Negative electrode active material, negative electrode for secondary battery including negative electrode active material, and secondary battery including negative electrode active material

Abstract

The negative active material according to the embodiment of the present disclosure includes: a first active material including a silicon-based material; and a second active material including a carbon-based material, wherein the second active material includes at least one of a first carbon-based material and a second carbon-based material, and a total length expansion rate or a total width expansion rate of a negative electrode including the negative active material satisfies the following expression 3: [Expression 3] a1 = k1 × x / y a2 = k2 × x / y, wherein a1 denotes the total length expansion rate, a2 denotes the total width expansion rate, k1 and k2 denote real numbers, x denotes a weight of the first carbon-based material, and y denotes a weight of the second carbon-based material.

Description

Technical Field

[0001] This disclosure relates to a negative electrode active material, a negative electrode for a secondary battery including the negative electrode active material, and a secondary battery including the negative electrode active material. Background Technology

[0002] With the rapid development of the electronics, communications, and computer industries, the application of energy storage technology is constantly expanding to fields such as cameras, mobile phones, laptops, personal computers, and even electric vehicles. Lightweight, durable, and highly reliable high-performance rechargeable batteries are precisely what these applications require.

[0003] Among currently used rechargeable batteries, lithium-ion batteries, developed in the early 1990s, have higher operating voltage and energy density compared to traditional batteries that use aqueous electrolyte solutions (such as Ni-MH batteries, Ni-Cd batteries, and lead-sulfur batteries). Therefore, lithium-ion batteries are already used as a power source for many portable devices.

[0004] Materials including graphite have been used as negative electrode active materials in lithium-ion batteries. Because graphite has an average potential of approximately 0.1–0.2V (based on Li / Li+) when absorbing / releasing lithium, and a relatively flat discharge potential, batteries using graphite have the advantage of high and constant voltage. However, a drawback of graphite is its very small theoretical capacity of 372 mAh / g.

[0005] Therefore, various anode active materials are being researched to further improve the capacity of lithium-ion batteries. Materials that form intermetallic compounds with lithium, such as silicon or tin, are expected to be promising anode active materials as high-capacity materials. In particular, silicon, an alloy-type anode active material, has a theoretical capacity (4,200 mAh / g) that is about 10 times higher than that of graphite, and is attracting much attention as a next-generation anode active material.

[0006] However, silicon-based anode active materials have a high material expansion rate, which is detrimental to the durability and stability of the battery.

[0007] The content described in this background section is only for enhancing the understanding of the background of this disclosure and should not be construed as an endorsement that it corresponds to prior art known to those skilled in the art. Summary of the Invention

[0008] The following summary provides a simplified overview of certain features. This summary is not an exhaustive overview, nor is it intended to identify key or important elements.

[0009] According to one aspect of the present invention, the negative electrode active material comprises: a first active material comprising a silicon-based material; and a second active material comprising a carbon-based material. The second active material comprises at least one of the first carbon-based material and the second carbon-based material. The weight ratio of the first carbon-based material and the second carbon-based material satisfies the following expression 1.

[0010] [Expression 1]

[0011] 0 ≤ x / y ≤ 0.15

[0012] Where x represents the weight of the first carbon-based material and y represents the weight of the second carbon-based material.

[0013] According to another aspect of the invention, the pellet density of the second carbon-based material can be 1.7 g / cm³. 3 Or higher.

[0014] According to one aspect of the present invention, the silicon-based material may include materials selected from Si, SiO2, etc. x At least one of (0 < x < 2) and SiC.

[0015] According to some aspects of the present invention, the following expression 2 can be satisfied.

[0016] [Expression 2]

[0017] 0 <z / (x+y+z)<0.15

[0018] Where x and y are as defined above, and z represents the weight of the silicon-based material.

[0019] In some aspects of the present invention, the overall length expansion rate or overall width expansion rate of the negative electrode including the negative electrode active material can satisfy the following expression 3.

[0020] [Expression 3]

[0021] a1=k1×x / y

[0022] a2=k2×x / y

[0023] Where x and y are defined as above, a1 represents the overall length expansion rate, a2 represents the overall width expansion rate, and k1 and k2 represent real numbers.

[0024] According to one or more aspects of the present invention, the first carbon-based material may be natural graphite.

[0025] According to one or more aspects of the present invention, the second carbon-based material may be artificial graphite.

[0026] According to another aspect of the invention, the negative electrode for a secondary battery may include the aforementioned negative electrode active material.

