Positive electrode composite material

Abstract

The present disclosure is related to a positive electrode composite material comprising a positive electrode active material and CNTs. The positive electrode composite material comprises Li, M', and O, wherein M' comprises: - Ni in a content x, wherein 20 at% ≤ x ≤ 50 at%, relative to M'; - Mn in a content y, wherein 30 at% ≤ y ≤ 70 at%, relative to M'; - Co in a content z, wherein 0 at% ≤ z ≤ 5 at%, relative to M'; - Al in a content a, wherein 0.01 at% < a ≤ 5 at%, relative to M', - D in a content b, wherein 0 at% ≤ b ≤ 5 at%, relative to M', wherein D is at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Na, Nb, Si, Sr, Ti, V, W, Y, Zn, and Zr; - S in a content of c, wherein 0.01 at% ≤ c ≤ 5 at%, relative to M', and - wherein x+y+z+a+b+c is 100 at%, wherein x, y, z, a, b, and c are measured by ICP.

Description

[0001] POSITIVE ELECTRODE COMPOSITE MATERIAL

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a positive electrode composite material comprising a positive electrode active material and carbon nanotubes (CNTs). The present disclosure relates to a positive electrode composite material comprising CNTs, lithium (Li), nickel (Ni), manganese (Mn), aluminum (Al), sulfur (S), oxygen (O), or a combination thereof; a method for preparing said positive electrode composite material; uses of said positive electrode composite material; a battery comprising said positive electrode composite material; and a use of said battery.

[0004] BACKGROUND

[0005] Secondary batteries have become increasingly vital in modern energy storage systems, powering a wide array of devices ranging from portable electronics to electric vehicles. As the development of small and lightweight electronic products, electronic devices, communication devices and the like have advanced rapidly and a need for electric vehicles has widely emerged with respect to environmental issues, there is a demand for improvement of performance of secondary batteries used as power sources for these products. With the growing demand for high-capacity, long-lasting, and stable rechargeable batteries, there is a critical need for the development of advanced positive electrode active materials that can meet the stringent requirements of various battery applications.

[0006] Many positive electrode active materials used in lithium-ion rechargeable batteries are metal oxides, which may not exhibit high conductivity. High conductivity is an important consideration for positive electrode active materials because highly conductive positive electrode active materials facilitate the efficient transport of electrons. In addition, high conductivity may help in reducing the internal resistance of the battery. In order to enhance the conductivity of positive electrode active materials, the addition of a conductive agent has been employed.

[0007] CNTs are known for use as a conductive agent in positive electrode active materials. CNTs have attracted attention due to their mechanical, electrical, and chemical properties.

[0008] For example, Guo et al., Metals, 2023, 13(1), 36 discloses that the lithium-ion rechargeable battery employing the positive electrode active material comprising nickel (Ni), cobalt (Co) and manganese (Mn) combined with CNTs as a conductive agent. The authors found the battery had a relatively poor cycle performance. They attempted to solve this problem by combining the positive electrode active material with the CNTs annealed at a temperature between 2000 and 2800 °C for at least 180 minutes. However, this requires a considerable amount of energy for annealing the CNTs.

[0009] The present disclosure provides a positive electrode composite material, which comprises a positive electrode active material and CNTs as a conductive agent, and exhibits improved cycle-life of lithium-ion rechargeable batteries.

[0010] The present disclosure provides a method for preparing said positive electrode composite material. The present disclosure provides uses of said positive electrode composite material.

[0011] The present disclosure provides a battery comprising said positive electrode composite material.

[0012] The present disclosure provides a use of said battery.

