Negative electrode for lithium secondary battery and lithium secondary battery comprising same

Abstract

The negative electrode comprises a negative electrode current collector; and a negative electrode active material layer of a multi-layer structure, the negative electrode active material layer of the multi-layer structure is arranged on at least one surface of the negative electrode current collector, and the negative electrode active material layer of the multi-layer structure comprises a first negative electrode active material layer and a second negative electrode active material layer. At least one of the first negative electrode active material layer and the second negative electrode active material layer contains a first silicon-based active material doped with a first metal, and the doping amount of the first metal is 1.5 wt% to 8 wt% based on the total weight of the first silicon-based active material.

Description

Technical Field

[0001] The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery comprising the negative electrode. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged. With the development of the information communications and display industries, secondary batteries are widely used as power sources for portable electronic communication devices such as laptops and mobile phones. Furthermore, in recent years, battery packs containing secondary batteries have been developed and used as power sources for environmentally friendly vehicles such as electric vehicles.

[0003] The positive electrode material of lithium secondary batteries can include NCM (nickel, cobalt, manganese), NCA (nickel, cobalt, aluminum), LFP (lithium, iron, phosphorus), etc. The negative electrode material of lithium secondary batteries can include natural graphite, artificial graphite, graphite, metal, etc.

[0004] Among the above-mentioned negative electrode materials, graphite has high stability and silicon has high energy density.

[0005] In recent years, as the application range of lithium-ion secondary batteries has expanded, demand for high energy density, high stability, and fast charging has been increasing. For example, batteries used in electric vehicles require higher capacities than existing lithium-ion secondary batteries. To meet these requirements, attempts are underway to use a combination of negative electrode materials. However, silicon's high volume expansion rate is difficult to control, and thus, during charging and discharging, cracks may form in the active material due to reactions with lithium, which can significantly reduce the lifespan and fast-charging characteristics of lithium-ion secondary batteries. Summary of the Invention

[0006] (1) Technical issues to be resolved

[0007] A technical problem of the present invention is to provide a negative electrode for a secondary battery having improved capacity characteristics and life characteristics.

[0008] A technical problem of the present invention is to provide a lithium secondary battery having improved capacity characteristics and lifespan characteristics.

[0009] (2) Technical solution

[0010] A negative electrode for a lithium secondary battery according to an embodiment of the present invention includes: a negative electrode current collector; and a multi-layered negative electrode active material layer, the multi-layered negative electrode active material layer being disposed on at least one side of the negative electrode current collector, the multi-layered negative electrode active material layer including a first negative electrode active material layer and a second negative electrode active material layer, wherein at least one of the first negative electrode active material layer and the second negative electrode active material layer includes a first silicon-based active material doped with a first metal. The doping amount of the first metal is 1.5% to 8% by weight of the total weight of the first silicon-based active material.

[0011] In some embodiments, the first metal may comprise magnesium.

[0012] In some embodiments, the first negative active material layer may include the first silicon-based active material, and the second negative active material layer may include a silicon-based negative active material different from the first silicon-based active material.

[0013] In some embodiments, the second negative active material layer may include a second silicon-based active material doped with a second metal, and the doping amount of the second metal may be 5 wt % or more based on the total weight of the second silicon-based active material.

[0014] In some embodiments, the doping amount of the second metal may be 5 wt % to 20 wt % based on the total weight of the second silicon-based active material.

[0015] In some embodiments, the second metal doped in the second silicon-based active material may include at least one of Li, Mg, Ca, Al, Fe, Ti, and V.

[0016] In some embodiments, the silicon-based negative electrode active material contained in the second negative electrode active material layer may include a silicon-carbon composite or SiO2 undoped with metal. x (0 <x<2)。

[0017] In some embodiments, the second negative active material layer may not include a silicon-based active material.

[0018] In some embodiments, the first negative active material layer may be in contact with at least one side of the negative current collector, and the second negative active material layer may be disposed on an upper surface of the first negative active material layer.

[0019] In some embodiments, the second negative active material layer may be in contact with at least one side of the negative current collector, and the first negative active material layer may be disposed on an upper surface of the second negative active material layer.

[0020] In some embodiments, the first negative electrode active material layer may be in contact with at least one side of the negative electrode current collector, the first negative electrode active material layer may include the first silicon-based active material, the second negative electrode active material layer may be disposed on an upper surface of the first negative electrode active material layer, and the second negative electrode active material layer may include a graphite-based active material and not a silicon-based active material.

[0021] In some embodiments, the first negative electrode active material layer may include the first silicon-based active material, the second negative electrode active material layer may include the second silicon-based active material, and the weight-based content of the first silicon-based active material in the total weight of the first negative electrode active material layer and the weight-based content of the second silicon-based active material in the total weight of the second negative electrode active material layer may be different from each other.

[0022] In some embodiments, the first negative electrode active material layer may be in contact with at least one side of the negative electrode current collector, the second negative electrode active material layer may be disposed on an upper surface of the first negative electrode active material layer, and the content of the first silicon-based active material in the total weight of the first negative electrode active material layer on a weight basis may be less than the content of the second silicon-based active material in the total weight of the second negative electrode active material layer on a weight basis.

[0023] In some embodiments, the first negative active material layer may include the first silicon-based active material and a graphite-based active material. The first negative active material layer may include 2 wt % to 20 wt % of the first silicon-based active material based on the total weight of the first negative active material layer.

[0024] In some embodiments, the doping amount of magnesium may be 2 wt % to 5 wt % based on the total weight of the first silicon-based active material.

[0025] A lithium secondary battery according to an embodiment of the present invention may include: the negative electrode according to the above embodiment; and a positive electrode disposed opposite to the negative electrode.

[0026] (3) Beneficial effects

[0027] In the negative electrode according to the exemplary embodiment of the present invention, generation of cracks of the silicon-based active material may be suppressed, and thus life characteristics of the lithium secondary battery at normal and high temperatures may be improved.

[0028] In some embodiments, the silicon-based active material may contain micropores therein, thereby reducing the energy generated inside the secondary battery when it shrinks / expands due to charge and discharge.

[0029] In some embodiments, the energy density of a lithium secondary battery may be increased by having an upper layer and a lower layer structure of a negative electrode active material layer having different compositions from each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic cross-sectional view illustrating a negative electrode for a lithium secondary battery according to an exemplary embodiment.

[0031] Figure 2 is a schematic cross-sectional view illustrating a negative electrode for a lithium secondary battery according to an exemplary embodiment.

