Silicon-based negative electrode and lithium secondary battery comprising same

Abstract

The present invention relates to a silicon-based negative electrode satisfying both high energy density and long lifespan, and a lithium secondary battery comprising same. Conventional lithium-ion batteries face challenges in improving energy density due to the capacity limitations of graphite negative electrode. To address this issue, high-capacity anode materials such as Si and SiOx have been researched. However, these materials suffer from electrode damage and accelerated electrolyte consumption caused by volume expansion of silicon during charge and discharge cycles. In order to overcome these problems, a lithium-ion battery anode was fabricated by combining silicon oxide with a silicon-carbon composite in the present invention. While silicon oxide offers high volumetric energy density, its cycle life is relatively short. Conversely, silicon-carbon composites mitigate volume expansion to extend cycle life but exhibit lower energy density. By adjusting the mixing ratio of these two materials, a negative electrode for a lithium secondary battery that achieves both high capacity and long lifespan is provided.

Description

Silicon-based cathode and lithium secondary battery containing the same

[0001] The present invention relates to a silicon-based negative electrode and a lithium secondary battery including the same.

[0002] Lithium-ion batteries are used in various industries due to their high energy density and lightweight properties. However, the current graphite anode has reached its capacity limit, making it difficult to meet the demand for high-capacity batteries. To solve this problem, silicon-based anodes have been studied, but problems such as instability in electrode bonding due to volume expansion during charge and discharge and excessive decomposition of the electrolyte are causing rapid reduction in lifespan. A representative example is silicon oxide (SiO). x ) and silicon-carbon composites (Si-C composites) have been developed, but silicon oxide has a short lifespan despite its high energy density, and silicon-carbon composites have limitations in that they are stable due to controlled volume expansion but have low energy density. Therefore, there is a need to develop a new silicon-based cathode that can satisfy both high energy density and long lifespan.

[0003] The present invention aims to provide a negative electrode in which silicon oxide and a silicon-carbon composite are mixed in an appropriate amount, and a lithium secondary battery having a high energy density and a long lifespan manufactured by including the negative electrode.

[0004] One aspect of the present invention is silicon oxide (SiO x ), a silicon-carbon composite, a carbon-based conductive material, and an aqueous binder are provided.

[0005] In one embodiment, the negative electrode composition for the lithium secondary battery may include 70 to 95 wt% of silicon oxide and silicon-carbon composite, and the weight ratio of silicon oxide: silicon-carbon composite may be 40 to 80:20 to 50.

[0006] In one aspect, the specific capacity of the silicon oxide may be 1000 to 3000 mAh / g.

[0007] In one embodiment, the specific capacity of the silicon-carbon composite may be 1500 to 2150 mAh / g.

[0008] In one aspect, the silicon-carbon composite may be in a form in which silicon particles are dispersed in a carbon material matrix.

[0009] In one aspect, the average particle diameter of the silicon particles may be 30 to 600 nm.

[0010] In one embodiment, the silicon-carbon composite may contain 100 to 200 parts by weight of silicon particles per 100 parts by weight of carbon material.

[0011] In one aspect, the carbon material matrix may be one or a mixture of two or more selected from the group consisting of graphene, graphite, and amorphous carbon.

[0012] In one embodiment, the carbon-based conductive material may be one or a mixture of two or more selected from the group consisting of carbon nanotubes (CNT), carbon black, acetylene black, and carbon nanofibers (CNF).

[0013] In one embodiment, the aqueous binder may be one or a mixture of two or more selected from carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol, polyacrylonitrile, polyvinylpyrrolidone, styrene butadiene rubber (SBR), and latex binder.

[0014] Another aspect of the present invention provides a negative electrode for a lithium secondary battery comprising the negative electrode composition for a lithium secondary battery of the above aspect.

[0015] Another aspect of the present invention provides a lithium secondary battery including the negative electrode for a lithium secondary battery of the above aspect.

[0016] In one aspect, the lithium secondary battery may have a capacity of 70% or more maintained after 500 charge / discharge cycles.

[0017] According to one aspect of the present invention, a negative electrode composition is manufactured by mixing silicon oxide and a silicon-carbon composite at an appropriate mixing ratio, and the combination of the two materials is mutually complementary, so that a negative electrode for a lithium ion battery manufactured thereby can have excellent conductivity and durability.

[0018] Additionally, a lithium ion battery manufactured with the above negative electrode can have high energy density and long lifespan.

[0019] Figure 1 shows the measured cycle performance of a lithium secondary battery according to one embodiment of the present invention and a comparative example.

[0020] The present invention will be described in more detail below. However, the following specific examples or embodiments are merely references for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

[0021] Additionally, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting.

