, including, but not limited to, aluminum foil, for example.

In some embodiments, the lithium supplement additive, the positive active material, the conductive agent, and the binder are mixed in a certain ratio and uniformly coated on a positive current collector (e.g., an aluminum current collector) to prepare the above-described positive electrode.

In some embodiments, the selection of the positive active material in the positive electrode is not limited in the embodiments of the present application, and may be selected according to the requirement. For example, the positive electrode active material includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive active material may include a lithium transition metal composite oxide.

In some embodiments, the positive active material includes, but is not limited to, at least one of LiFePO4, LiMnO2, LiCoO2, NCM, and NCA, wherein NCM and NCA are a Ni-Co-Mn ternary positive material and a Ni-Co-Al ternary positive material, respectively. It is to be understood that the positive electrode lithium supplement additive is not limited to lithium supplement of the positive electrode active material described above.

In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

In some embodiments, the negative active material layer includes a negative active material, a binder, and a conductive agent. The negative electrode active material is capable of reversibly intercalating and deintercalating lithium ions (sometimes referred to as "a negative electrode active material capable of absorbing/releasing lithium"). According to some embodiments of the present application, the specific kind of the negative active material is not particularly limited and may be selected as desired. In some embodiments, examples of the negative active material may include one or more of a carbon material, a metal compound, an oxide, a sulfide, a nitride of lithium, metallic lithium, a metal alloyed with lithium, and a polymer material. Among them, examples of the carbon material may include, but are not limited to: crystalline carbon, amorphous carbon, or mixtures thereof. The crystalline carbon may be amorphous, flake, platelet, spherical or fibrous natural or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or the like.

In some embodiments, the negative active material the positive active material includes, but is not limited to, one or more of graphite, hard carbon, tin, silicon oxygen, silicon carbon, and composites thereof.

In some embodiments, the negative electrode current collector may be a negative electrode current collector commonly used in the art. The negative electrode collector may be made of a metal foil or a porous metal plate, for example, a foil or a porous plate made of a metal such as copper, nickel, titanium, or iron, or an alloy thereof, such as copper foil.

In some embodiments, the structure of the negative electrode and the method for preparing the negative electrode are a negative electrode sheet structure that can be used in an electrochemical device and a method for preparing a negative electrode that can be used in an electrochemical device. Illustratively, the negative electrode may be obtained by: the active material, the conductive agent, and the binder are mixed in a solvent, and a thickener may be added as needed to prepare an active material composition, and the active material composition is coated on a current collector. In some embodiments, the solvent may include, but is not limited to, water, N-methyl pyrrolidone.

In order to achieve the effect of lithium supplement, it is necessary to satisfy the requirement that the first effect of the positive active material in the lithium ion battery is greater than that of the negative active material in principle, and the larger the difference between the first effects of the positive electrode and the negative electrode is, the more significant the lithium supplement is in the improvement of the battery capacity.

The first effect of the positive active material is the ratio of the first discharging gram capacity to the first charging gram capacity of the positive active material in the half cell. The first effect of the negative active material is the ratio of the first charge gram capacity to the first discharge gram capacity of the negative active material in the half-cell.

In some embodiments, the separator may be any of a variety of materials known in the art for use as separators for electrochemical energy storage devices, and may for example include, but are not limited to, polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, natural fibers, or a combination of one or more of aramid. For example, the polyethylene includes at least one component selected from the group consisting of high density polyethylene, low density polyethylene, and ultra high molecular weight polyethylene. In particular polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of lithium ion batteries by means of a shutdown effect.

The material and shape of the separator are not particularly limited in the embodiments of the present application, and any known separator having a porous structure and having electrochemical stability and chemical stability may be used, for example, the separator includes a substrate layer, and the substrate layer is a nonwoven fabric, a membrane or a composite membrane having a porous structure. In some embodiments, the substrate layer of the separator is, for example, one or more of Polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), a composite of polyethylene and polypropylene, fiberglass, and non-woven fabric.

