CN117542961A

CN117542961A - Battery monomer, battery and power consumption device

Info

Publication number: CN117542961A
Application number: CN202410035861.7A
Authority: CN
Inventors: 李梅; 马云建; 邢柯; 姚萌
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2024-01-10
Filing date: 2024-01-10
Publication date: 2024-02-09

Abstract

The application relates to the technical field of batteries and provides a battery monomer, a battery and an electricity utilization device. The battery monomer comprises a positive electrode plate and a negative electrode plate; the positive electrode plate contains a positive electrode active material, the positive electrode active material comprises a positive electrode active material and a coating layer coated on the outer surface of the positive electrode active material, and the number of primary particles in the positive electrode active material is more than or equal to 50%; the negative electrode plate contains a negative electrode active material, the negative electrode active material comprises graphite, and the OI value of the graphite is 2-8. According to the embodiment of the application, the lithium loss in the circulation process is further reduced while the structural stability of the positive electrode active material is improved, and the system polarization lifting dynamics is reduced, so that the long-service life of the lithium ion battery is realized, and a thought is provided for the design of a long-service life system of the lithium ion battery.

Description

Battery monomer, battery and power consumption device

Technical Field

The application belongs to the technical field of batteries, and particularly relates to a battery monomer, a battery and an electricity utilization device.

Background

The lithium ion battery is widely applied to 3C electronic products, electric automobiles, hybrid electric automobiles and energy storage systems because of the advantages of high capacity, high energy density, small environmental pollution and no memory effect. Based on a market operation battery use model, the service life of the battery is prolonged, and win-win of battery manufacturers and users can be realized.

The positive electrode active material is used as an active lithium ion donor of a lithium ion battery and is important to the capacity and the cycle retention rate of the lithium battery. The negative electrode material is used as a carrier for active lithium ion deintercalation, and has great influence on the cycle performance and service life of the secondary battery. In order to further improve the cycle life of lithium ion batteries, higher requirements are put on the positive electrode active materials and the negative electrode materials of the batteries.

The statements are to be understood as merely provide background information related to the present application and may not necessarily constitute prior art.

Disclosure of Invention

The purpose of this application is to provide a battery monomer, battery and power consumption device, aims at improving the cyclic performance and the service life of battery monomer.

In order to achieve the purposes of the application, the technical scheme adopted by the application is as follows:

in a first aspect, the present application provides a battery cell comprising a positive electrode tab and a negative electrode tab;

the positive electrode plate contains a positive electrode active material, the positive electrode active material comprises a positive electrode active material and a coating layer coated on the outer surface of the positive electrode active material, and the number of primary particles in the positive electrode active material is more than or equal to 50%;

the negative electrode plate contains a negative electrode active material, the negative electrode active material comprises graphite, and the OI value of the graphite is 2-8.

The battery monomer provided by the embodiment of the application comprises the positive electrode plate and the negative electrode plate, the quantity of primary particles in the positive electrode active material is controlled to be in a ratio, so that the positive electrode active material shows higher dispersibility and structural stability, in this way, structural degradation and phase change of the positive electrode active material caused by structural internal stress are slowed down in the circulation process, so that lithium ions are reduced in migration resistance in crystal lattices, and are transmitted to the negative electrode plate at a faster diffusion rate; the existence of the coating layer can effectively ensure the structural stability of the anode active material, so that the battery monomer has higher capacity cycle retention rate and longer service life. The graphite with the OI value in the above range is used as the anode active material, so that the isotropy is improved, the system polarization lifting dynamics is effectively reduced, active ions are promoted to smoothly enter the ion diffusion channel, the intercalation and deintercalation rate of the active ions is further improved, the risk that the expansion force of the anode active material exceeds the threshold value in the single battery circulation process is lower, and the loss of lithium ions in the circulation process can be reduced.

In summary, the battery monomer provided by the embodiment of the application improves the structural stability of the positive electrode active material, promotes lithium ion transmission, and simultaneously further reduces lithium loss in the circulation process, and reduces system polarization lifting dynamics, thereby realizing that active ions rapidly complete charge exchange and intercalation and deintercalation, endowing a lithium ion battery with longer service life, and providing a thought for obtaining a long-life lithium ion battery system.

In some embodiments, the amount of primary particles in the positive electrode active material is 70% -80%.

The number of primary particles in the positive electrode active material is controlled to occupy a ratio, so that the dispersibility of the positive electrode active material is improved, the positive electrode active material maintains the structural stability of particles in the circulating process, and the positive electrode active material is not easy to crack.

In some embodiments, the OI value of the graphite is 2-5, oi=c004/C110, C004 is the peak area of the 004 characteristic diffraction peak in the graphite X-ray diffraction pattern, C110 is the peak area of the 110 characteristic diffraction peak in the graphite X-ray diffraction pattern, and the ratio of the two is the OI value.

The OI value can reflect the crystal face orientation of graphite, and the graphite orientation has a larger influence on an ion transmission path.

In some embodiments, the graphitization degree is 95% or more.

In some embodiments, the graphitization degree of the graphite is 97% -99%.

Under the condition of the graphitization degree, the crystal structure of the anode active material is closer to the complete lamellar structure of ideal graphite, and defects such as stacking faults, dislocation and the like in the crystal are fewer, so that the graphite has higher gram capacity.

In some embodiments, the coating layer comprises a first subcoating layer comprising at least one of an oxide, fluoride, phosphate, carbon material, lithium ion conductor; optionally, the first sub-coating layer comprises a lithium ion conductor. The first sub-coating materials such as oxide, fluoride, phosphate, carbon material and the like can effectively improve the interface stability between the electrolyte and the positive electrode active material, such as a lithium ion conductor, and simultaneously facilitate the transmission of lithium ions and improve the lithium intercalation/deintercalation kinetic performance of the lithium ions, thereby improving the capacity cycle retention rate of the positive electrode active material.

In some embodiments, the oxide comprises at least one of aluminum oxide, magnesium oxide, cerium oxide, zinc oxide, lanthanum oxide, zirconium oxide, titanium oxide, silicon oxide, bismuth trioxide, indium oxide, and tricobalt tetraoxide. The oxides can prevent the positive electrode active material from directly contacting with electrolyte, effectively reduce the occurrence of side reaction, improve the structural stability of the positive electrode active material, ensure that the positive electrode active material is not easy to generate phase change in the circulating process, and further endow the battery with higher circulating stability.

In some embodiments, the fluoride comprises at least one of aluminum trifluoride and calcium fluoride. The fluoride can effectively reduce the side reaction of the positive electrode active material, improve the interface stability between the positive electrode active material and the electrolyte, and ensure that the positive electrode active material is not easy to generate phase change in the circulating process, thereby improving the energy density and the circulating life of the battery monomer.

In some embodiments, the phosphate comprises at least one of aluminum phosphate, cobalt phosphate, nickel phosphate, and iron phosphate. The phosphates can effectively reduce the occurrence of side reactions of the positive electrode active material, improve the structural stability of the positive electrode active material, ensure that the positive electrode active material is not easy to generate phase change in the circulating process, and further improve the energy density and the circulating life of the battery monomer.

In some embodiments, the carbon material comprises at least one of graphene and carbon nanotubes. The carbon materials can effectively improve the conductivity of the positive electrode active material while improving the structural stability of the positive electrode active material, and enhance the capability of the positive electrode active material for transmitting active ions, so that the battery shows lower direct current impedance, and the cycle performance of the battery is further improved.

In some embodiments, the lithium ion conductor comprises at least one of lithium phosphate, lithium iron phosphate, lithium tantalate, lithium metaaluminate, lithium dititanium tetraoxide, lithium zirconate, lithium silicate, lithium orthovanadate, lithium carboborate. The lithium ion conductors can improve the lithium ion transmission rate of the positive electrode active substance, and in addition, at least part of the lithium ion conductors can play a role in supplementing lithium in the primary charging process and serve as a sacrificial agent for supplementing a lithium source, so that the primary coulombic efficiency of the battery monomer is improved.

In some embodiments, the first sub-coating layer comprises 0.1wt% to 0.5wt% of the positive electrode active material. The first sub-coating layer may be effectively coated on the surface of the positive electrode active material by controlling the content of the first sub-coating layer within the above range.

In some embodiments, the coating layer further includes a second sub-coating layer disposed on a side of the first sub-coating layer remote from the positive electrode active material, the second sub-coating layer comprising a conductive polymer.

The first sub-coating layer and the second sub-coating layer are coated on the surface of the positive electrode active material, and the second sub-coating layer contains a conductive polymer. The first sub-coating layer is used as an inner layer, and can effectively protect the positive electrode active material, so that the positive electrode active material can be prevented from being in direct contact with electrolyte, transition metal contained in the positive electrode active material is prevented from being dissolved out, the occurrence of side reaction on the surface of the positive electrode active material is reduced, and the lithium ion transmission rate and/or the electronic conductivity of the positive electrode active material can be improved by the first sub-coating layer; the second sub-coating layer is used as an outer layer, and conductive polymer is used as a material, so that on one hand, the electronic conductivity of the positive electrode active material can be effectively improved, the reaction resistance of electrons on the surface of the positive electrode active material is small, the charge transmission rate is high, and the dynamic performance of a battery monomer is improved; on the other hand, the first coating layer of the inner layer can be protected, and the structural stability of the positive electrode active material is improved, so that the battery cell has higher energy density and cycle performance.

In some embodiments, the conductive polymer includes at least one of polypyrrole, polythiophene, polyaniline, and polyacetylene. The conductive polymers have the advantages of high electronic conductivity, good electrocatalytic performance and the like, so that the electron transfer rate of the anode active material is improved, the reaction kinetics is improved, and the service life of the battery is prolonged. Therefore, the embodiment of the application adopts the conductive polymer such as polypyrrole, polythiophene, polyaniline and the like to uniformly coat the surface of the positive electrode active material, so that the dissolution of transition metal in the positive electrode active material under high voltage can be limited, the occurrence of side reaction can be restrained, the conductive polymer can be used as an electron conductive layer to further improve the conductivity of the positive electrode active material, the dynamics of the whole chemical system can be effectively improved, and the battery shows excellent multiplying power performance and cycle stability.