[0032] Figure 3 and Figure 4 are a schematic plan view and a schematic cross-sectional view illustrating a lithium secondary battery according to an exemplary embodiment.

[0033] Description of reference numerals:

[0034] 100: positive electrode; 105: positive electrode current collector

[0035] 107: positive electrode lead; 110: positive electrode active material layer

[0036] 120: negative electrode active material layer; 122: first negative electrode active material layer

[0037] 124: second negative electrode active material layer; 125: negative electrode current collector

[0038] 127: negative lead; 130: negative electrode

[0039] 140: diaphragm; 150: electrode assembly

[0040] 160: Shell DETAILED DESCRIPTION

[0041] According to an embodiment of the present invention, a negative electrode for a lithium secondary battery is provided. The negative electrode for a lithium secondary battery includes a multilayer structure of negative electrode active material layers, wherein the multilayer structure of the negative electrode active material layers includes a first negative electrode active material layer and a second negative electrode active material layer, wherein the first negative electrode active material layer includes a first silicon-based active material doped with a first metal. In addition, a lithium secondary battery including the negative electrode is provided.

[0042] In this specification, a “graphite-based active material” may refer to an active material containing carbon elements and not silicon elements.

[0043] In this specification, "silicon-based active material" may refer to an active material containing silicon element.

[0044] The present invention will be described in more detail below with reference to the accompanying drawings and embodiments. However, the following drawings and embodiments attached and described in this specification are intended to illustrate preferred embodiments of the present invention and, together with the above-described contents, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be construed as being limited to the contents described in these drawings and embodiments.

[0045] <Negative Electrode for Lithium Secondary Batteries>

[0046] A negative electrode for a lithium secondary battery according to an embodiment of the present invention includes: a negative electrode current collector; and a negative electrode active material layer provided on at least one side of the negative electrode current collector.

[0047] Reference Figure 1 or Figure 2 The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 formed on the negative electrode current collector 125 .

[0048] For example, the negative electrode current collector 125 may include a metal that has high conductivity, strong adhesion to the negative electrode slurry, and does not cause chemical changes within the operating voltage range of the secondary battery. Specifically, the negative electrode current collector 125 may include copper, stainless steel, aluminum, nickel, titanium, or alloys thereof. Alternatively, the negative electrode current collector 125 may include copper or stainless steel that has been surface-treated with carbon, nickel, titanium, or silver.

[0049] The negative electrode current collector 125 may have a thickness of 3 μm to 500 μm, and may include a structure for improving adhesion with a negative electrode active material on a surface of the current collector.

[0050] In some embodiments, the negative electrode 130 may include a negative active material layer 120 formed on at least one side of a negative current collector 125 , and the negative active material layer 120 may include a first negative active material layer 122 and a second negative active material layer 124 .

[0051] The first negative electrode active material layer 122 or the second negative electrode active material layer 124 may be in contact with at least one side of the negative electrode current collector 125. In addition, a multilayer structure may be formed, including a layer in contact with at least one side of the negative electrode current collector and a layer provided on an upper surface of the layer in contact with one side of the negative electrode current collector.

[0052] The stacking order of the first negative electrode active material layer 122 and the second negative electrode active material layer 124 is not limited. For example, the first negative electrode active material layer 122 can be disposed on the upper surface of the negative electrode current collector 125, and the second negative electrode active material layer 124 can be disposed on the upper surface of the first negative electrode active material layer 122. Alternatively, the second negative electrode active material layer 124 can be disposed on the upper surface of the negative electrode current collector 125, and the first negative electrode active material layer 122 can be disposed on the upper surface of the second negative electrode active material layer 124.

[0053] In some embodiments, the first negative active material layer 122 may include a first silicon-based active material.

[0054] The first silicon-based active material may be doped with a first metal. The first silicon-based active material doped with the first metal may be formed by mixing a silicon-based active material source and a first metal source, heating, cooling, and pulverizing them.

[0055] In some embodiments, the first metal may include at least one of Mg, Ca, Al, Fe, Ti, and V. In one embodiment, the first metal may include magnesium (Mg).

[0056] The silicon-based active material source may be a mixture of silicon (Si) and silicon dioxide (SiO2). The molar ratio of silicon to silicon dioxide may be 1:0.5 to 1.5. The first metal source may include a magnesium source, which may be solid magnesium.

[0057] For example, the silicon-based active material source and the first metal source may be mixed to form a first primary active material composition.

[0058] During the preparation of the first silicon-based active material, the first metal source may include a magnesium source. The content of the magnesium source may be 1.5 wt % to 8 wt % based on the total weight of the first primary active material composition.

[0059] Within the above range, generation of forsterite in the crystal structure of doped magnesium may be reduced, so that the size of silicon crystals per unit cell in the active material may be reduced, and the ratio of micropores may be increased.

[0060] For example, the first primary active material composition may be calcined at 1000° C. to 1800° C. and then cooled to precipitate a silicon oxide composite containing the first metal. The silicon oxide composite containing the first metal may be pulverized and classified to form the first silicon-based active material.

[0061] In some embodiments, the first silicon-based active material may not include an alloy-based active material. The alloy-based active material may refer to an active material comprising, for example, at least one of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, and rare earth elements, or a combination thereof, and silicon. When the first silicon-based active material includes an alloy-based active material, the crystal structure of the first silicon-based active material may change.

[0062] In some embodiments, the first silicon-based active material may be doped with the first metal in an amount ranging from 1.5 wt % to 8 wt % based on the total weight of the first silicon-based active material.

[0063] In some embodiments, the doped first metal may include magnesium.

[0064] In one embodiment, the first metal doped in the first silicon-based active material may include magnesium, and the doping amount of magnesium may be 1.6 wt % to 7 wt %, 1.8 wt % to 6 wt %, or 2 wt % to 5 wt % of the total weight of the first silicon-based active material.

[0065] The first silicon-based active material doped with magnesium may contain micropores, thereby suppressing the generation of cracks during shrinkage / expansion of the secondary battery due to charge and discharge, and improving the life characteristics of the secondary battery at room temperature and high temperature.

[0066] When the content of magnesium doped in the first silicon-based active material exceeds the above range, the crystal structure of the first silicon-based active material containing silicon, oxygen and magnesium corresponds to forsterite (Mg2SiO4), so a dense stacking may be formed, and the space occupied by silicon in each unit cell increases, so that the proportion of micropores may be reduced.

