CN111900473A - Lithium ion battery electrolyte for improving performance of anode material and lithium ion battery - Google Patents

Lithium ion battery electrolyte for improving performance of anode material and lithium ion battery Download PDF

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CN111900473A
CN111900473A CN202010684186.2A CN202010684186A CN111900473A CN 111900473 A CN111900473 A CN 111900473A CN 202010684186 A CN202010684186 A CN 202010684186A CN 111900473 A CN111900473 A CN 111900473A
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lithium
ion battery
lithium ion
electrolyte
performance
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CN111900473B (en
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潘洪革
姚智豪
高明霞
刘永锋
沈晓彦
徐嘉
王兴威
周建新
黄斌
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Jiangsu Highstar Battery Manufacturing Co ltd
Zhejiang University ZJU
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Jiangsu Highstar Battery Manufacturing Co ltd
Zhejiang University ZJU
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
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    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

The invention discloses a lithium ion battery electrolyte for improving the performance of a positive electrode material and a lithium ion battery4、LiAlH4And NaBH4At least one of (1). The lithium ion battery electrolyte for improving the performance of the anode material is prepared in a simple adding mode, the cycle performance, the capacity and the first coulombic efficiency of the anode material, particularly the lithium-rich manganese oxide anode material and the lithium ion battery thereof are effectively improved, and the discharge midpoint voltage of the material is not reduced.

Description

Lithium ion battery electrolyte for improving performance of anode material and lithium ion battery
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery electrolyte for improving the performance of a positive electrode material and a lithium ion battery.
Background
Lithium ion batteries have been widely used in portable electronic products, electric vehicles, hybrid vehicles, energy storage power stations, and other fields due to their high volume/weight energy storage density. Meanwhile, the performance requirements of the lithium ion battery are continuously improved. Currently, as key materials affecting the performance of lithium ion batteries, high-performance cathode materials and electrolytes matched with the high-performance cathode materials face many challenges. The development of high-performance lithium ion battery anode materials and electrolyte matched with the high-performance lithium ion battery anode materials is very key to the improvement of the performance of the lithium ion battery. And LiCoO as commercial positive electrode material2(capacity ≈ 140mAh/g), LiFePO4(capacity is approximately equal to 160mAh/g) and lithium manganate LiMn2O4(capacity is approximately equal to 120mAh/g) and nickel-cobalt-manganese ternary material LiNi1-x-yCoxMnyO2(0<x，y<1，0<x+y<1, more typically LiNi1/3Co1/3Mn1/3O2) (the capacity is approximately equal to 160-210 mAh/g), and the layered lithium-rich manganese oxide positive electrode material (the basic composition formula is xLi)2MnO3·(1-x)LiNi0.33Co0.33Mn0.33O2Wherein x is more than 0 and less than 1), the specific capacity is more than 260mAh/g (the discharge potential is 2.0-4.8V), and the preparation method also has the advantages of low cost, simple preparation process, high safety and the like, and is a high-capacity capacitor with great potentialAmount and high energy density of the positive electrode material.
However, the layered lithium-rich manganese oxide positive electrode material has the problems of poor cycling stability and rate capability, low first coulombic efficiency, voltage attenuation in the cycling process and the like, and the practical application of the layered lithium-rich manganese oxide positive electrode material is severely restricted. Transition Metal (TM) is dissolved in electrolyte in the circulation process of the layered lithium-rich manganese oxide positive electrode material, TM ions migrate in the circulation process, the rearrangement of a lithium-rich manganese crystal structure can be caused, and the layered structure part of the initial lithium-rich manganese oxide is converted to a spinel structure, so that the capacity and voltage attenuation of the layered lithium-rich manganese oxide positive electrode material in the circulation process are caused. In the first charge (delithiation reaction), lithium ions are derived from Li in the high potential region2MnO3The mid-extraction results in the release of oxygen and the formation of Li2O, resulting in its higher first irreversible capacity. In the cycle, oxygen deposition is always accompanied in the high-potential lithium removal process.
