CN120878817A

CN120878817A - Positive electrode material, preparation method thereof, positive electrode plate, battery and energy storage device

Info

Publication number: CN120878817A
Application number: CN202511053182.3A
Authority: CN
Inventors: 贺伟
Original assignee: Xiamen Hithium Energy Storage Technology Co Ltd
Current assignee: Xiamen Hithium Energy Storage Technology Co Ltd
Priority date: 2025-07-29
Filing date: 2025-07-29
Publication date: 2025-10-31

Abstract

This application provides a cathode material and its preparation method, a cathode electrode sheet, a battery, and an energy storage device. The cathode material includes first lithium iron phosphate particles and lithium iron phosphate-iron phosphate composite particles. Based on the total number of the first lithium iron phosphate particles and the lithium iron phosphate-iron phosphate composite particles, the percentage of the number of lithium iron phosphate-iron phosphate composite particles is a, where 3% ≤ a ≤ 30%. Iron phosphate is fused into the interior of the lithium iron phosphate-iron phosphate composite particles. In the cross-section of the lithium iron phosphate-iron phosphate composite particles, the area of iron phosphate accounts for the proportion of the total cross-sectional area of the cross-section of the lithium iron phosphate-iron phosphate composite particles to the total cross-sectional area, which is K, where 10% ≤ K ≤ 60%.

Description

Positive electrode material, preparation method thereof, positive electrode plate, battery and energy storage device

Technical Field

The application relates to the technical field of energy storage, in particular to a positive electrode material, a preparation method thereof, a positive electrode plate, a battery and an energy storage device.

Background

The secondary battery (such as a lithium ion battery) has the characteristics of large specific energy, high working voltage, low self-discharge rate, small volume, light weight and the like, and is widely applied to various fields of electric energy storage, portable electronic equipment, electric automobiles and the like.

Although lithium ion batteries based on lithium iron phosphate cathode materials have the advantage of high safety and stability, the energy efficiency and capacity of secondary batteries have yet to be improved under high compacted density conditions, for example, compacted densities greater than 2.45g/cm ³.

Disclosure of Invention

In order to solve the technical problems, the application discloses a positive electrode material, a preparation method thereof, a positive electrode plate, a battery and an energy storage device, so as to improve the energy efficiency and the capacity of a secondary battery.

In a first aspect, the present application provides a positive electrode material comprising first lithium iron phosphate particles and lithium iron phosphate-iron phosphide composite particles, wherein the number percentage of the lithium iron phosphate-iron phosphide composite particles is a,3% or more and 30% or less, based on the total number of the first lithium iron phosphate particles and the lithium iron phosphate-iron phosphide composite particles, the iron phosphide is fused inside the lithium iron phosphate-iron phosphide composite particles, the area of the iron phosphide in the cross section of the lithium iron phosphate-iron phosphide composite particles is K, and the ratio of the area of the iron phosphide in the total area of the cross section is 10% or more and 60% or less.

In some embodiments of the application, the positive electrode material further comprises second lithium iron phosphate particles and third lithium iron phosphate particles, the first lithium iron phosphate particles and the lithium iron phosphate-iron phosphate composite particles having an average size of Φ ₁, the second lithium iron phosphate particles having an average size of Φ ₂, and the third lithium iron phosphate particles having an average size of Φ ₃,Φ₁＞Φ₂＞Φ₃.

In some embodiments of the application, the positive electrode material meets at least one of the following characteristics:

a) The iron-phosphorus ratio of the second lithium iron phosphate particles to the third lithium iron phosphate particles is b ₁,0.95≤b₁ to be less than or equal to 0.985;

b) The iron-phosphorus ratio of the first lithium iron phosphate particles is b ₂,0.9≤b₂ to be less than or equal to 0.965;

c) The lithium iron phosphate-ferric phosphate composite particles are provided with a lithium iron phosphate region and a ferric phosphate region, and the iron-phosphorus ratio of the lithium iron phosphate region is b ₃,0.82≤b₃ to or less than 0.94.

d)Φ₁≥1μm;

e)250nm≤Φ₂<1μm;

f)Φ₃<250nm。

In some embodiments of the application, the positive electrode material has a resistivity ρ of 2Ω·cm+.ρ+.20Ω·cm.

In some embodiments of the application, the positive electrode material further comprises a doping element selected from at least one of titanium, magnesium, niobium, vanadium, sodium, scandium, and cerium.

In a second aspect, the present application provides a method for preparing the positive electrode material according to the first aspect, comprising the steps of:

mixing a lithium source, an iron source, a phosphorus source and a carbon source to prepare a positive electrode material precursor, wherein the iron source comprises nano ferric oxide;

and sintering the positive electrode material precursor at 800-820 ℃ to obtain the positive electrode material.

In some embodiments of the application, the nano-iron oxide has a mass percentage of c in the iron source of 0.2% c≤2%.

In some embodiments of the application, the method of preparation meets at least one of the following characteristics:

g) The lithium source includes at least one of Li ₂CO₃、Li₃PO₄, liOH, and LiH ₂PO₄;

h) The iron source further comprises at least one of FePO ₄、Fe₃(PO₄)₂, fe, and FeC ₂O₄;

i) The phosphorus source includes at least one of H ₃PO₄、NH₄H₂PO₄ and (NH ₄)₂HPO₄;

j) The carbon source comprises at least one of glucose, polyethylene glycol, sucrose and fructose;

k) The positive electrode precursor further comprises a doping element, and the oxide of the doping element comprises at least one of TiO ₂、MgO、Nb₂O₅、V₂O₅、Na₂O、Sc₂O₃ and CeO ₂;

l) the Dv50 of the nano ferric oxide is D ₁,200nm≤D₁ which is less than or equal to 600nm.

In a third aspect, the present application provides a positive electrode sheet, including a positive electrode current collector, where at least one surface of the positive electrode current collector has a positive electrode material layer, where the positive electrode material layer includes the positive electrode material of the first aspect, or where the positive electrode material layer includes the positive electrode material manufactured by the manufacturing method of the second aspect.

In some embodiments of the application, the sheet resistivity of the positive electrode sheet is R,0.1Ω≤R≤0.35Ω.

In some embodiments of the application, the positive electrode sheet meets at least one of the following characteristics:

m) the carbon content in the positive electrode material layer is d, d is more than or equal to 1% and less than or equal to 3%;

n) the thickness of the positive electrode material pole piece is H, and H is more than or equal to 140 mu m and less than or equal to 300 mu m;

o) the compaction density of the positive electrode plate is PD,2.45g/cm ³≤PD≤2.7g/cm³.

In a fourth aspect, the present application provides a battery, including the positive electrode sheet according to the third aspect.

In a fifth aspect, the present application provides an energy storage device, including a case and at least one battery according to the fourth aspect, where the battery is accommodated in the case.

In a sixth aspect, the present application provides a powered device, including the energy storage device of the fifth aspect, where the energy storage device supplies power to the powered device.

Compared with the prior art, the application has at least the following beneficial effects:

The application provides a positive electrode material and a preparation method thereof, a positive electrode plate, a battery and an energy storage device, wherein the positive electrode material comprises first lithium iron phosphate particles and lithium iron phosphate-iron phosphate composite particles, the quantity percentage of the lithium iron phosphate-iron phosphate composite particles is a,3% -30% or less based on the total quantity of the first lithium iron phosphate particles and the lithium iron phosphate-iron phosphate composite particles, iron phosphate is fused into the interior of the lithium iron phosphate-iron phosphate composite particles, the area ratio of the area of the iron phosphate in the cross section of the lithium iron phosphate-iron phosphate composite particles is K, and K is 10% -60% or less. By synergistically regulating the values of a and K within the scope of the present application, the specific capacity of the positive electrode material under high-pressure conditions can be improved, thereby increasing the capacity of the secondary battery and improving the energy efficiency of the secondary battery.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of an energy storage system according to an embodiment of the present application;

FIG. 2 is a schematic diagram of an energy storage system according to another embodiment of the present application;

FIG. 3 is a schematic diagram of an energy storage system according to yet another embodiment of the present application;

FIG. 4 is a SEM back-scattered photograph of an embodiment of the present application marked with areas of lithium iron phosphate and areas of iron phosphide;

FIG. 5 is an SEM back-scattered photograph of a positive electrode sheet of example 1 of the present application;

fig. 6 is an SEM back-scattered photograph of the positive electrode sheet of comparative example 2.

