CN110600806A

CN110600806A - Lithium ion battery electrolyte and lithium ion battery containing same

Info

Publication number: CN110600806A
Application number: CN201910882998.5A
Authority: CN
Inventors: 古兴兴; 赖超
Original assignee: Chongqing Technology and Business University
Current assignee: Chongqing Technology and Business University
Priority date: 2019-09-18
Filing date: 2019-09-18
Publication date: 2019-12-20
Also published as: CN111276748B; CN111276748A

Abstract

The invention relates to a lithium ion battery electrolyte and a lithium ion battery containing the same, belonging to the technical field of energy materials. The content and the type of the octylphenol polyoxyethylene ether in the electrolyte are reasonably controlled, so that the finally formed electrolyte has excellent lithium-philic performance, and is combined with lithium ions to form a stable polyether/lithium complex, and the uniform deposition of the lithium ions can be regulated. Meanwhile, the formed polyether/lithium complex can be self-assembled to form a template for constructing a stable SEI film, so that the growth of lithium dendrites is limited, and the cycle life of a lithium negative electrode is prolonged. The viscosity of the electrolyte is reduced by controlling the content of the octyl phenol polyoxyethylene ether in the electrolyte, and Li is further improved⁺The tolerance of the lithium negative electrode to high current density is improved by transmission in the charging and discharging processes. The lithium ion battery containing the electrolyte has excellent cycle performance and rate capability.

Description

Lithium ion battery electrolyte and lithium ion battery containing same

Technical Field

The invention belongs to the technical field of energy materials, and particularly relates to a lithium ion battery electrolyte and a lithium ion battery containing the same.

Background

Along with the increasing demand of the modern society on energy storage of portable equipment, electric automobiles and large-scale power grids, the rapid penetration of high-energy-density lithium batteries is stimulatedThe development of (1). Li-O₂And Li-S batteries have attracted increasing attention due to the combination of a high capacity positive electrode with a highest capacity metallic lithium negative electrode, but with Li-O₂And the intensive research of Li-S batteries, it was found that a great obstacle to their commercialization was actually the problem of metallic lithium negative electrodes, not their positive electrodes. Among the major problems with metallic lithium negative electrodes are the growth of lithium dendrites, infinite volume change and extreme instability of the solid-liquid interfacial film (SEI). In the past decades, researchers have developed strategies to solve the challenges of metallic lithium cathodes, such as replacing metallic lithium with a metallic lithium alloy as a cathode, designing a two-dimensional and three-dimensional material to load metallic lithium, modifying a separator, developing a new electrolyte or optimizing the components of the electrolyte, and artificially constructing a robust and electrochemically stable metallic lithium cathode protection layer, etc., in the above solutions, the components of the electrolyte are modified to construct a robust SEI film, which not only effectively inhibits the growth of lithium dendrites and reduces the continuous consumption of the electrolyte, but also effectively avoids the disadvantages of increased cost and reduced specific energy density of the battery, such as modification of the separator and construction of an artificial protection layer.

Polyoxyethylene (PEO) compounds have been studied in the lithium battery field for decades as a solid polymer electrolyte with great development prospects (Journal of the Electrochemical Society,1998,145, 2340-. Because ether chains on polyoxyethylene can combine with lithium ions to form PEO/Li salt complexes, and Li⁺Directional movement in nanochannels formed by PEO chains can also accelerate Li⁺Thereby improving the ionic conductivity, and thus PEO-based compounds are used as electrolyte additives to adjust Li⁺Uniform deposition, achieving a conductive ionic surface to address the problem of lithium dendrite growth is highly feasible. Researchers have tried to improve the cycling stability of a PEO compound, polyethylene glycol dimethyl ether (PEGDME), as an electrolyte additive for protecting lithium negative electrodes (Journal of the Electrochemical Society,1998,145, 2340-. But because a layer of stability is not formedThe SEI film is fixed, so that the electrolyte is continuously consumed, and thus the assembled lithium battery cannot maintain a long cycle life. Therefore, an effective PEO electrolyte additive was sought, on the one hand in combination with Li⁺So that the lithium deposition is uniform; on the other hand, a firm and stable SEI film is formed, and continuous consumption of additives and electrolyte is avoided; not only is the technical innovation on the electrolyte modification strategy, but also has theoretical guiding significance on screening of the electrolyte additive of the metal lithium battery.

Disclosure of Invention

In view of the above, an object of the present invention is to provide an electrolyte for a lithium ion battery; the second purpose is to provide a lithium ion battery containing the electrolyte. The invention is subsidized by the natural science fund project in Chongqing city, and the subsidized project number is as follows: cstc2019jcyj-msxm 1407; the youth project of the science and technology research project of the Chongqing city is funded, and the funded project number is as follows: KJQN 201800808.

In order to achieve the purpose, the invention provides the following technical scheme:

1. the electrolyte of the lithium ion battery contains lithium hexafluorophosphate, propylene carbonate, ethylene carbonate, diethyl carbonate and octyl phenol polyoxyethylene ether.

Preferably, the volume fraction of the octylphenol polyoxyethylene ether in the electrolyte is 5-8%.

Preferably, the octylphenol polyoxyethylene ether is one of octylphenol polyoxyethylene ether OP-7, octylphenol polyoxyethylene ether OP-10 or octylphenol polyoxyethylene ether OP-15.