[0067] For example, when the content of magnesium doped in the first silicon-based active material is less than 5% by weight of the total weight of the first silicon-based active material, the crystal form of the magnesium-doped silicon-based active material may not contain forsterite. When the content of magnesium doped in the first silicon-based active material is within the above range, swelling during shrinkage / expansion at high temperatures (e.g., above 60°C) can be reduced, thereby improving the lifespan characteristics of the lithium secondary battery.

[0068] In some embodiments, the first silicon-based active material may include a graphite-based active material. The graphite-based active material may include natural graphite or artificial graphite. In some embodiments, the first silicon-based active material may include artificial graphite.

[0069] In some embodiments, the first negative active material layer may include 2 wt % to 20 wt % of the first silicon-based active material.

[0070] In some embodiments, the first negative electrode active material layer may contain 3 wt% to 15 wt%, 4 wt% to 15 wt%, or 5 wt% to 10 wt% of a first silicon-based active material.

[0071] When the content of the first silicon-based active material exceeds the above range, the volume expansion rate of the secondary battery may increase compared to the increase in energy density. When the content of the first silicon-based active material is less than the above range, the energy density of the secondary battery may not increase.

[0072] According to some embodiments, when XRD analysis is performed on the first silicon-based active material, peaks generated by forsterite (Mg2SiO4) may not appear.

[0073] In some embodiments, the second negative electrode active material layer 124 may contain a silicon-based negative electrode active material different from the first silicon-based active material. In addition, the second negative electrode active material layer 124 may contain a graphite-based active material.

[0074] For example, the second negative electrode active material layer 124 may contain a second silicon-based active material, a silicon-carbon composite, or undoped metal SiO as a silicon-based negative electrode active material having a composition different from that of the first silicon-based active material x (0 < x < 2).

[0075] In some embodiments, the second negative electrode active material layer 124 may not contain a silicon-based active material and may contain a graphite-based active material.

[0076] In some embodiments, the second negative electrode active material layer 124 may contain only one of a second silicon-based active material, a silicon-carbon composite, undoped metal SiO x (0 < x < 2), and a graphite-based active material, or may contain a combination of two or more of a second silicon-based active material, a silicon-carbon composite, undoped metal SiO x (0 < x < 2), and a graphite-based active material.

[0077] In some embodiments, the second silicon-based active material may be doped with a second metal. The second silicon-based active material doped with the second metal may be formed by mixing, heating, cooling, and pulverizing a silicon-based active material source and a second metal source. The silicon-based active material source may be silicon (Si) or a mixture of silicon (Si) and silicon dioxide (SiO2). When silicon and silicon dioxide are included, the molar ratio of silicon to silicon dioxide may be 1:0.5 to 1.5.

[0078] The second metal that may be doped into the second silicon-based active material may include at least one of Li, Mg, Ca, Al, Fe, Ti, and V. The second metal may be the same type of metal as the first metal or a different type of metal.

[0079] In some embodiments, the second metal may comprise magnesium.

[0080] For example, the silicon-based active material source and the second metal source may be mixed to form a second primary active material composition.

[0081] During the preparation of the second silicon-based active material, the second metal source may comprise 5% by weight or greater of the total weight of the second primary active material composition. For example, the second metal source may comprise 5% by weight to 20% by weight of the total weight of the second primary active material composition.

[0082] The content of the second metal in the second primary active material composition during the preparation of the second silicon-based active material can be different from the content of the first metal in the first primary active material composition during the preparation of the first silicon-based active material. Therefore, a multilayered negative electrode active material layer with different compositions can be formed on the negative electrode current collector. This multilayered structure can increase the capacity of the secondary battery.

[0083] For example, when the content of the second metal in the second primary active material composition during the preparation of the second silicon-based active material is less than the above range, the crystal structure becomes similar to that of the first silicon-based active material, and thus the high-temperature life characteristics of the secondary battery may be reduced. For example, when the content of the second metal in the second silicon-based active material exceeds the above range, cracks may form inside the secondary battery, and thus the life characteristics of the secondary battery may be reduced.

[0084] For example, the second primary active material composition may be calcined at 1000° C. to 1800° C. and then cooled to precipitate a silicon oxide composite containing the second metal. The silicon oxide composite containing the second metal may be pulverized and classified to form the second silicon-based active material.

[0085] In some embodiments, the second silicon-based active material may be doped with a second metal in an amount of 5% by weight or more of the total weight of the second silicon-based active material. In one embodiment, the doping amount of the second metal in the second silicon-based active material may be 5% to 20% by weight, 6% to 18% by weight, 7% to 18% by weight, or 7.5% to 15% by weight of the total weight of the second silicon-based active material.

[0086] In some embodiments, the metal doped in the second silicon-based active material may include at least one of Li, Mg, Ca, Al, Fe, Ti, and V.

[0087] In some embodiments, the second silicon-based active material may further include an alloy-based active material, wherein the alloy-based active material may be, for example, an active material including at least one of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, and rare earth elements, or a combination thereof, and silicon.

[0088] In some embodiments, the second negative electrode active material layer may include a second silicon-based active material. The second silicon-based active material may be present in an amount of 5 wt % to 30 wt % based on the total weight of the second negative electrode active material layer.

[0089] In some embodiments, the second negative electrode active material layer may include a second silicon-based active material. The content of the second silicon-based active material in the total weight of the second negative electrode active material layer may be 8 wt % to 30 wt %, 10 wt % to 27 wt %, or 10 wt % to 25 wt %.

[0090] In some embodiments, the second negative electrode active material layer may include a silicon-carbon composite or SiO2 undoped with metal. x (0 <x<2)。

[0091] In some embodiments, the second negative active material layer may not include a silicon-based active material.

[0092] In one embodiment, the second negative active material layer may include a graphite-based active material and exclude a silicon-based active material.

[0093] The graphite-based active material contained in the second negative electrode active material layer may be natural graphite or artificial graphite.

[0094] According to some embodiments, the first silicon-based active material, the second silicon-based active material, or the silicon-carbon composite may each further include a carbon coating formed on the silicon-based active material particles. Thus, the silicon-based active material particles can be prevented from contacting moisture in the atmosphere and / or water in the negative electrode slurry. As a result, a decrease in the discharge capacity of the secondary battery can be suppressed.

[0095] For example, the carbon coating may be at least one of amorphous carbon, carbon nanotubes, carbon nanofibers, graphite, graphene, graphene oxide, and reduced graphene oxide.

[0096] For example, at least one of the first silicon-based active material, the second silicon-based active material, and the silicon-carbon composite may be provided with the carbon coating on the outermost layer.