Reference numerals illustrate 200-battery, 400-energy storage system, 410-first power conversion device, 420-first user load, 430-second user load, 440-energy storage device, 450-high voltage cable, 460-second power conversion device, 470-car, 480-light storage charging station.

Detailed Description

The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.

In the present application, the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate an azimuth or a positional relationship based on that shown in the drawings. These terms are only used to better describe the present application and its embodiments and are not intended to limit the scope of the indicated devices, elements or components to the particular orientations or to configure and operate in the particular orientations.

Also, some of the terms described above may be used to indicate other meanings in addition to orientation or positional relationships, for example, the term "upper" may also be used to indicate some sort of attachment or connection in some cases. The specific meaning of these terms in the present application will be understood by those of ordinary skill in the art according to the specific circumstances.

Furthermore, the terms "mounted," "configured," "provided," "connected," and "connected" are to be construed broadly. For example, they may be fixedly connected, detachably connected, or of unitary construction, they may be mechanically or electrically connected, they may be directly connected, or they may be indirectly connected through intermediaries, or they may be in internal communication between two devices, elements or components. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art according to the specific circumstances.

Furthermore, the terms "first," "second," and the like, are used primarily to distinguish between different devices, elements, or components (the particular species and configurations may be the same or different), and are not used to indicate or imply the relative importance and number of devices, elements, or components indicated. Unless otherwise indicated, the meaning of "a plurality" is two or more.

In the present application, a lithium ion battery is used as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium ion battery.

The inventors have found that, as the particle size of the positive electrode material increases, the compacted density of the positive electrode sheet can be increased, but the migration path of lithium ions and electrons becomes longer, and the energy efficiency of the lithium ion battery decreases, and the specific capacity of the positive electrode material decreases, and this problem is more remarkable especially when the compacted density is 2.45g/cm ³ or more.

In view of this, the present application provides a positive electrode material comprising first lithium iron phosphate particles and lithium iron phosphate-iron phosphide composite particles, the percentage of the number of the lithium iron phosphate-iron phosphide composite particles being a,3% or less than 30%, for example, a being 3%, 5%, 8%, 10%, 15%, 18%, 20%, 25%, 28% or 30%, based on the total number of the first lithium iron phosphate particles and the lithium iron phosphate-iron phosphide composite particles, the iron phosphide being fused to the inside of the lithium iron phosphate-iron phosphide composite particles, the proportion of the area of the iron phosphide in the cross section of the lithium iron phosphate-iron phosphide composite particles being K,10% or less than 60% or less than the total area of the cross section. For example, K is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%.

The positive electrode material contains first lithium iron phosphate particles and lithium iron phosphate-iron phosphide composite particles, wherein the first lithium iron phosphate particles are mainly used for providing capacity for a lithium ion battery, and the lithium iron phosphate-iron phosphide composite particles are used for improving the energy efficiency of the lithium ion battery besides providing the capacity. This is because iron phosphide (Fe ₂ P) is fused inside the lithium iron phosphate-iron phosphide composite particles, and lithium ions and electrons can be deintercalated only at the periphery of the lithium iron phosphate-iron phosphide composite particles, so that deintercalation inside the lithium iron phosphate-iron phosphide composite particles is reduced, the energy barrier for migration of lithium ions and electrons is reduced, and the energy efficiency is improved. The inventors have further found that it is not preferable that the values of a and K are too small or too large, when the value of a is too small (for example, less than 3%), the number of lithium iron phosphate-iron phosphate composite particles is too small, resulting in a decrease in the contribution of lithium iron phosphate-iron phosphate composite particles to the energy efficiency, when the value of a is too large (for example, more than 30%), the number of first lithium iron phosphate particles is too small, resulting in a decrease in the contribution of first lithium iron phosphate particles to the capacity, and when the value of K is too small (for example, less than 10%), the area of Fe ₂ P in the lithium iron phosphate-iron phosphate composite particles is too small, resulting in a decrease in the increase in the energy efficiency of the lithium iron phosphate-iron phosphate composite particles, and when the value of K is too large (for example, more than 60%), the area of lithium iron phosphate in the lithium iron phosphate-iron phosphate composite particles is too small, resulting in a decrease in the contribution of lithium iron phosphate-iron phosphate composite particles to the capacity. Based on the above, the application can improve the specific capacity of the positive electrode material under the high-pressure dense condition by cooperatively regulating the values of a and K in the above range, thereby improving the capacity of the lithium ion battery and improving the energy efficiency of the lithium ion battery.

In an alternative embodiment, the positive electrode material further comprises second lithium iron phosphate particles and third lithium iron phosphate particles, the average size of the first lithium iron phosphate particles and the lithium iron phosphate-iron phosphate composite particles is phi ₁, the average size of the second lithium iron phosphate particles is phi ₂, and the average size of the third lithium iron phosphate particles is phi ₃,Φ₁＞Φ₂＞Φ₃, so that the positive electrode material with the grain size grading of the application is beneficial to obtaining, improving the specific capacity of the positive electrode material under the high-pressure density condition and the energy efficiency of the lithium ion battery.

In the present application, the average size of the first lithium iron phosphate particles and the lithium iron phosphate-iron phosphide composite particles refers to the average of the longest distances of the particles measured by SEM, the average size of the second lithium iron phosphate particles refers to the average of the longest distances of the particles measured by SEM, and the average size of the third lithium iron phosphate particles refers to the average of the longest distances of the particles measured by SEM.

In an alternative embodiment, the iron to phosphorus ratio of the second lithium iron phosphate particles to the third lithium iron phosphate particles is b ₁,0.95≤b₁ +.0.985. For example, b ₁ is 0.95, 0.96, 0.97, 0.98, or 0.985.

In an alternative embodiment, the first lithium iron phosphate particles have an iron to phosphorus ratio b ₂,0.9≤b₂ ∈0.965. For example, b ₂ is 0.9, 0.92, 0.95, 0.96, or 0.965.

In an alternative embodiment, referring to FIG. 5, the lithium iron phosphate-iron phosphide composite particles have lithium iron phosphate regions and iron phosphide regions therein, the lithium iron phosphate regions having an iron to phosphorus ratio b ₃,0.82≤b₃ +.0.94. For example, the iron to phosphorus ratio is 0.82, 0.85, 0.9, 0.92 or 0.94.

In the present application, the iron-phosphorus ratio means a molar ratio of iron element to phosphorus element, that is, an atomic number ratio of iron element to phosphorus element.

The size of the positive electrode material particles generally decreases with the increase of the iron-phosphorus ratio in the positive electrode material, and on the basis of the size of the positive electrode material particles, the specific capacity of the positive electrode material and the energy efficiency of the lithium ion battery under the high-pressure density condition are improved by regulating the iron-phosphorus ratio of the second lithium iron phosphate particles, the third lithium iron phosphate particles, the first lithium iron phosphate particles and the lithium iron phosphate-iron phosphide composite particles within the above range.

In an alternative embodiment of the present invention, phi ₁ is more than or equal to 1 mu m. For example, Φ ₁ is 1 μm, 2 μm or 3 μm. Thus, the compaction density of the positive electrode material is improved, and the volume energy density of the lithium ion battery is improved.

