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 50 at% ≤ x ≤ 95 at%, relative to M'; - Mn in a content y, wherein 0 at% ≤ y ≤ 30 at%, relative to M'; - Co in a content z, wherein 0 at% ≤ z ≤ 20 at%, relative to M'; - Al in a content a, wherein 0 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 0.5 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), 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] The demand for lithium-ion rechargeable batteries has been consistently high in recent years due to their widespread use in various applications such as consumer electronics, electric vehicles (EVs), energy storage systems, and more. 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.

[0006] 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.

[0007] For example, Guo et al., Metals, 2023, 13(1), 36 discloses that the lithium-ion rechargeable battery employing the positive electrode active material comprising 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.

[0008] 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.

[0009] The present disclosure provides a method for preparing said positive electrode composite material. The present disclosure provides uses of said positive electrode composite material.

[0010] The present disclosure provides a battery comprising said positive electrode composite material.

[0011] The present disclosure provides a use of said battery. SUMMARY OF THE DISCLOSURE

[0012] The present positive electrode composite material comprises a positive electrode active material and CNTs. The positive electrode active material comprises Li, M’, and O, wherein M’ comprises:

[0013] Ni in a content x, wherein about 50 at% < x < about 95 at%, relative to M’;

[0014] Mn in a content y, wherein 0 at% < y < about 30 at%, relative to M’;

[0015] Co in a content z, wherein 0 at% < z < about 20 at%, relative to M’;

[0016] Al in a content a, wherein 0 at% < a < about 5 at%, relative to M’,

[0017] D in a content b, wherein 0 at% < b < about 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;

[0018] S in a content of c, wherein about 0.5 at% < c < about 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).

[0019] Said Al and S may be incorporated by mixing a metal oxide essentially comprising Li and Ni with a solution comprising aluminum sulfate (Al2(SO4)3) 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.

[0020] The present inventors have surprisingly found that the cycle-life of a positive electrode composite material comprising a positive electrode active material and CNTs may be improved by incorporating Al and S into the positive electrode active material.

[0021] 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 a solution comprising Al2(SO4)3 to obtain a first mixture; heating the first mixture in an oxidizing atmosphere at a temperature of about 250°C or more, preferably about 300°C or more, about 500°C or less, preferably about 400°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 drying the second mixture to obtain a positive electrode composite material.

[0022] 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.

[0023] BRIEF DESCRIPTION OF THE FIGURES

[0024] Figure 1 is the SEM image of CEX1 .1 (magnified 3000 times by JEOL JSM 71 OOF under 9.6x105Pa at

[0025] 25 °C).

[0026] Figure 2 is the SEM image of EX1 (magnified 3000 times by JEOL JSM 71 OOF under 9.6x10-5Pa at

[0027] 25 °C).

[0028] Figure 3 is the SEM-EDS image of CEX1.1 (magnified 10,000 times by JEOL JSM 71 OOF with a 50 mm2X-MaxN EDS sensor from Oxford instruments).

[0029] Figure 4 is the SEM-EDS image of EX1 (magnified 10,000 times by JEOL JSM 71 OOF with a 50 mm2X- MaxN EDS sensor from Oxford instruments).

[0030] DETAILED DESCRIPTION OF THE DISCLOSURE

[0031] 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.

[0032] 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, B1) ICP measurement.” 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 Eawiis a standard atomic weight (molecular weight) of the first element E-i, Ewtt is wt% of an Ithelement E, EaWj is a standard atomic weight (molecular weight) of said Ithelement E, and n is an integer which represents the number of types of all elements included in the material.

[0033] "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.

[0034] Positive Electrode Composite Material

[0035] The present disclosure relates to a positive electrode composite material comprising a positive electrode active material and CNTs. The present positive electrode active material comprises Li, M’, and O, wherein M’ comprises:

[0036] Ni in a content x, wherein about 50 at% < x < about 95 at%, relative to M’;

[0037] Mn in a content y, wherein 0 at% < y < about 30 at%, relative to M’;

[0038] Co in a content z, wherein 0 at% < z < about 20 at%, relative to M’;

[0039] Al in a content a, wherein 0 at% < a < about 5 at%, relative to M’,

[0040] D in a content b, wherein 0 at% < b < about 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;

[0041] S in a content of c, wherein about 0.5 at% < c < about 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.

[0042] 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.

[0043] 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 long-term performance and durability of a rechargeable battery. Cycle-life can be measured by the method described in “EXPERIMENTAL TESTS USED IN THE EXAMPLES AND THE COMPARATIVE EXAMPLES, F) Single-layer Pouch Cell Testing, F2) Cycle Test.”

[0044] Batteries employing a positive electrode active material to which CNTs are added can exhibit relatively poor cycle-lifes. 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. The measurement method of CQ1 is described in “EXPERIMENTAL TESTS USED IN THE EXAMPLES AND THE COMPARATIVE EXAMPLES, G) Coin cell testing.”

[0045] 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%.

[0046] In a preferred embodiment, about 1 at% < y < about 25 at%, preferably about 5 at% < y < about 20 at%, more preferably about 7 at% < y < about 15 at%, more preferably still about 8 at% < y < about 12 at%.

