CN114843600A - A kind of electrolyte for lithium battery and preparation method thereof and lithium battery - Google Patents

Abstract

The invention discloses an electrolyte for a lithium battery, comprising a lithium salt, a non-aqueous organic solvent and an additive. The additive is an alkyl boric acid, and the weight percentage of the additive is 0.5-2.0 wt%. The alkylboronic acid is one or a mixture of n-propylboronic acid, n-hexylboronic acid and n-octylboronic acid. The present invention also discloses a method for preparing the above-mentioned electrolyte for lithium batteries, and a lithium battery prepared by using the above-mentioned electrolyte. The invention adopts an electrolyte for a lithium battery, a preparation method thereof, and a lithium battery, which can solve the problem of low charging and discharging times of the existing lithium battery, and has the advantages of good cycle stability and slow decay of specific capacity.

Description

A kind of electrolyte for lithium battery and preparation method thereof and lithium battery

technical field

The invention relates to the technical field of lithium batteries, in particular to an electrolyte for a lithium battery, a preparation method thereof, and a lithium battery.

Background technique

Lithium batteries have the advantages of green environmental protection, no memory effect, relatively high energy density, etc., and are welcomed by the energy storage equipment market. Energy density refers to the energy that can be stored/released per unit mass or unit volume of lithium battery, and is one of the important indicators to measure battery quality. Generally, vehicle power batteries need to have high energy density. Common methods to improve the energy density of batteries include increasing the positive electrode voltage and increasing the electrode specific capacity.

At present, most commercial lithium batteries use graphite as the negative electrode, but the theoretical specific capacity of the graphite negative electrode is only 372mAh/g, which is difficult to meet the market demand for high energy density battery electrode materials. In contrast, the metallic lithium anode has a theoretical capacity of up to 3860 mAh/g and a lower lithium storage potential, all of which help to improve the energy density of the battery. However, side reactions due to excessive reactivity; and the growth of lithium dendrites caused by disordered lithium deposition lead to low charge-discharge times and potential safety hazards, which hinder the large-scale application of metal lithium anodes.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an electrolyte for a lithium battery, which solves the problem of low charging and discharging times of the existing lithium battery. Another object of the present invention is to provide a method for preparing the above electrolyte for lithium batteries, and a lithium battery comprising the above electrolyte for lithium batteries.

In order to achieve the above object, the present invention provides an electrolyte for a lithium battery, comprising a lithium salt, a non-aqueous organic solvent and an additive, the additive is an alkyl boric acid, and the weight percentage of the additive is 0.5-2.0 wt%;

Described alkyl boronic acid is one or more mixtures in n-propyl boronic acid, n-hexyl boronic acid and n-octyl boronic acid;

The structural formula of n-propylboronic acid is:

The structural formula of n-hexylboronic acid is:

The structural formula of n-octylboronic acid is:

Preferably, the concentration of the lithium salt is 1M, and the lithium salt is LiPF ₆ , LiBF ₄ , LiBOB, LiDFOB, LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ or LiN(SO ₂ F) ₂ one or more mixtures.

Preferably, the non-aqueous organic solvent is a mixture of cyclic carbonate and chain carbonate, and the volume ratio of cyclic carbonate and chain carbonate is 3:7-7:3; the cyclic carbonate is One or more mixtures of ethylene carbonate, propylene carbonate or butylene carbonate, and the chain carbonate is dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or propyl methyl carbonate. one or a mixture of several.

A preparation method of the above-mentioned lithium battery electrolyte, comprising the following steps:

S1. In the glove box, H ₂ O <0.1ppm, O ₂ <0.1ppm, weigh an appropriate amount of lithium salt and dissolve it in a non-aqueous organic solution, the concentration of the lithium salt is 1M, to obtain the parent electrolyte;

S2, adding an additive whose mass percentage is 0.5-2.0 wt % in the parent electrolyte, and stirring evenly to obtain an electrolyte for a lithium battery.

A lithium battery containing the above-mentioned electrolyte for a lithium battery comprises a battery case, a positive electrode, a negative electrode, a separator and an electrolyte located in the battery case.

Preferably, the positive electrode includes a positive electrode current collector and a positive electrode material located on the positive electrode current collector, and the positive electrode material includes a positive electrode active material.

Preferably, the positive active material is LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCo _{1-y My} O ₂ , LiNi _{1-y My} O ₂ , LiMn _{2-y My} O ₄ and LiNi _x Co One or more mixtures of _y Mn _z M _1-xyz O ₂ ; wherein, M is Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V Or a mixture of one or more of Ti, and 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1.

