Battery system, method of using the same, and battery pack including the same

Abstract

The present invention provides a battery system, which includes: one or more secondary batteries, each of the one or more secondary batteries including: a negative electrode containing a silicon-based active material, a positive electrode facing the negative electrode, a separator and an electrolyte arranged between the negative electrode and the positive electrode; and a control unit, which is constructed in a manner for setting a driving voltage range for charging and discharging the secondary battery, wherein the maximum driving voltage of the secondary battery set by the control unit is in the range of 4.00V to 4.08V, and the minimum driving voltage of the secondary battery set by the control unit is in the range of 2.98V to 3.07V.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2019-0117068, filed on September 23, 2019, the disclosure of which is hereby incorporated by reference in its entirety. Technical Field

[0004] The present invention relates to a battery system, a method of using the same, and a battery pack including the same. Background Art

[0005] Batteries are widely used in various fields, such as: mobile devices, such as mobile phones, laptops, smart phones, smart tablets, etc.; vehicles powered by electricity (electric vehicles (EV), hybrid electric vehicles (HEV) or plug-in hybrid electric vehicles (PHEV); or large-capacity energy storage systems (ESS).

[0006] The battery can generally be installed on a device or equipment in the form of one or more battery modules or battery packs. The battery may include one or more secondary batteries and may also include electronic components such as a battery management system (BMS) or a housing in addition to the secondary batteries. A secondary battery refers to a rechargeable battery that is different from a non-rechargeable primary battery. In particular, among various secondary batteries, lithium secondary batteries are lightweight and have high energy density, and thus have attracted much attention as a power source for driving portable devices. Therefore, research and development to improve the performance of lithium secondary batteries have been actively attempted.

[0007] Lithium secondary batteries typically include a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, an electrolyte, an organic solvent, and the like. Furthermore, in the positive and negative electrodes, an active material layer containing a positive electrode active material or a negative electrode active material may be formed on a current collector. Typically, lithium-containing metal oxides such as LiCoO2 and LiMn2O4 are used as the positive electrode active material in the positive electrode, while lithium-free carbon-based active materials or silicon-based active materials are used as the negative electrode active material in the negative electrode.

[0008] Silicon-based active materials have attracted significant attention among negative electrode active materials because they have a capacity approximately 10 times that of carbon-based active materials and offer the advantage of achieving high energy density even with thin electrodes due to their high capacity. However, silicon-based active materials are not widely used due to the following issues: volume expansion due to charging and discharging deteriorates lifespan characteristics.

[0009] Therefore, there is a need to develop a secondary battery capable of improving lifespan characteristics while achieving high capacity and high energy density of silicon-based active materials.

[0010] Korean Unexamined Patent Publication No. 10-2017-0074030 relates to a negative electrode active material for a lithium secondary battery, a preparation method thereof, and a lithium secondary battery including the same, and discloses a negative electrode active material including a porous silicon-carbon composite material, but has limitations in solving the above-mentioned problems.

[0011] Prior art literature

[0012] [Patent Document]

[0013] Korean Unexamined Patent Publication No. 10-2017-0074030 Summary of the Invention

[0014] Technical issues

[0015] The present invention is directed to providing a battery system capable of exhibiting improved capacity, energy density, and lifespan characteristics by adjusting a driving voltage range of a secondary battery.

[0016] The present invention also aims to provide a method of using a battery system capable of exhibiting improved capacity, energy density, and lifespan characteristics by adjusting a driving voltage range of a secondary battery.

[0017] The present invention also aims to provide a battery pack comprising the battery system.

[0018] Technical Solution

[0019] One aspect of the present invention provides a battery system, which includes: one or more secondary batteries, each of the one or more secondary batteries including: a negative electrode containing a silicon-based active material, a positive electrode facing the negative electrode, a separator and an electrolyte arranged between the negative electrode and the positive electrode; and a control unit, which is constructed in a manner for setting a driving voltage range for charging and discharging the secondary battery, wherein the maximum driving voltage of the secondary battery set by the control unit is in the range of 4.00V to 4.08V, and the minimum driving voltage of the secondary battery set by the control unit is in the range of 2.98V to 3.07V.

[0020] Another aspect of the present invention provides a method for using a battery system, the method comprising: manufacturing a battery system comprising one or more secondary batteries and a control unit constructed in a manner for setting a driving voltage range for charging and discharging the secondary batteries; and setting the driving voltage range and charging and discharging the secondary battery for at least one cycle in a manner such that the maximum driving voltage of the secondary battery is in the range of 4.00V to 4.08V and the minimum driving voltage of the secondary battery is in the range of 2.98V to 3.07V through the control unit, wherein the secondary battery comprises a negative electrode containing a silicon-based active material, a positive electrode facing the negative electrode, a separator and an electrolyte arranged between the negative electrode and the positive electrode.

[0021] Yet another aspect of the present invention provides a battery pack including the above battery system.

[0022] Beneficial effects

[0023] The battery system of the present invention includes a secondary battery containing a silicon-based active material and a control unit capable of setting the driving voltage range of the secondary battery to a specific range. The battery system is capable of charging and discharging the secondary battery within the driving voltage range set by the control unit. Consequently, the battery system of the present invention prevents the volume of the silicon-based active material from expanding to a desired level, thereby improving the lifespan of the silicon-based active material while achieving high energy density.