At present, the commonly used modification method for improving the electrochemical performance of the lithium-rich manganese positive electrode mainly modifies the components and the structure of the lithium-rich manganese positive electrode material, and mainly comprises the following steps: coating oxides on the surface of lithium-rich manganese material during the preparation of the material, such as Al2O3、CeO2ZnO and AlPO4Etc.; carrying out ion doping/substitution on the lithium-rich manganese material, such as doping and substitution of Mg, Fe and Ti; the content of Li, Ni, Mn, Co and other elements in the material is regulated, and the like, so that the component and structure stability of the lithium-rich manganese oxide positive electrode material is improved, the cycle performance of the lithium-rich manganese oxide positive electrode material is improved, the voltage decline in the cycle process is inhibited, and the first coulombic efficiency of the lithium-rich manganese oxide positive electrode material is improved. However, the problems of the contradiction between high capacity and low cycling stability of the lithium-rich manganese oxide cathode material and low coulombic efficiency of the lithium-rich manganese oxide cathode material for the first time are still not completely solved, and the large-scale application of the lithium-rich manganese oxide cathode material is hindered.
Disclosure of Invention
Aiming at the problems, the invention discloses a lithium ion battery electrolyte for improving the performance of a positive electrode material, which effectively improves the cycle performance, the capacity and the first coulombic efficiency of the positive electrode material, particularly a lithium-rich manganese oxide positive electrode material and a lithium ion battery thereof, and does not reduce the discharge midpoint voltage of the material.
The specific technical scheme is as follows:
the lithium ion battery electrolyte for improving the performance of the anode material comprises lithium salt, an anhydrous organic solvent and an additive, wherein the additive is selected from LiBH4、LiAlH4And NaBH4At least one of (1).
Preferably, the positive electrode material is selected from lithium manganate, nickel cobalt manganese ternary material or layered lithium-rich manganese oxide; further preferably, the positive electrode material is selected from layered lithium-rich manganese oxides.
The basic component of the layered lithium-rich manganese oxide cathode material adopts xLi2MnO3·(1-x)LiNi0.33Co0.33Mn0.33O2Wherein x is more than 0 and less than 1. Preferably, 0.4 < x < 0.6, and more preferably, x is 0.5. The layered lithium-rich manganese oxide cathode material with the preferred composition has good comprehensive electrochemical performance and is a variety commonly used in the field.
Besides the basic component, the layered lithium-rich manganese oxide cathode material also comprises a cathode material obtained by introducing metals such as Mg, Fe, Ti and the like through ion doping/substitution, or regulating and controlling the content of elements such as Li, Ni, Mn, Co and the like in the basic component.
Compared with the other two anode materials, the layered lithium-rich manganese oxide has higher specific capacity and better application prospect, but has the problems of poor cycle stability, low first coulombic efficiency and voltage attenuation in the cycle process.
According to the invention, the functional additive is added into the basic electrolyte, so that the component characteristics of the electrolyte are changed to improve the electrochemical performance of the anode material such as lithium manganate, nickel cobalt manganese ternary material or layered lithium-rich manganese oxide, and especially the electrochemical performance of the anode material of the lithium-rich manganese oxide is improved remarkably. Particularly, taking a lithium-rich manganese oxide cathode material as an example, the additive disclosed by the invention is LiBH4、LiAlH4And NaBH4Has strong or strong reducibility, and is reacted with electrolyte and/or lithium-rich manganese oxideThe cathode material reacts to form a protective film on the surface of the lithium-rich manganese oxide cathode material, wherein the protective film comprises unit or multi-element oxides of Li, B, Al and Na elements, so that the dissolution of active substances in the lithium-rich manganese cathode material in an electrolyte in a circulating process is inhibited, the corrosion of the electrolyte on the lithium-rich manganese cathode material is slowed down, and the stability of a crystal structure of the lithium-rich manganese material is improved. The strong or strong reducibility of the additive can also inhibit oxygen evolution reaction of the lithium-rich manganese oxide in the first and subsequent circulation processes, and stabilize electrode components and crystal structures. LiBH4、LiAlH4And NaBH4The lithium-rich manganese-based composite material has the advantages that the lithium-rich manganese-based composite material has good contact with lithium-rich manganese materials due to the dissolution characteristic in basic electrolyte, and the formed protective layer is uniform. The above multiple effects effectively improve the stability of the components, the crystal structure and the electrode morphology structure of the lithium-manganese-rich material in the circulation process, thereby achieving the technical effect of effectively improving the circulation stability, the capacity and the first coulomb efficiency of the lithium-manganese-rich electrode and the corresponding lithium ion battery thereof on the premise of not reducing the discharge midpoint voltage of the material.
Tests show that due to the complex reaction mechanism in the lithium ion battery electrolyte, additives with similar performance and strong or strong reducibility, such as LiH and NaAlH, are adopted4However, the cycling stability, capacity and first coulombic efficiency of the lithium-rich manganese electrode and the corresponding lithium ion battery cannot be effectively improved.
