CN115911534A

CN115911534A - Lithium ion battery electrolyte and lithium ion battery containing same

Info

Publication number: CN115911534A
Application number: CN202111106575.8A
Authority: CN
Inventors: 邱阳; 朱学全; 黄慧聪; 付向天; 张晓宇; 赵倩
Original assignee: Shanshan Advanced Materials Quzhou Co ltd
Current assignee: Shanshan Advanced Materials Quzhou Co ltd
Priority date: 2021-09-22
Filing date: 2021-09-22
Publication date: 2023-04-04

Abstract

The invention belongs to the technical field of lithium ion batteries, and discloses a lithium ion battery electrolyte and a lithium ion battery containing the same. The lithium ion battery electrolyte comprises a non-aqueous organic solvent, lithium salt and an additive, wherein the additive comprises a conventional additive and a compound A, and the structure of the compound A is shown as the formula (I):

Description

Lithium ion battery electrolyte and lithium ion battery containing same

Technical Field

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

Background

High energy density is a constant pursuit of lithium ion batteries, and due to successful commercialization of the lithium ion batteries, the energy density of the batteries is significantly improved, but the current lithium ion batteries still cannot meet the increasing demands of electric automobiles and portable electronic devices. In order to realize higher energy density of a commercial ternary lithium ion battery, two paths are mainly used, namely, the proportion of the nickel content in the ternary cathode material is gradually increased, and the cut-off voltage of the cathode material is stably increased. However, either approach puts higher demands on the stability of the electrolyte: the positive electrode material is high in nickel content, the stability of the electrolyte under a high-temperature condition can be influenced, and gas is easily generated through continuous charge and discharge; the conventional electrolyte is easy to generate side reaction with the surface of the anode material under high voltage, and the performance of the high-voltage ternary anode material is influenced. In response to the above problems, in addition to utilizing a synergistic combination of conventional additives, there is a need to develop new film-forming additives.

Disclosure of Invention

The invention aims to overcome the defects of the background technology and provides a lithium ion battery electrolyte and a lithium ion battery containing the same. The lithium ion battery electrolyte disclosed by the invention can effectively solve the high-temperature storage performance and the cycle performance of the lithium ion battery by optimizing the formula and under the synergistic effect of multiple uniquely combined components, so that an electrolyte system has high energy density and high safety performance, the requirements of the storage performance and the safety performance of the electrolyte at high temperature are favorably met, and the electrochemical performance of the lithium ion battery is further improved.

In order to achieve the purpose, the lithium ion battery electrolyte comprises a non-aqueous organic solvent, lithium salt and additives, wherein the additives comprise conventional additives and a compound A, and the structure of the compound A is shown as the formula (I):

wherein R is independently selected from one of alkyl, alkenyl, isocyanic acid group, fluoroalkyl, phenyl, silicon group and substitution thereof with 1-4 carbon atoms.

Further, in some embodiments of the present invention, the compound a is selected from at least one of the compounds represented by the following structural formula:

preferably, in some embodiments of the present invention, the content of the compound a additive is 0.5 to 1.0% of the total mass of the lithium ion battery electrolyte.

Further, in some embodiments of the present invention, the lithium ion battery electrolyte further comprises other additives selected from at least one of fluoroethylene carbonate (FEC), vinylene Carbonate (VC), vinyl sulfate (DTD), 1,3 Propane Sultone (PS), 1, 3-Propene Sultone (PST), tris (trimethylsilyl) borate (TMSB), tris (trimethylsilyl) phosphate (TMSP), tetravinylsilane (TVS), and Citraconic Anhydride (CA).

Preferably, in some embodiments of the present invention, the content of the other additive is 0.5 to 3.0% of the total mass of the lithium ion battery electrolyte.

Further, in some embodiments of the present invention, the lithium salt is selected from lithium hexafluorophosphate (LiPF) ₆ ) Lithium tetrafluoroborate (LiBF) ₄ ) Lithium difluorophosphate (LiDFP), lithium bis (fluorosulfonylimide) (LiFSI), lithium bis (oxalato) borate (LiBOB), lithium bis (oxalato) borate (LiDFOB), lithium tetrafluorooxalato phosphate (LiOTFP), lithium bis (oxalato) phosphate (LiDFOP).