In some embodiments, the electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte solution including a lithium salt and a non-aqueous solvent. The electrolyte that may be used in the embodiments of the present application may be an electrolyte known in the art.

Lithium salts that may be used in the electrolytes of embodiments of the present application include, but are not limited to: inorganic lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiSbF6, LiSO3F, LiN (FSO2)2, and the like; fluorine-containing organic lithium salts such as LiCF3SO3, LiN (FSO2) (CF3SO2), LiN (CF3SO2)2, LiN (C2F5SO2)2, cyclic 1, 3-hexafluoropropane disulfonimide lithium, cyclic 1, 2-tetrafluoroethane disulfonimide lithium, LiPF4(CF3)2, LiN (CF3SO2) (C4F9SO2), LiC (CF3SO2)3, LiPF4(CF3SO2)2, LiPF4(C2F5)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2) 2; the dicarboxylic acid complex-containing lithium salt may, for example, be lithium bis (oxalato) borate, lithium difluorooxalato borate, lithium tris (oxalato) phosphate, lithium difluorobis (oxalato) phosphate, lithium tetrafluoro (oxalato) phosphate, or the like. The electrolyte may be used alone or in combination of two or more. For example, in some embodiments, the lithium salt is selected to include LiPF6 because it can give high ionic conductivity and improve cycling characteristics.

In some embodiments, the non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.

In some embodiments, the carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.

In some embodiments, examples of the chain carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), or a combination thereof. Examples of the fluoro carbonate compound are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1,2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or a combination thereof.

In some embodiments, examples of carboxylate compounds are methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonic lactone, caprolactone, methyl formate, or combinations thereof.

In some embodiments, examples of ether compounds are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

In some embodiments, examples of other organic solvents are dimethyl sulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, phosphate esters, or combinations thereof.

The electrochemical device of the present application may be a lithium ion battery or a lithium metal battery, and may be any other suitable electrochemical device. For example, the electrochemical device in the embodiments of the present application includes any device in which an electrochemical reaction occurs, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors, without departing from the disclosure of the present application. In particular, the electrochemical device is a lithium secondary battery including, but not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

Electronic equipment

In some embodiments, the present application provides an electronic device comprising the aforementioned electrochemical device.

According to the positive electrode lithium supplement agent and the preparation method thereof, the positive electrode lithium supplement agent has the advantages of high specific capacity, good stability, proper and low decomposition voltage platform and the like, can be used as a positive electrode lithium supplement additive, makes up irreversible capacity loss in the charging and discharging processes of a battery, improves the electrochemical performance of an electrochemical device, and enables the electrochemical device manufactured by the lithium supplement additive to be suitable for electronic equipment in various fields.

The use of the electrochemical device of the present application is not particularly limited, and it can be used for any electronic apparatus known in the art. For example, the electronic devices include, but are not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copiers, portable printers, headphones, video recorders, liquid crystal televisions, portable cleaners, portable CDs, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, lighting fixtures, toys, game machines, clocks, electric tools, flashlights, cameras, large household batteries, lithium ion capacitors, and the like. In addition, the electrochemical device of the present application is applicable to an energy storage power station, a marine vehicle, and an air vehicle, in addition to the above-exemplified electronic devices. The air transport carrier device comprises an air transport carrier device in the atmosphere and an air transport carrier device outside the atmosphere.

Fifth, example

The present application will be described in more detail with reference to specific examples and comparative examples, but the present application is not limited to these examples as long as the gist thereof is not deviated. In the following examples and comparative examples, reagents, materials and instruments used therefor were commercially available unless otherwise specified. The positive electrode current collectors in the examples and comparative examples were all aluminum foils, and the negative electrode current collectors were all copper foils.

The lithium ion batteries in examples and comparative examples were prepared by the following preparation methods.

