Secondary battery electrolyte additive comprising milled magnesium silicate, secondary battery electrolyte comprising same, and method for producing same

Abstract

The present invention relates to a secondary battery electrolyte additive comprising milled magnesium silicate, a secondary battery electrolyte comprising same, and a method for producing same and, more specifically, to magnesium silicate for a secondary battery electrolyte additive which is prepared by subjecting a mixture of magnesium silicate and a methyl ethyl ketone (MEK) solvent to primary milling using a bead mill and to secondary milling using a nano mill, as well as to a secondary battery electrolyte comprising same and a method for producing same. The present invention can provide an optimal content of the secondary battery electrolyte additive for enhancing capacity retention in a secondary battery electrolyte, and can provide a method for producing nano-sized magnesium silicate capable of reducing the process time through mechanical milling.

Description

Secondary battery electrolyte additive comprising milled magnesium silicate, secondary battery electrolyte comprising the same, and method for producing the same

[0001] The present invention relates to a secondary battery electrolyte additive comprising milled magnesium silicate, a secondary battery electrolyte comprising the same, and a method for producing the same. More specifically, the present invention relates to a method for producing magnesium silicate for a secondary battery electrolyte additive comprising milling a mixture of magnesium silicate and methyl ethyl ketone (MEK) solvent, first milling the mixture using a bead mill, and second milling the mixture using a nano mill. The present invention also relates to a secondary battery electrolyte comprising the same, and a method for producing the same.

[0002] Nanoporous materials with large surface areas and uniform pores are widely used as adsorbents, catalyst supports, separation and purification processes, and ion exchange media. In particular, synthetic methods for novel nanostructured materials are continuously being researched in the field of new materials.

[0003] Among them, magnesium silicate is a porous inorganic chemical synthesized through a precipitation reaction of a water-soluble magnesium salt and sodium silicate, and can be used in fields such as industrial use, food refining, and cosmetic raw materials based on its strong adsorption performance.

[0004] Conventional nano-scale magnesium silicate synthesis methods such as hydrothermal synthesis and sol-gel method have been used. The hydrothermal synthesis refers to a method of synthesizing or growing crystals by utilizing the properties that depend on the solubility, temperature, pressure, and solvent concentration of a metal salt, oxide, hydrate, or metal powder in a solution or suspension state, and the sol-gel method refers to a method of gelling a solution of an organic or inorganic compound of a metal and heat-treating it to produce an oxide solid.

[0005] Hydrothermal synthesis requires high temperature and high pressure conditions to form nanoscale magnesium silicate. This means that the synthesis process can take more than 12 hours, making it difficult to mass-produce nanoscale magnesium silicate. In fact, only 0.5 g of magnesium silicate can be recovered from a 500 mL hydrothermal synthesizer.

[0006] In addition, hydrothermal synthesis uses TEOS, a high-purity silicon source, which increases the unit cost of manufacturing nano-scale magnesium silicate. In fact, TEOS is approximately 180,000 won per L based on Sigma-Aldrich reagent, which is approximately 1,000 times more expensive than water glass (108 won per L). Therefore, this is a factor in the increase in the cost of nano-scale magnesium silicate, and it has the advantage of being able to change the silicon source during milling, which allows for a dramatic cost reduction.

[0007] Accordingly, there is a growing need to shorten the process time and reduce the cost to facilitate the mass synthesis of nano-grade magnesium silicate.

[0008] The present invention is designed to solve the problems described above, and more specifically, the purpose of the present invention is to provide a secondary battery electrolyte additive comprising milled magnesium silicate.

[0009] Another object of the present invention is to provide a method for producing nano-grade magnesium silicate, which can shorten the process time through mechanical grinding.

[0010] The technical problems to be solved by the invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the art from the description of the present invention.

[0011] The present invention provides a secondary battery electrolyte comprising a secondary battery electrolyte additive comprising milled magnesium silicate, characterized in that the secondary battery electrolyte additive is included in an amount of 0.3 to 0.8 wt% based on the total wt% of the liquid electrolyte.

