Search

EP-4737400-A1 - POSITIVE ACTIVE MATERIAL HAVING SPINEL NANOCOMPOSITE STRUCTURE FOR SECONDARY BATTERY AND METHOD THEREOF

EP4737400A1EP 4737400 A1EP4737400 A1EP 4737400A1EP-4737400-A1

Abstract

The positive active material for lithium secondary batteries according to the present invention includes a secondary particle composed of a plurality of primary particles, wherein the primary particles contain a nanocomposite in which spinel (Fd3m) and layered (R3m) structures coexist at the nanoscale. Although the spinel structure offers high structural stability, it has the drawback of low initial capacity. However, the positive material of the present invention addresses this limitation by introducing a nanocomposite structure in which layered and spinel structures are mixed at the nanoscale. This innovation provides higher structural stability and improved electrochemical performance compared to conventional single-structure positive materials. By incorporating the spinel structure into the nanocomposite, the invention enhances structural stability, minimizes deformation during charge-discharge cycles, and simultaneously provides a three-dimensional lithium-ion diffusion pathway. This results in faster lithium-ion transport, significantly improving rate capability and high-rate charge-discharge performance.

Inventors

  • PARK, JANG UK
  • CHOI, Kyoung Ran

Assignees

  • Battery Solution

Dates

Publication Date
20260506
Application Date
20250211

Claims (15)

