KR102075091B1 - Electrolyte additive for secondary battery, electrolyte for secondary battery, and secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte additive for a secondary battery represented by the following formula (1). As a result, the internal pressure of the cell is reduced by removing residual lithium in the nickel-rich anode, and a positive electrode-electrolyte intermediate phase (CEI) protective layer is formed on the surface of the anode to improve surface stability and to suppress decomposition of the electrolyte to Cycle characteristics can be improved.
[Formula 1]

Description

ELECTROLYTE ADDITIVE FOR SECONDARY BATTERY, ELECTROLYTE FOR SECONDARY BATTERY, AND SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to an electrolyte additive for a secondary battery, an electrolyte for a secondary battery and a secondary battery comprising the same, and more particularly, to improve surface stability of a cathode material in a secondary battery, in particular, a lithium ion battery using a lithium-rich cathode material. The present invention relates to an electrolyte additive for a secondary battery capable of improving cycle characteristics, an electrolyte for a secondary battery including the same, and a secondary battery.

As environmental crises evolve around the world, electric vehicles (EVs) are attracting attention as an environmentally friendly alternative transportation. However, insufficient mileage of EVs is an obstacle to widespread use of EVs. The mileage of an electric vehicle is highly related to the energy density of the battery, and therefore, much effort has been made to develop improved electrode materials that provide high specific capacity at high voltages of Li-ion batteries (LIBs). Among the improved anode materials, layered nickel / cobalt / manganese oxide (LiNi _x Co _y Mn _z O ₂ , NCM) has been attracting attention as a high specific amount compared to conventional lithium cobalt oxide (LiCoO ₂ ). In particular, the specific amount of NCM can be improved as the Ni content in the layered structure increases; Nickel containing 60% Ni - rich NCM cathode material is 170 mA hg ^- contrast can provide a specific capacity of at least ^1, the conventional LCO showed a specific capacity of 150 mA hg ^-1 at 4.3 V cutoff condition.

Despite the advantages of this energy density, Ni-rich NCM anode materials have low surface stability, which leads to a continuous deterioration of cycling characteristics. Degradation of the electrolyte easily occurs at the nickel-rich surface. Because there is a tendency that is triggered by a non-reversible electrolytic oxidation stable Ni ^{4 +} conversion in a stable Ni ^{3 +.} This resulted in the continuous accumulation of electrochemically decomposed byproducts on the nickel-rich anode surface, resulting in increased cell resistance and reduced cycle characteristics. In addition, many residual lithiums (lithium hydroxide, lithium carbonate, etc.) remain on the nickel-rich anode surface due to the lithium precursor used in the firing step for the synthesis of the nickel-rich NCM anode material.

This residual lithium species is decomposed by electrochemical reactions in cells above 4.0 V (vs. Li / Li ⁺ ), which also causes the problem of rapid expansion of cells by the formation of gaseous by-products such as oxygen, hydrogen, and carbon dioxide. Generate. Since such intrinsic surface properties of nickel-rich NCM cathode materials deteriorate the electrochemical properties and stability of lithium-ion batteries, these problems are solved in order to achieve high efficiency of lithium-ion batteries using nickel-rich cathode materials. You need to get over it.

Korean Registered Patent Publication No. 10-1007504

Another object of the present invention is to improve the stability of the positive electrode by removing residual lithium, such as lithium hydroxide, lithium carbonate and the like remaining on the surface of the nickel-rich anode in the cell, oxygen, hydrogen and The present invention provides an electrolyte additive, an electrolyte and a secondary battery including the same, which can reduce the internal pressure of a cell by preventing rapid expansion of the cell due to gas by-products such as carbon dioxide.

It is an object of the present invention to form an anode-electrolyte intermediate phase (CEI) protective layer on the surface of a cathode by adding an additive to an electrolyte of a secondary battery, in particular, a lithium ion battery including a nickel-rich cathode, and by-products generated by decomposition of the electrolyte. The present invention provides an electrolyte additive, an electrolyte and a secondary battery including the same, which can improve the stability of the positive electrode by preventing the accumulation of and improve the cycle characteristics.

According to one aspect of the invention,

There is provided an electrolyte additive for a secondary battery comprising a compound represented by the following Chemical Formula 1.

[Formula 1]

In Formula 1,

R ¹ to R ³ are the same as or different from each other, and each independently a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C1 to C30 heterocycloalkyl group, a substituted or An unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C1 to C30 heteroaryl group.