[0012] In the present invention, the milling treatment is characterized in that a mixture of 2 to 8 wt% of magnesium silicate mixed with a methyl ethyl ketone (MEK) solvent is first ground using a bead mill to produce a first ground mixture, and the first ground mixture is secondarily ground using a nano mill.

[0013] In the present invention, the first pulverization is characterized by first pulverizing a mixture of 2 to 8 wt% of magnesium silicate mixed with a methyl ethyl ketone (MEK) solvent using a bead mill at 2,000 to 4,000 rpm for 30 minutes to 1 hour, and the second pulverization is characterized by second pulverizing the first pulverized mixture using a nano mill at 2,000 to 4,000 rpm for 1 to 4 hours.

[0014] In addition, the present invention provides a method for producing milled magnesium silicate for a secondary battery electrolyte additive, comprising the steps of: a) producing magnesium silicate; b) heat-treating the produced magnesium silicate; c) mixing 2 to 8 wt% of the heat-treated magnesium silicate with a methyl ethyl ketone (MEK) solvent to produce a mixture; d) first crushing the mixture using a bead mill to produce a first crushed mixture; e) second crushing the first crushed mixture using a nano mill to produce a second crushed mixture; and f) filtering and drying the second crushed mixture.

[0015] In the present invention, the step d) is characterized in that the mixture is first ground using a bead mill at 2,000 to 4,000 rpm for 30 minutes to 1 hour, and the step e) is characterized in that the mixture that has been first ground is secondarily ground using a nano mill at 2,000 to 4,000 rpm for 1 to 4 hours.

[0016] The present invention can provide a secondary battery electrolyte additive comprising milled magnesium silicate.

[0017] In addition, the present invention can provide an optimal content of the secondary battery electrolyte additive that improves capacity retention in a secondary battery electrolyte.

[0018] In addition, the present invention can provide a method for producing nano-grade magnesium silicate that can shorten the process time through mechanical crushing.

[0019] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0020] Figure 1 is a drawing showing the results of measuring the shape, Mg / Si element ratio, and average particle size of magnesium silicate according to the present invention.

[0021] Figure 2 is a schematic diagram showing a method for manufacturing a positive electrode half coin cell including magnesium silicate as an electrolyte additive according to the present invention.

[0022] Figure 3 is a graph showing the results of analyzing the initial charge / discharge efficiency of a secondary battery according to the content of a magnesium silicate additive according to the present invention.

[0023] Figure 4 is a graph showing the results of analyzing the capacity retention rate of a secondary battery according to the content of a magnesium silicate additive and the presence or absence of milling treatment according to the present invention.

[0024] The terms used in this specification have been selected from widely used, current terms, taking into account the functions of the present invention. However, these terms may vary depending on the intentions of those skilled in the art, precedents, the emergence of new technologies, etc. Furthermore, in certain cases, terms may be arbitrarily selected by the applicant, and in such cases, their meanings will be described in detail in the relevant description of the invention. Therefore, the terms used in this invention should not be defined simply as names, but rather based on their inherent meanings and the overall content of the present invention.

[0025] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0026] Numerical ranges are inclusive of the numbers defined in the ranges above. Every maximum numerical limitation given throughout this specification includes every lower numerical limitation, as if that lower numerical limitation were explicitly stated. Every minimum numerical limitation given throughout this specification includes every higher numerical limitation, as if that higher numerical limitation were explicitly stated. Every numerical limitation given throughout this specification will include every better numerical range within that broader numerical range, as if that narrower numerical limitation were explicitly stated.

[0027]

[0028] Hereinafter, the present invention will be described in detail.

[0029]

[0030] Method for producing magnesium silicate

[0031] The present invention can provide a method for producing magnesium silicate for use as an electrolyte additive for a secondary battery.

[0032] The method for producing the above magnesium silicate may include: a) a step of producing magnesium silicate; b) a step of heat-treating the produced magnesium silicate; c) a step of mixing 2 to 8 wt% of the heat-treated magnesium silicate with a methyl ethyl ketone (MEK) solvent to produce a mixture; d) a step of first crushing the mixture using a bead mill to produce a first crushed mixture; e) a step of second crushing the first crushed mixture using a nano mill to produce a second crushed mixture; and f) a step of filtering and drying the second crushed mixture.