[0097] For example, the negative electrode active material layer 120 may be formed by coating a negative electrode active material composition on the negative electrode current collector 125 and drying and calendering it, wherein the negative electrode active material composition contains the first silicon-based active material, the second silicon-based active material, undoped metal SiO x (0 < x < 2) or one or more of graphite-based active materials.

[0098] For example, a first negative electrode active material composition containing a first silicon-based active material doped with a first metal may be coated on the negative electrode current collector and dried and calendered to form a first negative electrode active material layer 122, and a second negative electrode active material composition containing a second silicon-based active material doped with a second metal may be coated on the first negative electrode active material layer 122 and dried and calendered to form a second negative electrode active material layer 124.

[0099] The first silicon-based active material, the second silicon-based active material, the silicon-carbon composite, undoped metal SiO x (0 < x < 2) or one or more of graphite-based active materials may be mixed with a negative electrode binder in a solvent to prepare a negative electrode active material composition, and the negative electrode active material composition may optionally further contain a conductive material, a dispersant, a thickener, etc.

[0100] As the solvent, water-based solvents such as water, pure water, deionized water, distilled water, hydrochloric acid aqueous solution, sodium hydroxide aqueous solution, etc.; alcohol-based solvents such as ethanol, isopropyl alcohol, methanol, acetone, n-propanol, tert-butanol, etc.; or non-aqueous solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. may be used.

[0101] As the negative electrode binder, styrene-butadiene rubber (SBR)-based binders, carboxymethyl cellulose (CMC), polyacrylic acid-based binders, poly(3,4-ethylenedioxythiophene) (PEDOT)-based binders, etc. may be used.

[0102] The conductive material may be included to facilitate electron migration between active material particles. For example, the conductive material may include graphite-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes, and / or metal-based conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3 perovskite materials.

[0103] As the thickener, for example, carboxymethyl cellulose (CMC) can be used.

[0104] In one embodiment, the first negative electrode active material layer 122 may be in contact with at least one side of the negative electrode current collector 125, and the second negative electrode active material layer 124 may be provided on an upper surface of the first negative electrode active material layer 122. In addition, in one embodiment, the second negative electrode active material layer 124 may be in contact with at least one side of the negative electrode current collector 125, and the first negative electrode active material layer 122 may be provided on an upper surface of the second negative electrode active material layer 124.

[0105] In some embodiments, the first negative electrode active material layer 122 may be in contact with at least one side of the negative electrode current collector, and the first negative electrode active material layer 122 may include the above-mentioned first silicon-based active material, and the second negative electrode active material layer 124 may be arranged on the upper surface of the first negative electrode active material layer 122, and the second negative electrode active material layer 124 may include the above-mentioned second silicon-based active material.

[0106] In one embodiment, the first negative electrode active material layer 122 may be in contact with at least one side of the negative electrode current collector 125, and the first negative electrode active material layer 122 may include the first silicon-based active material, and the second negative electrode active material layer 124 may be disposed on the upper surface of the first negative electrode active material layer 122, and the second negative electrode active material layer 124 may include a graphite-based active material and no silicon-based active material.

[0107] In one embodiment, the first negative electrode active material layer 122 may be in contact with at least one side of the negative electrode current collector 125, and the first negative electrode active material layer 122 may include the first silicon-based active material, and the second negative electrode active material layer 124 may be disposed on the upper surface of the first negative electrode active material layer 122, and the second negative electrode active material layer 124 may include a graphite-based active material and a silicon-based active material.

[0108] In one embodiment, the first negative electrode active material layer 122 may be in contact with at least one side of the negative electrode current collector 125, and the first negative electrode active material layer 122 may include a graphite-based active material and not a silicon-based active material, and the second negative electrode active material layer 124 may be disposed on the upper surface of the first negative electrode active material layer 122, and the second negative electrode active material layer 124 may include the first silicon-based active material.

[0109] In one embodiment, the first negative electrode active material layer 122 and the second negative electrode active material layer 124 may each contain the first silicon-based active material, and the weight-based content of the first silicon-based active material in the total weight of the first negative electrode active material layer 122 and the weight-based content of the first silicon-based active material in the total weight of the second negative electrode active material layer 124 may be different from each other.

[0110] In one embodiment, the first negative electrode active material layer 122 can be in contact with at least one side of the negative electrode current collector 125, the second negative electrode active material layer 124 can be arranged on the upper surface of the first negative electrode active material layer 122, and the weight-based content of the first silicon-based active material in the total weight of the first negative electrode active material layer 122 can be greater than the weight-based content of the first silicon-based active material in the total weight of the second negative electrode active material layer 124.

[0111] In one embodiment, the first negative electrode active material layer 122 may include the first silicon-based active material, and the second negative electrode active material layer 124 may include the second silicon-based active material, and the weight-based content of the first silicon-based active material in the total weight of the first negative electrode active material layer 122 and the weight-based content of the second silicon-based active material in the total weight of the second negative electrode active material layer 124 may be different from each other.

[0112] In one embodiment, the first negative electrode active material layer 122 can be in contact with at least one side of the negative electrode current collector 125, the second negative electrode active material layer 124 can be arranged on the upper surface of the first negative electrode active material layer 122, and the weight-based content of the first silicon-based active material in the total weight of the first negative electrode active material layer 122 can be less than the weight-based content of the second silicon-based active material in the total weight of the second negative electrode active material layer 124.

[0113] For example, a first negative electrode active material layer 122 having a relatively low magnesium content can be provided on the upper surface of the negative electrode current collector 125. Since the first negative electrode active material layer 122 on the upper surface of the negative electrode current collector 125 has a high proportion of micropores, the occurrence of bulging inside the secondary battery can be reduced, and the lifetime capacity retention rate of the secondary battery at high temperatures can be improved.

[0114] In one embodiment, the first negative electrode active material layer 122 and the second negative electrode active material layer 124 may each include the first silicon-based active material. When the same silicon-based active material is used, a multilayer structure of negative electrode active materials having similar chemical compositions can be formed, and structural stability can be ensured.

[0115] In one embodiment, the first negative electrode active material layer 122 may include the first silicon-based active material, and the second negative electrode active material layer 124 may include the second silicon-based active material. The weight-based content of the first silicon-based active material in the total weight of the first negative electrode active material layer 122 and the weight-based content of the second silicon-based active material in the total weight of the second negative electrode active material layer 124 may be different from each other.

