EP-3800709-B1 - ANODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY AND SECONDARY BATTERY COMPRISING SAME

Inventors

• LEE, KWAN HEE
• RYU, DUK HYUN

Dates

Publication Date

20260506

Application Date

20191122

Claims (10)

1. A negative electrode active material for a lithium secondary battery including a carbon-based material and a silicon-based material, wherein the carbon-based material includes low-expansion artificial graphite, wherein a volume of the low-expansion artificial graphite expands by less than 25% when a battery is charged and discharged; the expansion characteristics being determined by the change of the active material layer thickness of the low-expansion artificial graphite, using a negative electrode using a low-expansion artificial graphite as an active material and a secondary battery having such a negative electrode, the charge and discharge cycle being repeated until there is no change in the thickness of the negative electrode active material layer, the negative electrode using 94 wt% of a low-expansion artificial graphite as an active material, 2 wt% of multilayer carbon nanotubes having an average diameter of 20 nm and an average length of 2 µm as a conductive material, and 4 wt% of polyvinylidene fluoride as a binder, and the charge/discharge cycle being as follows: discharging to 2.5V after charging to 4.25V; and wherein the low-expansion artificial graphite occupies 65 to 95% of the total weight of the negative electrode active material.
2. The negative electrode active material of claim 1, wherein the low-expansion artificial graphite occupies 75 to 85% of the total weight of the negative electrode active material.
3. The negative electrode active material of claim 1, wherein the carbon-based material is made of natural graphite and artificial graphite
4. The negative electrode active material of claim 1, wherein the silicon-based material occupies 1 to 10 % of the total weight of the negative electrode active material.
5. The negative electrode active material of claim 1, wherein the silicon-based material occupies 3 to 7 % of the total weight of the negative electrode active material.
6. The negative electrode active material of claim 1, wherein the silicon-based material is silicon dioxide (SiO 2 ).
7. The negative electrode active material of claim 1, wherein a volume of the low-expansion artificial graphite expands by less than 23% when a battery is charged and discharged.
8. A negative electrode for a lithium secondary battery, the negative electrode comprising: a current collector; and a negative electrode active material layer formed on at least one surface of the current collector and including a negative electrode active material, wherein the negative electrode active material is a negative electrode active material according to claim 1.
9. A lithium secondary battery comprising a positive electrode, a negative electrode and a separator interposed between the positive electrode and negative electrode, wherein the negative electrode is a negative electrode according to claim 8.
10. The lithium secondary battery of claim 9, wherein the lithium secondary battery is a cylindrical secondary battery.

Description

[Technical Field] The present invention relates to a negative electrode active material for a lithium secondary battery and a secondary battery including the same, and more particularly, to a negative electrode active material including low-expanded artificial graphite exhibiting low expansion characteristics during charging and discharging, and a lithium secondary battery including the same. This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0160091, filed on December 12, 2018. [Background Art] As the price of energy sources increases due to depletion of fossil fuels and the interest in environmental pollution increases, the demand for environmentally friendly alternative energy sources becomes an indispensable factor for future life. Especially, as technology development and demand for mobile devices are increasing, demand for secondary batteries as energy sources is rapidly increasing. Typically, in terms of the shape of the battery, there is a high demand for a prismatic secondary battery and a pouch-type secondary battery that can be applied to products such as mobile phones with a small thickness. In terms of materials, there is a high demand for lithium secondary batteries such as lithium ion batteries and lithium ion polymer batteries having high energy density, discharge voltage, and output stability. Generally, in order to prepare a secondary battery, first, a positive electrode and a negative electrode are formed by applying an electrode mixture containing an electrode active material to a surface of a current collector, then a separate is interposed therebetween to thereby make an electrode assembly, which is then mounted in a cylindrical or rectangular metal can or inside a pouch-type case of an aluminum laminate sheet, and a liquid electrolyte in injected or impregnated into the electrode assembly or a solid electrolyte to prepare a secondary battery. In general, the negative electrode of a lithium secondary battery uses a carbon material such as graphite, but the theoretical capacity density of carbon is 372 mAh/g (833 mAh/cm3). Therefore, in order to improve the energy density of the negative electrode, silicon (Si), tin (Sn), oxides and alloys thereof which are alloyed with lithium are considered as negative electrode materials. Among them, silicon-based materials have attracted attention due to their low cost and high capacity (4200 mAh/g). However, although the silicon-based material exhibits a much higher theoretical capacity than graphite, when the silicon is mixed with lithium ions, the volume expands four times or more, and when containing more than a predetermined amount, as the cycle progresses, a volume expansion of the entire electrode is caused, which causes a loss of the conductive network of the battery, thereby rapidly decreasing the charge/discharge capacity. In addition, as the cycle initial efficiency is lowered, the advantage of the silicon-based material capable of realizing a high energy density may disappear. Particularly, in the case of a cylindrical battery, when the volume of the silicon-based material is expanded and the diameter of the wound cell is increased, it becomes difficult to store the battery, thereby making it difficult to increase the energy density. Therefore, while overcoming the low energy density limit of the carbon-based negative electrode active material, research has been continuously conducted to reduce side effects due to the expansion characteristics of the silicon-based material. Japanese Laid-Open Patent Publication No. 2018-008405 describes a method of preparing a composite of carbon particles having fine unevenness and using it as a negative electrode material together with silicon oxide so that the cycle characteristics are not deteriorated in the expansion and contraction of silicon oxide during charging and discharging. On the other hand, Korean Patent Publication No. 2017-0136878 discloses a method of improving the life characteristics and high temperature storage characteristics by using a secondary particle artificial graphite containing a primary particle having a specific average particle diameter as a negative electrode active material. In addition, Korean Patent No. 1704103 discloses a method for improving the life characteristics by suppressing the volume expansion of the negative electrode active material and solving the short-circuit problem by including together the porous silicon-based particles and fine carbon particles having different average particle diameters. In addition, in the negative electrode active material including a carbon-based material and a silicon-based material to realize high energy density, in order to reduce side effects due to volume expansion of silicon-based materials, various methods such as adding metal-based materials, preparing new composites, or changing particle sizes have been studied. The publication CHEN HEDONG ET AL: "Mass-producible method for pr