[0033] The above step a) may include a1) a step of preparing a first mixture by mixing magnesium sulfate, sodium silicate, and water; and a2) a step of filtering and drying the mixture.

[0034]

[0035] The above step a1) can prepare a first mixture by mixing magnesium sulfate, sodium silicate and water and reacting them while stirring at 20 to 40°C for 1 to 3 hours, preferably, the first mixture can be prepared by mixing magnesium sulfate, sodium silicate and water and reacting them while stirring at 25 to 35°C for 1.5 to 2.5 hours, more preferably, the first mixture can be prepared by mixing magnesium sulfate, sodium silicate and water and reacting them while stirring at 30°C for 2 hours.

[0036] The first mixture prepared in the above step a1) may contain 10 to 14 parts by weight of sodium silicate and 55 to 65 parts by weight of water relative to 30 parts by weight of magnesium sulfate, preferably 12 parts by weight of sodium silicate and 60 parts by weight of water relative to 30 parts by weight of magnesium sulfate, and more preferably 30 kg of magnesium sulfate, 12 kg of sodium silicate, and 60 L of water.

[0037] The above step a2) is a step of filtering and drying the first mixture prepared in the above step a1), and the filtering may be performed using a filter press, and preferably, the filtering may be performed using a concave plate filter press. The drying may be performed in an air dryer, and preferably, the inlet temperature is 230 to 250°C, the outlet temperature is 100 to 120°C, and the air volume is 850 to 950 m 3 / h, and more preferably, the inlet temperature is 240°C, the outlet temperature is 110°C, and the air volume is 900 m 3 It can be dried in an air dryer operating under conditions of / h.

[0038]

[0039] The step b) above is a step of heat-treating the magnesium silicate manufactured in the step a), and may be characterized by heat-treating using an electric furnace. In addition, the step b) may be performed by heat-treating the magnesium silicate manufactured in the step a) at 530 to 570°C for 2 to 4 hours at a heating rate of 4 to 6°C / min, preferably at 540 to 560°C for 2.5 to 3.5 hours at a heating rate of 4.5 to 5.5°C / min, and more preferably at 550°C for 3 hours at a heating rate of 5°C / min.

[0040]

[0041] The above step c) is a step of preparing a second mixture by mixing the magnesium silicate heat-treated in the above step b) into a methyl ethyl ketone (MEK) solvent. The magnesium silicate heat-treated in the above step b) is added to the methyl ethyl ketone solvent and stirred at 300 to 400 rpm for 10 to 30 minutes to prepare the second mixture. Preferably, the second mixture can be prepared by stirring at 340 to 360 rpm for 15 to 25 minutes, and more preferably, the second mixture can be prepared by stirring at 350 rpm for 20 minutes.

[0042] The second mixture may comprise 2 to 8 wt% of the magnesium silicate heat-treated in step b), preferably 4 to 6 wt% of the magnesium silicate heat-treated in step b), and more preferably 5 wt% of the magnesium silicate heat-treated in step b).

[0043]

[0044] The above step d) is a step of first grinding the second mixture manufactured in the above step b) using a bead mill to manufacture a first grinded mixture, and the first grinding may be characterized by using a bead mill, and may be characterized by grinding for 30 minutes to 1 hour with a feed pump rpm of 700 to 900 and a bead mill rpm of 2,500 to 3,500. Preferably, the grinding may be characterized by grinding for 40 to 50 minutes with a feed pump rpm of 750 to 850 and a bead mill rpm of 2,800 to 3,200, and more preferably, the grinding may be characterized by grinding for 45 minutes with a feed pump rpm of 800 and a bead mill rpm of 3,000.

[0045] The term "Feed pump rpm" used in the above step d) may refer to the speed at which nano-sized magnesium silicate is fed into the bead mill using a pump from the vessel in which it is being synthesized. The above bead mill rpm may refer to the rotation speed of the screw inside the bead mill.