The basic electrolyte adopted by the invention is a lithium ion battery electrolyte which is well known in the technical field, and the components of the basic electrolyte comprise lithium salt and anhydrous organic solvent. The lithium salt is selected from at least one of lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium bistrifluoromethanesulfonylimide and lithium bisoxalato borate. The anhydrous organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate and propyl butyrate.
Preferably, in the lithium ion battery electrolyte, the molar concentration of lithium salt is 0.5-2M; more preferably 0.8 to 1.2M.
Further preferably, the composition of the base electrolyte is:
1M lithium hexafluorophosphate, using an anhydrous organic solvent of Ethylene Carbonate (EC) in a weight ratio of 1:1: 1: diethyl carbonate (DEC): ethyl Methyl Carbonate (EMC);
1M lithium bis (oxalato) borate (LiBOB), with the solvent EC: DEC;
1M LiClO4(lithium perchlorate), the solvent is EC: DMC (dimethyl carbonate).
Preferably, the mass of the additive is 0.05-1.00 wt% of the total mass of the lithium ion battery electrolyte; more preferably 0.10 to 0.50 wt%. Preferably 0.10-0.30 wt%; still more preferably 0.10 wt%.
Further preferably, the additive is selected from LiBH4。
Tests show that the cycle stability, the capacity and the first coulombic efficiency of the finally prepared lithium ion battery are improved continuously by continuously optimizing the types and the contents of the additives.
The invention also discloses a lithium ion battery, which comprises a positive electrode material, a negative electrode material and electrolyte, wherein the electrolyte is selected from the lithium ion battery electrolyte.
The positive electrode material is selected from lithium manganate, nickel cobalt manganese ternary materials or layered lithium-rich manganese oxide, and further preferably layered lithium-rich manganese oxide.
The negative electrode material is a lithium ion battery negative electrode material well known in the technical field, and includes but is not limited to at least one of a carbon-based negative electrode material, a metal oxide-based negative electrode material, a Si-based negative electrode material and a Sn-based negative electrode material.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a lithium ion battery electrolyte for improving the performance of a positive electrode material, which adopts a mode of directly adding an additive into a basic electrolyte, and has the advantages of simple method and easy operation.
The invention discloses a special additive which is LiBH4、LiAlH4And NaBH4At least one of the positive electrode material and the lithium-rich manganese oxide positive electrode material has strong or strong reducibility and specific element composition, and the stability of components, crystal structures and electrode morphology structures of the positive electrode material, especially the lithium-rich manganese oxide positive electrode material, in the circulation process is effectively improved through multiple effects.
Drawings
Fig. 1 is a graph of a battery assembled with the lithium manganese rich positive electrode material of the electrolyte prepared in example 1, showing (a) a first charge-discharge curve at a charge-discharge current density of 20mA/g, (b) a cycle performance curve at a charge-discharge current density of 20mA/g, (c) a cycle performance curve at a charge-discharge current density of 200mA/g, (d) a change in a discharge midpoint voltage at a charge-discharge current density of 20mA/g during a cycle, (e) a positive electrode sheet SEM morphology after 150 cycles of charge-discharge at 20mA/g, (f) a positive electrode sheet SEM morphology after 300 cycles of charge-discharge at 200mA/g, and (g) an SEM morphology of an initial positive electrode sheet before charge-discharge;
fig. 2 is a graph of the first charge and discharge curves at (a)20mA/g charge and discharge current density, (b) the cycle performance curves at 20mA/g charge and discharge current density, (c) the cycle performance curves at 200mA/g charge and discharge current density, and (d) the change in discharge midpoint voltage at 20mA/g charge and discharge current density over the course of a cycle for a battery assembled with a lithium manganese rich positive electrode material using the electrolyte prepared in example 2;
fig. 3 is a graph of the first charge and discharge curve at 20mA/g charge and discharge current density, (b) the cycle performance curve at 20mA/g charge and discharge current density, (c) the cycle performance curve at 200mA/g charge and discharge current density, (d) the SEM morphology of the positive plate after 150 cycles at 20mA/g charge and discharge current density, (e) the SEM morphology of the positive plate after 300 cycles at 200mA/g charge and discharge current density for a battery assembled with the lithium manganese rich positive electrode material of the electrolyte prepared in example 3;
FIG. 4 is a graph of cycling performance at 20mA/g charge-discharge current density for a battery assembled with a lithium manganese rich positive electrode material using the electrolyte prepared in example 4;