Preferably, R ¹ to R ³ are the same as or different from each other, and each independently may be a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C1 to C30 heteroaryl group.

More preferably, R ¹ to R ³ may be the same or different from each other, and each independently a substituted or unsubstituted C 6 to C 30 aryl group.

The secondary battery electrolyte additive may be triphenyl borate.

According to another aspect of the invention,

Provided is a secondary battery electrolyte including an electrolyte additive for a secondary battery represented by Formula 1 below.

[Formula 1]

In Formula 1,

R ¹ to R ³ are the same as or different from each other, and each independently a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C1 to C30 heterocycloalkyl group, a substituted or An unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C1 to C30 heteroaryl group.

The electrolyte may be a solvent containing at least one selected from ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC); An electrolyte salt containing lithium hexafluorophosphate (LiPF ₆ ); And the electrolyte additive for the secondary battery.

The solvent may be ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1: 1 to 1: 3.

The concentration of the electrolyte additive may be 1 to 3%.

According to another aspect of the invention,

A secondary battery comprising the secondary battery electrolyte is provided.

The cathode material in the secondary battery may be a nickel-rich cathode material.

The nickel-rich anode material may be any one selected from lithium nickel cobalt manganese oxide and lithium nickel cobalt oxide.

The nickel-rich anode material may be lithium nickel cobalt manganese oxide.

The nickel-rich anode material may include 50 to 70 wt% nickel (Ni).

In the secondary battery, a cathode-electrolyte interphase protective film may be formed on the surface of the nickel-rich cathode material by the electrolyte additive after a charge and discharge cycle.

The secondary battery may be any one selected from a lithium ion battery, a lithium metal battery, a lithium-sulfur battery, a lithium-air battery, a magnesium ion battery, a sodium ion battery, a potassium ion battery, and an aluminum ion battery.

According to another aspect of the invention,

An electric device comprising the secondary battery electrolyte is provided.

The electrical device may be any one selected from a communication device, a transportation device, an energy storage device, and an acoustic device.

The electrolyte additive for a secondary battery of the present invention improves the stability of the positive electrode by removing residual lithium such as lithium hydroxide and lithium carbonate remaining on the surface of the nickel-rich positive electrode in the cell, and generates oxygen, The pressure inside the cell can be reduced by preventing the cell from expanding rapidly due to the formation of gas by-products such as hydrogen and carbon dioxide.

In addition, the electrolyte additive for a secondary battery of the present invention is added to an electrolyte including a nickel-rich anode to form a cathode-electrolyte intermediate phase (CEI) protective layer on the surface of the anode, and to prevent accumulation of by-products generated by decomposition of the electrolyte. The stability of the positive electrode can be improved, and the cycle characteristics of secondary batteries such as lithium ion batteries can be improved.

1 shows the structure of triphenyl borate and its functionality as an additive.
Figure 2 shows the results of the residual lithium removal effect analysis according to Test Example 1.
3 shows the results of quantitative analysis of residual lithium removal according to Test Example 2.
4 shows the results of analyzing the electrochemical behavior of TPB according to Test Example 3.
5 shows cycle characteristics analysis results according to TPB concentration according to Test Example 4.
6 shows an SEM image of the electrode according to Test Example 5.
7 shows the XPS analysis result of the electrode according to Test Example 6.
8 shows quantitative analysis results of nickel solubility according to Test Example 7.

Hereinafter, various aspects and various embodiments of the present invention will be described in more detail. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. However, the following descriptions are not intended to limit the present invention to specific embodiments, and detailed descriptions of well-known technologies related to the present invention will be omitted when it is determined that the present invention may obscure the gist of the present invention. . The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "having" are intended to indicate that there is a feature, number, step, operation, component, or combination thereof described in the specification, and one or more other features or It is to be understood that the present invention does not exclude the possibility of adding or presenting numbers, steps, operations, components, or combinations thereof.

