KR-20260067979-A - LITHIUM SECONDARY BATTERY

KR20260067979AKR 20260067979 AKR20260067979 AKR 20260067979AKR-20260067979-A

Abstract

The present invention relates to a lithium secondary battery exhibiting excellent capacity characteristics and improved rapid charging characteristics. The lithium secondary battery comprises: a positive electrode including a positive active material including a lithium-ion manganese-based oxide; a negative electrode including a negative current collector and a negative active material layer formed on the negative current collector and including a negative active material; and a separator or electrolyte layer between the positive electrode and the negative electrode. The negative active material layer has a pore ratio of 1 to 1.4 between a lower layer that is in contact with the negative current collector and corresponds to 50% of the total thickness of the negative active material layer, and an upper layer excluding the lower layer, and the average pore ratio of the entire negative active material layer can be 6% to 15%.

Inventors

장다은
조일영
노남규

Assignees

주식회사 엘지에너지솔루션

Dates

Publication Date: 20260513
Application Date: 20250930
Priority Date: 20241104

Claims (13)

A cathode comprising a cathode active material comprising a lithium manganese-based oxide having a layered crystal structure, wherein the molar ratio of lithium to the total number of moles of metals excluding lithium exceeds 1, and manganese among the total metals excluding lithium is contained in an amount of 50 mol% or more; A cathode comprising a cathode current collector and a cathode active material layer formed on the cathode current collector and including a cathode active material; and It includes a separator or electrolyte layer between the anode and the cathode, and The above-mentioned negative electrode active material layer is in contact with the negative electrode current collector and, between the lower layer corresponding to 50% of the total thickness of the negative electrode active material layer and the remaining upper layer excluding the lower layer, the pore ratio of Formula 1 below is 1 to 1.4. A lithium secondary battery in which the average pore ratio of the entire negative electrode active material layer is 6% to 15%: [Equation 1] Pore ratio (%) = (Pore ratio of the upper layer of the cathode active material layer) / (Pore ratio of the lower layer of the cathode active material layer) In the above Equation 1, the pore ratio of each upper and lower layer is calculated from the area of the pores relative to the total area of the upper or lower layer when the cross-section in the thickness direction of the cathode active material layer is analyzed using an electron microscope.
In claim 1, the above-mentioned lithium manganese-based oxide is a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1] Li 1+a [Mn 1-(b+c) Ni b M c ]O 2+d In the above chemical formula 1, M comprises one or more selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, and 0.05≤a≤0.45, 0<b≤0.5, 0≤c≤0.5, 0<b+c≤0.5, 0≤d≤1, and
In claim 1, the lithium secondary battery having a structure in which the over-lithium manganese oxide comprises a rock salt-type lithium manganese oxide and a layered lithium transition metal oxide.
In claim 3, the above-mentioned lithium manganese-based oxide is a positive active material represented by the following chemical formula 2: [Chemical Formula 2] X Li 2 MnO 3 · ( 1- In the above chemical formula 2, 0.2≤X≤0.5, 0.4≤y<1, 0≤z≤0.1, 0≤w≤0.2, and M' includes one or more selected from the group consisting of Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr.
A lithium secondary battery according to claim 1, wherein the pore ratio of the lower layer among the negative electrode active material layers is 5% to 15%.
A lithium secondary battery according to claim 1, wherein the pore ratio of the upper layer among the negative electrode active material layers is 6% to 18%.
In claim 1, the negative electrode active material layer comprises the negative electrode active material, a conductive material, and a binder, forming a lithium secondary battery.
A lithium secondary battery according to claim 1, wherein in the negative electrode active material layer, the upper layer and the lower layer comprise negative electrode active materials having different compositions, particle shapes, sphericity, or particle hardness.
A lithium secondary battery according to claim 1, wherein in the negative electrode active material layer, the upper layer and the lower layer comprise carbon-based negative electrode active materials having different particle shapes or sphericities in a rolled state.
In claim 9, the carbon-based negative electrode active material comprises natural graphite, artificial graphite, or a mixture thereof in a lithium secondary battery.
In claim 10, the lithium secondary battery wherein the lower layer comprises a greater content of natural graphite than the upper layer.
A lithium secondary battery according to claim 10, wherein the carbon-based negative electrode active material of the lower layer is composed of natural graphite, and the carbon-based negative electrode active material of the upper layer is composed of a mixture of natural graphite and artificial graphite or artificial graphite.
A lithium secondary battery according to claim 1, further comprising an electrolyte including a lithium salt and a non-aqueous organic solvent.