[0022] Additionally, the singular forms used in the specification and the appended claims are intended to include the plural forms as well, unless the context clearly dictates otherwise.

[0023] Additionally, when a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0024] Additionally, unless otherwise specifically defined in the present invention, when a layer or member is said to be “located on” another layer or member, this includes not only cases where a layer or member is in contact with another layer or member, but also cases where another layer or another member exists between the two layers or two members.

[0025] In addition, the terms “about,” “substantially,” etc. used in this specification are used in a meaning close to or at the numerical value when manufacturing and material tolerances inherent to the meanings mentioned are presented, and are used to prevent unscrupulous infringers from unfairly using the disclosure contents in which exact or absolute values ​​are mentioned to aid in the understanding of the present invention.

[0026] To solve the above problems, the inventors of the present invention have produced a lithium-ion battery anode capable of simultaneously realizing high energy density and long life by mixing two anode materials, silicon oxide and silicon-carbon composite, in an appropriate ratio to complement the respective shortcomings.

[0027] The present invention will be described below.

[0028] The present invention relates to a silicon oxide (SiO x ), a silicon-carbon composite, a carbon-based conductive material and a binder are provided.

[0029] In one embodiment, the negative electrode composition for the lithium secondary battery may include silicon oxide and silicon-carbon composite in an amount of 70 to 95 wt%, 80 to 95 wt%, and the weight ratio of silicon oxide: silicon-carbon composite may be 40 to 80: 20 to 60, 50 to 70: 30 to 50. Mixing silicon oxide and silicon-carbon composite in the above weight ratio range is preferred because it allows for the production of a negative electrode having excellent energy density and durability, but is not limited thereto.

[0030] In one embodiment, the negative electrode composition for the lithium secondary battery may contain 10 to 100 parts by weight, 20 to 90 parts by weight, or 30 to 80 parts by weight of the silicon-carbon composite relative to 100 parts by weight of silicon oxide, and a lithium secondary battery including the negative electrode manufactured in the above content range may have excellent energy density and lifespan, which is preferred, but is not limited thereto.

[0031] In one embodiment, the specific capacity of the silicon oxide may be 1000 to 3000 mAh / g, 1500 to 2800 mAh / g, or 2000 to 2500 mAh / g, and a lithium secondary battery including a negative electrode manufactured with silicon oxide having the specific capacity range may have excellent energy density and lifespan, and is therefore preferred, but is not limited thereto.

[0032] In one aspect, the silicon oxide is SiO x (0.1≤x≤10), SiO x (1≤x≤5), SiO x (1≤x≤2) can be used.

[0033] In one embodiment, the specific capacity of the silicon-carbon composite may be 1500 to 2150 mAh / g, 1600 to 2000 mAh / g, or 1800 to 2000 mAh / g. A lithium secondary battery including an anode manufactured from a silicon-carbon composite having the specific capacity range is preferred because it can have excellent energy density and lifespan, but is not limited thereto.

[0034] In one embodiment, the silicon-carbon composite may have a structure in which silicon particles are dispersed within a carbon matrix. The silicon-carbon composite having the above structure may minimize damage to the carbon matrix even when the volume of the silicon particles changes, so that the electrode structure may respond flexibly without being broken. In addition, the carbon matrix may prevent the silicon particles and the electrolyte from directly contacting each other to form a solid electrolyte interface (SEI) and prevent the electrolyte from being excessively decomposed. Therefore, in a lithium ion battery negative electrode, SiO- x It can provide long life and stable cycle performance.

[0035] In one embodiment, the average particle diameter of the silicon particles may be 30 to 600 nm, 80 to 500 nm, or 100 to 400 nm. The silicon particles within the above average particle diameter range can be uniformly distributed within the carbon material of the silicon-carbon composite, thereby providing a leading effect. In addition, the silicon-carbon composite including the silicon particles within the above average particle diameter range may alleviate volume expansion of the negative electrode and increase reactivity with lithium ions, thereby providing excellent conductivity, but is not limited thereto.

[0036] In one embodiment, the silicon-carbon composite may contain silicon particles in an amount of 100 to 200 parts by weight, 110 to 180 parts by weight, or 120 to 150 parts by weight, based on 100 parts by weight of the carbon material. Including silicon particles in the above content range is preferred because it enables the manufacture of a negative electrode for a lithium battery having excellent conductivity, mechanical stability, and durability, but is not limited thereto.

[0037] In one embodiment, the carbon material may be one or a mixture of two or more selected from the group consisting of graphene, graphite, and amorphous carbon, but any carbon material capable of uniformly dispersing silicon particles or forming a core-shell structure, etc., thereby controlling volume expansion of silicon and maintaining mechanical strength of the electrode may be used without limitation.