FIG. 5 is a graph of cycling performance at 20mA/g charge-discharge current density for a battery assembled with a lithium manganese rich positive electrode material using the electrolyte prepared in example 5;
FIG. 6 is a graph of cycling performance at 20mA/g charge-discharge current density for a battery assembled with a lithium manganese rich positive electrode material using the electrolyte prepared in example 6;
fig. 7 is a graph of the first charge and discharge curve at 20mA/g charge and discharge current density, (b) the cycle performance curve at 20mA/g charge and discharge current density, (c) the cycle performance curve at 200mA/g charge and discharge current density, (d) the change in discharge midpoint voltage at 20mA/g charge and discharge current density during cycling, (e) the SEM morphology of the lithium-manganese-rich positive plate after 150 cycles at 20mA/g charge and discharge current density, (f) the SEM morphology of the lithium-manganese-rich positive plate after 300 cycles at 200mA/g charge and discharge current density for a battery assembled with the lithium-manganese-rich positive material of the base electrolyte of comparative example 1;
fig. 8 is a first charge-discharge curve (a) and a cycle performance curve (b) at a charge-discharge current density of 20mA/g for a battery assembled with a lithium-manganese rich cathode material of the electrolyte prepared in comparative example 2;
fig. 9 is a first charge-discharge curve (a) and a cycle performance curve (b) at a charge-discharge current density of 20mA/g for a battery assembled with a lithium-manganese rich cathode material of the electrolyte prepared in comparative example 3.
Detailed Description
The present invention is further illustrated by the following specific examples, but the scope of the present invention is not limited to the following examples.
Example 1
The formulation of a 0.1 wt% LiBH in a glove box filled with high purity argon4The electrolyte of the additive adopts a basic electrolyte of lithium hexafluorophosphate with the lithium salt concentration of 1M and adopts an anhydrous organic solvent of Ethylene Carbonate (EC) with the weight ratio of 1:1: 1: diethyl carbonate (DEC): and (4) methyl ethyl carbonate (EMC) and uniformly mixing. LiBH accounting for 0.1 wt% of the total weight of the electrolyte is added into the basic electrolyte4And uniformly mixing to obtain the required electrolyte.
The electrolyte is used for assembling a test battery, a 2025 button cell is adopted, and the electrolyte is usedThe cathode material is 0.5Li2MnO3·0.5LiNi0.33Co0.33Mn0.33O2The lithium-rich manganese material has a particle size of about 200-500 nm, Super P is used as a conductive agent, and sodium carboxymethylcellulose (CMC) is used as a binder, and the weight ratio of the Super P to the CMC is 85:10: 5. The reference electrode and the counter electrode are metal lithium sheets, and the diaphragm is Celgard-2400.
And testing the cycle performance of the assembled battery at room temperature within the range of 2.0-4.8V vs. lithium potential at 20mA/g and 200mA/g current density respectively, wherein the adopted electrochemical tester is a Shenzhen Xinwei battery testing system (Neware BTS-610). Disassembling the recycled battery in a glove box, cleaning the disassembled positive pole piece by using dimethyl carbonate (DMC), and removing residual LiPF on the surface6And observing the surface appearance of the substances by adopting a Scanning Electron Microscope (SEM), and observing the surface appearance change of the electrode after circulation.
Fig. 1(a) is a first charge-discharge curve of the lithium-manganese-rich positive electrode of the embodiment at a current density of 20mA/g, the first specific discharge capacity is 272mAh/g, the first irreversible capacity is 66mAh/g, and the first coulombic efficiency is 80%. And comparative example 1, using no LiBH addition4Compared with the positive electrode performance of the electrolyte, the first discharge specific capacity and the first coulombic efficiency of the lithium-manganese-rich positive electrode material are effectively improved by adopting the electrolyte. FIGS. 1(b) and (c) are graphs of the cycling performance of lithium-rich manganese anodes at 20mA/g and 200mA/g current densities, respectively. Under 20mA/g, the discharge specific capacity is kept at 242mAh/g after 150 cycles, and the capacity retention rate is 88.9%. Under 200mA/g, the first discharge specific capacity is 212mAh/g, the discharge specific capacity after 300 cycles is 196mAh/g, and the capacity retention rate is 92.4%. Compared with the comparative example 1, the electrolyte can effectively improve the discharge specific capacity, the cycling stability and the first coulombic efficiency of the lithium-manganese-rich cathode material. Fig. 1(d) shows the change of the discharge midpoint voltage of the lithium-rich manganese positive electrode material of the present example during the cycle at 20 mA/g. Compared with the comparative example 1, the discharge midpoint voltages of the two are basically equal, which shows that the discharge midpoint voltage of the material is not reduced by adopting the electrolyte of the invention on the premise of improving the cycle performance and the first coulombic efficiency of the electrode.
