CN112582579A

CN112582579A - Positive electrode, electrochemical device, and electronic device

Info

Publication number: CN112582579A
Application number: CN202011429826.1A
Authority: CN
Inventors: 陈鹏伟
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2020-12-07
Filing date: 2020-12-07
Publication date: 2021-03-30

Abstract

The application relates to the technical field of batteries, in particular to a positive electrode for a secondary battery, and an electrochemical device and an electronic device using the positive electrode, wherein the positive electrode comprises a positive electrode current collector and a diaphragm layer arranged on the surface of the positive electrode current collector, and the diaphragm layer comprises an active conductive layer arranged on the surface of the positive electrode current collector and an active material layer arranged on the surface of the active conductive layer; the active conductive layer comprises an active conductive material, the active conductive material comprises a lithium-containing phosphate compound and a coating layer positioned on the surface of the lithium-containing phosphate compound, and the coating layer comprises an organic conductive polymer layer. The secondary battery adopting such a structure has improved safety performance such as nail penetration and heat box, and less resistance increase.

Description

Positive electrode, electrochemical device, and electronic device

Technical Field

The present invention relates to the field of battery technology, and in particular, to a positive electrode for a secondary battery, and an electrochemical device and an electronic device using the same.

Background

The positive electrode material is used as an important component of the lithium ion battery, and 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. With the updating of electronic products, the pursuit of high energy density becomes a development trend of the anode material of the lithium ion battery. Lithium cobaltate, the earliest commercialized lithium ion cathode material, has been widely and deeply studied, has the best overall performance in the aspects of reversibility, discharge capacity, charge efficiency, voltage stability and the like, and is the largest cathode material in the application amount of the lithium ion batteries at present. Through decades of development, the structural characteristics and electrochemical properties of lithium cobaltate are also fully researched, and the synthesis process and industrial production are quite mature. Lithium cobaltate always dominates in the anode material of a consumer lithium ion battery by virtue of a higher discharge voltage platform and higher energy density, but the lithium cobaltate battery also has some obvious defects, such as poorer safety performance of the lithium cobaltate battery. The lithium cobalt oxide battery can not pass safety tests such as nail penetration and falling all the time due to the influence of better conductivity of the lithium cobalt oxide.

The existing method for improving the safety performance of the lithium cobaltate battery is mainly to improve the materials, the electrolyte, the battery structure and the like. For example, lithium cobaltate is doped and coated for modification, so that the thermal stability of the material is improved, or more inert additives are added into the electrolyte, or a thicker diaphragm and an outer package are adopted in the battery structure, and the like.

The dilemma faced by the prior art is that the improvement of the safety performance of the battery is extremely limited by improving materials and electrolyte, the battery structure and the like, and the dynamic performance, the cycle performance and the energy density of the battery are deteriorated. When the traditional lithium cobaltate electrode single-layer membrane works under a high voltage condition, the thermal stability and the electrical conductivity of the traditional lithium cobaltate electrode single-layer membrane are poor, so that the battery faces a plurality of hidden dangers in the aspect of safety, for example, the battery cannot pass safety performance tests such as battery nail penetration and falling, and the safety performance of a mobile phone is finally influenced.

Therefore, it is required to develop a positive electrode having more excellent safety and electrochemical properties to further improve the performance of a lithium ion battery.

Disclosure of Invention

The present application is directed to overcoming the disadvantages of the prior art and providing a positive electrode for improving the safety of a secondary battery and the electrochemical performance of the secondary battery.

The purpose of the application is achieved through the following technical scheme.

One aspect of the present disclosure provides a positive electrode, where the positive electrode includes a positive current collector and a membrane layer disposed on a surface of the positive current collector, and the membrane layer includes an active conductive layer disposed on the surface of the positive current collector and an active material layer disposed on a surface of the active conductive layer; the active conductive layer comprises an active conductive material, the active conductive material comprises a lithium-containing phosphate compound and a coating layer positioned on the surface of the lithium-containing phosphate compound, and the coating layer comprises an organic conductive polymer layer.

In some embodiments of the positive electrode described herein, the lithium-containing phosphate compound comprises at least one of the compounds represented by formula 1:

Li_xM_yN_zPO₄ general formula 1

M comprises at least one of Fe and Mn; n comprises at least one of Al, Ti, V, Cr, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb and Si; wherein x is more than or equal to 0.8 and less than or equal to 1.3, y is more than or equal to 0.95 and less than or equal to 1, and z is more than or equal to 0 and less than or equal to 0.05.