As used herein, "substituted" means that at least one hydrogen atom is deuterium, C1 to C30 alkyl group, C3 to C30 cycloalkyl group, C2 to C30 heterocycloalkyl group, C1 to C30 halogenated alkyl group, C6 to C30 aryl group, C1 to C30 hetero Aryl group, C1 to C30 alkoxy group, C2 to C30 alkenyl group, C2 to C30 alkynyl group, C6 to C30 aryloxy group, silyloxy group (-OSiH ₃ ), -OSiR ¹ H ₂ (R ¹ is C1 to C30 alkyl group Or C6 to C30 aryl group), -OSiR ¹ R ² H (R ¹ and R ² are each independently C1 to C30 alkyl group or C6 to C30 aryl group), -OSiR ¹ R ² R ³ , (R ¹ , R ² And R ³ are each independently C1 to C30 alkyl group or C6 to C30 aryl group), C1 to C30 acyl group, C2 to C30 acyloxy group, C2 to C30 heteroaryloxy group, C1 to C30 sulfonyl group, C1 to C30 Alkylthiol group, C6 to C30 arylthiol group, C1 to C30 heterocyclothiol group, C1 to C30 phosphate Group, silyl group (SiR ¹ R ² R ³ ₎ (R ¹ , R ² , and R ³ are each independently a hydrogen atom, a C1 to C30 alkyl group or a C6 to C30 aryl group), an amine group (-NRR ') (here R and R 'are each independently a substituent selected from the group consisting of a hydrogen atom, a C1 to C30 alkyl group, and a C6 to C30 aryl group), a carboxyl group, a halogen group, a cyano group, a nitro group, an azo group, and hydroxy Mean substituted by a substituent selected from the group consisting of groups.

Hereinafter, the electrolyte additive for a secondary battery of the present invention will be described.

The electrolyte additive for a secondary battery of the present invention includes a compound represented by the following formula (1).

[Formula 1]

In Formula 1,

R ¹ to R ³ are the same as or different from each other, and each independently a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C1 to C30 heterocycloalkyl group, a substituted or An unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C1 to C30 heteroaryl group.

Preferably, R ¹ to R ³ are the same as or different from each other, and each independently may be a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C1 to C30 heteroaryl group.

More preferably, R ¹ to R ³ may be the same or different from each other, and each independently a substituted or unsubstituted C 6 to C 30 aryl group.

Still more preferably, the secondary battery electrolyte additive may be triphenyl borate. The structural formula of triphenyl borate is shown in FIG. 1. Referring to FIG. 1, when triphenyl borate is used as an additive in an electrolyte of a secondary battery, the following two roles may be performed.

First, boron (B) is characterized by having several valence electrons that do not satisfy the octet rule. Thus, boron can easily receive two additional electrons from the electron-rich molecule to fill the empty valence 2p orbitals. The use of TPB can be effective to reduce the amount of lithium remaining in the cell. This is because electron-deficient boron can bind with OH ^- and CO ₃ ^{2 -} anions. In other words, the use of TPB can reduce the pressure inside the cell by removing residual lithium, and can improve the stability of the cell.

Secondly, the borate functional group can effectively suppress electrolyte decomposition by electrochemical reaction to improve cell cycle characteristics, and form a positive electrode-electrolyte intermediate phase (CEI) protective layer on the electrode surface to improve the surface stability of the nickel-rich anode. Can be improved.

Hereinafter, the secondary battery electrolyte of the present invention will be described.

The secondary battery electrolyte of the present invention includes an electrolyte additive for a secondary battery represented by the following Chemical Formula 1.

[Formula 1]

In Formula 1,

R ¹ to R ³ are the same as or different from each other, and each independently a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C1 to C30 heterocycloalkyl group, a substituted or An unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C1 to C30 heteroaryl group.

Preferably, R ¹ to R ³ are the same as or different from each other, and each independently may be a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C1 to C30 heteroaryl group.

More preferably, R ¹ to R ³ may be the same or different from each other, and each independently a substituted or unsubstituted C 6 to C 30 aryl group.

Still more preferably, the secondary battery electrolyte additive may be triphenyl borate.

The electrolyte may include a solvent, an electrolyte salt, and an additive, and specifically, a solvent including at least one selected from ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC); An electrolyte salt containing lithium hexafluorophosphate (LiPF ₆ ); And the electrolyte additive for the secondary battery.

The solvent may be a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1: 1 to 1: 3, and most preferably mixed in a volume ratio of 1: 2. have.

The concentration of the electrolyte additive is preferably 1 to 3%, most preferably 2%.

Hereinafter, the secondary battery of the present invention will be described.

The secondary battery of the present invention is characterized in that it comprises the secondary battery electrolyte.

The cathode material in the secondary battery may be a nickel-rich cathode material.