In some embodiments, the second sub-coating layer comprises 0.5wt% to 1wt% of the positive electrode active material.

The effective coating of the positive electrode active material can be achieved by controlling the mass ratio of the second sub-coating layer within the above range.

In some embodiments, the thickness ratio of the first sub-cladding layer to the second sub-cladding layer is 1:1-4:1.

By optimizing and controlling the ratio of the layer thicknesses of the first sub-coating layer and the second sub-coating layer, the structural stability of the positive electrode active material can be effectively improved.

In some embodiments, the thickness of the cladding layer is 5nm to 50nm.

The thickness of the coating layer is set to be 5-50 nm, so that the structural stability of the positive electrode active material is effectively improved, and meanwhile, the lithium ion conductivity and the electron conductivity of the positive electrode active material can be improved, so that the battery monomer has higher energy density and cycle performance.

In some embodiments, the average volume particle diameter Dv50 of the positive electrode active material is 3.0 μm to 5.0 μm.

By controlling the average volume particle diameter of the positive electrode active material within the above range, the positive electrode active material can be ensured to have better processability and electrochemical properties.

In some embodiments, the positive electrode active material has the chemical formula LiNi _x Co _y Mn _1-x-y O ₂ Wherein x is more than or equal to 0.5 and less than or equal to 0.8,0.06 and y is more than or equal to 0.15.

In the positive electrode active material, lithium ions and nickel ions have a radius close to each other, so that lithium and nickel are easily dislocated, and migration of lithium ions in a crystal lattice is hindered, and kinetics is deteriorated. In the embodiment of the application, the Co atoms in the positive electrode active material are controlled in the range, so that the discharge degree of lithium and nickel can be reduced, the layered structure is stabilized, and the polarization loss is reduced, therefore, the positive electrode active material provided by the embodiment of the application is stable in structure and not easy to generate phase change, and the probability of side reaction with electrolyte is reduced; meanwhile, the increase of the Co content can also increase the gram capacity of the positive electrode active material, so that the positive electrode active material of the chemical formula enables the battery cell to have higher capacity cycle retention rate.

In a second aspect, embodiments of the present application provide a battery comprising the battery cell provided in the first aspect of embodiments of the present application.

The battery provided by the embodiment of the application comprises the battery monomer, and the battery is higher in cycle stability and energy density.

In a third aspect, embodiments of the present application provide an electrical device, which includes a battery provided in the second aspect of embodiments of the present application, where the battery is configured to provide electrical energy.

The foregoing description is only an overview of the technical solutions of the present application, and may be implemented according to the content of the specification in order to make the technical means of the present application more clearly understood, and in order to make the above-mentioned and other objects, features and advantages of the present application more clearly understood, the following detailed description of the present application will be given.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Also, like reference numerals are used to designate like parts throughout the accompanying drawings. In the drawings:

FIG. 1 is a schematic structural view of a positive electrode active material according to some embodiments of the present application;

FIG. 2 is a schematic illustration of a vehicle configuration in some embodiments of the present application;

fig. 3 is an exploded view of a battery according to some embodiments of the present application;

fig. 4 is a schematic structural view of a battery cell according to some embodiments of the present application;

FIG. 5 is a scanning electron micrograph of the positive electrode active material provided in example 1 of the present application;

fig. 6 is a scanning electron micrograph of the positive electrode active material provided in comparative example 3 of the present application.

Wherein, each reference sign in the figure:

1000. a vehicle;

100. battery 200, controller 300, motor;

10. the box body comprises a box body 11, an upper box body 12 and a lower box body;

20. a battery cell, 21, a case, 22, an electrode assembly, 23, a cap plate;

4. a positive electrode active material; 5. a coating layer; 51. a first sub-cladding layer; 52. and a second sub-cladding layer.

Detailed Description

Embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical solutions of the present application, and thus are only examples, and are not intended to limit the scope of protection of the present application.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having" and any variations thereof in the description and claims of the present application and in the description of the figures above are intended to cover non-exclusive inclusions.

In the description of the embodiments of the present application, the technical terms "first," "second," etc. are used merely to distinguish between different objects and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated, a particular order or a primary or secondary relationship. In the description of the embodiments of the present application, the meaning of "plurality" is two or more unless explicitly defined otherwise.

Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those of skill in the art will explicitly and implicitly appreciate that the embodiments described herein may be combined with other embodiments.

In the description of the embodiments of the present application, the term "and/or" is merely an association relationship describing an association object, which means that three relationships may exist, for example, a and/or B may mean: a exists alone, A and B exist together, and B exists alone. In addition, the character "/" herein generally indicates that the front and rear associated objects are an "or" relationship.

In the description of the embodiments of the present application, the term "plurality" refers to two or more (including two), and similarly, "plural sets" refers to two or more (including two), and "plural sheets" refers to two or more (including two).

In the description of the embodiments of the present application, the orientation or positional relationship indicated by the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. are based on the orientation or positional relationship shown in the drawings, and are merely for convenience of describing the embodiments of the present application and for simplifying the description, rather than indicating or implying that the apparatus or element referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the embodiments of the present application.

In the description of the embodiments of the present application, unless explicitly specified and limited otherwise, the terms "mounted," "connected," "secured" and the like are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally formed; or may be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the embodiments of the present application will be understood by those of ordinary skill in the art according to the specific circumstances.

In the present application, "at least one" means one or more, and "a plurality" means two or more. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (individual) of a, b, or c," or "at least one (individual) of a, b, and c," may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.

It should be understood that, in various embodiments of the present application, the sequence number of each process does not mean that the sequence of execution is sequential, and some or all of the steps may be executed in parallel or sequentially, where the execution sequence of each process should be determined by its functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

The weights of the relevant components mentioned in the embodiments of the present application may refer not only to specific contents of the components, but also to the proportional relationship between the weights of the components, and thus, any ratio of the contents of the relevant components according to the embodiments of the present application may be enlarged or reduced within the scope disclosed in the embodiments of the present application. Specifically, the mass described in the specification of the embodiment of the present application may be a mass unit that is well known in the chemical industry field such as μ g, mg, g, kg.

The term "NCM" is short for nickel manganese cobalt ternary materials.

In the description of the embodiment of the present application, the SEI film is abbreviated as "solid electrolyte interface" and refers to a solid electrolyte interface film having the characteristics of a solid electrolyte, that is, a film formed by a passivation layer covering the surface of a negative electrode material, where an electrode material and an electrolyte react on a solid-liquid phase interface during the first charge and discharge process of a liquid lithium ion battery.

In the description of the embodiment of the present application, the CEI film is abbreviated as "cathode electrolyte interphase" and refers to a solid electrolyte interface film having the characteristics of a solid electrolyte, that is, a film formed by a passivation layer covering the surface of a positive electrode material, where the positive electrode material and an electrolyte react on a solid-liquid phase interface during the first charge and discharge process of a liquid lithium ion battery.

During long-term cycling and storage, the electrochemical performance of lithium ion batteries can gradually decline, which is mainly represented by decline of battery capacity, increase of internal resistance and expansion pressure, wherein the decline of battery capacity can be represented by shorter service life of the battery. According to researches, the factors influencing the service life of the lithium ion battery mainly comprise the following aspects:

(1) Structural stability of the positive electrode active material. During long-term circulation and storage of the battery, the dissolution of the positive electrode active material due to the occurrence of side reactions, the reduction in the amount of active material, and the formation of metal ions such as Mn by the side reactions ²⁺ 、Fe ²⁺ And Co ²⁺ And the like can be reduced and deposited on the surface of the anode, thereby preventing lithium ion transmission; at the same time, a part of side reaction products of the electrolyte are deposited on the surface of the positive electrode active material, resulting in an increase in its resistance. That is, the structural stability of the positive electrode active material is not ideal, so that the cycle performance and the service life of the lithium ion battery are not ideal.

(2) Volume effect of the anode active material. The negative electrode can repeatedly shrink and expand due to the volume effect when the battery is charged and discharged, and stress generated by volume change enables the negative electrode active material particles to crack layers so as to reduce the capacity of the negative electrode active material particles, and enables the binding force between the negative electrode active material and a current collector to be reduced, even the negative electrode active material falls off, so that the capacity of the battery is attenuated.

Based on the above, the embodiment of the application is beneficial to improving the particle stability of the positive electrode active material in the circulation process by controlling the number proportion of primary particles in the positive electrode active material, so that the positive electrode active material is not easy to crack, and the diffusion path of active ions can be shortened, so that lithium ions in the positive electrode active material are transmitted to the negative electrode plate at a faster rate; in addition, the coating layer is formed on the surface of the positive electrode active material, so that the structural stability of the positive electrode active material is further improved, and the interface stability between the positive electrode active material and the electrolyte is improved, thereby effectively reducing the corrosion risk of the electrolyte to the positive electrode active material, reducing the occurrence of side reaction between the positive electrode active material and the electrolyte, simultaneously, the coating can also reduce the dissolution of transition metal ions in the positive electrode active material, and avoiding the repeated formation and loss of an anode SEI film; meanwhile, graphite with high consistency of crystal plane orientation degree is adopted, and the specific expression is that the OI value is 2-8, so that the ion transmission dynamics can be effectively improved, the system polarization is reduced, the active ions are subjected to deintercalation and charge exchange at a high speed, and the risk of rupture of the anode active material caused by overlarge expansion force of the anode active material in the circulation process can be effectively reduced; based on the above, the battery system constructed by the positive pole piece and the negative pole piece can quickly transmit active ions to the negative pole piece, meanwhile, the structural stability of the material is maintained, and the negative pole piece can quickly receive the active ions, namely, ion deintercalation and charge transfer are realized, so that the battery has high cycle capacity retention rate and rate capability.