The positive pole of this application adopts double-deck coating technique, namely, coats different active material on the positive pole in proper order range upon range of, and the pole piece upper strata is active material layer, and active material layer occupies higher proportion (thickness is great) in the diaphragm, and the active lithium of secondary cell working process mainly is provided by active material layer. The lower layer is an active conducting layer which is provided with a lithium-containing phosphate compound, and the stability of the membrane can be ensured under high voltage due to the stable structure of the lithium-containing phosphate compound. Meanwhile, the lithium-containing phosphate material has active lithium and can participate in the transmission of lithium ions in the charging and discharging processes, so that the battery has a special discharging platform between 2.8V to 3.2V and 3.9V to 4.1V, and the energy density of the battery is improved to a great extent. Meanwhile, the resistance of the lithium-containing phosphate compound after delithiation is significantly increased, so that an inert layer is provided between the positive active material layer and the positive current collector (aluminum foil substrate). The inert layer can well protect the high potential of the positive terminal of the secondary battery in the electrochemical process, can improve the internal resistance of the battery and improve the safety performance of the battery. When the secondary battery is subjected to safety tests such as nail penetration, falling and the like, the lithium-containing phosphate compound inert layer coated on the surface of the positive current collector (aluminum foil) can well isolate the positive current collector (aluminum foil) from the negative electrode, so that the positive current collector (aluminum foil) is prevented from contacting the negative electrode, and the safety of the secondary battery is greatly improved. In addition, the organic conductive polymer layer exists on the surface of the lithium-containing phosphate compound, and the organic conductive polymer has good stability under high voltage and cannot be easily dropped or oxidized, so that the conductive network of the lithium-containing phosphate compound in the positive electrode is well protected, and the impedance of the battery can be kept to a small level even after the secondary battery is stored at high temperature.

In some embodiments of the positive electrode described herein, the organic conductive polymer comprises at least one of polyacetylene, polythiophene, polypyrrole, polyaniline, polyphenylene vinylene, or polydiyne.

In some embodiments of the positive electrode described herein, the active conductive layer has a thickness of 1 μm to 4 μm.

In some embodiments of the positive electrode described herein, the organic conductive polymer layer has a thickness of 1nm to 8 nm.

In some embodiments of the positive electrode described herein, the active conductive material has an average particle size of 1.0 μm to 3.0 μm.

In some embodiments of the positive electrode described herein, the membrane layer has a resistance of 0.03 Ω to 0.5 Ω.

In some embodiments of the positive electrode described herein, the membrane layer has a compacted density of3.5g/cm³To 4.5g/cm³。

In some embodiments of the positive electrode described herein, the active conductive layer further comprises a conductive agent.

In some embodiments of the positive electrode described herein, the conductive agent is present in an amount of 0.5 to 3.0% by mass, preferably 0.5 to 2.0% by mass, based on the mass of the active conductive layer.

In some embodiments of the positive electrode described herein, the conductive agent includes at least one of conductive carbon black, acetylene black, ketjen black, Super P (SP), graphene, and carbon nanotubes.

In some embodiments of the positive electrode described herein, the active material layer comprises a lithium transition metal composite oxide comprising at least one lithium having the formula Li_x1Ni_y1Co_z1Mn_kZ_qO_b-aT_aA compound of (a), wherein Z includes at least one of B, Mg, Al, Si, P, S, Ti, Cr, Fe, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb, and Ce, T is a halogen, and x1, Y1, Z1, k, q, a, and B satisfy: 0.2<x1 is less than or equal to 1.2, y1 is less than or equal to 1 and less than or equal to 0, z1 is less than or equal to 1 and less than or equal to 0, k is less than or equal to 1 and less than or equal to 0, q is less than or equal to 1 and less than or equal to 0, a is less than or equal to 0 and less than or equal to 1 and b is. Preferably 0.8. ltoreq. x 1. ltoreq.1.1, 0. ltoreq. y 1. ltoreq.1, 0<z1 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, a is more than or equal to 0 and less than or equal to 1, and<b≤2。

yet another aspect of the present application provides an electrochemical device, including: the positive electrode comprises a positive electrode, a negative electrode, a separation film and an electrolyte, wherein the positive electrode is the positive electrode.