Preferably, the polyoxyethylene octylphenol ether is polyoxyethylene octylphenol ether OP-10, and the volume fraction of the polyoxyethylene octylphenol ether OP-10 in the electrolyte is 5%.

Preferably, the concentration of lithium hexafluorophosphate in the electrolyte is 0.5 to 1.5 mol/L.

Preferably, the volume ratio of the propylene carbonate to the ethylene carbonate to the diethyl carbonate in the electrolyte is 0.5-1.5:3.5-4.5: 4.5-5.5.

2. The lithium ion battery containing the lithium ion battery electrolyte.

The invention has the beneficial effects that: the invention provides a lithium ion battery electrolyte and a lithium ion battery containing the same, wherein the content and the type of octyl phenol polyoxyethylene ether in the electrolyte are reasonably controlled, so that the finally formed electrolyte has excellent lithium affinity, and is combined with lithium ions to form a stable polyether/lithium complex, thereby being capable of regulating and controlling the uniform deposition of the lithium ions. Meanwhile, the formed polyether/lithium complex can be self-assembled to form a template for constructing a stable SEI film, so that the growth of lithium dendrites is limited, and the cycle life of a lithium negative electrode is prolonged. In addition, the content of the octylphenol polyoxyethylene ether in the electrolyte is controlled, so that the viscosity of the electrolyte is reduced, and Li is promoted⁺The tolerance of the lithium negative electrode to high current density is improved by transmission in the charging and discharging processes. When the electrolyte is used for assembling a lithium ion battery, the battery has excellent cycle performance and rate performance.

Drawings

In order to make the object, technical scheme and beneficial effect of the invention more clear, the invention provides the following drawings for explanation:

FIG. 1 is a graph of the cycle performance test results for 5 Li | Li symmetric cells of example 1;

FIG. 2 is a graph showing Zeta potential measurement results of 5 kinds of Li | Li symmetrical batteries in example 1;

FIG. 3 is a graph of the cycle performance test results for 5 Li | Li symmetric cells of example 2;

FIG. 4 is a graph showing Zeta potential measurement results of 5 kinds of Li | Li symmetrical batteries in example 2;

FIG. 5 is a graph of the contact angle test results on lithium negative electrodes in 5 Li | Li symmetric cells and lithium negative electrodes in a control cell in example 2;

FIG. 6 is a graph of the results of viscosity tests on lithium negative electrodes in 5 Li | Li symmetric cells and lithium negative electrodes in a control cell in example 2;

FIG. 7 is a graph showing the results of tests on the effect of OP-10 on lithium dendrite growth of a Li | Li symmetric cell in example 3; (a in FIG. 7 is a graph showing the result of Li dendrite growth test for Li | Li symmetric battery in-situ test containing blank electrolyte, and b in FIG. 7 is a graph showing the result of Li dendrite growth test for Li | Li symmetric battery in-situ test containing OP-10 electrolyte with a volume fraction of 5%)

FIG. 8 is a graph showing the results of differential capacitance measurements of a white electrolyte, 5 volume percent PEGDME electrolyte and 5 volume percent OP-10 electrolyte in example 4;

FIG. 9 is a graph of the results of testing the contact angle and viscosity of a white electrolyte, a volume fraction of 5% PEGDME electrolyte, and a volume fraction of 5% OP-10 electrolyte in example 4; (in FIG. 9, a is the contact angle test result of three electrolytes, and in FIG. 9, b is the viscosity test result of three electrolytes)

FIG. 10 is a graph showing the results of testing the ability of OP-10 to deposit lithium on a copper electrode in a Li-Cu cell in example 5; (in FIG. 10, a and b are SEM images after deposition of Li on a copper electrode in a Li-Cu cell containing a blank electrolyte, and in FIG. 10, c and d are SEM images after deposition of Li on a copper electrode in a Li-Cu cell containing an OP-10 electrolyte in a volume fraction of 5%)

FIG. 11 is a graph showing the results of testing the lithium-stripping ability of OP-10 in example 5 on a copper electrode in a Li-Cu cell; (in FIG. 11, a and b are SEM images after peeling Li from a copper electrode in a Li-Cu battery containing a blank electrolyte solution; in FIG. 11, c and d are SEM images after peeling Li from a copper electrode in a Li-Cu battery containing a PEGDME electrolyte solution in a volume fraction of 5%; and e and f are SEM images after peeling Li from a copper electrode in a Li-Cu battery containing an OP-10 electrolyte solution in a volume fraction of 5%)

FIG. 12 is a graph showing the results of cycle performance tests of the Li | Li symmetric cell containing a blank electrolyte and the Li | Li symmetric cell containing 5 volume percent OP-10 electrolyte of example 6;

FIG. 13 is an SEM image of lithium negative electrodes in a Li | Li symmetric cell containing a blank electrolyte and a Li | Li symmetric cell containing 5 volume percent OP-10 electrolyte after 50 cycles in example 6; (in FIG. 13, a, b, and c are SEM images of a Li | Li symmetrical battery including a blank electrolyte after 50 cycles of circulation of the lithium negative electrode, and in FIG. 13, d, e, and f are SEM images of a Li | Li symmetrical battery including an OP-10 electrolyte with a volume fraction of 5% after 50 cycles of circulation of the lithium negative electrode)

FIG. 14 is a graph showing the results of rate performance tests for Li | Li symmetric cells containing a blank electrolyte and Li | Li symmetric cells containing 5 volume percent OP-10 electrolyte in example 6;