[0046]

[0047] The step e) above is a step of producing a second-ground mixture by second-grounding the mixture first ground in the step d) using a nano mill, and may be characterized by using a nano mill, and may be characterized by grinding for 1 to 4 hours with a feed pump rpm of 900 to 1,100 and a nano particle mill rpm of 2,500 to 3,500. Preferably, the step may be characterized by grinding for 2 to 3 hours with a feed pump rpm of 950 to 1,050 and a nano particle mill rpm of 2,800 to 3,200, and more preferably, the step may be characterized by grinding for 2.5 hours with a feed pump rpm of 1,000 and a nano particle mill rpm of 3,000.

[0048]

[0049] The term "Feed pump rpm" used in the above step e) may refer to the speed at which nano-sized magnesium silicate, which has been first crushed with a bead mill in the above step d), is fed into the nano particle mill using a pump in a vessel connected to the nano particle mill. The nano particle mill rpm may refer to the rotation speed of a screw inside the nano particle mill.

[0050]

[0051] The step f) above is a step of filtering and drying the mixture secondarily ground in the step e), and more specifically, the step may be characterized by filtering the secondarily ground mixture under reduced pressure to separate the solvent and magnesium silicate, and then drying the separated magnesium silicate at 15 to 25°C for 1 to 5 hours. Preferably, the separated magnesium silicate may be dried at 18 to 22°C for 2 to 4 hours, and even more preferably, the separated magnesium silicate may be dried at 20°C for 3 hours.

[0052]

[0053] magnesium silicate

[0054] The present invention can provide magnesium silicate manufactured according to the method for manufacturing magnesium silicate described above.

[0055] The magnesium silicate according to the present invention may be characterized by having a form in which round particles are aggregated.

[0056] The Mg / Si element ratio of the magnesium silicate according to the present invention may be 1:2.5 to 3.5, preferably 1:2.9 to 3.0, and more preferably 1:2.93.

[0057] The average particle size of the magnesium silicate according to the present invention may be characterized as being 400 to 460 nm, preferably 430 to 440 nm, and more preferably 435 nm.

[0058]

[0059] Secondary battery electrolyte containing magnesium silicate

[0060] The present invention can provide a secondary battery electrolyte comprising magnesium silicate, and preferably, a secondary battery electrolyte comprising milled magnesium silicate.

[0061] According to one embodiment of the present invention, when a secondary battery electrolyte including magnesium silicate that has not been milled is used, the capacity retention rate of the secondary battery may decrease, and when a secondary battery electrolyte including magnesium silicate that has been milled is used, the capacity retention rate of the secondary battery may be improved.

[0062] The secondary battery electrolyte according to the present invention may include magnesium silicate manufactured according to the magnesium silicate manufacturing method described above.

[0063] A method for producing a secondary battery electrolyte according to the present invention may include the steps of: preparing a solvent by mixing ethylene carbonate (EC) and diethyl carbonate (DEC); dissolving LiPF6 as a solute in the solvent to produce a solution; and adding the magnesium silicate according to the present invention to the solution.

[0064] The above solvent can be prepared by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1.

[0065] A solution can be prepared by dissolving 0.5 to 1.5 M LiPF6 as a solute in the above solvent, preferably a solution can be prepared by dissolving 0.8 to 1.2 M LiPF6 as a solute, and more preferably a solution can be prepared by dissolving 1.0 M LiPF6 as a solute.

[0066] In the step of adding the magnesium silicate according to the present invention to the above solution, the solution may refer to a liquid electrolyte. In the step, the amount of the magnesium silicate added may be 0.3 to 0.8 parts by weight of the magnesium silicate according to the present invention, preferably 0.4 to 0.6 parts by weight, and more preferably 0.5 parts by weight, based on 100 parts by weight of the total solution.

[0067] Additionally, the magnesium silicate according to the present invention may be added in an amount of 0.3 to 0.8 wt% relative to the total wt% of the solution, preferably 0.4 to 0.6 wt%, and more preferably 0.5 wt%.

[0068] When the magnesium silicate according to the present invention is added to the electrolyte in an amount of less than 0.3 wt%, the capacity retention rate of the secondary battery may decrease compared to when the magnesium silicate is added in an amount of 0.3 to 0.8 wt%. In addition, when the magnesium silicate according to the present invention is added to the electrolyte in an amount exceeding 0.8 wt%, the capacity retention rate of the secondary battery may actually decrease compared to when the magnesium silicate is not added.