FIGS. 1(e) and (f) are surface SEM appearances of lithium-rich manganese positive electrode sheets after the test cells are cycled for 150 and 300 times at 20mA/g and 200mA/g current densities, respectively, and surface cracks of the electrode sheets are fewer under the two cycling conditions. FIG. 1(g) is an SEM topography of the surface of an initial lithium manganese rich positive plate. In contrast, in comparative example 1, a large number of cracks were generated on the surface of the positive electrode after the corresponding cycles (fig. 7(e) to (f)). The comparison shows that the electrolyte provided by the invention has an obvious stabilizing effect on the positive electrode structure, and can effectively prevent the cracking of the lithium-rich manganese positive electrode active material. In addition, under the two circulation conditions, the surface cracks of the pole piece are less, the pulverization degree of the lithium-rich manganese material particles is low, and the change is smaller compared with the initial morphology.
Example 2
The formulation of a 0.3 wt% LiBH in a glove box filled with high purity argon4The electrolyte of the additive, the base electrolyte used, was the same as in example 1. Adding LiBH accounting for 0.3 wt% of the total weight of the electrolyte into a base electrolyte4And uniformly mixing to obtain the required electrolyte. The capacity and the cycle performance of the lithium-rich manganese anode material are tested by adopting the electrolyte. The lithium-rich manganese cathode material used was the same as in example 1. The preparation of the lithium-rich manganese positive electrode and the preparation method of the test cell were the same as in example 1, except that the electrolyte was different. The electrochemical performance of the lithium manganese rich positive electrode was tested using the same test method as in example 1.
Fig. 2(a) is a first charge-discharge curve of the lithium-manganese-rich cathode material of the present embodiment under the charge-discharge condition of 20mA/g, the first specific discharge capacity is 280mAh/g, the first irreversible capacity is 79mAh/g, and the first coulombic efficiency is 78.0%, and compared with comparative example 1, the first specific discharge capacity and the first coulombic efficiency are both improved. FIGS. 2(b) and (c) are graphs of the cycling performance of lithium-rich manganese cathode materials at 20mA/g and 200mA/g current densities, respectively. Under the condition of charging and discharging of 20mA/g, the specific discharge capacity after 150 cycles is kept to be 247mAh/g, and the capacity retention rate is 88.3%. Under the charging and discharging condition of 200mA/g, the first discharging specific capacity is 222mAh/g, the discharging specific capacity after 300 cycles is kept to be 191mAh/g, and the capacity retention rate is 86.2%. Compared with the comparative example 1, the electrolyte can effectively improve the specific discharge capacity and the cycling stability of the lithium-manganese-rich cathode material. FIG. 2(d) is the change in discharge midpoint voltage during cycling at 20mA/g for the Li-Mn rich cathode material of this example. Compared with the comparative example 1, the discharge midpoint voltages of the two are basically equal, which shows that the discharge midpoint voltage of the material is not reduced by adopting the electrolyte of the invention on the premise of improving the cycle performance and the first coulombic efficiency of the electrode.
Example 3
The formulation of a 0.5 wt% LiBH in a glove box filled with high purity argon4The electrolyte of the additive, the base electrolyte used, was the same as in example 1. Adding LiBH accounting for 0.5 wt% of the total weight of the electrolyte into a base electrolyte4And uniformly mixing to obtain the required electrolyte. The capacity and the cycle performance of the lithium-rich manganese anode material are tested by adopting the electrolyte. The lithium-rich manganese cathode material used was the same as in example 1. The preparation of the lithium-rich manganese positive electrode and the preparation method of the test cell were the same as in example 1, except that the electrolyte was different. The electrochemical performance of the lithium manganese rich positive electrode was tested using the same test method as in example 1.
