CN113795953A - Positive plate, electrochemical device comprising same and electronic device - Google Patents

Positive plate, electrochemical device comprising same and electronic device Download PDF

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Publication number
CN113795953A
CN113795953A CN202180003229.9A CN202180003229A CN113795953A CN 113795953 A CN113795953 A CN 113795953A CN 202180003229 A CN202180003229 A CN 202180003229A CN 113795953 A CN113795953 A CN 113795953A
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positive electrode
active material
phosphorus
material layer
electrode active
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程世杨
下羽淳平
郎野
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The application provides a positive electrode sheet, an electrochemical device and an electronic device. The positive plate comprises a positive active material layer, and the element content of the surface of the positive active material layer satisfies the following conditions: the molar ratio of the manganese element to the phosphorus element is 70:1 to 450: 1. The electrochemical device comprises the positive plate. The electronic device comprises the electrochemical device. The positive plate has better interface stability in electrolyte, and can obviously improve the high-temperature storage and high-temperature cycle performance of an electrochemical device.

Description

Positive plate, electrochemical device comprising same and electronic device
Technical Field
The application relates to the technical field of energy storage, in particular to a positive plate, an electrochemical device comprising the positive plate and an electronic device comprising the positive plate.
Background
With the popularization of consumer electronics products such as notebook computers, mobile phones, tablet computers, mobile power sources, unmanned aerial vehicles and the like, the requirements on electrochemical devices (such as lithium ion batteries) therein are becoming stricter. For example, the lithium ion battery is required to have a higher specific capacity and to be stable even in a high temperature environment. However, the specific capacity of the conventional lithium ion battery is seriously attenuated at high temperature, which causes the occurrence of side reactions inside the lithium ion battery at high temperature, so that the structure of an electrode active material is damaged, and the stability and the service life of the lithium ion battery are influenced. Therefore, a lithium ion battery having a long life span at a high temperature is required.
Disclosure of Invention
The application aims to provide a positive plate, an electrochemical device comprising the positive plate and an electronic device, so as to improve the stability of the electrochemical device in a high-temperature environment.
In some embodiments, the present application provides a positive electrode sheet including a positive electrode active material layer having a surface element content satisfying: the molar ratio of the manganese element to the phosphorus element is 70:1 to 450: 1. In some embodiments, the molar ratio of the manganese element to the phosphorus element ranges from 70:1 to 200: 1.
In some embodiments, the thickness of the positive electrode active material layer is H, and the molar ratio of the phosphorus element to the manganese element on the surface of the positive electrode active material layer is Po(ii) a The molar ratio of phosphorus element to manganese element in the depth region from H/4 to H/3 of the surface of the positive active material layer is Pi，Po/PiIs 0.5 to 2. In some embodiments, Po/PiIs 1 to 1.38.
In some embodiments, the surface of the positive electrode active material layer has an XRD pattern of IAIndicates a characteristic peak intensity in the range of 20 DEG to 21 DEG, IBIndicating a characteristic peak intensity in the range of 18 DEG to 18.6 DEG, I of 0.12. ltoreq.A/IB≤0.2。
In some embodiments, the positive electrode active material layer includes a positive electrode active material having an average particle diameter of D1 and a phosphorus-containing compound having an average particle diameter of D2, 0.33. ltoreq. D1/D2. ltoreq.100. In some embodiments, 2 ≦ D1/D2 ≦ 100.
In some embodiments, the surface of the positive electrode active material has the phosphorus-containing compound, and the thickness h of the phosphorus-containing compound is 10nm to 30 nm.
In some embodiments, the average particle diameter D1 of the positive electrode active material is 2 μm to 30 μm, and the average particle diameter D2 of the phosphorus-containing compound is 0.1 μm to 30 μm. In some embodiments, D1 is 10 μm to 25 μm and D2 is 0.1 μm to 5 μm.
In some embodiments, the phosphorus-containing compound comprises AxPOyWherein A comprises at least one of Li, Na, K, Mg, Ca, Y, Sr, Ba, Zn, Al or Si, x is more than or equal to 1 and less than or equal to 4, and Y is more than or equal to 3 and less than or equal to 4.
In some embodiments, the positive active material includes at least one of compound a) or compound b): compound a) Lix1Mn2-y1 Zy1O4Wherein Z comprises at least one of Mg, Al, B, Cr, Ni, Co, Zn, Cu, Zr, Ti or V, x1 is more than or equal to 0.8 and less than or equal to 1.2, and y1 is more than or equal to 0 and less than or equal to 0.1; compound b) Lix2Niy2CozMnkMqOb-aTaWherein M comprises at least one of 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 halogen, and x2, y2, z, k, q, a, and b satisfy: x2 is more than or equal to 0.2 and less than or equal to 1.2, y2 is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, 0<k≤1、0≤q≤1、1<b is less than or equal to 2 and a is less than or equal to 1 and more than or equal to 0.
In some embodiments, the mass ratio of the positive electrode active material to the phosphorus-containing compound is 95 to 97: 0.5-3.
In some embodiments, the present application also provides an electrochemical device comprising the positive electrode sheet as described herein before.
In some embodiments, the present application further provides an electronic device comprising the electrochemical device as described herein.
The technical scheme of the application has at least the following beneficial effects: when the molar ratio of the manganese element to the phosphorus element on the surface of the positive active material layer meets the range of 70:1 to 450:1, the interface stability of the manganese-containing positive plate in the electrolyte can be improved, and the high-temperature storage and high-temperature cycle performance of the electrochemical device can be obviously improved.
