CN103730688A - Lithium ion battery and electrolyte thereof - Google Patents

Abstract

The invention provides a lithium ion battery and its electrolyte. The electrolyte solution of the lithium ion battery of the present invention includes a non-aqueous organic solvent; a lithium salt dissolved in the non-aqueous organic solvent; and an additive dissolved in the non-aqueous organic solvent. The additives include: fluoroethylene carbonate (FEC), with a mass percentage of 1% to 15% in the electrolyte; 1,3-propane sultone (PS), with a mass percentage of 1,3-propane sultone (PS) in the electrolyte content of 0.5% to 10%; and the oxalate ester with two double bonds having the structure of formula I, the mass percentage in the electrolyte is 0.01% to 5%, wherein, in formula I, n is selected from An integer from 0 to 4. The lithium ion battery of the present invention comprises a positive pole piece; a negative pole piece; a separator, spaced between adjacent positive pole pieces and negative pole pieces; and the above electrolyte. The lithium ion battery of the invention has excellent charge and discharge cycle performance under high temperature and high voltage.

Description

Lithium-ion battery and its electrolyte

technical field

The invention relates to the field of batteries, in particular to a lithium ion battery and its electrolyte.

Background technique

With the popularity of electronic mobile devices such as notebook computers, mobile phones, handheld game consoles, and tablet computers, people have higher and higher performance requirements for electronic mobile devices. However, the higher the performance and the more fancy the function of electronic products, the faster the power consumption, so people urgently need lithium-ion batteries with higher energy density.

When increasing the energy density of the lithium-ion battery (such as increasing the voltage of the lithium-ion battery), it is equivalent to increasing the activity of the electrochemical reaction of the electrolyte. At this time, the electrolyte will undergo a violent redox reaction on the positive and negative electrodes, but at the same time Along with a large number of side reactions, the performance of Li-ion batteries will be very negatively affected. In actual use, electronic products are also faced with continuous use of heat or an increase in the ambient temperature of lithium-ion batteries. These factors may cause lithium-ion batteries to be in a high temperature state. At this time, the electrolyte will be more strictly tested. Since the oxidative decomposition of the electrolyte will lead to a decrease in the cycle performance of lithium-ion batteries under high temperature conditions, the development of suitable additives to effectively form a protective film on the positive and negative electrodes that can reduce the reaction between the electrolyte and the positive and negative electrodes has always been concerned. topic of.

Among them, controlling the interface reaction between the electrolyte and the electrode is the key to improving the charge-discharge cycle performance of lithium-ion batteries. In lithium-ion batteries, additives 1,3-propane sultone (PS) and fluoroethylene carbonate (FEC) are often used to improve cycle performance. The Chinese patent application publication number CN102005606A discloses a certain amount of PS The electrolyte with FEC can form a film on the surface of the negative electrode to improve the cycle performance of the lithium-ion battery, but when the voltage is increased to 4.4V, this combination cannot meet the requirements for improving the cycle performance of the lithium-ion battery.

Contents of the invention

In view of the problems existing in the background technology, the purpose of the present invention is to provide a lithium ion battery and its electrolyte solution with excellent charge-discharge cycle performance under high temperature and high voltage.

In order to achieve the above object, in the first aspect of the present invention, the present invention provides an electrolyte solution for a lithium ion battery, comprising a non-aqueous organic solvent; a lithium salt dissolved in a non-aqueous organic solvent; and an additive dissolved in a non-aqueous organic solvent in organic solvents. The additives include: fluoroethylene carbonate (FEC), with a mass percentage of 1% to 15% in the electrolyte; 1,3-propane sultone (PS), with a mass percentage of 1,3-propane sultone (PS) in the electrolyte content of 0.5% to 10%; and the oxalate ester with two double bonds having the structure of formula I, the mass percentage in the electrolyte is 0.01% to 5%, wherein, in formula I, n is selected from An integer from 0 to 4.

In the second aspect of the present invention, the present invention provides a lithium ion battery, comprising: a positive pole piece; a negative pole piece; a separator spaced between adjacent positive pole pieces and negative pole pieces; and an electrolyte. The electrolyte is the electrolyte of the first aspect of the present invention.

Compared with the prior art, the beneficial effects of the present invention are:

The lithium ion secondary battery of the invention has excellent charge and discharge cycle performance under high temperature and high voltage.

Detailed ways

The lithium ion battery according to the present invention and its electrolyte, as well as comparative examples and examples are described in detail below.