[0027] According to another aspect of the invention, the secondary battery may include the aforementioned negative electrode. Attached Figure Description

[0028] The above and other aspects, features, and advantages of this disclosure will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0029] Figure 1 It is a schematic diagram used to describe the negative electrode of one or more examples according to this disclosure; and

[0030] Figure 2 These are the measurement results of capacity retention rates of the embodiments and comparative examples of this disclosure. Detailed Implementation

[0031] The embodiments disclosed in this specification will now be described in detail with reference to the accompanying drawings. In the following description, the same or similar parts are referred to by the same or similar reference numerals, and repeated descriptions may be omitted.

[0032] Unless otherwise defined, the terms used herein (including technical or scientific terms) shall have the meanings commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0033] In this specification, the terms “comprising,” “including,” or “having” mean the presence of the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but do not exclude the prior presence of any features, numbers, steps, operations, components, parts, or combinations thereof.

[0034] Unless the context otherwise requires, the singular expressions used herein may include the plural meaning, and this also applies to the singular expressions described in the claims.

[0035] For the purposes of this application and claims, the exemplary phrases “at least one of A, B, or C” or “at least one of A, B, or C” are used to mean “at least one A, or at least one B, or at least one C, or any combination of at least one A, at least one B, and at least one C.” Furthermore, exemplary phrases used herein, such as “A, B, or C,” “at least one of A, B, and C,” “at least one of A, B, or C,” etc., may refer to each listed item or all possible combinations of listed items. For example, “at least one of A or B” may refer to (1) at least one A; (2) at least one B; or (3) at least one A and at least one B.

[0036] The term “about” and its grammatical equivalents used herein, in relation to a reference value, may include the reference value itself and a range of values ​​±10% of that reference value. For example, the term “about 10” includes 10 and any value between 9 and 11 (inclusive). In some cases, the term “about” in relation to a reference value may also include a range of values ​​±10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% of that reference value. In some embodiments, “about” in relation to a value or range of values ​​measured by a particular method indicates that the given value includes values ​​determined by the variability of the method. The values ​​and ranges disclosed herein may include exact values ​​and may also include, or alternatively include, approximations of the disclosed values.

[0037] Unless the context otherwise requires, expressions such as “first” or “second” as used herein are used to distinguish one object from another when referring to multiple similar objects, without limiting their order or importance. For example, multiple chips according to this disclosure can be distinguished from each other by referring to them respectively as “first chip” and “second chip”.

[0038] As used in this article, the word “based on” is intended to include phrases or sentences that describe one or more factors that influence a determination or decision, and the expression does not exclude any other factors that influence a determination or decision.

[0039] The negative electrode active material according to one or more embodiments of the present invention may include a first active material and a second active material.

[0040] The first active material may include silicon-based materials.

[0041] Silicon-based materials can be silicon-based particles. In some embodiments, silicon-based materials may include materials selected from Si and SiO2. x At least one of (0 < x < 2) and SiC.

[0042] The second active material may include carbon-based materials.

[0043] The second active material may include at least one first carbon-based material and at least one second carbon-based material.

[0044] In some embodiments, the first carbon-based material may be natural graphite. In some embodiments, the second carbon-based material may be synthetic graphite. In some embodiments, the second carbon-based material may have a tablet density of approximately 1.7 g / cm³. 3 Or even higher quality materials. For example, the second carbon-based material could have a tablet density of approximately 1.7 g / cm³. 3Or even higher levels of artificial graphite. The tablet density is defined as the density measured after pouring the second carbon-based material into a circular mold with a diameter of 13 mm and applying a compression pressure of 4 tons. The tablet density of the second carbon-based material is approximately 1.7 g / cm³. 3 Or even higher, it can absorb the volume expansion of the first active material during charging and discharging. The second carbon-based material can buffer the expansion of the first active material. Furthermore, it can delay or prevent the degradation of the electrode including the negative electrode active material.

[0045] The D10 of the second carbon-based material can be from about 4.5 to about 8.5 μm. The D50 of the second carbon-based material can be from about 11 to about 17 μm. The D90 of the second carbon-based material can be from about 25 to about 30 μm. Because the particle size of the second carbon-based material is within the above range, it can absorb the expansion of the silicon-based material.

[0046] The weight ratio of the first carbon-based material and the second carbon-based material in the second active material can satisfy the following expression 1.