[0024] In addition, according to the method of using a battery system of the present invention, by adjusting the driving voltage range for charging and discharging a secondary battery containing a silicon-based active material to a specific level, the volume expansion degree of the silicon-based active material can be reduced to an appropriate level, and thereby the battery system can be driven, thereby significantly improving the life performance while being able to exhibit high energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Graphs showing evaluations of capacity retention rates of secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 7. DETAILED DESCRIPTION

[0026] The terms or words used in this specification and claims should not be construed as limited to ordinary or dictionary meanings, and should be construed as meanings and concepts consistent with the essence of the invention on the basis of the principle that the inventor can appropriately define the concepts and terms to best explain the inventor's invention.

[0027] The terms used in this specification are only used to describe specific various embodiments and are not intended to limit the present invention. It should be understood that the singular form includes the plural form unless the context clearly indicates otherwise.

[0028] It should be understood that the terms "comprises", "contains", "includes" and / or "has" used herein are intended to clarify the existence of stated features, integers, steps, operations, elements, components and / or combinations thereof, but do not preclude the existence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0029] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% in the particle size distribution curve based on cumulative volume. The average particle size (D) can be measured using, for example, laser diffraction. 50 Laser diffraction can be used to measure particle sizes ranging from submicrometers to several millimeters, and can obtain results with high reproducibility and high resolution.

[0030] Hereinafter, the present invention will be described in detail.

[0031] <Battery System>

[0032] The present invention relates to a battery system, in particular to a battery system for a lithium secondary battery.

[0033] Specifically, the battery system of the present invention includes: at least one secondary battery, the at least one secondary battery including: a negative electrode containing a silicon-based active material, a positive electrode facing the negative electrode, a separator and an electrolyte arranged between the positive electrode and the negative electrode; and a control unit, the control unit is constructed in a manner for setting a driving voltage range for charging and discharging the secondary battery, wherein the maximum driving voltage of the secondary battery set by the control unit is in the range of 4.00V to 4.08V, and the minimum driving voltage of the secondary battery set by the control unit is in the range of 2.98V to 3.07V.

[0034] Typically, secondary batteries can operate by charging and discharging within a voltage range of 4.3V to 2.5V. However, when using a negative electrode and secondary battery containing a silicon-based active material, the volume expansion / contraction of the silicon-based active material can be excessive when charged and discharged within this range, resulting in rapid degradation of lifespan performance. To prevent this, narrowing the voltage range for charging and discharging the secondary battery can make it impossible to achieve the required energy density.

[0035] Therefore, in the present invention, the driving voltage range for charging and discharging the secondary battery is set to a specific range to prevent the volume expansion / contraction of the silicon-based active material to an appropriate level. As a result, high energy density can be achieved while significantly improving battery life performance.

[0036] The secondary battery includes: a negative electrode containing a silicon-based active material; a positive electrode facing the negative electrode; a separator disposed between the negative electrode and the positive electrode; and an electrolyte.

[0037] The negative electrode contains a silicon-based active material and can control the driving voltage range for charging and discharging described later, so that while preventing volume expansion / contraction of the silicon-based active material, it can preferably exhibit high capacity and energy density of the silicon-based active material.

[0038] The negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, and the negative electrode active material layer may contain a silicon-based active material.

[0039] There is no particular limitation on the negative electrode current collector as long as it has high conductivity and does not cause chemical changes in the battery. Specifically, as the negative electrode current collector, the following can be used: copper, stainless steel, aluminum, nickel, titanium, calcined carbon; copper or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc.; aluminum-cadmium alloy, etc.

[0040] The thickness of the negative electrode current collector can be in the range of 3 μm to 500 μm, preferably 5 μm to 50 μm and more preferably 7 μm to 20 μm, in order to thin the negative electrode containing the silicon-based active material.

[0041] The negative electrode current collector may have fine concavities and convexities formed on its surface to improve the binding force of the negative electrode active material. For example, the negative electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0042] The silicon-based active material may contain a compound represented by SiO x (0 ≤ x < 2). SiO2 may not react with lithium ions, and thus may not store lithium. Therefore, it is preferred that x is within the above range.

[0043] Specifically, the silicon-based active material may contain silicon (Si). Conventionally, the advantage of Si is that its capacity is about 2.5 to 3 times that of silicon oxides (such as SiO x (0 < x < 2)), but the problem is that compared with silicon oxides, due to the very high degree of volume expansion / contraction of Si caused by charging and discharging, it is not easy to commercialize. However, according to the present invention, since the driving voltage range of the secondary battery is controlled within the above range, the volume expansion / contraction of Si can be minimized, thereby effectively solving the problem of deterioration of life characteristics, and preferably achieving the advantages of high capacity, excellent rate characteristics and high energy density of Si.

[0044] The average particle size (D) of the silicon-based active material is 1000 nm, which is smaller than that of the active material, in order to ensure the structural stability of the active material during charge and discharge, to more stably form a conductive network for maintaining conductivity, and to make it easier to fix it on the binder for combining the active material and the current collector. 50 ) can be 1 μm to 10 μm, preferably 1.5 μm to 4 μm.

[0045] Considering that the high capacity of the silicon-based active material in the secondary battery is fully realized while minimizing the influence of the volume expansion / contraction of the silicon-based active material on the battery, the content of the silicon-based active material in the negative electrode active material layer can be 60 wt % to 90 wt %, preferably 70 wt % to 80 wt %.