[0116] The composition of the negative electrode active material layer 120 can be adjusted based on the difference in the content of the silicon-based active material contained in the first negative electrode active material layer 122 and the second negative electrode active material layer 124. The content of each metal doped in the first silicon-based active material and the second silicon-based active material can be different, and the lifespan characteristics of the lithium secondary battery can be improved based on the difference in the content of the doped metals.

[0117] In one embodiment, the first negative active material layer 122 may include the first silicon-based active material and the second silicon-based active material, and the second negative active material layer 124 may include the first silicon-based active material and the second silicon-based active material.

[0118] In one embodiment, the second negative active material layer 124 may include the second silicon-based active material, and may further include a silicon-carbon composite.

[0119] In one embodiment, the first negative electrode active material layer 122 may include the first silicon-based active material and the graphite-based active material. The first negative electrode active material layer 122 may include 2 wt % to 20 wt % of the first silicon-based active material based on the total weight of the first negative electrode active material layer 122 .

[0120] In one embodiment, the second negative electrode active material layer 124 may include the second silicon-based active material and a graphite-based active material. The second negative electrode active material layer 124 may include 5 wt % to 30 wt % of the second silicon-based active material based on the total weight of the second negative electrode active material layer 124 .

[0121] In one embodiment, one of the first negative electrode active material layer 122 and the second negative electrode active material layer 124 may include: a graphite-based active material; and a silicon-carbon composite or SiO2 undoped with metal. xOne or more of (0 < x < 2).

[0122] <Lithium secondary battery>

[0123] Figure 3 and Figure 4 are a schematic plan view and a schematic cross-sectional view respectively showing a lithium secondary battery according to an exemplary embodiment. For example, Figure 4 is a cross-sectional view taken in the thickness direction along the I-I' line of Figure 3 .

[0124] Referring to Figure 3 and Figure 4 , the lithium secondary battery may include an electrode assembly, and the electrode assembly may include a positive electrode 100 and a negative electrode 130. In some embodiments, the electrode assembly may further include a separator 140 interposed between the positive electrode and the negative electrode. The electrode assembly may be accommodated in a case 160 together with an electrolyte and immersed in the electrolyte.

[0125] The positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver.

[0126] The positive electrode active material layer may include a positive electrode active material. The positive electrode active material may include a compound capable of reversibly inserting and extracting lithium ions.

[0127] According to an exemplary embodiment, the positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0128] For example, the lithium-nickel metal oxide may be represented by the following Chemical Formula 1.

[0129] [Chemical Formula 1]

[0130] Li x Ni 1-y M y O 2+z [[ID=-47]]

[0131] In Chemical Formula 1, it may be 0.9 ≤ x ≤ 1.2, 0 ≤ y ≤ 0.7, -0.1 ≤ z ≤ 0.1. M may represent one or more elements selected from Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, Sn, or Zr. <00OO334>

[0132] In some embodiments, in Chemical Formula 1, the molar ratio or concentration (1-y) of Ni may be greater than 0.8, for example, the molar ratio or concentration (1-y) of Ni may exceed 0.8.

[0133] The chemical structure represented by Chemical Formula 1 represents the bonding relationship contained in the layered structure or crystal structure of the positive electrode active material, and does not exclude other additional elements. For example, M may include Co and / or Mn, and Co and Mn may be provided together with Ni as the main active elements (main active element) of the positive electrode active material. Chemical Formula 1 is provided to represent the bonding relationship of the main active elements, and it should be understood that Chemical Formula 1 is a formula including the introduction and substitution of additional elements.

[0134] In one embodiment, in addition to the main active element, an auxiliary element for enhancing the chemical stability of the positive electrode active material or the layered structure / crystal structure may be further included. The auxiliary element may be mixed into the layered structure / crystal structure to form a bond, and it should be understood that this case is also included in the chemical structure represented by Chemical Formula 1.

[0135] The auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary element may function as an auxiliary active element that contributes to the capacity / power activity of the positive electrode active material together with Co or Mn, such as Al.

[0136] For example, the positive electrode active material may be dispersed in a solvent to prepare a positive electrode mixture. The positive electrode mixture may be coated on a positive electrode current collector 105, dried, and rolled to produce the positive electrode 100. The positive electrode mixture may further include a binder and may optionally further include a conductive material, a thickener, and the like.

[0137] Non-limiting examples of the solvent used to prepare the positive electrode mixture include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, and the like.

[0138] The binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (poly(vinylidene fluoride-co-hexafluoropropylene)), polyacrylonitrile, polymethyl methacrylate, acrylonitrile-butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PVDF-based binder may be used as a positive electrode binder.

[0139] The conductive material may be added to enhance the conductivity of the positive electrode active material layer and / or the mobility of lithium ions or electrons. For example, the conductive material may include graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber and other graphite-based conductive materials and / or metal-based conductive materials including perovskite minerals such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0140] As the thickener, for example, carboxymethyl cellulose (CMC) can be used.

[0141] The negative electrode 130 may include the negative electrode including the negative electrode current collector, the first negative electrode active material layer, and the second negative electrode active material layer.

[0142] A separator 140 may be provided between the positive electrode 100 and the negative electrode 130. The separator can prevent a short circuit between the positive electrode and the negative electrode and maintain the flow of ions.

[0143] The separator 140 may include a porous polymer film or a porous non-woven fabric. For example, the porous polymer film may include ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. The porous non-woven fabric may include high-melting-point glass fiber, polyethylene terephthalate fiber, etc.

[0144] The separator 140 may also include a ceramic-based material. For example, inorganic particles may be coated on or dispersed in the polymer film to improve heat resistance.

[0145] According to an exemplary embodiment, a battery cell is defined by a positive electrode 100, a negative electrode 130, and a separator 140, and a plurality of battery cells may be stacked to form, for example, an electrode assembly 150 in the form of a jelly roll. For example, the electrode assembly 150 may be formed by winding, laminating, folding, or the like the separator 140.

[0146] In one embodiment, the electrode assembly may be formed by cutting or separating the positive electrode 100 , the negative electrode 130 , and the separator 140 of each layer from one another and repeatedly stacking them.

[0147] The electrode assembly 150 is housed in the case 160 together with an electrolyte, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte may use a non-aqueous electrolyte.

[0148] The non-aqueous electrolyte may comprise a lithium salt and an organic solvent. The lithium salt may be, for example, Li + X - Represented, and as the anion of the lithium salt (X - ), we can exemplify F - 、Cl - Br - , I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - 、(CF3CF2SO2)2N - wait.