[0038] In one embodiment, the carbon-based conductive material may be one or a mixture of two or more selected from the group consisting of carbon nanotubes (CNT), carbon black, acetylene black, and carbon nanofibers (CNF), but is not limited to a carbon-based conductive material that is used together with silicon to increase conductivity and effectively alleviate volume expansion of silicon.

[0039] The above carbon black may be a subtype of carbon black such as Ketjen black, channel black, furnace black, lamp black, summer black, etc., but is not limited thereto.

[0040] In one embodiment, the aqueous binder may be one or a mixture of two or more selected from carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol, polyacrylonitrile, polyvinylpyrrolidone, styrene butadiene rubber (SBR), and latex binders, but any aqueous binder used in a negative electrode for a lithium ion battery may be used without limitation thereto.

[0041] Another aspect of the present invention provides a negative electrode for a lithium secondary battery comprising the negative electrode composition for a lithium secondary battery.

[0042] Another aspect of the present invention provides a lithium secondary battery including a lithium secondary battery negative electrode manufactured from the above lithium secondary battery negative electrode composition.

[0043] The above lithium secondary battery may be an all-solid-state battery in one embodiment, or may be a lithium secondary battery including an electrolyte and a separator.

[0044] One aspect of the above all-solid-state battery may include a positive electrode, a negative electrode, and a solid electrolyte positioned within a separator and a gap between the positive electrode and the negative electrode.

[0045] Or it may include a positive electrode, a negative electrode, and a separator and a liquid electrolyte between the positive electrode and the negative electrode.

[0046] The above cathode may include the cathode composition provided in the present invention, and other than that, any cathode, separator, solid electrolyte, and liquid electrolyte commonly used in the relevant field may be used without limitation.

[0047] For example, the positive electrode is not limited to a positive electrode commonly used in lithium ion batteries, such as lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, and lithium manganese oxide. For example, lithium cobalt oxide composite oxide (LiCoO2), spinel crystalline lithium manganate oxide composite oxide (LiMn2O4), lithium manganate oxide composite oxide (LiMnO2), lithium nickelate oxide composite oxide (LiNiO2), lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), lithium iron pyrophosphate (Li2FeP2O7), lithium niobate oxide composite oxide (LiNbO2), lithium ferrate oxide composite oxide (LiFeO2), lithium magnesium oxide composite oxide (LiMgO2), lithium cuprate oxide composite oxide (LiCuO2), lithium zincate oxide composite oxide (LiZnO2), lithium molybdate oxide composite oxide (LiMoO2), lithium tantalate oxide composite oxide (LiTaO2), lithium tungstate oxide composite oxide Lithium permanganate nickel cobalt composite oxide (LiWO2), lithium permanganate nickel cobalt composite oxide (xLi2MnO3(1-x)LiMn1-y-zNiyCozO2), lithium nickel cobalt aluminum composite oxide (LiNi 0.8 Co 0.15 Al 0.05 O2), lithium nickel cobalt manganese composite oxide (LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.4 Co 0.2 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi0.7 Co 0.15 Mn 0.15 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2) and manganese nickel oxide (LiNi 0.5 Mn 1.5 O4) etc. can be used, but are not limited to these.

[0048] The liquid electrolyte may include a non-aqueous solvent and a lithium salt. The non-aqueous solvent may include, for example, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), vinylene carbonate (VC), and fluoroethylene carbonate (FEC). The lithium salt may include, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO4, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(x,y are natural numbers), LiCl, and lithium salts such as LiI, but are not limited thereto.

[0049] The above solid electrolyte may be composed of a crystalline organic electrolyte, or may be a composite solid electrolyte including a crystalline organic electrolyte, a fluorine-based polymer binder, and inorganic particles.

[0050] For example, the crystalline organic electrolyte may include a sulfone solvent represented by the following chemical formula 1 and lithium bis(fluorosulfonyl)imide (LiFSI).

[0051] [Chemical Formula 1]

[0052] R 1 R 2 SO2

[0053] (In the above chemical formula 1, the R 1 and R 2 are each independently an alkyl having 1 to 10 carbon atoms, an alkoxy having 1 to 10 carbon atoms, an aryl having 6 to 12 carbon atoms, or a combination thereof, and R 1 and R 2 ) wherein alkyl, alkoxy and aryl are each independently substituted or unsubstituted with halogen, amino or nitro.