Preferably, in some embodiments of the present invention, the content of the lithium salt is 15 to 17% of the total mass of the lithium ion battery electrolyte.

Further, in some embodiments of the present invention, the non-aqueous organic solvent is one or more of a chain carbonate, a cyclic carbonate.

Preferably, in some embodiments of the present invention, the cyclic carbonate is one or more of ethylene carbonate, propylene carbonate; the chain carbonate is one or more of methyl ethyl carbonate, dimethyl carbonate and diethyl carbonate.

More preferably, in some embodiments of the present invention, the non-aqueous organic solvent is a mixture of Ethylene Carbonate (EC), diethyl carbonate (DEC), ethyl Methyl Carbonate (EMC).

On the other hand, the invention also provides a lithium ion battery, which comprises a positive pole piece, a negative pole piece, an isolating membrane arranged between the positive pole piece and the negative pole piece and the lithium ion battery electrolyte.

Preferably, in some embodiments of the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode membrane on the surface of the positive electrode current collector, the positive electrode membrane includes a positive electrode active material, a conductive agent and a binder, and the positive electrode active material is LiNi _1-x-y-z Co _x Mn _y Al _z O ₂ Lithium nickel manganese oxide, lithium cobaltate, lithium-rich manganese-based solid solution and lithium manganese oxide, wherein: x is more than or equal to 0 and less than or equal to 1, y 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 more than or equal to 0 and less than or equal to 1, wherein the negative electrode active substance is artificial graphite, lithium metal, coated natural graphite, a silicon-carbon negative electrode and a silicon negative electrode.

Compared with the prior art, the invention has the advantages that:

(1) On one hand, the compound A with a specific structure in the lithium ion battery electrolyte can be preferentially reduced into a stable SEI film by EC at the negative electrode, and the film forming impedance is low; on the other hand, the additive containing the trimethylsilyl structure in the compound A can be combined with trace HF and moisture released under the high-temperature environment of the electrolyte, so that the damage to the electrode material is reduced.

(2) The lithium ion battery electrolyte fully exerts the performance of the lithium ion battery by optimizing the formula, particularly under the synergistic action of the uniquely combined mixed lithium salt, the cathode film-forming additive, the anode protective additive and the compound A with a specific structure, and prolongs the calendar and the cycle life of the lithium ion battery.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. It is to be understood that the following description is only illustrative of the present invention and is not to be construed as limiting the present invention.

The terms "comprises," "comprising," "includes," "including," "has," "having," "contains," "containing," or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

When an amount, concentration, or other value or parameter is expressed as a range, preferred range, or range defined by a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2 and 4 to 5", "1 to 3 and 5", and the like. When a range of values is described herein, unless otherwise stated, the range is intended to include the endpoints thereof and all integers and fractions within the range.

The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. "optional" or "any" means that the subsequently described event or events may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

The indefinite articles "a" and "an" preceding an element or component of the invention are used without limitation to the number requirement (i.e., the number of occurrences) of the element or component. Thus, "a" or "an" should be read to include one or at least one, and the singular form of an element or component also includes the plural unless the number clearly indicates the singular.

Furthermore, the description below of the terms "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily for the same embodiment or example. Further, the technical features of the embodiments of the present invention may be combined with each other as long as they do not conflict with each other.

The structural formula of compound a in the examples and comparative examples is characterized as follows:

example 1

The lithium ion battery electrolyte is prepared by the following method: ethylene Carbonate (EC), diethyl carbonate (DEC), and Ethyl Methyl Carbonate (EMC) were uniformly mixed in a glove box filled with argon gas (moisture < 0.1ppm, oxygen < 0.1 ppm) at a mass ratio of 30 ₆ ) Lithium difluorophosphate (LiDFP) in an amount of 1.0% and lithium difluorobis (oxalato) phosphate (LiDFOP) in an amount of 0.5% were stirred until they were completely dissolved, and then A9 in an amount of 0.5% based on the total mass of the electrolyte, 1% of vinyl sulfate (DTD) and 0.5% of 1, 3% of Propenylsulfonate (PST) were added and stirred uniformly to obtain the electrolyte for a lithium ion battery of example 1.

