CN112886002B

CN112886002B - Electrochemical device and electronic apparatus including the same

Info

Publication number: CN112886002B
Application number: CN202110047949.7A
Authority: CN
Inventors: 陈鹏伟
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2021-01-14
Filing date: 2021-01-14
Publication date: 2022-06-24
Anticipated expiration: 2041-01-14
Also published as: CN112886002A

Abstract

The present disclosure relates to the field of energy storage technologies, and more particularly, to an electrochemical device and an electronic apparatus including the same. The electrochemical device includes a positive electrode material including: an active material; and a first material at the surface of the active material; wherein the first material comprises a lattice spacing of

To

Of the second material of (1). An electrochemical device using the positive electrode material can exhibit excellent cycle stability at high voltage, and can also improve charge capacity and energy density.

Description

Electrochemical device and electronic apparatus including the same

Technical Field

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

Background

With the popularization of consumer electronics products such as mobile phones, notebook computers, tablet computers, wearable devices, mobile power sources, unmanned aerial vehicles and the like, the requirements of people on electrochemical devices (for example, lithium ion batteries) therein are becoming stricter. For example, batteries are required to be lightweight, and to have characteristics such as high energy density and good cycle stability at high voltage.

The positive electrode material as an important component of the lithium ion battery has a significant influence on the performance of the lithium ion battery, so that continuous optimization and improvement of the positive electrode material are particularly important. The lithium cobaltate anode material is the earliest commercialized anode material of the lithium ion battery, has been widely and deeply researched, has the best comprehensive performance in the aspects of reversibility, discharge capacity, charging efficiency, voltage stability and the like, and is the anode material with larger application amount in the lithium ion battery at present. However, with the continuous pursuit of energy density, the working voltage of lithium cobaltate is continuously increased, and some disadvantages of the conventional lithium cobaltate material are continuously shown, for example, when the conventional lithium cobaltate positive electrode material works under a high voltage condition, the structural stability and the electrochemical stability are poor, the cycle performance under the high voltage is poor, the impedance is continuously increased, the side reaction with the electrolyte is continuously intensified, and the application of the material is influenced.

In view of the above, there is a need for an improved electrochemical device having good cycling performance at high voltage and an electronic apparatus including the same.

Disclosure of Invention

An object of the present application is to provide 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 one aspect of the present application, there is provided an electrochemical device including a positive electrode material including: an active material; and a first material at the surface of the active material; wherein the first material comprises a lattice spacing of

To

Of the second material of (1).

According to some embodiments of the present application, the lattice spacing is tested when the electrochemical device is in a fully discharged state.

According to some embodiments of the present application, the second material has a spinel-type structure.

According to some embodiments of the present application, the second material comprises lithium cobalt oxide.

According to some embodiments of the present application, the average grain size of the second material is 50nm to 300 nm.

According to some embodiments of the present application, an X-ray diffraction (XRD) pattern of the cathode material has a characteristic peak in a range of 44.5 ° to 45.5 °.

According to some embodiments of the present application, the positive electrode material has a characteristic peak intensity I in an X-ray diffraction pattern in a range of 44.5 ° to 45.5 °_AWith a characteristic peak intensity in the range of 22.5 DEG to 23.5 DEGI_BRatio of (1)_A/I_B0.5 to 4.8 percent. According to further embodiments of the present application, I_A/I_B0.9% to 3.7%.

According to some embodiments of the application, the second material comprises Li_mCoO_nWherein m is more than or equal to 0.5 and less than or equal to 5, and n is more than or equal to 1 and less than or equal to 4.

According to some embodiments of the application, the first material further comprises a third material comprising Co₃O₄。

According to some embodiments of the present application, the first material has an average particle size in a range of less than or equal to 1000 nm. According to other embodiments of the present application, the first material has an average particle size in a range of less than or equal to 800 nm. According to other embodiments of the present application, the first material has an average particle size in a range of less than or equal to 600 nm.

According to some embodiments of the present application, the active material includes at least one of a lithium transition metal oxide, a lithium transition metal phosphate compound.