In an alternative embodiment, 250 nm≤Φ ₂ <1 μm. For example, Φ ₂ is 250nm, 500nm, 800nm or 900nm. Thus, the particle size graded positive electrode material is beneficial to obtaining, and the specific capacity of the positive electrode material under the high-pressure density condition and the energy efficiency of the lithium ion battery are improved.

In an alternative embodiment, Φ ₃ <250nm. For example, Φ ₃ is 50nm, 100nm or 240nm. Thus, the particle size graded positive electrode material is beneficial to obtaining, and the specific capacity of the positive electrode material under the high-pressure density condition and the energy efficiency of the lithium ion battery are improved.

In an alternative embodiment, the positive electrode material has a resistivity ρ of 2Ω·cm+.ρ+.20Ω·cm. For example, ρ is2Ω·cm, 5Ω·cm, 8Ω·cm, 10Ω·cm, 12Ω·cm, 15Ω·cm, 18Ω·cm, or 20Ω·cm. Therefore, the specific resistance of the membrane of the positive electrode plate is reduced, and the specific capacity of the positive electrode material and the energy efficiency of the lithium ion battery under the high-pressure density condition are further improved.

In an alternative embodiment, the positive electrode material further comprises a doping element selected from at least one of titanium, magnesium, niobium, vanadium, sodium, scandium, and cerium. Therefore, the migration rate of lithium ions and electrons can be further improved, and the improvement of the energy efficiency of the lithium ion battery is facilitated.

In an alternative embodiment, the percentage of the number of the first lithium iron phosphate particles is e,70% or less e≤97%, e.g., 70%, 72%, 75%, 80%, 82%, 85%, 90%, 92%, 95% or 97%, based on the total number of the first lithium iron phosphate particles and the lithium iron phosphate-iron phosphide composite particles.

The present application is not particularly limited in terms of the number ratio of the first lithium iron phosphate particles, the lithium iron phosphate-iron phosphide composite particles, the second lithium iron phosphate particles and the third lithium iron phosphate particles in the cathode material, as long as the object of the present application can be achieved. For example, based on the total number of particles in the positive electrode material, the number percentage of the first lithium iron phosphate particles is 2.01% -14%, the number percentage of the lithium iron phosphate-iron phosphide composite particles is 0.09% -6%, the number percentage of the second lithium iron phosphate particles is 50% -92%, and the number percentage of the third lithium iron phosphate particles is 5% -30%, so that the positive electrode material with the grain size grading of the present application is advantageously obtained.

The application also provides a preparation method of the positive electrode material, which comprises the following steps:

step A, mixing a lithium source, an iron source, a phosphorus source and a carbon source to prepare a positive electrode material precursor, wherein the iron source comprises nano ferric oxide;

And B, sintering the precursor of the positive electrode material at 800-820 ℃ to obtain the positive electrode material.

In the step a, a lithium source, an iron source, a phosphorus source and a carbon source may be mixed according to a designed stoichiometric ratio of the positive electrode material, and then ground to further uniformly disperse the raw materials, and then spray-dried to obtain a precursor of the positive electrode material.

In the step B, nano Fe ₂O₃ is added into an iron source, and by regulating the sintering temperature within the range, as nano Fe ₂O₃ has higher activity, a reaction starting point can be formed in the sintering process, lithium iron phosphate around nano Fe ₂O₃ can grow around nano Fe ₂O₃ to form Fe ₂ P, so that the lithium iron phosphate-ferric phosphide composite particles with Fe ₂ P fused and condensed inside are formed. And, after the sintering treatment, lithium iron phosphate particles having different size ranges, specifically including first lithium iron phosphate particles, second lithium iron phosphate particles, and third lithium iron phosphate particles, are also formed.

In an alternative embodiment, the nano-iron oxide has a mass percentage of c in the iron source of 0.2% c≤2%. For example, c is 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8% or 2%. Is favorable for forming a reaction starting point in the sintering process, and promotes the formation of lithium iron phosphate-ferric phosphide composite particles with Fe ₂ P solidified after internal melting.

In an alternative embodiment, the lithium source includes at least one of lithium carbonate (Li ₂CO₃), lithium phosphate (Li ₃PO₄), lithium hydroxide (LiOH), and lithium dihydrogen phosphate (LiH ₂PO₄).

In an alternative embodiment, the iron source further comprises at least one of iron phosphate (FePO ₄), ferrous phosphate (Fe ₃(PO₄)₂), elemental iron (Fe), and ferrous oxalate (FeC ₂O₄).

When iron phosphate is included in the iron source, the iron phosphate may be selected from iron phosphate raw materials having different iron-to-phosphorus ratios, for example, may be selected from at least one of a first iron phosphate raw material having an iron-to-phosphorus ratio of 0.968 and a second iron phosphate raw material having an iron-to-phosphorus ratio of 0.962.

In an alternative embodiment, the phosphorus source includes at least one of phosphoric acid (H ₃PO₄), ammonium dihydrogen phosphate (NH ₄H₂PO₄), and diammonium hydrogen phosphate ((NH ₄)₂HPO₄)).

In an alternative embodiment, the carbon source comprises at least one of glucose, polyethylene glycol (PEG), sucrose, and fructose.

In an alternative embodiment, the positive electrode precursor further includes a doping element, and the oxide of the doping element includes at least one of TiO ₂、MgO、Nb₂O₅、V₂O₅、Na₂O、Sc₂O₃ and CeO ₂, so that the migration rate of lithium ions and electrons can be further improved.

In an alternative embodiment, the nano-iron oxide has a Dv50 of D ₁,200nm≤D₁ nm or less than 600nm. For example, D ₁ is 200nm, 300nm, 400nm, 500nm, or 600nm. Is favorable for forming a reaction starting point in the sintering process and promoting the formation of lithium iron phosphate-iron phosphide composite particles with Fe ₂ P fused and condensed inside.

In the present application, dv50 means that the particles reach a particle size of 50% by volume accumulation from the small particle size side in the particle size distribution on a volume basis.

According to the preparation method of the positive electrode material, nano Fe ₂O₃ is added into an iron source, and the sintering temperature is regulated and controlled cooperatively within the range of the preparation method, so that the positive electrode material with the lithium iron phosphate-iron phosphide composite particles is prepared.

The application also provides a positive electrode plate, which comprises a positive electrode current collector, wherein at least one surface of the positive electrode current collector is provided with a positive electrode material layer, the positive electrode material layer comprises the positive electrode material of any embodiment, or the positive electrode material layer comprises the positive electrode material prepared by the preparation method of any embodiment.

In an alternative embodiment, the sheet resistance of the positive electrode sheet is R,0.1 Ω cm≤R≤0.35 Ω cm. For example, R is 0.1 Ω -cm, 0.15 Ω -cm, 0.2 Ω -cm, 0.25 Ω -cm, 0.3 Ω -cm, or 0.35 Ω -cm. Thus, it is advantageous to improve the capacity and energy efficiency of the lithium ion battery.

In an alternative embodiment, the carbon content in the positive electrode material layer is d,1% d≤3%. The carbon in the positive electrode material layer of the present application may be derived from a carbon source, a conductive agent, a binder, or the like. For example, d is 1%, 1.5%, 2%, 2.5%, or 3%. The lithium ion battery can have higher capacity, energy efficiency and cycle stability by regulating d in the range. The conductive agent includes, but is not limited to, conductive carbon black (Super-P), carbon nanotubes, etc., and the binder includes, but is not limited to, polyvinylidene fluoride (PVDF), etc.