In the electrochemical device of the present application, the electrolyte includes a lithium salt and an organic solvent.

In the electrochemical device of the present application, there is no particular limitation on the organic solvent in the electrolyte, and the organic solvent may be an organic solvent commonly used in the art for the electrolyte. As an example, the organic solvent may be selected from at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, and ethyl propionate.

In the electrochemical device of the present application, there is no particular limitation on the lithium salt in the electrolyte, and the lithium salt may be a lithium salt commonly used in the art for the electrolyte. As an example, the lithium salt may be selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, and lithium tetrafluoroborate.

In the electrochemical device of the present application, in order to improve the performance of the electrolyte, a suitable additive may be added to the electrolyte.

In the electrochemical device of the present application, the negative electrode is a material capable of accepting and extracting lithium ions, such as soft carbon, hard carbon, artificial graphite, natural graphite, silicon-oxygen compound, silicon-carbon composite, lithium titanate, a metal capable of forming an alloy with lithium, or the like.

Yet another aspect of the present application also provides an electronic device comprising an electrochemical device as described above.

The technical scheme provided by the application can achieve the following beneficial effects:

the application provides a positive pole and electrochemical device of double-deck coating with high security performance, this positive pole have compound bilayer structure, and two-layer structure is two-layer totally different structure. The secondary battery adopting such a structure has improved safety performance such as nail penetration and heat box, and less resistance increase.

The double-layer coating structure of the anode has obvious improvement on the safety performance and the impedance property of the secondary battery, and has higher application value.

Drawings

FIG. 1 is a schematic of a positive electrode of the present application;

FIG. 2 is a polyacetylene-coated LiCo prepared in example 1_0.01Mn_0.6Fe_0.4PO₄A transmission electron microscope photograph of (a);

fig. 3 is a graph showing the increase in high-temperature storage resistance of the battery.

Reference numerals:

1-positive electrode current collector

2-film layer

21-active conductive layer

22-active material layer

3-insulating layer

4-pole ear

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application more clearly apparent, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

The preparation of the positive electrode and its use are described below with specific examples.

Example 1

As shown in fig. 1, fig. 1 shows a structure of a positive electrode (with tab) according to the present invention. In fig. 1, the positive electrode includes a positive electrode current collector 1, a membrane layer 2 disposed on both surfaces of the positive electrode current collector, and an insulating layer 3. The membrane layer 2 includes an active conductive layer 21 and an active material layer 22. The active conductive layer 21 includes an active conductive material, and the active material layer includes a positive electrode active material (e.g., lithium cobaltate). In fig. 1, a tab 4 provided on the positive electrode collector is also shown.

The following describes in detail the preparation process of the double-layer positive electrode described in the present application.

According to the preset coating thickness, lithium-containing phosphate compound LiCo with different feeding amounts is added_0.01Mn_0.6Fe_0.4PO₄Mixing with polyacetylene in a ball milling tank, and ball milling for 6 hours to obtain polyacetylene-coated LiCo_0.01Mn_0.6Fe_0.4PO₄The active conductive material of (1). Polyacetylene coated LiCo_0.01Mn_0.6Fe_0.4PO₄See fig. 2 for a transmission electron micrograph of the active conductive material.

Polyacetylene coated LiCo_0.01Mn_0.6Fe_0.4PO₄The active conductive material (the grain diameter is 1.0 mu m), the conductive agent Super P (SP) and the adhesive polyvinylidene fluoride (PVDF) are coated on the aluminum foil according to the weight ratio of 97:1.5:1.5 and dried to obtain the active conductive layer, and the coating thickness is 3 mu m. The positive electrode material Lithium Cobaltate (LCO), the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are mixed according to the proportion of 97: 2: 1 in an N-methyl pyrrolidone solvent system, coating the mixture on an active conductive layer, drying and cold pressing to obtain the double-layer anode.

Examples 2 to 4

A double-layered positive electrode was prepared according to the method of example 1 except that the particle size of the active conductive material was different.

Examples 5 to 6

A double-layered positive electrode was prepared according to the method of example 2 except that the thickness of the active conductive layer was different.

Examples 7 to 8, 21 to 22

A double-layered positive electrode was prepared according to the method of example 2 except that the SP content in the active conductive layer was different.

Example 9

A double-layered positive electrode was prepared according to the method of example 2 except that the active conductive material was coated with polythiophene.