[0069] Hereinafter, examples of the present invention will be described in detail, but it is obvious that the present invention is not limited to the following examples.

[0070]

[0071] Example 1. Preparation of a secondary battery electrolyte containing 0.5 wt% of magnesium silicate

[0072]

[0073] 1-1. Manufacturing of magnesium silicate

[0074] 30 kg of magnesium sulfate (MgSO4), 12 kg of sodium silicate (Na2SiO3), and 60 L of water were added to the reactor and reacted for 2 hours with stirring at 30°C. Then, the cake obtained by filtering with a concave plate filter press was dried in an air dryer to produce magnesium silicate. The air dryer had an inlet temperature of 240°C, an outlet temperature of 110°C, and an air flow of 900 m 3 It worked under the condition of / h.

[0075]

[0076] 1-2. Manufacturing of milled nano-sized magnesium silicate

[0077] The magnesium silicate produced in Example 1-1 was heat-treated using an electric furnace at 550°C for 3 hours at a heating rate of 5°C / min. 5 wt% of the heat-treated magnesium silicate was added to a methyl ethyl ketone (MEK) solvent and stirred at 350 rpm for 20 minutes to produce a mixture. The mixture was subjected to primary pulverization using a bead mill at a feed rpm of 800 and a bead mill rpm of 3,000 for 45 minutes. The primary pulverized mixture was subjected to secondary pulverization using a nanomill at a feed pump rpm of 1,000 and a mill rpm of 3,000 for 2.5 hours. The secondary pulverized mixture was filtered under reduced pressure to separate the solvent and magnesium silicate. The above separated magnesium silicate was dried at room temperature for 3 hours and mechanically ground to produce milled nano-sized magnesium silicate.

[0078]

[0079] 1-3. Manufacturing of secondary battery electrolyte

[0080] An electrolyte was prepared by dissolving 1.0 M LiPF6 as a solute in a solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1, and then adding 0.5 wt% of the magnesium silicate prepared in Examples 1-1 and 1-2 to the total wt% of the liquid electrolyte.

[0081]

[0082] Comparative Example 1. Preparation of secondary battery electrolyte containing 1.0 wt% of magnesium silicate

[0083] Magnesium silicate was prepared in the same manner as in Examples 1-1 and 1-2 above. 1.0 M LiPF6 was dissolved as a solute in a solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in a volume ratio of 1:1, and then an electrolyte solution was prepared by adding 1.0 wt% of the milled nano-sized magnesium silicate prepared above to the total wt% of the liquid electrolyte.

[0084]

[0085] Comparative Example 2. Preparation of a secondary battery electrolyte containing 2 wt% of magnesium silicate.

[0086] Magnesium silicate was prepared in the same manner as in Examples 1-1 and 1-2 above. 1.0 M LiPF6 was dissolved as a solute in a solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in a volume ratio of 1:1, and then an electrolyte solution was prepared by adding 2.0 wt% of the milled nano-sized magnesium silicate prepared above to the total wt% of the liquid electrolyte.

[0087]

[0088] Comparative Example 3. Preparation of secondary battery electrolyte not containing magnesium silicate

[0089] A secondary battery electrolyte that does not contain magnesium silicate was prepared by dissolving 1.0 M LiPF6 as a solute in a solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in a volume ratio of 1:1.

[0090]

[0091] Comparative Example 4. Preparation of a secondary battery electrolyte containing 0.5 wt% of non-milled magnesium silicate.

[0092] Magnesium silicate was prepared in the same manner as in Example 1-1, and unlike Example 1, the milling treatment of Example 1-2 was omitted to prepare non-milled magnesium silicate. Next, 1.0 M LiPF6 was dissolved as a solute in a solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in a volume ratio of 1:1, and then an electrolyte solution was prepared by adding 0.5 wt% of the non-milled magnesium silicate to the total wt% of the liquid electrolyte.

[0093]

[0094] Experimental Example 1. Material Characteristics Analysis of Nano-scale Magnesium Silicate

[0095]

[0096] 1-1. Field emission scanning electron microscope (FE-SEM) observation

[0097] The nano-scale magnesium silicate manufactured in Examples 1-1 and 1-2 was observed using a field emission scanning electron microscope (FE-SEM), and the results are shown in Fig. 1. Referring to Fig. 1, the magnesium silicate manufactured in Examples 1-1 and 1-2 was observed in the form of aggregated round particles.