Drawings
Fig. 1a is a Raman (Raman) spectrum of a positive electrode sheet used in the lithium ion battery of example 1, respectively, in a fresh state, after formation and after storage; fig. 1b is a Raman (Raman) spectrum of the positive electrode sheet used for the lithium ion battery formation of comparative example 1 in a fresh state, after formation and after storage, respectively;
FIG. 2 is an EDX-Mapping P spectrum of the surface of the positive active material layer of the positive plate, which is determined by the SEM-EDX method after the lithium ion battery is formed and disassembled; wherein, the control group in fig. 2 corresponds to the positive electrode sheet of the proportion 1, and the experimental group in fig. 2 corresponds to the positive electrode sheet of the embodiment 1;
fig. 3 is XRD patterns of the positive electrode active material layer surfaces of the positive electrode sheets disassembled after formation of the lithium ion batteries of example 1 and comparative example 1.
Detailed Description
It is to be understood that the disclosed embodiments are merely exemplary of the application that may be embodied in various forms and that, therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present application.
For the sake of brevity, only some numerical ranges are explicitly disclosed herein. However, any lower limit may be combined with any upper limit to form ranges not explicitly recited: and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and similarly any upper limit may be combined with any other upper limit to form a range not explicitly recited. Also, although not explicitly recited, each point or individual value between endpoints of a range is encompassed within the range. Thus, each point or individual value can form a range not explicitly recited as its own lower or upper limit in combination with any other point or individual value or in combination with other lower or upper limits.
In the present application, the average particle diameter refers to the particle diameter R (diameter) of each material particle obtained by imaging and observing the material powder by SEM, randomly selecting 10 material particles from the SEM image by using image analysis software, and then obtaining the area of each material particle, and assuming that the material particle is spherical, by the following formula: R2X (S/Pi)1/2(ii) a Wherein S is the area of the material particles; the average particle diameter of the material particles was determined by performing a process of determining the particle diameter R of the material particles on 10 SEM images and arithmetically averaging the particle diameters of the 100(10 × 10) material particles obtained.
[ Positive electrode sheet ]
In a first aspect of the embodiments of the present application, a positive electrode sheet is provided.
In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is disposed on a surface of the positive electrode current collector. In some embodiments, the positive current collector is a metal, such as, but not limited to, aluminum foil. In some embodiments, the positive electrode active material layer includes a manganese element and a phosphorus element.
When the positive electrode active material layer contains a manganese element, at least a part of the manganese element is usually Mn3+For example, a lithium manganate-based material, a nickel cobalt lithium manganate-based material. Since the electrolyte of an electrochemical device generally contains trace amounts of moisture, water reacts with lithium salt LiPF in the electrolyte6Easy to react to form HF, Mn under the action of HF3+Easily generate Mn by disproportionation reaction4+And Mn2+(ii) a In one aspect, Mn2+Easy dissolution, especially further accelerated dissolution at high temperature, the dissolution process causing the particle structure of the positive electrode material to be destroyed, and on the other hand, Mn dissolved in the electrolyte during charging2+The manganese element is diffused from the anode to the cathode and is deposited on the surface of the cathode in a metal form, so that an SEI film on the surface of the cathode is damaged. The positive active material layer contains phosphorus which can be complexed with HF, so that the content of HF in the electrolyte is obviously reduced, and the stability of the electrochemical device is improved; meanwhile, the present applicationThe element content of the surface of the positive electrode active material layer is set so that the molar ratio of the manganese element to the phosphorus element is in the range of 70:1 to 450:1, and in some embodiments, the molar ratio of the manganese element to the phosphorus element is in the range of 70:1 to 200: 1. The surface of the positive active material layer in this application means the surface of keeping away from the mass flow body in the positive active material layer, satisfies certain scope through the amount of the phosphorus element on control positive active material layer surface, can fully complex the HF near positive active material layer surface, avoids manganese element to dissolve in electrolyte, can improve electrochemical device stability under the high temperature condition, prolongs electrochemical device's life. When the content of the phosphorus element is higher than the range, the impedance of the surface of the positive electrode active material layer is overlarge; when the content of the phosphorus element is less than this range, the effect of improving the high-temperature performance is not good.
In the examples of the present application, the contents of the manganese element and the phosphorus element on the surface of the positive electrode active material layer may be measured by any method known in the art capable of measuring the contents of the manganese element and the phosphorus element. In some embodiments, the present application may employ the following SEM-EDX test methods for determination: firstly, selecting an area of 200 mu m multiplied by 200 mu m from an SEM-EDX picture of the surface of the positive active material layer, and testing the number of P atoms and N atoms in the whole area1(ii) a The number of Mn atoms N in the range within this area was then tested2(ii) a The molar ratio of Mn to P in the area is W1＝N2/N1。
In the embodiments of the present application, the method of preparing the positive electrode active material layer is not particularly limited, and a preparation method known to those skilled in the art may be employed. For example, the positive electrode active material layer may be prepared by mixing a positive electrode active material containing Mn element and a phosphorus-containing compound in a positive electrode slurry, and then coating the positive electrode slurry on a positive electrode current collector. When preparing the positive electrode active material layer with the phosphorus-containing compound having different concentrations in the thickness direction, the phosphorus-containing compound can have different concentrations in the thickness direction of the positive electrode active material layer by controlling the drying temperature and the drying rate by utilizing the difference in deposition rate and filling property caused by the difference in density and particle size between the phosphorus-containing compound and the positive electrode active material. In addition, the positive electrode active material layers with different concentrations of phosphorus-containing compounds in the thickness direction can be prepared in a layered coating mode, wherein the layered coating mode is to coat positive electrode slurry on a positive electrode current collector layer by layer, the proportion of the positive electrode active material to the phosphorus-containing compounds in the positive electrode slurry coated on each layer can be the same or different, and the content difference of the phosphorus-containing compounds in the thickness direction of the positive electrode active material layers can be controlled by setting the proportion of the positive electrode active material to the phosphorus-containing compounds in the positive electrode slurry coated on each layer to be different.