[0047] In a preferred embodiment, about 1 at% < z < about 18 at%, preferably about 5 at% < z < 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% < a < about 2 at%, more preferably about 0.2 at% < a < about 1 at%, more preferably still about 0.2 at% < a < about 0.5 at%.

[0049] 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 0.6 at% < c < about 3 at%, preferably about 0.65 at% < c < about 2 at%, more preferably about 0.7 at% < c < about 1.5 at%, more preferably still about 0.75 at% < c < about 1.2 at%.

[0051] 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. Figure 2 shows the SEM image of EX1 , where the CNTs cover at least a part of the surface of EX1 .

[0052] 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 < d < about 12000 ppm, more preferably about 1500 ppm < d < about 1 1000 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. The method of measuring the carbon content by carbon analyzer is described in “EXPERIMENTAL TESTS USED IN THE EXAMPLES AND THE COMPARATIVE EXAMPLES, C) Carbon analysis.”

[0053] 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. SWCNTs are available from OCSiAl and MWCNTs are available from LG Chem.

[0054] 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 cyclelife 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.

[0055] 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.

[0056] In a preferred embodiment, the soluble sulfur content ranges from about 0.35 at% to about 1.5 at%, preferably from about 0.5 at% to about 1 at%, preferably from about 0.6 at% to about 0.9 at%, as measured by ICP, wherein the content of soluble sulfur is equal to a decrease of a content of S relative to M’ as measured by ICP after having contacted the positive electrode composite material into deionized water for at least 5 minutes at 25 °C to form a slurry, filtered the slurry to form a filtered slurry, and dried the filtered slurry. The content of soluble sulfur can be associated to the amount of Ah(SO4)3 added during the preparation of the positive electrode composite material according to the first aspect of the present disclosure. The specific method of measuring the carbon content by carbon analyzer is described in “EXPERIMENTAL TESTS USED IN THE EXAMPLES AND THE COMPARATIVE EXAMPLES, B) ICP analysis, B2) Soluble sulfur measurement.”

[0057] Method for Preparing Positive Electrode Composite Material

[0058] 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 a solution comprising Ah(SO4)3 to obtain a first mixture; heating the first mixture in an oxidizing atmosphere in a furnace at a temperature between 250°C and 500°C, preferably between 300°C and 400°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 drying the second mixture to obtain the positive electrode composite material.

[0059] Any suitable lithium transition metal-based oxide compound may be used herein. For example, the lithium transition metal-based oxide compound may comprise Li, Ni and O. The lithium transition metal-based oxide compound may further comprise Mn, Co, and combinations thereof. The lithium transition metalbased 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.

[0060] 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 Ni, optionally, Mn, and optionally, Co. The Li source is preferably LiOH. While not wishing to be bound by theory, it is believed LiOH allows 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.

[0061] In a preferred embodiment, the Al2(SO4)3 used herein is dissolved in water, preferably deionized water. Any suitable amount of Al2(SO4)3 may be used herein. For example, from about 0.1 wt% to about 20 wt%, from about 1 wt% to about 10 wt%, from about 2 wt% to about 5 wt%, from about 3 wt% to about 4 wt%, relative to the total weight of the solution.

[0062] The positive electrode active material obtained by heating the mixture of the lithium transition metal-based oxide compound and the solution comprising Al2(SO4)3 may be ground and sieved, 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.

[0063] 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 1-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.

[0064] 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.

[0065] Batery

[0066] 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 450 or greater, about 475 or greater, about 500 or greater.

[0067] Use of Batery

[0068] The present disclosure further relates to a use of the present battery. For example, use in an electric or hybrid-electric vehicle.

[0069] 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] B1) ICP measurement

[0076] 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.

[0077] B2) Soluble sulfur measurement

[0078] To investigate the soluble S content in the lithium transition metal-based oxide particles according to the disclosure, washing and filtering processes are performed. 5g of the positive electrode composite material powder and 100g of ultrapure water are measured out in a beaker. The positive electrode composite material powder is dispersed in the water for 5 minutes at 25°C using a magnetic stirrer. The dispersion is vacuum filtered, and the dried powder is analyzed by the above ICP measurement to determine the amount of soluble S containing compound.

[0079] C) Carbon analysis

[0080] The content of carbon of the positive electrode active material powder is measured by Horiba Emia-Expert carbon / sulfur analyzer. 1 gram of the positive electrode active material powder is placed in a ceramic crucible in a high frequency induction furnace. 1.5 grams of tungsten and 0.2 grams of tin are added into the crucible as accelerators. The powder is heated at a programmable temperature wherein gases produced during the combustion are then analyzed by Infrared detectors. The analysis of CO2 and CO determines the carbon concentration.

[0081] D) Scanning Electron Microscope (SEM) measurement

[0082] 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 71 OOF under a high vacuum environment of 9.6x105Pa at 25 °C.

[0083] E) Energy-dispersive X-ray spectroscopy (EDS) analysis

[0084] 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 71 OOF SEM equipment with a 50 mm2X-MaxN EDS sensor from Oxford instruments.