[0047] [Expression 1]

[0048] 0 ≤ x / y ≤ 0.15

[0049] Where x represents the weight of the first carbon-based material and y represents the weight of the second carbon-based material. In some embodiments, y may represent a tablet density of approximately 1.7 g / cm³. 3 Or the weight of a higher second carbon-based material.

[0050] By satisfying Expression 1 above, the second active material can act as a buffer when the first active material, which includes silicon-based materials, expands. Specifically, when the negative electrode active material is applied to the negative electrode, it can prevent the overall length or width of the negative electrode from expanding. Furthermore, by using a negative electrode active material that satisfies Expression 1, the durability and stability of the secondary battery can be improved.

[0051] The negative electrode active material according to one or more embodiments of this disclosure can satisfy the following expression 2.

[0052] [Expression 2]

[0053] 0 <z / (x+y+z)<0.15

[0054] Where x and y are as defined above, and z represents the weight of the silicon-based material. In some embodiments, y may represent a tablet density of approximately 1.7 g / cm³. 3 Or a higher weight of the second carbon-based material. In some embodiments, x + y + z = 100, where x, y, and y are all in wt%.

[0055] In some embodiments, the overall length expansion rate or overall width expansion rate of the negative electrode, including the negative electrode active material, can satisfy the following expression 3.

[0056] [Expression 3]

[0057] a1=k1×x / y

[0058] a2=k2×x / y

[0059] Where x and y are as defined above, a1 represents the overall length expansion rate of the negative electrode, a2 represents the overall width expansion rate of the negative electrode, and k1 and k2 represent real numbers. In some embodiments, y can represent a tablet density of approximately 1.7 g / cm³. 3 Or a higher weight of the second carbon-based material. According to some embodiments, 0 <k1≤8,0<k2≤8。

[0060] The overall length expansion rate can be calculated according to the following formula 4, and the overall width expansion rate can be calculated according to the following formula 5.

[0061] [Formula 4]

[0062]

[0063] [Formula 5]

[0064]

[0065] When the negative electrode active material satisfies Expression 2, the overall length expansion rate or overall width expansion rate can be proportional to x / y. Furthermore, when the negative electrode active material satisfies Expression 2, Expression 3 can be used to predict the value of the overall length expansion rate or overall width expansion rate of the negative electrode.

[0066] In some embodiments, the content of the first active material may be greater than about 8 wt% and less than about 15 wt% relative to the total weight of the negative electrode active material. For example, the content of the first active material may be from about 10 wt% to about 14 wt% relative to the total weight of the negative electrode active material. When the content of the first active material is within the above range, the battery capacity can be increased.

[0067] In some embodiments of the negative electrode active material, the content of the first carbon-based material can be from 0 wt% to about 13.5 wt% relative to the total weight of the negative electrode active material. For example, the content of the first carbon-based material can be from 0 wt% to about 10 wt% relative to the total weight of the negative electrode active material.

[0068] In some embodiments of the negative electrode active material, the content of the second carbon-based material can be greater than about 85 wt% and less than about 92 wt% relative to the total weight of the negative electrode active material. For example, the content of the second carbon-based material can be from about 86 wt% to about 90 wt% relative to the total weight of the negative electrode active material.

[0069] According to one or more embodiments of the present disclosure, even if the negative electrode active material includes a silicon-based material with a high expansion rate, negative electrode expansion can be prevented. That is, when the negative electrode active material of the present disclosure is applied to a negative electrode for a secondary battery, overall length expansion or overall width expansion of the negative electrode can be avoided. Furthermore, when the negative electrode active material of the present disclosure is applied to a secondary battery, the durability and stability of the secondary battery can be improved.

[0070] The negative electrode for a secondary battery according to one or more embodiments of this disclosure may include the aforementioned negative electrode active material. For example, the content of the negative electrode active material may be from about 95 wt% to about 98 wt%, relative to, for example, the entire negative electrode for a secondary battery.

[0071] The negative electrode according to one or more embodiments of this disclosure may further include at least one of a conductive material, an adhesive, and a thickener.

[0072] Conductive materials can be used to impart conductivity to electrodes. Any conductive material can be used, as long as it does not cause a chemical change in the battery and is conductive. For example, conductive materials may include at least one selected from carbon black, acetylene black, Ketjen black, channel black, paneth black, lampblack, thermal cracking black, conductive fibers, fluorocarbons, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium dioxide, polyphenylene derivatives, carbon nanotubes, sheet graphite, graphene, graphene oxide, and graphite flakes.