[0046] In addition to the above-mentioned silicon-based active material, the negative electrode active material layer may further include a conductive material and / or a binder.

[0047] The binder can be used to improve the adhesion between the negative electrode active material layer and the negative electrode current collector described later, or to improve the binding force between silicon-based active materials.

[0048] Specifically, in view of further improving the electrode adhesion and imparting sufficient resistance to the volume expansion / contraction of the silicon-based active material, the binder may include at least one selected from the group consisting of styrene-butadiene rubber (SBR), nitrile rubber, acrylic rubber, butyl rubber, fluororubber, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN) and polyacrylamide (PAM).

[0049] Preferably, the binder may include at least one selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyacrylonitrile, and polyacrylamide, preferably polyvinyl alcohol and polyacrylic acid, in order to provide high strength, excellent resistance to volume expansion / contraction of the silicon-based active material, and excellent flexibility to prevent distortion and bending of the electrode. When the binder includes polyvinyl alcohol and polyacrylic acid, the weight ratio of polyvinyl alcohol to polyacrylic acid may be 50:50 to 90:10, preferably 55:45 to 80:20, in order to further enhance the above-mentioned effects.

[0050] The binder may include one in which hydrogen is replaced by Li, Na, or Ca, considering making it easier to disperse the binder in an aqueous solvent such as water when preparing a slurry for forming a negative active material layer and easier to coat the active material to improve bonding strength.

[0051] The content of the binder in the negative electrode active material layer can be 5 wt % to 30 wt %, preferably 10 wt % to 20 wt %, and when the content of the binder is within the above range, the binder is more easily combined with the silicon-based active material, thereby minimizing the volume expansion problem of the active material, facilitating the dispersion of the binder during the preparation of the slurry for forming the negative electrode active material layer, and improving the coating performance and phase stability of the slurry.

[0052] Conductive materials can be used to assist and improve the conductivity of secondary batteries, and there are no particular restrictions as long as they do not cause chemical changes and have conductivity. Specifically, the conductive material can include at least one selected from the following: graphite such as natural graphite, artificial graphite, etc.; carbon black substances such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc.; conductive fibers such as carbon fibers, metal fibers, etc.; conductive tubes such as carbon nanotubes, etc.; fluorocarbons; metal powders such as aluminum powder, nickel powder, etc.; conductive whiskers such as zinc oxide, potassium titanate, etc.; conductive metal oxides such as titanium oxide, etc.; and polyphenylene derivatives, and in view of achieving high conductivity, preferably carbon black can be included.

[0053] In order to promote the dispersion of the conductive material and further improve the conductivity when preparing the slurry for forming the negative electrode active material layer, the conductive material may have a thickness of 80 m 2 / g to 200m 2 / g and preferably 100m 2 / g to 150m 2 / g specific surface area.

[0054] The content of the conductive material in the negative active material layer may be 5 wt % to 20 wt %, preferably 7 wt % to 15 wt %, and the amount of the conductive material within this range is preferred in view of forming an excellent conductive network while alleviating an increase in resistance due to the binder.

[0055] In consideration of realizing a thin film electrode and achieving high energy density, the negative electrode active material layer may have a thickness of 35 μm to 50 μm and preferably 36 μm to 45 μm.

[0056] The negative electrode may have an energy density of 575Wh / L or more and preferably 600Wh / L. The battery system of the present invention can achieve high energy density while solving the volume expansion / contraction problem of the silicon-based active material by adjusting the maximum driving voltage and the minimum driving voltage.

[0057] The negative electrode may be manufactured by applying a negative electrode slurry including a negative electrode active material and optionally a binder, a conductive material, and / or a solvent for forming the negative electrode slurry onto a negative electrode current collector, followed by drying and roll-pressing.

[0058] For example, the solvent for forming the negative electrode paste may include at least one selected from the following: distilled water, ethanol, methanol, and isopropyl alcohol, and distilled water is preferably included in consideration of promoting the dispersion of the negative electrode active material, binder, and / or conductive material.

[0059] In consideration of the viscosity, coating performance, dispersibility, etc. of the negative electrode paste, the solvent for forming the negative electrode paste is included in the negative electrode paste such that the concentration of the solid content including the negative electrode active material and optionally the binder and conductive material is in the range of 15 wt% to 45 wt%, preferably 20 wt% to 30 wt%, and more preferably 24 wt% to 27 wt%.

[0060] The positive electrode may be disposed facing the negative electrode.

[0061] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0062] There is no particular limitation on the positive electrode current collector as long as it has high conductivity and does not cause chemical changes in the battery. Specifically, as the positive electrode current collector, the following can be used: copper, stainless steel, aluminum, nickel, titanium, calcined carbon; aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc.; aluminum-cadmium alloy, etc.

[0063] The positive electrode current collector generally may have a thickness of 3 μm to 500 μm.

[0064] The positive electrode current collector may have fine concavo-convex formed on its surface to improve the binding force of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0065] The positive electrode active material layer may include a positive electrode active material.

[0066] The positive electrode active material is a compound capable of reversibly embedding and de-embedding lithium, and specifically may include a lithium-transition metal composite oxide containing lithium and at least one transition metal selected from nickel, cobalt, manganese, and aluminum.