Description

Lithium Secondary Battery The present invention relates to a lithium secondary battery exhibiting excellent capacity characteristics and improved rapid charging characteristics. A lithium secondary battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive and negative electrodes include an active material capable of lithium ion intercalation and deintercalation. Lithium cobalt oxide ( LiCoO2 ), lithium nickel oxide ( LiNiO2 ), lithium manganese oxide ( LiMnO2 or LiMnO4, etc.), and lithium iron phosphate compounds ( LiFePO4 ) have been used as cathode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantage of high operating voltage and excellent capacity characteristics, but it is difficult to apply it commercially to large-capacity batteries due to the high cost and unstable supply of cobalt, which is the raw material. Lithium nickel oxide has poor structural stability, making it difficult to achieve sufficient lifespan characteristics. Meanwhile, lithium manganese oxide with a spinel structure has excellent stability but has the problem of poor capacity characteristics. Accordingly, lithium composite transition metal oxides containing two or more transition metals have been developed and are being used to compensate for the problems of lithium transition metal oxides containing Ni, Co, or Mn alone. Among these, as it has become known that oxides containing an excess of lithium while having a higher Mn content than other metals excluding lithium (hereinafter referred to as “high-lithium manganese oxides”) can secure high energy density as high-capacity active materials, research and interest in this area are increasing significantly. However, while lithium-rich manganese oxides have relatively high capacity and energy density, lithium secondary batteries containing them as cathode active materials have the disadvantage of insufficient rapid charging and output characteristics. This appears to be because, in addition to the above-mentioned lithium-rich manganese oxide cathode active material, a high-loading negative electrode must be applied, which may result in insufficient lithium ion mobility between the electrodes. Accordingly, there is a need to develop a lithium secondary battery that exhibits excellent capacity characteristics and energy density unique to the above-mentioned lithium manganese-based oxide cathode active material, while also exhibiting improved rapid charging characteristics. FIG. 1 is a schematic diagram illustrating the technical principle that enables rapid diffusion of lithium ions and rapid charging within the negative electrode in a lithium secondary battery of one embodiment of the invention. Figures 2a and 2b are electron microscope images of cross-sections in the thickness direction of the negative electrode active material layer included in the lithium secondary batteries of Comparative Examples 1 and 2, respectively. Figures 2c and 2d are electron microscope images of cross-sections in the thickness direction of the negative electrode active material layer included in the lithium secondary batteries of Examples 1 and 2, respectively. Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention. In the following specification, “lithium manganese oxide” may refer to a lithium metal oxide that includes a layered crystal structure, has a molar ratio of lithium to the total number of moles of metals excluding lithium exceeding 1, and contains manganese in an amount of 50 mol% or more among the total number of metals excluding lithium. In addition, "D 50 " refers to the particle size at the 50% reference of the volume cumulative particle size distribution of the positive active material. The above D 50 can be measured using the laser diffraction method. For example, after dispersing the positive active material powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiated with ultrasound of approximately 28 kHz at an output of 60 W, and then obtained a volume cumulative particle size distribution graph, and the particle size corresponding to 50% of the volume cumulative amount can be measured. Specific embodiments of the invention will be described in detail below. A lithium secondary battery according to one embodiment of the invention comprises: a positive electrode comprising a positive active material including a lithium-rich manganese oxide; a negative electrode comprising a negative current collector and a negative active material layer formed on the negative c