FIG. 15 is a graph of the results of AC impedance testing of a Li | Li symmetric cell containing a blank electrolyte and a Li | Li symmetric cell containing 5 volume percent OP-10 electrolyte in example 6;

FIG. 16 is a graph of the cycle performance test results for a Li | Li symmetric cell of example 6 containing 5 volume percent PEGDME electrolyte and 5 volume percent OP-10 electrolyte;

FIG. 17 shows 3 Li | LiFePO types in example 7₄A cycle performance test result chart of the full cell;

FIG. 18 shows 3 Li | LiFePO samples after 1000 cycles of the cycle in example 7₄SEM image of lithium negative electrode in full cell;

FIG. 19 shows 3 Li | LiFePO types in example 7₄The AC impedance performance test result chart of the full cell;

FIG. 20 is a Li | LiFePO containing a blank electrolyte in example 7₄Full cell and Li | LiFePO containing 5% volume fraction of OP-10 electrolyte₄A multiplying power performance test result chart of the full cell;

FIG. 21 shows 2 kinds of Li in example 8₄Ti₅O₁₂A cycle performance test result chart of the full cell;

FIG. 22 shows 2 kinds of Li in example 8₄Ti₅O₁₂Constant current charge-discharge voltage curve diagram of the full cell.

Detailed Description

The preferred embodiments of the present invention will be described in detail below.

The electrolytes referred to in the following examples were prepared as follows:

(1) mixing propylene carbonate, ethylene carbonate and diethyl carbonate according to the volume ratio of 1:4:5 to form a mixed solution, and then adding lithium hexafluorophosphate into the mixed solution until the final concentration of lithium hexafluorophosphate is 1mol/L to obtain the blank electrolyte.

(2) And (3) adding 0.5mL of polyethylene glycol dimethyl ether (PEGDME) into 9.5mL of the blank electrolyte prepared in the step (1), uniformly mixing, and standing for 24h to prepare the PEGDME electrolyte with the volume fraction of 5%.

(3) And (2) adding 0.5mL of octyl phenol polyoxyethylene ether OP-4(4 ether chains) into 9.5mL of the blank electrolyte prepared in the step (1), uniformly mixing, and standing for 24h to prepare OP-4 electrolyte with the volume fraction of 5%.

(4) And (2) adding 0.5mL of octyl phenol polyoxyethylene ether OP-7(7 ether chains) into 9.5mL of the blank electrolyte prepared in the step (1), uniformly mixing, and standing for 24h to prepare OP-7 electrolyte with the volume fraction of 5%.

(5) And (2) adding 0.1mL of octyl phenol polyoxyethylene ether OP-10(10 ether chains) into 9.9mL of the blank electrolyte prepared in the step (1), uniformly mixing, and standing for 24h to prepare the OP-10 electrolyte with the volume fraction of 1%.

(6) And (2) adding 0.2mL of octyl phenol polyoxyethylene ether OP-10(10 ether chains) into 9.8mL of the blank electrolyte prepared in the step (1), uniformly mixing, and standing for 24h to prepare OP-10 electrolyte with the volume fraction of 2%.

(7) And (2) adding 0.5mL of octyl phenol polyoxyethylene ether OP-10(10 ether chains) into 9.5mL of the blank electrolyte prepared in the step (1), uniformly mixing, and standing for 24h to prepare OP-10 electrolyte with the volume fraction of 5%.

(8) And (2) adding 0.8mL of octyl phenol polyoxyethylene ether OP-10(10 ether chains) into 9.2mL of the blank electrolyte prepared in the step (1), uniformly mixing, and standing for 24h to prepare OP-10 electrolyte with the volume fraction of 8%.

(9) And (2) adding 1.0mL of octyl phenol polyoxyethylene ether OP-10(10 ether chains) into 9.0mL of the blank electrolyte prepared in the step (1), uniformly mixing, and standing for 24h to prepare the OP-10 electrolyte with the volume fraction of 10%.

(10) And (2) adding 0.5mL of octyl phenol polyoxyethylene ether OP-15(15 ether chains) into 9.5mL of the blank electrolyte prepared in the step (1), uniformly mixing, and standing for 24h to prepare OP-15 electrolyte with the volume fraction of 5%.

(11) Weighing 1.975g of octyl phenol polyoxyethylene ether OP-50(50 ether chains) and dissolving in 10mL of the blank electrolyte prepared in the step (1) until the OP-50 is completely dissolved, thus obtaining the OP-50 electrolyte with the volume fraction of 5%.

Example 1

Testing the electrochemical performance of Li | Li symmetrical battery containing octyl phenol polyethenoxy ether electrolyte with different ether chain lengths

5 types of Li | Li symmetrical batteries are obtained by assembling 5 types of electrolyte of OP-4 with volume fraction of 5%, OP-7 with volume fraction of 5%, OP-10 with volume fraction of 5%, OP-15 with volume fraction of 5% and OP-50 with volume fraction of 5% respectively as the electrolyte of Li | Li symmetrical batteries according to the following method:

in a button 2032 battery die, stacking a copper sheet (as a current collector) with the diameter of 16mm, a lithium sheet with the diameter of 14mm and the thickness of 0.6mm, a diaphragm (celgard2300) with the diameter of 16mm, a lithium sheet with the diameter of 10mm and a copper sheet with the diameter of 10mm from bottom to top in sequence, then dropwise adding 30uL of electrolyte into the battery die, finally sealing the button battery by a tablet press, and assembling to obtain each Li | Li symmetrical battery.