[0067] Specifically, the lithium-transition metal composite oxide may be a lithium-manganese-based oxide (such as LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (such as LiCoO2, etc.), a lithium-nickel-based oxide (such as LiNiO2, etc.), a lithium-nickel-manganese-based oxide (such as LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < z < 2), etc.), a lithium-nickel-cobalt-based oxide (such as LiNi 1- Y1 CoY1 O2 (where 0 < Y1 < 1), etc., lithium-manganese-cobalt oxides (such as LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2- Z1 Co Z1 O4 (where 0 < z1 < 2), etc., lithium-nickel-manganese-cobalt oxides (such as Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc., or lithium-nickel-cobalt-manganese-transition metal (M) oxides (such as Li(Ni p2 Co q2 Mn r3 M s2 )O2 (where M is selected from: Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, p2, q2, r3, and s2 are each the atomic fraction of an element independent of each other, and 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, p2 + q2 + r3 + s2 = 1), etc.). The substances can be used alone or in mixtures of two or more of them. Among them, considering the improvement of the capacity characteristics and stability of the battery, the lithium-transition metal composite oxide can be LiCoO2, LiMnO2, LiNiO2, lithium-nickel-manganese-cobalt oxide (such as Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.) or lithium-nickel-cobalt-aluminum oxide (such as Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.). And considering to achieve significant improvement effects by controlling the type and content ratio of the constituent elements forming the lithium-transition metal composite oxide, the lithium-transition metal composite oxide can be Li(Ni 0.6 Mn​​​)O2、Li(Ni 0.5 Mn 0.3 Co 0.2 )O2、Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, said substances may be used alone or as a mixture of two or more thereof.

[0068] More specifically, the lithium-transition metal composite oxide may contain: a transition metal including nickel, cobalt, and manganese; and lithium, and in this case, lifespan characteristics and energy density may be significantly improved within a driving voltage range of a battery system, which will be described below.

[0069] In consideration of fully expressing the capacity of the positive electrode active material, the content of the positive electrode active material in the positive electrode active material layer may be 80 wt % to 99 wt %, preferably 92 wt % to 98.5 wt %.

[0070] The positive electrode active material layer may further include a binder and / or a conductive material in addition to the positive electrode active material described above.

[0071] The binder is a component that facilitates the bonding between the active material and the conductive material and the binding to the current collector. Specifically, the binder may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, and may preferably include polyvinylidene fluoride.

[0072] The content of the binder in the positive electrode active material layer may be 1 wt % to 20 wt %, preferably 1.2 wt % to 10 wt %, in consideration of sufficiently ensuring binding force between components such as the positive electrode active material.

[0073] Conductive materials can be used to assist and improve the conductivity of secondary batteries, and there are no particular restrictions as long as they do not cause chemical changes and have conductivity. Specifically, the conductive material can include at least one selected from the following: graphite such as natural graphite, artificial graphite, etc.; carbon black substances such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc.; conductive fibers such as carbon fibers, metal fibers, etc.; conductive tubes such as carbon nanotubes, etc.; fluorocarbons; metal powders such as aluminum powder, nickel powder, etc.; conductive whiskers such as zinc oxide, potassium titanate, etc.; conductive metal oxides such as titanium oxide, etc.; and polyphenylene derivatives, and in view of improving conductivity, carbon black can be preferably included.

[0074] In order to promote the dispersion of the conductive material and further improve the conductivity when preparing the slurry for forming the positive electrode active material layer, the conductive material may have a thickness of 80 m 2 / g to 200m 2 / g and preferably 100m 2 / g to 150m 2 / g specific surface area.

[0075] In view of sufficiently ensuring conductivity, the content of the conductive material in the positive electrode active material layer may be 1 wt % to 20 wt %, preferably 1.2 wt % to 10 wt %.

[0076] Considering the capacity balance of the negative and positive electrodes and minimizing the influence of volume expansion / contraction of the silicon-based active material in the negative electrode, the positive active material layer may have a thickness of 30 to 400 μm and preferably 50 to 110 μm.

[0077] The positive electrode may be manufactured by applying a positive electrode slurry including a positive electrode active material and optionally a binder, a conductive material, and a solvent for forming the positive electrode slurry onto a positive electrode current collector, followed by drying and roll-pressing.

[0078] When containing a positive electrode active material and an optional binder, a conductive material, etc., the solvent for forming the positive electrode slurry may include an organic solvent such as N-methyl-2-pyrrolidone (NMP) and the like and may be used in an amount suitable for achieving a preferred viscosity. For example, the solvent for forming the positive electrode slurry may be included in the positive electrode slurry so that the concentration of the solid content containing the positive electrode active material and the optional binder and the conductive material is in the range of 50 wt % to 95 wt % and preferably 70 wt % to 90 wt %.

[0079] The secondary battery structure may have an N / P ratio calculated by the following Formula 1 of 1.5 to 3.5 and preferably 1.8 to 2.3,

[0080] [Formula 1]

[0081] N / P ratio=discharge capacity per unit area of negative electrode / discharge capacity per unit area of positive electrode.

[0082] In the present invention, “discharge capacity per unit area” refers to the discharge capacity per unit area of the negative electrode or the positive electrode at the first cycle.