In some embodiments, the thickness of the positive electrode active material layer is H, and the molar ratio of the phosphorus element to the manganese element on the surface of the positive electrode active material layer is PoThe molar ratio of phosphorus element to manganese element in the depth region from H/4 to H/3 of the surface of the positive electrode active material layer is Pi，Po/PiIs 0.5 to 2. The amount of the phosphorus element on the surface of the positive active material layer is ensured to meet a certain range, and meanwhile, the phosphorus element close to the surface is ensured to be present in a considerable amount, so that the side reaction in the positive active material layer can be reduced, and the high-temperature stability of the electrochemical device is further improved. In some embodiments, Po/PiIs 1 to 1.38.
In the examples of the present application, the molar ratio of the phosphorus element and the manganese element on the surface of the positive electrode active material layer was PoThe molar ratio of the phosphorus element to the manganese element in a depth region from H/4 to H/3 of the surface of the positive electrode active material layer is PiAny method known in the art capable of determining the content of elemental phosphorus and elemental manganese may be used, and in some embodiments, the present application may use the following SEM-EDX test method: firstly, an area with the size of 200 mu m multiplied by 200 mu m is selected from a surface SEM-EDX picture of a positive electrode active material layer, and the molar ratio P of phosphorus element and manganese element in the whole area is testedo(ii) a Then, an area of 200 μm × 200 μm is selected from SEM-EDX pictures of a depth region from H/4 to H/3 of the surface of the positive electrode active material layer, and the molar ratio P of phosphorus element and manganese element in the whole area is testedi(ii) a Taking the ratio of the two as Po/Pi。
In the examples of the present application, when preparing positive electrode active material layers having different concentrations of phosphorus-containing compounds in the thickness direction by means of layered coating, P can be obtained by coating a positive electrode slurry having a relatively low phosphorus-containing compound ratio first and then coating a positive electrode slurry having a relatively high phosphorus-containing compound ratio secondo/PiThe value is greater than 1 and equal to or less than 1.38.
In some embodiments, the positive electrode active material layer includes a positive electrode active material. In some embodiments, the positive active material includes at least one of compound a) or compound b): compound a) Lix1Mn2-y1 Zy1O4Wherein Z comprises at least one of Mg, Al, B, Cr, Ni, Co, Zn, Cu, Zr, Ti or V, x1 is more than or equal to 0.8 and less than or equal to 1.2, and y1 is more than or equal to 0 and less than or equal to 0.1; compound b) Lix2Niy2CozMnkMqOb-aTaWherein M comprises at least one of 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 halogen, and x2, y2, z, k, q, a, and b satisfy: x2 is more than or equal to 0.2 and less than or equal to 1.2, y2 is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, 0<k≤1、0≤q≤1、1<b is less than or equal to 2 and a is less than or equal to 1 and more than or equal to 0.
The manganese element is added into the positive electrode active material layer in the form of a lithium manganate positive electrode active material and/or a ternary positive electrode active material. Lithium manganate-based material (Li)x1Mn2-y1 Zy1O4) The lithium ion battery positive active material has high theoretical specific capacity and high safety performance, has high commercial performance cost ratio relative to the average potential of a lithium electrode of about 3.9V, but has serious specific capacity attenuation particularly under high temperature (higher than 60 ℃) in the charging and discharging process, and can avoid Mn in the lithium ion battery material by better complexing HF in electrolyte3+Disproportionation reaction is carried out to avoid Mn2+The formation of (2) is carried out, so that the structure of lithium manganate is prevented from being damaged, the Jahn-Teller effect of spinel lithium manganate in the charging and discharging process can be avoided, the crystal distortion when the manganese valence degree is lower than +3.5 is avoided, and the cubic phase to the tetragonal phase are prevented from being formedThe lattice distortion caused by the transformation can effectively solve the problem that the specific capacity of the lithium manganate material is attenuated under the high temperature condition.
The phosphorus element is added to the positive electrode active material layer in the form of a phosphorus-containing compound. In some embodiments, the positive active material layer includes a phosphorus-containing compound including AxPOyWherein A comprises at least one of Li, Na, K, Mg, Ca, Y, Sr, Ba, Zn, Al or Si, x is more than or equal to 1 and less than or equal to 4, and Y is more than or equal to 3 and less than or equal to 4.
In some embodiments, the cathode active material has an average particle diameter of D1, and the phosphorus-containing compound has an average particle diameter of D2, 0.33 ≦ D1/D2 ≦ 100. When the positive electrode active material and the phosphorus-containing compound satisfy the above conditions, the phosphorus-containing compound can be uniformly dispersed in the positive electrode active material layer, and when D1/D2<0.33, the particle size of the phosphorus-containing compound is relatively excessively large, resulting in difficulty in uniform distribution of the phosphorus-containing compound in the positive electrode active material layer, and poor stability due to lack of effective protection of the phosphorus-containing compound locally; when D1/D2>100, the particle size of the phosphorus-containing compound is relatively too small, and the phosphorus-containing compound is more deposited in the lower layer of the positive electrode active material layer during coating and fills in the pores between the positive electrode active materials, resulting in lack of effective protection of the phosphorus-containing compound on the surface of the positive electrode active material layer, and the phosphorus-containing compound having a small particle size is liable to agglomerate and is also difficult to disperse uniformly.
In some embodiments, the surface of the positive electrode active material has the phosphorus-containing compound, and the thickness h of the phosphorus-containing compound is 10nm to 30 nm. When the positive electrode active material and the phosphorus-containing compound meet the conditions, a solid solution interface is formed between the phosphorus-containing compound and the positive electrode active material, so that the surface of the positive electrode active material can be effectively protected, and the problem of impedance increase caused by overlarge thickness is avoided. During preparation, the precursor of the positive active material is uniformly mixed with a lithium source and a phosphorus-containing compound in a high-speed mechanical mixing mode, and the mixture is sintered to obtain the positive active material with the surface coated with the phosphorus-containing compound.