Some embodiments of the present application provide a battery cell comprising a positive electrode tab and a negative electrode tab;

the positive electrode plate contains a positive electrode active material, and referring to fig. 1, the positive electrode active material comprises a positive electrode active material 4 and a coating layer 5 coated on the outer surface of the positive electrode active material 4, wherein the quantity of primary particles in the positive electrode active material is more than or equal to 50%;

The battery monomer provided by the embodiment of the application comprises the positive electrode plate and the negative electrode plate, and the quantity of primary particles in the positive electrode active material is controlled to be in proportion, so that the stability and dispersibility of particles in the circulating process of the positive electrode active material are improved, structural degradation and phase change of the positive electrode active material in the circulating process are reduced due to structural internal stress, so that migration resistance of lithium ions in crystal lattices is reduced, the lithium ions are transmitted to the negative electrode plate at a faster diffusion rate, in addition, the positive electrode active material is in a core-shell structure, the coating layer can effectively play a role in protecting the positive electrode active material, not only can the positive electrode active material and electrolyte be prevented from being directly contacted, but also transition metal contained in the positive electrode active material is prevented from being dissolved, for example Mn can be diffused to the negative electrode, anode SEI film loss is caused, system polarization is increased, circulation retention rate is reduced, and side reaction of the surface of the positive electrode active material is reduced, and the positive electrode active material is isolated from external moisture and carbon dioxide, so that the positive electrode active material has higher structural stability and lower lithium consumption, and abundant lithium ions can be provided, and the battery has higher circulation retention rate; meanwhile, graphite with high orientation degree is adopted, the specific expression is that the OI value is 2-8, the isotropy is improved, so that the system polarization is effectively reduced, the ion transmission dynamics is improved, active ions can be subjected to deintercalation and charge exchange at a relatively high speed, and the risk of rupture of the anode active material caused by overlarge expansion force of the anode active material in the circulation process can be effectively reduced; based on the above, in the battery system, the positive electrode plate can rapidly transmit a large amount of active ions to the negative electrode plate, at this time, enough active ions to be subjected to charge exchange with the negative electrode active material exist in the negative electrode plate, and the negative electrode plate can rapidly realize charge exchange and intercalation and deintercalation of the active ions to complete transmission of the active ions, so that the battery has high cycle capacity retention rate and rate capability.

In summary, according to the embodiment of the application, by combining the positive electrode active material and the negative electrode active material, the reaction kinetics of active ions is effectively improved, the conduction rate of lithium ions is further improved, the active ions in the battery monomer complete charge exchange and intercalation and deintercalation at a faster rate, the loss of the active ions is reduced, and the cycle life of the battery monomer is further prolonged.

It is understood that the positive electrode active material includes primary particles and secondary particles, wherein the secondary particles are formed by agglomerating a plurality of primary particles. The number ratio of primary particles in the positive electrode active material is calculated by the following formula:

（I）。

wherein in formula (I): w refers to the number of primary particles in the positive electrode active material, n1 refers to the number of primary particles in the positive electrode active material, and n2 refers to the number of secondary particles in the positive electrode active material.

In an exemplary embodiment, the number of primary particles in the positive electrode active material may be, but not limited to, 50%, 60%, 70%, 75%, 80%, etc. typical values.

It is understood that oi=c004/C110, C004 is the peak area of the 004 characteristic diffraction peak in the X-ray diffraction pattern of graphite, and C110 is the peak area of the 110 characteristic diffraction peak in the X-ray diffraction pattern of graphite. Illustratively, the graphite has an OI value of 2, 3, 4, 5, 6, 7, 8, etc., which are typical but not limiting. The OI value can reflect the degree of orientation of crystal faces in graphite, and the OI value is 2-8, which means that the graphite has stronger isotropy, so that the ion transmission dynamics of the graphite can be effectively improved, the ion intercalation resistance is small, and the deintercalation of active ions and the transfer of charges can be more easily completed.

According to the embodiment of the application, the quantity of primary particles in the positive electrode active material is controlled to be the ratio, so that the positive electrode active material still keeps stable particle structure in the circulating process, cracking is not easy to occur, the occurrence of side reaction of the positive electrode plate is greatly reduced, and the loss of the positive electrode active material caused by active site loss is reduced. By way of example, the number of primary particles in the positive electrode active material may be 70%, 72%, 75%, 78%, 80%, etc. of typical but non-limiting value.

In some embodiments, the graphite has an OI value of 2 to 5. Illustratively, the graphite has an OI value of 2, 2.5, 3, 3.5, 4, 4.5, 5, etc., which is typical but not limiting.

In general, during battery charging, the negative electrode tab is subjected to the following electrochemical process: (1) Active ions separated from the positive active material enter electrolyte and enter the pore canal of the negative membrane along with the electrolyte to complete liquid phase conduction of the active ions in the pore canal, wherein the liquid phase conduction comprises liquid phase diffusion and electromigration; (2) The active ions and electrons complete charge exchange on the surface of the anode active material; (3) The active ions are solid-phase-conducted from the surface of the anode active material to the inside of the anode active material crystal. The OI value of the anode active material may reflect the degree of stacking orientation of the anode active material particles. In the OI value range of the graphite provided by the embodiment of the application, the graphite has higher isotropy, the graphite is more oriented to extend and expand along the length direction of the pole piece after lithium is intercalated, the rebound in the thickness direction is small, and the structure is very favorable for lithium ions to smoothly enter a lithium ion transmission channel, so that the intercalation and deintercalation in the graphite are realized, and the conduction rate of the lithium ions is further improved. In addition, when the (110) crystal face of the graphite contacts with the electrolyte, an SEI film can be formed on the crystal face of the graphite more easily, so that the density of the SEI film formed on the surface of the anode active material layer is improved, the consumption of active lithium ions in the charging and discharging process of the battery is delayed, the capacity attenuation of the battery is reduced, and the cycle performance of a battery monomer is further improved.

In some embodiments, the graphitization degree of the graphite is 95% or more.

In some embodiments, the graphitization degree of the graphite is 97% -99%.

Illustratively, the graphitization degree of the graphite may be a typical, but non-limiting, value of 95%, 96%, 97%, 98%, 99%, etc.

The graphitization degree of graphite can be calculated according to the following formula (II),

。

in the formula (II), g is graphitization degree; d, d ₀₀₂ The interlayer spacing of the (002) crystal face of the carbon material is measured in nm.

Ions are extracted from the positive electrode active material when the battery cell is charged, and are embedded into the negative electrode active material through electrolyte, and meanwhile electrons are transferred to the negative electrode through an external circuit so as to keep charge balance; the opposite is true when discharging. Taking graphite as an example, one of the mechanisms of ion intercalation of graphite is that an intercalation compound is formed in the structure of crystallites of the ion-intercalated layered graphite, and therefore the graphitization degree and the interlayer spacing of graphite are closely related to the ion intercalation amount of graphite. In the range of graphitization degree provided by the embodiment of the application, the higher graphitization degree means that the graphite has smaller corresponding interlayer spacing d002, higher ordered degree of a crystal structure and more embeddable ion quantity, thereby being more beneficial to improving the gram capacity of the battery monomer.

In some embodiments, the average volume particle diameter Dv50 of the graphite is 8 μm to 18 μm.

In some embodiments, the average volume particle diameter Dv50 of the graphite is 10 μm to 15 μm.

Exemplary, but non-limiting, values for the average volume particle diameter Dv50 of the graphite are 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, etc.

In the present application, dv50 represents: the particle size corresponding to a cumulative volume distribution percentage of material of 50% each can be determined using instruments and methods known in the art. For example, the particle size distribution can be measured by a laser particle size analyzer by referring to GB/T19077-2016 laser diffraction method. The test instrument may be a Mastersizer 2000E laser particle size analyzer, malvern instruments, uk.

By optimizing and controlling the average volume particle diameter of the graphite, on one hand, the anode active material can provide a proper amount of end surfaces for active ion deintercalation, and the diffusion resistance of active ions among anode active material particles is smaller; on the other hand, the dispersibility of the anode active material is higher, and the consistency of the electrochemical performance of the anode piece is higher.

In some embodiments, the graphite has a specific surface area of 1m ² /g~3m ² And/g. Illustratively, the graphite may have a specific surface area of 1.0m ² /g、1.5m ² /g、1.8m ² /g、2.0m ² /g、2.5m ² /g、3.0m ² /g, etc. typical but not limiting values.

In some embodiments, the graphite has a specific surface area of 1m ² /g~1.5m ² And/g. Illustratively, the graphite may have a specific surface area of 1.0m ² /g、1.1m ² /g、1.2m ² /g、1.3m ² /g、1.4m ² /g、1.5m ² /g, etc. typical but not limiting values.

It is understood that the specific surface area refers to the total area that a mass of material has. Specific surface area of the above materials was measured by measuring specific surface area of solid matters by referring to GB/T19587-2004 gas adsorption BET method.

The specific surface area of graphite is controlled within the range, so that the anode active material provides a proper amount of active sites, on one hand, active ions and electrons can exchange charges on the surface of the anode active material at a high speed, and on the other hand, side reactions between the anode active material and electrolyte can be reduced, thereby reducing irreversible capacity loss in the circulation process, and further, the battery cell can have electrochemical characteristics of high energy density, long cycle life and the like.

In some embodiments, the negative electrode active material has a compacted density of 1.4g/cm ² ~1.9g/cm ² 。

In some embodiments, the negative electrode active material has a compacted density of 1.5g/cm ² ~1.8g/cm ² 。

Illustratively, the negative electrode active material may have a compacted density of 1.4g/cm ² 、1.5g/cm ² 、1.6g/cm ² 、1.7g/cm ² 、1.8g/cm ² 、1.9g/cm ² Etc. typical but non-limiting values.

The compacted density of the negative electrode sheet was tested by the following procedure:

compacted density = areal density/(thickness of rolled pole piece minus copper foil (aluminum foil) thickness).

The unit of areal density is g/m ² The calculation formula of the surface density is: weight divided by area (m/s), m being the weight of the pole piece and s being the area of the pole piece.

According to the embodiment of the application, the stability and the pore channel structure of the anode active material in the circulation process can be considered by controlling the compaction density of the anode active material in the range, so that the contact interface between the anode active materials is kept complete, and the circulation performance of the materials is improved. Of course, in this compacted density range, the negative electrode active material can be made to have an appropriate amount of effective end faces available for active ion deintercalation, and thus, the graphite can be made to have a lower OI value, thereby imparting the graphite with the properties as described above, further improving the cycle performance of the battery cell.

