Lithium ion battery and application thereof

Abstract

The present application relates to the technical field of lithium ion batteries, in particular to a lithium ion battery and application thereof.The lithium ion battery of the present application comprises an electrolyte, wherein the electrolyte comprises an organic solvent, a lithium salt, a first additive and a second additive; the first additive comprises at least one compound having the structure shown in formula (I); the second additive comprises at least one compound having the structure shown in formula (II); in the formula, R1-R4 are each independently selected from H, halogen, phenyl, substituted or unsubstituted C1-C10 hydrocarbon group; when substituted, the substituted group comprises any one of a silicon-oxygen bond, an ester group, a hydroxyl group, an isocyanate group and an ether group.The lithium ion battery of the present application can form a stable passivation film by adding a compound containing a nitrogen heterocyclic structure in the electrolyte, inhibit electrolyte decomposition, inhibit the increase of interface impedance, and thus improve the electrochemical performance of the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a lithium ion battery and application thereof. BACKGROUND

[0002] In ternary positive electrode materials, with the increase of Ni content, under high voltage or high temperature conditions, the electrolyte is oxidized and decomposed to produce a large amount of gas, and a large amount of high impedance decomposition products are accumulated on the surface of the positive electrode, which increases the impedance; thereby seriously damaging the cycle stability of the lithium ion battery and causing safety hazards. On the other hand, the SEI film generated by the first formation of the graphite electrode plays a crucial role in the performance of the battery. If the impedance of the formed SEI film is too large, the initial polarization of the battery will be intensified, which may easily lead to the deposition of metal lithium on the surface of the negative electrode, consume the active lithium in the battery, and greatly reduce the reversible capacity of the battery.

[0003] Therefore, it is urgent to develop a lithium ion battery, in which the electrolyte can form a stable passivation film with small impedance on both positive and negative electrode interfaces, protect the positive electrode, inhibit the swelling problem caused by the oxidative decomposition of the electrolyte and the dissolution of transition metals caused by the attack of HF on the positive electrode material; in addition, it also protects the negative electrode, forms an SEI film with certain mechanical strength and low impedance, so that lithium ions can quickly pass through, reduce polarization, and improve the lithium deposition window.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The first object of the present application is to provide a lithium ion battery, which contains a compound containing a nitrogen-containing heterocyclic structure in the electrolyte, can form a stable passivation film containing a nitrogen atom, inhibit electrolyte decomposition, inhibit the increase of interface impedance, and thereby improve the high voltage stability and fast charging ability of the lithium ion battery.

[0006] The second object of the present application is to provide an electric device comprising the lithium ion battery as described above.

[0007] In order to achieve the above object of the present application, the following technical solutions are adopted:

[0008] The present application provides a lithium ion battery, comprising an electrolyte, wherein the electrolyte comprises an organic solvent, a lithium salt, a first additive and a second additive;

[0009] The first additive comprises at least one compound having the structure as shown in formula (I);

[0010] The second additive comprises at least one compound having the structure as shown in formula (II);

[0011]

[0012] wherein R1-R4 are each independently selected from H, halogen, phenyl, substituted or unsubstituted C1-C10 hydrocarbyl; when substituted, the substituted group includes any one of a siloxane bond, an ester group, a hydroxyl group, an isocyanate group, and an ether group.

[0013] Further, at least one of R1-R3 in formula (I) has at least one of the following groups:

[0014]

[0015] R4 is selected from H,

[0016] Further, the first additive is selected from one or more of the following compounds having the following structure:

[0017]

[0018] The second additive is selected from one or more of the following compounds having the following structure:

[0019]

[0020] Further, the lithium ion battery at least satisfies one of the following conditions:

[0021] (1) the mass of the first additive is 0.01% to 3% of the total mass of the electrolyte; (2) the mass of the second additive is 0.01% to 5% of the total mass of the electrolyte; (3) the mass ratio of the first additive to the second additive is 1: (3-4).