First, the electrolyte solution of the lithium ion battery according to the first aspect of the present invention will be described.

The electrolyte solution for lithium ion batteries according to the first aspect of the present invention comprises: a non-aqueous organic solvent; a lithium salt dissolved in the non-aqueous organic solvent; and an additive dissolved in the non-aqueous organic solvent. The additives include: fluoroethylene carbonate (FEC), with a mass percentage of 1% to 15% in the electrolyte; 1,3-propane sultone (PS), with a mass percentage of 1,3-propane sultone (PS) in the electrolyte The content is 0.5% to 10%; and the oxalate ester with two double bonds having the structure of formula I, the mass percentage in the electrolyte is 0.01% to 5%, and n in formula I is selected from 0 to Integer of 4.

In the electrolyte solution of the lithium ion battery according to the first aspect of the present invention, the mass percentage of the additive fluoroethylene carbonate (FEC) in the electrolyte solution may be 1%-5%.

In the electrolyte solution of the lithium ion battery according to the first aspect of the present invention, the mass percentage content of the additive 1,3-propane sultone (PS) in the electrolyte solution may be 1%-5%.

In the electrolyte solution of the lithium-ion battery according to the first aspect of the present invention, the weight percentage of the additive oxalate ester having two double bonds having the structure of formula I in the electrolyte solution may be 0.5%-3%. When its mass percentage in the electrolyte is less than 0.5%, a stable SEI film cannot be formed on the negative electrode, and the cycle performance of lithium-ion batteries is not significantly improved; and when its mass percentage in the electrolyte When it is higher than 3%, the resistance of the formed SEI film will increase sharply, thereby deteriorating the cycle performance of the lithium-ion battery.

In the electrolyte of the lithium-ion battery according to the first aspect of the present invention, the molecular structure of the compound represented by formula I contains two double bonds, which is easy to undergo a reduction reaction on the surface of the negative electrode, and an oxidation reaction to occur on the surface of the positive electrode, thereby electrochemical Polymerization produces a polymer passivation film. From the structural analysis of the compound with the structure of formula I, when n is greater than 4, the molecular weight of the compound with the structure of formula I increases, which has a great influence on the viscosity of the electrolyte and will reduce the conductivity of the electrolyte.

In a high-temperature and high-voltage environment, the positive electrode has a strong oxidizing effect on the electrolyte, resulting in poor high-temperature cycle performance of the lithium-ion battery. 1,3-Propane sultone (PS) can promote the formation of SEI film of fluoroethylene carbonate (FEC) and improve the high-temperature storage performance of lithium-ion batteries. A simple oxalate ester with two double bonds with the structure of formula I cannot inhibit the exfoliation of graphite by the non-aqueous organic solvent propylene carbonate (PC), while fluoroethylene carbonate (FEC) can promote the graphite with the structure of formula I. The oxalate ester containing two double bonds forms a good and dense SEI film, which makes it have good stability at high temperature, thereby effectively passivating the surface of the positive and negative electrodes, inhibiting the oxidative decomposition of the electrolyte components on the surface of the positive electrode and Reductive decomposition on the negative electrode surface. Carbonate additives containing two double bonds (such as dipropylene carbonate), alone or in combination with fluoroethylene carbonate (FEC), cannot effectively form a stable SEI film.

In the electrolyte solution of the lithium ion battery according to the first aspect of the present invention, the non-aqueous organic solvent may include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) one or more.

In the electrolyte solution of the lithium ion battery according to the first aspect of the present invention, the lithium salt may be selected from LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (wherein, x, y is a positive integer), LiPF ₆ , LiBF ₄ , LiTFSI, LiBOB, LiAsF ₆ , Li(CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ and LiClO ₄ .

Next, the lithium ion battery according to the second aspect of the present invention will be described.

According to the lithium ion battery of the second aspect of the present invention, it comprises: a positive pole piece; a negative pole piece; a separator, spaced between adjacent positive pole pieces and negative pole pieces; and an electrolyte. Wherein, the electrolyte is the electrolyte of the lithium ion battery according to the first aspect of the present invention.

In the lithium ion battery according to the second aspect of the present invention, the charging cut-off voltage of the lithium ion battery may be greater than or equal to 4.4V.