Preferably, the positive electrode active material is LiFe _1-x M _x PO ₄ , wherein M is one of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti One or several mixtures, and 0≤x<1.

Preferably, the negative electrode includes a negative electrode current collector and a negative electrode material located on the negative electrode current collector, and the negative electrode material is graphite, hard carbon, soft carbon, silicon carbon composite material, silicon oxygen carbon composite material, metal lithium, metal lithium One or a mixture of several alloys.

Preferably, the separator is one or more of polyolefin porous membrane, non-woven fabric, fiber coating, ceramic coating, and inorganic solid electrolyte coating.

In the electrolyte for a lithium battery, a preparation method thereof, and a lithium battery according to the present invention, an alkyl boric acid additive is added to the electrolyte, and the alkyl boric acid additive reacts with the metal lithium negative electrode to generate lithium in situ on the surface of the metal lithium negative electrode. Boron alloys, lithium-boron alloys have high lithium conductivity, so they can inhibit the growth of lithium dendrites and improve the battery cycle stability and safety performance. The full-cell stability of Li||NCM622 is improved due to the suppressed dendrite growth.

The technical solutions of the present invention will be further described in detail below through the accompanying drawings and embodiments.

Description of drawings

Fig. 1 is the cycle life diagram of the lithium symmetrical battery prepared by the implementation electrolyte solution 1 of a kind of lithium battery electrolyte of the present invention and preparation method thereof and lithium battery;

2 is a cycle life diagram of a lithium symmetric battery prepared by implementing a lithium battery electrolyte 2 of the present invention and a preparation method thereof and a lithium battery;

3 is a cycle life diagram of a lithium symmetric battery prepared by using an electrolyte for a lithium battery of the present invention, a preparation method thereof, and an implementation electrolyte 3 of the lithium battery;

4 is a cycle life diagram of a lithium symmetric battery prepared by using an electrolyte for a lithium battery of the present invention, a preparation method thereof, and an implementation electrolyte 4 of the lithium battery;

5 is a cycle life diagram of a lithium symmetric battery prepared by using an electrolyte for a lithium battery of the present invention, a preparation method thereof, and an implementation electrolyte 5 of the lithium battery;

6 is a cycle life diagram of a lithium symmetric battery prepared by using an electrolyte for a lithium battery of the present invention, a preparation method thereof, and an implementation electrolyte 6 of the lithium battery;

7 is a cycle life diagram of a lithium symmetric battery prepared by using an electrolyte for a lithium battery and a preparation method thereof and the implementation electrolyte 7 of the present invention;

8 is a cycle life diagram of a lithium symmetric battery prepared by using an electrolyte for a lithium battery of the present invention, a preparation method thereof, and a comparative electrolyte 1 for a lithium battery;

FIG. 9 is a cycle performance diagram of a full battery prepared by using an electrolyte for a lithium battery of the present invention, a preparation method thereof, and an implementation electrolyte 1 of the lithium battery and a comparative electrolyte 1. FIG.

Detailed ways

An electrolyte for a lithium battery includes a lithium salt, a non-aqueous organic solvent and an additive. The additive is alkylboric acid, and the weight percentage of the additive is 0.5-2.0 wt %.

The alkyl boronic acid is one or a mixture of n-propyl boronic acid, n-hexyl boronic acid and n-octyl boronic acid.

The structural formula of n-propylboronic acid R ₁ is:

The structural formula of n-hexylboronic acid R ₂ is:

The structural formula of n-octylboronic acid _R3 is:

The alkyl boric acid additive reacts with the metal lithium negative electrode, and a lithium boron alloy is formed on the surface of the metal lithium negative electrode in situ. The lithium boron alloy has high lithium conductivity, so it can inhibit the growth of lithium dendrites and improve the battery cycle stability and safety performance. Furthermore, the full-cell stability of Li||NCM622 is improved due to the suppressed growth of dendrites.

The concentration of lithium salt is 1M, and the lithium salt is LiPF ₆ , LiBF ₄ , LiBOB, LiDFOB, LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiC(SO ₂ ) One or more mixtures of CF ₃ ) ₃ or LiN(SO ₂ F) ₂ .