[0022] Further, the lithium salt includes lithium hexafluorophosphate and a second lithium salt, the second lithium salt including one or more of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluoro-bis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, lithium bisfluorosulfonylimide, and lithium bis(trifluoromethylsulfonyl)imide.

[0023] Further, the mass of the lithium hexafluorophosphate is 5% to 10% of the total mass of the electrolyte, and the mass of the second lithium salt is 1% to 7% of the total mass of the electrolyte.

[0024] Further, the organic solvent is selected from one or more of propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, dimethyl sulfoxide, and sulfolane.

[0025] Further, the charging cutoff voltage of the lithium ion battery is 4.2 to 4.6 V. ​

[0026] Further, the lithium ion battery further comprises a positive electrode active material, the chemical formula of the positive electrode active material is Li a Ni x Co y Mn z O2, wherein 0.9≤a≤1.1, 0.33≤x≤0.96, 0.01≤y≤0.33, 0.01≤z≤0.33.

[0027] The application further provides a power utilization device comprising the lithium ion battery as described above.

[0028] Compared with the prior art, the application has the following beneficial effects:

[0029] The lithium ion battery of the application can significantly improve the high-voltage stability and fast-charging capability of the lithium ion battery and reduce the impedance by adding a compound containing a nitrogen heterocyclic structure as an electrolyte additive in the electrolyte. The introduction of a nitrogen heteroatom in the electrolyte additive helps to improve the conductivity of lithium ions, form a stable passivation film on the electrode surface, inhibit the decomposition of the electrolyte, and inhibit the increase of the interface impedance, thereby effectively improving the electrochemical performance of the lithium ion battery. DETAILED DESCRIPTION

[0030] The technical solutions of the application will be described below in detail with reference to the specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the application, not all the embodiments, and are only used to illustrate the application, and should not be regarded as limiting the scope of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application. The specific conditions are not specified in the embodiments, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0031] The lithium ion battery and the application method thereof according to an embodiment of the application will be described in detail below.

[0032] In some embodiments of the application, a lithium ion battery is provided, comprising an electrolyte, the electrolyte comprising an organic solvent, a lithium salt, a first additive and a second additive;

[0033] The first additive comprises at least one of the compounds having the structure as shown in formula (I);

[0034] The second additive comprises at least one of the compounds having the structure as shown in formula (II);

[0035]

[0036] wherein R1-R4 are each independently selected from H, halogen, phenyl, substituted or unsubstituted C1-C10 hydrocarbyl; when substituted, the substituents include any of siloxane bond, ester group, hydroxyl group, isocyanate group, and ether group. Specifically, the hydrocarbyl group can be one of saturated or unsaturated alkane, saturated or unsaturated alkene, or saturated or unsaturated alkyne.

[0037] The electrolyte of the present application contains a compound having the structure shown in formula (I) and a compound having the structure shown in formula (II) as described above, as an electrolyte additive; both compounds contain a nitrogen heterocyclic group in their structure, and the nitrogen atom helps to improve the ion conductivity by entering the interface film. The unsaturated nitrile group in the compound having the structure shown in formula (II) also helps to form a stable passivation film containing a nitrogen atom on the surface of the positive and negative electrodes, respectively, to inhibit electrolyte decomposition and increase in interface impedance. The lithium salt in the electrolyte can form a stable passivation film on the surface of the positive and negative electrodes, respectively, to inhibit electrolyte decomposition. The above effects improve the high-voltage stability and fast-charging performance of the lithium ion battery.

[0038] The electrolyte additive in the lithium ion battery of the present application can adjust the ability of the compound to participate in the film formation process by regulating the side chain structure in the structure, and introduce a nitrogen atom into the interface film to regulate the lithium ion transport capacity of the interface film. In addition, the solvation structure can also be changed by regulating the electrolyte composition, thereby promoting the reduction and decomposition of lithium salt anions and electrolyte additives on the electrode surface to form LiF and nitrogen-containing compounds, wherein LiF and nitrogen-containing compounds exist in the interface film, and both of them synergistically promote Li + Transport in the interface film.