In the lithium ion battery according to the second aspect of the present invention, the positive electrode active material of the positive electrode sheet can be selected from lithium transition metal oxides, compounds obtained by adding other transition metals or non-transition metals to lithium transition metal oxides, or their at least one of the combinations. The lithium transition metal oxide may be selected from at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

In the lithium ion battery according to the second aspect of the present invention, the negative electrode active material of the negative pole piece is selected from soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide compound, silicon carbon composite, lithium titanate , metals or alloys that can form alloys with lithium, metal oxides that can insert and extract lithium, or at least one of their combinations.

In the lithium-ion battery according to the second aspect of the present invention, the separator can be selected from polyethylene (PE) porous polymer film, PE/polypropylene (PP) multilayer composite porous polymer film, or ceramic-treated porous polymer film object film.

Next, the examples, comparative examples and test results of the lithium ion battery and its electrolyte according to the present invention will be described.

Comparative example 1

(1) Preparation of positive pole piece: active material LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , conductive agent acetylene black, binder polyvinylidene fluoride (PVDF) in the solvent N-methyl After fully stirring and mixing in pyrrolidone, coating on current collector Al foil, drying and cold pressing to obtain positive electrode sheet.

(2) Preparation of negative pole piece: active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC) according to the weight ratio of 95:2:2:1 After fully stirring and mixing uniformly in deionized water as a solvent, it is coated on a current collector Cu foil, dried, and cold pressed to obtain a negative electrode sheet.

(3) Preparation of electrolyte: LiPF ₆ with a concentration of 1M was used as the lithium salt, and a mixture of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) was used as the non-aqueous organic solvent. The mass ratio of EC:PC:DEC=40:40:20. In addition, the electrolyte solution also contains 1,3-propane sultone (PS) with a mass percent content of 3%.

(4) Preparation of lithium-ion battery: stack the positive pole piece, the separator PE porous polymer film and the negative pole piece in order, so that the separator PE porous polymer film is in the middle of the positive pole piece and the negative pole piece for isolation role, and wound to get the bare cell. Putting the bare cell in the outer package, injecting the prepared electrolyte and packaging it to obtain a lithium-ion battery.

Comparative example 2

Lithium-ion batteries were prepared in the same manner as Comparative Example 1, except that the additive was only 5% by mass fluoroethylene carbonate (FEC) when preparing the electrolyte (ie, step (3)).

Comparative example 3

A lithium-ion battery was prepared according to the same method as Comparative Example 1, except that when preparing the electrolyte (ie, step (3)), the additive was only dipropylene oxalate with a mass percentage of 1%.

Comparative example 4

Lithium-ion batteries were prepared in the same manner as Comparative Example 1, except that when preparing the electrolyte (ie, step (3)), the additives were 3% by mass of 1,3-propane sultone (PS) and Fluoroethylene carbonate (FEC) with a mass percentage of 5%.

Comparative example 5

Lithium-ion batteries were prepared according to the same method as Comparative Example 1, except that when preparing the electrolyte (ie step (3)), the additives were 1,3-propane sultone (PS) with a mass percentage of 3%, 5% by mass of fluoroethylene carbonate (FEC) and 6.5% by mass of dipropylene oxalate.

Comparative example 6

Lithium-ion batteries were prepared in the same manner as Comparative Example 1, except that when preparing the electrolyte (i.e. step (3)), the concentration was 0.95M LiPF ₆ and 0.05M LiBF ₄ were lithium salts, and the additives were mass percentages of 3% of 1,3-propane sultone (PS), 20% by mass of fluoroethylene carbonate (FEC), and 1.5% by mass of dipropylene oxalate.

Example 1

Lithium-ion batteries were prepared according to the same method as Comparative Example 1, except that when preparing the electrolyte (ie step (3)), the additives were 1,3-propane sultone (PS) with a mass percentage of 3%, 5% by mass of fluoroethylene carbonate (FEC) and 1% by mass of dipropylene oxalate.

Example 2

Lithium-ion batteries were prepared according to the same method as Comparative Example 1, except that when preparing the electrolyte (ie step (3)), the additives were 1,3-propane sultone (PS) with a mass percentage of 3%, 5% by mass of fluoroethylene carbonate (FEC) and 1% by mass of divinyl oxalate.

Example 3

Lithium-ion batteries were prepared according to the same method as in Example 1, except that when preparing the electrolyte (ie step (3)), the additives were 1,3-propane sultone (PS) with a mass percentage of 3%, 5% by mass of fluoroethylene carbonate (FEC) and 3% by mass of dipropylene oxalate.

Example 4

Lithium-ion batteries were prepared according to the same method as in Example 1, except that when preparing the electrolyte (ie step (3)), the additives were 1,3-propane sultone (PS) with a mass percentage of 3%, 5% by mass of fluoroethylene carbonate (FEC) and 0.5% by mass of dipropylene oxalate.