Examples 10 to 12

A double-layered positive electrode was prepared according to the method of example 2 except that the kind of the organic conductive polymer coated with the active conductive material was different.

Examples 13 to 16

A double-layered positive electrode was prepared according to the method of example 2, except that the composition of the lithium-containing phosphate compound/the particle size of the active conductive material were different.

Examples 17 to 20

A double-layered positive electrode was prepared according to the method of example 2 except that the coating thickness of polyacetylene on the surface of the active conductive material was varied.

Comparative example 1

A positive electrode was prepared according to the method of example 1, except that the positive electrode material LCO slurry was directly coated on an empty aluminum foil without providing an active conductive layer, to prepare a single-layer positive electrode-coated battery.

Comparative example 2

LiCo without organic conductive polymer coating_0.01Mn_0.6Fe_0.4PO₄A material (particle diameter of 1.5 μm), a conductive agent Super P (SP), and a binder polyvinylidene fluorideCoating the alkene (PVDF) on an aluminum foil according to the weight ratio of 97:1.5:1.5, and drying to obtain an active conductive layer, wherein the coating thickness is 3 micrometers; the anode material LCO, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are mixed according to the weight ratio of 97: 2: and 1, fully stirring and uniformly mixing in an N-methylpyrrolidone solvent system, coating on the active conductive layer, drying and cold pressing to obtain the double-layer anode.

Comparative example 3

LiCo coated with conventional carbon_0.01Mn_0.6Fe_0.4PO₄Coating the material (the grain diameter is 1.5 mu m), the conductive agent Super P (SP) and the binder polyvinylidene fluoride (PVDF) on an aluminum foil according to the weight ratio of 97:1.5:1.5, and drying to obtain an active conductive layer, wherein the coating thickness is 3 mu m; the anode material LCO, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are mixed according to the weight ratio of 97: 2: and 1, fully stirring and uniformly mixing in an N-methylpyrrolidone solvent system, coating on the active conductive layer, drying and cold pressing to obtain the double-layer anode.

Battery preparation

(1) Preparation of the Positive electrode

The positive electrode was prepared according to the methods of examples 1 to 16 and comparative examples 1 to 3 above.

(2) Preparation of the negative electrode

Mixing artificial graphite serving as a negative electrode active material, sodium carboxymethyl cellulose (CMC) serving as a thickening agent and Styrene Butadiene Rubber (SBR) serving as a binder according to a weight ratio of 97:1.5:1.5, adding deionized water, and obtaining negative electrode slurry under the action of a vacuum stirrer, wherein the solid content of the negative electrode slurry is 54 wt%; uniformly coating the negative electrode slurry on a copper foil of a negative electrode current collector; and drying the copper foil at 85 ℃, then carrying out cold pressing, cutting and slitting, and drying for 12h at 120 ℃ under a vacuum condition to obtain the cathode.

(3) Preparation of the electrolyte

In a dry argon atmosphere glove box, Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC) were mixed in a mass ratio of EC: PC: DEC ═ 3: 3: 4, followed by addition of a lithium salt LiPF₆And mixing uniformly to obtain the electrolyte. Wherein, LiPF₆The concentration of (2) is 1 mol/L.

(4) Preparation of the separator

Polyethylene (PE) film with a thickness of 7 μm was selected as the separator.

(5) Preparation of lithium ion battery

Stacking the anode, the isolating film and the cathode in sequence to enable the isolating film to be positioned between the anode and the cathode to play an isolating role, and then winding to obtain a winding assembly; and (3) after welding the tabs, placing the winding assembly in an outer packaging foil aluminum-plastic film, injecting the prepared electrolyte into the dried winding assembly, and performing vacuum packaging, standing, formation, shaping, capacity test and other processes to obtain the soft package lithium ion battery.

Performance testing of lithium ion batteries

High temperature storage and impedance testing

The cells in examples and comparative examples were each charged to a voltage of 4.45V at a constant current of 0.5C rate at normal temperature, and further charged to a current of 0.05C at a constant voltage of 4.45V so as to be in a full charge state of 4.45V, taking 5 cells each. The impedance IMP of the fully charged battery before test storage is denoted as I0. The fully charged cells were then placed in an oven at 85 ℃ and six hours later, the cells were removed and their impedance immediately after storage was tested and recorded as I1.

Calculating the IMP growth rate before and after the storage of the battery according to the following formula

ε＝(I1-I0)/I0×100％

The average impedance growth rate of each group of the resulting cells is shown in fig. 3 and table 1.