In some embodiments, as shown in fig. 1, the coating 5 includes a first sub-coating 51, the first sub-coating 51 including at least one of an oxide, a fluoride, a phosphate, a carbon material, and a lithium ion conductor. The first sub-coating materials such as oxide, fluoride, phosphate, carbon material and the like can effectively improve the interface stability between the electrolyte and the positive electrode active material, reduce the occurrence of side reaction of the positive electrode active material, inhibit the phase change of the positive electrode active material, and particularly, the lithium ion conductor can also improve the transmission capacity of lithium ions and improve the intercalation/deintercalation kinetic performance of lithium ions, thereby improving the capacity cycle retention rate of the positive electrode active material.

In some embodiments, the first subcoating layer comprises a lithium ion conductor. The lithium ion conductor is coated on the surface of the positive electrode active material, so that the lithium ion transmission rate of the positive electrode active material can be effectively improved, and in addition, in the primary charging process, at least part of the lithium ion conductor can play a role in supplementing lithium and is used as a sacrificial agent for supplementing a lithium source, so that the primary coulomb efficiency of the battery monomer is further improved.

In some embodiments, the oxide comprises at least one of aluminum oxide, magnesium oxide, cerium oxide, zinc oxide, lanthanum oxide, zirconium oxide, titanium oxide, silicon oxide, bismuth trioxide, indium oxide, and tricobalt tetraoxide. The oxides can effectively reduce the occurrence of side reactions of the positive electrode active material, improve the structural stability of the positive electrode active material, and ensure that the positive electrode active material is not easy to generate phase change in the circulating process, thereby endowing the battery monomer with higher circulating stability.

In some embodiments, the carbon material comprises at least one of graphene and carbon nanotubes. The carbon materials can effectively improve the conductivity of the positive electrode active material while improving the structural stability of the positive electrode active material, so that the secondary battery shows lower direct current impedance, and the capability of the positive electrode active material for transmitting active ions is improved, thereby further improving the cycle performance of the battery.

In some embodiments, the lithium ion conductor comprises at least one of lithium phosphate, lithium iron phosphate, lithium tantalate, lithium metaaluminate, lithium dititanium tetraoxide, lithium zirconate, lithium silicate, lithium orthovanadate, and lithium carboborate. The lithium ion conductors can improve the lithium ion transmission rate of the positive electrode active substance, and in addition, at least part of the lithium ion conductors can play a role in supplementing lithium in the primary charging process and serve as a sacrificial agent for supplementing a lithium source, so that the primary coulombic efficiency of the battery monomer is improved.

It is understood that the lithium carboborate has the chemical formula of Li _2+x C _1-x B _x O ₃ Wherein 0 is<x<1。

In some embodiments, the first subcoating layer comprises a lithium carbo-borate having the formula Li _2+x C _1-x B _x O ₃ ，0<x<1. The lithium carbo-borate can effectively improve the lithium ion conductivity of the positive electrode active material, simultaneously effectively relieve the oxidative decomposition of electrolyte and the accumulation of surface byproducts caused by the strong oxidizing property of the positive electrode active material in a high lithium removal state, inhibit the occurrence of side reactions of the positive electrode active material, further improve the structural stability of the positive electrode active material and effectively improve the cycle performance of the positive electrode active material.

In some embodiments, the first sub-coating layer comprises 0.1wt% to 0.5wt% of the positive electrode active material. Illustratively, the first subcoating layer may comprise typical but non-limiting values of 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, etc. of the positive electrode active material.

It is understood that when the coating layer includes only the first sub-coating layer, the mass ratio of the first sub-coating layer is the mass ratio of the coating layer; when a plurality of sub-coating layers are included in the coating layer, the ratio of the first sub-coating layer is only the ratio of the first sub-coating layer, and the mass ratio of the coating layers is the sum of the mass ratios of the respective coating layers.

According to the embodiment of the application, the mass ratio of the first sub-coating layer is controlled within the range, the effective coating of the coating layer on the anode active material can be realized, the anode active material and the electrolyte can be prevented from being in direct contact, transition metal contained in the anode active material is prevented from being dissolved out, the occurrence of side reaction on the surface of the anode active material is reduced, and the anode active material is isolated from moisture and carbon dioxide in the outside, so that the anode active material has higher structural stability and lower lithium consumption, abundant lithium ions can be provided, and higher capacity cycle retention rate of the battery monomer is endowed.

In some embodiments, a method of preparing a positive electrode active material coated with a first sub-coating layer includes the steps of:

step S10, providing a precursor of a positive electrode active material, a lithium source and a material of a first sub-coating layer;

step S20, performing first sintering treatment and first grinding treatment on a positive electrode active material precursor and a lithium source to obtain a positive electrode active material;

and step S30, mixing the positive electrode active material with the material of the first sub-coating layer, performing second grinding treatment and second sintering treatment, and forming a first sub-coating layer for coating the positive electrode active material on the surface of the positive electrode active material to obtain the positive electrode active material.

By adopting the preparation method, the material of the first sub-coating layer can be tightly coated on the surface of the positive electrode active material, and the formed first sub-coating layer is not easy to fall off, so that the protection of the positive electrode active material can be effectively realized, the occurrence of side reaction of the positive electrode active material is reduced, the positive electrode active material is not easy to generate phase change, and the damage of external water vapor or carbon dioxide to the positive electrode active material is avoided.

In some embodiments, in step S10, the lithium source comprises at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium formate, lithium silicate, lithium sulfate, lithium phosphate, lithium oxalate, lithium octoate, lithium citrate, lithium salicylate, lithium orthosilicate, lithium permanganate, lithium trifluoroacetate, lithium acetoacetate, lithium difluorophosphate, lithium hexafluorophosphate, lithium benzoate, lithium metaphosphate, lithium pyruvate, lithium acetate, lithium fluoride, lithium bromide, lithium methoxide, lithium ethoxide, lithium oxide, lithium nitride, lithium sulfide.

In some embodiments, in step S10, the material of the first subcoating layer is as described above, including at least one of an oxide, fluoride, phosphate, carbon material, lithium ion conductor.

In some embodiments, the methods for preparing the oxides, fluorides, phosphates are not limited in this application, and methods of preparation well known to those skilled in the art can be employed. Exemplary, may include, but are not limited to, preparing the resulting oxide by sol-gel, precipitation, calcination, acid-base, and hydrothermal methods. For example, an alkaline substance such as sodium hydroxide or aluminum hydroxide is reacted with bauxite to produce aluminum hydroxide, and the aluminum hydroxide is calcined at a high temperature of 800 ℃ for 10 hours to obtain aluminum oxide. Illustratively, the phosphate salt may include, but is not limited to, those obtained by sol-gel, vapor deposition, and hydrothermal processes. For example, a proper amount of phosphoric acid and ferric hydroxide are dissolved in water to generate a ferric phosphate solution, water is evaporated by heating, and when the solution is concentrated, ferric phosphate crystals are precipitated, centrifuged, filtered and dried to obtain high-purity ferric phosphate. Illustratively, sodium fluoride and calcium chloride are mixed and heated, reacted to form calcium fluoride and sodium chloride, filtered and dried to obtain pure calcium fluoride.

In some embodiments, when the material of the first sub-coating layer comprises a carbon material, the carbon source may include, but is not limited to, activated carbon, acetylene black, ketjen black, graphene, carbon nanotubes, and carbon fibers.

In some casesIn specific embodiments, the preparation method of the lithium ion conductor is not limited, and preparation methods well known to those skilled in the art can be used. Illustratively, lithium phosphate is synthesized by precipitation at a molar ratio of 3:1, lithium hydroxide and monoammonium phosphate are taken as raw materials, and under the condition of stirring, the lithium hydroxide solution is dripped into the monoammonium phosphate solution at a constant speed, and white powder lithium phosphate is obtained after the reaction. Exemplary, lithium borate and lithium carbonate are uniformly mixed according to the mol ratio of B atom to C atom of x to 1-x, and sintered at 800-950 ℃ for 8-10h to obtain the chemical formula Li _2+x C _1-x B _x O ₃ Of (2) lithium carboborate of 0<x<1。

In some embodiments, in step S20, the temperature of the first sintering treatment is 500-900 ℃, the time is 5-10 h, and the temperature rising rate is 3-10 ℃/min.

In some embodiments, the temperature of the first sintering process is 700-900 ℃, the time is 9-10 hours, and the temperature rising rate is 5-10 ℃/min.

By way of example, the temperature of the first sintering process may be, but is not limited to, values of 500 ℃, 600 ℃, 700 ℃, 750 ℃,800 ℃, 850 ℃, 900 ℃, and the like. The time of the first sintering treatment may be typical but non-limiting values of 5h, 6h, 7h, 8h, 9h, 10h, etc. The heating rate of the first sintering treatment may be, but is not limited to, typical values of 3 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min, 10 ℃/min, and the like.

Under the sintering treatment conditions, for example, by controlling the temperature rising rate, the sintering time and the sintering temperature within the above ranges, the particle diameter obtains a proper growth rate, so that primary particles with large particle diameter are obtained, and the action mechanism is that the molecular thermal motion is increased along with the temperature rising, so that the crystal particles obtain larger kinetic energy to penetrate through the energy barrier to form crystals. Through the sintering condition, the number of primary particles in the positive electrode active material is increased, so that the structural stability of the positive electrode active material in the circulating process is improved, cracking is not easy to occur, the occurrence of side reaction of the positive electrode active material is greatly reduced, and the loss of the positive electrode active material caused by active site loss is reduced.

In some embodiments, in step S20, the rotation speed of the first polishing treatment is 400rpm to 500rpm, and the time is 6h to 10h. By way of example, the rotational speed of the first grinding process may be a typical, but non-limiting, value of 400rpm, 420rpm, 450rpm, 480rpm, 500rpm, etc. The time of the first grinding treatment may be typical but not limiting values of 6h, 7h, 8h, 9h, 10h, etc.

Illustratively, the first milling process employs a ball milling process.

Under the grinding treatment condition, the agglomeration effect of the positive electrode active material can be reduced, and the number proportion of primary particles in the positive electrode active material is increased, so that the stability of the particle structure of the positive electrode active material in the circulating process is improved, and the positive electrode active material is not easy to crack.