Example 5

Lithium-ion batteries were prepared according to the same method as Comparative Example 1, except that when preparing the electrolyte (ie, step (3)), the concentration was 1M LiBF ₄ as lithium salt, ethylene carbonate (EC), propylene carbonate (PC ) and dimethyl carbonate (DMC) is a non-aqueous organic solvent, the mass ratio of each carbonate is EC:PC:DMC=30:30:40, and the additive is 1,3- Propane sultone (PS), 10% by mass of fluoroethylene carbonate (FEC) and 5% by mass of divinyl oxalate.

Example 6

Lithium-ion batteries were prepared according to the same method as in Example 5, except that when preparing the electrolyte (ie step (3)), the additives were 1,3-propane sultone (PS) with a mass percentage of 1%, 1% by mass of fluoroethylene carbonate (FEC) and 5% by mass of divinyl oxalate.

Example 7

Lithium-ion batteries were prepared in the same manner as Comparative Example 1, except that when preparing the electrolyte (ie, step (3)), the additives were 0.5% by mass of 1,3-propane sultone (PS), 15% by mass of fluoroethylene carbonate (FEC) and 1% by mass of dibutylene oxalate.

Example 8

Lithium-ion batteries were prepared in the same manner as Comparative Example 1, except that when preparing the electrolyte (i.e. step (3)), the concentration was 0.95M LiPF ₆ and 0.05M LiBF ₄ were lithium salts, and the additives were mass percentages of 3% of 1,3-propane sultone (PS), 5% by mass of fluoroethylene carbonate (FEC), and 1.5% by mass of dipropylene oxalate.

Example 9

Lithium-ion batteries were prepared according to the same method as Comparative Example 1, except that when preparing the electrolyte (ie, step (3)), the concentration was 0.95M LiPF ₆ and 0.05M LiTFSI were lithium salts, and the additives were 3% by mass. % of 1,3-propane sultone (PS), 5% by mass of fluoroethylene carbonate (FEC) and 1% by mass of dipropylene oxalate.

Example 10

Lithium-ion batteries were prepared according to the same method as Comparative Example 1, except that when preparing the electrolyte (ie step (3)), the additives were 1,3-propane sultone (PS) with a mass percentage of 3%, 5% by mass of fluoroethylene carbonate (FEC) and 1% by mass of dibutylene oxalate.

Finally, the performance test process and test results of the lithium-ion battery based on Comparative Examples 1-6 and Examples 1-10 are given.

Cycle performance test:

Take 5 lithium-ion batteries in each group, repeatedly charge and discharge the lithium-ion batteries through the following steps, and calculate the discharge capacity retention rate of the lithium-ion batteries, and use the average value of the discharge capacity retention rates of the 5 lithium-ion batteries as the lithium-ion battery. Discharge capacity retention of ion batteries.

First, charge and discharge for the first time in an environment of 45°C, and carry out constant current and constant voltage charging at a charging current of 0.5C (that is, the current value that completely discharges the theoretical capacity within 2h) until the upper limit voltage is 4.4 V, and then perform constant current discharge at a discharge current of 0.7C until the final voltage is 3V, record the discharge capacity of the first cycle; then perform 200 charge and discharge cycles, and record the discharge capacity of the 200th cycle.

Discharge capacity retention rate=(discharge capacity of the 200th cycle/discharge capacity of the first cycle)×100%.

Next, the performance test results of the lithium-ion secondary battery are analyzed.

Table 1 shows the parameters and performance test results based on Comparative Examples 1-6 and Examples 1-10.

Table 1 The parameters and performance test results of comparative examples 1-6 and embodiments 1-10

From the comparison of Comparative Examples 1-6 and Examples 1-10, it can be seen that the introduction of dipropylene oxalate (Comparative Example 3) alone cannot improve the cycle performance of lithium-ion batteries at high temperature and high voltage. Lithium-ion batteries The discharge capacity retention rate is even lower than that of 1,3-propane sultone (PS) and/or fluoroethylene carbonate (FEC) alone (Comparative Example 1, Comparative Example 2 and Comparative Example 4), which It is because 1,3-propane sultone (PS) can promote the formation of SEI film of fluoroethylene carbonate (FEC), thereby improving the high-temperature storage performance of lithium-ion batteries. When the oxalate ester with two double bonds with the structure of formula I is used in combination with 1,3-propane sultone (PS) and fluoroethylene carbonate (FEC), it can significantly improve the performance of lithium-ion batteries at high temperatures. Cycling performance at high voltage, this is because fluoroethylene carbonate (FEC) can promote the formation of a good and dense SEI film of the oxalate ester with the structure of formula I containing two double bonds, so that it has good performance at high temperature Stability, thereby effectively passivating the surface of the positive electrode and the surface of the negative electrode, inhibiting the oxidation and decomposition of the electrolyte components on the surface of the positive electrode and the reduction decomposition on the surface of the negative electrode.

