WO2023056636A1

WO2023056636A1 - Lithium cobalt oxide layered positive electrode material, and preparation method therefor and use thereof

Info

Publication number: WO2023056636A1
Application number: PCT/CN2021/122867
Authority: WO
Inventors: 潘锋; 黄伟源; 赵庆贺; 张明建; 李建元; 林海
Original assignee: 北京大学深圳研究生院
Priority date: 2021-10-09
Filing date: 2021-10-09
Publication date: 2023-04-13
Also published as: CN114938686B; CN114938686A

Abstract

A lithium cobalt oxide layered positive electrode material, and a preparation method therefor and the use thereof. Cobalt is contained in a lithium layer of the crystal structure of the lithium cobalt oxide layered positive electrode material; reversible structural phase transition and reversible oxygen valence variation reaction during a high-voltage charging and discharging process greater than or equal to 4.5 V are achieved; and the reversible lithium intercalation amount and gram capacity of the lithium cobalt oxide material are improved, such that excellent electrochemical properties are shown under a high-voltage charging and discharging condition. Moreover, the preparation method for the lithium cobalt oxide layered positive electrode material containing cobalt in the lithium layer is simple and easy for large-scale industrial production.

Description

A kind of lithium cobalt oxide layered cathode material and its preparation method and application

technical field

The present application relates to the field of lithium ion battery materials, in particular to a lithium cobalt oxide layered positive electrode material and its preparation method and application.

Background technique

Since the first commercial application of lithium cobalt oxide in 1991, the development, research and commercial application of lithium cobalt oxide system have great value for mankind to solve the energy crisis. In the past few decades, increasing the charging voltage has been an effective means to simultaneously achieve high energy density and high power density of lithium cobalt oxide materials.

At present, the limiting factor restricting the step-up of lithium cobalt oxide materials is mainly the severe structural phase transition around 4.5V. This structural phase transition leads to drastic expansion/contraction of the lattice parameters, which reduces the electrochemical reaction kinetics; meanwhile, the incomplete reversibility of the phase transition leads to rapid capacity fading. Excessive de-Li on the surface of lithium cobaltate materials under high pressure leads to a sharp increase in the reactivity of Co in the surface structure, and reacts with the electrolyte to overflow gas, accompanied by the dissolution of Co. At the same time, the oxidative decomposition products of the solid-liquid interface form a CEI film on the surface of lithium cobalt oxide, which greatly increases the internal resistance of the battery and intensifies the capacity fading process.

In response to the above problems, people use coating methods to coat the interface of lithium cobalt oxide to isolate the direct contact between the lithium cobalt oxide material and the electrolyte; although this increases the high voltage to a certain extent, for example, the potential is higher than 4.4V. , the cycle stability of the lithium cobalt oxide cathode; however, the introduction of the surface coating inevitably reduces the energy density and power density of the material.

Therefore, how to obtain higher energy density and power density by increasing the voltage under the premise of ensuring the structural stability and interface stability of the material is the research focus and difficulty of lithium cobalt oxide cathode materials.

Contents of the invention

The purpose of this application is to provide a new lithium cobalt oxide layered positive electrode material and its preparation method and application.

The application adopts the following technical solutions:

One aspect of the present application discloses a lithium cobaltate layered positive electrode material, wherein the lithium layer of the crystal structure of the lithium cobaltate layered positive electrode material contains cobalt.

It should be noted that the lithium cobaltate layered positive electrode material refers to lithium cobaltate formed in a layered arrangement of cobalt layer, lithium layer and oxygen layer in the crystal structure of lithium cobaltate. Generally speaking, lithium layer and cobalt The layers are arranged according to the layered distribution, the lithium layer will not contain cobalt, and the cobalt layer will not contain lithium. However, the present application found that by introducing Co into the Li layer of the lithium cobalt oxide crystal structure, more Li ⁺ can be reversibly intercalated and deintercalated from the lithium cobalt oxide material, which can be used at higher voltages, such as charging voltages. 4.65V, which improves the reversible charge-discharge capacity of lithium cobalt oxide positive electrode, and has high cycle stability. Therefore, the lithium cobalt oxide layered positive electrode material of the present application can effectively increase the voltage while ensuring the energy density and power density of the material. In one implementation of the present application, under the charging voltage of 4.65V vs. Li ⁺ /Li, the reversible charge-discharge capacity of the lithium cobalt oxide positive electrode is ≥240mAh g ^-1 , as shown in Figure 1, and has a relatively high cycle Stability, as shown in Figure 2.

It should also be noted that the inclusion of cobalt in the lithium layer in this application means that part of the lithium sites in the lithium layer in the microscopic crystal structure are replaced by cobalt, which is essentially different from the existing lithium cobalt oxide doping. The research of this application found that for lithium cobalt oxide layered positive electrode materials, in order to ensure that the lithium layer will not collapse, only a small part of lithium in the lithium layer will be reversibly intercalated and deintercalated, which is the main factor limiting the boosting of lithium cobalt oxide materials. The reason; and after introducing cobalt into the lithium layer in this application, the cobalt ions can support the stability of the lithium layer and avoid the collapse of the lithium layer, so it can support the reversible intercalation and extraction of more lithium ions and support higher charge and discharge voltages.

In one implementation of the present application, both the bulk phase of the crystal structure of the lithium cobaltate layered positive electrode material and the lithium layer in the surface interface region contain cobalt, and the cobalt and oxygen in the lithium layer in the surface interface region form a cobalt-oxygen link structure.

In one implementation of the present application, the cobalt in the lithium layer in the surface interface region and the cobalt oxygen in the cobalt layer are linked to each other, forming a connected network of cobalt oxygen structure on the surface of the lithium cobalt oxide layered positive electrode material.

In one implementation of the present application, the cobalt-oxygen structures in the crystal structure of the surface interface region are interconnected to form a connected network that runs through the phases and interfaces of the crystal structure.

In an implementation manner of the present application, the lithium layer in the bulk phase of the crystal structure contains 0.1%-5% cobalt.

Preferably, the lithium layer in the bulk phase of the crystal structure contains no more than 3% cobalt.

In an implementation manner of the present application, the lithium layer in the surface interface region of the crystal structure contains not less than 30% cobalt.