In some embodiments, the average particle diameter D1 of the positive electrode active material is 2 μm to 30 μm. In some embodiments, the average particle size D2 of the phosphorus-containing compound is 0.1 μm to 30 μm.
In some embodiments, the average particle diameter D1 of the positive electrode active material is 10 μm to 25 μm. In some embodiments, the average particle size D2 of the phosphorus-containing compound is 0.1 μm to 5 μm.
The mass ratio of the positive active material to the phosphorus-containing compound influences the distribution of the manganese element and the phosphorus element in the positive active material layer, and when the mass ratio of the positive active material to the phosphorus-containing compound meets a certain range, the distribution of the phosphorus element in the positive active material layer is favorably adjusted, the complexation of P and HF is promoted, and the high-temperature stability of the electrochemical device is further improved. In some embodiments, the mass ratio of the positive electrode active material to the phosphorus-containing compound is 95 to 97: 0.5-3.
In some embodiments, the surface of the positive electrode active material layer has an XRD pattern of IAIndicates a characteristic peak intensity in the range of 20 DEG to 21 DEG, IBIndicating a characteristic peak intensity in the range of 18 DEG to 18.6 DEG, I of 0.12. ltoreq.A/IBLess than or equal to 0.2. The characteristic peak intensity in the range of 20-21 degrees corresponds to the content of the phosphorus-containing compound in the positive electrode active material layer, and the characteristic peak intensity in the range of 18-18.6 degrees corresponds to the content of lithium manganate in the positive electrode active material layer.
In some embodiments, the positive active material layer further includes a positive binder. The positive electrode binder is used to improve binding properties between positive electrode active material particles and between the positive electrode active material particles and a positive electrode current collector. The positive electrode binder is a binder known in the art that can be used as a positive electrode active material layer. In some embodiments, the positive electrode binder comprises at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy, nylon.
In some embodiments, the positive electrode active material layer further includes a positive electrode conductive agent. The positive electrode conductive agent is used for improving the conductivity of the positive electrode sheet. The positive electrode conductive agent is a conductive agent known in the art that can be used as a positive electrode active material layer. In some embodiments, the positive electrode conductive agent includes at least one of graphite, conductive carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, graphene, metal powder, metal fiber. In some embodiments, the metal in the metal powder and metal fibers comprises at least one of copper, nickel, aluminum, silver.
The mixing ratio of the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent in the positive electrode active material layer is not particularly limited, and may be controlled according to the desired electrochemical device performance.
[ electrochemical device ]
A second aspect of embodiments of the present application provides an electrochemical device. The electrochemical device of the present application is, for example, a primary battery or a secondary battery. The secondary battery is, for example, 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. In some embodiments, the electrochemical device comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, the positive electrode sheet being the positive electrode sheet of the first aspect of the present application.
In some embodiments, the electrochemical device is stored for 1 day at 80 ℃ after being discharged to 25% charge state, and the anode plate is washed by dimethyl carbonate solvent and dried for 12 hours at 85 ℃ after being disassembled, and then Raman test is adopted at 258-846cm-1Two peaks exist in the wavelength range, and the ratio of the most intense peak to the less intense peak is: 1.6-2.0, which shows that the surface layer lithium manganate still has an initial crystal structure and is well protected.
Negative plate
The negative electrode tab is a negative electrode tab known in the art that may be used in an electrochemical device. In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative active material layer is disposed on a surface of the negative current collector.
In some embodiments, the negative current collector is a metal such as, but not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or combinations thereof.
In some embodiments, the negative active material layer includes a negative active material. The negative active material may be selected from a variety of conventionally known materials capable of intercalating and deintercalating active ions or a conventionally known material capable of doping and dedoping active ions, which are known in the art and may be used as an electrochemical device. In some embodiments, the negative active material includes at least one of a carbon material, a silicon material, lithium metal, a lithium metal alloy, and a transition metal oxide. In some embodiments, the carbon material comprises at least one of natural graphite, synthetic graphite, soft carbon, hard carbon, mesophase pitch carbonization products, fired coke.
In some embodiments, the negative active material layer further includes a negative binder. The negative electrode binder is used to improve binding properties between the negative electrode active material particles and the negative electrode current collector. The negative electrode binder is a binder known in the art that can be used as a negative electrode active material layer. In some embodiments, the negative electrode binder comprises at least one of polyvinyl alcohol, carboxymethyl cellulose, 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.
In some embodiments, the negative active material layer further includes a negative conductive agent. The negative electrode conductive agent is used to improve the conductivity of the negative electrode sheet. The negative electrode conductive agent is a conductive agent known in the art that can be used as a negative electrode active material layer. In some embodiments, the negative electrode conductive agent includes at least one of conductive carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, graphene, metal powder, metal fiber, and polyphenylene derivative. In some embodiments, the metal in the metal powder and the metal fiber comprises at least one of copper, nickel, aluminum and silver.
In some embodiments, the method of preparing the negative electrode sheet is a method of preparing a negative electrode sheet that may be used for an electrochemical device, which is well known in the art. In some embodiments, in the preparation of the negative electrode slurry, a solvent, a negative electrode active material, and a negative electrode binder are generally added, and a negative electrode conductive agent and a thickener are added as needed to prepare a negative electrode slurry. The solvent is evaporated during the drying process. The solvent is a solvent known in the art that can be used as the negative electrode active material layer, and the solvent is, for example, but not limited to, water, N-methylpyrrolidone. The thickener is a thickener known in the art that can be used as the negative electrode active material layer, and is, for example, but not limited to, sodium carboxymethyl cellulose. The mixing ratio of the negative electrode active material, the negative electrode binder, the negative electrode conductive agent, and the thickener in the negative electrode active material layer is not particularly limited, and may be controlled according to the desired electrochemical device performance.