Examples 2 to 14

Examples 2-14 are also specific examples of electrolytes, and the parameters and preparation method are the same as in example 1 except for the parameters shown in Table 1.

Comparative examples 1 to 5

In comparative examples 1 to 5, the parameters and preparation method were the same as in example 1 except for the parameters shown in Table 1.

TABLE 1 composition ratios of the electrolyte components of examples 1-14 and comparative examples 1-5

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Note: the concentration of the lithium salt is the mass percentage content in the electrolyte;

the content of the compound A is the mass percentage content in the electrolyte;

the content of each component in other additives is the mass percentage content in the electrolyte;

the proportion of each component in the solvent is mass ratio.

Lithium ion battery performance testing

Preparing a lithium ion battery:

LiNi as positive electrode active material _0.6 Co _0.2 Mn _0.2 O ₂ (622) The conductive agent acetylene black, the carbon nano tube and the binder polyvinylidene fluoride (PVDF) are fully stirred and uniformly mixed in an N-methyl pyrrolidone solvent system in a dry environment filled with nitrogen according to the mass ratio of (2.8) ³ 。

Preparing a negative electrode active material graphite, a conductive agent acetylene black and a carbon nano tube: the binder Styrene Butadiene Rubber (SBR) and the thickener sodium carboxymethylcellulose (CMC) are fully stirred and uniformly mixed in a deionized water solvent system according to the mass ratio of 96.8. Polyethylene (PE) is used as a base film (14 μm) and a nano alumina coating (2 μm) is coated on the base film to be used as a diaphragm.

And stacking the positive pole piece, the diaphragm and the negative pole piece in sequence to enable the diaphragm to be positioned between the positive pole piece and the negative pole piece to play an isolating role, and winding to obtain the bare cell. And (3) placing the bare cell in an outer package, injecting the electrolyte prepared in each embodiment and comparative example, and carrying out procedures of packaging, laying aside, formation, aging, secondary packaging, capacity grading and the like to obtain the high-nickel NCM622/AG-4.3V ternary positive electrode material soft package lithium ion battery. The performance tests were performed on each of the batteries of the examples and comparative examples, and the test results are shown in table 2, in which:

1) Normal temperature cycle performance

Charging the NCM622 battery to 4.3V at constant current and constant voltage of 1C and with cutoff current of 0.05C at normal temperature (25 +/-2 ℃); standing for 5min, then discharging at constant current of 1C to 3.0V, standing for 5min, circularly charging and discharging, and recording the cycle life of the battery when the charge-discharge cycle capacity reaches 80% of the initial capacity.

2) High temperature cycle performance

Under the condition of high temperature (45 ℃), the NCM622 batteries are respectively charged to 4.3V at a constant current and a constant voltage of 1C, and the cut-off current is 0.05C; standing for 5min, then discharging at constant current of 1C to 3.0V, standing for 5min, circularly charging and discharging, and recording the cycle life of the battery when the charge-discharge cycle capacity reaches 80% of the initial capacity.

3) High temperature storage Property

The lithium ion battery is subjected to 1C/1C charging and discharging (the discharge capacity is recorded as D) at normal temperature (25 +/-2 ℃), and _C0 ) Then, the NCM622/AG battery is respectively charged to 4.3V under the condition of 1C constant current and constant voltage; the fully charged lithium ion battery is stored in a high-temperature box at 60 ℃ for 14 days, and 1C discharge is carried out under normal temperature conditions (the discharge capacity is marked as D) _C1 ) (ii) a Then, 1C/1C charging and discharging (discharge capacity is denoted by D) were performed at ordinary temperature _C2 ). The capacity retention rate and the capacity recovery rate of the lithium ion battery are calculated by using the following formulas.

Capacity retention ratio (%) at day seven = D _C1 /D _C0 ×100％；

Capacity recovery (%) at day seven = D _C2 /D _C0 ×100％；

Table 2 lithium ion battery performance test results of each comparative example and example

The lithium ion batteries of examples 1 and 2 were greatly improved in terms of normal and high temperature cycles and high temperature storage performance, as compared to comparative examples 4 and 5. The comparison results show that the effect of the compound A is not obvious and that the addition of a proper amount of the compound A is important to exert the performance of the additive.