In an alternative embodiment, the thickness of the positive electrode material sheet is H,140 μm≤H≤300 μm. For example, H is 140 μm, 150 μm, 200 μm, 250 μm or 300 μm. By regulating H in the above range, higher volumetric energy density and energy efficiency of the lithium ion battery can be realized.

In an alternative embodiment, the positive electrode sheet has a compacted density PD of 2.45g/cm ³≤PD≤2.7g/cm³. For example, PD is 2.45g/cm ³、2.5g/cm³、2.55g/cm³、2.6g/cm³、2.65g/cm³ or 2.7g/cm ³. And the PD is regulated and controlled within the range, so that the capacity performance of the lithium ion battery is improved.

The manner of controlling the number percentage a of the lithium iron phosphate-iron phosphide composite particles is not particularly limited in the present application, as long as the object of the present application can be achieved. Illustratively, the value of a generally increases with increasing mass percent of the iron-to-phosphorus ratio b ₂ and/or the nano-Fe ₂O₃ of the first lithium iron phosphate particles, based on which the value of a can be regulated by adjusting the mass percent of the iron-to-phosphorus ratio b ₂ and/or the nano-Fe ₂O₃ of the first lithium iron phosphate particles during the preparation of the cathode material.

The manner of controlling the ratio K of the area of the iron phosphide to the total area of the cross section is not particularly limited in the present application, as long as the object of the present application can be achieved. Illustratively, the value of K generally increases with an increase in the iron-to-phosphorus ratio b ₂ and/or the sintering temperature of the first lithium iron phosphate particles, based on which the value of K may be regulated during the preparation of the positive electrode material by adjusting the iron-to-phosphorus ratio b ₂ and/or the sintering temperature of the first lithium iron phosphate particles.

The mode of controlling the iron-phosphorus ratio b ₁、b₂、b₃ is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, in the process of preparing the positive electrode material, different kinds of iron sources and phosphorus sources can be selected according to the designed iron-phosphorus ratio of the lithium iron phosphate, and the iron-phosphorus ratio of lithium iron phosphate particles in the prepared positive electrode material can be changed by adjusting the stoichiometric ratio of the iron sources and the phosphorus sources.

In the application, lithium source, the precursor, nano Fe ₂O₃ and phosphorus source (such as H ₃PO₄) can be mixed according to a certain proportion by selecting two precursors of lithium iron phosphate (such as FePO ₄、Fe₃(PO₄)₂ which can be used as one of iron sources) with different iron-phosphorus ratios affecting b ₁、b₂, and the lithium iron phosphate particles with different iron-phosphorus ratios of b ₁、b₂、b₃ can be obtained through high-temperature sintering. Wherein b ₁、b₂ is affected by the iron-to-phosphorus ratio of its precursor, and b ₃ is due to the reaction of part of the precursor of the first lithium iron phosphate particles with Fe ₂O₃, resulting in a part of the regions of the lithium iron phosphate-iron phosphide composite particles being Fe ₂ P with a high iron content and a part of the regions being lithium iron phosphate with a low iron content (iron-to-phosphorus ratio b ₃). Based on this, a positive electrode material containing lithium iron phosphate particles with different iron-phosphorus ratios can be obtained by one sintering.

The application also provides a battery, which comprises the positive electrode plate of any embodiment.

In the present application, the positive electrode material layer may be provided on one surface in the thickness direction of the positive electrode current collector, or may be provided on both surfaces in the thickness direction of the positive electrode current collector. In the application, the positive electrode material layer is arranged on the surface of the positive electrode current collector, namely, the positive electrode material layer can be arranged in a partial area of one surface of the positive electrode current collector, and can also be arranged in all areas of one surface of the positive electrode current collector. In the present application, the positive electrode current collector is not particularly limited as long as the object of the present application can be achieved, and may include, for example, but not limited to, aluminum foil, aluminum alloy foil, composite current collector, or the like. In the present application, the thickness of the positive electrode current collector is not particularly limited as long as the object of the present application can be achieved, and for example, the thickness is 4 μm to 15 μm. The thickness of one side of the positive electrode material layer of the application can be 60-140 mu m.

The lithium ion battery of the application also comprises a negative pole piece. The negative electrode tab is not particularly limited as long as the object of the present application can be achieved, for example, the negative electrode tab generally includes a negative electrode current collector and a negative electrode material layer. The anode material layer may be provided on one surface or both surfaces in the thickness direction of the anode current collector. In the application, the anode material layer is arranged on the surface of the anode current collector, namely, the anode material layer can be arranged in a partial area of one surface of the anode current collector, and can also be arranged in all areas of one surface of the anode current collector. The negative electrode current collector is not particularly limited as long as the object of the present application can be achieved, and may include, for example, but not limited to, copper foil, copper alloy foil, nickel foil, composite current collector, or the like. In the present application, the thickness of the negative electrode current collector is not particularly limited as long as the object of the present application can be achieved, and for example, the thickness is 4 μm to 12 μm. The thickness of one side of the negative electrode material layer of the application can be 70-200 mu m.

In the present application, the anode material layer includes an anode material, wherein the anode material is not particularly limited as long as the object of the present application can be achieved, and for example, may include at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, silicon, and silicon carbon.

In the present application, a negative electrode binder may be further included in the negative electrode material layer. The negative electrode binder of the present application is not particularly limited as long as the object of the present application can be achieved, and may include, for example, at least one of acrylic acid ester, polyamide, polyimide, polyamideimide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, and potassium carboxymethyl cellulose.

The lithium ion battery of the application further comprises a separator. The separator is not particularly limited in the present application, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved. For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.

The battery of the present application further comprises an electrolyte. The electrolyte is not particularly limited in the present application, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved. For example, it is preferable that at least one of Ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC), ethyl Propionate (EP), propyl Propionate (PP), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), vinylene Carbonate (VC), ethylene carbonate (VEC), fluoroethylene carbonate (FEC) and the like is mixed in a certain mass ratio or volume ratio to obtain a nonaqueous organic solvent, and then lithium salt is added to dissolve and mix uniformly. The kind of the lithium salt is not limited in the present application as long as the object of the present application can be achieved. For example, the lithium salt may include at least one of LiPF₆、LiBF₄、LiAsF₆、LiClO₄、LiB(C₆H₅)₄、LiCH₃SO₃、LiCF₃SO₃、LiN(SO₂CF₃)₂、LiC(SO₂CF₃)₃、LiSiF₆、 bis (fluorosulfonyl) imide lithium salt (LIFSI), lithium dioxaborate (LiBOB), or lithium difluoroborate.

The concentration of the lithium salt in the electrolyte is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the concentration of the lithium salt is 1.0mol/L to 2.0mol/L.

The battery of the present application further includes a case, and the present application is not particularly limited to the case, and may be selected according to actual needs by those skilled in the art as long as the object of the present application can be achieved. For example, the housing may comprise an aluminium plastic film.

The method for preparing the battery is not particularly limited, and a method known in the art may be selected as long as the object of the present application can be achieved. For example, the method for manufacturing the battery includes, but is not limited to, stacking a positive electrode sheet, a separator and a negative electrode sheet in order, winding, folding and the like as needed to obtain a bare cell of a winding structure, placing the bare cell into a packaging bag, injecting an electrolyte into the packaging bag, and sealing to obtain the battery.

The application also provides an energy storage device which comprises a box body and at least one battery in any embodiment, wherein the battery is accommodated in the box body. The energy storage device with the battery has excellent performance and is beneficial to the use of the energy storage device. The battery is accommodated in the box body, so that the fixing and protecting effects on the battery can be improved, and the service life of the energy storage device is prolonged. It will be appreciated that the energy storage device may have one or more batteries therein, and that when the energy storage device comprises a plurality of batteries, the plurality of batteries may be connected in at least one of parallel and series.