Electrolyte solution
The electrolyte is well known in the art and may be used in electrochemical devices. In some embodiments, the electrolyte includes an organic solvent, an electrolyte salt, and an additive.
The organic solvent may be an organic solvent known in the art to be used for the electrolyte. In some embodiments, the organic solvent includes at least one of Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, and ethyl propionate.
The electrolyte salt may be one known in the art to be used for the electrolytic solution. In some embodiments, the electrolyte salt is a lithium salt, the lithium salt including at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt comprises lithium hexafluorophosphate (LiPF)6) Lithium tetrafluoroborate (LiBF)4) Lithium difluorophosphate (LiPO)2F2) Lithium bis (trifluoromethanesulfonylimide) LiN (CF)3SO2)2(LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO)2F)2) (LiFSI) bis oxalic acidLithium borate LiB (C)2O4)2(LiBOB) and lithium difluoro (oxalato) borate LiBF2(C2O4) (LiDFOB). In some embodiments, the lithium salt comprises lithium hexafluorophosphate (LiPF)6). In some embodiments, the molar concentration of lithium in the lithium salt is from about 0.5mol/L to about 3mol/L, from about 0.5mol/L to about 2mol/L, or from about 0.8mol/L to about 1.5mol/L, based on the volume of the electrolyte.
The additive may be one known in the art to be used for the electrolyte.
In some embodiments, the positive electrode sheet is placed in a volume ratio of ethylene carbonate to dimethyl carbonate of 3: 7. LiPF6In the electrolyte with the concentration of 1M, the volume ratio of the mass of the positive active material layer contained in the positive plate to the electrolyte is 1g/100mL, and after the positive active material layer is soaked for 1 day at 80 ℃, the mass percentage z of Mn element and Li element contained in the electrolyte is less than or equal to 0.5 percent, which shows that the electrochemical device has higher high-temperature stability because HF in the electrolyte is complexed by phosphorus element and Mn element is less dissolved in the electrolyte.
Isolation film
The separator is a separator known in the art that can be used in an electrochemical device. The separator is disposed between the positive electrode tab and the negative electrode tab for preventing a short circuit.
The material and shape of the separator are not particularly limited in the present application. In some embodiments, the separator includes a polymer or inorganic formed of a material that is stable to the electrolyte of the present application.
In some embodiments, the barrier film includes a substrate layer and a surface treatment layer disposed on at least one surface of the substrate layer.
In some embodiments, the substrate layer is a nonwoven fabric, a film, or a composite film having a porous structure. In some embodiments, the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. In some embodiments, the substrate layer is selected from any one of a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film.
In some embodiments, the surface treatment layer is a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. In some embodiments, the inorganic layer comprises inorganic particles selected from the group consisting of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate, and a binder selected from the group consisting of polyvinylidene fluoride, copolymers of vinylidene fluoride-hexafluoropropylene, polyamides, polyacrylonitrile, polyacrylates, polyacrylic acids, polyacrylates, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. In some embodiments, the polymer layer comprises a polymer of a material selected from at least one of a polyamide, a polyacrylonitrile, an acrylate polymer, a polyacrylic acid, a polyacrylate, a polyvinylpyrrolidone, a polyvinyl ether, a polyvinylidene fluoride, or a poly (vinylidene fluoride-hexafluoropropylene).
Outer packing shell
In some embodiments, the electrochemical device further comprises an overwrap housing. The outer packaging case is a well known outer packaging case in the art that can be used for electrochemical devices and is stable to the electrolyte used, such as, but not limited to, a metal-based outer packaging case.
[ electronic device ]
A third aspect of the embodiments of the present application provides an electronic device. The electronic device of the present application is any electronic device such as, but not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handy cleaner, a portable CD player, a mini disc, a transceiver, an electronic notebook, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large-sized household battery, and a lithium ion capacitor. Note that 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.
In some embodiments, the electronic device comprises the electrochemical device of the second aspect of the present application.
The present application is further illustrated below with reference to examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present application.
In the following examples and comparative examples, reagents, materials and instruments used were commercially available or synthetically available, unless otherwise specified.
Example 1
(1) Preparation of the electrolyte
Under dry argon atmosphere, organic solvents Propylene Carbonate (PC), Ethylene Carbonate (EC), diethyl carbonate (DEC) were as follows: 1: 1, adding fully dried lithium salt LiPF6Dissolving in the organic solvent, and mixing thoroughly to obtain electrolyte with lithium salt concentration of 1.15 mol/L.
(2) Preparation of positive plate
Mixing the positive active material LiMn2O4(average particle diameter D1 is 10 μm), phosphorus-containing compound Al (PO)3)3(average particle diameter D2 was 5 μm), conductive carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a ratio of 97.5: 0.5: 1: 1, then adding a proper amount of N-methyl pyrrolidone (NMP) as a solvent, fully stirring and uniformly mixing to prepare positive electrode slurry with a solid content of 75% and a viscosity of 5000 mPas.
And then uniformly coating the positive electrode slurry on an aluminum foil, drying at 80 ℃, rolling, wherein the thickness of one surface of a positive electrode active material layer is 40 mu m, and repeating the steps on the other surface of the positive electrode plate to obtain the positive electrode plate with double-coated surfaces.
(3) Preparation of the separator
Polyethylene (PE) porous polymeric films were used as separators.