[0013] SUMMARY

[0014] The present positive electrode composite material comprises a positive electrode active material and CNTs. The positive electrode active material is a lithium transition metal-based oxide comprising Li, M', and O, wherein M' comprises:

[0015] Ni in a content x, wherein 20 at% < x < 50 at%, relative to M';

[0016] Mn in a content y, wherein 30 at% < y < 70 at%, relative to M';

[0017] Co in a content z, wherein 0 at% < z < 5 at%, relative to M';

[0018] - Al in a content a, wherein 0.01 at% < a < 5 at%, relative to M',

[0019] D in a content b, wherein 0 at% < b < 5 at%, relative to M', wherein D is at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Na, Nb, Si, Sr, Ti, V, W, Y, Zn, and Zr;

[0020] S in a content of c, wherein 0.01 at% < c < 5 at%, relative to M', and wherein x+y+z+a+b+c is 100 at%, wherein x, y, z, a, b, and c are measured by Inductively Coupled Plasma (ICP).

[0021] Said Al may be incorporated by mixing a metal oxide essentially comprising Li and Mn during the preparation of the positive electrode active material. Said CNTs may be incorporated by mixing the positive electrode active material with a solution comprising CNTs.

[0022] By presence of Al and S in a positive electrode active material, the cycle-life of a positive electrode composite material comprising the positive electrode active material and CNTs improves.

[0023] The present disclosure provides a method comprising consecutive steps of: preparing a lithium transition metal-based oxide compound; mixing the lithium transition metal-based oxide compound with AI2O3 to obtain a first mixture; heating the first mixture in an oxidizing atmosphere at a temperature of about 250°C or more, preferably about 500°C or more, about 1000°C or less, preferably about 950°C or less, for a time of about 1 hour or more, preferably 2 hours or more, about 20 hours or less, preferably about 15 hours or less to obtain a positive electrode active material; mixing the positive electrode active material with a suspension comprising CNTs to obtain a second mixture; and

[0024] - drying the second mixture to obtain a positive electrode composite material.

[0025] The present disclosure provides the use of said positive electrode composite material for the production of a battery. The present disclosure provides the use of said positive electrode composite material improving the life cycle of a battery. The present disclosure provides a battery comprising said positive electrode composite material. The present disclosure provides the use of said battery comprising said positive electrode composite material.

[0026] BRIEF DESCRIPTION OF THE FIGURES

[0027] Figure 1 is a graph that shows the DCR value according to the number of cycles of each example and comparative examples.

[0028] DETAILED DESCRIPTION OF THE DISCLOSURE

[0029] In the following detailed description, preferred embodiments are described in detail to enable practice of the present disclosure. Although the present disclosure is described with reference to these specific preferred embodiments, it will be understood that the present disclosure is not limited to these preferred embodiments. To the contrary, the present disclosure includes numerous alternatives, modifications and equivalents as will become apparent from consideration of the following detailed description and accompanying drawings. Unless otherwise indicated, it is not meant that the alternatives, modifications, and equivalents described herein are understood as separate, non-combinable, embodiments. That is, provided it is technically feasible, the different parts of the present disclosure may be combined with one another.

[0030] In this specification, "at%" signifies atomic percentage. The at% or "atomic percent" of a given element means a percentage of atoms of said element among all atoms in a claimed composition. ICP provides weight percent (wt%) of each element included in a material whose composition is determined by this technique. As used herein, ICP means Inductively Coupled Plasma, and the measurement by ICP may be performed as described in "EXPERIMENTAL TESTS USED IN THE EXAMPLES AND THE COMPARATIVE EXAMPLES, B) ICP analysis." Conversion from wt% to at% is as follows: at% of a first element Ei (Eati) in a material can be converted from a given wt% of said first element Ei Ewti) in said material by applying the following formula, wherein Eawi is a standard atomic weight (molecular weight) of the first element EifEwti is wt% of an ithelement Ei, EaWiis a standard atomic weight (molecular weight) of said ithelement Ei, and n is an integer which represents the number of types of all elements included in the material.