The application also provides electric equipment, which comprises the energy storage device in the embodiment, and is beneficial to improving the product competitiveness and the service performance of the electric equipment. In an alternative embodiment, the powered device comprises a powered device body, and the energy storage device is configured to power the powered device body. In an alternative embodiment, the electric device body includes a device anode and a device cathode, the positive electrode piece of the battery in the energy storage device is used for electrically connecting the device anode of the electric device body, and the negative electrode piece of the battery in the energy storage device is used for electrically connecting the device cathode of the electric device body to supply power to the electric device.

The electric device of the present application may include, but is not limited to, a container, an electric car, a ship, a spacecraft, an electric toy, and an electric tool, etc., wherein the spacecraft is, for example, an airplane, a rocket, a space plane, a spacecraft, etc., the electric toy includes, for example, a fixed or mobile electric toy, specifically, for example, an electric car toy, an electric ship toy, an electric airplane toy, etc., and the electric tool includes, for example, a metal cutting electric tool, an abrasive electric tool, an assembly electric tool, and a railway electric tool, specifically, for example, an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact electric drill, a concrete vibrator, and an electric planer.

Because of the strong timeliness and space properties of energy required by people, in order to reasonably utilize the energy and improve the utilization rate of the energy, one energy form needs to be stored by one medium or equipment and then converted into another energy form, and the energy is released in a specific energy form based on future application. At present, the main way of generating green electric energy is to develop green energy sources such as photovoltaic, wind power and the like to replace fossil energy sources,

At present, the generation of green electric energy generally depends on photovoltaic, wind power, water potential and the like, but wind energy, solar energy and the like generally have the problems of strong intermittence and large fluctuation, which can cause unstable power grid, insufficient peak electricity consumption, too much electricity consumption and unstable voltage can cause damage to the electric power, so that the problem of 'wind abandoning and light abandoning' possibly occurs due to insufficient electricity consumption requirement or insufficient power grid acceptance, and the problem needs to be solved by relying on energy storage. The energy is converted into other forms of energy through physical or chemical means and is stored, the energy is converted into electric energy when needed and released, in short, the energy storage is similar to a large-scale 'charge pal', the electric energy is stored when the photovoltaic and wind energy are sufficient, and the stored electric power is released when needed.

Taking electrochemical energy storage as an example, the present embodiment provides an energy storage device 440, which is applied to an energy storage system 400, wherein a group of chemical batteries are disposed in the energy storage device 440, and chemical elements in the batteries are mainly used as energy storage media, and the charge and discharge process accompanies chemical reaction or change of the energy storage media.

The present energy storage (i.e. energy storage) application scenario is relatively wide, including aspects such as power generation side energy storage, grid side energy storage, and power utilization side energy storage, the types of the corresponding energy storage device 440 include:

(1) The energy storage power station is used as a high-quality active/reactive power regulating power supply in a power supply side, realizes load matching of electric energy in time and space, enhances the capacity of renewable energy consumption, reduces instantaneous power change, reduces impact on a power grid, improves the problem of new energy power generation and has great significance in standby of a power grid system, relieving peak load power supply pressure and peak regulation and frequency modulation;

(2) The energy storage prefabricated cabin is applied to the power grid side, has the functions of mainly regulating peak, regulating frequency and relieving the blocking peak regulation of the power grid, and can realize peak clipping and valley filling of the power consumption load, namely, the energy storage battery is charged when the power consumption load is low, and the stored electric quantity is released in the peak period of the power consumption load, so that the balance between power production and power consumption is realized;

(3) The small energy storage cabinet applied to the electricity utilization side has the main functions of spontaneous electricity utilization, peak Gu Jiacha arbitrage, capacity cost management and power supply reliability improvement. According to the different application scenes, the electricity-side energy storage can be divided into an industrial and commercial energy storage cabinet, a household energy storage device, an energy storage charging pile and the like, and is generally matched with the distributed photovoltaic. The energy storage can be used by industrial and commercial users for valley peak price difference arbitrage and capacity cost management. In the electric power market implementing peak-valley electricity price, the energy storage system is charged when the electricity price is low, and the energy storage system is discharged when the electricity price is high, so that peak-valley electricity price difference arbitrage is realized, and the electricity cost is reduced. In addition, the energy storage system is suitable for two industrial enterprises with electricity price, can store energy when electricity is used in low valley and discharge the energy when the electricity is used in peak load, so that peak power and the declared maximum demand are reduced, and the purpose of reducing the capacity electricity fee is achieved. The household photovoltaic distribution and storage can improve the spontaneous self-use level of the electric power. Due to high electricity prices and poor power supply stability, the photovoltaic installation requirements of users are pulled. Considering that the photovoltaic power generation is performed in daytime, and the load of a user is generally higher at night, the photovoltaic power can be better utilized through configuration of energy storage, the spontaneous self-use level is improved, and meanwhile the power consumption cost is reduced. In addition, the fields of communication base stations, data centers and the like need to be configured with energy storage for standby power.

In some embodiments, referring to fig. 1, fig. 1 is a schematic diagram of an energy storage system 400 according to an embodiment of the application, in which a home energy storage scenario in a user side energy storage is taken as an example in the embodiment of fig. 1, the energy storage device 440 according to the application is not limited to the home energy storage scenario.

The present application provides an energy storage system 400, wherein the energy storage system 400 includes a first power conversion device 410 (photovoltaic panel), a first user load 420 (household lamp), a second user load 430 (household appliance such as an air conditioner), etc., and an energy storage device 440, the energy storage device 440 is a small-sized energy storage box, and can be mounted on an outdoor wall through a wall-hanging manner, and the energy storage device 440 is not limited to the wall-hanging manner, but can be placed on a user's residence through other manners. In particular, the photovoltaic panel may convert solar energy into electric energy during low electricity price period, and the energy storage device 440 is used to store the electric energy and supply the electric energy to lamps and household appliances for use during peak electricity price period or supply power during power failure/power outage of the power grid.

In some embodiments, please refer to fig. 2, fig. 2 is a schematic diagram of a second structure of an energy storage system 400 according to an embodiment of the present application, and the embodiment of fig. 2 is illustrated by taking a power generation/distribution side shared energy storage scenario as an example, and the energy storage device 440 according to the present application is not limited to the power generation/distribution side energy storage scenario.

The application provides an energy storage system 400, which comprises a high-voltage cable 450, a first electric energy conversion device 410, a second electric energy conversion device 460 and an energy storage device 440 provided by the application, wherein in some embodiments of a power generation side scene, the second electric energy conversion device 460 can be a wind power electric energy conversion device, because fluctuation, randomness and intermittence of electric energy generated by wind power electric energy conversion can be generated, unstable electric energy output by the wind power electric energy conversion device can be stored to the energy storage device 440 firstly through grid connection, the energy storage device 440 is connected with the high-voltage cable and outputs smooth electric energy to be supplied to a power distribution network for use, peak regulation and frequency modulation are realized, the power grid is stably operated, or the wind power electric energy conversion device is always connected with the high-voltage cable, the electric energy output by the wind power electric energy conversion device is supplied to the power distribution network for use through the high-voltage cable under the ordinary power generation condition, and when the wind power electric energy conversion device generates surplus electricity, the multiple generated electric energy is stored to the energy storage device 440 firstly, the wind rejection and the light rejection rate is reduced, the problem of new energy generation can be solved, and when the power consumption load is high, the peak regulation and frequency modulation is realized, the power grid is supplied to the power grid is cut off, the peak regulation and the power grid is supplied to the power grid for the power grid, the peak regulation and the power supply is fully used, the peak regulation and the power grid is supplied to the power grid, and the peak regulation and the power grid is fully used, and the power grid power has a peak regulation and voltage service mode.