For the 5 Li | Li symmetric batteries obtained above, the charging and discharging current is 2.0mA/cm²The fixed charging and discharging capacity is 1mAh/cm²The cycle performance test was performed under the conditions, and as shown in FIG. 1, it can be seen from FIG. 1 that the Li | Li symmetrical battery containing OP-10 electrolyte with a volume fraction of 5% exhibited the best cycle stability, and that the Li | Li symmetrical battery containing OP-15 electrolyte with a volume fraction of 5% and the Li | Li symmetrical battery containing OP-7 electrolyte with a volume fraction of 5% exhibited the better cycle stability, because the PEO/Li was not sufficiently efficiently formed when the ether chain was too short⁺The complex regulates the uniform distribution of lithium ions and inhibits the growth of lithium dendrites, while an excessively long ether chain is disadvantageous to the formation of a stable SEI film.

Zeta potential measurements were carried out on the lithium negative electrodes of the 5 Li | Li symmetric batteries obtained as described above, and as shown in FIG. 2, it can be seen from FIG. 2 that the lithium negative electrode of the Li | Li symmetric battery containing 5% by volume of OP-10 electrolyte exhibited the highest Zeta potential, and that the lithium negative electrode of the Li | Li symmetric battery containing 5% by volume of OP-15 electrolyte and the lithium negative electrode of the Li | Li symmetric battery containing 5% by volume of OP-7 electrolyte exhibited higher Zeta potentials in this order, due to the formation of OP-10/Li in the three batteries⁺Complex layer, OP-15/Li⁺Complex layer, OP-7/Li⁺The complex layer is stable, thereby inducing stable SEI film formation.

Example 2

Testing the electrochemical Performance of Li | Li symmetric cells containing different volume fractions of OP-10 electrolyte

Respectively using 1% by volume of OP-10 electrolyte, 2% by volume of OP-10 electrolyte, 5% by volume of OP-10 electrolyte, 8% by volume of OP-10 electrolyte and 10% by volume of OP-10 electrolyte as electrolytes of the Li | Li symmetrical battery, and assembling the above-mentioned two electrolytes by the battery assembling method in example 1 to obtain 5 Li | Li symmetrical batteries as experimental group batteries; in addition, a Li | Li symmetric battery was assembled by the battery assembling method in example 1 using a blank electrolyte as the electrolyte of the Li | Li symmetric battery, and used as a control battery.

For 5 Li | Li symmetric batteries in the experimental group obtained above, the charging and discharging current was 2.0mA/cm²The fixed charging and discharging capacity is 1mAh/cm²The cycle performance test was performed under the conditions, and as a result, as shown in FIG. 3, it can be seen from FIG. 3 that the Li | Li symmetrical cell containing OP-10 electrolyte at a volume fraction of 5% exhibited the best cycle stability and the minimum polarization voltage, and the Li | Li symmetrical cell containing OP-10 electrolyte at a volume fraction of 2% exhibited the better cycle stability and the smaller polarization voltage, because when the OP-10 concentration was too low, the compact and uniform OP-10/Li was not sufficiently self-assembled on the surface of the lithium negative electrode⁺A complex layer to induce lithium deposition; and the excessive concentration changes some excellent intrinsic properties in the blank electrolyte and is not beneficial to forming a stable SEI film.

Zeta potential measurements were performed on a lithium negative electrode in a Li | Li symmetric cell containing 2% by volume of OP-10 electrolyte, 5% by volume of OP-10 electrolyte, 8% by volume of OP-10 electrolyte and 10% by volume of OP-10 electrolyte, respectively, and a lithium negative electrode in a control cell, as shown in FIG. 4. from FIG. 4, it can be seen that the lithium negative electrode in a Li | Li symmetric cell containing 5% by volume of OP-10 electrolyte exhibited the highest Zeta potential, and the lithium negative electrode in a Li | Li symmetric cell containing 8% by volume of OP-10 electrolyte exhibited a higher Zeta potential, because the OP-10 concentration was either too high or too low, both of which were determined to be too high or too lowThe decrease of the Zeta potential value of the lithium negative electrode is made, and especially after the concentration is higher than 8%, the decrease of the Zeta potential value is more serious, which is not favorable for constructing stable OP-10/Li⁺The complex layer induces the formation of a stable SEI film.

The contact angles of the lithium negative electrodes of the 5 Li | Li symmetric batteries in the experimental group and the lithium negative electrode of the control group were respectively tested, and as shown in fig. 5, it can be seen from fig. 5 that the contact angle of the lithium negative electrode in each battery first decreased and then increased as the OP-10 concentration increased, wherein the contact angle of the lithium negative electrode of the Li | Li symmetric battery containing 5% of OP-10 electrolyte was the smallest, and the smaller contact angle proves the better lithium affinity of the electrolyte.

The viscosities of the lithium negative electrodes of the 5 Li | Li symmetric batteries in the experimental group and the lithium negative electrode of the control group were measured, respectively, and as shown in fig. 6, it can be seen from fig. 6 that the viscosity of the lithium negative electrode of each battery was increased after being decreased as the OP-10 concentration was increased, wherein the viscosity of the lithium negative electrode of the Li | Li symmetric battery containing 5% by volume of OP-10 electrolyte was the smallest, and the smaller viscosity was more favorable for the Li negative electrode⁺To be transmitted.