(4) Preparation of negative plate
Mixing a negative electrode active material artificial graphite, a binder styrene-butadiene rubber and a thickener carboxymethylcellulose sodium (abbreviated as CMC) according to a ratio of 96: 2: 2 in a proper amount of deionized water solvent, and fully stirring and mixing to form uniform cathode slurry; and coating the negative electrode slurry on a copper foil with the thickness of 12 mu m, drying, cold pressing, cutting into pieces, and welding a tab to obtain the negative electrode sheet.
(5) Preparation of lithium ion battery
Stacking the prepared positive plate, the isolating film and the negative plate in sequence to enable the isolating film to be positioned between the positive plate and the negative plate to play an isolating role, and then winding to obtain a bare cell; placing the bare cell in an outer package, leaving a liquid injection port, injecting the prepared electrolyte from the liquid injection port, and completing the preparation of the lithium ion battery through the procedures of vacuum packaging, standing, formation, shaping and the like.
Example 2
Different from example 1 is the preparation of a positive electrode sheet. Positive electrode active material LiMn2O4Phosphorus-containing compound Al (PO)3)3The weight ratio of the conductive agent, conductive carbon black (Super P) and the binder, namely polyvinylidene fluoride (PVDF), is 97: 1: 1: 1. and uniformly coating the anode slurry on an aluminum foil, quickly drying at 120 ℃, and rolling.
Example 3
Different from example 1 is the preparation of a positive electrode sheet. Positive electrode active material LiMn2O4Phosphorus-containing compound Al (PO)3)3The weight ratio of the conductive agent, conductive carbon black (Super P) and the binder, namely polyvinylidene fluoride (PVDF), is 97: 1: 1: 1.
example 4
Different from example 3 is the preparation of the positive electrode sheet. And (3) coating the positive electrode slurry with a low phosphorus compound ratio on the aluminum foil in a layered coating mode, drying, coating the positive electrode slurry with a high phosphorus compound ratio, drying and rolling.
Example 5
Different from example 3 is the preparation of the positive electrode sheet. And (3) coating the positive electrode slurry with a high phosphorus compound ratio on the aluminum foil in a layered coating mode, drying, coating the positive electrode slurry with a low phosphorus compound ratio, drying and rolling.
Example 6
Different from example 1 is the preparation of a positive electrode sheet. Positive electrode active material LiMn2O4Phosphorus-containing compound Al (PO)3)3The weight ratio of the conductive agent, the conductive carbon black (Super P) and the binder, namely polyvinylidene fluoride (PVDF), is 96.5: 1.5: 1: 1. and (3) uniformly coating the anode slurry on an aluminum foil, drying at 100 ℃, and rolling.
Example 7
Different from example 1 is the preparation of a positive electrode sheet. Positive electrode active material LiMn2O4Phosphorus-containing compound Al (PO)3)3The weight ratio of the conductive agent, conductive carbon black (Super P) and the binder polyvinylidene fluoride (PVDF) is 95: 3: 1: 1. and (3) uniformly coating the anode slurry on an aluminum foil, drying at 100 ℃, and rolling.
Example 8
Different from example 1 is the preparation of a positive electrode sheet. Positive electrode active material LiMn2O4(average particle diameter D1 is 20 μm) and the phosphorus-containing compound is LiPO3(average particle diameter D2 is 5 μm), conductive carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 97: 1: 1: 1.
example 9
Different from example 8 is the preparation of a positive electrode sheet. The phosphorus-containing compound is Ce (PO)3)3(average particle diameter D2 was 5 μm).
Example 10
Different from example 8 is the preparation of a positive electrode sheet. Positive electrode active material LiMn2O4(average particle diameter D1 is 25 μm) and the phosphorus-containing compound is NaPO3(average particle diameter D2 was 5 μm).
Example 11
Different from example 1 is the preparation of a positive electrode sheet. Mixing the positive active material LiMn2O4And LiNi0.5Co0.2Mn0.3O2(average particle diameter D1 is 10 μm), phosphorus-containing compound Al (PO)3)3(average particle diameter D2 was 5 μm), conductive carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a ratio of 87.3: 7.8: 1: 1: 1 by weight ratio.
Example 12
Different from example 1 is the preparation of a positive electrode sheet. Positive electrode active material LiNi0.5Co0.2Mn0.3O2Phosphorus-containing compound Al (PO)3)3The weight ratio of the conductive agent, conductive carbon black (Super P) and the binder, namely polyvinylidene fluoride (PVDF), is 97: 1: 1: 1.
example 13
The difference from example 2 was the preparation of the positive electrode sheet. Phosphorus-containing compounds Al (PO)3)3(the average particle diameter D2 was 0.1. mu.m).
Example 14
The difference from example 2 was the preparation of the positive electrode sheet. Phosphorus-containing compounds Al (PO)3)3(the average particle diameter D2 was 0.2. mu.m).
Example 15
The difference from example 2 was the preparation of the positive electrode sheet. Phosphorus-containing compounds Al (PO)3)3(the average particle diameter D2 was 0.5. mu.m).
Example 16
The difference from example 2 was the preparation of the positive electrode sheet. The positive active material is a phosphorus compound Al (PO)3)3Coated LiMn2O4The coating thickness was 20 nm.
Comparative example 1
Different from example 1 is the preparation of a positive electrode sheet. Mixing the positive active material LiMn2O4(average particle diameter D1 is 10 μm), conductive carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 98: 1: 1 by weight ratio.