In some embodiments on the distribution network side, the first power conversion device 410 may be a photovoltaic panel, the energy storage device 440 is connected to the high-voltage cable 450 and installed between the downstream of the high-voltage cable 450 and the user load, and the power output by the photovoltaic power conversion device is stored in the energy storage device 440, and responds to serve as a standby power source in time when the power grid/distribution network fails, or provides power supply support to delay the economic pressure generated by the power grid/distribution capacity expansion when the power grid of the high-voltage cable 450 is blocked to relieve the line blockage and the power grid planning expansion occurs.

In some embodiments, please refer to fig. 3, fig. 3 is a schematic diagram of an energy storage system 400 according to an embodiment of the application, and the embodiment of fig. 3 is illustrated by taking an industrial and commercial side energy storage scenario as an example, and the energy storage device 440 of the application is not limited to the industrial and commercial side energy storage scenario.

The application provides an energy storage system 400, wherein the energy storage system 400 comprises an energy storage device 440, a high-voltage cable 450, a factory provided with a first electric energy conversion device 410, a photo-electricity storage charging station 480 and a car 470, in some embodiments of a factory side scene, the first electric energy conversion device 410 can be a photovoltaic panel, solar energy is converted into electric energy to be stored in the energy storage device 440 of the factory, when a power grid fails, the energy storage device 440 is used for supplying power to ensure that the factory is safe and stable without stopping production operation, or when the power grid is in a high-level state, the power grid gives an instruction, the electric quantity stored by the energy storage device 440 is cooperated with the high-voltage cable 450 to jointly transmit the electric energy to the factory in a grid connection mode, so that various services such as peak regulation/frequency regulation, standby and the like are provided for the power grid operation, in addition, the first electric energy conversion device 410 can also convert the solar energy into the electric energy to be stored in the energy storage device 440 of the photo-electricity storage charging station 480, and the car 470 is directly charged through the photo-electricity storage charging station 480, and the car 470 is fast and convenient.

Alternatively, the first electric energy conversion device 410 may include, but is not limited to, a photovoltaic panel, and the second electric energy conversion device 460 may include, but is not limited to, a wind power electric energy conversion device, and the first electric energy conversion device 410 and the second electric energy conversion device 460 may convert at least one of solar energy, light energy, wind energy, heat energy, tidal energy, biomass energy, mechanical energy, and the like into electric energy.

Optionally, the energy storage device 440 may include, but is not limited to, energy storage applications for energy storage power stations, hydro/thermal/wind power generation systems, solar power generation systems, mobile power systems, smart home systems, or temporary power supply systems, and may be used in various fields such as data centers, military equipment, aerospace, charging piles, electric vehicles, and the like.

Alternatively, the energy storage device 440 may include, but is not limited to, a single battery, or a battery module composed of single batteries, a battery pack, a battery cluster, a mobile power source, an energy storage cabinet/energy storage pre-compartment, and the like. The practical application of the energy storage device 440 according to the embodiment of the present application may be, but not limited to, the listed products, and may be other application, and the embodiment of the present application does not strictly limit the application of the energy storage device 440.

Alternatively, the unit cell may be, but is not limited to, at least one of a cylindrical cell, a prismatic cell, or other shaped cell.

Alternatively, the unit cell may be a secondary battery, and the secondary battery refers to a unit cell that can be continuously used by activating the active material in a charging manner after the unit cell is discharged. The single battery may be a lithium ion battery, a sodium lithium ion battery, a lithium metal battery, a sodium metal battery, a lithium sulfur battery, a magnesium ion battery, a nickel hydrogen battery, a nickel cadmium battery, a lead storage battery, etc., which is not particularly limited in the present application.

Examples

Hereinafter, embodiments of the present application will be described in more detail with reference to preparation examples, examples and comparative examples. The various tests and evaluations were carried out according to the following methods.

Example 1

< Preparation of Positive electrode sheet >

< Preparation of cathode Material >

Mixing a lithium source Li ₂CO₃, an iron source nano Fe ₂O₃ (Dv 50 is 420nm, the adding amount is 0.4wt% of the total mass of the iron source) and ferric phosphate (FePO ₄, the adding amount is 99.6wt% of the total mass of the iron source), and a phosphorus source H ₃PO₄ according to the stoichiometric ratio of 104:100:0.1 to obtain a mixture A, wherein the ferric phosphate consists of two ferric phosphate raw materials with different iron-phosphorus ratios, namely a first ferric phosphate raw material with the iron-phosphorus ratio of 0.968 and a second ferric phosphate raw material with the iron-phosphorus ratio of 0.962, the mass ratio of the first ferric phosphate raw material to the second ferric phosphate raw material is 7:3, adding the mixture A into a reaction kettle, then adding carbon source glucose and TiO ₂ to obtain a mixture B, wherein the adding amount of glucose is 10wt% of the total mass of the mixture A, the adding amount of TiO ₂ is 2wt% of the total mass of the mixture A, grinding the mixture B, performing spray drying to obtain a positive electrode material precursor, wherein the spray drying is performed at the spray drying frequency of 400 ℃ to obtain the positive electrode material, the positive electrode material is sintered at the positive electrode material temperature of 220 ℃ after the spray drying is carried out, and the sintering temperature is kept at the positive electrode temperature of the positive electrode material is at the sintering temperature of 220 ℃.

< Preparation of Positive electrode Material layer >

Mixing the prepared positive electrode material, conductive carbon black (Super-P) and a binder PVDF according to the mass ratio of 94:3:3, adding N-methyl pyrrolidone (NMP) as a solvent, preparing into positive electrode slurry with the solid content of 60wt%, uniformly stirring, uniformly coating the positive electrode slurry on one surface of a positive electrode current collector aluminum foil with the thickness of 15 mu m, and drying, cold pressing, slitting and cutting to obtain the positive electrode plate. The thickness of one side of the positive electrode material layer was 100. Mu.m, and the compacted density was 2.55g/cm ³.

< Preparation of negative electrode sheet >

The negative electrode material artificial graphite, thickener sodium carboxymethylcellulose (CMC), conductive carbon black (Super-P) and binder styrene-butadiene rubber emulsion (SBR) are mixed according to the mass ratio of 96 to 2 to 1, deionized water is added, and the mixture is prepared into negative electrode slurry with the solid content of 50 weight percent, and the mixture is uniformly stirred. And uniformly coating the negative electrode slurry on one surface of a negative electrode current collector copper foil with the thickness of 6 mu m, and drying, cold pressing, slitting and cutting to obtain a negative electrode plate. The thickness of one side of the negative electrode material layer was 70. Mu.m.

< Preparation of electrolyte >

In an argon atmosphere glove box with the moisture content less than or equal to 1ppm, mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate (EMC) according to the mass ratio of 1:1:1, dissolving a dried solute into a solvent, and stirring until the solute is completely and uniformly dissolved to obtain an electrolyte. Wherein the solute in the electrolyte is lithium hexafluorophosphate, and the molar concentration of the lithium hexafluorophosphate is 1.2mol/L.

< Preparation of separator >

A Polyethylene (PE) porous polymer film having a thickness of 16 μm was used as a separator.

< Assembling of lithium ion Battery >

And after welding the electrode lugs, placing the bare cell in an outer packaging shell, drying, injecting the electrolyte, and carrying out vacuum packaging, standing, formation, shaping and the like to prepare the lithium ion battery.

Example 2 to example 4

The procedure of example 1 was repeated except that the mass percentage of nano Fe ₂O₃ in the iron source was controlled in accordance with table 1 in < preparation of cathode material >, thereby controlling the number percentage a of lithium iron phosphate-iron phosphide composite particles.

Examples 5 to 7

The procedure of example 1 was repeated except that in < preparation of positive electrode material >, the mass percentage of nano Fe ₂O₃ in the iron source was controlled according to table 1, and the sintering temperature was controlled according to table 1, thereby controlling the ratio K of the area of iron phosphide to the total area of the cross section.

