Search

EP-4080610-B1 - A MANUFACTURING METHOD OF A NEGATIVE ACTIVE MATERIAL FOR A LITHIUM SECONDARY BATTERY, A NEGATIVE ACTIVE MATERIAL FOR A LITHIUM SECONDARY BATTERY, AND A LITHIUM SECONDARY BATTERY CONTAINING THIS NEGATIVE ACTIVE MATERIAL

EP4080610B1EP 4080610 B1EP4080610 B1EP 4080610B1EP-4080610-B1

Inventors

  • KIM, YONG JUNG
  • CHO, Moonkyu
  • YOU, SEUNG JAE
  • WOO, JUNG GYU

Dates

Publication Date
20260506
Application Date
20201211

Claims (13)

  1. A method of manufacturing a negative active material for lithium secondary battery, comprising: coating precursors for a negative active material containing Si with crude tar or soft pitch; and annealing the resulting coating product, wherein, the crude tar contains a low molecular weight component that can be removed by a distillation process in an amount of 20 wt% or less and a weight ratio of the precursors for a negative active material and the crude tar or the soft pitch is 2 wt% to 20 wt% with respect to 100 wt% of the precursors for the negative active material, wherein the step of coating with the crude tar or the soft pitch is performed by: mixing the precursors for the negative active material and crude tar or soft pitch, and stirring the mixture at a speed of 50 rpm to 100 rpm for 10 minutes to 60 minutes.
  2. The method of claim 1, wherein: the low molecular weight component has a weight average molecular weight (Mw) of 78 to 128.
  3. The method of claim 1, wherein: in the step of the coating Si with the crude tar or the soft pitch, a coating solution prepared by adding crude tar or soft pitch to a solvent, at a concentration of 50 wt% to 70 wt%, is used.
  4. The method of claim 3, wherein: the solvent is N-methyl pyrrolidone, dimethylformaldehyde, dimethyl sulfoxide, tetrahydrofuran, acetone or combination thereof.
  5. The method of claim 1, wherein: the step of annealing a resulting coating product is carried out at 800°C to 950°C for 0.5 hours to 2 hours.
  6. The method of claim 1, wherein: the step of annealing a resulting coating product is performed by raising a temperature to a final temperature of 800 to 950 °C or less at a temperature increase speed of 2 °C / min to 10 °C / min.
  7. The method of claim 1, wherein: the step of annealing an obtained coating product is performed by: raising a temperature first to 300°C to 400°C at a temperature increase speed of 2°C/min to 10°C/min, holding it at this temperature for 0.5 hours to 2 hours, and then raising a temperature second to a final temperature of 800 to 950°C or less at a temperature increase rate of 2°C/min to 10°C/min.
  8. The method of claim 1, wherein: the precursor for a negative active material containing the Si is Si, Si-C composite, Si oxide or combination thereof.
  9. A negative active material for lithium secondary battery, comprising: a core comprising Si; and an amorphous carbon positioned on the core surface; wherein a Brunauer-Emmett-Teller (BET) specific surface area is 1 m 2 / g to 2.91 m 2 /g, wherein the core comprising Si is an Si-C composite, wherein a span value is 1.41 or less.
  10. The negative active material of claim 9, wherein: the amorphous carbon exists as a layer that continuously covers the core surface.
  11. The negative active material of claim 9, wherein: the amorphous carbon exists as an island that is positioned discontinuously on the core surface.
  12. The negative active material of claim 9, wherein: the amorphous carbon is crude tar or soft pitch converted to amorphous carbon.
  13. A lithium secondary battery, comprising: a negative electrode comprising the negative active material of any one of claims 9 to 12; a positive electrode comprising a positive electrode active material; and a non-aqueous electrolyte.

Description

BACKGROUND OF THE INVENTION (a) Field of the Invention Disclosed are a manufacturing method of a negative active material for a lithium secondary battery, a negative active material for a lithium secondary battery manufactured by this method, and a lithium secondary battery including the negative active material. (b) Description of the Related Art A lithium ion secondary battery (lithium ion secondary battery, LIB) is receiving a lot of attention as a next-generation energy storage device while environmental issues are becoming an international issue. Compared to typical secondary battery systems such as nickel cadmium batteries and nickel metal hydride batteries, lithium ion secondary batteries have excellent characteristics in terms of high operation voltage and energy density and memory effects, so they are being broadly applied to various applications. As the demand for a high energy density secondary battery such as Ni-Cd battery and nickel metal hydride battery increases, the use of silicon-based or silicon oxide-based materials having an effective capacity 10 times or more than that of carbon-based materials is increasing as an negative electrode active material for lithium secondary batteries. A lithium ion secondary battery is composed of a positive electrode, a negative electrode, a separator and an electrolyte, so the performance of the battery is closely related to all the characteristics of the constituent elements. Among them, for the negative active material constituting the negative electrode, hard carbon/soft carbon or graphite-based material, which is a carbon material, has been used for nearly 30 years since 1991, when the lithium ion secondary battery was developed. Currently, most commercial batteries mainly use graphite material, and various combinations of graphite compositions are applied depending on the battery maker. Graphite material, which is currently most commonly used as a negative active material for lithium ion secondary batteries, has merit in terms of low working voltage, stable cycle-life characteristic, efficiency, price, and environmentally-friendly merit. However, there is a drawback that the theoretical capacity is limited to a maximum of 372mAh/g. Due to the limitations of the theoretical capacity, it is difficult to secure the mileage of electric vehicles, and there are also problems that it is difficult to apply to various fields of application. As a next-generation material considered to overcome the capacity of graphite, oxides of various elements and Group 4 elements represented by Si are included. Among them, Si is being actively considered as a high-capacity active material candidate from the viewpoint of price and versatility. Theoretically, silicon-based negative active material has a capacity more than 10 times higher than commercially available graphite-based negative active material. However, when the silicon-based negative active material is charged, the volume change reaches 400%. Due to the stress (strain) generated during discharge, there is a problem of battery performance deterioration due to short circuit with the current collector and collapse of the electrode itself. There is a problem that it is difficult to be commercially available. That is, in the silicon-based negative active material, the Si crystal structure is repeatedly changed electrochemically during charging and discharging, and thus the expansion/contraction of the active material is repeated. Accordingly, the conductive network is lost due to the collapse and deformation of the active material particles. As the local inertness in the electrode is amplified, the non-reversible capacitance and cycle characteristic deteriorate. In addition, when the formation of SEI is considered, fractures or crack occurs on the SEI surface formed due to the contraction/expansion of the electrode, and a new surface is exposed according to the occurrence of the fracture and crack. As the charging and discharging proceed, the occurrence of fractures and cracks accelerates, and as a new surface is continuously exposed, the non-surface area increases even more. The newly exposed surface is in contact with the electrolyte solution again, and a new SEI is formed and grows repeatedly. As a result, the battery characteristics are significantly degraded through an increase in the diffusion path of lithium ion, an increase in electrolyte solution consumption, conductive deterioration, reduction of coulomb efficiency, consumption of lithium source, and an increase in resistance. Ultimately, the result is that the battery cannot be used. This problem also occurs when using a composite active material of Si and carbon. Therefore, a method to suppress an expansion and a continuous formation of and SEI was researched. As the method, the method to minimize the non-surface area by the high-pressure molding process basically and the method to suppress the mechanical expansion and control the non-surface area by formin