[0054] For example, the above R 1 and R 2 Each independently may be an alkyl having 1 to 7 carbon atoms, preferably an alkyl having 1 to 3 carbon atoms, and the R 1 and R 2 may be identical to each other. In this case, due to the symmetrical structure of the solvent compound molecules, a solid electrolyte having the melting point range desired by the present invention can be easily implemented compared to solvent compound molecules having an asymmetrical structure. Specifically, the sulfone-based solvent may include at least one selected from the group consisting of dimethyl sulfone and diethyl sulfone, and most preferably, dimethyl sulfone. Dimethyl sulfone has the advantage of having a high dielectric constant and excellent electrochemical stability, being inexpensive, and being harmless to the human body.

[0055] The above crystalline organic electrolyte is a solid at room temperature, and may be manufactured by eutecticizing a sulfone-based solvent represented by the above chemical formula 1 and a bis(fluorosulfonyl)imide alkali metal salt (MFSI) and then cooling the eutectic solution, thereby forming a eutectic system. The above crystalline organic electrolyte may have a cocrystal structure, and the melting point of the crystalline organic electrolyte may be determined depending on the melting point and mixing ratio of the sulfone-based solvent and the metal salt itself.

[0056] The above crystalline organic electrolyte may contain the lithium bis(fluorosulfonyl)imide (LiFSI) and the sulfone solvent represented by the chemical formula 1 in a molar ratio of 1 to 4:9 to 6, and specifically, in a molar ratio of 1 to 3:9 to 7.

[0057] The above crystalline organic electrolyte may have a melting point of 50 to 170°C, and specifically, may have a melting point of 60 to 170°C.

[0058] The above separator may be a polypropylene, polyethylene, a polypropylene / polyethylene / polypropylene multilayer separator, a ceramic coated separator, a polybenzimidazole separator, etc., but is not limited to a separator typically used in lithium secondary batteries.

[0059] In one embodiment, the lithium secondary battery may have a capacity of 70% or more, 80% or more, 85% or more, or, without particular limitation, 95% or less, or 90% or less after 500 charge / discharge cycles. A lithium secondary battery that maintains a capacity within the above range is preferred because it can have a high energy density and a long lifespan, but is not limited thereto.

[0060]

[0061] The present invention will be described in more detail based on the following examples and comparative examples. However, the following examples and comparative examples are merely illustrative examples for further explaining the present invention, and the present invention is not limited by the following examples and comparative examples.

[0062] [measurement method]

[0063] 1. Measuring the cycle performance of lithium-ion batteries

[0064] The cycle performance of a lithium-ion battery was measured at a temperature of 25±1 ℃, a voltage range of 2.7 to 4.45 V, and 500 cycles, and the results are shown in Fig. 1.

[0065] [Example 1]

[0066] 1) Cathode

[0067] 2300 mAH / g of silicon oxide (average particle size D 50 This 50 ㎛) 70.2 wt%, 1855 mAH / g silicon-carbon composite (average particle size D 50 24 wt% of 50 ㎛), 1 wt% of carbon nanotubes, 1.5 wt% of carbon black, 3.3 wt% of an aqueous binder containing styrene-butadiene rubber and carboxymethyl cellulose at a weight ratio of 1:0.5 were mixed. 60 parts by weight of water was added to 100 parts by weight of the prepared mixture to prepare an anode slurry. The silicon-carbon composite used 120 parts by weight of silicon particles having an average particle diameter of 80 nm for 100 parts by weight of carbon material (graphene). The anode slurry was coated on a Cu foil current collector with a thickness of 50 ㎛ using a doctor blade method, and dried with hot air at a temperature of 80°C to prepare an anode for a lithium ion battery.

[0068] 2) Solid electrolyte

[0069] Lithium bis(fluorosulfonyl)imide (LiFSI) and dimethyl sulfone (DMS) were mixed in a molar ratio of 2.5:7.5, heated to 90°C to eutecticize, and then cooled to room temperature to prepare a crystalline organic electrolyte.

[0070] 3) Bipolar

[0071] A cathode material slurry was prepared by adding N-methylpyrrolidone to a cathode material content of 40 wt% in a weight ratio of cathode active material (NCM811) / conductive material (carbon black) / binder (PVDF) 94 / 3 / 3. The cathode material slurry was applied to an aluminum (Al) thin film having a thickness of 18 μm using a doctor blade, dried with hot air at 80°C, and vacuum-dried at 120°C for 24 hours to form a cathode active material layer having a thickness of 20 μm, which was then rolled to a constant thickness.

[0072] 4) Manufacturing of lithium-ion batteries

[0073] A lithium-ion battery was manufactured using the positive and negative electrodes manufactured as described above. The solid electrolyte was melted at 90°C and then injected into an assembly in which a separator (a polyolefin-based porous membrane having a thickness of 9 μm) was positioned between the positive and negative electrodes, thereby manufacturing a lithium-ion battery.