[0098]

[0099] 1-2. Energy Dispersive Spectroscopy (EDS) Analysis

[0100] In order to measure the Mg / Si weight ratio of the nano-sized magnesium silicate manufactured in Examples 1-1 and 1-2, energy dispersive X-ray spectroscopy (EDS) was performed, and the results are shown in Fig. 1. Referring to Fig. 1, the Mg / Si weight ratio of the magnesium silicate manufactured in Examples 1-1 and 1-2 was measured to be 1:2.93, respectively.

[0101]

[0102] 1-3. Dynamic Light Scattering (DLS) Analysis

[0103] In order to measure the average particle size of the nano-sized magnesium silicate manufactured in Examples 1-1 and 1-2, dynamic light scattering (DLS) was performed, and the results are shown in Fig. 1. Referring to Fig. 1, the average particle size of the magnesium silicate manufactured in Examples 1-1 and 1-2 was measured to be 435 nm, respectively.

[0104]

[0105] Experimental Example 2. Analysis of the initial charge-discharge efficiency of secondary batteries according to the content of magnesium silicate additives.

[0106]

[0107] 2-1. Manufacturing of bipolar half-coin cells

[0108] As shown in Fig. 2, a positive electrode half coin cell was manufactured, and the electrode materials were mixed at a ratio of 94 wt% of NCM622 (positive electrode active material), 3 wt% of Denka black (conductive material), and 3 wt% of Solef5130 (binder). Detailed information on the electrode materials is shown in Table 1 below. A positive electrode half coin cell was manufactured using the electrolytes manufactured in Example 1 and Comparative Examples 1 to 3, respectively.

[0109]

[0110] Electrode informationAl foil weight (g)0.0082Electrode weight (g)0.014~0.016Active material ratio (%)94Active material amount (g)0.5~0.7Rated capacity (mAh)0.9~1.1

[0111]

[0112] In the above Table 1, the Al foil weight refers to the weight of the Al foil used as the positive electrode collector, and is a value required to measure the amount of active material coated on the actual coin cell electrode. The electrode weight is a value including the weight of the positive electrode collector and the coated active material, and was obtained by measuring the weight after manufacturing the coin cell electrode. The active material ratio refers to the positive electrode active material ratio of NCM622. The active material amount is a value obtained by subtracting the Al foil weight from the electrode weight, and refers to the amount of NCM622 actually loaded on the positive electrode collector, and can be viewed as a factor determining the actual rated capacity. The rated capacity is a value obtained by multiplying the active material amount (g) by the active material ratio (0.94), and is a factor used in actual coin cell electrode test conditions.

[0113]

[0114] 2-2. Initial charge-discharge efficiency analysis

[0115] As described in Experimental Example 2-1 above, the initial charge / discharge efficiency of the positive electrode half coin cells manufactured using the electrolytes manufactured in Example 1 and Comparative Examples 1 to 3 was analyzed. The initial charge / discharge efficiency test experimental method is as follows, and is specifically described in Table 2 below.

[0116] After an initial pause time of 10 minutes, charging was performed in CC / CV Mode at a charge rate (C-rate) of 0.2C and a voltage of 4.2V, and the battery was moved to the next step when the capacity reached 5% of 0.2C. Afterwards, a second pause time of 10 minutes was performed, and discharging was performed in CC Mode at a discharge rate identical to the charge rate but with a negative value, and the condition for moving to the next step was set to 3.0V. Finally, after a third pause time of 10 minutes, the same process was repeated twice.

[0117] More specifically, since the positive half coin cell was manufactured in the above Experimental Example 2-1, in order to calculate the rated capacity, the weight of the Al foil, which is the current collector, is subtracted from the total weight of the manufactured coin cell electrode, and the resulting positive electrode coating weight is multiplied by the active material ratio to determine the final amount of active material. By multiplying the amount of active material (g) by the theoretical capacity of the positive electrode (155 mAh / g in the case of NCM622), the rated capacity at 1C is obtained. By multiplying the rated capacity value at 1C by the charging rate of 0.2C to be used in the IC TEST, the final result value to be input into the IC TEST is obtained.