[0031] "about” as used herein referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of + / -20% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -1% or less, and still more preferably + / -0.1% or less of and from the specified value, in so far such variations are appropriate to perform in the present disclosure. However, it is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

[0032] Positive Electrode Composite Material

[0033] The present disclosure relates to a positive electrode composite material comprising a positive electrode active material and CNTs. The present positive electrode active material is a lithium transition metal-based oxide comprising Li, M', and O, wherein M' comprises:

[0034] Ni in a content x, wherein 20 at% < x < 50 at%, relative to M';

[0035] Mn in a content y, wherein 30 at% < y < 70 at%, relative to M';

[0036] Co in a content z, wherein 0 at% < z < 5 at%, relative to M';

[0037] - Al in a content a, wherein 0.01 at% < a < 5 at%, relative to M',

[0038] D in a content b, wherein 0 at% < b < 5 at%, relative to M', wherein D is at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Na, Nb, Si, Sr, Ti, V, W, Y, Zn, and Zr;

[0039] S in a content of c, wherein 0.01 at% < c < 5 at%, relative to M', and wherein x+y+z+a+b+c is 100 at%, wherein x, y, z, a, b, and c are measured by ICP.

[0040] In the frame work of the present disclosure, CNTs are coaxial circular tubes mainly composed of a dozen of layers of carbon atoms arrayed in hexagon. CNTs typically have good mechanical, electrical, and chemical properties due to their light weight and hexagon structure. CNTs have a high aspect ratio and a large specific area, and can form three- dimensional (3D) conductive network by contacting other CNTs and a positive electrode active material. Therefore, it has been suggested that using CNTs as a conductive agent for a positive electrode in lithium-ion rechargeable batteries has advantages compared to other conductive agents such as carbon black, acetylene black, graphite, or the like. While not wishing to be bound by theory, it is believed CNTs show advantages because they require a lower loading than the mentioned conductive agents.

[0041] The cycle-life of a lithium-ion rechargeable battery may be affected by using CNTs as a conductive agent for a positive electrode active material. The cycle-life refers to the number of charge and discharge cycles a battery can undergo before its capacity degrades to a point where performance is negatively impacted. Cycle-life is a factor in determining the longterm performance and durability of a rechargeable battery.

[0042] Batteries employing a positive electrode active material to which CNTs are added can exhibit a relatively poor cycle-life. A positive electrode composite material comprising a positive electrode active material and CNTs as disclosed herein may provide batteries with an acceptable cycle-life. The cycle-life of the positive electrode composite material comprising Al and S with CNTs can be even greater than that of a positive electrode active material comprising Al and S without CNTs. It is believed that addition of CNTs to a positive electrode active material deteriorates the cycle-life. Furthermore, the positive electrode composite material comprising Al and S with CNTs can exhibit a higher initial charge capacity (CQ1) compared to a positive electrode active material comprising Al and S without CNTs or a positive electrode composite material with CNTs but not comprising Al or S.

[0043] In a preferred embodiment, about 60 at% < x < about 95 at%, preferably about 70 at% < x < about 93 at%, more preferably about 75 at% < x < about 90 at%, more preferably still about 78 at% < x < about 90 at%.

[0044] In a preferred embodiment, about 1 at% < y < about 25 at%, preferably about 5 at% < y

[0045] < about 20 at%, more preferably about 7 at% < y < about 15 at%, more preferably still about 8 at% < y < about 12 at%.

[0046] In a preferred embodiment, about 1 at% < z < about 18 at%, preferably about 5 at% < z

[0047] < about 15 at%, more preferably about 7 at% < z < about 13 at%, more preferably still about 8 at% < z < about 12 at%.

[0048] In a preferred embodiment, about 0.1 at% < a < about 3 at%, preferably about 0.15 at%

[0049] < a < about 2 at%, more preferably about 0.2 at% < a < about 1 at%, more preferably still about 0.3 at% < a < about 0.7 at%. In a preferred embodiment, 0 at% < b < about 3 at%, preferably 0 at% < b < about 2 at%, more preferably 0 at% < b < about 1 at%, more preferably still 0 at% < a < about 0.5 at%.

[0050] In a preferred embodiment, about 0.01 at% < c < about 3 at%, preferably about 0.01 at%

[0051] < c < about 2 at%, more preferably about 0.01 at% < c < about 1.5 at%, more preferably about 0.01 at% < c < about 1 at%, more preferably about 0.01 at% < c < about 0.5 at%, more preferably about 0.05 at% < c < about 0.5 at%, more preferably still about 0.1 at%

[0052] < c < about 0.5 at%.