The preparation of the lithium supplement additive in each example included: under the condition of argon atmosphere, weighing Li2S, a metal simple substance and a metal sulfide raw material according to a metering ratio, uniformly mixing, and carrying out high-energy ball milling under the protection of argon atmosphere, wherein the rotating speed is 3500r/min, and the ball milling time is 24 h; and after the ball milling is finished, sieving the mixture by a 400-mesh sieve to obtain the lithium supplement additive.

Example 1

(1) Preparing a lithium supplement additive: under the condition of argon atmosphere, weighing Li2S, nano iron powder, nano copper powder, nano cobalt powder and sulfide raw materials according to a metering ratio, uniformly mixing, and carrying out high-energy ball milling under the protection of argon atmosphere, wherein the rotating speed is 3500r/min, and the ball milling time is 24 h; and after the ball milling is finished, sieving the mixture by a 400-mesh sieve to obtain the lithium supplement additive, wherein the lithium supplement additive is marked as LPD-1.

The nominal components and designations of the lithium supplement additives in each example are shown in table 1 below.

(2) Preparation of the positive electrode: dissolving polyvinylidene fluoride (PVDF) serving as an adhesive in N-methylpyrrolidone (NMP), respectively adding a positive electrode active material (LiFePO4), conductive carbon (SP) serving as a conductive agent and a lithium supplement additive LPD-1, uniformly stirring to obtain positive electrode slurry, coating the positive electrode slurry on the front side and the back side of an aluminum foil with the thickness of 13 mu m, performing forced air drying at 85 ℃, performing cold pressing and splitting, and rolling to obtain the positive electrode. Wherein the mass ratio of LiFePO4, PVDF and SP is 90: 5: 5. the mass fraction of the lithium supplement additive LPD-1 relative to the positive electrode active material is 0.5%.

(3) Preparation of a negative electrode: styrene butadiene rubber emulsion (SBR) as a binder and sodium carboxymethyl cellulose (CMC) as a thickener are dissolved in deionized water, and then the artificial graphite as a negative electrode active material and conductive carbon (SP) as a conductive agent are respectively added. Wherein the mass ratio of the artificial graphite to the SBR to the CMC to the SP is 97: 1.5: 0.5: 1. and after uniformly stirring, coating the obtained negative electrode slurry on the front and back surfaces of a 9-micron copper foil, then performing forced air drying at 105 ℃, performing cold pressing and stripping, and rolling to obtain the negative electrode.

(4) Preparing a lithium ion battery: sequentially stacking the prepared positive electrode, the prepared isolating film and the prepared negative electrode, wherein the isolating film is positioned between the positive electrode piece and the negative electrode piece to play a role in isolating electron transmission and allowing lithium ions to pass through, and then winding to obtain a bare cell; placing the bare cell in an aluminum-plastic film packaging bag, carrying out top sealing and vacuum drying, injecting electrolyte (1M LiPF6 is dissolved in an organic solvent formed by mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC) according to a volume ratio of 1: 1: 1), and carrying out vacuum packaging, standing, formation and other processes to obtain the lithium ion battery.

And carrying out capacity test and cycle performance test on the lithium ion battery.

Example 2

A lithium ion battery was prepared and subjected to a capacity test and a cycle performance test by the method of example 1.

Example 2 differs from example 1 in that: in the step (2), the mass fraction of the lithium supplement additive LPD-1 relative to the positive electrode active material is 1.0%.

Example 3

Example 3 differs from example 1 in that: in the step (2), the mass fraction of the lithium supplement additive LPD-1 relative to the positive electrode active material is 3.0%.

Example 4

Example 4 differs from example 1 in that: in the step (2), the mass fraction of the lithium supplement additive LPD-1 relative to the positive electrode active material is 5.0%.

Example 5

Example 5 differs from example 1 in that: in the step (2), the mass fraction of the lithium supplement additive LPD-1 relative to the positive electrode active material is 7.0%.