Comparative example 2
Different from example 1 is the preparation of a positive electrode sheet. Positive electrodeActive material LiMn2O4(average particle diameter D1 is 10 μm), phosphorus-containing compound Al (PO)3)3(average particle diameter D2 is 0.5 μm), conductive carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 94: 4: 1: 1.
comparative example 3
Different from example 1 is the preparation of a positive electrode sheet. Positive electrode active material LiMn2O4(average particle diameter D1 is 10 μm), phosphorus-containing compound Al (PO)3)3(the average particle diameter D2 is 5 μm), the weight ratio of the conductive agent conductive carbon black (Super P) to the binder polyvinylidene fluoride (PVDF) is 94: 4: 1: 1.
comparative example 4
Different from example 1 is the preparation of a positive electrode sheet. Positive electrode active material LiMn2O4(average particle diameter D1 is 10 μm), phosphorus-containing compound Al (PO)3)3(average particle diameter D2 is 0.1 μm), conductive carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 97: 1: 1: 1.
comparative example 5
Different from example 1 is the preparation of a positive electrode sheet. Mixing the positive active material LiMn2O4And LiNi0.5Co0.2Mn0.3O2(average particle diameter D1 was 10 μm), conductive carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were mixed in a ratio of 88.2: 9.8: 1: 1 by weight ratio.
Test method of lithium ion battery
Element mole ratio test:disassembling the formed lithium ion battery to obtain a positive plate, (1) testing the distribution condition of Mn elements and P elements in the surface of the positive active material layer by adopting an SEM-EDX test method, selecting an area with the size of 200 microns multiplied by 200 microns from an SEM-EDX picture, and testing to obtain the ratio of the number of Mn atoms to the number of P atoms in the whole area. (2) Testing the distribution of surface P element and P element at 10 μm depth from the surface in the positive active material layer by SEM-EDX test method, selecting 200 μm × 200 μm area in the surface SEM-EDX picture of the positive active material layer, and testing phosphorus element and manganese in the whole areaMolar ratio P of elementso(ii) a Then, an area of 200 μm × 200 μm was selected from SEM-EDX pictures at a depth of 10 μm from the surface of the positive electrode active material layer, and the molar ratio P of phosphorus element to manganese element was measured over the entire areai(ii) a Further obtain Po/Pi。
XRD test:keeping the surface of the dried positive plate smooth, placing the positive plate in a sample platform of an XRD testing instrument (model Bruk, D8), and scanning the positive plate at a scanning angle ranging from 10 degrees to 90 degrees at a scanning speed of 2 degrees/min to obtain an XRD (X-ray diffraction) spectrum.
Average particle size test:taking the average particle diameter D2 of the phosphorus-containing compound as an example, the material powder was observed by scanning electron microscopy using SEM, 10 particles of the phosphorus-containing compound were randomly selected from the SEM photograph using image analysis software, and the area of each of the particles of the phosphorus-containing compound was determined, and then, assuming that the material particles were spherical, the particle diameter R (diameter) of each particle was determined by the following formula: R2X (S/Pi)1/2(ii) a Wherein S is the area of the phosphorus-containing compound particles; the particle diameter R of the phosphorus-containing compound particles was determined by subjecting 10 SEM images, and the particle diameters of 100(10 × 10) phosphorus-containing compound particles were arithmetically averaged to determine the average particle diameter D2 of the phosphorus-containing compound particles.
And (3) Raman spectrum testing:discharging the lithium ion battery to 25% SOC, storing for 1 day at 80 ℃, after disassembling, washing the positive plate by dimethyl carbonate solvent, drying for 12h at 85 ℃, placing the positive plate in a Raman testing instrument sample stage, performing peak position correction by using a silicon wafer, randomly focusing a point on the positive plate at 10+ long focal length, and performing ion exchange at 258--1Two peaks exist in the wavelength range, and the ratio of the strongest peak to the second strongest peak is taken; 10 spots were randomly focused and the average was recorded as the raman peak intensity ratio.
And (3) performing electric deduction test:cleaning one surface of the dried positive active material layer with N-methylpyrrolidone (NMP), vacuum baking at 85 deg.C for 2h, taking out the positive electrode, punching small round piece required by 2025 button cell, assembling the button cell according to foamed nickel, lithium piece, isolation film and positive round piece, and injecting 50 microliter of electrolyteThe electrolyte consists of EC: PC: DEC ═ 1: 1: 1, and LiPF in the electrolyte6The concentration of (2) is 1.15 mol/L.
The assembled button cell was charged and discharged at a cutoff voltage of about 2.7 to about 4.3V at 25 ℃ at a current of 0.2C, and tested for gram capacity, which is the discharge capacity per mass of the positive active material.
And (3) charging the assembled button cell at 45 ℃ with a constant current of 0.5 ℃, then discharging at a constant current of 0.5 ℃, circulating for 50 times, and calculating the ratio of the electric quantity discharged by the 50 th discharge to the initial discharge capacity.
Mn/Li content test in electrolyte: placing the positive plate in a state that the volume ratio of ethylene carbonate to dimethyl carbonate is 3: 7. LiPF6In the electrolyte with the concentration of 1M, the mass ratio of the positive active material layer to the volume ratio of the electrolyte is 1g/100mL, after the electrolyte is soaked for 1 day at the temperature of 80 ℃, the electrolyte is filtered by a 450nm filter head, and the content of Mn in the filtrate is measured by a plasma optical direct-reading spectrometer (ICP).
And (3) high-temperature storage test:discharging the lithium ion battery to 30% SOC, and recording the 100% SOC as an initial capacity; and (3) storing the lithium ion battery in an oven at 60 ℃ for 7 days, then charging and discharging for 3 times by adopting 0.2C current, and measuring the capacity of the lithium ion battery at the moment and recording the capacity recovered after standing. Recovery capacity retention (%) — recovery capacity after standing/initial capacity.
High-temperature cycle test:after the lithium ion battery is formed, charging at a constant current of 0.5C at 45 ℃, then discharging at a constant current of 1C, and after circulating for 500 times, calculating the ratio of the electric quantity discharged by the 500 th discharge to the initial discharge capacity.