[0149] The organic solvent may include an organic compound that has sufficient solubility for the lithium salt and additives and is non-reactive in the battery. The organic solvent may include, for example, at least one of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent. As the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylpropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), ethyl fluoroacetate (FEA), ethyl difluoroacetate (DFEA), ethyl trifluoroacetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEC), dibutyl ether (DMC), dibutyl ... dimethylether (DEGDME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethanol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone and propylene sulfite. These can be used alone or in combination of two or more.

[0150] The non-aqueous electrolyte may further include additives such as cyclic carbonate-based compounds, fluorine-substituted carbonate-based compounds, sultone-based compounds, cyclic sulfate-based compounds, cyclic sulfite-based compounds, phosphate-based compounds, and borate-based compounds.

[0151] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and the like.

[0152] The fluorine-substituted carbonate-based compound may include fluoroethylene carbonate (FEC) and the like.

[0153] The sultone-based compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, and the like.

[0154] The cyclic sulfate-based compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, and the like.

[0155] The cyclic sulfite-based compound may include ethylene sulfite, butylene sulfite, and the like.

[0156] The phosphate-based compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, and the like.

[0157] The borate-based compound may include lithium bis(oxalate) borate and the like.

[0158] In some embodiments, a solid electrolyte can be used instead of the non-aqueous electrolyte. In this case, the lithium secondary battery can be made into an all-solid-state battery. Furthermore, a solid electrolyte layer can be provided between the positive electrode 100 and the negative electrode 130 instead of the separator.

[0159] The solid electrolyte may include a sulfide-based electrolyte. As non-limiting examples, the sulfide-based electrolyte may include Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers, and Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (where p and q are positive numbers, and M is P, Si, Ge, B, Al, Ga or In), Li7-xPS6-xCl x (0 ≤ x ≤ 2), Li7-xPS6-xBr x (0 ≤ x ≤ 2), Li7-xPS6-xI x (0 ≤ x ≤ 2), etc. These can be used alone or in combination of two or more.

[0160] In one embodiment, the solid electrolyte may further include oxide-based amorphous solid electrolytes such as Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li2O-B2O3-ZnO, etc.

[0161] Hereinafter, to help understand the present invention, experimental examples including specific examples and comparative examples are presented, but these are only for illustrating the present invention and do not limit the claims. Various changes and modifications can be made to the examples within the scope and technical idea of the present invention, which are obvious to those skilled in the art, and such variations and modifications are naturally within the scope of the claims.

[0162] Example 1

[0163] (1) Preparation of silicon-based active material

[0164] 1) Preparation of silicon-based active material

[0165] Add an amount of magnesium corresponding to 2% by weight of the total weight of silicon oxide (SiO x , 0 < x < 2, D50: 6 μm) and magnesium and mix to obtain a first silicon-based active material doped with magnesium.

[0166] Specifically, silicon (Si), SiO2, and magnesium were mixed to prepare a powder mixture. The total weight of the silicon and SiO2 was adjusted to 98% by weight (a 1:1 molar ratio of silicon to SiO2), and the magnesium content was 2% by weight, relative to the total weight of the powder mixture. The powder mixture was then calcined at 1500°C under reduced pressure for 5 hours and cooled to precipitate a silicon oxide composite containing magnesium. The precipitated silicon oxide composite was mechanically pulverized and classified to an average particle size of 6 μm, producing a first silicon-based active material (2% by weight of magnesium).

[0167] 2) Preparation of silicon-based active materials with different magnesium contents

[0168] A second silicon-based active material having a different magnesium content (Mg is 7.5 wt %) was prepared by the same method as the preparation process of the first silicon-based active material, except that the content was changed so that magnesium was 7.5 wt % and the sum of silicon and SiO2 was 92.5 wt % (molar ratio of 1:1) relative to the total weight of the powder mixture.

[0169] (2) Manufacturing of negative electrode

[0170] 92.825 wt % of artificial graphite (D50: 20 μm) as a graphite-based active material, 5 wt % of the first silicon-based active material, 0.15 wt % of single-walled carbon nanotubes (SWCNT) as a conductive material, 0.225 wt % of carbon nanotubes (CNT) as a conductive material dispersant, and 1.8 wt % of carboxymethyl cellulose (CMC) / styrene-butadiene rubber (SBR) as a binder (weight ratio of 1.3:0.5) were mixed to prepare a first negative electrode active material composition in the form of a slurry.

[0171] In addition, 68.2 wt % of artificial graphite as a graphite-based active material, 25 wt % of the second silicon-based active material, 3 wt % of multi-walled carbon nanotubes (MWCNTs) as a graphite-based conductive material, and 3.8 wt % of carboxymethyl cellulose (CMC) / styrene-butadiene rubber (SBR) as a binder (weight ratio of 1.3:2.5) were mixed to prepare a second negative electrode active material composition in the form of a slurry.

[0172] Afterwards, the first negative electrode active material composition and the second negative electrode active material composition were sequentially coated on one side of a copper foil current collector with a thickness of 8 μm, dried and rolled, thereby sequentially forming a first negative electrode active material layer and a second negative electrode active material layer on the current collector.

[0173] (3) Manufacturing of lithium secondary batteries

[0174] 98.08 wt% of Li[Ni 0.88 Co 0.1 Mn 0.02 ]O2 (66.86 wt% polycrystalline, 29.42 wt% single crystal), 0.6 wt% MWCNT as a conductive material, 0.12 wt% CNT as a conductive material dispersant, and 1.2 wt% polyvinylidene fluoride (PVDF) as a binder were mixed to prepare a slurry. The slurry was evenly coated on a 12 μm thick aluminum foil and vacuum dried to produce a secondary battery positive electrode.

[0175] The positive electrode and the negative electrode are cut (notching) into the specified size and stacked, and a separator (polyethylene, 13 μm thick) is inserted between the positive electrode and the negative electrode to form a battery cell, and then the tabs of the positive and negative electrodes are welded respectively. The welded positive electrode / separator / negative electrode assembly is placed in a soft bag, and the three surfaces except the electrolyte injection surface are sealed. At this time, the portion with the tab is included in the sealing portion. The electrolyte is injected through the remaining surfaces except the sealing portion, and the remaining surfaces are sealed, and then immersed for more than 12 hours.