Example 3

Testing the Effect of OP-10 on lithium dendrite growth of Li | Li symmetric cells

In-situ test battery assembly of a Li | Li symmetric battery containing a blank electrolyte: and adding 5mL of blank electrolyte into a transparent mold, inserting one lithium sheet into the electrolyte to connect a negative electrode, inserting the other lithium sheet into the electrolyte to connect a positive electrode, and placing the positive electrode under an optical microscope.

Li symmetric cell in situ test cell assembly with 5% volume fraction OP-10 electrolyte: 5mL of OP-10 electrolyte with volume fraction of 5% is added into a transparent mould, one lithium sheet is inserted into the electrolyte and connected to a negative electrode, the other lithium sheet is inserted into the electrolyte and connected to a positive electrode, and the positive electrode is arranged under an optical microscope.

Discharging the two in-situ test batteries for 1-15min at constant current of 3.14mA, and observing the whole process in situ by using an optical microscope, wherein the result is shown in figure 7, wherein a in figure 7 is a lithium dendrite growth test result diagram of a Li | Li symmetrical battery in-situ test battery containing blank electrolyte, and as can be seen from a in figure 7, the growth phenomenon of lithium dendrite begins to occur after 1min, then, as time increases, more and more lithium dendrites grow, and after 6min, the lithium dendrite grows everywhere on the surface of the whole lithium sheet; fig. 7 b is a diagram of the result of lithium dendrite growth test of Li | Li symmetric battery in-situ test containing 5% by volume of OP-10 electrolyte, and it can be seen from fig. 7 b that after 6min, no lithium dendrite growth is observed in the lithium plate of the battery.

Example 4

Differential capacitance tests are carried out on blank electrolyte, 5% of PEGDME electrolyte and 5% of OP-10 electrolyte, and the results are shown in FIG. 8, as can be seen from FIG. 8, compared with the blank electrolyte, the differential capacitance values of 5% of PEGDME electrolyte and 5% of OP-10 electrolyte are obviously reduced, and new capacitance peaks appear at-0.56V in 5% of PEGDME electrolyte and 5% of OP-10 electrolyte, but compared with PEGDME, OP-10 has long lithium-phobic phenyl carbon chains, and on one hand, the self-assembly can form a template SEI film; on the other hand, when the ether chain end is adsorbed to the lithium surface, the lithium-phobic phenyl carbon chain in the OP-10 repels the lithium-philic electrolyte solvent to contact the lithium surface, so that the electrolyte is prevented from participating in the formation of the SEI film, and the defect that the SEI film is unstable due to the participation of the electrolyte in the formation of the SEI film is effectively avoided.

The contact angle and viscosity tests are performed on the blank electrolyte, the 5% volume fraction PEGDME electrolyte and the 5% volume fraction OP-10 electrolyte, and the results are shown in FIG. 9, wherein a in FIG. 9 is the contact angle test result of three electrolytes, and b in FIG. 9 is the viscosity test result of three electrolytes, as can be seen from FIG. 9, the contact angle and viscosity of the 5% volume fraction OP-10 electrolyte are the minimum, while the smaller contact angle proves that the electrolyte has better lithium affinity, which is beneficial for being adsorbed on the surface of the lithium cathode to adjust the uniform distribution of lithium ions, while the smaller viscosity is more beneficial for Li cathode surface⁺The electrochemical performance of the lithium negative electrode is improved.

Example 5

OP-10 was tested for its ability to deposit and strip lithium on copper electrodes in Li-Cu cells

Blank electrolyte, PEGDME electrolyte with volume fraction of 5% and OP-10 electrolyte with volume fraction of 5% are respectively used as the electrolyte of the Li-Cu battery, and 3 Li-Cu batteries are obtained by assembling according to the following methods:

in a button 2032 battery die, stacking a copper sheet (as a current collector) with the diameter of 16mm, a lithium sheet with the diameter of 14mm and the thickness of 0.6mm, a diaphragm (celgard2300) with the diameter of 16mm and a copper sheet with the diameter of 10mm from bottom to top in sequence, then dripping 30uL of electrolyte into the battery die, finally sealing the button battery by a tablet press, and assembling to obtain each Li-Cu battery.

Depositing Li on the copper electrodes of a Li-Cu cell containing a blank electrolyte and a Li-Cu cell containing an OP-10 electrolyte with a volume fraction of 5%, respectively, by the following method: connecting one side of a copper electrode in each of the two Li-Cu batteries with a positive electrode, discharging for 24min at constant current of 0.3925mA, taking out a copper sheet in a glove box, and drying to obtain a deposition Li sample. Observing the sample by using a scanning electron microscope, wherein the result is shown in fig. 10, wherein a and b in fig. 10 are SEM images of a blank electrolyte-containing Li-Cu battery after Li is deposited on a copper electrode, and it can be known that the lithium deposition thereon is very uneven, and a large number of large holes and cracks appear on the surface, which causes continuous consumption of the electrolyte; in fig. 10, c and d are SEM images after depositing Li on the copper electrode in the Li-Cu battery containing OP-10 electrolyte at a volume fraction of 5%, it can be seen that the lithium deposition is very uniform and hardly any large pores and cracks appear at the surface.