Nail penetration test

Each of the batteries of examples and comparative examples was charged to a voltage of 4.45V at a constant current of 0.5C rate at normal temperature, and further charged to a current of 0.05C at a constant voltage of 4.45V so as to be in a full charge state of 4.45V, 10 batteries were used. And (3) performing a needle punching experiment on the surface of the battery at the speed of 30mm/s by using a steel nail with the diameter of 4mm at normal temperature, judging whether the battery catches fire or explodes, and if the battery does not catch fire or explode, passing the test.

Drop test

Each of the batteries of examples and comparative examples was charged to a voltage of 4.45V at a constant current of 0.5C rate at normal temperature, and further charged to a current of 0.05C at a constant voltage of 4.45V so as to be in a full charge state of 4.45V, 10 batteries were used. A round bar with the diameter of 15.8 plus or minus 0.2mm and the length of at least 7cm is perpendicular to a battery sample at normal temperature, the surface of the battery is impacted, a 9.1 plus or minus 0.1Kg of heavy hammer is used for dropping in a perpendicular free state at a distance of 61 plus or minus 2.5cm from the intersection of the round bar and the sample to complete a dropping experiment, and whether the battery catches fire or explodes is judged. The test was passed if the battery did not catch fire or explode.

The relevant parameters and performance test results of the lithium ion batteries prepared from the above examples and comparative examples are shown in table 1 below.

TABLE 1

In Table 1, as is apparent from the test results of example 1 and comparative example 1, LiCo was used_0.01Mn_0.6Fe_0.4PO₄The active conductive material has extremely high improvement on the safety performance of the battery, and the passing rate of a nail penetration experiment and a drop experiment of the battery is obviously improved. The main reason is that the structural characteristics of the phosphate can ensure the stability of the material under high voltage, and an active conductive layer containing a lithium-containing phosphate compound is always arranged between the positive electrode lithium cobaltate and the aluminum foil substrate in the process of charging and discharging of the battery. The active conducting layer can well protect the high potential of the positive terminal in the electrochemical process. Meanwhile, when the battery is subjected to safety tests such as nail penetration, falling and the like, the safety performance of the battery is greatly improved.

From the test results of examples 1 to 4 and comparative example 1, it can be concluded that LiCo, an active conductive material, is an active conductive material_0.01Mn_0.6Fe_0.4PO₄The particle size of (b) also has some influence on the initial resistance of the battery and the increase in resistance after high-temperature storage. The increase in resistance after high temperature storage is reduced with increasing particle size, but too large a particle size affects the processability of the thin coating. Although an increase in the particle diameter of the active conductive material is accompanied by an improvement in the stability of the particles, the increase in the particles adversely affects the conductive network in the membrane sheet, and thus it is necessary to control the particle diameter of the active conductive material within an appropriate range.

It can be understood from the test results of examples 2, 5, 6 and comparative example 1 that the thickness of the positive active conductive layer is also one of the factors affecting the improvement of the safety performance of the battery. When the thickness of the active conductive layer is 1 μm, the passing rate of the nail penetration test and the drop test of the battery is slightly deteriorated, which may be due to the fact that the insulating effect of the inert layer is affected when the thickness is thinner; and when the thickness of the active conductive layer reaches 7 μm, the safety performance is good, but the energy density is reduced.

As can be understood from the test results of examples 2, 7, 8, 21 to 22 and comparative example 1, the SP content in the positive active conductive layer formulation is also one of the factors affecting the function of the positive active conductive layer. The increase of the SP content improves the high-temperature impedance increase of the battery to a certain extent, but also deteriorates the safety performance such as nail penetration and the like to a certain extent.

From the test results of examples 2, 9 to 12 and comparative example 1, it can be concluded that LiCo is coated with the exception of polyacetylene_0.01Mn_0.6Fe_0.4PO₄As active conductive material, other organic conductive polymer such as coated LiCo coated with polythiophene, polypyrrole, polyaniline, polyphenylene ethylene_0.01Mn_0.6Fe_0.4PO₄The active conductive material can improve the safety performance of the battery to different degrees, and the impedance growth rate of the battery is lower. Has higher application value.