Example 8

Except that in < preparation of a positive electrode material >, a lithium source Li ₂CO₃, an iron source (nano Fe ₂O₃ and iron phosphate (FePO ₄) in a mass ratio of 0.4:99.6) and a phosphorus source H ₃PO₄ were mixed in a stoichiometric ratio of 104:100:0.15 to obtain a mixture a, wherein iron phosphate was composed of two iron phosphate raw materials having different iron-phosphorus ratios, namely, a first iron phosphate raw material having an iron-phosphorus ratio of 0.962 and a second iron phosphate raw material having an iron-phosphorus ratio of 0.960, respectively, and the mass ratio of the first iron phosphate raw material to the second iron phosphate raw material was 7:3, and parameters such as b ₁、b₂、b₃ and the like of the prepared positive electrode material were changed as shown in table 2, the rest was the same as in example 1.

Example 9

The procedure of example 1 was repeated except that in the < preparation of the positive electrode material >, a lithium source Li ₂CO₃, an iron source (nano Fe ₂O₃ and iron phosphate (FePO ₄) in a mass ratio of 0.4:99.6) and a phosphorus source H ₃PO₄ were mixed in a stoichiometric ratio of 104:100:0.05 to obtain a mixture a, wherein the iron phosphate was composed of two iron phosphate raw materials having different iron-phosphorus ratios, namely, a first iron phosphate raw material having an iron-phosphorus ratio of 0.972 and a second iron phosphate raw material having an iron-phosphorus ratio of 0.965, and the mass ratio of the first iron phosphate raw material and the second iron phosphate raw material was 7:3, and parameters such as b ₁、b₂、b₃ of the prepared positive electrode material were changed as shown in table 2.

Examples 10 to 11

The procedure of example 1 was repeated except that the positive electrode sheet was adjusted in the following manner in < preparation of positive electrode material >.

Comparative example 1

The procedure of example 1 was repeated except that the positive electrode material was prepared in the same manner as in example 1.

< Preparation of cathode Material >

Mixing lithium source Li ₂CO₃, iron source ferric phosphate (FePO ₄) and phosphorus source H ₃PO₄ according to the stoichiometric ratio of 104:100:0.1 to obtain a mixture A, wherein the ferric phosphate consists of two ferric phosphate raw materials with different iron-phosphorus ratios, namely a first ferric phosphate raw material with the iron-phosphorus ratio of 0.968 and a second ferric phosphate raw material with the iron-phosphorus ratio of 0.962, the mass ratio of the first ferric phosphate raw material to the second ferric phosphate raw material is 7:3, adding the mixture A into a reaction kettle, adding carbon source glucose and TiO ₂ to obtain a mixture B, wherein the addition amount of glucose is 10wt% of the total mass of the mixture A, the addition amount of TiO ₂ is 2wt% of the total mass of the mixture A, grinding the mixture B, and then spray-drying to obtain a positive electrode material precursor, wherein the spray-dried atomizer frequency is 400Hz, the drying tower pressure is-0.8, the drying temperature is 220 ℃, the sintering treatment is carried out on the positive electrode material precursor, the sintering temperature is 760C, and the positive electrode material is prepared after the positive electrode material is crushed.

Comparative example 2

< Preparation of first cathode Material >

The positive electrode material prepared in comparative example 1 was used as a first positive electrode material.

< Preparation of second cathode Material >

Mixing lithium source Li ₂CO₃, iron source ferric phosphate (FePO ₄) and phosphorus source H ₃PO₄ according to the stoichiometric ratio of 104:100:0.1 to obtain a mixture A, wherein the ferric phosphate is composed of two ferric phosphate raw materials with different iron-phosphorus ratios, namely a first ferric phosphate raw material with the iron-phosphorus ratio of 0.968 and a second ferric phosphate raw material with the iron-phosphorus ratio of 0.962, the mass ratio of the first ferric phosphate raw material to the second ferric phosphate raw material is 7:3, adding the mixture A into a reaction kettle, adding carbon source glucose and TiO ₂ to obtain a mixture B, wherein the addition amount of glucose is 10wt% of the total mass of the mixture A, the addition amount of TiO ₂ is 2wt% of the total mass of the mixture A, grinding the mixture B, and then spray drying to obtain a positive electrode material precursor, wherein the spray-dried atomizer frequency is 400Hz, the drying tower pressure is-0.8 ℃, the drying temperature is 220 ℃, the sintering treatment is carried out on the positive electrode material precursor, the sintering temperature is 810 ℃, the pure positive electrode material is obtained, and pure positive electrode material containing Fe particles with the second positive electrode material is prepared by crushing the pure material at ₂ ℃ and the positive electrode material is prepared.

And then mixing the first positive electrode material and the second positive electrode material according to the mass ratio of 7:3 to obtain the positive electrode material containing pure Fe ₂ P particles.

Comparative examples 3 to 4

The procedure of example 1 was repeated except that the addition amount of nano Fe ₂O₃ was controlled so that the number percentage a of the lithium iron phosphate-iron phosphide composite particles was controlled as shown in table 1 in < preparation of cathode material >.

Comparative examples 5 to 6

The procedure of example 1 was repeated except that in < preparation of a cathode material >, the sintering temperature was controlled so that the ratio K of the area of iron phosphide to the total area of the cross-section was controlled as shown in Table 1.

TABLE 1 preparation parameters for examples 1 to 7 and comparative examples 1 to 6

TABLE 2 preparation parameters of example 1, example 8-example 11

Test method and apparatus:

Observation of pure Fe ₂ P particles, lithium iron phosphate-iron phosphide composite particles, pure lithium iron phosphate particles:

The prepared cathode material is placed under a Scanning Electron Microscope (SEM), and a back scattering (HDBSD) mode is adopted to observe whether the cathode material has pure Fe ₂ P particles, lithium iron phosphate-ferric phosphate composite particles or pure lithium iron phosphate particles or not, and the quantity of the particles is counted.

The number percentage a of the lithium iron phosphate-iron phosphide composite particles is tested:

The prepared cathode material was placed under SEM, and any one of 26 μm×38 μm rectangular areas was selected, and the number of first lithium iron phosphate particles having a size of 1 μm or more in the area was counted, and denoted as N ₁, and the number of lithium iron phosphate-iron phosphate composite particles, denoted as N ₂, and a=n ₂/(N₁+N₂) ×100%, and the number percentage of first lithium iron phosphate particles was b=100% -a.

Area of iron phosphide in total area of cross section, ratio K test:

Placing a positive pole piece on a sample table, opening a heater switch, cutting the positive pole piece into a rectangular pole piece sample with the length of 1.1cm multiplied by 0.8cm, adhering the pole piece sample and the sample table together through an adhering rod, then clamping the sample table from the heater by using tweezers, closing the heater, moving the sample table through the tweezers when the adhesive is not cooled and adhered firmly, enabling the pole piece sample to protrude from the sample table at one end for 1-2 mm, polishing the cross section of a positive pole material layer of the protruding pole piece sample by using argon sputtering of an ion cutting machine to obtain a cross section sample, placing the cross section sample under an SEM for photographing, introducing the photo into imageJ software, marking the area of lithium iron phosphate in the cross section, marking the area of iron phosphate in the cross section as S ₁, marking the area of iron phosphate in the cross section as S ₂, and K= [ S ₂/(S₁+S₂) ]multipliedby 100%.

Test of the size of each particle in the positive electrode material:

The prepared cathode material was placed under SEM for photographing, the photographs were imported into ImageJ software, and the sizes of pure lithium iron phosphate particles and lithium iron phosphate-iron phosphide composite particles were analyzed by the software.