According to some embodiments of the present application, the lithium transition metal oxide comprises lithium having the formula Li_xNi_yCo_zMn_kM_qO_b-aT_aWherein M comprises at least one of the elements B, Mg, Al, Si, P, S, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb, or Ce, T is a halogen, and x, Y, z, k, q, a, and B satisfy, respectively: 0.2<x is less than or equal to 1.2, y is less than or equal to 0 and less than or equal to 1, z is less than or equal to 0 and less than or equal to 1, k is less than or equal to 0 and less than or equal to 1, q is less than or equal to 0 and less than or equal to 1, b is less than or equal to 1 and less than or equal to 2, and a is less than or equal to 0 and less than or equal to 1. According to other embodiments of the present application, 0.6 ≦ x ≦ 1.2, 0 ≦ y ≦ 1, 0<z is less than or equal to 1, k is more than or equal to 0 and less than or equal to 1, q is more than or equal to 0 and less than or equal to 1, b is more than or equal to 1.5 and less than or equal to 2, and a is more than or equal to 0 and less than or equal to 0.5.

According to another aspect of the present application, there is provided an electronic device comprising an electrochemical device according to the present application.

The technical scheme of the application has at least the following beneficial effects: the present application provides a positive electrode material having high energy density and good cycle stability at high voltage, and an electrochemical device and an electronic apparatus including the same. In at least one aspect, compared with the positive electrode material provided by the prior art, the positive electrode material provided by the application can ensure the stable structure of the positive electrode material in the high-voltage charging and discharging process, relieve the side reaction of the material and the electrolyte, and reduce the interface side reaction, thereby improving the cycle performance of the electrochemical device under high voltage; the cathode material can improve the polarization level of the surface of the material, improve potential polarization in the charge-discharge process, improve gram capacity of the cathode material and further improve energy density of an electrochemical device.

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 of some example only. 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 is an SEM image of a positive electrode material provided in an exemplary embodiment of the present application;

fig. 2 is a schematic diagram of cycle performance of a lithium ion battery provided in an embodiment of the present application;

fig. 3 is a schematic view of a bulk distribution in a positive electrode material provided in an embodiment of the present application.

Detailed Description

Embodiments of the present application will be described in detail below. Throughout the specification, the same or similar components and components having the same or similar functions are denoted by like reference numerals. The embodiments described herein with respect to the figures are illustrative in nature, are diagrammatic in nature, and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application.

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.

In the detailed description and claims, a list of items connected by the term "at least one of," "one or more 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.

As used herein, "fully discharged state" refers to a state when the electrochemical device is discharged to a 0% state of charge (SOC).

Positive electrode material and electrochemical device using same

The gram discharge capacity of the anode material can be improved along with the increase of the working voltage. In pursuit of high energy density, the charge cut-off voltage of the positive electrode material is continuously increased, that is, the current method for improving the energy density of the positive electrode material mainly increases the charge cut-off voltage, and the reversible capacity is increased by removing more lithium ions from the positive electrode material. However, as the charge cut-off voltage of the lithium ion battery is continuously increased, the structure of the positive electrode material undergoes irreversible phase change and structural collapse, so that the structure of the positive electrode material is damaged. Therefore, side effects brought by improving the cut-off voltage are more and more obvious, such as poor high-temperature circulation under high voltage, continuous increase of impedance, continuous aggravation of side reactions with electrolyte, reduction of the service life of the battery and influence on the application of the anode material under high voltage.

Based on at least the above-mentioned insight into the prior art, and in view of the crucial importance of the positive electrode material on the electrochemical performance of the electrochemical device, the present application has conducted further extensive research on the surface structure of the positive electrode material in order to improve the electrochemical performance of the electrochemical device, in particular the gram-capacity, energy density and cycle performance of the electrochemical device, in an effort to obtain an electrochemical device capable of stable operation over a long period of time, in particular at high voltages.

In some embodiments of the present application, an electrochemical device is provided that includes a positive electrode, a negative electrode, an electrolyte, and a separator between the positive electrode and the negative electrode, as described below.

[ Positive electrode ]

According to some embodiments of the application, the positive electrode comprises: the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on one or both surfaces of the positive electrode current collector, the positive electrode active material layer including a positive electrode material therein. The positive electrode active material layer may be one or more layers, and each of the plurality of positive electrode active material layers may contain the same or different positive electrode materials. Taking an electrochemical device as an example of a lithium ion battery, the positive electrode material is any substance capable of reversibly intercalating and deintercalating metal ions such as lithium ions.