[0118]

[0119] IC TEST Experiment methodStateModeTest conditionRest-10 minChargeCC / CV Mode0.2 C, 4.2 V Cut-off 5%Rest-10 minDischargeCC Mode0.2 C Cut-off 3.0 VRest-10 minCycle-2 cycle

[0120]

[0121] The results of the initial charge / discharge efficiency analysis of the above experimental example 2-2 are shown in Fig. 3 and Table 3.

[0122]

[0123] Electrolyte Additive Information 1st Charge (mAh / g) 1st Discharge (mAh / g) 2nd Charge (mAh / g) 2nd Discharge (mAh / g) Example 1 (0.5 wt%) 152.15 128.92 129.09 129.73 Comparative Example 1 (1 wt%) 182.16 155.58 156.36 157.33 Comparative Example 2 (2 wt%) 182.95 157.29 158.02 158.29 Comparative Example 3 (0 wt%) 183.66 156.80 157.30 157.76

[0124]

[0125] The initial charge / discharge efficiency was calculated using the following calculation formula 1.

[0126]

[0127] [Calculation Formula 1]

[0128] Charge / discharge efficiency (%) = discharge capacity (mAh / g) / charge capacity (mAh / g) * 100

[0129]

[0130] Referring to FIG. 3 and Table 3, the initial charge / discharge efficiencies of the positive half coin cells using the electrolytes manufactured in Example 1, Comparative Examples 1, 2, and 3 were calculated to be 84.73%, 85.40%, 85.97%, and 85.38%, respectively.

[0131] Therefore, the initial charge / discharge efficiency of the positive half coin cell using the electrolytes manufactured in Example 1 and Comparative Examples 1 to 3 has an error range of about 0.6%, and thus it was confirmed that there was no change in the initial charge / discharge efficiency depending on the magnesium silicate content.

[0132]

[0133] Experimental Example 3. Analysis of secondary battery capacity retention according to magnesium silicate additive content and milling treatment.

[0134] Bipolar half-coin cells were manufactured using the electrolytes manufactured in Example 1, Comparative Examples 1, 2, 3, and 4 using the same method as in Experimental Example 2-1. The experimental method for measuring capacity retention is as follows, and is specifically described in Table 4 below.

[0135] After an initial pause time of 10 minutes, charging was performed in CC / CV Mode at a charge rate (C-rate) of 1.0C and a voltage of 4.2V, and the battery was moved to the next stage when the capacity reached 5% of 1.2C. Next, a second pause time of 10 minutes was performed, and discharging was performed in CC Mode at a discharge rate that was the same as the charge rate but with a negative value, and the condition for moving to the next stage was set to 3.0V. Finally, after a third pause time of 10 minutes, the same process was repeated 200 times.

[0136] More specifically, since the positive half coin cell was manufactured in the above Experimental Example 2-1, in order to calculate the rated capacity, the weight of the Al foil, which is the current collector, is subtracted from the total weight of the manufactured coin cell electrode, and the resulting positive electrode coating weight is multiplied by the active material ratio to determine the final active material amount. By multiplying the above active material amount (g) by the positive electrode theoretical capacity (155 mAh / g for NCM622), the rated capacity at 1C is obtained, which is then input as the rated capacity.

[0137]

[0138] Cycle retention test Experimental methodStateModeTest conditionRest-10 minChargeCC / CV Mode1.0 C, 4.2 V Cut-off 5%Rest-10minDischargeCC Mode1.0 C, Cut-off 3.0 VRest-10 minCycle-200 cycle

[0139]

[0140] The results of the capacity retention rate analysis of the above experimental example 3 are shown in Fig. 4 and Table 5.