The non-aqueous organic solvent is a mixture of cyclic carbonate and chain carbonate, and the volume ratio of cyclic carbonate and chain carbonate is 3:7-7:3; the cyclic carbonate is ethylene carbonate, carbonic acid The mixture of one or more in propylene ester or butylene carbonate, described chain carbonate is one or more in dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate or methyl propyl carbonate mixture. The mixed solution of cyclic carbonate organic solvent with high dielectric constant and low-viscosity chain carbonate organic solvent is used as the solvent of lithium ion battery electrolyte, so that the mixed solution of organic solvent has high ionic conductivity, high Dielectric constant and low viscosity.

A preparation method of the above-mentioned lithium battery electrolyte, comprising the following steps:

S1. In the glove box, H ₂ O <0.1ppm, O ₂ <0.1ppm, weigh an appropriate amount of lithium salt and dissolve it in a non-aqueous organic solution, the concentration of the lithium salt is 1M, to obtain the parent electrolyte;

S2, adding an additive whose mass percentage is 0.5-2.0 wt % in the parent electrolyte, and stirring evenly to obtain an electrolyte for a lithium battery.

A lithium battery containing the above-mentioned electrolyte for a lithium battery comprises a battery case, a positive electrode, a negative electrode, a separator and an electrolyte located in the battery case.

The positive electrode includes a positive electrode current collector and a positive electrode material on the positive electrode current collector, the positive electrode material including a positive electrode active material.

Alternatively, the positive electrode active material is LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCo _{1-y My} O ₂ , LiNi _{1-y My} O ₂ , LiMn _{2- y My} O ₄ , and LiNi _x Co _y Mn _z One or more mixtures of M _1-xyz O ₂ ; wherein, M is Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti One or more mixtures of , and 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1.

The positive electrode active material is LiFe _1-x M _x PO ₄ , wherein M is one or more of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti , and 0≤x<1.

The negative electrode includes a negative electrode current collector and a negative electrode material located on the negative electrode current collector, and the negative electrode material is one of graphite, hard carbon, soft carbon, silicon carbon composite material, silicon oxygen carbon composite material, metal lithium, and an alloy of metal lithium or a mixture of several.

The separator is one or more of polyolefin porous membrane, non-woven fabric, fiber coating, ceramic coating, and inorganic solid electrolyte coating.

The technical solutions of the present invention will be further described below through the accompanying drawings and embodiments.

Example 1

In a glove box (H ₂ O<0.1ppm, O ₂ <0.1ppm), weigh an appropriate amount of lithium hexafluorophosphate (LiPF ₆ ) and dissolve it in a non-aqueous organic solution to obtain a parent electrolyte.

Lithium salt concentration: 1M lithium hexafluorophosphate (LiPF ₆ );

Non-aqueous organic solvent: mixed solvent of ethylene carbonate (EC): dimethyl carbonate (DMC)=1:1 (v:v);

A compound represented by n-hexylboronic acid R ₂ in a mass fraction of 1.0 wt % was added to the parent electrolyte, and the electrolyte solution 1 was obtained after stirring uniformly.

Example 2

The electrolyte solution was prepared by the method described in Example 1, except that n-propylboronic acid R ₁ with a mass fraction of 1.0 wt % was added to the parent electrolyte solution to obtain the implementation electrolyte solution 2 .

Example 3

The electrolyte solution was prepared by the method described in Example 1, the difference was that 1.0 wt% n-octylboronic acid R ₃ was added to the parent electrolyte solution to obtain the implementation electrolyte solution 3.

Example 4

The electrolyte solution was prepared by the method described in Example 1, except that n-hexylboronic acid R ₂ with a mass fraction of 0.5 wt % was added to the parent electrolyte solution to obtain the implementation electrolyte solution 4 .

Example 5

The electrolyte solution was prepared by the method described in Example 1, except that n-hexylboronic acid R ₂ with a mass fraction of 2.0 wt % was added to the parent electrolyte solution to obtain the implementation electrolyte solution 5 .

Example 6

Adopt the method described in Example 1 to configure the electrolyte, the difference is that in the parent electrolyte, the mixed solvent ratio of ethylene carbonate (EC): dimethyl carbonate (DMC) is 7:3 (v:v), and is implemented Electrolyte 6.

Example 7

Adopt the method described in Example 1 to configure the electrolyte, the difference is that in the parent electrolyte, the mixed solvent ratio of ethylene carbonate (EC): dimethyl carbonate (DMC) is 3:7 (v:v), and is implemented Electrolyte 7.