In order to accurately reflect the structure of the cathode material provided by the present application, a transmission electron microscope (hereinafter, TEM) and/or an X-ray diffraction test (hereinafter, XRD test) are used to characterize the relevant parameters of the cathode material, such as the parameters of crystal lattice, crystal face, etc., during the charging and discharging processes of the electrochemical device. In some embodiments, the electrochemical performance of the electrochemical device can be significantly improved when the cathode material satisfies the following conditions: the positive electrode material includes, when the electrochemical device is in a fully discharged state: an active material; and a first material at a surface of the active material; wherein the first material comprises a lattice spacing of

To

Of the second material of (1). The above lattice spacing corresponds to the 003 plane of the material.

In some embodiments, the positive electrode material of the present application is characterized in that it is provided with a first material on at least a part of the surface of the active material, wherein the first material comprises a lattice spacing of

To

Of the second material of (1). Therefore, the positive electrode material becomes a positive electrode material with a pre-lithiation coating layer and high cycling stability, and the positive electrode material can be a Co-based layered oxide material coated with a first material, so that the positive electrode material not only has high lithium removal capacity, but also has good high-voltage cycling stability.

Specifically, the pursuit of energy density leads to the continuous increase of the application voltage of the positive electrode material, and when the battery works under a high voltage condition, the thermal stability and the electrochemical stability of the positive electrode material are poor, so that the battery faces a plurality of hidden dangers in circulation, such as battery short circuit caused by the dissolution of transition metal, and the problem of battery core flatulence caused by the reaction of the positive electrode and the electrolyte. Therefore, the improvement of the charge capacity of the whole material without increasing the charge voltage obviously is regarded as a new direction for improving the energy density, and the quantity of reversible lithium is increased by coating a layer of material of the pre-lithiation agent on the surface of the active material and decomposing the coating material to generate lithium ions in the first charge process of the material. The invention is based on the idea of coating the surface of an active material (such as a lithium cobaltate material) with a layer of pre-lithiation agent material which has a high gram capacity and can decompose and release more lithium ions during charging, and the remaining product can comprise a material with a lattice spacing of

To

Of the 003 crystal plane (e.g. lithium-deficient spinel)The Co-containing oxide with the structure) can be stably coated on the surface of active material particles to play a role in stabilizing an interface, so that the side reaction of the anode material and electrolyte can be relieved, the side reaction of the interface is reduced, and the high-temperature cycle performance of the material is improved. Meanwhile, the positive electrode material can improve the polarization level of the particle surface and improve the potential polarization in the charging process, and the charging potential of the coated positive electrode material can be reduced by 0.03V to 0.05V and can be maintained after being cycled for a plurality of times. Particularly, the overall charge gram capacity of the anode material can be obviously improved, and in addition, the charge gram capacity of the material under different coating amounts is improved by 1.5mAh/g to 4mAh/g, so that the anode material has a good effect on improving the energy density.

In some embodiments, the second material has a spinel structure (belonging to the lithium deficient phase). The spinel-structured substance is beneficial to improving the gram capacity and the cycle performance of the material, reducing the residual lithium on the surface and improving the high-temperature cycle performance and the safety performance of the material.

In some embodiments, the positive electrode material, wherein the second material comprises lithium cobalt oxide. After the electrochemical device containing the cathode material is cycled for many times, the surface of the cathode material particle can still observe a lithium-deficient lithium cobalt oxide spinel structure coating, so that the cathode material not only has higher lithium removal capacity, but also has better high-voltage cycling stability.

In some embodiments, in the cathode material, the second material includes Li_mCoO_nWherein m is more than or equal to 0.5 and less than or equal to 5, and n is more than or equal to 1 and less than or equal to 4. The Li_mCoO_nThe structure stability of (2) is better, and the interface structure can be stabilized, so that the surface structure stability of the material particles is improved.

In some embodiments, in the cathode material, the average grain size of the second material is 50nm to 300 nm. In some embodiments, the average grain size of the second material is 60nm to 250 nm. In some embodiments, the average grain size of the second material is 80nm to 200 nm. In some embodiments, the average grain size of the second material is, for example, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm, and the like.

In some embodiments, the positive electrode material has an X-ray diffraction (XRD) pattern with a characteristic peak in the range of 44.5 ° to 45.5 °.

In some embodiments, the positive electrode material has a characteristic peak intensity I in the range of 44.5 ° to 45.5 ° in an X-ray diffraction pattern_AWith a characteristic peak intensity I in the range of 22.5 DEG to 23.5 DEG_BRatio of (1)_A/I_BIs 0.5 to 4.8 percent. Under such conditions, an electrochemical device including the cathode material can exhibit excellent electrochemical properties.