[0073] The adhesive can bond the negative electrode active material particles together well and also bond the negative electrode active material well to the current collector. The adhesive and / or thickener may include at least one selected from polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and polyacrylic acid, and may also include various copolymers thereof.

[0074] See Figure 1According to one or more embodiments of the present disclosure, the negative electrode 10 for a secondary battery, even when comprising a silicon-based material with a high expansion rate, can prevent overall length expansion or overall width expansion of the negative electrode 10. Therefore, the durability and stability of the secondary battery can be improved.

[0075] A secondary battery according to one or more embodiments of the present disclosure may include a negative electrode as described above and a positive electrode as described below.

[0076] The positive electrode may include a positive electrode active material, a conductive material, and a binder. The positive electrode active material may include at least one selected from, for example, lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), and lithium iron phosphate (LFP). In some embodiments, the positive electrode active material may include NCM.

[0077] A secondary battery according to one or more embodiments of the present disclosure may include a separator between a positive electrode and a negative electrode and an electrolyte.

[0078] The separator separates the negative and positive electrodes and provides a channel for lithium-ion movement. The separator can include a porous polymer membrane, such as a porous polymer membrane made of polyolefin polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or a two- or multi-layer laminated structure thereof. Alternatively, the separator can include a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc.

[0079] Electrolytes can include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc.

[0080] Using the secondary battery according to one or more embodiments of this disclosure, even if the negative electrode active material includes a silicon-based material with a high expansion rate, expansion of the negative electrode can be prevented. Therefore, performance degradation of the secondary battery can be prevented. Furthermore, this secondary battery exhibits excellent durability and stability.

[0081] Embodiments and comparative examples of this disclosure will now be described. The following embodiments are merely examples of this disclosure, and this disclosure is not limited to these embodiments.

[0082] Example

[0083] Anode active materials with the compositions shown in Table 1 below were prepared.

[0084] Si powder was prepared as the first active material. Natural graphite was prepared as the first carbon-based material in the second active material. Artificial graphite with a D10 of 6.50 μm, a D50 of 14.7 μm, a D90 of 27.6 μm, and a tablet density of 1.75 g / cm³ was prepared as the second carbon-based material in the second active material. For comparison, artificial graphite with a tablet density of 1.63 g / cm³ was also prepared as the second carbon-based material.

[0085] An adhesive was prepared by mixing styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) in a 1:1 ratio. Carbon black was prepared as a conductive material, and CMC was prepared as a thickener.

[0086] The prepared negative electrode active material, binder, conductive material, and thickener were mixed in a weight ratio of 96:2:1:1 and then dispersed in water to prepare a negative electrode slurry. This negative electrode slurry was coated onto a copper film, dried in an oven at 80°C for approximately 2 hours, rolled under a pressure of 3.8 MPa, and then further dried in a vacuum oven at 110°C for 12 hours to produce a negative electrode for secondary batteries.

[0087] A nickel-cobalt-manganese (NCM) based cathode was prepared. The electrolyte was a mixed solution of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and ethyl propionate (EP) containing 0.5 M LiFSi and 0.5 M LiPF6.

[0088] Pouch cells are manufactured using well-known manufacturing processes.

[0089] The overall length expansion rate and overall width expansion rate of the battery negative electrode were measured, and the results are shown in Table 1 below. The overall length expansion rate was calculated using Formula 4, and the overall width expansion rate was calculated using Formula 5.

[0090] [Formula 4]

[0091]

[0092] [Formula 5]

[0093]

[0094] At the same time, the capacity retention rate was also measured, and the results were as follows: Figure 2 As shown.

[0095] [Table 1]

[0096]

[0097] Referring to Table 1 above, in the embodiments that satisfy Expression 1 below, it is confirmed that the overall length expansion rate and the overall width expansion rate are 0.

[0098] [Expression 1]

[0099] 0 ≤ x / y ≤ 0.15

[0100] Meanwhile, in Comparative Example 1 with x / y of 1.93 and Comparative Example 3 with x / y of 0.17, it was confirmed that both the overall length expansion rate and the overall width expansion rate showed values ​​of 0.5% or higher.

[0101] Furthermore, in Comparative Example 2, which contained only natural graphite as the second active material, it was confirmed that the overall length expansion rate and overall width expansion rate were the highest, resulting in the worst durability performance.

[0102] In Comparative Example 4, tablets with a density of less than 1.7 g / cm³ were used. 3 Artificial graphite, as a second carbon-based material, exhibits an overall length expansion rate and an overall width expansion rate of 1% or higher.