In one implementation of the present application, the amount of cobalt contained in the lithium layer in the crystal structure gradually decreases from the interface to the bulk phase.

It should be noted that the research of this application found that the introduction of Co into the Li layer of the lithium cobalt oxide crystal structure can allow more Li ⁺ to be reversibly intercalated and deintercalated from the lithium cobalt oxide material; further, through the lithium layer at the interface Introduce a large amount of cobalt, such as cobalt that accounts for no less than 30% of the lithium layer, and a large number of cobalt-oxygen link structures in the surface area, which can conduct electricity and conduct lithium, and do not participate in redox reactions, further realizing the high-voltage lithium cobalt oxide. Reversible high energy density and high power density. In one implementation of the present application, this optimization of the interface is further consolidated and realized by replacing the surface crystal framework with elements, and plays the role of isolating the electrolyte, avoiding the lithium cobaltate positive electrode material and the electrolyte. Direct contact; for example, after sintering the lithium cobalt oxide layered positive electrode material or the lithium cobalt oxide layered positive electrode material doped with metal elements in the crystal structure phase, further soaking in solution and heat treatment are used to make the lithium layer in the surface interface region Lithium and/or cobalt in are further replaced.

It can be understood that there can be a large amount of cobalt in the lithium layer of the crystal structure in the surface interface region in order to stabilize the surface structure, conduct electricity and conduct lithium; however, the cobalt content in the bulk phase should not be too high, otherwise it will affect the reversible The total amount of intercalated and extracted Li ⁺ , therefore, the lithium layer in the bulk domain crystal structure contains 0.1%-5% cobalt, preferably no more than 3%. With such a cobalt content, it can not only ensure that the total amount of reversible intercalation and deintercalation of Li ⁺ is not greatly affected, but also stabilize the structure of the lithium layer, allowing more Li ⁺ to be reversibly intercalated from the lithium cobalt oxide material. Escape effect. Moreover, after the cobalt in the surface area replaces the lithium site in the lithium layer, the formed cobalt-oxygen two-dimensional link structure runs through the phase and interface of the crystal structure, which can better conduct electricity and lead lithium, and improve the overall performance of the battery.

In an implementation manner of the present application, lithium and/or cobalt in the lithium layer in the surface interface region are partially replaced by metal elements, and these metal elements are at least one of Mg, Al, B and Ti.

In an implementation of the present application, more specifically, the lithium and/or cobalt in the lithium layer in the surface interface region are partially replaced by Mg, and the cobalt in the cobalt layer in the surface interface region is replaced by at least Al, B and Ti A partial replacement.

In an implementation manner of the present application, the proportion of metal elements replacing lithium and/or cobalt in the lithium layer in the surface interface region is not less than 40%.

In one implementation of the present application, the oxygen in the surface interface region of the crystal structure is partially or completely replaced by fluorine.

It should be noted that this application designs element substitution in the crystal structure of the surface region of the lithium cobaltate layered positive electrode material. As mentioned above, the purpose is to further realize the conduction and lithium conduction, and not participate in the redox reaction. , effectively isolate the electrolyte from the lithium cobalt oxide, and avoid direct contact between the lithium cobalt oxide cathode material and the electrolyte.

In an implementation manner of the present application, the thickness of the surface interface region of the lithium cobalt oxide layered positive electrode material is less than or equal to 5 nm.

In one implementation of the present application, the bulk phase of the crystal structure is doped with metal elements, the metal elements are doped in the lithium layer and/or the cobalt layer, and these metal elements are at least one of Mg, Al and Ti.

In an implementation manner of the present application, the proportion of metal elements doped in the bulk crystal structure does not exceed 1%.

It should be noted that the element doping of lithium cobalt oxide positive electrode material is a technical solution that has been studied and reported in the prior art. The lithium cobalt oxide layered positive electrode material of the present application can also be element doped according to requirements. The specific element doping For the solution, reference may be made to the prior art, and no specific limitation is made here.

In an implementation manner of the present application, the lithium cobalt oxide layered positive electrode material is primary micro-nano particles or secondary micro-nano particles.

In an implementation manner of the present application, the particle size of the lithium cobalt oxide layered positive electrode material is 0.5-40 microns.

It should be noted that the primary micro-nanoparticles in this application refer to nanoparticles or microparticles with a single crystal structure formed by the growth of crystal nuclei, and the secondary micronanoparticles refer to particles formed by agglomeration of nanoparticles or microparticles with a single-crystal structure; It can be understood that the lithium cobalt oxide layered positive electrode material of the present application may be primary micro-nano particles or secondary micro-nano particles, which are not specifically limited here.

The other side of the present application discloses the preparation method of the lithium cobalt oxide layered positive electrode material of the present application, including mixing the lithium source and the cobalt source, and sintering at 750-950°C for 1-12 hours in an air atmosphere, and then, Microwave or quenching process is carried out to obtain the lithium cobalt oxide layered positive electrode material containing cobalt in the lithium layer of the crystal structure, especially the lithium cobalt oxide layered positive electrode material containing cobalt in the lithium layer of the bulk phase of the crystal structure.

It should be noted that, in the preparation method of the present application, the lithium cobaltate material sintered at high temperature for a certain period of time is quenched or treated with microwaves, so that the lithium layer of the crystal structure of the lithium cobaltate layered positive electrode material obtained by sintering contains cobalt, Thereby obtaining the lithium cobalt oxide layered positive electrode material of the present application.

In one implementation of the present application, the preparation method of the present application also includes mixing the metal element doped in the bulk phase of the crystal structure with the lithium source and the cobalt source and sintering to obtain the metal element doped in the bulk phase of the crystal structure. Elemental lithium cobalt oxide layered cathode material.