In some embodiments, the first material further comprises a third material comprising Co₃O₄。

The electrochemical device containing the cathode material can decompose the coating material on the surface of the active material during charge and discharge, and the decomposition product can comprise lithium-deficient phase Li which is not completely decomposed according to the decomposition degree of the coating material_mCoO_nAnd may also include completely decomposed Co₃O₄The interlayer spacing and the lithium content of the positive electrode material are obviously different, and the spinel phase is generated in situ after the surface coating of the positive electrode material is decomposed, so that the positive electrode material has better atomic fusion degree. Coating material Li on surface of positive electrode material_mCoO_nAnd Co₃O₄The coating can be stably coated on the surface of the active material, the effect of stabilizing an interface is achieved, the side reaction of the anode material and the electrolyte is relieved, the existence of the interface side reaction under the condition of higher cut-off voltage is reduced, and the cycle performance of the material can be improved.

In some embodiments, the first material has an average particle size in a range of less than or equal to 1000 nm. In some embodiments, the first material has an average particle size in a range of less than or equal to 800 nm. In some embodiments, the first material has an average particle size of 500nm to 800 nm. In some embodiments, the average particle size of the first material is, for example, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, and the like. The particle size of the first material affects the electrochemical surface of the cathode material in the electrochemical device, and the average particle size of the first material is within the above range, so that the electrochemical active potential provided by the first material is appropriate, the specific discharge capacity is appropriate, and side effects caused by the excessively large particle size are reduced or avoided.

In some embodiments, the active material comprises at least one of a lithium transition metal oxide, a lithium transition metal phosphate compound.

In some embodiments, the lithium transition metal oxide comprises Li having the formula_xNi_yCo_zMn_kM_qO_b-aT_aWherein M comprises at least one of the elements B, Mg, Al, Si, P, S, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb, or Ce, T is a halogen, and x, Y, z, k, q, a, and B satisfy, respectively: 0.2<x is less than or equal to 1.2, y is less than or equal to 0 and less than or equal to 1, z is less than or equal to 0 and less than or equal to 1, k is less than or equal to 0 and less than or equal to 1, q is less than or equal to 0 and less than or equal to 1, b is less than or equal to 1 and less than or equal to 2, and a is less than or equal to 0 and less than or equal to 1. In some embodiments, 0.6 ≦ x ≦ 1.2, 0 ≦ y ≦ 1, 0<z is less than or equal to 1, k is more than or equal to 0 and less than or equal to 1, q is more than or equal to 0 and less than or equal to 1, b is more than or equal to 1.5 and less than or equal to 2, and a is more than or equal to 0 and less than or equal to 0.5.

In some embodiments, the lithium transition metal phosphate compound comprises at least one of lithium iron phosphate, lithium manganese iron phosphate.

In some embodiments, the active material comprises a combination of one or more of a Lithium Cobaltate (LCO), a lithium nickel cobalt manganate material, or a lithium nickel cobalt aluminate material.

Of course, these active materials are shown by way of example only for illustrative purposes and are not intended to limit the present application, and one of ordinary skill in the art may select other suitable active materials according to actual needs.

In some embodiments, the positive electrode material comprises an active material lithium cobaltate, at least a portion of the surface of which is covered with a layer of at least one cobalt-containing compound with good structural stability.

In some embodiments of the present application, the positive electrode active material layer includes the positive electrode material as described above, further includes a binder, and optionally includes a conductive material.

The binder can improve not only the bonding of the positive electrode material particles to each other but also the bonding of the positive electrode material to the positive electrode current collector. In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy, nylon, and the like.

Conductive materials may be used to enhance the conductivity of the electrode. Any conductive material may be employed as the conductive agent provided that the conductive material does not cause unwanted chemical changes. In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material may be selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material may be selected from metal powders, metal fibers, copper, nickel, aluminum, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

In some embodiments, the positive current collector may be a positive current collector commonly used in the art, such as, but not limited to, an aluminum foil or a nickel foil.

In some embodiments, the method of preparing the positive electrode is a method of preparing a positive electrode sheet that can be used in an electrochemical device, which is well known in the art. For example, the positive electrode can be obtained by: the positive electrode material, the conductive material, and the binder are mixed in a solvent to prepare a slurry, and the slurry is coated on a current collector. In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone, and the like.