In some embodiments, in step S30, the mass ratio of the positive electrode active material to the material of the first sub-coating layer is 100:0.1 to 0.5. Illustratively, the mass ratio of the positive electrode active material to the material of the first subcoating layer is 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5, etc. typical but non-limiting values. Within this ratio range, the material of the first sub-coating layer may form a first sub-coating layer whose effective coating is formed on the surface of the positive electrode active material.

In some embodiments, in step S30, the rotation speed of the second polishing process is 400rpm to 500rpm, and the time is 8h to 12h. By way of example, the rotational speed of the second grinding process may be a typical, but non-limiting, value of 400rpm, 420 rpm, 450 rpm, 480 rpm, 500rpm, etc. The time of the second grinding treatment may be typical but not limiting values of 8h, 9h, 10h, 11h, 12h, etc.

Illustratively, the second milling process employs a ball milling process.

In some embodiments, in step S30, the temperature of the second sintering treatment is 800 ℃ to 1000 ℃, the time is 5h to 10h, and the temperature rising rate is 3 ℃ to 5 ℃/min.

By way of example, the temperature of the second sintering process may be, but is not limited to, typical values of 800 ℃, 850 ℃, 900 ℃, 950 ℃, 1000 ℃, and the like. The time of the second sintering treatment may be typical but non-limiting values of 5h, 6h, 7h, 8h, 9h, 10h, etc. The rate of temperature rise of the second sintering process may be, but is not limited to, typical values of 3 ℃/min, 3.5 ℃/min, 4 ℃/min, 4.5 ℃/min, 5 ℃/min, etc.

Under the sintering condition, a first sub-coating layer for coating the positive electrode active material can be formed on the surface of the positive electrode active material, and the coating layer is not easy to fall off.

In some embodiments, the coating layer further comprises a second sub-coating layer disposed on a side of the first sub-coating layer remote from the positive electrode active material, the second sub-coating layer comprising a conductive polymer.

Referring to fig. 1, in some embodiments, the surface of the positive electrode active material 4 is coated with a coating layer 5, and the coating layer 5 includes a first sub-coating layer 51, where the first sub-coating layer 51 includes at least one of an oxide, a fluoride, a phosphate, a carbon material, and a lithium ion conductor. For convenience of distinction, a coating layer containing at least one of an oxide, a fluoride, a phosphate, a carbon material, and a lithium ion conductor is defined as the first sub-coating layer 51. The coating comprises a first sub-coating 51, in some embodiments the coating 5 may comprise only the first sub-coating 51, in other embodiments the coating 5 may comprise further sub-coatings.

Referring to fig. 1, in some embodiments, the coating layer 5 further includes a second sub-coating layer 52, the second sub-coating layer 52 being disposed on a side of the first sub-coating layer 51 remote from the positive electrode active material 4, the second sub-coating layer 52 including a conductive polymer.

Specifically, the coating layer 5 includes at least two sub-coating layers, namely, a first sub-coating layer 51 and a second sub-coating layer 52, wherein the first sub-coating layer 51 directly coats the surface of the positive electrode active material 4, and the second sub-coating layer 52 is disposed outside the first sub-coating layer 51, that is, the first sub-coating layer 51 is disposed between the positive electrode active material 4 and the second sub-coating layer 52. The first sub-coating layer 51 and the second sub-coating layer 52 may be in direct contact or may be disposed at intervals.

The first sub-coating layer 51 and the second sub-coating layer 52 are coated on the surface of the positive electrode active material 4, and the second sub-coating layer 52 contains a conductive polymer. The first sub-coating layer 51 is used as an inner layer, the first sub-coating layer 51 can effectively play a role in protecting the positive electrode active material, so that the positive electrode active material 4 can be prevented from being in direct contact with electrolyte, transition metal contained in the positive electrode active material 4 is prevented from being dissolved out, the occurrence of side reaction on the surface of the positive electrode active material is reduced, and of course, the first sub-coating layer 51 can also improve the lithium ion transmission rate and/or the electronic conductivity of the positive electrode active material 4; the second sub-coating layer 52 is used as an outer layer, and conductive polymer is used as a material, so that on one hand, the electron conductivity of the positive electrode active material 4 can be effectively improved, the reaction resistance of electrons on the surface of the positive electrode active material is small, the charge transmission rate is high, and the dynamic performance of the battery monomer is improved; on the other hand, the first sub-coating layer 51 of the inner layer can be protected, which is more advantageous to improve the structural stability of the positive electrode active material 4, thereby enabling the battery cell to have higher energy density and cycle performance.

In some embodiments, the conductive polymer includes at least one of polypyrrole, polythiophene, polyaniline, and polyacetylene. The conductive polymers have good conductivity, so that the electron conductivity of the positive electrode active material is improved, the activity and the cycle performance of the positive electrode active material are obviously improved, the electron conductivity and the stability of a CEI film (solid electrolyte interface layer cathode electrolyte interphase) are improved, and the positive electrode active material is endowed with higher structural stability.

In some embodiments, the thickness ratio of the first sub-coating layer to the second sub-coating layer is 1.5:1-3:1.

By way of example, the thickness ratio of the first sub-cladding layer to the second sub-cladding layer may be typical, but not limiting, of 1:1, 1.5:1, 2:1, 3:1, 4:1, etc.

The preparation method of the positive electrode active material coated with the first sub-coating layer 51 and the second sub-coating layer 52 includes the following steps, and the material of the second sub-coating layer 52 is exemplified by polypyrrole:

Step S40, providing sodium paratoluenesulfonate (doping agent), anhydrous ferric chloride (oxidizing agent) and pyrrole monomer (monomer of the second sub-coating layer), wherein the ratio of the doping agent, pyrrole monomer and oxidizing agent is 1:3:9.

And S50, dissolving sodium paratoluenesulfonate and pyrrole monomers into absolute ethyl alcohol, stirring and dissolving for 2 hours, then adding the material prepared in the step S20 (the positive electrode active material with the surface coated with the first sub-coating layer 51), continuing stirring, then adding anhydrous ferric chloride solution dropwise under the ice bath condition, continuing stirring, forming a second sub-coating layer 52 on the surface of one side of the first sub-coating layer 51 far away from the positive electrode active material 4, centrifuging, separating, washing and drying to obtain the positive electrode active material.

In some embodiments, the thickness of the cladding layer is 5nm to 50nm. By way of example, the coating may be any point value or range between any two point values of 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm.

The thickness of the clad refers to the total thickness of the clad, and when a plurality of sub-clad are included in the clad, the thickness of the clad is the sum of the thicknesses of the respective clad. As an example, when the coating layer 5 includes only the first sub-coating layer 51, the thickness of the coating layer is the thickness of the first sub-coating layer 51. As an example, when the coating layer 5 includes the first sub-coating layer 51, the second sub-coating layer 52, the thickness of the coating layer is the sum of the thicknesses of the two.

Through setting the thickness of the coating layer to be 5 nm-50 nm, a proper amount of positive electrode active substances are contained in the positive electrode active material, so that abundant active ions are provided, and effective coating of the positive electrode active substances can be realized, so that the structural stability of the positive electrode active material is effectively improved, meanwhile, the lithium ion conductivity and the electronic conductivity of the positive electrode active material are improved, and the battery monomer has higher energy density and cycle performance.

In some embodimentsThe positive electrode active material had a compacted density of 3.0g/cm ² ~3.5g/cm ² 。

In some embodiments, the positive electrode active material has a compacted density of 3.25g/cm ² ~3.45g/cm ² 。

Exemplary, the positive electrode active material may have a compacted density of 3.0g/cm ² 、3.1 g/cm ² 、3.2 g/cm ² 、3.25 g/cm ² 、3.3 g/cm ² 、3.4 g/cm ² 、3.45 g/cm ² 、3.5 g/cm ² Etc. typical but non-limiting values.

The compacted density is related to the particle size, density, and grading of the particles of the positive electrode active material, and in general, a large compacted density indicates that the positive electrode active material particles have a good normal distribution. It will be appreciated that the higher the compacted density, the higher the mass of active material per unit volume of the positive electrode sheet, and the higher the volumetric capacity and energy density exhibited by the positive electrode sheet. By controlling the compaction density of the positive electrode plate within the range, the positive electrode plate has higher capacity and good particle size characteristics, is favorable for migration of lithium ions, and gives the positive electrode plate higher energy density.

In some embodiments, the average volume particle diameter Dv50 of the positive electrode active material is 3.5 μm to 4.5 μm.

By way of example, the average volume particle diameter Dv50 of the positive electrode active material may be typical but not limiting values of 3.0 μm, 3.5 μm, 3.8 μm, 4.0 μm, 4.2 μm, 4.5 μm, 5.0 μm, etc.

The Dv50 particle diameter of the positive electrode active material is controlled within the above range, and the positive electrode active material has higher lithium ion migration efficiency and lower agglomeration effect, thereby being beneficial to improving the energy density of the positive electrode active material. If the Dv50 particle size of the positive electrode active material is lower than the above range, the agglomeration effect of the positive electrode active material is obvious, and the positive electrode active material particles are easy to crack in the circulation process, so that the side reaction of the positive electrode active material and the electrolyte is increased; if the Dv50 particle diameter of the positive electrode active material is higher than the above range, the transmission path of lithium ions is excessively long, thereby affecting the transmission rate of lithium ions.

In some embodiments, the specific surface area of the positive electrode active material is 0.5m ² /g~0.9m ² /g。

In some embodiments, the specific surface area of the positive electrode active material is 0.6m ² /g~0.8m ² /g。

Exemplary, the specific surface area of the positive electrode active material may be 0.5m ² /g、0.6 m ² /g、0.7m ² /g、0.8 m ² /g、0.9m ² /g, etc. typical but not limiting values.

By controlling the specific surface area of the positive electrode active material within the above-described range, the positive electrode active material has an appropriate lithium ion transmission path and a high lithium ion deintercalation efficiency, so that the positive electrode active material has a high capacity.