It can be understood that in the lithium cobalt oxide layered positive electrode material of the present application, metal elements can be doped in the bulk phase of the crystal structure according to requirements, and the doping of metal elements in the bulk phase is mainly achieved through the sintering process. As for the element replacement in the surface interface region, it is mainly realized by solution immersion and subsequent heat treatment. That is to say, in the lithium cobalt oxide layered positive electrode material of the present application, the element substitution at the interface and the element doping in the bulk phase are not carried out simultaneously; the element doping in the bulk phase is carried out during the sintering process of the lithium cobalt oxide material Formed; Among them, the doping of Mg is generally in the lithium layer, and the doping of B, Al, and Ti is generally in the cobalt layer. Element substitution at the interface is formed during immersion and heat treatment, in which Al, B, and Ti partially replace cobalt in the cobalt layer, Mg partially replaces lithium and/or cobalt in the Li layer, and F completely or partially replaces cobalt in the lattice framework. O.

Therefore, in one implementation of the present application, the preparation method of the present application also includes soaking the lithium cobaltate layered positive electrode material or the lithium cobaltate layered positive electrode material doped with metal elements in the crystal structure phase with a slightly acidic solution, After the immersion is completed, it is heat-treated to obtain lithium and/or cobalt in the lithium layer in the surface interface area is partially replaced by metal elements, cobalt in the cobalt layer in the surface interface area is partially replaced by metal elements, or oxygen is partially or completely replaced by fluorine Lithium cobalt oxide layered positive electrode material; wherein, the slightly acidic solution contains Li ⁺ , and at least one of Mg ²⁺ , Al ³⁺ , borate, Ti ⁴⁺ and F ^- ; the soaking condition is at 0-160 Soaking at ℃ for 0.1-48h, and maintaining a stirring speed of 50-1000r/min throughout the process; heat treatment conditions are heating at 200-700°C for 0.1-36h, and the atmosphere conditions for heat treatment are inert atmosphere or reducing atmosphere. Among them, the slightly acidic solution, in an implementation manner of the present application, specifically uses a slightly acidic electrolyte solution containing lithium with a pH value of 2-6.

It should be noted that the research of this application found that the lithium layer, cobalt layer and oxygen in the surface interface area can be further replaced by solution immersion and heat treatment; and, in the process of immersion and heat treatment, the surface interface area can also be realized The increase of cobalt content in the lithium layer; in fact, the cobalt in the lithium layer in the surface interface region of the crystal structure can be much higher than the cobalt in the bulk lithium layer, mainly through soaking and heat treatment, in this process, the surface Part of Li ⁺ in the lithium layer in the interface region will be lost, so that part of the cobalt in the cobalt layer will enter the lithium layer from the cobalt layer, thereby increasing the cobalt content in the lithium layer in the surface interface region to 30%-60%.

Another aspect of the present application discloses the application of the lithium cobalt oxide layered positive electrode material of the present application in the preparation of power lithium batteries, or lithium ion batteries for 3C consumer electronics products, drones or electronic cigarettes.

It can be understood that the lithium cobalt oxide layered positive electrode material of the present application has the advantages of high voltage, high reversible charge and discharge capacity, high energy density, high power density, and good stability, and can be better used in power lithium batteries, such as electric Cars or other medium and large electric equipment. Similarly, the lithium cobalt oxide layered positive electrode material of the present application can also be used in lithium-ion batteries of 3C consumer electronics products, drones or electronic cigarettes.

Another aspect of the present application discloses a lithium ion battery using the lithium cobalt oxide layered cathode material of the present application.

It can be understood that the lithium ion battery of the present application, due to the use of the lithium cobalt oxide layered positive electrode material of the present application, makes the battery work at a higher charge and discharge voltage, and has a higher reversible charge and discharge capacity, and stability good. The lithium ion battery of the present application can achieve high energy density and high power density at high voltage.

The beneficial effect of this application is:

The lithium cobaltate layered positive electrode material of the present application contains cobalt in the lithium layer of its crystal structure, which realizes reversible structural phase transition and reversible oxygen valence change reaction in the process of charging and discharging at a high voltage greater than or equal to 4.5V, and improves the The reversible lithium intercalation amount of the lithium cobalt oxide material increases the gram capacity, thus exhibiting excellent electrochemical performance under high-voltage charge-discharge conditions. Moreover, the lithium cobalt oxide layered positive electrode material of the present application has a simple preparation method for containing cobalt in the lithium layer, and is easy for large-scale industrial production.

Description of drawings

Fig. 1 is the scanning electron microscope result figure of lithium cobalt oxide layered cathode material in the embodiment of the present application;

Fig. 2 is the Rietveld XRD refinement diagram of lithium cobalt oxide layered positive electrode material in the embodiment of the present application;

Fig. 3 is a high-resolution transmission electron microscopy result diagram of the bulk phase and surface area of the lithium cobalt oxide layered positive electrode material in the embodiment of the present application;

Fig. 4 is the charge-discharge curve of lithium cobalt oxide layered positive electrode material under 15mAg ^-1 electric current condition in the embodiment of the application;

Fig. 5 is the rate curve diagram of lithium cobalt oxide layered positive electrode material in the embodiment of the present application;

Fig. 6 is a graph showing the cycle stability of the lithium cobalt oxide layered positive electrode material at 5C and 10C current densities in the examples of the present application.

Detailed ways

Although the industry has strongly called for increasing the energy density of lithium cobaltate by increasing the charging voltage in recent years, the problem of rapid capacity decay caused by increasing the charging voltage has always been difficult to solve. The study of this application believes that this rapid capacity decay is mainly due to two aspects: 1) the structural phase transition of lithium cobalt oxide is intensified in the high delithiation state, and the Co-O layer collapses, resulting in the blockage of Li ⁺ diffusion channels; 2) the high delithiation state Excessive delithiation of the lithium cobaltate surface structure under high voltage leads to a sharp increase in the reactivity of Co, intensified side reactions in contact with the electrolyte, and a large number of CEI films, resulting in increased battery internal resistance and increased capacity fading.