Fig. 3(a) is a first charge-discharge curve of the lithium-manganese-rich cathode material of this embodiment under the charge-discharge condition of 20mA/g, the first specific discharge capacity of 276mAh/g, the first irreversible capacity of 71mAh/g, and the first coulombic efficiency of 79.0%, and compared with comparative example 1, the first specific discharge capacity and the first coulombic efficiency are both improved. FIGS. 3(b) and (c) are graphs of cycling performance of lithium-rich manganese cathode materials at 20mA/g and 200mA/g current densities, respectively. Under the condition of the charge-discharge current density of 20mA/g, the discharge specific capacity after 150 cycles is 212mAh/g, and the capacity retention rate is 77.1%. Under the charging and discharging current density of 200mA/g, the first discharging specific capacity is 224mAh/g, the discharging specific capacity after 300 cycles is 197mAh/g, and the capacity retention rate is 87.8%. Compared with the comparative example 1, the electrolyte can effectively improve the specific discharge capacity and the cycling stability of the lithium-manganese-rich cathode material.
The recycled battery is disassembled in a glove box, the disassembled lithium-manganese-rich positive plate is cleaned by dimethyl carbonate (DMC), and residual LiPF on the surface is removed6And observing the surface appearance of the substances by adopting SEM, and observing the surface appearance change of the electrode after circulation.
Fig. 3(d) and (e) are SEM images of the lithium-rich manganese positive electrode sheet after the test cell was cycled 150 and 300 times at 20mA/g and 200mA/g current densities, respectively, and it can be seen that the positive electrode sheet cracked on the surface after cycling, but the degree of cracking was significantly lower than that of comparative example 1, but was slightly more severe than that of example 1.
Example 4
The preparation of a high purity argon-filled glove box containing 0.5 wt% NaBH4The electrolyte of the additive, the base electrolyte used, was the same as in example 1. Adding NaBH accounting for 0.5 wt% of the total weight of the electrolyte into a basic electrolyte4And uniformly mixing to obtain the required electrolyte. The capacity and the cycle performance of the lithium-rich manganese anode material are tested by adopting the electrolyte. The lithium-rich manganese cathode material used was the same as in example 1. The preparation of the lithium-rich manganese positive electrode and the preparation method of the test cell were the same as in example 1, except that the electrolyte was different. The electrochemical performance of the lithium manganese rich positive electrode was tested using the same test method as in example 1.
FIG. 4 is a cycle performance curve of the battery tested in this embodiment at a current density of 20mA/g, the first specific discharge capacity is 268mAh/g, the specific discharge capacity after 150 cycles is 215mAh/g, and the capacity retention rate is 80.2%. The first coulombic efficiency was 76%. Compared with the comparative example 1, the electrolyte can effectively improve the cycling stability of the lithium-rich manganese anode material. However, compared with the electrolyte prepared in the embodiments 1 to 3, the lithium-manganese-rich positive electrode prepared in the embodiments of the present invention has slightly low first discharge capacity, cycle stability and first coulombic efficiency.
As can be seen from the appearance characterization of SEM, after the battery assembled in the embodiment is cycled for 150 times under the current density of 20mA/g, the surface cracks of the lithium-rich manganese positive pole piece are less.
Example 5
LiAlH with a content of 0.2 wt% was prepared in a glove box filled with high purity argon4Electrolyte of additive, and the adopted basic electrolyte is 1M LiClO4(lithium perchlorate) and the solvent is EC (ethylene carbonate) with the weight ratio of 1: DMC (dimethyl carbonate). LiAlH is added into the basic electrolyte and accounts for 0.2 wt% of the total weight of the electrolyte4And uniformly mixing to obtain the required electrolyte. MiningThe electrolyte is used for testing the capacity and the cycle performance of the lithium-rich manganese cathode material. The lithium-rich manganese cathode material used was the same as in example 1. The preparation of the lithium-rich manganese positive electrode and the preparation method of the test cell were the same as in example 1, except that the electrolyte was different. The electrochemical performance of the lithium manganese rich positive electrode was tested using the same test method as in example 1.
FIG. 5 is a cycle performance curve of the lithium-rich manganese positive electrode material using the electrolyte of example 5 of the present invention at a charge/discharge current density of 20 mA/g. The first discharge specific capacity is 266mAh/g, the discharge specific capacity after 150 cycles is 205mAh/g, and the capacity retention rate is 77.0%. The first coulombic efficiency was 80.1%. By adopting the electrolyte of the embodiment, the cycle performance and the first coulombic efficiency of the lithium-manganese-rich cathode material are obviously improved.