[0176] The electrolyte used was an electrolyte prepared as follows: 1.1 M LiPF6 was dissolved in a mixed solvent of EC / EMC (25 / 75; volume ratio), and then 8 wt% of fluoroethylene carbonate (FEC), 0.5 wt% of 1,3-propylene sultone (PRS), and 1.0 wt% of 1,3-propane sultone (PS) were added.

[0177] Afterwards, heat press pre-charging was performed for 60 minutes at an average current of 0.5C. After stabilization for at least 12 hours, degassing was performed and aging was performed for at least 24 hours. Formation charge and discharge were then performed (charge conditions were CC-CV 0.25C 4.2V 0.05C cut-off; discharge conditions were CC 0.25C 2.5V cut-off).

[0178] After that, standard charge and discharge were performed (charge conditions were CC-CV 0.33C 4.2V 0.05C cut-off, and discharge conditions were CC 0.33C 2.5V cut-off).

[0179] Example 2

[0180] A first silicon-based active material, a negative electrode, and a lithium secondary battery were manufactured by the same method as in Example 1, except that the magnesium content in the second silicon-based active material contained in the second negative electrode active material composition was changed to 2 wt %.

[0181] Example 3

[0182] A first silicon-based active material, a negative electrode, and a lithium secondary battery were manufactured by the same method as in Example 1, except that the magnesium content in the second silicon-based active material contained in the second negative electrode active material composition was changed to 15 wt %.

[0183] Example 4

[0184] A negative electrode and a lithium secondary battery were manufactured by the same method as in Example 1, except that the content of magnesium in the second silicon-based active material included in the second negative electrode active material composition was changed to 20 wt %.

[0185] Example 5

[0186] A negative electrode and a lithium secondary battery were manufactured by the same method as in Example 1, except that the content of magnesium in the second silicon-based active material included in the second negative electrode active material composition was changed to 25 wt %.

[0187] Example 6

[0188] A negative electrode and a lithium secondary battery were manufactured by the same method as in Example 1, except that the content of magnesium in the first silicon-based active material contained in the first negative electrode active material composition was changed to 5 wt %, and the content of the second silicon-based active material contained in the second negative electrode active material composition was changed to 20 wt %.

[0189] Example 7

[0190] A negative electrode and a lithium secondary battery were manufactured by the same method as in Example 1, except that the content of magnesium in the first silicon-based active material contained in the first negative electrode active material composition was changed to 7 wt %, and the content of the second silicon-based active material contained in the second negative electrode active material composition was changed to 20 wt %.

[0191] Example 8

[0192] A negative electrode and a lithium secondary battery were manufactured by the same method as in Example 1, except that the second negative electrode active material composition did not include a second silicon-based active material and 93.2 wt % of artificial graphite (D50: 20 μm) was used.

[0193] Example 9

[0194] The negative electrode and the lithium secondary battery are manufactured by the same method as in Example 1, except that the second silicon-based active material is not included in the second negative electrode active material composition, and 78.2% by weight of artificial graphite and 15% by weight of a silicon / carbon composite (Si / C) are used.

[0195] Comparative Example 1

[0196] The negative electrode is manufactured by the same method as in Example 1, except that when manufacturing the negative electrode, 80.51% by weight of artificial graphite (D50: 20 μm) and 15% by weight of undoped magnesium silicon oxide (SiO x , 0 < x < 2, D50: 6 μm) are used, and the content is adjusted while maintaining the ratio of the conductive material, the conductive material dispersant, and the binder, so as to replace the first negative electrode active material composition and the second negative electrode active material composition, and a single-layer negative electrode active material layer is formed. At this time, the thickness of the negative electrode active material layer is formed to be the same as the total thickness of the first negative electrode active material layer and the second negative electrode active material layer in Example 1.

[0197] Comparative Example 2

[0198] The negative electrode is manufactured by the same method as in Example 1, except that when manufacturing the negative electrode, the second negative electrode active material composition is omitted, and a single-layer negative electrode active material layer is formed. At this time, the thickness of the negative electrode active material layer is formed to be the same as the total thickness of the first negative electrode active material layer and the second negative electrode active material layer in Example 1.

[0199] Comparative Example 3

[0200] The negative electrode is manufactured by the same method as in Example 1, except that when manufacturing the negative electrode, the second negative electrode active material composition is omitted, the magnesium content in the first silicon-based active material is changed to 15% by weight, and a single-layer negative electrode active material layer is formed. At this time, the thickness of the negative electrode active material layer is formed to be the same as the total thickness of the first negative electrode active material layer and the second negative electrode active material layer in Example 1.

[0201] Comparative Example 4

[0202] The first silicon-based active material, the negative electrode, and the lithium secondary battery are manufactured by the same method as in Example 1, except that the magnesium content in the first silicon-based active material included in the first negative electrode active material composition is changed to 10% by weight.

[0203] Comparative Example 5

[0204] A first silicon-based active material, a negative electrode, and a lithium secondary battery were manufactured by the same method as in Example 1, except that the magnesium content in the first silicon-based active material contained in the first negative electrode active material composition was changed to 1 wt %.

[0205] The magnesium content in the silicon-based active material and the silicon-based active material content according to the examples and comparative examples are shown in Table 1 below.

[0206] [Table 1]

[0207]

[0208] Experimental example

[0209] (1) Evaluation of fast charge life characteristics

[0210] The lithium secondary batteries manufactured according to the embodiments and comparative examples were charged at a rate (C-rate) of 3.25C / 3.0C / 2.75C / 2.5C / 2.25C / 2.0C / 1.75C / 1.5C / 1.25C / 1.0C / 0.75C / 0.5C according to a step charging method so that the depth of discharge (DOD) reached 72% within 35 minutes and then discharged at 1 / 3C. The above charging and discharging was regarded as 1 cycle, the cycle was repeated, and the fast charging life characteristics were evaluated. A 10-minute rest time was set between the charge and discharge cycles, 150 cycles and 300 cycles were repeated, and then the respective fast charging capacity retention rates were measured.

[0211] (2) Evaluation of life characteristics at room temperature (25°C)

[0212] For the lithium secondary batteries manufactured according to the examples and comparative examples, the normal charge life characteristics within the range of DOD 94% (SOC 4% to 98%) were evaluated while maintaining the temperature at 25°C in a chamber. Under constant current / constant voltage (CC / CV) conditions, the batteries were charged at 0.3C to a voltage corresponding to SOC 98%, then cut off at 0.05C. Then, under constant current (CC) conditions, the batteries were discharged at 0.3C to a voltage corresponding to SOC 4%, and the discharge capacity was measured. This operation was repeated for 300 and 600 cycles, and the discharge capacity retention rate for each normal temperature life characteristic evaluation was measured.