The study of this application shows that by controlling the sintering temperature and sintering time, combined with efficient material processing methods such as microwave and quenching, a new type of lithium cobalt oxide material containing cobalt in the bulk phase of the crystal structure and the lithium layer at the interface can be obtained. This special bulk phase structure can not only allow more Li ⁺ to be extracted from the lithium layer under high voltage conditions, but also can effectively suppress the structural collapse of the Co-O layer of lithium cobalt oxide material during high voltage charging, so A very high reversible discharge capacity is obtained. In one implementation of the present application, the gram capacity of the novel lithium cobalt oxide is ≥240mAh g ⁻¹ . Further, replacing the lithium, cobalt and oxygen in the crystal structure of the surface interface region of this new type of high-voltage lithium cobalt oxide material with other elements can further promote electrical conduction, lithium conduction, and inhibit the electrochemical side reaction process, which can further Obtain extremely high reversible discharge capacity. This element replacement treatment within the surface micro-region not only physically blocks the direct contact between the high-valent Co catalytic active center on the surface of lithium cobaltate and the electrolyte under high voltage, suppresses the side reaction at the interface, but also ensures the reversible oxygen valence change reaction. , so that the new lithium cobalt oxide material exhibits excellent electrochemical performance.

Based on the above research and understanding, this application creatively proposes a new lithium cobalt oxide layered positive electrode material containing cobalt in the lithium layer of the crystal structure. The bulk phase Li layer and the interface of the crystal structure of the new lithium cobalt oxide positive electrode material Both Li layers contain Co.

According to the study of this application, the effect of Co contained in the bulk Li layer and the interface Li layer on improving capacity and cycle stability is that the Co contained in the bulk Li layer realizes the reversible intercalation/extraction of more Li ⁺ ions and improves the structure. The reversibility of the phase transition increases the discharge capacity of lithium cobaltate; there is a large amount of cobalt in the lithium layer in the crystal structure of the lithium cobaltate interface region, and the replacement of effective elements in the surface micro-region can isolate the lithium cobaltate material from the lithium cobaltate to a certain extent. The direct contact of the electrolyte reduces the side reactions at the interface under high voltage, and at the same time realizes the reversible oxygen valence change. Therefore, the new high-voltage lithium cobalt oxide material of this application exhibits excellent electrochemical performance under high-voltage charge and discharge conditions; in one implementation of this application, its reversible gram capacity exceeds 240mAh g ^-1 , which is the first report by humans .

The present application will be described in further detail below through specific examples. The following examples only further illustrate the present application, and should not be construed as limiting the present application.

Embodiment one

The new high-voltage lithium cobalt oxide layered positive electrode material in this example contains 2% Co in the lithium layer of the crystal structure, and most of the Li and Co in the surface micro-region are replaced by Co and Al, respectively. In this example, high-temperature sintering, solution immersion, and subsequent heat treatment were used to synthesize a new high-voltage lithium cobaltate cathode material containing 2% Co in the lithium layer. Specifically include:

1) Synthesis and sintering of lithium cobaltate: After mixing battery-grade Li ₂ CO ₃ (Ganfeng Lithium Industry) and analytically pure CoO (Aladdin, D50=3-6 microns) according to the Li/Co ratio of 1.00, In the air atmosphere, sinter at 900°C for 12 hours, and then pour the lithium cobalt oxide material in the high temperature state directly into cold water for quenching treatment. After quenching, the material was suction filtered, washed with deionized water and alcohol, and baked in a vacuum oven at 80°C for 24 hours. The obtained dried lithium cobaltate particles are successively crushed by a double roller compactor and sieved with 200 meshes to prepare lithium cobaltate for later use.

2) Solution soaking: Weigh 1 mol of lithium cobaltate prepared in step 1) and 1 g of polyethylene glycol (molecular weight greater than 2000), add 1000 mL of deionized water, stir to form a black suspension, and pour it into a hydrothermal reaction kettle middle. During the stirring process, 0.045 mol of lithium sulfate and 0.015 mol of aluminum sulfate were added to form a solution A; the solution A was continuously stirred at 60° C. for 6 hours. After the liquid phase reaction is completed, use a vacuum filtration device to perform suction filtration and cleaning, and bake in a vacuum oven at 120°C for 24 hours; the dried samples are sieved with a 100-mesh sieve, and set aside.

3) Subsequent heat treatment: put the lithium cobalt oxide sample obtained in step 2) in a rotary tube furnace for subsequent heat treatment. After 6 hours of heat preservation, the temperature was naturally lowered; the obtained material was sieved through a 100-mesh sieve, and was vacuum-packed and stored in an aluminum-plastic bag; the obtained material was named "LCO-LAO-1#".

4) Electrochemical test: Using NMP as a solvent, LCO-LAO-1#, carbon black and PVDF were evenly mixed in a mass ratio of 8:1:1 to prepare a positive pole piece. The active material loading of the pole piece was about It is 4.5mg cm ^-2 . Use 2032 button cells to prepare half batteries with lithium sheet as negative electrode, use Celgard 2035 diaphragm and high voltage electrolyte (mass ratio LiPF ₆ : EMC: FEC=15:55:30), this half battery is at 3-4.65V ( vs. Li/Li ⁺ ), the N/P ratio of the full battery is about 1.15, and the commercial graphite carbon microsphere anode is provided by Shenzhen BTR New Energy Materials Company.

SEM and XRD were used to observe the new high-voltage lithium cobaltate "LCO-LAO-1#" containing 2% Co in the lithium layer prepared in this example, and the results are shown in Figure 1 and Figure 2. The results show that in this example, lithium cobalt oxide secondary particle materials with D ₅₀ between 3-4 microns were prepared, and Rietveld XRD refinement results showed that there were 2.0% Li/Co antisites in the material, because the surface area was in the whole The proportion of lithium cobaltate particles is very small, so it can be considered that LCO-LAOF-1# in the Li layer contains 2.0% Co. Through XPS semi-quantitative analysis, it is determined that the Co content in the Li layer in the surface interface region is about 40%. Furthermore, the thickness of the surface region is below 5 nm, as shown in Fig. 3.

In this example, the charge and discharge curves of the new high-voltage lithium cobalt oxide "LCO-LAO-1#" cathode material at a current density of 0.1C between 3-4.65V (vs. Li/Li ⁺ ), the results are shown in Figure 4 Show. Among them, 1C=150mAh g ^-1 . The results in Fig. 3 show that the material has a reversible discharge capacity of 255mAh g ^-1 under the condition of a current density of 0.1C.