[0141]

[0142] Electrolyte additive informationInitial capacity (mAh / g)100 cycle capacity (mAh / g)200 cycle capacity (mAh / g)Capacity retention rate after 200 cycles (%)Increase rate compared to Ref (%)Example 1 (0.5 wt%)143.24140.87136.9495.6036.38Comparative example 4 (milling treatment X, 0.5 wt%)147.32140.8139.6426.91-54.56Comparative example 1 (1 wt%)146.67142.5467.8646.27-21.87Comparative example 2 (2 wt%)143.77139.5165.6145.64-22.93Comparative example 3 (0 wt%)145.60140.2086.2359.22-

[0143]

[0144] Referring to FIG. 4 and Table 5, the positive half coin cells using the electrolytes manufactured in Example 1 and Comparative Examples 1 to 4 all had similar initial capacities, and showed a tendency to gradually decrease as 100 and 200 cycles of repeated charge and discharge were performed.

[0145] However, in the case of the positive half coin cell using the electrolyte manufactured in Example 1, the capacity retention rate was improved by 36.38% compared to Comparative Example 3 (Reference, Ref).

[0146] On the other hand, in the case of the positive half coin cell using the electrolyte manufactured in Comparative Examples 1 and 2, the capacity retention rate was confirmed to be reduced by 21.87 and 22.93% compared to Comparative Example 3.

[0147] In addition, in the case of the positive half coin cell using the electrolyte containing the non-milled magnesium silicate manufactured in Comparative Example 4, it was confirmed that the capacity retention rate was reduced by as much as 54.56% compared to Comparative Example 3.

[0148] Therefore, when using an electrolyte containing 0.5 wt% of magnesium silicate, the capacity retention rate of the secondary battery was improved by 36.38% compared to when no magnesium silicate was added, but when using an electrolyte containing 1 or 2 wt% of magnesium silicate, it was confirmed that the capacity retention rate of the secondary battery was actually reduced compared to when no magnesium silicate was added.

[0149] In addition, even when using an electrolyte containing the same 0.5 wt% of magnesium silicate, the capacity retention rate was different depending on whether the magnesium silicate was milled or not, and more specifically, it was confirmed that the capacity retention rate was greatly reduced when the magnesium silicate was not milled.

[0150] To summarize the above results, it can be said that using an electrolyte containing 0.5 wt% of milled magnesium silicate is the optimal condition for optimizing the capacity retention rate of a secondary battery.

[0151]

[0152] From the above description, those skilled in the art will understand that the present invention can be implemented in other specific forms without altering its technical spirit or essential features. In this regard, it should be understood that the embodiments described above are illustrative in all respects and are not limiting.

Claims

1. A secondary battery electrolyte comprising a secondary battery electrolyte additive comprising milled magnesium silicate.

2. In paragraph 1, The above milling treatment A mixture of 2 to 8 wt% of magnesium silicate mixed with methyl ethyl ketone (MEK) solvent is first ground using a bead mill to prepare a first ground mixture. A secondary battery electrolyte characterized in that the above-mentioned firstly ground mixture is secondarily ground using a nanomill.

3. In paragraph 2, The above first crushing It is characterized by first grinding a mixture of 2 to 8 wt% of magnesium silicate mixed with methyl ethyl ketone (MEK) solvent using a bead mill at 2,000 to 4,000 rpm for 30 minutes to 1 hour. The above secondary crushing A secondary battery electrolyte characterized in that the above-mentioned first-pulverized mixture is secondarily pulverized using a nanomill at 2,000 to 4,000 rpm for 1 to 4 hours. 4.a) Step of manufacturing magnesium silicate; b) A step of heat treating the manufactured magnesium silicate; c) A step of preparing a mixture by mixing 2 to 8 wt% of the heat-treated magnesium silicate in a methyl ethyl ketone (MEK) solvent; d) A step of producing a first-milled mixture by first grinding the mixture using a bead mill; e) a step of producing a second-milled mixture by second-milling the first-milled mixture using a nanomill; and f) A method for producing milled magnesium silicate for secondary battery electrolyte additive, comprising the step of filtering and drying the secondarily milled mixture.

5. In paragraph 4, Step d) above The mixture is characterized in that it is first ground using a bead mill at 2,000 to 4,000 rpm for 30 minutes to 1 hour, Step e) above A method for producing milled magnesium silicate for a secondary battery electrolyte additive, characterized in that the first-milled mixture is secondarily milled using a nanomill at 2,000 to 4,000 rpm for 1 to 4 hours.

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