As can be seen from the appearance characterization of SEM, after the battery assembled in the embodiment is cycled for 150 times under the current density of 20mA/g, the surface cracks of the lithium-rich manganese positive pole piece are less.
Example 6
The formulation of a 0.1 wt% LiBH in a glove box filled with high purity argon4+0.1wt％LiAlH4The electrolyte of the additive adopts 1M lithium bis (oxalato) borate (LiBOB) as a basic electrolyte, and the solvent is EC (ethylene carbonate) with the weight ratio of 1: DEC (diethyl carbonate). Respectively adding LiBH accounting for 0.1 wt% of the total weight of the electrolyte into the basic electrolyte4And 0.1 wt% LiAlH4And uniformly mixing to obtain the required electrolyte. The capacity and the cycle performance of the lithium-rich manganese anode material are tested by adopting the electrolyte. The lithium-rich manganese cathode material used was the same as in example 1. The preparation of the lithium-rich manganese positive electrode and the preparation method of the test cell were the same as in example 1, except that the electrolyte was different. The electrochemical performance of the lithium manganese rich positive electrode was tested using the same test method as in example 1.
By adopting the electrolyte of the embodiment, the cycle performance and the first coulombic efficiency of the lithium-manganese-rich cathode material are obviously improved. FIG. 6 is a graph showing the cycle performance of the lithium-rich manganese positive electrode material using the electrolyte of example 6 of the present invention at a charge/discharge current density of 20 mA/g. The first discharge specific capacity is 270mAh/g, the discharge specific capacity after 150 cycles is 207mAh/g, and the capacity retention rate is 76.7%. The first coulombic efficiency was 79.0%. By adopting the electrolyte of the embodiment, the cycle performance and the first coulombic efficiency of the lithium-manganese-rich cathode material are improved.
As can be seen from the appearance characterization of SEM, after the battery assembled in the embodiment is cycled for 150 times under the current density of 20mA/g, the surface cracks of the lithium-rich manganese positive pole piece are less.
Comparative example 1
The same basic electrolyte as in example 1 was used, i.e. lithium hexafluorophosphate was used in a concentration of 1M as the lithium salt and Ethylene Carbonate (EC) was used in a weight ratio of 1:1:1 as the anhydrous organic solvent: diethyl carbonate (DEC): ethyl Methyl Carbonate (EMC) and mixing well without adding other additives. The same lithium-rich manganese cathode material as in example 1 was used. The positive electrode sheet and test cell were prepared as in example 1. The method for testing the electrochemical performance of the lithium-manganese-rich cathode material is the same as that of example 1.
Disassembling the circulated battery in a glove box, cleaning the disassembled positive pole piece by using DMC (DMC), and removing residual LiPF on the surface6And observing the surface appearance under a scanning electron microscope.
Fig. 7(a) is a first charge-discharge curve of the positive electrode material of the comparative example at a current density of 20mA/g, the first specific discharge capacity is 263mAh/g, the first irreversible capacity is 88mAh/g, and the first coulombic efficiency is 75.1%, and both the first specific discharge capacity and the first coulombic efficiency are lower than those of the embodiment of the present invention. FIGS. 7(b) and (c) are graphs of the cycling performance of the cell at 20mA/g and 200mA/g current densities, respectively. Under 20mA/g, the discharge specific capacity is 178mAh/g after 150 cycles, and the capacity retention rate is 67.7%. Under 200mA/g, the first discharge specific capacity is 207mAh/g, the discharge specific capacity after 300 cycles is 169mAh/g, and the capacity retention rate is 81.8%, so that the discharge specific capacity and the cycle stability of the lithium ion battery are lower than those of the lithium ion battery disclosed by the embodiment of the invention. FIG. 7(d) is a graph of the change in discharge midpoint voltage during cycling at 20mA/g for the lithium manganese rich positive electrode material of this comparative example.
FIGS. 7(e) and (f) are SEM images of the surface of the positive plate of the present example after 150 and 300 cycles at current densities of 20mA/g and 200mA/g, and it can be seen that the surface of the positive plate after cycles both have cracks, indicating that the structure of the positive plate is seriously damaged during the cycles.
Comparative example 2
The same basic electrolyte as in example 1 was used, to which 0.5 wt% of NaAlH was added4. The same lithium-rich manganese cathode material as in example 1 was used. The positive electrode sheet and test cell were prepared as in example 1. The method for testing the electrochemical performance of the lithium-manganese-rich cathode material is the same as that of example 1.