In this example, the rate curve of the new high-voltage lithium cobalt oxide "LCO-LAO-1#" cathode material between 3-4.65V (vs. Li/Li ⁺ ), the results are shown in Figure 4. Among them, 1C=150mAh g ^-1 . The results in Figure 5 show that the discharge capacity of the positive electrode material at 0.5C, 1C, 2C, 5C, 10C, 20C and 30C are 249.4, 244.2, 233.1, 216.1, 201.4, 176.6 and 159.3mAh g ^-1 , respectively. high rate performance.

In this example, the cycle curves of the new high-voltage lithium cobaltate “LCO-LAO-1#” cathode material at 5C and 10C between 3-4.65V (vs. Li/Li ⁺ ), the results are shown in Figure 5. The results in Figure 6 show that the capacity retention of the positive electrode material after 500 cycles at 5C and 10C is 80.8% and 82.5%, respectively, showing extremely high electrochemical stability.

The above results show that the new high-voltage lithium cobalt oxide "LCO-LAO-1#" cathode material of this example has excellent capacity, rate and cycle stability under high-voltage charge-discharge conditions.

Embodiment two

In the new high-voltage lithium cobalt oxide in this example, the lithium layer contains 1.2% Co, and the interface layer of Li-Co-Mg-O-F is formed in the surface area. In this example, high-temperature sintering, immersion in a slightly acidic solution, and subsequent heat treatment were used in sequence to synthesize a new high-voltage lithium cobaltate cathode material containing 1.2% Co in the lithium layer. Specifically include:

1) Synthesis and sintering of lithium cobalt oxide: mix battery-grade Li ₂ CO ₃ (Ganfeng Lithium Industry) with battery-grade Co ₃ O ₄ (Huayou Cobalt Industry, D50=4-8 microns) according to the Li/Co ratio of 1.03 After the material is uniform, it is sintered at 900° C. for 6 hours in an air atmosphere, and then the lithium cobalt oxide material in a high temperature state is directly poured into water for quenching treatment to obtain a powder sample. The obtained lithium cobaltate particles are successively crushed by a double roller compactor, and sieved with 200 meshes to prepare lithium cobaltate, which is set aside. At the same time, as comparative samples, we also prepared samples sintered at 800°C and 850°C for 6 hours as controls.

2) Solution soaking: Weigh 1 mol of lithium cobaltate prepared in step 1) and 1 g of polyethylene glycol (molecular weight greater than 2000), add 1000 mL of deionized water, stir to form a black suspension, and pour it into a hydrothermal reaction kettle middle. During the stirring process, 0.05 mol of lithium nitrate and 0.02 mol of magnesium nitrate were added to form a solution A; the solution A was continuously stirred at 60° C. for 6 hours. After the liquid phase reaction is completed, use a vacuum filtration device to carry out suction filtration and cleaning, and bake in a blast oven at 80°C for 24 hours; the dried samples are sieved with a 100-mesh sieve and set aside.

3) Subsequent heat treatment: The lithium cobaltate sample obtained in step 2) was placed in a rotary tube furnace for subsequent heat treatment. The heat treatment conditions were: nitrogen atmosphere, the temperature was raised to 550 °C at a heating rate of 5 °C/min, and at 550 °C After 6 hours of heat preservation, the temperature was naturally lowered; the obtained material was sieved through a 200-mesh sieve, and was vacuum-packed and stored in an aluminum-plastic bag; the obtained material was named "LCO-LMO-900".

In addition, in this example, two comparative samples were obtained by sintering at 800°C and 850°C for 6 hours under an air atmosphere, and the rest of the conditions were the same, for example, the same solution immersion and subsequent heat treatment were also carried out. The two obtained materials were named " LCO-LMO-800" and "LCO-LMO-850".

4) Electrochemical test: Using NMP as a solvent, LCO-LMO-1#, carbon black and PVDF were uniformly mixed in a mass ratio of 8:1:1 to prepare a positive electrode sheet. The active material loading of the electrode sheet was about It is 4.5mg cm ^-2 . Use 2032 button cells to prepare half batteries with lithium sheet as negative electrode, use Celgard 2035 diaphragm and high voltage electrolyte (mass ratio LiPF ₆ : EMC: FEC=15:55:30), this half battery is at 3-4.65V ( vs. Li/Li ⁺ ), the N/P ratio of the full battery is about 1.15, and the commercial graphite carbon microsphere (MCMB) anode material is provided by Shenzhen BTR New Energy Materials Company. The pole pieces of LCO-LMOF-800 and LCO-LMOF-850 are also prepared by the same preparation process.

The observation results of the morphology of the three samples show that in this example, three lithium cobaltate secondary particle materials with D ₅₀ between 3-4 microns were prepared. At the same time, the results of Rietveld XRD crystal structure analysis showed that the bulk phase structure lithium layers of LCO-LMO-800, LCO-LMO-850 and LCO-LMO-900 contained 5.6%, 3.4% and 1.2% cobalt respectively, XPS The results of semi-quantitative analysis show that the cobalt content in the lithium layer in the surface area of the three materials is about 40%. For the above results, the analysis shows that the cobalt content in the surface Li layer is related to the solution immersion and subsequent heat treatment process, so there is little difference between the three; however, the cobalt content in the lithium layer in the bulk phase is related to the sintering preparation process, so the difference between the three Larger; in general, the lower temperature sintering process leads to an increase in the cobalt content in the lithium layer. In this example, the charge-discharge curve results of the new high-voltage lithium cobaltate “LCO-LMO-900” cathode material at a current density of 0.1C between 3-4.65V (vs. Li/Li ⁺ ) show that the reversible discharge capacity is 251mAh g ^-1 . In this example, the new high-voltage lithium cobalt oxide "LCO-LMO-900" cathode material has a capacity retention rate of 81.2% after 500 cycles of 5C cycles between 3-4.65V (vs. Li/Li ⁺ ), showing extremely high electrochemical stability.

In comparison, the discharge capacities of LCO-LMO-800 and LCO-LMO-850 cathode materials at 0.1C current density between 3-4.65V (vs. Li/Li ⁺ ) are 240mAh g ^-1 and 232mAh g ^-1 .

In summary, the above results show that the novel high-voltage lithium cobalt oxide “LCO-LMO-900” cathode material of this example has high capacity and cycle stability under high-voltage charge-discharge conditions.