Figure BDA0003337525000000161
The data analysis in table 1 shows that when the molar ratio of the manganese element to the phosphorus element on the surface of the positive active material layer satisfies the range of 70:1 to 450:1, the interface stability of the manganese-containing positive plate in the electrolyte can be improved, and the high-temperature storage and high-temperature cycle performance of the lithium ion battery can be remarkably improved. From comparative examples 2 to 3, it is understood that when the molar ratio of the manganese element to the phosphorus element on the surface of the positive electrode active material layer is less than 70:1, the surface resistance is increased and the cycle performance is lowered due to the excessive amount of the phosphorus-containing compound on the surface. As can be seen from comparative example 4, when the particle diameter D2 of the phosphorus-containing compound is small relative to the particle diameter D1 of the active material, the drying rate is slow, and the phosphorus-containing compound is liable to fill in the gaps between the active materials and thus to be concentrated in the lower layer of the active material layer, resulting in the unsatisfactory molar ratio of the manganese element and the phosphorus element at the surface, and the high-temperature storage and cycle can not be improved as well.
From the data of examples 2 to 5, it can be seen that when the total amount of the phosphorus element in the positive electrode active material layer is the same, the distribution amount of the phosphorus element on and near the surface of the positive electrode active material layer affects the performance of the lithium ion battery. When the surface of the positive active material layer and the inner part close to the surface of the positive active material layer are ensured to have equivalent phosphorus elements, the high-temperature storage and high-temperature cycle performance of the lithium ion battery can be better improved. Example 4 shows that when Po/Pi is 2, the high temperature performance is degraded because the phosphorus-containing compound content inside the layer near the surface of the positive electrode active material layer is relatively low and cannot be well protected. On the other hand, example 5 shows that when Po/Pi is 0.5, the resistance of the surface layer of the positive electrode active material layer increases due to the relatively large content of the phosphorus-containing compound in the inside near the surface of the positive electrode active material layer, and thus the cycle performance thereof is lowered.
From the data of examples 2, 13-15, it can be seen that when the average particle diameter D1 of the positive electrode active material and the average particle diameter D2 of the phosphorus-containing compound satisfy 0.33. ltoreq. D1/D2. ltoreq.100, the phosphorus-containing compound particles can be uniformly distributed in the positive electrode active material layer by controlling the drying rate, and a considerable amount of phosphorus-containing compound can be present on the surface of the positive electrode active material layer and inside of the surface close to the positive electrode active material layer, and the high-temperature storage and high-temperature cycle performance of the lithium ion battery can be better improved.
From the data of example 16, it can be seen that the high-temperature storage and high-temperature cycle performance of the lithium ion battery can be also well improved when the surface of the positive electrode active material is coated with the phosphorus-containing compound.

Claims (10)

1. A positive electrode sheet comprising a positive electrode active material layer, the element content of the surface of the positive electrode active material layer satisfying: the molar ratio of the manganese element to the phosphorus element is 70:1 to 450: 1.
2. The positive electrode sheet according to claim 1, wherein the thickness of the positive electrode active material layer is H, and the molar ratio of phosphorus element and manganese element on the surface of the positive electrode active material layer is Po; the molar ratio of phosphorus element to manganese element in the depth region from H/4 to H/3 of the surface of the positive active material layer is Pi，Po/PiIs 0.5 to 2.
3. The positive electrode sheet according to claim 2, wherein the positive electrode sheet satisfies at least one of the following conditions:
1) the element content of the surface of the positive active material layer satisfies the following conditions: the molar ratio of the manganese element to the phosphorus element is 70:1 to 200: 1;
2)Po/Piis 1.0 to 1.38.
4. The positive electrode sheet according to claim 2, wherein in an XRD pattern of a surface of the positive electrode active material layer, IAIndicates a characteristic peak intensity in the range of 20 DEG to 21 DEG, IBIndicating a characteristic peak intensity in the range of 18 DEG to 18.6 DEG, I of 0.12. ltoreq.A/IB≤0.2。
5. The positive electrode sheet according to claim 1, wherein the positive electrode active material layer comprises a positive electrode active material and a phosphorus-containing compound, and at least one of the following conditions is satisfied:
i) the average particle size of the positive electrode active material is D1, the average particle size of the phosphorus-containing compound is D2, and D1/D2 are not less than 0.33 and not more than 100;
ii) the surface of the positive electrode active material has the phosphorus-containing compound, and the thickness h of the phosphorus-containing compound is 10nm to 30 nm.
6. The positive electrode sheet according to claim 5, wherein the D1 is 2 to 30 μm, and the D2 is 0.1 to 30 μm.
7. The positive electrode sheet according to claim 5, said phosphorus-containing compound comprising AxPOyWherein A comprises at least one of Li, Na, K, Mg, Ca, Y, Sr, Ba, Zn, Al or Si, x is more than or equal to 1 and less than or equal to 4, and Y is more than or equal to 3 and less than or equal to 4.
8. The positive electrode sheet according to claim 5, wherein the positive electrode active material comprises at least one of compound a) or compound b):
compound a) Lix1Mn2-y1 Zy1O4Wherein Z comprises at least one of Mg, Al, B, Cr, Ni, Co, Zn, Cu, Zr, Ti or V, x1 is more than or equal to 0.8 and less than or equal to 1.2, and y1 is more than or equal to 0 and less than or equal to 0.1;
compound b) Lix2Niy2CozMnkMqOb-aTaWherein M comprises at least one of 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 halogen, and x2, y2, z, k, q, a, and b satisfy: x2 is more than or equal to 0.2 and less than or equal to 1.2, y2 is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, 0<k≤1、0≤q≤1、1<b is less than or equal to 2 and a is less than or equal to 1 and more than or equal to 0.
9. An electrochemical device comprising the positive electrode sheet according to any one of claims 1 to 8.
10. An electronic device comprising the electrochemical device as claimed in claim 9.
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