Example 6

Example 6 differs from example 1 in that: in the step (1), the prepared lithium supplement additive is LPD-2; in the step (2), the mass fraction of the lithium supplement additive LPD-2 relative to the positive electrode active material is 4.0%.

Example 7

Example 7 differs from example 1 in that: in the step (1), the prepared lithium supplement additive is LPD-3; in the step (2), the mass fraction of the lithium supplement additive LPD-3 relative to the positive electrode active material is 5.0%.

Example 8

Example 7 differs from example 1 in that:

the lithium supplement additive prepared in the step (1) is LPD-2.

Preparing the anode in the step (2): dissolving polyvinylidene fluoride (PVDF) serving as a binder in N-methylpyrrolidone (NMP), respectively adding a positive electrode active material (LiCoO2), conductive carbon (SP) serving as a conductive agent and a lithium supplement additive LPD-2, uniformly stirring to obtain positive electrode slurry, coating the positive electrode slurry on the front side and the back side of an aluminum foil with the thickness of 13 mu m, performing forced air drying at 85 ℃, performing cold pressing and splitting, and rolling to obtain the positive electrode. Wherein the mass ratio of LiCoO2, PVDF and SP is 90: 5: 5. the mass fraction of the lithium supplement additive LPD-2 relative to the positive electrode active material is 2.0%.

Preparing a negative electrode in the step (3): styrene butadiene rubber emulsion (SBR) as a binder and sodium carboxymethyl cellulose (CMC) as a thickener are dissolved in deionized water, and then artificial graphite (C/15% SiO) compounded with 15% SiO as a negative electrode active material and conductive carbon (SP) as a conductive agent are respectively added. Wherein the mass ratio of C/15% SiO, SBR, CMC and SP is 95: 1.5: 0.5: 3. and after uniformly stirring, coating the obtained negative electrode slurry on the front and back surfaces of a 9-micron copper foil, then performing forced air drying at 105 ℃, performing cold pressing and stripping, and rolling to obtain the negative electrode.

Example 9

A lithium ion battery was prepared and tested for capacity and cycle performance using the method of example 8.

Example 9 differs from example 8 in that: in the step (2), the mass fraction of the lithium supplement additive LPD-2 relative to the positive electrode active material is 3.0%.

Example 10

Example 10 differs from example 8 in that: in the step (2), the mass fraction of the lithium supplement additive LPD-2 relative to the positive electrode active material is 5.0%.

Example 11

Example 11 differs from example 8 in that: in the step (2), the mass fraction of the lithium supplement additive LPD-2 relative to the positive electrode active material is 8.0%.

Example 12

Example 12 differs from example 8 in that: in the step (1), the prepared lithium supplement additive is LPD-1; in the step (2), the mass fraction of the lithium supplement additive LPD-1 relative to the positive electrode active material is 3.0%.

Example 13

Example 13 differs from example 8 in that: in the step (1), the prepared lithium supplement additive is LPD-3; in the step (2), the mass fraction of the lithium supplement additive LPD-3 relative to the positive electrode active material is 4.5%.

Example 14

Example 14 differs from example 8 in that: in the step (1), the prepared lithium supplement additive is LPD-1; in the step (2), the mass fraction of the lithium supplement additive LPD-1 relative to the positive active material is 2.0%; and (4) preparing the cathode in the step (3), wherein the cathode active material is hard carbon.

Example 15

Example 15 differs from example 8 in that: in the step (2), the mass fraction of the lithium supplement additive LPD-2 relative to the positive active material is 2.5%; and (4) preparing the cathode in the step (3), wherein the cathode active material is hard carbon.

Example 16

Example 16 differs from example 8 in that: in the step (1), the prepared lithium supplement additive is LPD-3; in the step (2), the mass fraction of the lithium supplement additive LPD-31 relative to the positive active material is 4.0%; and (4) preparing the cathode in the step (3), wherein the cathode active material is hard carbon.