[ negative electrode ]

In some embodiments, the negative electrode of the electrochemical device of the present application includes a negative electrode current collector and a negative electrode active material layer disposed on 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 active material is capable of reversibly intercalating and deintercalating lithium ions. In some embodiments, the negative active material may include or be selected from one or more of the following materials: carbonaceous materials, siliceous materials, alloy-based materials, lithium metal-containing composite oxide materials, and the like. In some embodiments, non-limiting examples of carbonaceous materials include crystalline carbon, amorphous carbon, and mixtures thereof. The crystalline carbon may be natural graphite or artificial graphite in an amorphous form or in a form of a flake, a platelet, a sphere or a fiber. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or the like.

The specific kind of the negative electrode active material is not particularly limited and may be selected as desired. In some embodiments, the negative active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres (abbreviated as MCMB), hard carbon, soft carbon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO₂Spinel-structured lithiated TiO₂-Li₄Ti₅O₁₂And Li-Al alloy.

In some embodiments, the negative electrode current collector may be a negative electrode current collector commonly used in the art, including, but not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metals, and combinations thereof.

In some embodiments, the types of the binder and the conductive agent in the negative electrode can be as described above, and are not described herein in detail.

In some embodiments, the structure of the negative electrode is a negative electrode tab structure known in the art that can be used in electrochemical devices.

In some embodiments, the method of preparing the negative electrode is a method of preparing a negative electrode that can be used in an electrochemical device, which is well known in the art. Illustratively, the negative electrode may be obtained by: the negative active material, the conductive material, and the binder are mixed in a solvent to prepare an active material composition, and the active material composition is coated on a current collector. In some embodiments, the solvent may include water, and the like, but is not limited thereto.

[ electrolyte ]

When an electrolyte system is further improved on the basis of modification of a positive electrode active material, the electrochemical device can better exhibit cycle performance at high voltage. The electrolyte may be classified into an aqueous electrolyte and a non-aqueous electrolyte, wherein an electrochemical device using the non-aqueous electrolyte may operate under a wider voltage window than the aqueous electrolyte, thereby achieving a higher energy density. In some embodiments, the non-aqueous electrolyte includes an organic solvent, a lithium salt, and an additive. The organic solvent of the electrolyte according to the present application may be any organic solvent known in the art that can be used as a solvent of the electrolyte. In some embodiments, the organic solvent of the electrolyte of the present application comprises or is selected from: at least one of Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, methyl acetate, and ethyl propionate.

In some embodiments, the lithium salt of the electrolyte of the present application comprises or is selected from: lithium hexafluorophosphate (LiPF)₆) At least one of phosphorus pentafluoride, lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluoroborate, trimethyl lithium or lithium chloride.

The additive may be an additive known in the art that can be used to improve the electrochemical performance of a battery according to the electrolyte of the present application. In some embodiments, the additive includes, but is not limited to, at least one of a polynitrile compound, a sulfur containing additive, fluoroethylene carbonate (FEC), 1, 3-Propane Sultone (PS), 1,4 butane sultone.

[ isolation film ]

The material and shape of the separation film used in the electrochemical device are not particularly limited, and may be any of those disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance or the like formed of a material stable to the electrolyte of the present application.

In some embodiments, the release film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure. The material of the substrate layer may include or be selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polyethylene porous film, a polypropylene porous film, a polyethylene nonwoven fabric, a polypropylene-polyethylene-polypropylene porous composite film, or the like can be used.

The surface treatment layer may be, but is not limited to, a polymer layer, an inorganic layer, or a mixed layer formed of a polymer and an inorganic substance.

The inorganic layer may include inorganic particles and a binder, among others. The inorganic particles may comprise or be selected from one or a combination of more of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminium hydroxide, magnesium hydroxide, calcium hydroxide and barium sulphate. The binder may comprise or be selected from one or a combination of polyvinylidene fluoride, copolymers of vinylidene fluoride-hexafluoropropylene, polyamides, polyacrylonitriles, polyacrylates, polyacrylic acids, polyacrylates, polyvinylpyrollidones, polyvinyl ethers, polymethyl methacrylates, polytetrafluoroethylene, and polyhexafluoropropylene. Wherein the polymer layer may comprise a polymer. The material of the polymer may include or be selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, poly (vinylidene fluoride-hexafluoropropylene).

Second, application

It will be understood by those skilled in the art that the electrochemical device of the present application may be a lithium ion battery, but may also be any other suitable electrochemical device. 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, solar cells, or capacitors, without departing from the disclosure of the present application. In particular, the electrochemical device is a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The use of the electrochemical device of the present application is not particularly limited, and it can be used for various known uses.