[0083] The "discharge capacity per unit area of the negative electrode" can be calculated by the following method. Specifically, a half-cell is manufactured using a negative electrode sample containing a negative electrode active material and a counter electrode (such as a lithium metal electrode) facing the negative electrode sample. The discharge capacity measured by charging and discharging the half-cell is divided by the weight of the negative electrode active material to obtain the "discharge capacity of the negative electrode sample per unit weight of the negative electrode active material". A secondary battery is manufactured using a negative electrode containing the same negative electrode active material as the negative electrode active material used in the half-cell and a positive electrode containing a positive electrode active material. The value obtained by multiplying the "discharge capacity of the negative electrode sample per unit weight of the negative electrode active material" by the weight of the negative electrode active material contained in the secondary battery is divided by the area of the negative electrode contained in the secondary battery to obtain the "discharge capacity per unit area of the negative electrode".

[0084] The "discharge capacity per unit area of the positive electrode" can be calculated by the following method. Specifically, a half-cell is manufactured using a positive electrode sample containing a positive electrode active material and a counter electrode (such as a lithium metal electrode) facing the positive electrode sample. The discharge capacity measured by charging and discharging the half-cell is divided by the weight of the positive electrode active material to obtain the "discharge capacity of the positive electrode sample per unit weight of the positive electrode active material". A secondary battery is manufactured using a positive electrode containing the same positive electrode active material as the positive electrode active material used in the half-cell and a negative electrode containing a negative electrode active material. The value obtained by multiplying the "discharge capacity of the positive electrode sample per unit weight of the positive electrode active material" by the weight of the positive electrode active material contained in the secondary battery is divided by the area of the positive electrode contained in the secondary battery to obtain the "discharge capacity per unit area of the positive electrode".

[0085] When the N / P ratio (the ratio of the positive electrode discharge capacity to the negative electrode discharge capacity) of the secondary battery of the present invention is adjusted to the above range, the discharge capacity of the negative electrode is designed to be greater than the discharge capacity of the positive electrode by a specific level, whereby when lithium is inserted from the positive electrode into the negative electrode, the ratio of lithium to all silicon-based active materials in the negative electrode is reduced. Therefore, the proportion of silicon-based active materials used in the negative electrode is reduced to a specific level, and thus, the deterioration of the life characteristics of the entire battery level caused by the volume expansion of the negative electrode can be minimized. In addition, because the N / P ratio is adjusted to the above range, a secondary battery having high energy density, rate characteristics, and capacity characteristics due to the silicon-based active material can be achieved while minimizing the degradation of the battery life characteristics caused by the above-mentioned volume expansion.

[0086] There is no particular limitation on the separator, as long as it is generally used as a separator in a lithium secondary battery to separate the negative electrode from the positive electrode and provide a path for the movement of lithium ions. In particular, it is preferred that the separator has low resistance to the movement of electrolyte ions and has excellent ability to be impregnated with an electrolyte. Specifically, it is possible to use: a porous polymer film, for example, a porous polymer film formed of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer; or a laminated structure having two or more layers thereof. In addition, a conventional porous non-woven fabric can be used, such as a non-woven fabric formed of a high melting point glass fiber or a polyethylene terephthalate fiber. In addition, in order to ensure heat resistance or mechanical strength, a coated separator comprising a ceramic component or a polymer material can be used, and can be selectively used in a single-layer or multi-layer structure.

[0087] In addition, as the electrolyte used in the present invention, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used to manufacture a secondary battery may be used, but the present invention is not limited thereto.

[0088] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0089] There is no specific limitation on the organic solvent, as long as it is used as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, there can be used: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene or fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) or propylene carbonate (PC); alcohol solvents such as ethanol or isopropanol; nitrile solvents such as R-CN (R is a linear, branched or cyclic C2 to C20 hydrocarbon group and may contain a double bond, an aromatic ring or an ether bond); amide solvents such as dimethylformamide; dioxolane solvents such as 1,3-dioxolane; or sulfolane solvents. Wherein, preferably use carbonate solvent, and more preferably use the mixture of cyclic carbonate such as ethylene carbonate or propylene carbonate that can improve the charge / discharge performance of battery with high ion conductivity and high dielectric constant and straight chain carbonate compound (such as ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate etc.) with low viscosity.In this case, when mixing cyclic carbonate and chain carbonate with the volume ratio of about 1:1 to about 1:9, electrolyte can show excellent performance.

[0090] Lithium salt can be used without particular limitation, as long as it is a compound that can provide lithium ions for lithium secondary batteries. Specifically, as lithium salts, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. can be used. The concentration of the lithium salt is preferably in the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thereby showing excellent electrolyte performance, and lithium ions can be efficiently moved.

[0091] One or more secondary batteries may be included in the battery system.

[0092] For example, the secondary battery may be included in the battery system in the form of a secondary battery cell made of one secondary battery or a secondary battery module which is an aggregate of a plurality of secondary batteries.

[0093] The secondary battery can be manufactured by a conventional method of manufacturing a secondary battery, that is, by inserting a separator between the above-mentioned negative electrode and positive electrode and injecting an electrolyte.

[0094] The control unit may set a driving voltage range for charging and discharging the secondary battery. Therefore, the secondary battery may be charged and discharged within the driving voltage range of the secondary battery set by the control unit.

[0095] The control unit is not particularly limited as long as it can control the driving voltage range for charging and discharging the secondary battery, and can be, for example, an electrochemical charging and discharging device. Specifically, the control unit can be embedded in a battery management system (BMS) included in the battery pack.