[0074] [Example 2]

[0075] A lithium ion battery was manufactured in the same manner as in Example 1, except that the negative electrode was manufactured with the composition shown in Table 1 below.

[0076] [Comparative Example 1]

[0077] A lithium ion battery was manufactured in the same manner as in Example 1, except that the negative electrode was manufactured with the composition shown in Table 1 below.

[0078] [Comparative Example 2]

[0079] A lithium ion battery was manufactured in the same manner as in Example 1, except that the negative electrode was manufactured with the composition shown in Table 1 below.

[0080] (wt%) Silicon oxide Silicon-carbon composite Carbon nanotube Carbon black Water-based binder Example 170.2 24 11.5 3.3 Example 253.5 4 0 11.54 Comparative example 1950 11.5 2.5 Comparative example 2092.5 11.55

[0081] As shown in Fig. 1, the lithium secondary batteries of Examples 1 and 2 were confirmed to have both excellent volumetric capacity and lifespan. In the case of Comparative Example 1, it was confirmed that the capacity was high but the lifespan was short, and in the case of Comparative Example 2, the lifespan was long but the capacity was low. In addition, it was confirmed that when the content of the silicon-carbon composite was between 24 and 40 wt%, the lifespan of the battery was improved by more than twice that of the battery using only silicon oxide.

[0082] Therefore, by using the negative electrode composition used in the present invention, it is possible to solve the problems of capacity and lifespan, which are shortcomings of conventional lithium secondary batteries, while providing a silicon-based negative electrode with high energy density and long lifespan and a lithium secondary battery including the same. Furthermore, it was confirmed that the capacity and lifespan of a lithium secondary battery can be controlled as desired by adjusting the composition of the silicon oxide and silicon-carbon composite included in the negative electrode.

[0083] As described above, the present invention has been described through specific matters and limited examples, but these are provided only to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and those skilled in the art to which the present invention pertains can make various modifications and variations based on this description.

[0084] Therefore, the idea of ​​the present invention should not be limited to the described embodiments, and all things that are equivalent or equivalent to the following claims as well as the claims are considered to fall within the scope of the idea of ​​the present invention.

Claims

1. Silicon oxide (SiO x ), a negative electrode composition for a lithium secondary battery comprising a silicon-carbon composite, a carbon-based conductive material, and an aqueous binder.

2. In paragraph 1, The negative electrode composition for a lithium secondary battery comprises 70 to 95 wt% of silicon oxide and a silicon-carbon composite, and the weight ratio of silicon oxide: silicon-carbon composite is 40 to 80:20 to 50.

3. In paragraph 1, A negative electrode composition for a lithium secondary battery, wherein the specific capacity of the silicon oxide is 1000 to 3000 mAh / g.

4. In paragraph 1, A negative electrode composition for a lithium secondary battery, wherein the specific capacity of the above silicon-carbon composite is 1500 to 2150 mAh / g.

5. In paragraph 1, The above silicon-carbon composite is a negative electrode composition for a lithium secondary battery in which silicon particles are dispersed in a carbon material matrix.

6. In paragraph 5, A negative electrode composition for a lithium secondary battery, wherein the average particle diameter of the above silicon particles is 30 to 600 nm.

7. In paragraph 5, The above silicon-carbon composite is a negative electrode composition for a lithium secondary battery, which contains 100 to 200 parts by weight of silicon particles per 100 parts by weight of carbon material.

8. In paragraph 5, A negative electrode composition for a lithium secondary battery, wherein the carbon material matrix is ​​one or a mixture of two or more selected from the group consisting of graphene, graphite, and amorphous carbon.

9. In paragraph 1, A negative electrode composition for a lithium secondary battery, wherein the carbon-based conductive material is one or a mixture of two or more selected from the group consisting of carbon nanotubes (CNT), carbon black, acetylene black, and carbon nanofibers (CNF).

10. In paragraph 1, A negative electrode composition for a lithium secondary battery, wherein the aqueous binder is one or a mixture of two or more selected from carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol, polyacrylonitrile, polyvinylpyrrolidone, styrene butadiene rubber (SBR), and a latex binder.

11. A negative electrode for a lithium secondary battery comprising a negative electrode composition for a lithium secondary battery selected from any one of claims 1 to 10.

12. A lithium secondary battery comprising the negative electrode for a lithium secondary battery of Article 11.

13. In paragraph 12, The above lithium secondary battery is a lithium secondary battery in which the capacity is maintained at 70% or more after 500 charge and discharge cycles.

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