The nickel-rich anode material is preferably any one selected from lithium nickel cobalt manganese oxide and lithium nickel cobalt oxide, and more preferably lithium nickel cobalt manganese oxide.

The nickel-rich anode material may include 50 to 70 wt% nickel (Ni).

In the secondary battery, a cathode-electrolyte interphase protective film may be formed on the surface of the nickel-rich cathode material by the electrolyte additive after a charge and discharge cycle.

The secondary battery may be a lithium ion battery, lithium metal battery, lithium-sulfur battery, lithium-air battery, magnesium ion battery, sodium ion battery, potassium ion battery, aluminum ion battery, etc., but the scope of the present invention is not limited thereto. Do not.

In addition, the present invention may be an electric device including the electrolyte for the secondary battery, the electric device may be a communication device, a transportation device, an energy storage device, and an acoustic device, but the scope of the present invention is not limited thereto.

Hereinafter, an embodiment according to the present invention will be described in detail.

EXAMPLE

Example

To a mixture of ethyl carbonate (EC): ethyl methyl carbonate (EMC) (1: 2 vol. Ratio), standard electrolyte (PanaxEtec), 1M of LiPF ₆ was added and triphenylborate (TPB) as an additive was added at a concentration of 2%. To prepare an electrolyte for a lithium ion battery.

Comparative example

The standard electrolyte was used as it is without using the triphenylborate (TPB) as an additive.

[Test Example]

Test Methods

(1) Chemical Reactivity Test of TPB and Residual Lithium

The chemical reactivity of triphenylborate (TPB) with residual lithium is 1.0 mmol of LiOH (Aldrich) and Li ₂ CO ₃ (Aldrich) in 10.0 mmol of TPB (Aldrich) dimethyl carbonate (DMC) solution (10 ml). Calculated by adding to. The mixture was then vigorously stirred and filtered for 24 hours to remove insoluble LiOH and Li ₂ CO ₃ . The filtered result was analyzed by NMR analyzer (NMR, ASCEND 400, Bruker) to confirm the change in the chemical environment of TPB. The net effect of the TPB to the removal of the residual lithium in the stream is TPB solution nickel was demonstrated by dipping the O-rich _{LiNi 0 .7 Co 0 .2 Mn 0} .1 cathode material ₂ (Ecopro, NCM721) for 24 hours, treated The remaining lithium of NCM721 was analyzed in potentiometric titrator (Metrohm 848 Titrino Plus). As a control, NCM721 was performed under the same conditions in DMC without TPB dissolved.

(2) Calculation of Chemical Reaction Enthalpy

The chemical reaction enthalpy value was calculated by first-principles calculation. The ground state structure was fully optimized using density functional theory (DFT) with B3PW91 functional and 6-311G (d, p) base systems. Vibration frequency analysis was performed at the same level as the theory. Relative enthalpy energy was measured at 298.15 K and 1 atm. In addition, a conductor-like polarizable continuum model (CPCM) was used, which places the solute in the molecular cavities embedded in continuous dielectric media. The dielectric constant was adopted as ε = 3.107 of DMC. All DFT calculations were performed using the Gaussian09 program package.

(3) In-situ pressure behavior measurement of the cell during the charging process

In-situ pressure behavior of the cell during the charging process was observed by making the following NCM721 electrodes. The NCM721 electrode comprises NCM721, polyvinylidene fluoride (PVdF) (KF1100, Kureha), and carbon black (Super P) in N-methyl-2-pyrrolidone (NMP, Aldrich) in a 92: 4: 4 ratio. It is prepared by dispersing. The resulting mixture was then stirred for 6 hours and coated onto aluminum foil. Next, it was dried under vacuum at 120 ° C. for 12 hours. The loading density of the NCM721 electrode was fixed at about 15.31 ± 0.5 mg cm ^-2 . The NCM721 electrode was then placed in the in-situ pressure / potential monitoring instrument as the working electrode, and lithium metal was placed on the other side as the counter and counter electrodes. The chemical composition of the standard electrolyte (PanaxEtec) was to include or not include 1M LiPF ₆ and TPB in a mixture of ethyl carbonate (EC): ethyl methyl carbonate (EMC) (1: 2 volume ratio). . Poly (ethylene) (PE, Asahi) was used as the separator. These cells were galvanostatically charged to 4.3 V (vs. Li / Li ⁺ ) and the internal pressure was recorded as a function of time.