Comparative example 1, embodiment 2 and embodiment 10 can find out, add 1% divinyl oxalate, 1% dipropylene oxalate and 1% dibutyl oxalate and all reach better improvement effect; But Compared with the former two, 1% dibutyl oxalate has a lower discharge capacity retention rate of the lithium-ion battery, which may be related to the chain length of the organic salt in the SEI film component. The longer the molecular chain, the better the The greater the influence of the viscosity of the electrolyte, the lower the conductivity of the electrolyte.

From the comparison of Comparative Example 5, Example 1, Example 3 and Example 4, it can be seen that changing the concentration will also affect the cycle performance of lithium-ion batteries. When the mass percentage of dipropylene oxalate was small, lithium The capacity retention rate of the ion battery is relatively high; when the mass percentage of dipropylene oxalate is too high (comparative example 5), the impedance of the formed SEI film will increase sharply, which will deteriorate the cycle performance of the lithium ion battery. Similarly, when the mass percentage of fluoroethylene carbonate (FEC) is too high (Comparative Example 6), the cycle performance of the lithium-ion battery will also be deteriorated.

It can be seen from Examples 8 and 9 that the proper introduction of LiBF ₄ and LiTFSI in lithium salts can significantly improve the cycle performance of lithium-ion batteries.

Claims (10)

1. An electrolyte for a lithium-ion battery, comprising: Non-aqueous organic solvents; Lithium salts, dissolved in non-aqueous organic solvents; and additives, dissolved in non-aqueous organic solvents, It is characterized by: The additives include: Fluoroethylene carbonate (FEC), the mass percentage in the electrolyte is 1% to 15%; 1,3-propane sultone (PS), the mass percentage content in the electrolyte is 0.5% to 10%; And the oxalate ester containing two double bonds having the structure of formula I, the mass percentage in the electrolyte is 0.01% to 5%,

Wherein, n in formula I is an integer selected from 0-4. 2 . The electrolyte solution for lithium-ion batteries according to claim 1 , wherein the mass percentage of the additive fluoroethylene carbonate (FEC) in the electrolyte solution is 1% to 5%. 3. The electrolyte solution for lithium ion batteries according to claim 1, characterized in that the mass percentage of the additive 1,3-propane sultone (PS) in the electrolyte solution is 1% to 5% . 4. the electrolyte of lithium-ion battery according to claim 1, is characterized in that, the mass percentage composition of the oxalic acid ester containing two double bonds of formula I structure in electrolyte is 0.5%～ 3%. 5. the electrolytic solution of lithium-ion battery according to claim 1, is characterized in that, described non-aqueous organic solvent comprises one or more in ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate kind. 6. The electrolyte solution of lithium ion battery according to claim 1, characterized in that, the lithium salt is selected from LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (wherein, One or more of x and y are positive integers), LiPF ₆ , LiBF ₄ , LiTFSI, LiBOB, LiAsF ₆ , Li(CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO ₃ and LiClO ₄ . 7. A lithium ion battery, comprising: Positive pole piece; Negative pole piece; a separator spaced between adjacent positive and negative pole pieces; and electrolyte; It is characterized in that the electrolyte is the electrolyte of the lithium ion battery according to any one of claims 1-6. 8 . The lithium-ion battery according to claim 7 , wherein the charging cut-off voltage of the lithium-ion battery is greater than or equal to 4.4V. 9. The lithium ion battery according to claim 8, wherein the positive active material of the positive electrode sheet is selected from lithium transition metal oxides, compounds obtained by adding other transition metals or non-transition metals to lithium transition metal oxides , or at least one of their combinations. 10. Lithium-ion battery according to claim 8, is characterized in that, the negative electrode active material of described negative electrode sheet is selected from soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide compound, silicon carbon compound , lithium titanate, metals or alloys capable of forming alloys with lithium, metal oxides capable of inserting and extracting lithium, or at least one of their combinations.