[0103] In Comparative Examples 1 and 3 and the embodiments that satisfy Expression 2 below, it is confirmed that the overall length expansion rate or the overall width expansion rate of the negative electrode satisfies Expression 3 below. That is, it is confirmed that the overall length expansion rate or the overall width expansion rate is proportional to x / y.

[0104] [Expression 2]

[0105] 0 <z / (x+y+z)<0.15

[0106] [Expression 3]

[0107] a1=k1×x / y

[0108] a2=k2×x / y

[0109] (0 <k1≤8,0<k2≤8)

[0110] refer to Figure 2 It was confirmed that, in the embodiments, the capacity did not decrease significantly even after 300 cycles, compared to the comparative examples. In other words, this demonstrates that durability can be maintained even when incorporating Si, which has a high volumetric expansion rate.

[0111] Using the negative electrode active material of one or more embodiments of this disclosure, even if the negative electrode active material includes a silicon-based material with a high expansion rate, negative electrode expansion can be prevented. That is, when the negative electrode active material of this disclosure is applied to the negative electrode of a secondary battery, overall length or overall width expansion of the negative electrode can be prevented. Furthermore, when this negative electrode active material is applied to a secondary battery, the durability and stability of the secondary battery can be improved.

[0112] The effects of this disclosure are not limited to those described above, and those skilled in the art will clearly understand other effects not mentioned from the following description.

[0113] Embodiments of this disclosure have been described above with reference to the accompanying drawings. These are illustrative, and this disclosure is not limited to the embodiments and drawings described above.

[0114] It is obvious to those skilled in the art that modifications can be made to this disclosure within the scope of the disclosed technical concepts. The described embodiments should be considered as part of this disclosure, and the scope of this disclosure should not be limited to the described embodiments.

[0115] The scope of this disclosure should be determined by the technical concepts described in the claims. Furthermore, even if the effects or functions based on the described structure are not explicitly described in the description of embodiments of this disclosure, the effects or functions foreseeable based on that structure should also be considered part of this disclosure.

Claims

1. A negative electrode active material, comprising: The first active material includes silicon-based materials; and The second active material includes carbon-based materials. Wherein, the second active material includes at least one of a first carbon-based material and a second carbon-based material, and The overall length expansion rate or overall width expansion rate of the negative electrode, including the negative electrode active material, satisfies the following expression 3: [Expression 3] a1=k1×x / y a2 = k2 × x / y, Where a1 represents the overall length expansion rate, a2 represents the overall width expansion rate, k1 and k2 represent real numbers, x represents the weight of the first carbon-based material, and y represents the weight of the second carbon-based material.

2. The negative electrode active material according to claim 1, wherein the compression density of the second carbon-based material is 1.7 g / cm³. 3 Or higher.

3. The negative electrode active material according to claim 1, wherein the silicon-based material comprises materials selected from Si, SiO2, etc. x At least one of (0 < x < 2) and SiC.

4. The negative electrode active material according to claim 1, wherein the following expression 2 is satisfied: [Expression 2] 0 <z / (x+y+z)<0.15 Where z represents the weight of the silicon-based material.

5. The negative electrode active material according to claim 1, wherein the first carbon-based material is natural graphite.

6. The negative electrode active material according to claim 1, wherein the second carbon-based material is artificial graphite.

7. A negative electrode for a secondary battery, comprising a negative electrode active material according to any one of claims 1-6.

8. A secondary battery comprising a negative electrode according to claim 7.

9. A negative electrode active material, comprising: The first active material includes materials selected from Si and SiO. x Silicon-based materials of (0 < x < 2) and SiC; and The second active material comprises a first carbon-based material and a second carbon-based material, wherein the first carbon-based material is natural graphite and the second carbon-based material is artificial graphite. The weight ratio of the silicon-based material, the first carbon-based material, and the second carbon-based material satisfies the following expression 2: [Expression 2] 0 <z / (x+y+z)<0.15, Where x represents the weight of the first carbon-based material, y represents the weight of the second carbon-based material, and z represents the weight of the silicon-based material.

10. The negative electrode active material according to claim 9, wherein the compression density of the second carbon-based material is 1.7 g / cm³. 3 Or higher.

11. A negative electrode for a secondary battery, comprising the negative electrode active material according to claim 9 or 10.

12. A secondary battery comprising a negative electrode according to claim 11.

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