[0096] The maximum driving voltage of the secondary battery set by the control unit is within the range of 4.00 V to 4.08 V, and the minimum driving voltage of the secondary battery set by the control unit is within the range of 2.98 V to 3.07 V. Charging and discharging of the secondary battery can be performed within the range from the set maximum driving voltage to the set minimum driving voltage.

[0097] When the maximum driving voltage is less than 4.00 V, the driving voltage range becomes narrow, and thus the desired energy density level may not be achieved. When the maximum driving voltage is greater than 4.08 V, the volume expansion of the silicon-based active material cannot be adequately controlled as the capacity exhibited by the active material increases, and thus the lifespan performance may deteriorate rapidly.

[0098] When the minimum driving voltage is less than 2.98 V, inter-particle separation may occur due to shrinkage of the active material, and the conductive connection between the active materials may be destroyed, thereby rapidly degrading the life performance. When the minimum driving voltage is greater than 3.07 V, the driving voltage range becomes narrow, and the required energy density level may not be achieved.

[0099] Specifically, the maximum driving voltage of the secondary battery set by the control unit may be in the range of 4.03 V to 4.07 V, and the minimum driving voltage of the secondary battery set by the control unit may be in the range of 3.03 V to 3.06 V. When the driving voltage is within the above range, the above-mentioned effects of simultaneously improving life characteristics and energy density can be more preferably achieved.

[0100] <How to use the battery system>

[0101] The present invention provides a method for using a battery system, and more specifically, provides a method for using the battery system. Specifically, the method for using the battery system can be a method for using a battery system for a lithium secondary battery.

[0102] Specifically, the method of using the battery system of the present invention includes: manufacturing a battery system, the battery system comprising at least one secondary battery and a control unit constructed in a manner for setting a driving voltage range for charging and discharging the secondary battery; and setting the driving voltage range and charging and discharging the secondary battery for at least one cycle in a manner such that the maximum driving voltage of the secondary battery is in the range of 4.00V to 4.08V and the minimum driving voltage of the secondary battery is in the range of 2.98V to 3.07V through the control unit, wherein the secondary battery comprises a negative electrode containing a silicon-based active material, a positive electrode facing the negative electrode, a separator and an electrolyte arranged between the negative electrode and the positive electrode.

[0103] In a method for using the battery system of the present invention, a control unit sets the maximum and minimum driving voltages to the aforementioned levels, and the battery system is operated by charging and discharging the secondary battery from the set maximum driving voltage to the set minimum driving voltage. In the secondary battery charged and discharged by adjusting the driving voltage range to the aforementioned levels, the volume expansion / contraction of the silicon-based active material is minimized, thereby achieving high energy density while improving lifespan performance.

[0104] The secondary battery and the control unit may be the same as those described above.

[0105] <Battery Pack>

[0106] Furthermore, the present invention provides a battery pack including the above battery system.

[0107] In addition to the aforementioned secondary battery and control unit, the battery pack may further include components known in the art, such as a BMS, a cooling system, and the like.

[0108] The battery system or battery pack according to the present invention can be used in the following fields: portable devices such as mobile phones, laptop computers, and digital cameras; and electric vehicles such as hybrid electric vehicles (HEVs). The battery system or battery pack is preferably used as a power source for devices requiring high power and large capacity, such as electric vehicles, HEVs, or power storage devices.

[0109] Hereinafter, examples of the present invention will be described in detail in a manner that enables those skilled in the art to easily implement the present invention. However, the present invention can be embodied in several different forms and is not limited to the examples described below.

[0110] <Manufacturing Example>

[0111] Manufacturing Example 1: Manufacturing of Secondary Battery

[0112] <Manufacturing of negative electrode>

[0113] The silicon active material Si (average particle size (D 50 ): 3.5 μm), carbon black (product name: Super C65, manufacturer: TIMCAL) as a conductive material, and a mixture obtained by mixing polyvinyl alcohol and polyacrylic acid in a weight ratio of 66:34 (weight average molecular weight: about 360,000 g / mol) as a binder were added to distilled water as a solvent for forming a negative electrode slurry in a weight ratio of 75:10:15 to prepare a negative electrode slurry (solid content concentration was 25 wt %).

[0114] The negative electrode slurry was prepared at 68.4 mg / 25 cm 2 The negative electrode was coated on one surface of a copper current collector (thickness: 8 μm) as a negative electrode current collector, roll-pressed, and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 44 μm), thereby manufacturing a negative electrode (the thickness of the negative electrode was 52 μm).

[0115] <Manufacturing of positive electrode>

[0116] LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2(average particle size(D 50):10 μm), carbon black as a conductive material (product name: Super C65, manufacturer: TIMCAL), and polyvinylidene fluoride (PVDF) as an adhesive were mixed at a weight ratio of 97:1.5:1.5, and the resulting mixture was added to N-methylpyrrolidone (NMP) as a solvent for forming the positive electrode paste to prepare a positive electrode paste (solid content concentration: 72 wt%).

[0117] The positive electrode paste was coated on one surface of an aluminum current collector (thickness: 12 μm) as the positive electrode current collector at a loading amount of 459.4 mg / 25 cm 2 , roll-pressed, and dried in a vacuum oven at 130 °C for 10 hours to form a positive electrode active material layer (thickness: 110 μm), thereby manufacturing a positive electrode (thickness of the positive electrode: 122 μm).