In some embodiments, an electronic device is provided that comprises an electrochemical device as described herein. The electronic devices include, but are not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, cellular phones, portable facsimile machines, portable copiers, portable printers, headphones, video recorders, liquid crystal televisions, portable cleaners, portable CDs, mini-discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, game machines, clocks, electric tools, flashlights, cameras, large household batteries or lithium ion capacitors, and the like. It is to be noted that the electrochemical device of the present application is applicable to an energy storage power station, a marine vehicle, 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.

The technical solution of the present invention is further described below by taking a lithium ion battery as an example and combining specific comparative examples and examples, but is not limited thereto. It will be understood by those skilled in the art that the preparation methods described in the present application are only exemplary embodiments, and that modifications or substitutions to the technical solution of the present invention can be made without departing from the scope of the technical solution of the present invention.

In the following examples and comparative examples, reagents, materials and instruments used were commercially available or synthetically available, unless otherwise specified.

Third, example

Preparation of lithium ion battery

The following preparation methods were used to prepare the positive electrode materials in examples and comparative examples into lithium ion batteries.

(1) Preparation of the positive electrode: the positive electrode materials prepared in the following examples and comparative examples, acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were mixed at a weight ratio of 94: 3: 3, fully stirring and uniformly mixing in N-methyl pyrrolidone to prepare anode slurry, uniformly coating the obtained anode slurry on an anode current collector aluminum foil, drying at 85 ℃, and then carrying out cold pressing, stripping, cutting and welding of an anode tab to obtain the anode.

Wherein, the preparation of the anode material comprises the following steps:

adding active material lithium cobaltate into a ball milling tank by adopting a solid phase method, and then respectively adding a Li source (Li)₂O、LiOH、Li₂CO₃At least one of), a Co source (CoOH, CoO, CoCl)₂At least one of the above) and ball-milling for 6 hours to obtain a base material; and then placing the obtained base material in an inert atmosphere, sintering for 4 to 8 hours at the temperature of between 400 and 800 ℃, and grinding the obtained powder to obtain the required cathode material.

(2) Preparation of a negative electrode: preparing a negative active material artificial graphite, a binder Styrene Butadiene Rubber (SBR), a thickening agent sodium carboxymethyl cellulose (CMC) according to a weight ratio of 96: 2: 2, fully stirring and uniformly mixing the mixture in deionized water to prepare negative electrode slurry, uniformly coating the negative electrode slurry on a negative electrode current collector copper foil, drying the negative electrode current collector copper foil at 85 ℃, and then carrying out cold pressing, stripping, cutting and welding of a negative electrode lug to obtain the negative electrode.

(3) Preparing an electrolyte: at water content<In a 10ppm argon atmosphere glove box, Ethylene Carbonate (EC), diethyl carbonate (DEC) and Propylene Carbonate (PC) were mixed in the following ratio 3: 4: 3, and then fully drying the lithium salt LiPF₆Dissolved in the non-aqueous solvent to form an electrolyte solution, wherein LiPF is present₆The content of (b) is 1 mol/L.

(4) Preparing an isolating membrane: as the separator, a ceramic-coated Polyethylene (PE) material was used, the ceramic coating layer having a thickness of 2.5 μm and the polyethylene layer having a thickness of about 10 μm.

(5) Assembling the lithium ion battery: and sequentially stacking the anode, the isolating film and the cathode to enable the isolating film to be positioned between the anode and the cathode to play an isolating role, then winding, placing in a packaging shell, injecting electrolyte, packaging, and forming to obtain the final lithium ion battery.

Capacity testing

Each of 5 batteries in each comparative example and example was charged at a constant current of 0.2C rate at normal temperature until the voltage reached 4.5V, and further charged at a constant voltage of 4.5V until the current was less than 0.05C, so that the batteries were in a full charge state of 4.5V. Then constant current discharge at 0.2C rate was stopped until the voltage was 3.0V. The capacity data are shown in table 1.

Cycle performance test

Taking 5 lithium ion batteries in each group of each proportion and the embodiment, repeatedly charging and discharging the lithium ion batteries through the following steps, and calculating the discharge capacity retention rate of the lithium ion batteries.