The method for stripping Li from the copper electrode in Li-Cu battery containing blank electrolyte, Li-Cu battery containing 5% volume fraction PEGDME electrolyte and Li-Cu battery containing 5% volume fraction OP-10 electrolyte is as follows: connecting one side of a copper electrode in the three Li-Cu batteries with an anode respectively, discharging for 24min at constant current of 0.3925mA, then charging for 24min at constant current of 0.3925mA, taking out a copper sheet after circulating for 3 weeks, and drying to obtain a stripped Li sample. Observing the sample by using a scanning electron microscope, wherein the result is shown in fig. 11, wherein a and b in fig. 11 are SEM images of a copper electrode in a Li-Cu battery containing a blank electrolyte after Li is stripped, and it can be known that the SEI film remaining on the surface of the copper sheet is not dense and is filled with large pores; in fig. 11, c and d are SEM images of a Li-Cu battery containing 5% by volume of the PEGDME electrolyte after Li is peeled off from the copper electrode, and it can be seen that the quality of the SEI film remaining on the surface of the copper sheet is improved, but many pinholes remain on the surface of the SEI film; in fig. 11, e and f are SEM images of the Li-Cu battery with 5 vol% OP-10 electrolyte after Li peeling off from the copper electrode, and it can be seen that the SEI film remained on the surface of the copper sheet is very dense and uniform.

Example 6

Testing of the electrochemical Performance of a Li | Li symmetrical cell containing a blank electrolyte, a PEGDME electrolyte with a volume fraction of 5% and an OP-10 electrolyte with a volume fraction of 5%

A blank electrolyte, a PEGDME electrolyte with a volume fraction of 5% and an OP-10 electrolyte with a volume fraction of 5% were used as the electrolytes of the Li | Li symmetric battery, and 3 Li | Li symmetric batteries were assembled according to the battery assembly method in example 1.

For Li | Li symmetrical battery containing blank electrolyte and Li | Li symmetrical battery containing OP-10 electrolyte with volume fraction of 5%, charging and discharging currents are 1.0, 2.0 and 4.0mA/cm respectively²Fixed charge and discharge capacities of 0.5, 1 and 1mAh/cm²The cycle performance test was carried out under the conditions, and the test results are shown in FIG. 12, and it can be seen from FIG. 12 that the current was 1.0, 2.0 or 4.0mA/cm²Under the charge and discharge current density, the cycle performance of the Li | Li symmetrical battery containing OP-10 electrolyte with the volume fraction of 5% is far better than that of the Li | Li symmetrical battery containing blank electrolyte, and the enlarged image on the right side in the figure shows that the Li | Li symmetrical battery containing blank electrolyte has obvious voltage fluctuation, which proves that the lithium cathode in the battery is unstable. With increasing number of cycles, the polarization of Li symmetric cells with blank electrolyte was significantly worse than Li symmetric cells with 5 volume percent OP-10 electrolyte. The lithium cathodes in the two batteries after 50 cycles of cycling were respectively detected by a scanning electron microscope, and the results are shown in fig. 13, where a, b, and c in fig. 13 are 50 cycles of cycling of the lithium cathode of the Li | Li symmetric battery containing blank electrolyteAfter 50 cycles, the SEM image shows that a large amount of lithium dendrites, dead lithium and huge cracks appear on the surface of the lithium negative electrode in the battery; in fig. 13, d, e, and f are SEM images of a lithium negative electrode of a Li | Li symmetric battery containing 5% by volume of OP-10 electrolyte after 50 cycles, and it can be seen that the surface of the lithium negative electrode in the battery hardly has any lithium dendrite, dead lithium, and large cracks after 50 cycles.

The rate capability test is carried out on the Li | Li symmetrical battery containing blank electrolyte and the Li | Li symmetrical battery containing OP-10 electrolyte with the volume fraction of 5 percent, and the charging and discharging current of the test is from 1.0mA/cm²Increased to 4.0mA/cm²Then, the temperature is reduced to 1.0mA/cm²As shown in fig. 14, it can be seen from fig. 14 that, when the Li | Li symmetric battery is subjected to the step discharge test, the Li | Li symmetric battery containing 5% by volume of the OP-10 electrolyte exhibits lower overvoltage and more stable charge-discharge voltage hysteresis, i.e., the difference between the charge voltage curve and the discharge voltage curve is smaller, which proves that the lithium negative electrode modified by 5% by volume of the OP-10 electrolyte is more stable.

Alternating current impedance test was performed on a Li | Li symmetric battery containing a blank electrolyte and a Li | Li symmetric battery containing an OP-10 electrolyte with a volume fraction of 5%, and the test frequency was from 100000Hz to 10mHz, and as can be seen from fig. 15, only one semicircle corresponded to the charge transfer resistance value (R) of the battery before discharge (R) is shown in fig. 15_ct) R of a Li | Li symmetrical battery containing 5% by volume of OP-10 electrolyte was found_ctThe larger value is due to the fact that, after the addition of OP-10, the adsorption of OP-10 on the surface of the lithium negative electrode can react with Li⁺Has a certain barrier effect on the transmission of the oil; however, after 100 cycles, two semicircles corresponding to the charge transfer resistance and the solid-liquid interface resistance (R) at high and low frequencies appear_SEI) R of Li | Li symmetrical battery containing 5% by volume of OP-10 electrolyte_SEIThe value is obviously less than the R of the Li | Li symmetrical battery containing blank electrolyte_SEIValue, R of Li | Li symmetric cell with blank electrolyte after 100 cycles_ctThe value increases significantly, while the R of a Li | Li symmetric cell containing 5% by volume of OP-10 electrolyte after 100 cycles_ctThe value is reduced, indicating that the volume fraction is 5%OP-10/Li in Li | Li symmetrical battery with OP-10 electrolyte⁺The complex layer induces stable SEI film formation during cycling, reducing the growth of lithium dendrites and the formation of dead lithium, thereby facilitating Li⁺To be transmitted.