[0118] <Manufacture of secondary battery>

[0119] A polyethylene / polypropylene / polyethylene separator was placed between the above-manufactured negative electrode and positive electrode, and an electrolyte was injected to manufacture the secondary battery of Production Example 1. An electrolyte was prepared by adding vinylene carbonate at 3 wt% relative to the total weight of the electrolyte to an organic solvent in which fluoroethylene carbonate (FEC) and DMC were mixed at a volume ratio of 30:70, and adding LiPF6 as a lithium salt at a concentration of 1 M.

[0120] <Measurement of N / P ratio>

[0121] The above-manufactured negative electrode was cut into a predetermined size to manufacture a negative electrode sample. A lithium metal electrode having the same size as the negative electrode sample was prepared and arranged facing the negative electrode sample. A polyethylene separator was inserted between the negative electrode sample and the lithium metal electrode, and then an electrolytic solution was injected to manufacture a coin-type half cell. An electrolytic solution was prepared by adding LiPF6 as a lithium salt at a concentration of 1 M to an organic solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 50:50. The discharge capacity obtained by charging / discharging the coin-type half cell at 0.1 C was divided by the weight of the negative electrode active material contained in the negative electrode sample, thereby obtaining the discharge capacity of the negative electrode sample per unit weight of the negative electrode active material.

[0122] In addition, the above-prepared positive electrode was cut into a predetermined size to fabricate a positive electrode sample. A lithium metal electrode having the same size as the positive electrode sample was prepared and arranged to face the positive electrode sample. A polyethylene separator was inserted between the positive electrode sample and the lithium metal electrode, and then an electrolyte solution was injected to fabricate a coin-type half cell. The electrolyte solution was prepared by adding LiPF6 as a lithium salt at a concentration of 1 M to an organic solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 50:50. The discharge capacity obtained by charging / discharging the coin-type half cell at 0.1 C was divided by the weight of the positive electrode active material contained in the positive electrode sample, thereby obtaining the discharge capacity of the positive electrode sample per unit weight of the positive electrode active material.

[0123] The value obtained by multiplying the discharge capacity of the negative electrode sample per unit weight of the negative electrode active material measured above by the weight of the negative electrode active material of the secondary battery fabricated in Production Example 1 was divided by the area of the negative electrode, thereby obtaining the discharge capacity per unit area of the negative electrode of Production Example 1. In addition, the value obtained by multiplying the discharge capacity of the positive electrode sample per unit weight of the positive electrode active material measured above by the weight of the positive electrode active material of the secondary battery fabricated in Production Example 1 was divided by the area of the positive electrode, thereby obtaining the discharge capacity per unit area of the positive electrode of Production Example 1.

[0124] The discharge capacity per unit area of the negative electrode was divided by the discharge capacity per unit area of the positive electrode, thereby obtaining an N / P ratio of 2.0.

[0125] Production Example 2: Fabrication of a secondary battery

[0126] <Fabrication of the negative electrode><000034​​​​​​​​​​​​​​​​​​​​​​

[0134] <Example>

[0135] Examples 1 to 3 and Comparative Examples 1 to 7

[0136] <Manufacturing of battery systems>

[0137] The secondary batteries of Manufacturing Examples 1 and 2 manufactured above were connected to an electrochemical charging and discharging device.

[0138] By adjusting the type of secondary battery and the maximum driving voltage and the minimum driving voltage set by the control unit as shown in Table 1 below, battery systems of Examples 1 to 3 and Comparative Examples 1 to 7 were manufactured.

[0139] [Table 1]

[0140]

[0141] Experimental example

[0142] Experimental Example 1: Thickness Expansion Rate When Fully Charged

[0143] The battery systems manufactured in Examples 1 to 3 and Comparative Examples 1 to 7 were charged at 0.5 C to the maximum voltage of Table 1 (maximum voltage of Table 1, 0.05 C current cut-off) in constant current (CC) / constant voltage (CV) mode, and the thickness expansion rate of the negative electrode in the fully charged state was measured according to the following formula 2:

[0144] [Formula 2]

[0145] Thickness expansion rate of negative electrode when fully charged (%) = {(d a2 -d a1 ) / d a1}×100

[0146] Among them, d a2 is the thickness of the negative electrode active material layer when fully charged, and d a1 The results are shown in Table 2 below.

[0147] Experimental Example 2: Thickness Change Difference During Full Charge / Full Discharge

[0148] The battery systems manufactured in Examples 1 to 3 and Comparative Examples 1 to 7 were charged and discharged under the following conditions to calculate the thickness change difference (%) at full charge / full discharge according to the following Formula 3.

[0149] <Charge and Discharge Conditions>

[0150] Charging: Charge at 0.5C in CC / CV mode to the maximum voltage in Table 1 (maximum voltage in Table 1, 0.05C current cutoff)

[0151] Discharge: Discharge at 0.5C in CC mode to the minimum voltage in Table 1 (cut off at the minimum voltage in Table 1)

[0152] [Formula 3]

[0153] Thickness change difference during full charge / full discharge (%) = {(d b2 -d b1 ) / d b1}×100

[0154] Among them, d b2 is the thickness of the negative electrode active material layer when fully charged, and d b1 The results are shown in Table 2 below.