[0053] The positive electrode active material constituting the positive electrode composite material according to the present disclosure may be covered with the CNTs on at least a part of its surface. While not wishing to be bound by theory, the CNTs are thought to form a conductive network through line-to-line conductive contacts with each other, covering the surface of the positive electrode active material and thereby establishing conductive contacts with the positive electrode active material.

[0054] In a preferred embodiment, the positive electrode composite material comprises carbon in a content of d, wherein about 600 ppm < d < about 15000 ppm, preferably about 1000 ppm

[0055] < d < about 12000 ppm, more preferably about 1500 ppm < d < about 11000 ppm, more preferably still about 1600 ppm < d < about 10500 ppm, relative to the total weight of the positive electrode composite material, as measured by carbon analyzer.

[0056] CNTs can exist in at least two forms: single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs). SWCNTs have a tubular structure composed of a single layer of carbon atoms arranged in a hexagonal lattice. MWCNTs have a cylindrical nanostructure composed of multiple concentric layers of carbon nanotubes nested within one another. The number of layers can vary, and the spacing between the layers may be typically on the order of a few angstroms.

[0057] In a preferred embodiment, the CNTs used herein are SWCNTs. Without wishing to be bound by any theory, when the weight of SWCNTs is comparable to that of MWCNTs, a positive electrode composite material comprising SWCNTs exhibits a greater cycle-life than the one comprising MWCNTs. The contents of MWCNTs and SWCNTs are based on the total weight of a positive electrode composite material. The cycle-life of a battery utilizing SWCNTs may exceed that of a battery utilizing MWCNTs, even when the ratio of MWCNTs content to SWCNTs content ranges from 2 to 50. When the added amount of SWCNTs is smaller than that of MWCNTs, the cycle-life of a battery utilizing SWCNTs may be comparable to that of a battery utilizing MWCNTs. In a preferred embodiment, when CNTs are SWCNTs, about 600 ppm < d < about 5000 ppm, preferably about 1000 ppm < d < about 4000 ppm, preferably about 1500 ppm < d < about 3500 ppm, preferably about 1600 ppm < d < about 3000 ppm.

[0058] Method for Preparing Positive Electrode Composite Material

[0059] The present disclosure relates to a method for preparing a positive electrode composite material, wherein the method comprises: preparing a lithium transition metal-based oxide compound; mixing the lithium transition metal-based oxide compound with AI2O3 to obtain a first mixture; heating the first mixture in an oxidizing atmosphere in a furnace at a temperature between 250°C and 1000°C, preferably between 500°C and 950°C, for a time between 1 hour and 20 hours, preferably between 3 hours and 15 hours to obtain a positive electrode active material; mixing the positive electrode active material with a suspension comprising CNTs to obtain a second mixture; and

[0060] - drying the second mixture to obtain the positive electrode composite material.

[0061] Any suitable lithium transition metal-based oxide compound may be used herein. For example, the lithium transition metal-based oxide compound may comprise Li, Mn and O. The lithium transition metal-based oxide compound may further comprise Ni, Co, and combinations thereof. The lithium transition metal-based oxide compound may further comprise at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Na, Nb, Si, Sr, Ti, V, W, Y, Zn, and Zr.

[0062] The lithium transition metal-based oxide compound may be prepared by any suitable method. For example, the method may comprise heating a mixture comprising a Li source and a transition metal composite precursor, wherein the transition metal composite precursor is (oxy) hydroxide or oxide comprising Mn and Ni. The Li source is preferably U2CO3 and U2SO4. While not wishing to be bound by theory, it is believed U2CO3 and U2SO4 allow rapid and complete synthesis of the lithium transition metal-based oxide at lower temperature, and can result in a good battery life cycle and safety profile.