Nano iron sesquioxide Dv50 test:

The Dv50 of the nano-iron sesquioxide was tested using a laser particle size analyzer.

Resistivity test of positive electrode material:

The powder resistivity of the positive electrode material powder at 8Mpa was tested using a powder resistance tester (yuanzhi technology, model: PRCD 3100).

And (3) testing the membrane resistance of the positive electrode plate:

The resistance value of the positive electrode sheet under the pressure of 0.4T (ton) is tested by using a sheet resistance meter (Yuan-Can technology, model: BER 2500).

Positive electrode material compaction density test:

The compacted density of the positive electrode material powder after pressure release at 3T was tested using an electronic pressure tester (force test, model: LD 43.305).

And (3) testing the energy efficiency and the first discharge specific capacity of the lithium ion battery:

Constant-current charge-discharge cycle test is carried out on the lithium ion battery on a charge-discharge instrument, the test temperature is 25 ℃, the charge-discharge multiplying power is 0.5 ℃, the charge-discharge voltage window is 2.5V-3.65V (namely, the charge cutoff voltage of the lithium ion battery is 3.65V, the discharge cutoff voltage of the lithium ion battery is 2.5V, when the charge cutoff voltage is more than or equal to 3.65V, the charge cutoff voltage of the lithium ion battery is generally considered to be higher), and the energy efficiency after cycle is calculated:

The energy efficiency calculation formula is (discharge energy after the 2 nd cycle/charge energy after the 2 nd cycle) ×100%. In general, the process of performing one complete charge and discharge is referred to as one charge and discharge cycle, that is, the battery is charged from 2.5V to 3.65V and then discharged from 3.65V to 2.5V, thereby forming one charge and discharge cycle. The above procedure is repeated n times after n times of circulation.

The specific capacity of the first discharge of the cycle is calculated, and the calculation formula is as follows:

specific capacity of cycle first discharge= (discharge capacity after first cycle/mass of positive electrode material) ×100%.

TABLE 3 Performance data for examples and comparative examples

From examples 1 to 7 and comparative examples 1 to 6, it can be seen that when the value of a is 0% and the value of K is 0% (for example, comparative example 1), although the specific capacity is not significantly reduced, the energy efficiency is low, which may be because nano Fe ₂O₃ is not introduced when the value of a is too large (for example, comparative example 4), it is difficult to form the positive electrode material of the present application, when the value of a is 0% and the amount of pure Fe ₂ P is 15% (for example, comparative example 2), both the specific capacity and the energy efficiency are low, which may be because nano Fe ₂O₃ is not introduced when the value of a is small (for example, comparative example 3) and the sintering temperature is too high, by-product Fe ₂ P particles are generated, when the value of a is too large (for example, comparative example 3), the energy efficiency is not significantly reduced, but the specific capacity is low, when the value of a is too large (for example, comparative example, 4), the specific capacity is not significantly reduced, and when the value of K is too small (for example, comparative example, the value of a is not significantly reduced, the specific capacity is not significantly reduced, and the lithium ion has a is significantly reduced, and the specific capacity is simultaneously, and the lithium ion has a significantly reduced in the range.

The iron-to-phosphorus ratio b ₁、b₂、b₃, the compacted density of the positive electrode material and other parameters also generally have an influence on the performance of the lithium ion battery. It can be further seen from examples 1, 8 to 11 that, on the basis of having the positive electrode material of the present application in the positive electrode sheet of the lithium ion battery, the above parameters are adjusted within the scope of the present application, which is favorable for obtaining the lithium ion battery with good capacity performance and energy efficiency.

Fig. 5 is an SEM back-scattered photograph of the positive electrode sheet of example 1, in which, as can be seen from fig. 5, there are lithium iron phosphate-iron phosphide composite particles (as indicated by the circular dotted line box in the figure), the white region of the cross section of which is an iron phosphide region, indicating that iron phosphide is fused inside the lithium iron phosphate-iron phosphide composite particles, and the region other than the iron phosphide region in the cross section of the composite particles is an iron phosphate region, and in addition, there are pure lithium iron phosphate particles (as indicated by the rectangular dotted line box in the figure) of a larger size, and pure lithium iron phosphate particles of a smaller size.

Fig. 6 is an SEM back-scattered photograph of the positive electrode sheet of comparative example 2, and it can be seen from fig. 6 that pure iron phosphide particles were present alone in the positive electrode material layer (as shown by the circular dotted line box in the figure) and were not fused with lithium iron phosphate particles, and that pure lithium iron phosphate particles having a larger size were also present therein (as shown by the rectangular dotted line box in the figure).

The above-mentioned embodiments are only used to help understand the technical solution and core application point of the embodiments of the present application, and meanwhile, for those skilled in the art, according to the idea of the present application, there are changes in the specific implementation manner and application range, and in summary, the present disclosure should not be construed as limiting the application.

Claims

1. A positive electrode material, which is characterized by comprising first lithium iron phosphate particles and lithium iron phosphate-iron phosphide composite particles, wherein the quantity percentage of the lithium iron phosphate-iron phosphide composite particles is a, and is more than or equal to 3% and less than or equal to 30% based on the total quantity of the first lithium iron phosphate particles and the lithium iron phosphate-iron phosphide composite particles;

the ferric phosphide is fused inside the lithium iron phosphate-ferric phosphide composite particles, and in the cross section of the lithium iron phosphate-ferric phosphide composite particles, the area of the ferric phosphide is more than or equal to 10% and less than or equal to 60% of the total area of the cross section.

2. The positive electrode material according to claim 1, further comprising second lithium iron phosphate particles and third lithium iron phosphate particles, wherein the first lithium iron phosphate particles and the lithium iron phosphate-iron phosphide composite particles have an average size of Φ ₁, the second lithium iron phosphate particles have an average size of Φ ₂, and the third lithium iron phosphate particles have an average size of Φ ₃,Φ₁＞Φ₂＞Φ₃.

3. The positive electrode material according to claim 2, wherein the positive electrode material satisfies at least one of the following characteristics:

4. The positive electrode material of claim 2, wherein the positive electrode material meets at least one of the following characteristics:

d)Φ₁≥1μm;

e)250nm≤Φ₂<1μm;

f)Φ₃<250nm。

5. the positive electrode material according to claim 1, wherein the positive electrode material has a resistivity ρ of 2Ω·cm+.ρ+.20Ω·cm.

6. The positive electrode material according to claim 1, further comprising a doping element selected from at least one of titanium, magnesium, niobium, vanadium, sodium, scandium, and cerium.

7. A method for preparing the positive electrode material according to any one of claims 1 to 6, comprising the steps of:

8. The preparation method according to claim 7, wherein the nano ferric oxide is c, and the mass percentage of the nano ferric oxide in the iron source is 0.2% to 2%.

9. The method of manufacture of claim 7, wherein the method of manufacture meets at least one of the following characteristics:

10. A positive electrode sheet, comprising a positive electrode current collector, wherein at least one surface of the positive electrode current collector is provided with a positive electrode material layer, the positive electrode material layer comprises the positive electrode material according to any one of claims 1 to 6, or the positive electrode material layer comprises the positive electrode material prepared by the preparation method according to any one of claims 7 to 9.

11. The positive electrode sheet according to claim 10, wherein the sheet resistance of the positive electrode sheet is R,0.1 Ω -R-0.35 Ω.

12. The positive electrode sheet of claim 10, wherein the positive electrode sheet meets at least one of the following characteristics:

13. A battery comprising the positive electrode sheet according to any one of claims 10 to 12.

14. An energy storage device comprising a housing and at least one battery of claim 13, wherein the battery is housed in the housing.

15. A powered device comprising the energy storage device of claim 14, the energy storage device providing power to the powered device.