(4) Measurement of electrochemical behavior of TPB

The electrochemical behavior of TPB was analyzed by measuring each electrolyte by linear sweep voltammetry (LSV). Glassy carbon electrodes were used as working electrodes and lithium metal was used as counter and counter electrodes. Electrochemical behavior was measured with an electrochemical workstation (Biologic, SP-300) with a scan rate of 10 mV s ^{−1 in} the range of 3.5 to 4.5 V (vs. Li / Li ⁺ ). Electrochemical properties were evaluated by fabricating 2032 half cells using NCM721 anode, lithium metal anode, PE separator. Cells were discharged to ^{4.3 V (vs. Li / Li +} ) is charged to ^{3.0 V (vs. Li / Li +} ). All the cells were cycled twice at room temperature at 0.1 C rate to form a CEI layer on the NCM721 electrode, and fast cycling at 1.0 C rate at room temperature. Once the cycle test was complete, the cells were disassembled in the glove box to recover the cycled NCM721 electrodes and quickly washed in the DMC. The surface morphology of the recovered NCM721 electrode was analyzed by FESEM microscopy (FESEM, Quanta 3D FEG, FEI) and the chemical composition was performed by XPS analysis (XPS, K alpha, Thermo-Scientific). The effect of the TPB-induced CEI layer on the Ni solubility was analyzed by producing a beaker cell using lithium metal as the NCM721 electrode, the counter electrode and the counter electrode as the working electrode. The cells were charged to 4.3 V (vs. Li / Li ⁺ ) and placed in a 60 ° C. oven for 2 weeks. After discharge of these cells, the recovered electrodes were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) (Aurora 60, Bruker) to quantify Ni dissolved in the electrolyte from the NCM721 electrode.

Test Example  1: residual Lithium  Elimination Effect Analysis

The effect of TPB on the removal of residual lithiums was analyzed by ex-situ NMR analysis of the supernatant after the chemical reaction between TPB, LiOH, and Li ₂ CO ₃ was completed, and the results are shown in FIG. 2. Figure 2 (a) is ¹¹ B-NMR analysis results, (b) shows the reaction mechanism between the TPB and the residual lithium.

According to this, the ¹¹ B-NMR of the recovered supernatant showed a new ¹¹ B-NMR peak at 2.1 ppm, which shifted to the downfield region when compared to the original TPB peak (18.8 ppm, not shown). This change in chemical shift from high to low indicates an increase in the electron density of the element analyzed. In other words, a new peak was observed in the chemical shift region, which typically lacked tetravalent boron (B). This result suggests that the trivalent valence of TPB binds boron (B) with OH ^- and CO ₃ ^{2 -} and thus shows a lower chemical shift, which causes boron to dissociate two electrons from the remaining lithium. I can accept it. The results of the DFT calculation showed that the reaction of TPB with LiOH and Li ₂ CO ₃ showed exothermicity (ΔH = −30.9 and −15.4 kcal / mol), respectively. In addition, Lewis acid group interactions are advantageous thermodynamically in nonpolar DMC solvents.

Test Example  2: residual Lithium  Quantitative Analysis of Removal

The quantitative analysis of the residual lithium from the NCM721 cathode material is shown in FIG. Figure 3 (a) is a result of quantitative analysis of the residual lithium of the NCM721 cathode before and after the TPB treatment, (b) shows the in-situ pressure / potential profile of the NCM721 anode. For the experiment, three types of NCM721 (NCM721 untreated, NCM721 treated only with DMC, and NCM721 treated with DMC-TPB) were prepared, and the amount of residual lithium was measured.

According to this, a very large amount (11,000 ppm) of residual lithium appeared in the untreated NCM721, and a large amount of residual lithium (8,500 ppm) was still found in the NCM721 treated with DMC only. In contrast, the residual lithiums of NCM721 treated in the DMC-TPB solution were found to be significantly reduced to 2,900 ppm LiOH and 1,300 ppm Li ₂ CO ₃ . These results indicate that TPB effectively dissolves LiOH and Li ₂ CO ₃ from the NCM721 surface by chemical reaction and significantly reduces the concentration of residual lithiums on the NCM721 surface. In addition, these results were found to correspond with the in-situ pressure / potential profile of the NCM721 cathode. Here the internal pressure of the cell with the TPB controlled electrolyte was well maintained after the cycle. In contrast, cells with standard electrolytes increased internal pressure continuously after a cycle, due to the electrochemical decomposition of lithium residues on the NCM721 surface. From these results, it can be concluded that TPB effectively removes residual lithiums from the NCM721 surface by chemical reaction, thus greatly improving the stability of the cell.