[0063] In a preferred embodiment, the AI2O3 used herein is powder. Any suitable amount of AI2O3 may be used herein. For example, from about 0.1 wt% to about 5 wt%, from about 0.1 wt% to about 3 wt%, from about 0.1 wt% to about 2 wt%, from about 0.1 wt% to about 1 wt%, relative to the total weight of the mixture. The positive electrode active material obtained by heating the mixture of the lithium transition metal-based oxide compound and AI2O3 may be mixed and heated, and then mixed with the CNTs. Grinding may be performed using a mortar, air classifier mill, universal mill, or planetary ball mill, with the condition that particles agglomerated due to heating can be separated. Sieving may be performed using a 300-mesh sieve to filter particles with a length greater than about 100 pm.

[0064] The CNTs used herein may be SWCNTs. The CNTs may be in any suitable form for combining with the positive electrode active material. For example, the CNTs may be suspended in N-methyl-2-pyrrolidone (NMP) solvent or water, preferably NMP solvent to form the suspension. The suspension comprising NMP solvent may further comprise a dispersing agent such as sodium dodecyl sulfate, polyvinylpyrrolidone, polyvinyl alcohol, dimethylformamide, and dimethyl sulfoxide, etc. to disperse the CNTs. The suspension comprising water may further comprise a dispersing agent such as sodium dodecyl sulfate, cetyltrimethylammonium bromide, polyvinylpyrrolidone, polyvinyl alcohol, and l-ethyl-3- methylimidazolium bromide, etc. Any suitable amount of SWCNTs may be used herein. For example, from about 0.01 wt% to about 0.5 wt%, from about 0.02 wt% to about 0.3 wt%, from about 0.03 wt% to about 0.2 wt%, from about 0.04 wt% to about 0.1 wt%, relative to the total weight of the suspension.

[0065] In certain embodiments, the mixture comprising SWCNTs and the positive electrode active material may be dried at temperature ranging from about 80 °C to about 180 °C, from about 90 °C to about 170 °C, from about 100 °C to about 160 °C, from about 110 °C to about 150 °C. The mixture may be dried for any suitable time, for example, from about 5 hours to about 17 hours, from about 7 hours to about 15 hours, from about 9 hours to about 14 hours, from about 10 hours to about 13 hours. As required, the mixture may be ground and sieved to obtain the positive electrode composite material. Sieving may be performed using a 300-mesh sieve to filter particles with a length greater than about 100 pm.

[0066] Battery

[0067] The present disclosure further relates to a battery comprising the positive electrode composite material as described herein. The present battery may have a cycle-life at 45°C of about 350 or greater, about 400 or greater, about 450 or greater.

[0068] Use of Battery

[0069] The present disclosure further relates to a use of the present battery. For example, use in an electric or hybrid-electric vehicle. As appreciated by a person skilled in the art, all embodiments directed to the positive electrode composite material as described herein may apply mutatis mutandis to the method for preparing said positive electrode composite material, the battery comprising said positive electrode composite material, and the use of said battery.

[0070] EXPERIMENTAL TESTS USED IN THE EXAMPLES AND THE COMPARATIVE EXAMPLES

[0071] The following analysis methods are used in the Examples:

[0072] A) Particle size distribution (PSD) analysis

[0073] The PSD is measured using a Malvern Mastersizer 3000 with Hydro MV wet dispersion accessory after dispersing examples as described herein below of positive electrode active material powders in an aqueous medium. To improve the dispersion of the positive electrode active material powder examples, sufficient ultrasonic irradiation and stirring is applied, and an appropriate surfactant is introduced. D50 is defined as the particle size at 50% of the cumulative volume % distribution.