[0039] In some embodiments of the present application, in formula (I), at least one of R1-R3 has at least one of the following groups:

[0040] In formula (II), R4 is selected from H, any one of the above.

[0041] In some embodiments of the present application, the first additive is selected from one or more of the compounds having the structure shown below:

[0042]

[0043]

[0044] In some embodiments of the present application, the second additive is selected from one or more of the compounds having the structure shown below:

[0045]

[0046] In some embodiments of the present application, when the electrolyte contains both the first additive and the second additive, the two additives have a synergistic effect, and the synergistic effect between the heteroatoms in the interfacial film can significantly reduce the impedance of the interfacial film.

[0047] In some embodiments of the present application, the lithium ion battery at least meets one of the following conditions:

[0048] (1) The mass of the first additive accounts for 0.01% to 3% of the total mass of the electrolyte;

[0049] (2) The mass of the second additive accounts for 0.01% to 5% of the total mass of the electrolyte;

[0050] (3) The mass ratio of the first additive to the second additive is 1:(3-4).

[0051] Typically but not limitedly, for example, the mass of the first additive accounts for 0.01%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or a range consisting of any two of them, of the total mass of the electrolyte; typically but not limitedly, for example, the mass of the second additive accounts for 0.01%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of them, of the total mass of the electrolyte. Too little additive can result in too little N atom content in the passivation film generated on the positive and negative electrode surfaces, and cannot play a role in improving the lithium ion transmission capacity of the interfacial film. Too much additive can cause the electrolyte to have too large a viscosity, increase the polarization of the battery, and reduce the ionic conductivity of the electrolyte.

[0052] In some embodiments of the present application, the mass ratio of the first additive to the second additive in the electrolyte is 1:(3-4); preferably, the mass ratio of the first additive to the second additive in the electrolyte is 1:(3-3.5).

[0053] In some embodiments of the present application, the lithium salt includes lithium hexafluorophosphate (LiPF6) and a second lithium salt, and the second lithium salt includes one or more of lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorophosphate bis(oxalato) (LiDFOP), lithium tetrafluorophosphate oxalate, lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0054] The mixed lithium salt of the present application can form a stable passivation film on the surface of the positive electrode and the negative electrode, respectively, and inhibit the decomposition of the electrolyte. Among them, the fluorine-containing lithium salt can form a stable passivation film on the surface of the electrode, and also improve the stability of the electrolyte, and the second lithium salt plays a role in improving the lithium ion transference number and forming a film on the surface of the negative electrode.

[0055] In some specific embodiments of the present application, the lithium salt comprises lithium hexafluorophosphate and lithium bisfluorosulfonylimide.

[0056] Lithium hexafluorophosphate has moderate ion transference number, moderate dissociation constant, good oxidation resistance and good aluminum foil passivation ability in commonly used non-aqueous organic solvents, and can match various positive and negative materials, and is one of the most important lithium salts in lithium ion batteries. Lithium bisfluorosulfonylimide has high electrolytic conductivity and good hydrolysis stability, which is beneficial to improving the rate performance and stability of the battery.

[0057] In some embodiments of the present application, the mass of lithium hexafluorophosphate in the electrolyte accounts for 5% to 10% of the total mass of the electrolyte, and the mass of the second lithium salt accounts for 1% to 7% of the total mass of the electrolyte; typically but not limited to, for example, the mass of lithium hexafluorophosphate in the electrolyte accounts for 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two of them of the total mass of the electrolyte; the mass of the second lithium salt in the electrolyte accounts for 1%, 2%, 3%, 4%, 5%, 6%, 7% or a range consisting of any two of them of the total mass of the electrolyte.

[0058] Too low concentration of lithium salt affects the conductivity of the electrolyte, and too high concentration of lithium salt increases the viscosity of the electrolyte, which also affects the conductivity of the electrolyte.