In some embodiments, the positive electrode active material has the chemical formula LiNi _x Co _y Mn _1-x-y O ₂ Wherein x is more than or equal to 0.5 and less than or equal to 0.8,0.06 and y is more than or equal to 0.15. Illustratively, the positive electrode active material may be LiNi _0.6 Co _0.1 Mn _0.3 O ₂ 、LiNi _0.6 Co _0.12 Mn _0.28 O ₂ 、LiNi _0.6 Co _0.13 Mn _0.27 O ₂ 、LiNi _0.6 Co _0.15 Mn _0.25 O ₂ 、LiNi _0.6 Co _0.07 Mn _0.33 O ₂ 、LiNi _0.7 Co _0.1 Mn _0.2 O ₂ 、LiNi _0.5 Co _0.1 Mn _0.4 O ₂ 。

In some embodiments, 0.10.ltoreq.y.ltoreq.0.15. Illustratively, the y value may be a typical, but non-limiting, value of 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, etc.

In the positive electrode active material, lithium ions and nickel ions have a radius close to each other, so that lithium and nickel are easily dislocated, and migration of lithium ions in a crystal lattice is hindered, and kinetics is deteriorated. In the embodiment of the application, the cobalt atom in the positive electrode active material is controlled in the range, so that the discharge degree of lithium and nickel can be reduced, the layered structure is stabilized, and the polarization loss is reduced, therefore, the positive electrode active material provided by the embodiment of the application is stable in structure and not easy to generate phase change, and the probability of side reaction with electrolyte is reduced; meanwhile, the increase of the cobalt content can also increase the gram capacity of the positive electrode active material, so that the positive electrode active material of the chemical formula enables the battery cell to have higher capacity cycle retention rate.

In some embodiments, the battery cell includes a positive electrode tab, a negative electrode tab, and further includes an electrolyte and a separator.

[ Positive electrode sheet ]

The positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer contains a positive electrode active material, and the positive electrode active material comprises the positive electrode active material.

As an example, the positive electrode current collector has two surfaces opposing in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two surfaces opposing the positive electrode current collector.

In some embodiments, the positive current collector may employ a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive electrode film layer further optionally includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluoroacrylate resin.

In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet may be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and (3) coating the positive electrode slurry on a positive electrode current collector, and obtaining a positive electrode plate after the procedures of drying, cold pressing and the like.

[ negative electrode sheet ]

The negative electrode tab includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material including the negative electrode active material described above.

As an example, the anode current collector has two surfaces opposing in its own thickness direction, and the anode film layer is provided on either one or both of the two surfaces opposing the anode current collector.

In some embodiments, the negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative electrode film layer further optionally includes a binder. The binder may be at least one selected from Styrene Butadiene Rubber (SBR), polyacrylic acid (PAA), sodium Polyacrylate (PAAs), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium Alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode film layer further optionally includes a conductive agent. The conductive agent is at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the negative electrode film layer may optionally further include other adjuvants, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

In some embodiments, the negative electrode sheet may be prepared by: dispersing the above components for preparing the negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; and coating the negative electrode slurry on a negative electrode current collector, and obtaining a negative electrode plate after the procedures of drying, cold pressing and the like.

[ electrolyte ]

The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. The type of electrolyte in the embodiments of the present application is not particularly limited, and may be selected according to the needs. For example, the electrolyte may be liquid, gel, or all solid.

In some embodiments, the electrolyte is an electrolyte. The electrolyte includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonyl imide, lithium bis-trifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxaato borate, lithium difluorodioxaato phosphate, lithium tetrafluorooxalato phosphate, lithium N-dialkylpyrrolidinium salt, lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethanesulfonyl) imide, and lithium N-ethylpyrrolidinium tetrafluoroborate.

In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1, 4-butyrolactone, sulfolane, dimethyl sulfone, methyl sulfone, and diethyl sulfone.

In some embodiments, the electrolyte further optionally includes an additive. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, and the like.

[ isolation Membrane ]

The type of the separator is not particularly limited in the embodiment of the present application, and any known porous separator having good chemical stability and mechanical stability may be used.

In some embodiments, the material of the isolating film may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

Some embodiments of the present application provide a battery that includes at least one of the above-described battery cells, typically including a plurality of battery cells, connected in series, parallel, or a series-parallel connection to increase the power capacity of the battery. In some cases, the battery further includes a case in which the battery cells are accommodated.

Thus, in an embodiment, the battery may include any one of a battery cell, a battery module, and a battery pack.

In some embodiments, when the battery according to the embodiments of the present application is a battery module, the battery module includes a plurality of the battery cells, and the plurality of battery cells may be sequentially arranged along a length direction of the battery module. Of course, the arrangement may be performed in any other way. The plurality of battery cells may further be secured by fasteners.

In some embodiments, the battery module may further include a housing having a receiving space in which the plurality of battery cells are received.

In some embodiments, when the battery according to the embodiments of the present application is a battery pack, the battery pack may contain a plurality of the above battery cells, and a plurality of the battery cells may be assembled into the above battery module. Thus, the specific number of battery cells or battery modules included in the battery pack may be adjusted according to the application and capacity of the battery pack.

As in the embodiment, a battery box and a plurality of battery modules disposed in the battery box may be included in the battery pack. The battery box comprises an upper box body and a lower box body, wherein the upper box body is used for covering the lower box body, and a closed space for accommodating the battery module is formed. The plurality of battery modules may be arranged in the battery case in any manner.

Some embodiments of the present application provide an electrical device, including a battery of embodiments of the present application. The battery in the embodiment of the application can be used as a power supply of the electric device and also can be used as an energy storage unit of the electric device. Therefore, the power utilization device is long in standby time or endurance time and good in safety performance.

The battery disclosed in some embodiments of the present application may be used in, but is not limited to, electrical devices such as vehicles, boats, or aircraft. A power supply system having the battery or the like disclosed in the present application constituting the power consumption device may be used.

Some embodiments of the present application provide an electrical device that uses a battery as a power source, which may be, but is not limited to, a vehicle, a cell phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, an electric tool, and the like. The vehicle can be but not limited to a fuel oil vehicle, a fuel gas vehicle or a new energy vehicle, and the new energy vehicle can be but not limited to a pure electric vehicle, a hybrid electric vehicle or an extended range vehicle; spacecraft including airplanes, rockets, space planes, spacecraft, and the like; the electric toy includes fixed or mobile electric toys, such as a game machine, an electric car toy, an electric ship toy, and an electric airplane toy; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railroad power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete shakers, and electric planers, among others.

For convenience of description, the following embodiments will take an electric device according to an embodiment of the present application as an example of a vehicle.

Referring to fig. 2, fig. 2 is a schematic structural diagram of a vehicle according to some embodiments of the present application. The vehicle 1000 may be a fuel oil vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or a range-extended vehicle. The interior of the vehicle 1000 is provided with a lithium ion battery 100, and the lithium ion battery 100 may be provided at the bottom or at the head or at the tail of the vehicle 1000. The lithium ion battery 100 may be used for power supply of the vehicle 1000, for example, the lithium ion battery 100 may serve as an operating power source of the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300, the controller 200 being configured to control the lithium ion battery 100 to power the motor 300, for example, for operating power requirements during start-up, navigation, and travel of the vehicle 1000.

In some embodiments of the present application, lithium ion battery 100 may not only be used as an operating power source for vehicle 1000, but also as a driving power source for vehicle 1000, instead of or in part instead of fuel oil or natural gas, to provide driving power for vehicle 1000.

In some embodiments of the present application, lithium ion battery 100 is a secondary battery that has many different forms, including but not limited to a battery cell, a battery module, a battery pack, and the like. The secondary battery herein refers to a battery that can be continuously used by activating an active material by means of charging after the battery is discharged.

Referring to fig. 3, fig. 3 is an exploded view of a lithium ion battery 100 according to some embodiments of the present disclosure. The lithium ion battery 100 includes a case 10 and a lithium ion battery cell 20, and the lithium ion battery cell 20 is accommodated in the case 10. The case 10 is used for providing an accommodating space for the lithium ion battery unit 20, and the case 10 may have various structures. In some embodiments, the case 10 may include an upper case 11 and a lower case 12, the upper case 11 and the lower case 12 being covered with each other, the upper case 11 and the lower case 12 together defining an enclosed space for accommodating the lithium ion battery cell 20. Of course, the case 10 formed by the upper case 11 and the lower case 12 may be of various shapes, such as a cylinder, a rectangular parallelepiped, etc. The plurality of battery cells 20 may be arranged in the battery case in any manner.

In the lithium ion battery 100, the number of the lithium ion battery cells 20 may be plural, and the plural lithium ion battery cells 20 may be connected in series or parallel or in series-parallel, and the series-parallel refers to that the plural lithium ion battery cells 20 are connected in series or parallel. The lithium ion battery monomers 20 can be directly connected in series or in parallel or in series-parallel, and then the whole formed by the lithium ion battery monomers 20 is accommodated in the box body 10; of course, the lithium ion battery 100 may also be a form of a lithium ion battery module formed by connecting a plurality of lithium ion battery cells 20 in series, parallel or series-parallel connection, and then connecting a plurality of lithium ion battery modules in series, parallel or series-parallel connection to form a whole, and then accommodating the whole in the case 10.

Referring to fig. 4, fig. 4 is an exploded view of a battery cell 20 according to some embodiments of the present application. The battery cell 20 refers to a basic unit for achieving the mutual conversion of chemical energy and electric energy, and is also a minimum unit constituting a battery. As shown in fig. 4, the battery cell 20 includes a case 21, a cap plate 23, an electrode assembly 22, and other functional components.

The housing 21 may include a bottom plate and a side plate coupled to the bottom plate, the bottom plate and the side plate enclosing to form a receiving cavity. The case 21 is a hollow structure having one end open, and the case 21 is used to cooperate with the cap plate 23 to form an internal environment that accommodates the electrode assembly 22, electrolyte, and other functional components. The housing 21 may be of various shapes and various sizes, such as rectangular parallelepiped, cylindrical, hexagonal prism, etc. Specifically, the shape of the case 21 may be determined according to the specific shape and size of the electrode assembly 22. The material of the housing 21 may be, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and is not limited thereto.