Comparative example 1

(1) Preparation of the positive electrode: dissolving polyvinylidene fluoride (PVDF) serving as a binder in N-methylpyrrolidone (NMP), respectively adding a positive electrode active material (LiFePO4) and conductive carbon (SP) serving as a conductive agent, uniformly stirring to obtain positive electrode slurry, coating the positive electrode slurry on the front side and the back side of an aluminum foil with the thickness of 13 mu m, performing forced air drying at 85 ℃, performing cold pressing and splitting, and rolling to obtain the positive electrode. Wherein the mass ratio of LiFePO4, PVDF and SP is 90: 5: 5.

(2) preparation of a negative electrode: styrene butadiene rubber emulsion (SBR) as a binder and sodium carboxymethyl cellulose (CMC) as a thickener are dissolved in deionized water, and then the artificial graphite as a negative electrode active material and conductive carbon (SP) as a conductive agent are respectively added. Wherein the mass ratio of the artificial graphite to the SBR to the CMC to the SP is 97: 1.5: 0.5: 1. and after uniformly stirring, coating the obtained negative electrode slurry on the front and back surfaces of a 9-micron copper foil, then performing forced air drying at 105 ℃, performing cold pressing and stripping, and rolling to obtain the negative electrode.

(3) Preparing a lithium ion battery: sequentially stacking the prepared positive electrode, the prepared isolating film and the prepared negative electrode, wherein the isolating film is positioned between the positive electrode piece and the negative electrode piece to play a role in isolating electron transmission and allowing lithium ions to pass through, and then winding to obtain a bare cell; placing the bare cell in an aluminum-plastic film packaging bag, carrying out top sealing and vacuum drying, injecting electrolyte (1M LiPF6 is dissolved in an organic solvent formed by mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC) according to a volume ratio of 1: 1: 1), and carrying out vacuum packaging, standing, formation and other processes to obtain the lithium ion battery.

Comparative example 2

A lithium ion battery was prepared and subjected to a capacity test and a cycle performance test by the method of comparative example 1.

Comparative example 2 differs from comparative example 1 in that:

preparing a positive electrode in the step (1): dissolving polyvinylidene fluoride (PVDF) serving as a binder in N-methylpyrrolidone (NMP), respectively adding a positive electrode active material (LiCoO2) and conductive carbon (SP) serving as a conductive agent, uniformly stirring to obtain positive electrode slurry, coating the positive electrode slurry on the front side and the back side of an aluminum foil with the thickness of 13 mu m, performing forced air drying at 85 ℃, performing cold pressing and striping, and rolling to obtain the positive electrode. Wherein the mass ratio of LiCoO2, PVDF and SP is 90: 5: 5.

preparing a negative electrode in the step (2): styrene butadiene rubber emulsion (SBR) as a binder and sodium carboxymethyl cellulose (CMC) as a thickener are dissolved in deionized water, and then artificial graphite (C/15% SiO) compounded with 15% SiO as a negative electrode active material and conductive carbon (SP) as a conductive agent are respectively added. Wherein the mass ratio of C/15% SiO, SBR, CMC and SP is 95: 1.5: 0.5: 3. and after uniformly stirring, coating the obtained negative electrode slurry on the front and back surfaces of a 9-micron copper foil, then performing forced air drying at 105 ℃, performing cold pressing and stripping, and rolling to obtain the negative electrode.

Comparative example 3

A lithium ion battery was prepared and subjected to a capacity test and a cycle performance test by the method of comparative example 3.

Comparative example 3 differs from comparative example 2 in that:

preparing a negative electrode in the step (2): styrene butadiene rubber emulsion (SBR) as a binder and sodium carboxymethyl cellulose (CMC) as a thickener are dissolved in deionized water, and then hard carbon as a negative electrode active material and conductive carbon (SP) as a conductive agent are respectively added. Wherein the mass ratio of the hard carbon to the SBR to the CMC to the SP is 95: 1.5: 0.5: 3. and after uniformly stirring, coating the obtained negative electrode slurry on the front and back surfaces of a 9-micron copper foil, then performing forced air drying at 105 ℃, performing cold pressing and stripping, and rolling to obtain the negative electrode.