Test Example  3: TPB Analysis of Electrochemical Behavior of

Electrochemical stability of TPB was analyzed by measuring the electrode stability by linear scanning potential (LSV), and the results are shown in FIG. 4. According to this, a distinct oxidation current was observed in cells controlled with TPB-based electrolyte at 4.0 V (vs. Li / Li ⁺ ), which is related to the electrochemical oxidation of TPB. This means that TPB forms a CEI layer on the surface of the NCM72 electrode by an electrochemical oxidation reaction.

Test Example  4: TPB  Cycle Characteristic Analysis by Concentration

5 is a result of analyzing the chemical properties of the NCM721 electrode according to the concentration of TPB. Figure 5 (a) shows the potential profile (potential profile), (b) shows the cycle characteristics according to the TPB concentration. According to this, all potential distribution forms are the same in the first cycle, but the initial discharge specific capacity was changed by the use of TPB. The 2% TPB-based electrolyte showed almost the same discharge specific capacity (205.7 mA hg ⁻¹ ) compared to the discharge specific capacity (205.1 mA hg ⁻¹ ) of the cells cycled using the standard electrolyte. However, the initial discharge specificity decreased as the amount of TPB increased in the electrolyte: the discharge specificities of the discharge specificities 202.4 and 196.1 mA hg ⁻¹ in cycled cells with 3% and 5% TPB-controlled electrolyte, respectively. Was observed. In terms of cycle characteristics, the 2% TPB-controlled electrolyte showed 88.6% retention at 100 cycles, while the 3% and 5% TPB-controlled electrolytes had a retention rate of 72.7% and 15.5%. The 3% and 5% TPB-based electrolytes showed lower retention rates compared to the 80.4% retention achieved with standard electrolytes. These results indicate that TPB concentration is one of the determinants of cycle characteristics, and 2% TPB is the optimal concentration to improve the cycle behavior of NCM721 anode material.

Test Example  5: SEM  Image analysis

The effect of TPB on the NCM721 surface was analyzed by observing the surface morphology by SEM of the cycled NCM721, and the results are shown in FIG. 6. (a) is NCM721 surface SEM image in standard electrolyte after 100 cycles, and (b) is NCM721 surface SEM image in 2% TPB electrolyte after 100 cycles. According to this, the recovered standard electrolyte The cycled NCM721 electrode showed many cracks in the particles and decomposed by-products on the NCM721 surface. On the other hand, the particles were preserved in the NCM721 electrode cycled in the recovered 2% TPB-based electrolyte, and the surface morphology was relatively clear when compared with the standard electrolyte. These results indicate that the TPB-induced CEI layer effectively improves the surface stability of the NCM721 anode by inhibiting electrolyte degradation.

Test Example  6: XPS  analysis

XPS analysis results of the cycled NCM721 electrode are shown in Figure 7, (a) C1s, (b) F1s, (c) P2p spectrum. According to this, most of the C signals overlapped between the two electrodes in the C1s spectrum, but the intensity of PVDF (at 290.7 eV) was higher in the cycling NCM721 electrode with 2% TPB-based electrolyte than in the standard electrolyte. These results indicate less electrochemical degradation of the electrolyte at the NCM721 surface in the 2% TPB-based electrolyte. Thus, after 100 cycles, a rather high binder strength appears. The F1s spectrum still showed higher PDVF intensity (at 687.7 eV) on the cycled NCM721 electrode in 2% TPB-based electrolyte. In addition, the LiF (at 685.5 eV) peak was smaller in the cycled NCM721 electrode with 2% TPB-based electrolyte than with the standard electrolyte. The formation of LiF on the anode surface is evidence of electrolyte degradation. This is because the decomposed by-products form LiF by reaction in the anode material. This means that TPB effectively inhibits the decomposition of the electrolyte on the NCM721 surface, thus lowering the LiF concentration. DFT calculations show that the reaction between LiF and TPB is exothermic (ΔH = -21.5 kcal / mol). In addition, three new peaks appeared at F1s (689.4 eV) and P2p (135.0 eV) similar to Li _x PO _y F _z . This means that a new chemical composition has occurred along the TPB-induced CEI layer on the NCM721 surface. This result means that TPB participates in forming the CEI layer on the NCM721 electrode.