The cover plate 23 refers to a member that is covered at the opening of the case 21 to isolate the internal environment of the battery cell 20 from the external environment. Alternatively, the shape of the cover plate 23 may be adapted to the shape of the housing 21 to fit the housing 21. Alternatively, the cover plate 23 may be made of a material having a certain hardness and strength (such as an aluminum alloy), so that the cover plate 23 is not easy to deform when being extruded and collided, so that the battery cell 20 can have a higher structural strength, and the safety performance can be improved. The material of the cover plate 23 may be, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and is not limited thereto.

The number of the electrode assemblies 22 included in the battery cell 20 may be one or more, and may be adjusted according to actual needs.

Examples

Hereinafter, embodiments of the present application are described. The embodiments described below are exemplary only for the purpose of illustrating the present application and are not to be construed as limiting the present application. The examples are not to be construed as limiting the specific techniques or conditions described in the literature in this field or as per the specifications of the product. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

Example 1

A battery cell comprising: positive pole piece, negative pole piece, barrier film and electrolyte.

The positive electrode plate contains a positive electrode active material, the positive electrode active material comprises a positive electrode active material and a coating layer coated on the outer surface of the positive electrode active material, and the material of the coating layer is Li _2.5 C _0.5 B _0.5 O ₃ The number of primary particles in the positive electrode active material was 70%.

The negative electrode plate contains a negative electrode active material, wherein the negative electrode active material comprises graphite, the OI value of the graphite is 5, the graphitization degree is 97%, the Dv50 particle size is 12 mu m, and the specific surface area is 1.5m ² /g。

A preparation method of a battery monomer comprises the following steps:

S1, preparing a positive electrode active material:

a positive electrode active material precursor (Ni _0.6 Co _0.1 Mn _0.3 (OH) ₂ ) Mixing with lithium hydroxide according to a molar ratio of 1:1, heating to 800 ℃ at a heating rate of 5 ℃/min, sintering for 6 hours, and grinding for 8 hours at a rotating speed of 450rpm to obtain the anode active material Ni _0.6 Co _0.1 Mn _0.3 O ₂ 。

Positive electrode active material and Li _2.5 C _0.5 B _0.5 O ₃ Mixing at a mass ratio of 100:0.1, grinding at 450rpm for 10 hr, heating to 1000deg.C at a heating rate of 3deg.C/min, sintering for 10 hr, and forming a coating layer (Li) _2.5 C _0.5 B _0.5 O ₃ ) And obtaining the positive electrode active material.

S2, preparing a positive plate: dissolving the positive electrode active material prepared in the step S1, acetylene black serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as a binder in a weight ratio of 96.5:1.5:2 in N-methylpyrrolidone (NMP), and fully stirring and uniformly mixing to obtain positive electrode slurry; and uniformly coating the anode slurry on an anode current collector with a bottom coating, and drying, cold pressing and cutting to obtain an anode plate.

S3, preparing a negative electrode plate: and (3) uniformly mixing the negative electrode active material graphite, the conductive agent acetylene black, styrene Butadiene Rubber (SBR) and the thickener sodium carboxymethylcellulose (CMC) in a weight ratio of 90:5:2:2:1 in solvent deionized water to prepare a negative electrode slurry, coating the slurry on a copper foil, drying, and carrying out cold pressing and slitting to obtain the negative electrode plate.

S4, preparing a battery monomer: and sequentially stacking the positive electrode plate, the isolating film and the negative electrode plate, enabling the isolating film to be positioned between the positive electrode plate and the negative electrode plate to play a role of isolation, then winding to obtain a bare cell, welding a tab for the bare cell, loading the bare cell into an aluminum shell, baking at 80 ℃ for removing water, injecting electrolyte, and sealing to obtain the uncharged battery. The uncharged battery is subjected to standing, hot and cold pressing,And (3) forming, shaping, capacity testing and the like to obtain a secondary battery product. The isolating film is PE membrane, and PVDF and alumina coating are coated on the surface of the isolating film to improve the adhesion and heat resistance. The preparation process of the electrolyte comprises mixing Ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) at a volume ratio of 1:1:1, and then mixing LiPF ₆ : liFSI (2:8) was uniformly dissolved in the above solution to obtain an electrolyte in which the concentration of lithium salt was 1mol/L.

Example 2

A battery cell differing from example 1 in that: the number of primary particles in the positive electrode active material is 60%, specifically, step S1 is:

a positive electrode active material precursor (Ni _0.6 Co _0.1 Mn _0.3 (OH) ₂ ) Mixing with lithium hydroxide according to a molar ratio of 1:1, heating to 750 ℃ at a heating rate of 4 ℃/min, sintering for 5.5 hours, and grinding for 8 hours at a rotating speed of 400rpm to obtain the positive electrode active material Ni _0.6 Co _0.1 Mn _0.3 O ₂ 。

Positive electrode active material and Li _2.5 C _0.5 B _0.5 O ₃ Mixing at a mass ratio of 100:0.1, grinding at 450rpm for 8 hr, heating to 1000deg.C at a heating rate of 3deg.C/min, sintering for 10 hr, and forming a coating layer (Li) _2.5 C _0.5 B _0.5 O ₃ ) And obtaining the positive electrode active material.

Otherwise, the same as in example 1 was used.

Example 3

A battery cell differing from example 1 in that: the number of primary particles in the positive electrode active material is 50%, specifically, step S1 is:

a positive electrode active material precursor (Ni _0.6 Co _0.1 Mn _0.3 (OH) ₂ ) Mixing with lithium hydroxide according to a molar ratio of 1:1, heating to 600 ℃ at a heating rate of 4 ℃/min, sintering for 7h, and grinding at a rotation speed of 400rpmTreating for 6h to obtain the positive electrode active material Ni _0.6 Co _0.1 Mn _0.3 O ₂ 。

Positive electrode active material and Li _2.5 C _0.5 B _0.5 O ₃ Mixing at a mass ratio of 100:0.1, grinding at 400rpm for 8 hr, heating to 1000deg.C at a heating rate of 3deg.C/min, sintering for 10 hr, and forming a coating layer (Li) _2.5 C _0.5 B _0.5 O ₃ ) And obtaining the positive electrode active material.

Otherwise, the same as in example 1 was used.

Example 4

A battery cell differing from example 1 in that: the number of primary particles in the positive electrode active material is 90%, specifically, step S1 is:

a positive electrode active material precursor (Ni _0.6 Co _0.1 Mn _0.3 (OH) ₂ ) Mixing with lithium hydroxide according to a molar ratio of 1:1, heating to 900 ℃ at a heating rate of 10 ℃/min, sintering for 6 hours, and grinding for 10 hours at a rotating speed of 450rpm to obtain the anode active material Ni _0.6 Co _0.1 Mn _0.3 O ₂ 。

Positive electrode active material and Li _2.5 C _0.5 B _0.5 O ₃ Mixing at a mass ratio of 100:0.1, grinding at 500rpm for 12 hr, heating to 1000deg.C at a heating rate of 3deg.C/min, sintering for 10 hr, and forming a coating layer (Li) _2.5 C _0.5 B _0.5 O ₃ ) And obtaining the positive electrode active material.

Otherwise, the same as in example 1 was used.

Example 5

A battery cell differing from example 1 in that: the OI value of graphite was 2, and the other was the same as in example 1.

Example 6

A battery cell differing from example 1 in that: the graphite had an OI value of 8, otherwise the same as in example 1.

Example 7

A battery cell differing from example 1 in that: the graphitization degree of graphite was 99%, and the other steps were the same as in example 1.

Example 8

A battery cell differing from example 1 in that: the graphitization degree of graphite was 90%, and the other was the same as in example 1.

Example 9

A battery cell differing from example 1 in that: positive electrode active material and Li _2.5 C _0.5 B _0.5 O ₃ The mass ratio of (2) was 100:0.5, and the other was the same as in example 1.

Example 10

A battery cell differing from example 1 in that: positive electrode active material and Li _2.5 C _0.5 B _0.5 O ₃ The mass ratio of (2) was 100:1, and the other was the same as in example 1.

Example 11

A battery cell differing from example 1 in that: positive electrode active material and Li _2.5 C _0.5 B _0.5 O ₃ The mass ratio of (2) was 100:0.05, and the other was the same as in example 1.

Example 12

A battery cell differing from example 1 in that: will coat the layer material Li _2.5 C _0.5 B _0.5 O ₃ Instead of alumina, the other materials were the same as in example 1.

Example 13

A battery cell differing from example 1 in that: will coat the layer material Li _2.5 C _0.5 B _0.5 O ₃ The other components were the same as in example 1 except that lithium phosphate was used instead.

Example 14

A battery cell differing from example 1 in that: the coating layer comprises a first sub-coating layer directly coated on the surface of the positive electrode active substance and a second sub-coating layer outside the first sub-coating layer, wherein the thickness ratio of the first sub-coating layer to the second sub-coating layer is as follows: 1.5:1, otherwise identical to example 1. Specifically, step S1 is as follows:

Positive electrode active material and Li _2.5 C _0.5 B _0.5 O ₃ Mixing according to the mass ratio of 100:0.5, heating to 1000 ℃ at the heating rate of 3 ℃/min, sintering for 10 hours, and forming a first sub-coating layer (the first sub-coating layer material is Li) for coating the positive electrode active material on the surface of the positive electrode active material _2.5 C _0.5 B _0.5 O ₃ ) Intermediate is obtained.

Sodium p-toluenesulfonate (dopant), anhydrous ferric chloride (oxidant), pyrrole monomer (monomer of the second subcoating layer) were provided, wherein the ratio of the amounts of the dopant, pyrrole monomer, oxidant was 1:3:9.

Dissolving sodium paratoluenesulfonate and pyrrole monomers into absolute ethyl alcohol, stirring and dissolving for 2 hours, then adding an intermediate, continuously stirring for 2 hours, then dropwise adding an anhydrous ferric chloride solution (with the concentration of 0.02 g/ml) under ice bath conditions, continuously stirring for 12 hours, forming a second sub-coating layer (the material of the second sub-coating layer is polypyrrole, the material of the second sub-coating layer accounts for 0.5 weight percent of the positive electrode active material) on the surface of one side of the first sub-coating layer, which is far away from the positive electrode active material, centrifugally separating, washing for 3 times by using absolute ethyl alcohol, and drying for 24 hours in a vacuum oven at 80 ℃ to obtain the positive electrode active material.