Table 1 lists the nominal compositions and indices of the lithium supplement additives and the theoretical gram capacities in the examples.

TABLE 1

Numbering	Nominal chemical composition	Theoretical specific capacity (mAh// g)
			LPD-1	0.66Li₂S·0.33Fe	725.6
LPD-2	0.62Li₂S·0.31Cu·0.03CuS₂	656.9
			LPD-3	0.65Li₂S·0.65Co·0.02CoS	497.8

Sixth, testing method and testing result

1. Capacity testing

Comparative example 1 and examples 1 to 7 were tested according to the following procedure: the test temperature is 45 ℃; standing for 30min, charging at a constant current of 0.1C with a small multiplying power for 1h, then charging at a constant current of 0.5C to 4.0V, and then charging at a constant voltage until the current is less than 0.02C to obtain a charging capacity of C0; standing for 5min, and discharging to 2.5V at constant current of 0.5C rate to obtain first discharge capacity D0.

Comparative example 2, comparative example 3 and examples 8 to 16 were tested according to the following procedure: the test temperature is 45 ℃; standing for 30min, charging at constant current of 0.05C and 0.1C with small multiplying power for 30min, then charging at constant current of 0.5C to 4.45V, and then charging at constant voltage until the current is less than 0.02C to obtain the charging capacity C1; standing for 5min, and discharging to 3.0V at constant current of 0.5C rate to obtain first discharge capacity D1.

η 1 is the first coulombic efficiency of the battery, i.e. the ratio of the first discharge capacity to the first charge capacity of the battery. η 1 ═ D0/C0, or η 1 ═ D1/C1.

η 2 is the utilization efficiency of the positive active material of the battery, i.e. the ratio of the first discharge capacity of the battery to the first charge capacity of the active material. Wherein the first charge capacity of the active material can be obtained by multiplying the mass of the active material in the battery by the charge capacity of the material.

Eta 1 is the first effect of the conventional battery, but has the defect that the lithium supplementing effect of the lithium supplementing additive cannot be truly reflected after the positive electrode lithium supplementing additive is added; η 2 can compensate the above defects, and can reflect the utilization efficiency of the positive active material after lithium supplement. When lithium supplement is not performed, η 1 ═ η 2.

2. Cycle performance test

And (3) respectively carrying out cycle performance tests on the numbered batteries at the charging and discharging rate of 1C/1C under the condition of 25 ℃, and recovering the battery capacity at the small-rate charging and discharging of 0.1C/0.1C for 100 circles of each cycle. The discharge capacity of the battery after the 200 th cycle was recorded by taking the discharge capacity of the 3 rd cycle as a reference value, and the discharge capacity of the battery after the 200 th cycle was compared with that of the battery after the 200 th cycle, i.e., the capacity retention rate of the battery after the 200 th cycle. Wherein the cycling voltage interval of comparative example 1 and examples 1-7 is 2.5V-3.6V, and the cycling voltage interval of comparative example 2, comparative example 3 and examples 8-16 is 3.0V-4.45V.

Table 2 shows the positive and negative electrode compositions and test results of examples 1 to 16 and comparative examples 1 to 3.