[0074] B) ICP analysis

[0075] The Ni, Mn, Co, Al, and S contents of the positive electrode active material powder is measured with the ICP method by using an Agilent ICP 720-ES. 2 grams of product powder sample is dissolved into 10 mL of high purity hydrochloric acid in an Erlenmeyer flask. The flask is covered by a glass and heated on a hot plate at 380°C until complete dissolution of the precursor. After being cooled to room temperature, the solution of the Erlenmeyer flask is poured into a 250 mL volumetric flask. Afterwards, the volumetric flask is filled with deionized water up to the 250 mL mark, followed by complete homogenization. An appropriate amount of solution is taken out by pipette and transferred into a 250 mL volumetric flask for the 2nddilution, where the volumetric flask is filled with internal standard and 10% hydrochloric acid up to the 250 mL mark and then homogenized. Finally, this 50 mL solution is used for ICP measurement.

[0076] C) Scanning Electron Microscope (SEM) measurement

[0077] The morphology and the primary particle size of the positive electrode active material are analyzed by a scanning electron microscopy (SEM) technique. The measurement is performed with a JEOL JSM 7100F under a high vacuum environment of 9.6xl0-5Pa at 25 °C.

[0078] D) Energy-dispersive X-ray spectroscopy (EDS) analysis

[0079] Using the sample of the positive electrode active materials, the carbon map is analyzed by energy-dispersive X-ray spectroscopy (EDS). The EDS is performed by JEOL JSM 7100F SEM equipment with a 50 mm2X-MaxN EDS sensor from Oxford instruments. E) Single-layer Pouch Cell Testing

[0080] El) Single-layer Pouch Cell preparation

[0081] 33 mAh pouch-type cells are prepared as follows: the positive electrode active material powder, Li-435 (Denka) as positive electrode conductive agents, and polyvinylidene fluoride (PVDF S5130, Solvay) as a positive electrode binder are added to N-methyl-2-pyrrolidone (NMP) as a dispersion medium so that the mass ratio of the positive electrode active material powder, the positive electrode conductive agents, positive electrode binder, positive electrode dispersant agent is set at 95.8 / 2.0 / 0.2 / 2.0. Thereafter, the mixture is mixed to prepare a positive electrode mixture slurry. The resulting positive electrode mixture slurry is then applied onto one side of a positive electrode current collector, made of a 20 pm thick aluminum foil. The positive electrode is punched to obtain a sheet with total area of 11.7 cm2. Typical loading weight of a positive electrode active material, conductive agent, and binder is about 12.0±lmg / cm2The electrode is then dried and calendared. In addition, an aluminum plate serving as a positive electrode current collector tab is arc-welded to an end portion of the positive electrode.

[0082] Commercially available negative electrodes are used. In short, a mixture of natural graphite, carbon (Super P (Imerys)), carboxy-methyl-cellulose-sodium, and styrene- butadiene-rubber, in a mass ratio of 95.0 / 1 / 1.5 / 2.5, is applied on one side of a copper foil. A nickel plate serving as a negative electrode current collector tab is arc-welded to an end portion of the negative electrode. Typical loading weight of a negative electrode active material is about 10 ± 1 mg / cm2.

[0083] A sheet of the positive electrode, a sheet of the negative electrode, and a sheet of the microporous polymer separator (13 pm) interposed between them. The assembly and the electrolyte are then put in an aluminum laminated pouch in a dry room with dew point of - 50°C, so that a flat pouch-type lithium secondary battery is prepared. The design capacity of the secondary battery is 33 mAh when discharged to 4.60 V. The cell testing procedure uses a 1 C current definition of 33 mA / g.

[0084] E2) Cycle test

[0085] A. Pre-charging and formation

[0086] The non-aqueous electrolyte solution is impregnated into the prepared cell for 12 hours at room temperature. The cell is pre-charged with the current of 0.1 C, time cut-off 3hr of its theoretical capacity at room temperature. The cell is then degassed using a pressure of - 760 mmHg for 30 seconds and the aluminum pouch is sealed. During measurement, the pouch is assembled in a press jig provided with silicon pad. The cell is charged with a current of 0.33 C in CC mode (constant current) up to 4.6 V and CV mode (constant voltage) until a cut-off current of C / 20 is reached. The cell is discharged with a current of 0.33 C in CC mode down to 2.0 V at 45 °C. After that, the cell is charged with a current of 0.33 C in CC mode (constant current) up to 4.4 and CV mode (constant voltage) until a cut-off current of C / 20 is reached. The cell is discharged with a current of 0.33 C in CC mode down to 2.5 V at 25 °C.

