Search

EP-3993098-B1 - NEGATIVE ELECTRODE FOR SECONDARY BATTERY, AND SECONDARY BATTERY INCLUDING SAME

EP3993098B1EP 3993098 B1EP3993098 B1EP 3993098B1EP-3993098-B1

Inventors

  • JEONG, KWANG HO
  • JANG, HYUN JOONG
  • CHUNG, Da Bin

Dates

Publication Date
20260506
Application Date
20211029

Claims (13)

  1. A negative electrode for a secondary battery, comprising: a current collector; a first negative electrode active material layer formed on the current collector and containing a first active material; and a second negative electrode active material layer formed on the first negative electrode active material layer and containing a second active material, wherein the second active material is a bimodal active material including small particles and large particles having different particle sizes, a particle size (D2) of the second active material is smaller than a particle size (D1) of the first active material, and the particle size of the second active material is an average particle size based on the weight ratio of the small particles and the large particles.
  2. The negative electrode for a secondary battery of claim 1, wherein the small particles have a particle size (D50) of 30 to 90% of a particle size (D50) of the large particles, wherein D50 is a particle diameter when a cumulative volume becomes 50% from a small particle size in particle size distribution measurement by a laser scattering method.
  3. The negative electrode for a secondary battery of claim 2, wherein the small particles have a particle size (D50) of 30 to 80% of the particle size (D50) of the large particles.
  4. The negative electrode for a secondary battery of claim 1, wherein the particle size (D2) of the second active material is 20% to 95% of the particle size (D1) of the first active material.
  5. The negative electrode for a secondary battery of claim 4, wherein the particle size (D2) of the second active material is 30% to 70% of the particle size (D1) of the first active material.
  6. The negative electrode for a secondary battery of claim 1, wherein the first and second active materials include one or more selected from the group consisting of natural graphite, artificial graphite, graphitized carbon fiber, graphitized mesocarbon microbeads, and amorphous carbon.
  7. The negative electrode for a secondary battery of claim 6, wherein the first and second active materials are artificial graphite.
  8. The negative electrode for a secondary battery of claim 6, wherein at least one of the first and second negative electrode active material layers further includes a silicon oxide-based active material (SiO x (0 < x < 2)).
  9. The negative electrode for a secondary battery of claim 8, wherein the silicon oxide-based active materials in the first and second negative electrode active material layers satisfy the following Relational Equation 1: W 2 > 2 * W 1 wherein W1 is a content of the silicon oxide-based active material in the first negative electrode active material layer, W2 is a content of the silicon oxide-based active material in the second negative electrode active material layer, and W1 ≥ 0).
  10. The negative electrode for a secondary battery of claim 1, wherein the first and second negative electrode active material layers further include a binder, and the binder is a water-soluble binder.
  11. The negative electrode for a secondary battery of claim 10, wherein the binder includes styrene-butadiene rubber.
  12. The negative electrode for a secondary battery of claim 1, wherein the negative electrode has a rolling density of 1.65 to 1.85 g/cc.
  13. A secondary battery comprising: the negative electrode of claim 1; a positive electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2020-0142111, filed on oct 29, 2020, in the Korean Intellectual Property Office. TECHNICAL FIELD The following disclosure relates to a negative electrode for a secondary battery, and a secondary battery including the same. BACKGROUND Recently, in accordance with an increase in the demand for electronic devices such as mobile devices, development of technologies for weight reduction and miniaturization of electrochemical batteries (secondary batteries) for increasing portability of the electronic devices has been expanded. In addition to such a trend, in accordance with a global trend toward tightening regulations on fuel efficiency and exhaust gas of automobiles, the growth of an electric vehicle (EV) market has been accelerated, such that the development of high-output and large-capacity batteries to be used in such electric vehicles has been demanded. Examples of negative electrodes for a secondary battery are disclosed in EP 3 678 228 A2, WO 2014/128946 A1, WO 2020/071814 A1, US 2020/185719 A1, US 2013/174370 A1. Among these batteries, a lithium secondary battery having a high energy density and voltage, a long cycle lifespan, and a low discharge rate has been widely used. The lithium secondary battery is a secondary battery that includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator, and an electrolyte and is charged and discharged by intercalation-desorption of lithium ions. A lithium metal has been mainly used as a negative electrode material for the lithium secondary battery in the early stage, but a separator damage caused by lithium atom growth on a surface of the metal lithium has occurred in accordance with the progress of charging and discharging. Therefore, recently, carbon-based materials have been mainly used as the negative electrode material for the lithium secondary battery. Among the carbon-based materials, graphite having a relatively low price and a long service lifespan has been used most. However, the graphite has a very small interlayer distance of 0.335 nm, has few sites for lithium ions to be intercalated, and has a long diffusion distance through a graphite basal plane is long, such that a capacity is 372 mAh/g, which is restrictive. In addition, due to a problem such as low packing density and poor particle orientation at the time of manufacturing an electrode using the graphite because the graphite has a plate-like structure, an intercalation rate of the lithium ions is slow, and thus, high output characteristics are not satisfied. Therefore, there is a need to develop a negative electrode having excellent lifespan characteristics while exhibiting a large capacity and a high output. SUMMARY An embodiment of the present invention is directed to providing a negative electrode having improved rapid charging characteristics without decreasing an electrode density of the negative electrode. Another embodiment of the present invention is directed to providing a negative electrode having stable lifespan characteristics without generating a decrease in adhesion between a current collector and a negative electrode active material layer even under a rapid charging condition. In one general aspect, a negative electrode for a secondary battery includes: a current collector; a first negative electrode active material layer formed on the current collector and containing a first active material; and a second negative electrode active material layer formed on the first negative electrode active material layer and containing a second active material, wherein the second active material is a bimodal active material including small particles and large particles having different particle sizes, a particle size (D2) of the second active material is smaller than a particle size (D1) of the first active material, and the particle size of the second active material is an average particle size of the small particles and the large particles. The small particles may have a particle size (D50) of 30 to 90% of a particle size (D50) of the large particles. The small particles may have a particle size (D50) of 30 to 80% of the particle size (D50) of the large particles. The particle size (D2) of the second active material may be 20% to 95% of the particle size (D1) of the first active material. The particle size (D2) of the second active material may be 30% to 70% of the particle size (D1) of the first active material. The first and second active materials may include one or more selected from the group consisting of natural graphite, artificial graphite, graphitized carbon fiber, graphitized mesocarbon microbeads, and amorphous carbon. The first and second active materials may be artificial graphite. At least one of the first and second negative electrode active material layers m