Example 15

A battery cell differing from example 14 in that: the thickness ratio of the first sub-coating layer to the second sub-coating layer is as follows: 1:1. Specifically, the second sub-coating layer material in step S1 accounts for 1wt% of the positive electrode active material, and the other components are the same as in example 14.

Comparative example 1

A battery cell differing from example 1 in that: no coating layer is added. Specific S1:

a positive electrode active material precursor (Ni _0.6 Co _0.1 Mn _0.3 (OH) ₂ ) Mixing with lithium hydroxide according to a molar ratio of 1:1, heating to 800 ℃ at a heating rate of 5 ℃/min, sintering for 6 hours, and grinding for 8 hours at a rotating speed of 450rpm to obtain the anode active material Ni _0.6 Co _0.1 Mn _0.3 O ₂ The positive electrode active material is used as a positive electrode active material.

Comparative example 2

A battery cell differing from example 1 in that: the OI value of the graphite was 10.

Comparative example 3

A battery cell differing from example 1 in that: the amount of primary particles in the positive electrode active material was 30%. Specifically, step S1 is as follows:

a positive electrode active material precursor (Ni _0.6 Co _0.1 Mn _0.3 (OH) ₂ ) Mixing with lithium hydroxide according to a molar ratio of 1:1, heating to 800 ℃ at a heating rate of 3 ℃/min, sintering for 12 hours, and grinding for 2 hours at a rotating speed of 400rpm to obtain an anode active material Ni _0.6 Co _0.1 Mn _0.3 O ₂ 。

Positive electrode active material and Li _2.5 C _0.5 B _0.5 O ₃ Mixing at a mass ratio of 100:0.1, grinding at 400rpm for 2 hr, heating to 1000deg.C at a heating rate of 3deg.C/min, sintering for 10 hr, and forming a coating layer (Li) _2.5 C _0.5 B _0.5 O ₃ ) And obtaining the positive electrode active material.

Performance testing

(1) OI value of graphite

X-ray diffraction analysis (XRD) is a commonly used method of analyzing the crystal structure of materials. When X-rays are irradiated onto graphite, if the wavelength λ of the X-rays, the interplanar distance d, and the angle θ between the direction of incidence of the X-rays and the crystal plane satisfy bragg formula 2dsin θ=nλ, constructive interference occurs between the reflected X-rays to be enhanced.

oi=c004/C110, C004 is the peak area of the 004 characteristic diffraction peak in the X-ray diffraction pattern of graphite, C110 is the peak area of the 110 characteristic diffraction peak in the X-ray diffraction pattern of graphite, and the ratio of the two is OI value.

(2) Degree of graphitization of graphite

The graphitization degree of graphite can be calculated according to the following formula,

。

wherein g represents the graphitization degree; d, d ₀₀₂ The interlayer spacing of the (002) crystal face of the carbon material is measured in nm.

(3) Thickness of coating layer in positive electrode active material

The coating thickness was measured by TEM transmission electron microscopy.

The transmission electron microscope can be used for carrying out the orthotopic analysis of the tissue morphology and the crystal structure of the material, and when the focused electron beam is accelerated and then projected onto the thinner material, the high-energy electrons collide with atoms in the material and scatter to change the movement direction due to the thinness of the sample. The size of the scattering angle is controlled by the thickness, density and element type of the material, so that images with different brightness can be formed, and the images are amplified by a specific image processing system and focused on a fluorescent screen for observation. The resolution of the transmission electron microscope is higher than that of the scanning electron microscope, and can reach a few tenths of nanometers.

(4) Primary particle number ratio in positive electrode active material

Scanning Electron Microscopy (SEM) was used to obtain material morphology and microstructure information. The basic principle is that the high-energy electron beam is used for bombarding the surface of a sample under the vacuum environment, and the signals related to the morphology of the back scattered electrons, secondary electrons and the like which are excited from the surface of the sample are collected and received by a detector and sent to a kinescope, so that SEM images are fed back to observe the surface morphology of the sample. The positive electrode active material includes primary particles and secondary particles, wherein the secondary particles are formed by agglomerating a plurality of primary (mono) particles. The number ratio of primary particles in the positive electrode active material is calculated by the following formula:

（I）。

Morphology features: as a result of scanning electron microscope analysis of the positive electrode active material prepared in example 1, as shown in fig. 5, it can be seen from the graph that the positive electrode active material prepared in the example of the present application is granular, has a distinct contour and uniform particles, and contains a relatively large amount of primary particles. The positive electrode active material prepared in comparative example 3 was subjected to scanning electron microscope analysis, and as shown in fig. 6, it can be seen from the figure that the particle agglomeration of the positive electrode active material was remarkable, and the secondary particle content was high.

(5) Dv50 particle diameter of positive electrode active material

A method for the quantitative digital representation of a particle size distribution, comprising a volume distribution DV & a quantity distribution DN. Such as: d10, D50, D90, etc.; dv50 represents: the particle size corresponding to the volume cumulative particle size distribution percentage of the sample reaches 50%. The physical meaning is that the particle size is greater than 50% of its particle size, and the particle size is less than 50% of its particle size, also called median particle size. Dv50 is often used to represent the average particle size of the powder.

(6) Specific surface area of positive electrode active material

The specific surface area is defined as: surface area sum, international dimension m of cathode particles per unit mass ² And/g. The specific surface area and pore size distribution information of the samples in this paper were tested using a Micromeritics ASAP 2020 specific surface area tester. And according to the test result, measuring the specific surface area of the sample by adopting a BET method.

Physical property characterization test of the positive electrode active materials prepared in examples 1 to 15 and comparative examples 1 to 3 are shown in table 1 below.

TABLE 1 results of physical Properties test of cathode active materials

To verify the progress of the examples of the present application, the battery cells prepared in examples 1 to 15 and comparative examples 1 to 3 were now tested as follows:

and step 1, after the preparation of the battery cell is finished, performing a first full-charge discharging flow test after forming a film and supplementing liquid. The discharge flow is as follows: standing for 5min, discharging the cell to 2.5V at constant current of 0.33C, and standing for 1 h.

And 2, fully charging to 4.4V at a constant current of 0.33 ℃, then charging to 4.4V at a constant voltage of 0.05 ℃, and standing for 5min.

And 3, discharging to 2.5V according to 0.33C, standing for 5min, and recording the discharge capacity as Cn. The charge and discharge process (step 2-3) is repeated until 1000cls is circulated, and the circulation capacity retention rate is calculated according to Cn/C1 (for example, the 100 th cls capacity retention rate is C100/C1). The test results are shown in Table 2.

TABLE 2 electrochemical Performance test results

As is apparent from a combination of table 1 and table 2, the particle size characteristics of the positive electrode active material and the structure of the coating layer are regulated, and graphite is used as the negative electrode active material, so that the formed battery monomer has high discharge capacity and capacity cycle retention rate, and the battery monomer has long service life.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the embodiments, and are intended to be included within the scope of the claims and description. In particular, the technical features mentioned in the respective embodiments may be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions falling within the scope of the claims.

Claims

1. The battery cell is characterized by comprising a positive electrode plate and a negative electrode plate;

the positive electrode plate contains a positive electrode active material, the positive electrode active material comprises a positive electrode active material and a coating layer coated on the outer surface of the positive electrode active material, and the quantity of primary particles in the positive electrode active material is more than or equal to 50%;

2. The battery cell according to claim 1, wherein the number of primary particles in the positive electrode active material is 70% -80%.

3. The battery cell of claim 1 or 2, wherein the graphite has an OI value of 2 to 5.

4. The battery cell of claim 1, wherein the graphite has a graphitization degree of 95% or more.

5. The battery cell of claim 4, wherein the graphite has a graphitization degree of 97% to 99%.

6. The battery cell of claim 1, wherein the coating comprises a first subcoating layer comprising at least one of an oxide, a fluoride, a phosphate, a carbon material, and a lithium ion conductor.

7. The battery cell of claim 6, wherein the first subcoating layer satisfies at least any one of the following conditions:

(1) The oxide comprises at least one of aluminum oxide, magnesium oxide, cerium oxide, zinc oxide, lanthanum oxide, zirconium oxide, titanium dioxide, silicon oxide, bismuth trioxide, indium oxide and cobaltosic oxide;

(2) The fluoride includes at least one of aluminum trifluoride and calcium fluoride;

(3) The phosphate comprises at least one of aluminum phosphate, cobalt phosphate, nickel phosphate and iron phosphate;

(4) The carbon material comprises at least one of graphene and carbon nanotubes;

(5) The lithium ion conductor includes at least one of lithium phosphate, lithium iron phosphate, lithium tantalate, lithium metaaluminate, lithium titanium tetraoxide, lithium zirconate, lithium silicate, lithium orthovanadate and lithium carboborate.

8. The battery cell according to any one of claims 6 to 7, wherein the first sub-coating layer comprises 0.1wt% to 0.5wt% of the positive electrode active material.

9. The battery cell of any one of claims 6-7, wherein the coating further comprises a second subcoating layer disposed on a side of the first subcoating layer remote from the positive electrode active material, the second subcoating layer comprising a conductive polymer.

10. The battery cell of claim 9, wherein the conductive polymer comprises at least one of polypyrrole, polythiophene, polyaniline, and polyacetylene.

11. The battery cell of claim 9, wherein the second subcoating layer comprises 0.5wt% to 1wt% of the positive electrode active material.

12. The battery cell of claim 9, wherein the thickness ratio of the first subcoating layer to the second subcoating layer is 1:1 to 4:1.

13. The battery cell of claim 1, wherein the coating layer has a thickness of 5nm to 50nm.

14. The battery cell according to claim 1, wherein the average volume particle diameter Dv50 of the positive electrode active material is 3.0 μm to 5.0 μm.

15. The battery cell according to claim 1, wherein the positive electrode active material has a chemical formula of LiNi _x Co _y Mn _1-x-y O ₂ Wherein x is more than or equal to 0.5 and less than or equal to 0.8,0.06 and y is more than or equal to 0.15.

16. A battery comprising a cell according to any one of claims 1 to 15.

17. An electrical device comprising a battery as claimed in claim 16 for providing electrical energy.