Firstly, carrying out first charging and discharging in an environment of 25 ℃, carrying out constant-current and constant-voltage charging under a charging current of 0.7C (namely a current value which completely discharges theoretical capacity within 2 h) until the upper limit voltage is 4.5V, then carrying out constant-current discharging under a discharging current of 0.5C until the final voltage is 3V, and recording the discharging capacity of the first circulation; then, 200 cycles of charge and discharge were performed, and the discharge capacity at the 200 th cycle was recorded.

The cycle capacity retention rate (discharge capacity at 200 th cycle/discharge capacity at first cycle) × 100%.

Measurement of lattice spacing, average grain size and average particle diameter

And after full discharge, disassembling the lithium ion battery to obtain a positive electrode material, performing TEM representation on the positive electrode material, and measuring the lattice fringe spacing of a coating in a TEM picture to obtain the lattice spacing of a second material.

In the TEM photograph, 10 crystal grains having a lattice spacing satisfying the requirement were selected, and then the respective areas of these crystal grains were determined using image analysis software, and then, assuming that the crystal grains were spherical, the respective diameters R were determined by the following formula: r is 2 × (S/π)^1/2(ii) a Wherein S is the area of the crystal grain; subjecting the obtained 1 toThe diameters of the 0 grains are arithmetically averaged to find the average grain size of the second material.

The average particle size of the first material is measured in the same manner as the average grain size.

Specific examples of the positive electrode material provided in the present application will be described in detail below.

Examples 1 to 12 and comparative example 1

Example 1: adding an active material lithium cobaltate into a ball milling tank by adopting a solid phase method, then respectively adding a Li source and a Co source, and carrying out ball milling for 6 hours to obtain a base material; and then, sintering the obtained base material in an inert atmosphere at 600 ℃, and grinding the obtained powder to obtain the required cathode material. In the obtained positive electrode material, the composition of the coating material is Li₆CoO₄The average particle diameter was 500nm, and the coating amount was 0.2%.

Example 2: the difference from example 1 is that: the coating amount was 1.0%.

Example 3: the difference from example 1 is that: the coating amount was 1.5%.

Example 4: the difference from example 1 is that: the coating amount was 2.0%.

Example 5: the difference from example 1 is that: the coating amount was 3.0%.

Example 6: the difference from example 1 is that: the coating amount was 5.0%.

Example 7: the difference from example 1 is that: the coating amount was 8.0%.

Example 8: the difference from example 1 is that: the coating amount was 10%.

Example 9: the difference from example 3 is that: the average particle size of the coating was adjusted to 300 nm.

Example 10: the difference from example 3 is that: the average particle size of the coating was adjusted to 600 nm.

Example 11: the difference from example 3 is that: the average particle size of the coating was adjusted to 800 nm.

Example 12: the difference from example 3 is that: the average particle size of the coating was adjusted to 1000 nm.

Comparative example 1: the existing lithium cobaltate material is directly subjected to performance test without any treatment.

The electrochemical properties of the lithium ion batteries obtained in examples 1 to 12 and comparative example 1 and the structural parameter information of the cathode material obtained after disassembly are listed in the following table 1. The intensity ratio refers to a ratio of a characteristic peak intensity in a range of 44.5 degrees to 45.5 degrees to a characteristic peak intensity in a range of 22.5 degrees to 23.5 degrees in an X-ray diffraction pattern of the cathode material obtained by fully discharging and disassembling the formed lithium ion battery.

TABLE 1

It is obvious from the test results of comparative example 1 and examples 1 to 8 that the performance of the lithium cobaltate material coated by the Co-based pre-lithiation agent is greatly improved, the gram charge capacity and the cycle performance of the battery are improved to different degrees, the coating amount is further preferably 1% to 5%, the content of the coating substance is increased along with the increase of the coating amount, the gram charge capacity of the lithium cobaltate is continuously improved, the cycle performance of the battery is also continuously improved, but when the coating amount is too high, the cycle improvement effect is not continuously improved any more. In addition, since the prelithiation agent itself decomposes after charging and does not have lithium intercalation ability, the decrease in gram discharge capacity of the material becomes more significant when the coating amount is too large. However, when the coating amount is 0.2%, the improvement in gram volume is not significant because the addition amount is too small. And the proper coating amount can ensure the improvement of the charge gram capacity of the lithium cobaltate, and simultaneously, the surface stability is better optimized. Characteristic peak intensity (corresponding to Co) in the range of 44.5 DEG to 45.5 DEG in X-ray diffraction pattern₃O₄) The ratio to the intensity of the characteristic peak in the range of 22.5 ° to 23.5 ° (corresponding to lithium cobaltate) characterizes the surface Co₃O₄With increasing pre-lithiation agent coating amount, residual Co after decomposition of the pre-lithiation agent coating material₃O₄The peak intensity ratio is increased gradually, and the peak intensity ratio is 0.9 percentTo examples 2-7, which ranged from 3.7%, both gram capacity and cycle stability were significantly improved. At the same time, the residual lattice spacing in the cladding material after formation is