Embodiment three

In the new high-voltage lithium cobalt oxide in this example, the lithium layer contains 1.6% Co, and the surface area is a mixed area of Li, Co, B, and O elements. In this example, high-temperature sintering, solution immersion, and subsequent heat treatment were used to synthesize a new high-voltage lithium cobaltate cathode material containing 1.6% Co in the lithium layer. Specifically include:

1) Synthesis and sintering of lithium cobalt oxide: mix battery-grade Li ₂ CO ₃ (Ganfeng Lithium Industry) with battery-grade Co ₃ O ₄ (Huayou Cobalt Industry, D50=4-8 microns) according to the Li/Co ratio of 1.03 After the material is uniform, it is sintered at 900°C for 6 hours in an air atmosphere. The obtained lithium cobaltate particles were successively crushed by a pair of roller compactors, and sieved through a 200-mesh sieve. Then put the obtained lithium cobaltate powder into a microwave reaction device under an air atmosphere, and carry out secondary roasting under a microwave power of 400W. The heating time is 20min. After the sintering is completed, sieve through 200 mesh to prepare lithium cobaltate ,spare.

2) Solution immersion: Weigh 1 mol of lithium cobalt oxide prepared in step 1), add 1000 mL of deionized water and 1 g of polyethylene glycol (molecular weight greater than 2000), stir to form a black suspension, and pour it into a hydrothermal reaction kettle middle. During the stirring process, 0.05 mol of lithium nitrate and 0.02 mol of boric acid were added to form a solution A; the solution A was rotated and stirred at 60° C. for 6 h. After the liquid phase reaction is completed, use a vacuum filtration device to carry out suction filtration and cleaning, and bake in a blast oven at 80°C for 24 hours; the dried samples are sieved with a 100-mesh sieve and set aside.

3) Subsequent heat treatment: put the lithium cobalt oxide sample obtained in step 2) in a rotary tube furnace for subsequent heat treatment. After 12 hours of heat preservation, the temperature was naturally lowered; the obtained material was sieved through a 200-mesh sieve, and vacuum-packed and stored in an aluminum-plastic bag; the obtained material was named "LCO-LBO-1#".

4) Electrochemical test: Using NMP as a solvent, LCO-LBO-1#, carbon black and PVDF were uniformly mixed in a mass ratio of 8:1:1 to prepare a positive pole piece. The active material loading of the pole piece was about It is 4.5mg cm ^-2 . Use 2032 button cells to prepare half batteries with lithium sheet as negative electrode, use Celgard 2035 diaphragm and high voltage electrolyte (mass ratio LiPF ₆ : EMC: FEC=15:55:30), this half battery is at 3-4.65V ( vs. Li/Li ⁺ ), the N/P ratio of the full battery is about 1.15, and the commercial graphite carbon microsphere (MCMB) anode material is provided by Shenzhen BTR New Energy Materials Company.

The analysis results of "LCO-LBO-1#" prepared in this example by Rietveld XRD show that the lithium layer in the bulk crystal structure of the material contains 1.6% cobalt, and the XPS semi-quantitative results show that the cobalt content in the lithium layer in the surface area is about around 45%, while the surface area thickness is less than 5nm. In this example, the charge and discharge curves of the new high-voltage lithium cobalt oxide "LCO-LBO-1#" cathode material at a current density of 0.1C between 3-4.65V (vs. Li/Li ⁺ ), as shown in Figure 3 . Among them, 1C=150mAh g ^-1 . The results show that the material has a reversible discharge capacity of 247mAh g ^-1 at a current density of 0.1C. At the same time, in this example, the new high-voltage lithium cobalt oxide “LCO-LBO-1#” positive electrode material has a capacity retention rate of 83.6% after 500 cycles of 5C cycles between 3-4.65V (vs. Li/Li ⁺ ), respectively. exhibited high electrochemical stability.

The above results show that the new high-voltage lithium cobalt oxide "LCO-LBO-1#" cathode material in this example has high capacity and cycle stability under high-voltage charge-discharge conditions.

Embodiment Four

In this example, on the basis of Example 1, the sintering temperature in step 1) and the heat treatment temperature in step 3) are respectively controlled to prepare lithium cobalt oxide layered cathode materials with different cobalt contents in the lithium layer. The specific parameters and test results of cobalt content are shown in Table 1.

Table 1 Lithium cobalt oxide layered positive electrode materials with different cobalt content in the lithium layer and their preparation parameters

The above thirteen kinds of lithium cobalt oxide layered cathode materials were tested by the same method as in Example 1, and the results are shown in Table 2.

Table 2 Test results of lithium cobalt oxide layered positive electrode materials with different cobalt content in the lithium layer

试验编号Test No.	可逆放电容量Reversible discharge capacity	5C循环500圈后容量保持率Capacity retention rate after 500 cycles of 5C cycle
11	231mAh g ^-1 231mAh g ^-1	85.3％85.3%
22	244mAh g ^-1 244mAh g ^-1	83.5％83.5%
33	251mAh g ^-1 251mAh g ^-1	80.3％80.3%
44	254mAh g ^-1 254mAh g ^-1	79.5％79.5%
55	236mAh g ^-1 236mAh g ^-1	73.2％73.2%
66	231mAh g ^-1 231mAh g ^-1	65.5％65.5%
77	224mAh g ^-1 224mAh g ^-1	43.5％43.5%
88	233mAh g ^-1 233mAh g ^-1	63.5％63.5%
99	250mAh g ^-1 250mAh g ^-1	80.5％80.5%
1010	251mAh g ^-1 251mAh g ^-1	83.5％83.5%

11

254mAh g ^-1

86.5%

The results in Table 2 show that when the cobalt content in the bulk lithium layer of the crystal structure is less than 0.1% or greater than 5%, the reversible discharge capacity is significantly reduced; when the cobalt content in the lithium layer in the surface interface region is not less than 30%, the 5C cycle After 500 cycles, the capacity retention rate increases significantly; the above results show that the lithium layer in the bulk phase of the crystal structure contains 0.1%-5% cobalt, and the lithium layer in the surface interface region contains no less than 30% cobalt. The reversible discharge capacity and capacity retention of the layered cathode material after 500 cycles at 5C are better. Moreover, when the bulk lithium layer contains no more than 3% cobalt, the reversible discharge capacity obviously increases with the increase of cobalt content in the lithium layer; however, when the cobalt content exceeds 3%, the reversible discharge capacity decreases instead. Therefore, preferably, the bulk lithium layer contains no more than 3% cobalt.