Test Example  7: Ni  Solubility Analysis

The quantitative analysis of nickel solubility analyzed according to ICP-MS is shown in FIG. 8. According to this, the surface stability was improved as a result of Ni solubility. Cyclized cells containing standard electrolytes showed significant Ni solubility of 283.3 ppm, whereas cycling cells containing 2% TPB electrolytes showed 21.3 ppm dissolution. If the surface is not stable, transition metal dissolution rapidly increases and unstable Ni ^{4 +} tends to dissolve in the electrolyte. This meant that the NCM721 surface was stabilized by the TPB-induced CEI layer, which effectively inhibited unwanted electrochemical reactions from occurring at the anode-electrolyte interface. The use of TPB is effective in improving the electrochemical properties of Ni-rich anode materials by forming a TPB-induced CEI layer on the surface of the nickel-rich anode, as well as improving stability by reducing the internal pressure of the cell. Judging.

In summary, the poor surface properties of nickel-rich anode materials can be achieved by using TPB as a two function additive. Electron deficient boron (B) allows TPB to selectively bind with the counterpart of residual lithiums from the nickel-rich anode material, which greatly reduces the concentration of residual lithiums from 11,000 to 4,200 ppm. Thus, the use of TPB effectively reduces the internal pressure of the cell and forms an effective CEI layer on the surface of the nickel-rich electrode by electrochemical oxidation. The TPB-induced CEI layer effectively alleviates electrolyte degradation, thus greatly improving the surface stability of the nickel-rich anode material. As a result, the cycled cell containing 2% TPB electrolyte showed a retention rate of 88.6% after 100 cycles at 60 ° C. In addition, Ni solubility is very suppressed in 2% TPB electrolyte (21.3 ppm). On the other hand, Ni dissolution was high in the cell with standard electrolyte (283.3 ppm). These results indicate that TPB is effective in improving both the stability and the electrochemical properties of nickel-rich anode materials. In addition, the present invention is not limited to lithium ion batteries, but may be extended to various secondary battery systems requiring high surface stability.

As described above, embodiments of the present invention have been described, but those skilled in the art may add, change, delete or add elements within the scope not departing from the spirit of the present invention described in the claims. The present invention may be modified and changed in various ways, etc., which will also be included within the scope of the present invention.

Claims (17)

An electrolyte comprising an electrolyte additive for a secondary battery including the compound represented by Formula 1; And
A nickel-rich anode material;
The nickel-rich anode material is any one selected from lithium nickel cobalt manganese oxide and lithium nickel cobalt oxide,
The nickel-rich anode material is 50 to 70wt% of nickel (Ni),
A cathode-electrolyte interphase protective film is formed on the surface of the nickel-rich anode material after the charge and discharge cycle by the electrolyte additive, and lithium hydroxide remaining on the surface of the nickel-rich cathode material. And residual lithium including at least one selected from lithium carbonate is removed.
[Formula 1]

In Formula 1,
R ¹ to R ³ are the same as or different from each other, and each independently a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C1 to C30 heterocycloalkyl group, a substituted or An unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C1 to C30 heteroaryl group. The method of claim 1,
R ¹ to R ³ are the same as or different from each other, and are each independently a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C1 to C30 heteroaryl group. The method of claim 1,
R ¹ to R ³ are the same as or different from each other, and each independently a substituted or unsubstituted C6 to C30 aryl group, characterized in that the lithium ion battery. The method of claim 1,
The electrolyte additive for the secondary battery is a lithium ion battery, characterized in that triphenyl borate (Triphenyl borate). delete The method of claim 1,
The electrolyte,
A solvent comprising at least one selected from ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC);
An electrolyte salt containing lithium hexafluorophosphate (LiPF ₆ ); And
The secondary battery electrolyte additive; Li-ion battery comprising a. The method of claim 6,
The solvent is a lithium ion battery, characterized in that ethylene carbonate (EC) and ethyl methyl carbonate (EMC) is mixed in a volume ratio of 1: 1 to 1: 3. delete delete delete delete The method of claim 1,
The nickel-rich anode material is lithium nickel cobalt manganese oxide lithium ion battery, characterized in that. delete delete delete An electrical device comprising the lithium ion battery of any one of claims 1 to 4, 6, 7, and 12. The method of claim 16,
The electrical device is any one selected from a communication device, a transportation device, an energy storage device, and an acoustic device.

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