To

The second material can be further decomposed in the subsequent cycle process to supplement lithium ions consumed due to side reactions, so that the cycle capacity retention rate of the lithium ion battery is improved.

The experimental results of comparative examples 3 and 9 to 12 show that the particle size of the coating material is also an important influence factor, the proper particle size setting can ensure that the pre-lithiation agent can better grow on the particle surface without influencing the structural characteristics of the LCO body, and the proper average particle size range is less than or equal to 1000 nm; too large a particle size may affect performance. Therefore, the material performance can be improved by optimizing the particle size of the coating material, and the improvement effect is better exerted.

In addition, fig. 3 shows a schematic diagram of the distribution of the bulk phase in the cathode material provided in the embodiment of the present application. Wherein the atomic ratio of the Co element to the O element at the 1-position is relatively high, indicating the presence of Co in the clad material₃O₄And (4) phase(s).

In fig. 3, the 1 position includes:

element(s)	Weight (D)	Atom(s)
				Percentage of	Percentage of
O K	29.45	60.41
			Al K	0.46	0.56
Co K	70.09	39.03
			Total amount of	100.00

In fig. 3, the 2 positions include:

element(s)	Weight (D)	Atom(s)
				Percentage of	Percentage of
O K	41.57	66.91
			Al K	0.42	0.50
Co K	58.01	32.59
			Total amount of	100.00

Reference throughout this specification to "an embodiment," "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some examples" means that at least one embodiment or example in this application includes a particular feature, structure, material, or characteristic described in the embodiment or example. Thus, throughout the specification, descriptions appear, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "by example," which do not necessarily refer to the same embodiment or example in this application. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

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. An electrochemical device comprising a positive electrode material, wherein the positive electrode material comprises:

an active material; and

a first material coated on the surface of the active material;

wherein the first material comprises a lattice spacing of

To

A second material of (a);

in an X-ray diffraction pattern of the cathode material, the characteristic peak intensity I in the range of 44.5 degrees to 45.5 degrees_AWith a characteristic peak intensity I in the range of 22.5 DEG to 23.5 DEG_BRatio of (1)_A/I_BFrom 0.5% to 4.8%;

the positive electrode material satisfies the following conditions:

d) the second material comprises Li_mCoO_nWherein m is more than or equal to 0.5 and less than or equal to 5, and n is more than or equal to 1 and less than or equal to 4;

e) the first material further comprises a third material comprising Co₃O₄。

2. The electrochemical device of claim 1, wherein said lattice spacing is measured when said electrochemical device is in a fully discharged state.

3. The electrochemical device of claim 1, wherein the second material satisfies at least one of the following conditions:

b) an average grain size of 50nm to 300 nm;

c) has a spinel structure.

4. The electrochemical device according to claim 1, wherein the positive electrode material has an X-ray diffraction pattern having a characteristic peak in a range of 44.5 ° to 45.5 °.

5. The electrochemical device according to claim 1, wherein the first material has an average particle size in a range of 1000nm or less.

6. The electrochemical device of claim 1, wherein said active material comprises at least one of a lithium transition metal oxide, a lithium transition metal phosphate compound.

7. The electrochemical device of claim 6, wherein said lithium transition metal oxide comprises Li having the formula_xNi_yCo_zMn_kM_qO_b-aT_aWherein M comprises at least one of the elements B, Mg, Al, Si, P, S, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb, or Ce, T is a halogen, and x, Y, z, k, q, a, and B satisfy, respectively: 0.2<x is less than or equal to 1.2, y is less than or equal to 0 and less than or equal to 1, z is less than or equal to 0 and less than or equal to 1, k is less than or equal to 0 and less than or equal to 1, q is less than or equal to 0 and less than or equal to 1, b is less than or equal to 1 and less than or equal to 2, and a is less than or equal to 0 and less than or equal to 1.

8. An electronic device comprising the electrochemical device according to any one of claims 1 to 7.