For a Li | Li symmetrical battery containing 5% volume fraction PEGDME electrolyte and 5% volume fraction OP-10 electrolyte, the charging and discharging current is 2.0mA/cm²The fixed charging and discharging capacity is 1mAh/cm²The cycle performance test was performed under the conditions, and the test results are shown in fig. 16, and it can be seen from fig. 16 that the Li | Li symmetric battery containing the OP-10 electrolyte with a volume fraction of 5% exhibited less voltage hysteresis and polarization compared to the Li | Li symmetric battery containing the PEGDME electrolyte with a volume fraction of 5%, indicating that the OP-10 modified lithium negative electrode had better stability

Example 7

Li | LiFePO containing a blank electrolyte, 5% by volume of PEGDME electrolyte and 5% by volume of OP-10 electrolyte was tested₄Electrochemical performance of the full cell

LiFePO₄Preparing a pole piece: the lithium iron phosphate, the superconducting carbon and the polyvinylidene fluoride are mixed according to the mass ratio of 7: 2: 1, the total mass of the three is 100mg, the weighed sample is placed in an agate mortar, 5 drops of N, N-dimethyl pyrrolidone are dripped, a grinding rod is used for grinding for 1.5h, then the slurry is transferred to an aluminum foil, a blade coater is used for blade coating, finally, vacuum drying is carried out for 12h at 60 ℃, and after drying, the pole piece is punched into LiFePO with the diameter of 10mm on a punching machine₄Pole pieces;

respectively taking blank electrolyte, PEGDME electrolyte with volume fraction of 5% and OP-10 electrolyte with volume fraction of 5% as Li | LiFePO₄The electrolyte of the whole battery is assembled according to the following method to obtain 3 Li | LiFePO₄All-battery: in a button 2032 battery die, a copper sheet (as a current collector) with the diameter of 16mm, a lithium sheet with the diameter of 14mm and the thickness of 0.6mm, a diaphragm (celgard2300) with the diameter of 16mm and LiFePO with the diameter of 10mm are sequentially arranged from bottom to top₄Stacking the pole pieces, then dripping 30uL electrolyte into a battery die, finally sealing the button cell by a tablet press, and assembling to obtain each Li | LiFePO₄And (4) full cell.

Testing the 3 Li | LiFePO by a constant current charge-discharge method₄The cycle performance of the full cell was tested in a charging and discharging potential interval of 2.5-4.2V and a current density of 10C (1C 170mA/g), and the test results are shown in fig. 17, and it can be seen from fig. 17 that after 1000 cycles of discharge, Li | LiFePO containing 5% volume fraction of OP-10 electrolyte was contained₄The full cell exhibits better cycling stability and higher reversible capacity, since the lithium negative electrode modified with OP-10 forms a stable SEI film during long cycling while limiting the growth of lithium dendrites, and thus the cycling performance is better.

After 1000 cycles, 3 Li | LiFePO are processed by a scanning electron microscope₄The lithium negative electrode in the full cell was tested, and the test results are shown in fig. 18, and it can be seen from fig. 18 that Li | LiFePO containing the blank electrolyte₄A large amount of lithium dendrites grow on the surface of the lithium negative electrode of the full cell, and no SEI film is observed; li | LiFePO containing PEGDME electrolyte with volume fraction of 5%₄The growth of lithium dendrites on the surface of a lithium cathode of the full-cell is inhibited to a certain extent, and an SEI film exists, but the SEI film is not dense and uniform and has a large number of cracks and holes; li | LiFePO containing OP-10 electrolyte with volume fraction of 5%₄The growth of lithium dendrites of the lithium negative electrode of the full cell was almost completely suppressed and a dense and uniform SEI film was clearly observed.

Testing of the above 3 Li | LiFePO₄The ac impedance performance of the full cell was measured at a frequency of 100000Hz to 10mHz, and the results are shown in fig. 19. Before discharge, only one semicircle corresponds to the charge transfer resistance value (R) of the battery_ct) Li | LiFePO containing 5% volume fraction of PEGDME electrolyte₄R of the full cell_ctLi | LiFePO with maximum value and 5% volume fraction of OP-10 electrolyte₄R of the full cell_ctLarge value, Li | LiFePO containing blank electrolyte₄R of the full cell_ctThe value is minimal. This is because the adsorption on the surface of the lithium negative electrode after the addition of PEGDME or OP-10 is directed to Li⁺Has a certain barrier effect, however, after 500 cycles, the Li | LiFePO containing blank electrolyte₄R of the full cell_ctThe value increases significantly, while Li | LiFePO containing 5% volume fraction of PEGDME electrolyte₄Full cell and Li | LiFePO containing 5% volume fraction of OP-10 electrolyte₄R of the full cell_ctThe value is significantly reduced, wherein Li | LiFePO of OP-10 electrolyte with volume fraction of 5%₄R of the full cell_ctThe value is significantly less than that of Li LiFePO containing a PEGDME electrolyte with a volume fraction of 5%₄R of the full cell_ctThe value is obtained. The above results further confirm that OP-10 electrolyte with an integral fraction of 5% is most favorable for Li⁺Thereby obviously improving the rate capability of the full cell.