  1. A positive active material for a lithium secondary battery, comprising a secondary particle consisting of a plurality of primary particles, wherein the primary particles include a nanocomposite structure in which a spinel (Fd3m) structure and a layered (R 3m ) structure are mixed at the nanoscale.
  2. The positive active material for a lithium secondary battery according to Claim 1, wherein SAED electron diffraction images show S(a, a, a + 2) and S(b, b, b - 2) electron diffraction spots.
  3. The positive active material for a lithium secondary battery according to Claim 2, wherein in the SAED electron diffraction image, the peak intensity of the L(0, -1, -2-3(m-1)) plane is greater than that of the S(a, a, a+2) plane (I(L(0, -1, -2-3(m-1))) > I(S(a, a, a+2))), and the peak intensity of the L(0, 1, 2+3(n-1)) plane is greater than that of the S(b, b, b-2) plane (I(L(0, 1, 2+3(n-1))) > I(S(b, b, b-2))).
  4. The positive active material for a lithium secondary battery according to one of claims 1 to 3, wherein the maximum length passing through the center of the cross-section of the spinel-formed region is between 1 nm and 100 nm, and the cross-sectional area of the spinel-formed region is between 1 nm 2 and 10,000 nm 2 .
  5. The positive active material for a lithium secondary battery according to one of claims 1 to 4, wherein the nanocomposite is located inside or on the surface of the primary particles, and inside or on the surface of the secondary particles.
  6. The positive active material for a lithium secondary battery according to one of claims 1 to 5, wherein the nanocomposite is observable before the start of the charge-discharge cycle.
  7. The positive active material for a lithium secondary battery according to one of claims 1 to 6, wherein the nanocomposite provides a three-dimensional (3D) Li + transport pathway in the charged state, thereby improving the rate capability of the positive material.
  8. The positive active material for a lithium secondary battery according to one of claims 1 to 7, wherein the nanocomposite observable before the charge-discharge cycle is also found after the cycle, and the nanocomposite found inside the primary particles after the cycle is distinguishable from impurity spinel that forms on the surface of the secondary particles due to electrode degradation.
  9. The positive active material for a lithium secondary battery according to one of claims 1 to 8, wherein the primary particles contain nickel (Ni), M1, and M2, M1 includes at least one of cobalt (Co), manganese (Mn), and aluminum (Al), Nickel (Ni) is present at ≥50 mol%M2 is a doping element and is present at 0.05 mol% to 10 mol%.
  10. The positive active material for a lithium secondary battery according to Claim 9, wherein M2 comprises at least one selected from cobalt (Co), manganese (Mn), titanium (Ti), magnesium (Mg), tantalum (Ta), niobium (Nb), tungsten (W), molybdenum (Mo), antimony (Sb), tellurium (Te), tin (Sn), ruthenium (Ru), boron (B), hafnium (Hf), gallium (Ga), germanium (Ge), chromium (Cr), vanadium (V), copper (Cu), calcium (Ca), zinc (Zn), barium (Ba), strontium (Sr), aluminum (Al), and zirconium (Zr).
  11. The positive active material for a lithium secondary battery according to Claim 9 or 10, wherein the material is obtained by mixing a composite metal hydroxide precursor (A(OH) 2 ) with M2 and performing high-temperature heat treatment, where A is at least one selected from Ni, Co, Mn, or Al, and/or wherein the material is obtained by mixing an M2-doped composite metal hydroxide precursor (M2-doped A(OH) 2 ) with a lithium precursor and performing high-temperature heat treatment, where A is selected from Ni, Co, Mn, or Al.
  12. The positive active material for a lithium secondary battery according to one of claims 9 to 11, wherein the material is obtained by mixing an M2-coated composite metal hydroxide precursor (M2-coated A(OH) 2 ) with a lithium precursor and performing high-temperature heat treatment, where A is selected from Ni, Co, Mn, or Al.
  13. The positive active material for a lithium secondary battery according to one of claims 9 to 12, wherein the material is obtained by mixing either an M2-doped A(OH) 2 precursor or an M2-coated A(OH) 2 precursor with a lithium precursor and additional M2, followed by high-temperature heat treatment, where A is selected from Ni, Co, Mn, or Al.
  14. The positive active material for a lithium secondary battery according toone of claims 1 to 13, wherein a concentration gradient of Ni, Co, or Mn is formed within the particles.
  15. The positive active material for a lithium secondary battery according to one of claims 1 to 14, wherein wherein the positive active material is obtained through a first calcination process by mixing at least one of a composite metal hydroxide A(OH) 2 precursor and a wet-doped composite metal hydroxide A(OH) 2 precursor with a lithium source, followed by a second calcination process in which a dry dopant is additionally introduced and subjected to further high-temperature heat treatment, for use in a lithium secondary battery.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to and the benefit of Korean Patent Application No. 10-2024-0152619 and Korean Patent Application No. 10-2025-0015772 filed in the Korean Intellectual Property Office on October 31, 2024 and February 7, 2025, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD The present invention relates to a positive active material for a lithium-ion secondary battery, and more specifically, to a positive active material for a lithium-ion secondary battery having a nano-composite structure in which a spinel structure and a layered structure are mixed at the nanoscale, as well as a method for producing the same. BACKGROUND ART The lithium-ion secondary battery has high energy density and long lifespan characteristics, making it widely used in various electronic devices, electric vehicles, and energy storage systems (ESS). One of the key factors determining the performance of a lithium-ion secondary battery is the positive active material, which is typically composed of transition metal oxides with either a layered structure, containing elements such as nickel (Ni), cobalt (Co), and manganese (Mn), or a spinel structure. Conventional high-nickel (high-Ni) positive active materials can provide high capacity; however, they suffer from structural instability during charge and discharge cycles, leading to capacity degradation and thermal deterioration. In particular, the layered structure undergoes significant structural deformation during cycling, making it prone to particle cracking. When particle cracking occurs, electrolyte penetration into the secondary particle can lead to the degradation of both the internal and external primary particle surfaces. This results in a decrease in electronic conductivity and an increase in interfacial resistance, significantly deteriorating battery performance. To address these issues, research has been conducted on the partial incorporation of the spinel structure. The spinel structure offers a three-dimensional lithium-ion diffusion pathway, enhancing conductivity and improving structural stability, thereby reducing deformation during charge and discharge cycles. However, relying solely on the spinel structure may lead to lower initial capacity. Therefore, an optimal technology that combines both layered and spinel structures is required to achieve superior performance. Conventionally, the spinel structure has been regarded as a trace of the degradation of layered positive materials. The spinel structure is thermodynamically more stable than the layered structure and develops as a result of positive material degradation, particularly at the secondary particle surface where the positive material comes into contact with the electrolyte. SUMMARY OF THE INVENTION The technical objects of the present disclosure are not limited to the foregoing technical objects, and other non-mentioned technical objects will be clearly understood by those skilled in the art from the description below. The present invention provides a nano-composite positive active material that enhances stability through doping with elements such as Mo, Ta, and W, while also improving rate capability and lifespan characteristics. The positive active material for a lithium-ion secondary battery according to the present invention includes secondary particles composed of a group of primary particles, wherein the primary particles comprise a nanocomposite in which a spinel (Fd3m) structure and a layered (R3m) structure are mixed at the nanoscale. Generally, the spinel structure is a trace of degradation found in a band-like form on the surface of primary particles in positive materials after charge and discharge cycles. However, the nanocomposite spinel structure according to the present invention is a structure observed in the initial state before the operation of the positive material and is not a trace of degradation. Furthermore, the spinel structure is characterized by being present in a nanocomposite form inside the primary particles rather than appearing as a band-like formation on the surface of the primary particles. Additionally, in the SAED electron diffraction image, electron diffraction spots S(a, a, a+2) and S(b, b, b-2) may be observed. S() represents the spinel structure, while L() represents the layered crystal structure. Furthermore, in the SAED electron diffraction image, the diffraction peak intensity obtained from the L(0, -1, -2-3(m-1)) plane and the S(a, a, a+2) plane may satisfy the relationship I(L(0, -1, -2-3(m-1))) > I(S(a, a, a+2)). Similarly, the diffraction peak intensity obtained from the L(0, 1, 2+3(n-1)) plane and the S(b, b, b-2) plane may satisfy the relationship I(L(0, 1, 2+3(n-1))) > I(S(b, b, b-2)). Additionally, the maximum length passing through the center of the cross-sectional area of the spinel-structured region may range from 1 nm to 100 nm, and the cross-sectional area of the spinel-s