[0087] B. Cycle life test

[0088] The cell is charged and discharged continuously under the following conditions at 45°C, to determine their charge-discharge cycle performance:

[0089] - Charge is performed in CC mode under 1 C rate up to 4.4 V, then CV mode until C / 20 is reached,

[0090] - The cell is then set to rest for 10 minutes,

[0091] - Discharge is done in CC mode at 1 C rate down to 2.5 V,

[0092] - The cell is then set to rest for 10 minutes,

[0093] - The charge-discharge cycles proceed until 400 cycles. Every 100 cycles, the discharge is done at 1 C rate in CC mode down to 2.5 V.

[0094] The internal resistance or direct current resistance (DCR) is measured at 2.5C for 10 s at the beginning of every 100 cycles repetition and the end of 400thcycles at room temp.

[0095] The cycle life is defined as the number of charge-discharge cycles when the capacity degrades to 80%.

[0096] EXAMPLES

[0097] The present disclosure is further illustrated in the following examples:

[0098] Comparative Example 1 (CEX1)

[0099] A positive electrode active material, further called CEX1, is prepared according to the following steps:

[0100] 1) Pre heating: a precursor having Nio.35Mno.65 in hydroxide or oxyhydroxide form was pre heated at 400°C under air atmosphere for 9hours and 30minutes followed by cooling, grinding, and sieving to prepare pre-heated material.

[0101] 2) First mixing: the pre-heated material and IJ2CO3, IJ2SO4 as a lithium source were homogeneously blended. Li2COs was added with a lithium to metal (Ni and Mn) ratio of 1.35 and Li2SO4 was added within 4~5 wt% of pre-heated material.

[0102] 3) First heating : the first mixture was heated at 925°C for llhours and 6minutes under air condition followed by cooling, grinding, and sieving to prepare first heated material. 4) Washing : the first heated material was performed by mixing with deionized water in a 1 : 1 ratio followed by drying in 150°C for 15hours under nitrogen atmosphere to prepare first washed material.

[0103] 5) Second heating : the first washed material was heated at 650°C for 12hours under air condition followed by cooling, grinding, and sieving to prepare CEX1.

[0104] Comparative Example 2 (CEX2)

[0105] CEX2 was prepared according to the same method as CEX1, except step 4) and 5). The carbon nano tube powder mixed with NMP solvent (0.06 wt%) was added in the Step 3) after heating followed by drying at 130°C for 12 hours, mortal grinding and sieving to prepare CEX2.

[0106] Example 1 (EXI)

[0107] EXI was prepared according to the same method as CEX1, except additional following steps:

[0108] 1) Second mixing : the prepared CEX1 was mixed homogeneously with AhO3(0.15 wt%) powder to prepare a second mixture.

[0109] 2) Second heating : the second heated material was heated at 650°C for 12 hours under air condition followed by cooling, grinding and sieving to prepare a third heated material.

[0110] 3) Third mixing : the third heated material was mixed homogeneously with carbon nano tube with N-methyl-2-pyrrolidone(NMP) solvent (0.06 wt%) followed by drying at 130°C for 12 hours, mortal grinding and sieving to prepare EXI.

[0111] Results

[0112] Table 1. Summary of the electrochemical performance analyzed by single-layer pouch cell testing.

[0113] Table 1 shows the electrochemical performances analyzed by single-layer pouch cell testing. EXI having aluminum, sulfur and carbon nano tube coating on the surface shows the highest value in CQ1 and DQ1 with the highest efficiency compared to CEX1 and CEX2. More importantly, it can be seen that the cycle life of EXI is significantly improved compared to CEX1 and CEX2, which means the improvement of electrochemical performances. Electrochemical performance improvement is also proven through DCR growth in table 1. DCR is the internal resistance or direct current resistance which is better with lower value. As Table 1 shows, EXI consistently has the lowest value for DCR growth percentage throughout the 400 cycles, which means it shows better performance than others.