Comparative Example 1

Comparative Example The parent electrolyte prepared by the method described in Example 1 was used as Comparative Electrolyte 1.

Lithium batteries were prepared using the above-described implementation electrolytes 1-7 and comparative electrolyte 1.

The preparation method of lithium battery is as follows:

Lithium symmetrical battery: in the glove box (H ₂ O <0.1ppm, O ₂ <0.1ppm), sequentially connect the positive electrode shell → lithium sheet → electrolyte → separator → electrolyte → lithium sheet → stainless steel gasket → negative electrode shell from the bottom Assembled above, and then transferred to a tablet press for stamping and packaging to obtain a finished lithium symmetric battery.

Full battery: In the glove box (H ₂ O <0.1ppm, O ₂ <0.1ppm), sequentially connect the positive shell → NCM622 pole piece → electrolyte → separator → electrolyte → lithium piece → stainless steel gasket → spring piece → negative electrode The case is assembled from bottom to top, and then transferred to a tablet press for stamping and packaging, resulting in a completed full cell.

The electrochemical performance of the assembled battery was tested by Xinwei test equipment. The specific experimental process is as follows: Lithium sheets are used as positive and negative electrodes to assemble a lithium symmetric battery for constant current charge-discharge tests; Lithium sheets are used as negative electrodes, and NCM622 (LiNi _0.6 Co _0.2 Mn _0.2 O ₂ ) is used as positive active material to match the assembly. Complete the battery for constant current charge-discharge test.

Fig. 1 is the cycle life diagram of the lithium battery symmetrical battery prepared by adopting a kind of electrolyte for lithium battery of the present invention and its preparation method and implementation of electrolyte 1 of the present invention, Fig. 2 is a diagram of adopting a kind of electrolyte for lithium battery of the present invention and Its preparation method and the cycle life diagram of the lithium battery symmetrical battery prepared by the implementation electrolyte 2 of the lithium battery, FIG. 3 is the lithium battery prepared by adopting an electrolyte for a lithium battery and the preparation method thereof of the present invention and the implementation electrolyte 3 of the lithium battery The cycle life diagram of the battery symmetric battery, FIG. 8 is the cycle life diagram of the lithium symmetric battery prepared by using an electrolyte for a lithium battery of the present invention, a preparation method thereof, and a lithium battery comparative electrolyte 1. As shown in the figure, the lithium symmetric battery prepared with the implementation of electrolyte 1 can make the polarization degree of the battery remain small after cycling for more than 350 hours, and the lithium symmetric battery prepared with the implementation of electrolyte 2 can make the battery cycle more than 250 hours. The degree is still small, and the lithium symmetric battery prepared with the implementation of electrolyte 3 can make the degree of polarization still small after the battery is cycled for more than 300 hours. The lithium symmetric battery prepared with Comparative Electrolyte 1 showed severe polarization after 120 hours of cycling. Therefore, adding n-propyl boric acid, n-hexyl boric acid and n-octyl boric acid to the electrolyte can effectively prolong the cycle life of the battery.

4 is a cycle life diagram of a lithium symmetric battery prepared by using an electrolyte for a lithium battery of the present invention and a preparation method thereof and the implementation of the electrolyte 4 of the lithium battery, and FIG. 5 is a diagram of a lithium battery using an electrolyte of the present invention and its Preparation method and implementation of lithium battery Cycle life diagram of lithium symmetric battery prepared by electrolyte 5. As shown in the figure, by changing the concentration of the additive n _- hexylboronic acid R2 in the electrolyte, the cycle life of the obtained lithium symmetric battery is also extended to a certain extent.

6 is a cycle life diagram of a lithium symmetric battery prepared by using an electrolyte for a lithium battery of the present invention, a preparation method thereof, and the implementation of the electrolyte 6 of the lithium battery, and FIG. 7 is a diagram of a lithium battery using an electrolyte of the present invention. Preparation method and implementation of lithium battery Cycle life diagram of lithium symmetric battery prepared by electrolyte 7. As shown in the figure, under the condition of different ratios of non-aqueous organic solvents, the n-hexylboronic acid R ₂ additive can still significantly prolong the cycle life of lithium symmetric batteries.

FIG. 9 is a cycle performance diagram of a full battery prepared by using an electrolyte for a lithium battery of the present invention, a preparation method thereof, and an implementation electrolyte 1 of the lithium battery and a comparative electrolyte 1. FIG. As shown in the figure, the cycle stability of the full battery assembled with the implementation of electrolyte 1 is greatly improved, and the capacity retention rate of 90.2% is still maintained after 150 cycles, and the specific capacity decay is relatively slow.