[0213] (3) Evaluation of high temperature (45°C) life characteristics

[0214] The lithium secondary batteries manufactured according to the examples and comparative examples were evaluated for high-temperature life characteristics while being maintained in a chamber at 45°C. Under the same conditions as the normal-temperature life characteristics evaluation described above, 300 and 600 cycles were repeated, and the discharge capacity retention rate for each high-temperature life characteristics evaluation was measured.

[0215] Table 2 shows the evaluation results of the above-mentioned experimental examples.

[0216] [Table 2]

[0217]

[0218] Referring to Table 2, in the case of the lithium secondary battery according to the embodiment including a certain content of the first silicon-based active material and a plurality of negative electrode active material layers, the capacity retention rate can be maintained above a certain level even if the number of cycles increases.

[0219] In the case of Example 2 including the second silicon-based active material having a doping amount of 2 wt % of magnesium, the fast charge capacity retention ratio decreased as the number of cycles increased.

[0220] In the case of Example 4 including the second silicon-based active material having a doping amount of 20 wt % of magnesium, the fast charge capacity retention ratio relatively decreases as the number of cycles increases.

[0221] In the case of Example 5 including the second silicon-based active material having a magnesium doping amount of 25 wt %, each capacity retention ratio decreased.

[0222] In the case of Example 7 including the first silicon-based active material having a magnesium doping amount of 7 wt %, the capacity retention ratio was relatively low.

[0223] In the case of Example 8 which does not include the second silicon-based active material and includes a graphite-based active material, the fast charge capacity retention ratio relatively decreases as the number of cycles increases.

[0224] In the case of silicon carbon composite (Si / C) instead of SiO x In the case of Example 9 using the second silicon-based active material, each capacity retention ratio is similar to that of Example 3.

[0225] In the case of the lithium secondary batteries according to Comparative Examples 1 to 3 including a single negative electrode active material layer, the rapid charge capacity retention ratio, the room temperature discharge capacity retention ratio, and the high temperature discharge capacity retention ratio sharply decreased with an increase in the number of cycles.

[0226] In the case of the lithium secondary battery according to Comparative Example 4 containing a first silicon-based active material with a magnesium doping amount of 10 wt % and the lithium secondary battery according to Comparative Example 5 containing a first silicon-based active material with a magnesium doping amount of 1 wt %, the capacity retention rate is reduced as a whole compared with the lithium secondary batteries according to the above embodiments.

Claims

1. A negative electrode for a lithium secondary battery, comprising: negative electrode current collector; as well as A multi-layer negative electrode active material layer, wherein the multi-layer negative electrode active material layer is arranged on at least one side of the negative electrode current collector, and the multi-layer negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer. At least one of the first negative electrode active material layer and the second negative electrode active material layer comprises a first silicon-based active material doped with a first metal, and the doping amount of the first metal is 1.5 wt % to 8 wt % in the total weight of the first silicon-based active material.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein The first metal comprises magnesium.

3. The negative electrode for a lithium secondary battery according to claim 1, wherein The first negative electrode active material layer includes the first silicon-based active material, and the second negative electrode active material layer includes a silicon-based negative electrode active material different from the first silicon-based active material.

4. The negative electrode for a lithium secondary battery according to claim 3, wherein The second negative electrode active material layer includes a second silicon-based active material doped with a second metal, and a doping amount of the second metal is greater than or equal to 5 wt % of the total weight of the second silicon-based active material.

5. The negative electrode for a lithium secondary battery according to claim 4, wherein The doping amount of the second metal is 5 wt % to 20 wt % in the total weight of the second silicon-based active material.

6. The negative electrode for a lithium secondary battery according to claim 4, wherein The second metal doped in the second silicon-based active material includes at least one selected from the group consisting of Li, Mg, Ca, Al, Fe, Ti, and V.

7. The negative electrode for a lithium secondary battery according to claim 3, wherein The silicon-based negative electrode active material contained in the second negative electrode active material layer comprises a silicon-carbon composite or SiO2 undoped with metal. x , 0 <x<2。 8. The negative electrode for a lithium secondary battery according to claim 1, wherein The second negative electrode active material layer does not contain a silicon-based active material.

9. The negative electrode for a lithium secondary battery according to claim 3, wherein The first negative electrode active material layer contacts at least one side of the negative electrode current collector, and the second negative electrode active material layer is disposed on an upper surface of the first negative electrode active material layer.

10. The negative electrode for a lithium secondary battery according to claim 3, wherein The second negative electrode active material layer contacts at least one surface of the negative electrode current collector, and the first negative electrode active material layer is disposed on an upper surface of the second negative electrode active material layer.

11. The negative electrode for a lithium secondary battery according to claim 1, wherein The first negative electrode active material layer contacts at least one side of the negative electrode current collector, and the first negative electrode active material layer includes the first silicon-based active material. The second negative electrode active material layer is provided on an upper surface of the first negative electrode active material layer, and the second negative electrode active material layer includes a graphite-based active material and does not include a silicon-based active material.

12. The negative electrode for a lithium secondary battery according to claim 4, wherein The first negative electrode active material layer includes the first silicon-based active material, and the second negative electrode active material layer includes the second silicon-based active material. The weight-based content of the first silicon-based active material in the total weight of the first negative electrode active material layer and the weight-based content of the second silicon-based active material in the total weight of the second negative electrode active material layer are different from each other.

13. The negative electrode for a lithium secondary battery according to claim 12, wherein The first negative electrode active material layer is in contact with at least one side of the negative electrode current collector, and the second negative electrode active material layer is provided on the upper surface of the first negative electrode active material layer. The weight-based content of the first silicon-based active material in the total weight of the first negative electrode active material layer is smaller than the weight-based content of the second silicon-based active material in the total weight of the second negative electrode active material layer.

14. The negative electrode for a lithium secondary battery according to claim 1, wherein The first negative electrode active material layer includes the first silicon-based active material and a graphite-based active material. The first negative active material layer includes 2 wt % to 20 wt % of the first silicon-based active material based on the total weight of the first negative active material layer.

15. The negative electrode for a lithium secondary battery according to claim 2, wherein The doping amount of magnesium is 2 wt % to 5 wt % in the total weight of the first silicon-based active material.

16. A lithium secondary battery comprising: The negative electrode for a lithium secondary battery according to claim 1; as well as A positive electrode is arranged opposite to the negative electrode for the lithium secondary battery.

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