As can be seen from the electrochemical performances of comparative examples 2 and 3 and examples 1 to 14 in Table 2, the additive of the compound A disclosed by the invention is combined with other additives, so that the additive has a better effect, and mainly the compound A with a specific structure can preferentially form a film on the surface of a negative electrode, so that the stability of the negative electrode is improved; meanwhile, other functional groups of the compound, such as isocyanate groups, are helpful for improving the stability of the positive protective layer and reducing the damage of the electrolyte to the electrode material; unsaturated groups also display good results in high-temperature storage.

It will be understood by those skilled in the art that the foregoing is only exemplary of the present invention, and is not intended to limit the invention to the particular forms disclosed, since various modifications, substitutions and improvements within the spirit and scope of the invention are possible and within the scope of the appended claims.

Claims

1. The lithium ion battery electrolyte is characterized by comprising a non-aqueous organic solvent, lithium salt and an additive, wherein the additive comprises a conventional additive and a compound A, and the structure of the compound A is shown as the formula (I):

wherein R is independently selected from one of alkyl, alkenyl, isocyanic acid group, fluoroalkyl, phenyl, silicon group and substitute thereof with 1-4 carbon atoms.

2. The lithium ion battery electrolyte of claim 1, wherein the compound a is selected from at least one of the compounds represented by the following structural formula:

3. the lithium ion battery electrolyte of claim 1, wherein the compound a additive is present in an amount of 0.5 to 1.0% of the total mass of the lithium ion battery electrolyte.

4. The lithium ion battery electrolyte of claim 1, further comprising other additives selected from at least one of fluoroethylene carbonate (FEC), vinylene Carbonate (VC), vinyl sulfate (DTD), 1,3 Propane Sultone (PS), 1, 3-Propene Sultone (PST), tris (trimethylsilyl) borate (TMSB), tris (trimethylsilyl) phosphate (TMSP), tetravinylsilane (TVS), and Citraconic Anhydride (CA).

5. The lithium ion battery electrolyte of claim 4, wherein the content of the other additives is 0.5 to 3.0% of the total mass of the lithium ion battery electrolyte.

6. The lithium ion battery electrolyte of claim 1, wherein the lithium salt is selected from at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorosulfonimide, lithium bis (oxalato) borate, lithium difluorooxalato borate, lithium tetrafluorooxalato phosphate, lithium difluorobis (oxalato) phosphate.

7. The lithium ion battery electrolyte of claim 1 or 6, wherein the lithium salt is present in an amount of 15 to 17% by weight of the total lithium ion battery electrolyte.

8. The lithium ion battery electrolyte of claim 1, wherein the non-aqueous organic solvent is one or more of a chain carbonate and a cyclic carbonate; preferably, the cyclic carbonate is one or more of ethylene carbonate and propylene carbonate; the chain carbonate is one or more of methyl ethyl carbonate, dimethyl carbonate and diethyl carbonate; preferably, the non-aqueous organic solvent is a mixture of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate.

9. A lithium ion battery, characterized in that, the lithium ion battery comprises a positive pole piece, a negative pole piece, a separation film arranged between the positive pole piece and the negative pole piece, and the lithium ion battery electrolyte of any one of claims 1 to 8.

10. The lithium ion battery of claim 9, wherein the positive electrode piece comprises a positive electrode current collector and a positive electrode membrane on the surface of the positive electrode current collector, the positive electrode membrane comprises a positive electrode active material, a conductive agent and a binder, and the positive electrode active material is LiNi _1-x-y-z Co _x Mn _y Al _z O ₂ Lithium nickel manganese oxide, lithium cobaltate, lithium-rich manganese-based solid solution and lithium manganese oxide, wherein: x is more than or equal to 0 and less than or equal to 1, y 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 more than or equal to 0 and less than or equal to 1, wherein the negative electrode active substance is artificial graphite, lithium metal, coated natural graphite, a silicon-carbon negative electrode and a silicon negative electrode.