Fig. 8 is a first charge-discharge curve (a) and a cycle performance curve (b) of the lithium-manganese-rich cathode material of the electrolyte prepared in the present comparative example at a current density of 20 mA/g. The first discharge capacity is 257mA/g, and the first coulombic efficiency is 74.6%. Under 20mA/g, the specific discharge capacity after 100 cycles is 195mAh/g, the capacity retention rate is only 75.7 percent, and the first discharge capacity, the first coulombic efficiency, the cycle performance and the average ratio of the discharge capacity to the capacity retention rate are realized by adopting the method without adding NaAlH4The base electrolyte of (2) is still low.
Comparative example 3
The same base electrolyte as in example 1 was used, to which 0.5 wt% LiH was added. The same lithium-rich manganese cathode material as in example 1 was used. The positive electrode sheet and test cell were prepared as in example 1. The method for testing the electrochemical performance of the lithium-manganese-rich cathode material is the same as that of example 1.
Fig. 9 is a first charge-discharge curve (a) and a cycle performance curve (b) of the lithium-manganese-rich cathode material of the electrolyte prepared in the present comparative example at a current density of 20 mA/g. The first discharge capacity is 265mA/g, and the first coulombic efficiency is only 64.3%. Under 20mA/g, the discharge specific capacity after 50 cycles is 228mAh/g, and the capacity retention rate is 86.1%, but after 50 cycles, the capacity is rapidly reduced, after 80 cycles, the capacity is only 165mAh/g, and the capacity retention rate is only 62.6%. The first coulombic efficiency, the cycle performance and the discharge capacity of the electrolyte are lower than those of the electrolyte adopting a basic electrolyte without adding LiH.
The following table 1 summarizes electrochemical properties of the lithium-rich manganese positive electrode material using the electrolytes of examples 1 to 7 and comparative examples 1 to 3 at a charge/discharge current density of 20 mA/g. The following table 2 summarizes electrochemical properties of the lithium-rich manganese cathode material using the electrolytes of examples 1 to 3 and comparative example 1 at a charge/discharge current density of 200 mA/g.
TABLE 1
Figure BDA0002586899410000141
TABLE 2
Figure BDA0002586899410000142

Claims (10)

1. The lithium ion battery electrolyte for improving the performance of the cathode material comprises lithium salt, an anhydrous organic solvent and an additive, and is characterized in that the additive is selected from LiBH4、LiAlH4And NaBH4At least one of (1).
2. The lithium ion battery electrolyte for improving the performance of the cathode material according to claim 1, wherein the mass of the additive is 0.05 to 1.00 wt% of the total mass of the lithium ion battery electrolyte.
3. The lithium ion battery electrolyte for improving the performance of a cathode material according to claim 1, wherein the lithium salt is at least one selected from lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium bistrifluoromethanesulfonylimide and lithium bisoxalato borate.
4. The lithium ion battery electrolyte for improving the performance of a positive electrode material according to claim 1, wherein the anhydrous organic solvent is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate and propyl butyrate.
5. The lithium ion battery electrolyte for improving the performance of the cathode material according to claim 1, wherein the molar concentration of lithium salt in the lithium ion battery electrolyte is 0.5-2M.
6. The lithium ion battery electrolyte solution for improving the performance of a cathode material according to claim 1, wherein the cathode material is selected from lithium manganate, nickel cobalt manganese ternary material or layered lithium-rich manganese oxide.
7. The lithium ion battery electrolyte for improving the performance of a cathode material according to claim 1, wherein the cathode material is selected from a layered lithium-rich manganese oxide;
the basic component of the layered lithium-rich manganese oxide is xLi2MnO3·(1-x)LiNi0.33Co0.33Mn0.33O2Wherein x is more than 0.4 and less than 0.6.
8. The lithium ion battery electrolyte for improving the performance of the cathode material according to any one of claims 1 to 7, wherein the mass of the additive is 0.10 to 0.50 wt% of the total mass of the lithium ion battery electrolyte.
9. A lithium ion battery comprises a positive electrode material, a negative electrode material and an electrolyte, and is characterized in that the electrolyte is selected from the lithium ion battery electrolyte according to any one of claims 1 to 8.
10. The lithium ion battery of claim 9, wherein the negative electrode material is selected from at least one of a carbon-based negative electrode material, a metal oxide-based negative electrode material, a Si-based negative electrode material, and a Sn-based negative electrode material.
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