[0059] In some embodiments of the present application, the organic solvent is selected from one or more of propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), γ-butyrolactone (γ-GBL), methyl acetate, ethyl acetate (EA), dimethyl sulfoxide and tetramethyl sulfone (TMS).

[0060] In some specific embodiments of the present application, a preparation method of the electrolyte is also provided, comprising the following steps:

[0061] (A) At room temperature, add lithium salt into the dehydrated organic solvent in an argon-filled glove box, continuously stir and cool, and finally obtain a colorless transparent liquid;

[0062] (B) Add an additive to the colorless transparent liquid to obtain an electrolyte.

[0063] The additive comprises a first additive and a second additive.

[0064] In some embodiments of the present application, in step (B), the lithium salt is added while the electrolyte is cooled by dry ice, and the temperature of the electrolyte is increased by no more than 2°C.

[0065] In some embodiments of the present application, the charging cut-off voltage of the lithium ion battery is 4.2-4.6 V.

[0066] In some embodiments of the present application, the lithium ion battery further comprises a positive electrode active material, and the chemical formula of the positive electrode active material is Li a Ni x Co y Mn z O2, wherein 0.9≤a≤1.1, 0.33≤x≤0.96, 0.01≤y≤0.33, and 0.01≤z≤0.33.

[0067] In some embodiments of the present application, the lithium ion battery further comprises a negative electrode active material; preferably, the negative electrode active material comprises graphite.

[0068] In some embodiments of the present application, a power device is also provided, comprising the lithium ion battery described above.

[0069] The present application provides a preparation method of a lithium ion battery, comprising the following steps:

[0070] The positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked with the separator between the positive electrode sheet and the negative electrode sheet, and then wound, heat-pressed, and shaped, and the tab is welded to obtain a bare cell, the bare cell is placed in an outer packaging aluminum plastic film, and then placed in an oven at 85±10°C for baking for 24 h, the electrolyte is injected into the dried battery, and then the battery is statically placed, formed, and distributed to obtain the lithium ion battery.

[0071] The preparation method of the positive electrode sheet comprises the following steps:

[0072] The positive electrode active material Li(Ni 0.8 Mn 0.1 Co 0.1 )O2 (NMC811), the conductive agent acetylene black (Super P), and the binder polyvinylidene fluoride (PVDF) are uniformly mixed at a mass ratio of NMC811:Super P:PVDF=94:3:3, and then uniformly dispersed in 1-methyl-2-pyrrolidone (NMP) to prepare a uniform black slurry, the prepared slurry is coated on both sides of an aluminum foil, and then baked, rolled, and cut to obtain the positive electrode sheet.

[0073] The preparation method of the negative electrode sheet comprises the following steps:

[0074] The negative active material graphite, the conductive agent acetylene black (Super P) and the binder SBR are mixed uniformly according to the mass ratio graphite: Super P: SBR = 94:3:3, and uniformly dispersed with deionized water to prepare a uniform black slurry, the prepared slurry is coated on both sides of a copper foil, and then the copper foil is baked, rolled, cut into pieces to obtain a negative electrode sheet.

[0075] The preparation method of the electrolyte comprises the following steps:

[0076] In an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm) at room temperature, the organic solvent is added to the lithium salt, stirring is continued and the temperature is lowered, and the lithium salt is added continuously to ensure that the temperature of the electrolyte increases by no more than 2 ℃, and the final colorless transparent liquid is obtained. After the molecular sieve is removed, the lithium salt is added to the organic solvent, stirring is continued and the temperature is lowered, and the lithium salt is added continuously to ensure that the temperature of the electrolyte increases by no more than 2 ℃, and the final colorless transparent liquid is obtained.

[0077] The preparation method of the electrolyte of the examples and the comparative examples and the lithium ion battery is referred to the above method, wherein the components in the electrolyte of each example and comparative example and the content thereof in the electrolyte are shown in Table 1.