Claims

CLAIMS1. A positive electrode composite material comprising a positive electrode active material and carbon nanotubes, wherein the positive electrode active material is a lithium transition metal-based oxide comprising lithium, M', and oxygen, wherein M' comprises:Ni in a content x, wherein 20 at% < x < 50 at%, relative to M';Mn in a content y, wherein 30 at% < y < 70 at%, relative to M';Co in a content z, wherein 0 at% < z < 5 at%, relative to M';- Al in a content a, wherein 0.01 at% < a < 5 at%, relative to M',D in a content b, wherein 0 at% < b < 5 at%, relative to M', wherein D is at least one element selected from the group consisting of B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Na, Nb, Si, Sr, Ti, V, W, Y, Zn, and Zr;S in a content of c, wherein 0.01 at% < c < 5 at%, relative to M', and wherein x+y+z+a+b+c is 100 at%, wherein x, y, z, a, b, and c are measured by ICP.

2. The positive electrode composite material according to claim 1, wherein 25 at% < x <45 at%, preferably 25 at% < x < 40 at%, more preferably 30 at% < x < 40 at%.

3. The positive electrode composite material according to claim 1 or 2, wherein 40 at% < y < 70 at%, preferably 50 at% < y < 70 at%, more preferably 60 at% < y < 70 at%.

4. The positive electrode composite material according to any of the previous claims, wherein 0 at% < z < 3 at%, preferably 0 at% < z < 2 at%, more preferably z is 0 at%.The positive electrode composite material according to any of the previous claims, wherein 0.1 at% < a < 3 at%, preferably 0.15 at% < a < 2 at%, more preferably 0.2 at% < a < 1 at%.

6. The positive electrode composite material according to any of the previous claims, wherein 0.01 at% < c < 3 at%, preferably 0.01 at% < c < 2 at%, more preferably 0.01 at% < c < 1.5 at%.

7. The positive electrode composite material according to claim 6, wherein 0.01 at% < c <1 at%, preferably 0.01 at% < c < 0.5 at%, more preferably 0.1 at% < c < 0.5 at%.

8. The positive electrode composite material according to any of the previous claims, wherein the positive electrode active material is covered with the carbon nanotubes on at least a part of a surface of the positive electrode active material.

9. The positive electrode composite material according to any of the previous claims, wherein the positive electrode composite material comprises carbon in a content of d, wherein 100 ppm < d < 15000 ppm, preferably 200 ppm < d < 12000 ppm, more preferably 300 ppm < d < 11000 ppm, relative to a total weight of the positive electrode composite material, as measured by carbon analyzer.

10. The positive electrode composite material according to claim 9, wherein the carbon nanotubes are single walled carbon nanotubes, and 400 ppm < d < 5000 ppm, preferably 500 ppm < d < 4000 ppm, more preferably 600 ppm < d < 3500 ppm.

11. A method for preparing a positive electrode composite material according to any of the previous claims, wherein the method comprises consecutive steps of: preparing a lithium transition metal-based oxide compound; mixing the lithium transition metal-based oxide compound with aluminum source to obtain a first mixture; heating the first mixture in an oxidizing atmosphere in a furnace at a temperature between 250°C and 1000°C, preferably between 500°C and 950°C, for a time between 1 hour and 20 hours, preferably between 3 hours and 15 hours to obtain a positive electrode active material; mixing the positive electrode active material with a suspension comprising carbon nanotubes to obtain a second mixture; and- drying the second mixture to obtain the positive electrode composite material.

12. The method according to claim 11, wherein aluminum source is AI2O3.

13. The method according to claim 11 or 12, wherein the carbon nanotubes are suspended in water or N-methyl-2-pyrrolidone(NMP).

14. A battery comprising the positive electrode composite material according to any of claims 1 to 10.

15. Use of the battery according to claim 14 in an electric vehicle or in a hybrid electric vehicle.

Images