[0155] Experimental Example 3: Capacity Retention

[0156] The capacity retention rates of the various battery systems manufactured in Examples 1 to 3 and Comparative Examples 1 to 7 were evaluated.

[0157] The secondary battery was charged and discharged under the following charging and discharging conditions until the 200th cycle. The capacity retention rate was evaluated using the following formula 4. The results are shown in Figure 1 and Table 2 below.

[0158] <Charge and Discharge Conditions>

[0159] Charging: Charge at 0.5C in CC / CV mode to the maximum voltage in Table 1 (maximum voltage in Table 1, 0.05C current cutoff)

[0160] Discharge: Discharge at 0.5C in CC mode to the minimum voltage in Table 1 (cut off at the minimum voltage in Table 1)

[0161] [Formula 4]

[0162] Capacity retention (%) = (discharge capacity at the 200th cycle / discharge capacity at the first cycle) × 100

[0163] Experimental Example 4: Energy Density

[0164] The battery systems manufactured in Examples 1 to 3 and Comparative Examples 1 to 7 were once charged and discharged under the following charging and discharging conditions.

[0165] <Charge and Discharge Conditions>

[0166] Charging: Charge at 0.5C in CC / CV mode to the maximum voltage in Table 1 (maximum voltage in Table 1, 0.05C current cutoff)

[0167] Discharge: Discharge at 0.5C in CC mode to the minimum voltage in Table 1 (cut off at the minimum voltage in Table 1)

[0168] Then, the energy density of the negative electrodes in the battery systems of Examples 1 to 3 and Comparative Examples 1 to 7 was measured and calculated by the following Formula 5,

[0169] [Formula 5]

[0170] Energy density (Wh / L) = {discharge capacity of the first cycle (Ah) × average voltage (V)} / (volume of the negative electrode at the completion of the first cycle (L))

[0171] The average voltage was obtained by multiplying the voltage, the current, and the discharge time at the time point when the discharge was terminated by reaching the minimum voltage and dividing the watt-hour (Wh) by the discharge capacity of the first cycle.

[0172] [Table 2]

[0173]

[0174] Referring to Table 2, it can be seen that in the case of Examples 1 to 3 using the battery system according to the present invention, lifespan characteristics and energy density are improved at the same time.

[0175] On the other hand, in the case of Comparative Examples 1 to 7 in which charging and discharging were not performed at the maximum driving voltage and the minimum driving voltage of the present invention, it can be seen that the energy density is too low due to the difficulty in expressing the sufficient capacity of the silicon-based active material, and the life characteristics are too low due to the difficulty in controlling the volume expansion of the silicon-based active material.

Claims

1. A battery system, comprising: One or more secondary batteries, each of the one or more secondary batteries comprising: a negative electrode containing a silicon-based active material, a positive electrode facing the negative electrode, a separator and an electrolyte provided between the negative electrode and the positive electrode; and a control unit configured to set a driving voltage range for charging and discharging the secondary battery, The maximum driving voltage of the secondary battery set by the control unit is within a range of 4.00V to 4.08V, and the minimum driving voltage of the secondary battery set by the control unit is within a range of 3.03V to 3.06V. 2 . The battery system according to claim 1 , wherein the silicon-based active material is silicon (Si).

3. The battery system according to claim 1, wherein The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, and The negative electrode active material layer includes the silicon-based active material, a binder, and a conductive material.

4. The battery system according to claim 3, wherein the binder comprises at least one selected from the group consisting of styrene-butadiene rubber, nitrile rubber, acrylic rubber, butyl rubber, fluororubber, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyacrylonitrile, and polyacrylamide.

5. The battery system according to claim 3, wherein The content of the silicon-based active material in the negative electrode active material layer is 60 wt % to 90 wt %. The content of the binder in the negative electrode active material layer is 5 wt % to 30 wt %, and The conductive material is contained in the negative electrode active material layer in an amount of 5 wt % to 20 wt %. 6 . The battery system according to claim 3 , wherein the negative electrode active material layer has a thickness of 35 μm to 50 μm.

7. The battery system according to claim 1, wherein an N / P ratio of the secondary battery calculated by the following formula 1 is in the range of 1.5 to 3.5, [Formula 1] N / P ratio=discharge capacity per unit area of negative electrode / discharge capacity per unit area of positive electrode.

8. The battery system according to claim 1, wherein: The positive electrode active material comprises a lithium-transition metal composite oxide, and The lithium-transition metal composite oxide contains lithium and at least one transition metal selected from the group consisting of nickel, cobalt, manganese, and aluminum.

9. A method of using a battery system, the method comprising: manufacturing a battery system including one or more secondary batteries and a control unit configured to set a driving voltage range for charging and discharging the secondary batteries; as well as setting the driving voltage range in such a manner that the maximum driving voltage of the secondary battery is within the range of 4.00 V to 4.08 V and the minimum driving voltage of the secondary battery is within the range of 3.03 V to 3.06 V by the control unit, and charging and discharging the secondary battery for at least one cycle, The secondary battery includes: a negative electrode containing a silicon-based active material, a positive electrode facing the negative electrode, a separator and an electrolyte provided between the negative electrode and the positive electrode. 10 . A battery pack comprising the battery system according to claim 1 .

Images