[0078] Table 1

[0079]

[0080]

[0081]

[0082] Note: The amount of lithium salt and additive refers to the content of each in the total mass of the electrolyte

[0083] The electrochemical performance of the examples and the comparative examples is tested, and the results are shown in Table 2.

[0084] The battery internal resistance DCR test method is as follows: at 25±2℃, the lithium ion battery prepared by the examples and the comparative examples is charged at 1C to 4.5V, then discharged at 1C capacity for 30min, adjusted to 50% SOC, then discharged at 5C constant current pulse for 10s and charged for 10s, the DCR is calculated, and the DCR=(voltage before pulse discharge-voltage after pulse discharge) / discharge current*100%.

[0085] The test method of the normal temperature high pressure cycle performance is as follows: at 25±2℃, the lithium ion battery prepared by the examples and the comparative examples is charged and discharged at 1C / 1C in the range of 3.5-4.8V, and the initial discharge specific capacity and the discharge specific capacity after 500 cycles of the battery are recorded. The capacity retention rate of 500 cycles = discharge specific capacity of 500 cycles / initial discharge specific capacity*100%.

[0086] Table 2

[0087]

[0088]

[0089] As can be seen from Table 1, the lithium ion battery prepared by the present application can effectively reduce the internal resistance of the battery, slow down the capacity attenuation of the battery during high-voltage cycling, and improve the high-voltage room temperature cycling retention rate of the battery by adding the compound containing a nitrogen-containing heterocyclic structure in the electrolyte. Among them, the simultaneous addition of two compounds containing a nitrogen-containing heterocyclic structure of the present application can significantly reduce the interface film impedance, and the two compounds have a synergistic effect, which is caused by the synergistic effect between the heteroatoms in the interface film.

[0090] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A lithium-ion battery, characterized in that: comprising an electrolyte, wherein the electrolyte comprises an organic solvent, a lithium salt, a first additive, and a second additive; The first additive includes at least one compound having a structure as shown in formula (I); The second additive includes at least one compound having a structure as shown in formula (II); (AND); (II); In formula (I), at least one of R1 to R3 has at least one of the following groups: 、 、 、 、 、 and ; In formula (II), R4 is selected from H, and Any of the following; The lithium-ion battery meets at least one of the following conditions: (1) The mass of the first additive accounts for 0.01% to 3% of the total mass of the electrolyte; (2) The mass of the second additive accounts for 0.01% to 5% of the total mass of the electrolyte; (3) The mass ratio of the first additive to the second additive is 1:(3~4).

2. The lithium-ion battery according to claim 1, wherein: The first additive is selected from one or more compounds having the following structures: (A1); (A2); (A3); (A4); (A5); (A6); The second additive is selected from one or more compounds having the following structures: (B1); (B2); (B3)。 3. The lithium-ion battery according to claim 1, wherein The lithium salt includes lithium hexafluorophosphate and a second lithium salt, wherein the second lithium salt includes one or more of lithium tetrafluoroborate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium bisfluorosulfonyl imide and lithium bistrifluoromethylsulfonyl imide.

4. The lithium-ion battery according to claim 3, characterized in that The mass of the lithium hexafluorophosphate accounts for 5% to 10% of the total mass of the electrolyte, and the mass of the second lithium salt accounts for 1% to 7% of the total mass of the electrolyte.

5. The lithium-ion battery according to claim 1, wherein The organic solvent is selected from one or more of propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, dimethyl sulfoxide and sulfolane.

6. The lithium-ion battery according to claim 1, wherein: The charging cut-off voltage of the lithium-ion battery is 4.2-4.6V.

7. The lithium-ion battery according to any one of claims 1 to 6, characterized in that The lithium-ion battery further comprises a positive electrode active material, the chemical formula of which is Li a Ni x Co y Mn z O2, where 0.9≤a≤1.1, 0.33≤x≤0.96, 0.01≤y≤0.33, 0.01≤z≤0.

33.

8. An electrical device, characterized in that: The lithium-ion battery comprises the lithium-ion battery according to any one of claims 1 to 7.

Images