TABLE 2

As can be seen from the data in table 2, by comparing the comparative example 1 with the examples 1 to 5, in the LiFePO 4/artificial graphite battery system, when the addition ratio of the positive electrode lithium supplement additive LPD-1 is less than 3%, the first efficiency η 1 of the whole battery is almost unchanged, mainly because the lithium supplement additive is additionally added, and the discharge capacity and the charge capacity are simultaneously increased after lithium supplement, so the influence on η 1 is small; when the adding proportion of the positive electrode lithium supplement additive LPD-1 is more than 3%, eta 1 starts to gradually decrease, because the amount of lithium which can be accommodated by the positive electrode active material approaches the material limit with the increase of the lithium supplement amount, the discharging capacity does not increase any more when the lithium supplement additive proportion is further increased, and meanwhile, the charging capacity is increased due to the increase of the lithium supplement additive proportion, so that eta 1 is reduced. When the addition amount of LPD-1 is 7%, the first effect of the battery is rapidly reduced from 90.4% to 83.9%. This is consistent with the trend of the utilization efficiency eta 2 of the positive electrode material along with the increase of the proportion of the lithium supplement additive. When the adding proportion of the positive electrode lithium supplement additive LPD-1 is low, eta 2 is increased along with the increase of the adding proportion of the LPD-1, namely the utilization rate of the positive electrode active material is increased along with the increase of the lithium supplement amount, but when the lithium supplement amount exceeds a certain limit and reaches the limit of lithium capacity, eta 2 is not increased any more and is stabilized at a specific value, and the value is approximately equal to the theoretical first effect of the positive electrode active material under the working condition. In addition, it can be seen that the cycle tendency of the example cell was significantly improved as compared to the comparative example cell with the increase of the addition ratio of LPD-1, and when the addition ratio of LPD-1 was 5.0% and 7.0%, the cell capacity was almost maintained at zero fade for 200 cycles, while the cell capacity of comparative example 1 was faded to 97.9% in the same case. Therefore, by comparing comparative example 1 and examples 1 to 5, it can be seen that, in examples 1 to 5 of the present application, the capacity retention rate, the first coulombic efficiency of the battery, and the utilization rate of the active material are improved by adding the lithium supplement additive, and it is more beneficial to compare examples 1 to 5 that the addition ratio of the lithium supplement additive is less than 5.0%.

In addition, fig. 3 shows the capacity retention rate of the batteries of comparative example 1 and example 4 as a function of the number of cycles, and it can be seen that the cycle stability of the batteries can be significantly improved by adding LPD-1. Although the higher the addition ratio of LPD-1, the better the cycling stability of the battery, the excessive addition of the lithium supplement additive may bring other negative effects, such as the increase of the thickness of the positive electrode plate, incomplete decomposition, increased side reactions and the like. From the relationship between η 1 and η 2 as a function of the amount of lithium supplement, it can be seen that the theoretical initial efficiency of the positive electrode active material LiFePO4 used in comparative example 1 and examples 1 to 5 was about 99.0%, and the optimum amount of lithium supplement for LPD-1 was about 3.0%. Further, it can be seen from comparative example 1 and examples 6 to 7 that the addition of 4.0% of LPD-2 or 5.0% of LPD-3 to the LiFePO 4/artificial graphite battery system can also improve the utilization efficiency of the positive electrode active material and the cycle stability.

In the LiFePO 4/artificial graphite battery system, fig. 1 shows the first charge and discharge curves of the batteries of comparative example 1 and example 4. As can be seen from FIG. 1, the charging capacity of the battery is significantly increased after 5.0% LPD-1 is added to LiFePO4, which is mainly due to the additional charging capacity provided by the decomposition of LPD-1 during the charging process. Obviously, the larger charging capacity can compensate the consumption of active lithium by an SEI film formed on the negative electrode in the first charging process, so that the discharge capacity is also improved. Fig. 2 shows XRD patterns of the positive electrode plate of the batteries in comparative example 1 and example 4 in a fully discharged state, and it can be seen from fig. 2 that the positive electrode plate shows a hetero-phase diffraction peak of FePO4 due to insufficient quantity of lithium ions inserted back, and FePO4 cannot be completely converted into LiFePO4, while the positive electrode plate of example 4 does not show a significant FePO4 diffraction peak, which indicates that the content of active lithium is increased by lithium insertion back through the positive electrode, and lithium ions can be fully inserted back to convert FePO4 into LiFePO4 during discharging.