Li | LiFePO containing blank electrolyte is tested by a step discharge method₄Full cell and Li | LiFePO containing 5% volume fraction of OP-10 electrolyte₄The rate capability of the whole battery, the charging and discharging potential interval of the test is 2.5-4.2V, the charging and discharging current density is from 1C to 10C (1C is 170mA/g), the test result is shown in figure 20, and as can be seen from figure 20, Li | LiFePO containing OP-10 electrolyte with 5% volume fraction₄The rate performance of the full battery is compared with that of Li | LiFePO containing blank electrolyte₄The rate performance of the full cell is obviously improved because the lithium cathode modified by OP-10 enables Li in the circulation process⁺Can be uniformly deposited and distributed, can inhibit the growth of lithium dendrites and is beneficial to Li⁺So that the best rate performance can be obtained.

Example 8

Li | Li containing a blank electrolyte and 5% volume fraction of OP-10 electrolyte was tested₄Ti₅O₁₂Electrochemical performance of the full cell

Li₄Ti₅O₁₂Preparing a pole piece: li₄Ti₅O₁₂The mass ratio of the superconducting carbon to the polyvinylidene fluoride is 7: 2: 1, and the total mass of the three is 100 mg. Putting the weighed sample into an agate mortar, dropwise adding 5 drops of N, N-dimethyl pyrrolidone, grinding for 1.5h by using a grinding rod, transferring the slurry onto an aluminum foil, blade-coating by using a blade coater, finally drying for 12h in vacuum at 60 ℃, and punching the pole piece into a Li with the diameter of 10mm on a punching machine after drying₄Ti₅O₁₂Pole pieces;

blank electrolyte and OP-10 electrolyte with volume fraction of 5 percent are respectively used as Li₄Ti₅O₁₂The electrolyte of the full cell is assembled to obtain 2 kinds of Li₄Ti₅O₁₂All-battery: in a button 2032 battery die, a copper sheet (as a current collector) with the diameter of 16mm, a lithium sheet with the diameter of 14mm and the thickness of 0.6mm, a diaphragm (celgard2300) with the diameter of 16mm and a Li with the diameter of 10mm are sequentially arranged from bottom to top₄Ti₅O₁₂Stacking the pole pieces, then dripping 30uL electrolyte into a battery die, finally sealing the button cell by a tablet press, and assembling to obtain each Li₄Ti₅O₁₂And (4) full cell.

Testing the 2 Li materials by constant current charge-discharge method₄Ti₅O₁₂The cycle performance of the full cell was tested at a charge-discharge potential interval of 1.0-2.5V and a current density of 5C (1C 175mA/g), and the test results are shown in fig. 21. as can be seen from fig. 21, after 1000 cycles of discharge, Li | Li of OP-10 electrolyte containing 5% volume fraction of OP-10 electrolyte₄Ti₅O₁₂The full cell exhibits better cycling stability and higher reversible capacity. FIG. 22 shows 2 types of Li₄Ti₅O₁₂FIG. 22 shows a constant current charge/discharge voltage curve of the whole battery, in which Li | Li of OP-10 electrolyte containing 5% by volume fraction₄Ti₅O₁₂The full cell has a more stable discharge voltage plateau and a smaller polarization voltage difference value because the lithium negative electrode modified by OP-10 forms a stable SEI film in a long cycle process and simultaneously limits the growth of lithium dendrites, so that the cycle performance and stability are better.

Finally, it is noted that the above-mentioned preferred embodiments illustrate rather than limit the invention, and that, although the invention has been described in detail with reference to the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

1. The lithium ion battery electrolyte is characterized by comprising lithium hexafluorophosphate, propylene carbonate, ethylene carbonate, diethyl carbonate and octylphenol polyoxyethylene ether.

2. The lithium ion battery electrolyte of claim 1 wherein the volume fraction of the octylphenol polyoxyethylene ether in the electrolyte is 5-8%.

3. The lithium ion battery electrolyte of claim 2 wherein the octylphenol polyoxyethylene ether is one of octylphenol polyoxyethylene ether OP-7, octylphenol polyoxyethylene ether OP-10 or octylphenol polyoxyethylene ether OP-15.

4. The lithium ion battery electrolyte of claim 3 wherein the octylphenol polyoxyethylene ether is octylphenol polyoxyethylene ether OP-10, and the volume fraction of octylphenol polyoxyethylene ether OP-10 in the electrolyte is 5%.

5. The lithium ion battery electrolyte of any of claims 1-4 wherein the concentration of lithium hexafluorophosphate in the electrolyte is 0.5 to 1.5 mol/L.

6. The lithium ion battery electrolyte of claim 5, wherein the volume ratio of propylene carbonate, ethylene carbonate and diethyl carbonate in the electrolyte is 0.5-1.5:3.5-4.5: 4.5-5.5.

7. A lithium ion battery comprising a lithium ion battery electrolyte according to any of claims 1 to 6.