Embodiment five

In the new high-voltage lithium cobaltate in this example, the cobalt content in the lithium layer is 1.8%, and the surface area is a mixed element area containing Li, Co, Ti, O and F. In this example, high-temperature sintering, solution immersion, and subsequent heat treatment were used to synthesize a new high-voltage lithium cobaltate cathode material containing 1.8% Co in the lithium layer. Specifically include:

1) Synthesis and sintering of lithium cobalt oxide: mix battery-grade Li ₂ CO ₃ (Ganfeng Lithium Industry) and battery-grade Co ₃ O ₄ (Huayou Cobalt Industry, D ₅₀ = 4-8 microns) according to the Li/Co ratio of 1.03 After mixing the materials uniformly, sinter at 900° C. for 6 hours in an air atmosphere. The obtained lithium cobaltate particles were successively crushed by a pair of roller compactors, and sieved through a 200-mesh sieve. Then put the obtained lithium cobaltate powder into a microwave reaction device under an air atmosphere, and carry out secondary roasting under a microwave power of 400W. The heating time is 20min. After the sintering is completed, sieve through 200 mesh to prepare lithium cobaltate ,spare.

2) Solution immersion: Weigh 1 mol of lithium cobalt oxide prepared in step 1), add it into 1000 mL of deionized water, stir to form a black suspension, and pour it into a hydrothermal reaction kettle. During the stirring process, add 0.05 mol of lithium nitrate and 0.02 mol of titanyl sulfate to form solution A; weigh 0.060 mol of ammonium fluoride and dissolve it in 1000 mL of deionized water to form solution B; Solution B was added dropwise to solution A under the same conditions. After the liquid phase reaction is completed, use a vacuum filtration device to carry out suction filtration and cleaning, and bake in a blast oven at 80°C for 24 hours; the dried samples are sieved with a 100-mesh sieve and set aside.

3) Subsequent heat treatment: put the lithium cobalt oxide sample obtained in step 2) in a rotary tube furnace for subsequent heat treatment. After 12 hours of heat preservation, the temperature was naturally lowered; the obtained material was sieved through a 200-mesh sieve, and vacuum-packed and stored in an aluminum-plastic bag; the obtained material was named "LCO-LTOF".

4) Electrochemical test: Using NMP as a solvent, LCO-LTOF, carbon black and PVDF were uniformly mixed at a mass ratio of 8:1:1 to prepare a positive electrode sheet. The active material loading of the electrode sheet was about 4.5mg cm ^-2 . Use 2032 button cells to prepare half batteries with lithium sheet as negative electrode, use Celgard 2035 diaphragm and high voltage electrolyte (mass ratio LiPF ₆ : EMC: FEC=15:55:30), this half battery is at 3-4.65V ( vs. Li/Li ⁺ ), the N/P ratio of the full battery is about 1.15, and the commercial graphite carbon microsphere (MCMB) anode material is provided by Shenzhen BTR New Energy Materials Company.

The analysis results of the "LCO-LTOF" prepared in this example by Rietveld XRD show that the bulk crystal structure of the material contains 1.8% cobalt in the lithium layer, and the XPS semi-quantitative results show that the cobalt content in the lithium layer in the surface area is about 45%. , while the thickness of the surface area is less than 5nm. In this example, the new high-voltage lithium cobaltate “LCO-LTOF” cathode material has a reversible discharge capacity of 243mAh g ^-1 at a current density of 0.1C between 3-4.65V (vs. Li/Li ⁺ ). At the same time, in this example, the new high-voltage lithium cobalt oxide "LCO-LTOF-1#" positive electrode material has a capacity retention rate of 86.5% after 500 cycles at 5C between 3-4.65V (vs. Li/Li ⁺ ), respectively. exhibited high electrochemical stability.

In summary, the above results show that the novel high-voltage lithium cobalt oxide "LCO-LTOF" cathode material in this case has high capacity and cycle stability under high-voltage charge-discharge conditions.

According to the above embodiments and the inventor's test analysis, the lithium cobalt oxide layered positive electrode material of the present application can be obtained by sintering at 750-950° C. for 1-12 hours, and then treated by microwave or quenching process. Further, in order to increase the replacement of the surface interface area of the crystal structure, immersion in slightly acidic solution and heat treatment process can be added. The soaking solution contains Li ⁺ , and at least one of Mg ²⁺ , Al ³⁺ , borate, Ti ⁴⁺ and F ^- ; wherein, the solution contains Li ⁺ , mainly to ensure that the lithium layer in the surface interface region other elements are used to replace lithium and/or cobalt in the lithium layer in the surface interface region, cobalt in the cobalt layer, or oxygen. The soaking condition is 0-160°C soaking for 0.1-48h, and the stirring speed is maintained at 50-1000r/min during the whole process. The heat treatment condition is heating at 200-700°C for 0.1-36h in an inert atmosphere or a reducing atmosphere. Among the above parameter conditions, sintering conditions and heat treatment conditions are the key factors affecting the cobalt content in the lithium layer of the crystal structure bulk phase and surface interface; specifically, the sintering temperature directly affects the cobalt content of the bulk lithium layer. In principle, the sintering temperature The lower the bulk phase lithium layer, the higher the cobalt content; the heat treatment temperature directly affects the cobalt content of the surface interface lithium layer, the higher the heat treatment temperature, the higher the cobalt content of the surface interface lithium layer. Considering the reversible discharge capacity of the battery and the capacity retention rate after 500 cycles at 5C, the lithium layer in the bulk phase of the preferred crystal structure contains 0.1%-5% cobalt, and the lithium layer in the surface interface region contains not less than 30% cobalt cobalt.