As can be seen from the test results of example 2 and comparative examples 2 to 3, in comparative example 2 without the organic conductive polymer coating, the battery was substantially inoperable due to excessively poor conductivity and excessive internal resistance of the active conductive material. In the case of comparative example 3 in which the conventional carbon was coated, since the carbon itself was unstable, it was oxidized at a high voltage, resulting in a serious increase in the internal resistance of the battery and a failure in normal operation. The organic conductive polymer in example 2 has the advantages that the polymer is stable at high voltage and the conductive network can normally exert the effect, so that the impedance of the battery is not remarkably increased, and the capacity of the battery can be maintained, thereby avoiding the influence on the exertion of the capacity due to overlarge impedance.

As can be seen from the test results of example 2, examples 17 to 20, and comparative examples 1 to 3, the coating thickness of the organic conductive polymer layer on the surface of the lithium phosphate-containing compound in the active conductive layer also affects the improvement of the performance, and when the thickness of the organic conductive polymer layer is 1nm, the resistance of the battery after high-temperature storage is poor, which may be due to the fact that the coating effect is insignificant when the thickness is thin; and when the thickness reaches 8nm, the safety performance is slightly deteriorated. The thickness of the coating is preferably in the range of 3 to 5 nm.

Table 2 shows the results of the nail penetration test and the drop test.

TABLE 2

It can be seen from table 2 that the lithium ion battery using the double-layer anode of the present application has significantly higher pass rate in both the drop test and the nail penetration test. Therefore, the lithium ion battery adopting the double-layer anode has higher safety.

Claims

1. The positive electrode is characterized by comprising a positive electrode current collector and a membrane layer arranged on the surface of the positive electrode current collector, wherein the membrane layer comprises an active conductive layer arranged on the surface of the positive electrode current collector and an active material layer arranged on the surface of the active conductive layer;

wherein the active conductive layer comprises an active conductive material; the active conductive material comprises a lithium-containing phosphate compound and a coating layer positioned on the surface of the lithium-containing phosphate compound, wherein the coating layer comprises an organic conductive polymer layer.

2. The positive electrode according to claim 1, wherein at least one of the following conditions is satisfied:

a. the thickness of the active conductive layer is 1-4 μm;

b. the organic conductive polymer layer has a thickness of 1nm to 8 nm;

c. the average particle diameter of the active conductive material is 1.0 to 3.0 [ mu ] m;

d. the resistance of the membrane layer is 0.03 omega to 0.5 omega;

e. the organic conducting polymer comprises at least one of polyacetylene, polythiophene, polypyrrole, polyaniline, polyphenylene ethylene or polydiyne;

f. the compacted density of the membrane layer is 3.5g/cm³To 4.5g/cm³。

3. The positive electrode of claim 1, wherein the active conductive layer further comprises a conductive agent.

4. The positive electrode according to claim 3, wherein at least one of the following conditions is satisfied:

g. the mass percentage content of the conductive agent is 0.5-3.0%, preferably 0.5-2.0%, based on the mass of the active conductive layer;

h. the conductive agent comprises at least one of conductive carbon black, acetylene black, Ketjen black, Super P, graphene and carbon nanotubes.

5. The positive electrode according to claim 1, wherein the lithium-containing phosphate compound comprises at least one of compounds represented by general formula 1;

Li_xM_yN_zPO₄general formula 1

6. The positive electrode of claim 1, wherein the active material layer comprises a lithium transition metal composite oxide comprising at least one lithium having the formula Li_x1Ni_y1Co_z1Mn_kZ_qO_b-aT_aA compound of (a), wherein Z includes at least one of B, Mg, Al, Si, P, S, Ti, Cr, Fe, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb, and Ce, T is a halogen, and x1, Y1, Z1, k, q, a, and B satisfy: 0.2<x1 is less than or equal to 1.2, y1 is less than or equal to 1 and less than or equal to 0, z1 is less than or equal to 1 and less than or equal to 0, k is less than or equal to 1 and less than or equal to 0, q is less than or equal to 1 and less than or equal to 0, a is less than or equal to 0 and less than or equal to 1 and b is.

7. An electrochemical device, comprising: a positive electrode according to any one of claims 1 to 6, a negative electrode, a separator, and an electrolytic solution.

8. The electrochemical device of claim 7, wherein the electrochemical device has an increase in impedance of less than 15% after 6 hours at 85 ℃ storage compared to the impedance before 85 ℃ storage in a fully charged state.

9. An electronic device comprising the electrochemical device of claim 7 or 8.