Furthermore, in a LiCoO 2/C/15% SiO battery system, by adding LPD-2, the utilization efficiency and the cycling stability of the battery positive electrode active material are improved. From the relationship between η 1 and η 2 with the amount of lithium supplement, it can be seen that the theoretical first effect of the positive electrode active material LiCoO2 used in comparative example 2 and examples 8 to 13 is about 92.5%, the optimal amount of lithium supplement of LPD-2 is about 5.0%, and at this time, the utilization rate of the positive electrode active material is improved by about 6.8%, and the cycle retention rate at 200 cycles is improved by about 0.9%.

Further, in a LiCoO 2/hard carbon battery system, by comparing comparative example 3 with example 14 to example 16, the utilization rate of the battery positive electrode active material is improved by adding the positive electrode lithium supplement additives LPD-1, LPD-2 and LPD-3 prepared by the method, namely the utilization rate is improved from 87.2% to about 92%, and the 200-turn cycle retention rate is improved from 83.4% to about 86.5%.

Although illustrative embodiments have been illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. The lithium supplement additive is characterized by comprising aLi2S bZ cZmSn, wherein a/(b + cm) >1, a is more than 0 and less than or equal to 1, b is more than 0 and less than or equal to 1, c is more than or equal to 0, m is more than 0, n is more than 0, and Z comprises transition metal.

2. The lithium supplement additive of claim 1, wherein Z comprises at least one of Fe, Co, Ni, Mn, Cu, Cr, or Mo;

and/or the ZmSn comprises at least one of FeS, FeS2, CoS2, NiS2, MoS2, CuS or CuS 2.

3. The lithium supplement additive according to claim 1, wherein the particle size of the lithium supplement additive is 1000 nm or less.

4. A method for preparing a lithium supplement additive according to any one of claims 1 to 3, comprising the steps of:

mixing Li2S, a transition metal simple substance and a transition metal sulfide according to a metering ratio, and carrying out high-energy ball milling in a protective atmosphere to obtain the lithium supplement additive.

5. The method for preparing the lithium supplement additive according to claim 4, wherein the high energy ball milling satisfies at least one of the following conditions:

a) the rotating speed of the high-energy ball mill is 3000r/min to 6000 r/min;

b) the high-energy ball milling time is 12h to 48 h;

c) the mass ratio of the ball materials of the high-energy ball mill is 10: 1 to 50: 1.

6. a method for preparing a lithium supplement additive according to any one of claims 1 to 3, comprising the steps of:

mixing transition metal sulfide and metal lithium according to a metering ratio, and sintering in a protective atmosphere to enable the transition metal sulfide and the metal lithium to generate an oxidation-reduction reaction, thereby obtaining the lithium supplement additive.

7. The method of claim 6, wherein the sintering temperature is 180 ℃ to 250 ℃.

8. An electrochemical device comprising a positive electrode, a negative electrode, an electrolyte and a separator, at least one of the positive electrode, the negative electrode and the separator comprising the lithium supplement additive according to any one of claims 1 to 3 or the lithium supplement additive produced by the production method according to any one of claims 4 to 7.

9. The electrochemical device according to claim 8, wherein the positive electrode comprises:

a positive current collector; and

10. The electrochemical device according to claim 8, wherein the positive electrode comprises:

a positive current collector;

11. The electrochemical device according to claim 8, wherein the positive electrode comprises:

a positive current collector;

12. The electrochemical device according to claim 8, wherein the separation film comprises:

a porous substrate; and

wherein the positive electrode lithium supplement layer is interposed between the porous substrate and the positive electrode.

13. The electrochemical device according to any one of claims 8 to 12, wherein the content of the lithium supplement additive is 0.1 to 5% by mass based on the mass of the positive electrode active material in the positive electrode.

14. An electronic device comprising the electrochemical device according to any one of claims 8 to 13.