According to the above analysis, it can be seen that the sintering process directly affects the elements of each layer of the crystal structure, and the solution immersion and heat treatment mostly affect the elements of the surface interface area of the crystal structure. Therefore, further, various metal elements can be doped in the bulk phase according to requirements, or replaced with other elements in the interface region. For example, other metal elements can be added during the sintering process to achieve bulk metal element doping. This doping can be doped in the bulk lithium layer and/or cobalt layer, for example, the bulk lithium layer is doped with Mg, cobalt The layer is doped with Al and/or Ti. However, since the lithium content of the bulk phase directly affects the amount of Li ⁺ that can be reversibly intercalated and deintercalated; therefore, the doping amount of the bulk metal element should not be too much. Generally speaking, the proportion of the doped metal element in the bulk phase should not exceed 1%. As for the element replacement in the interface region, it is mainly realized by solution immersion and heat treatment, for example, the lithium and/or cobalt in the lithium layer in the surface interface region are partially replaced by Mg, and the cobalt in the cobalt layer in the surface interface region is replaced by Al, B and At least one of Ti is partially substituted, and the oxygen in the surface interface region is partially or completely substituted by fluorine. It can be understood that the role of the surface interface region is mainly to conduct electricity and guide lithium, and not to participate in redox reactions, and to isolate the electrolyte; therefore, on the one hand, the cobalt content in the lithium layer in the interface region can exceed 30%; on the other hand , the proportion of metal elements replacing lithium and/or cobalt can also exceed 40%. The lithium layer in the interface area is replaced by a large amount of cobalt or metal elements, which can better conduct electricity, guide lithium, and isolate the electrolyte; of course, in order not to affect the reversible intercalation and extraction of Li ⁺ , the thickness of the surface interface area is generally less than Or equal to 5nm.

The above content is a further detailed description of the present application in conjunction with specific implementation modes, and it cannot be deemed that the specific implementation of the present application is limited to these descriptions. For those of ordinary skill in the technical field to which the present application belongs, some simple deduction or replacement can also be made without departing from the concept of the present application.

Claims

A lithium cobaltate layered positive electrode material, characterized in that: the lithium layer of the crystal structure of the lithium cobaltate layered positive electrode material contains cobalt.
The lithium cobalt oxide layered positive electrode material according to claim 1, characterized in that: the bulk phase of the crystal structure of the lithium cobalt oxide layered positive electrode material and the lithium layer in the surface interface region all contain cobalt, and the surface interface Cobalt and oxygen in the regional lithium layer form a cobalt-oxygen link structure;

Preferably, the cobalt in the lithium layer in the surface interface region and the cobalt oxygen in the cobalt layer are linked to each other, forming a connected network of cobalt oxygen structure on the surface of the lithium cobalt oxide layered positive electrode material;

Preferably, the lithium layer in the bulk phase of the crystal structure contains 0.1%-5% cobalt; more preferably, the lithium layer in the bulk phase contains no more than 3% cobalt;

Preferably, the lithium layer in the surface interface region contains not less than 30% cobalt.
The lithium cobalt oxide layered positive electrode material according to claim 2, characterized in that: the lithium and/or cobalt part in the lithium layer in the surface interface region is replaced by a metal element, and the metal element is Mg, Al, B and at least one of Ti;

Preferably, the lithium and/or cobalt in the lithium layer in the surface interface region is partially replaced by Mg, and the cobalt in the cobalt layer in the surface interface region is partially replaced by at least one of Al, B and Ti;

Preferably, the proportion of metal elements replacing lithium and/or cobalt in the lithium layer in the surface interface region is not less than 40%;

Preferably, the oxygen in the surface interface region is partially or completely replaced by fluorine.
The lithium cobaltate layered positive electrode material according to claim 3, characterized in that: the thickness of the surface interface region of the lithium cobaltate layered positive electrode material is less than or equal to 5 nm.
The lithium cobalt oxide layered positive electrode material according to claim 2, characterized in that: the bulk phase of the crystal structure is doped with metal elements, and the metal elements are doped in the lithium layer and/or the cobalt layer, the said The metal element is at least one of Mg, Al and Ti;

Preferably, the proportion of doped metal elements in the bulk phase is no more than 1%.
The lithium cobaltate layered positive electrode material according to any one of claims 1-5, characterized in that: the lithium cobaltate layered positive electrode material is primary micro-nano particles or secondary micro-nano particles;

Preferably, the particle size of the lithium cobalt oxide layered positive electrode material is 0.5-40 microns.
The preparation method of the lithium cobaltate layered positive electrode material according to any one of claims 1-6, characterized in that: after mixing the lithium source and the cobalt source, sintering at 750-950 ° C in an air atmosphere for 1 -12 hours, and then, carry out microwave or quenching process treatment to obtain the lithium cobalt oxide layered positive electrode material containing cobalt in the lithium layer of crystal structure.
The preparation method according to claim 7, characterized in that: it also includes mixing the metal element doped in the bulk phase of the crystal structure with the lithium source and the cobalt source and sintering to obtain the metal element doped in the bulk phase of the crystal structure Elemental lithium cobalt oxide layered positive electrode material;

Preferably, it also includes immersing the lithium cobaltate layered positive electrode material in a slightly acidic solution or the lithium cobaltate layered positive electrode material doped with metal elements in the crystal structure phase, and after the soaking is completed, it is heat-treated to obtain the surface interface region Lithium and/or cobalt in the lithium layer are partially replaced by metal elements, cobalt in the cobalt layer in the surface interface region is partially replaced by metal elements, or oxygen is partially or completely replaced by fluorine. Lithium cobaltate layered positive electrode material;

The slightly acidic solution contains Li + , and at least one of Mg 2+ , Al 3+ , borate, Ti 4+ and F - ;

The conditions for soaking in the slightly acidic solution are soaking at 0-160°C for 0.1-48h, and maintaining a stirring speed of 50-1000r/min throughout the process;

The heat treatment condition is heating at 200-700° C. for 0.1-36 hours, and the heat treatment atmosphere condition is an inert atmosphere or a reducing atmosphere.
Application of the lithium cobalt oxide layered positive electrode material according to any one of claims 1-6 in the preparation of power lithium batteries, or lithium ion batteries for 3C consumer electronics products, unmanned aerial vehicles or electronic cigarettes.
A lithium ion battery using the lithium cobaltate layered cathode material according to any one of claims 1-6.