Therefore, the present invention adopts an electrolyte for a lithium battery, a preparation method thereof, and a lithium battery, which can solve the problem of low charging and discharging times of the existing lithium battery, and has the advantages of good cycle stability and slow specific capacity decay.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: it is still The technical solutions of the present invention may be modified or equivalently replaced, and these modifications or equivalent replacements cannot make the modified technical solutions depart from the spirit and scope of the technical solutions of the present invention.

Claims (10)

1. An electrolyte for a lithium battery, characterized in that: the lithium salt, the nonaqueous organic solvent and the additive are included, wherein the additive is alkyl boric acid, and the weight percentage content of the additive is 0.5-2.0 wt%;

the alkyl boric acid is one or a mixture of more of n-propyl boric acid, n-hexyl boric acid and n-octyl boric acid;

the structural formula of n-propylboronic acid is:

the structural formula of n-hexylboronic acid is:

the structural formula of n-octylboronic acid is:

2. the electrolyte for a lithium battery as claimed in claim 1, wherein: the concentration of the lithium salt is 1M, and the lithium salt is LiPF ₆ 、LiBF ₄ 、LiBOB、LiDFOB、LiSbF ₆ 、LiAsF ₆ 、LiN(SO ₂ CF ₃ ) ₂ 、LiN(SO ₂ C ₂ F ₅ ) ₂ 、LiC(SO ₂ CF ₃ ) ₃ Or LiN (SO) ₂ F) ₂ One or a mixture of several of them.

3. The electrolyte for a lithium battery as claimed in claim 1, wherein: the non-aqueous organic solvent is a mixture of cyclic carbonate and chain carbonate, and the volume ratio of the cyclic carbonate to the chain carbonate is 3:7-7: 3; the cyclic carbonate is one or a mixture of more of ethylene carbonate, propylene carbonate or butylene carbonate, and the chain carbonate is one or a mixture of more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or propyl methyl carbonate.

4. A method of preparing an electrolyte for a lithium battery as claimed in any one of claims 1 to 3, characterized by comprising the steps of:

s1, in a glove box, H ₂ O<0.1ppm，O ₂ <0.1ppm, weighing a proper amount of lithium salt, and dissolving the lithium salt in a nonaqueous organic solution, wherein the concentration of the lithium salt is 1M, so as to obtain a matrix electrolyte;

and S2, adding 0.5-2.0 wt% of additive into the matrix electrolyte, and uniformly stirring to obtain the electrolyte for the lithium battery.

5. A lithium battery comprising the electrolyte for a lithium battery prepared according to claim 4, characterized in that: comprises a battery shell, a positive electrode, a negative electrode, a diaphragm and electrolyte which are positioned in the battery shell.

6. A lithium battery as claimed in claim 5, characterized in that: the positive electrode comprises a positive electrode current collector and a positive electrode material positioned on the positive electrode current collector, wherein the positive electrode material comprises a positive electrode active material.

7. A lithium battery as claimed in claim 6, characterized in that: the positive active material is LiCoO ₂ 、LiNiO ₂ 、LiMn ₂ O ₄ 、LiCo _1-y M _y O ₂ 、LiNi _1-y M _y O ₂ 、LiMn _2-y M _y O ₄ And LiNi _x Co _y Mn _z M _1-x-y-z O ₂ One or a mixture of several of them; wherein M is one or a mixture of more of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti, y is more than or equal to 0 and less than or equal to 1, x is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, and x + y + z is less than or equal to 1.

8. A lithium battery as claimed in claim 6, characterized in that: the positive active material is LiFe _1-x M _x PO ₄ Wherein M is one or a mixture of more of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti, and x is more than or equal to 0 and less than 1.

9. A lithium battery as claimed in claim 5, characterized in that: the negative electrode comprises a negative electrode current collector and a negative electrode material positioned on the negative electrode current collector, wherein the negative electrode material is one or a mixture of more of graphite, hard carbon, soft carbon, a silicon-carbon composite material, a silicon-oxygen-carbon composite material, metal lithium and an alloy of the metal lithium.

10. A lithium battery as claimed in claim 5, characterized in that: the diaphragm is one or more of polyolefin porous membrane, non-woven fabric, fiber coating, ceramic coating and inorganic solid electrolyte coating.

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