[0085] F) Single-layer Pouch Cell Testing

[0086] F1) Single-layer Pouch Cell preparation

[0087] 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 NMP as a dispersion medium so that the mass ratio of the positive electrode active material powder, the positive electrode conductive agents, and positive electrode binder is set at 97.1 / 1 .1 / 1.8. 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 15.0 ± 1 mg / cm2. The 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.

[0088] 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 95.5 / 1 / 1 .5 / 2.0, 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.

[0089] Non-aqueous electrolyte is obtained by dissolving lithium hexafluorophosphate (LiPFe) salt at a concentration of 1.2 mol / L in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1 :1 :1. It contains 1.0 wt% lithium difluorophosphate (IJPO2F2), and 1.0 wt% vinylene carbonate (VC) as additives.

[0090] 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 charged to 4.20 V. The cell testing procedure uses a 1 C current definition of 33 mA / g.

[0091] F2) Cycle test

[0092] A. Pre-charging and formation

[0093] 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 until 30% 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.

[0094] The cell is charged with a current of 0.33 C in CC mode (constant current) up to 4.2 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 2.5 V. The charge discharge process is repeated for 3 times.

[0095] B. Cycle-life test

[0096] The cell is charged and discharged continuously under the following conditions at 45°C, to determine their charge-discharge cycle performance:

[0097] - Charge is performed in CC mode under 1 C rate up to 4.2 V, then CV mode until C / 20 is reached,

[0098] - The cell is then set to rest for 10 minutes,

[0099] - Discharge is done in CC mode at 1 C rate down to 2.5 V, - The cell is then set to rest for 10 minutes,

[0100] - The charge-discharge cycles proceed until 400 cycles. Every 100 cycles, the discharge is done at 0.33 C rate in CC mode down to 2.5 V.

[0101] The internal resistance or direct current resistance (DCR) is measured at 2.5C for 30 s at the beginning of every 100 cycles repetition and the end of 400thcycles at room temp.

[0102] The cycle-life is defined as the number of charge-discharge cycles when the capacity degrades to 80%.

[0103] G) Coin cell testing

[0104] G1) Coin cell preparation

[0105] For the preparation of a positive electrode, a slurry that contains a positive electrode composite material powder, conductor (Super P, Timcal), binder (KF#9305, Kureha) - with a formulation of 96.5:1.5:2.0 by weight - in a solvent (NMP, Mitsubishi) is prepared by a high-speed homogenizer. The homogenized slurry is spread on one side of an aluminum foil using a doctor blade coater with a 170 pm gap. The slurry coated foil is dried in an oven at 120°C and then pressed using a calendaring tool. Then it is dried again in a vacuum oven to completely remove the remaining solvent in the electrode film. A coin cell is assembled in an argon-filled glovebox. A separator (Celgard 2320) is located between a positive electrode and a piece of lithium foil used as a negative electrode. 1 M LiPF6 in EC / DMC (1 :2) is used as electrolyte and is dropped between separator and electrodes. Then, the coin cell is completely sealed to prevent leakage of the electrolyte.

[0106] G2) Testing method

[0107] The testing method is a conventional “constant cut-off voltage” test. The conventional coin cell test in the present disclosure follows the schedule shown in Table 1 . Each cell is cycled at 25°C using a Toscat-3100 computer-controlled galvanostatic cycling station (from Toyo).

[0108] The schedule uses a 1 C current definition of 220 mA / g. The initial charge capacity (CQ1) is measured in constant current mode (CC) at C rate of 0.1 C in the 4.3V to 3.0V / Li metal window range.

[0109] Table 1 . Cycling schedule for Coin cell testing method

[0110] EXAMPLES

[0111] The present disclosure is further illustrated in the following examples: Comparative Examples 1.1 to 1.3

[0112] CEX1 .1 was obtained through a solid-state reaction between a lithium source and a transition metal-based source precursor running as follows:

[0113] 1) Co-precipitation: a transition metal-based precursor with metal composition of Nio aoMno ioCoo io was prepared by a co-precipitation process in a large-scale continuous stirred tank reactor (CSTR) with mixed nickel-manganese-cobalt sulfates, sodium hydroxide, and ammonia.

[0114] 2) Blending: the precursor prepared in step 1) and LiOH as a lithium source were homogenously blended at a lithium to metal (Ni, Mn, and Co) ratio of 1 .00 in an industrial blending equipment.

[0115] 3) Heating: the blend from Step 2) was heated at 820 °C for 8 hours under an oxygen atmosphere. The product was crushed, classified, and sieved to obtain CEX1.1 having a D50 of around 13 pm.

[0116] Figure 1 is the SEM image of CEX1 .1 . Figure 3 is the EDS mapping of carbon for the corresponding SEM image in Figure 1 .

[0117] CEX1 .2 was obtained through the following process:

[0118] 1) Wet mixing: The CEX1 .1 was mixed with Ah(SO4)3 solution, which was prepared by dissolving Ah(SO4)3 powder into 3.5 wt% of deionized water with respect to the weight of the CEX1 .1 to obtain a mixture having 1000 ppm Al with respect to weight of the CEX1 .1 .

[0119] 2) Heating: The mixture obtained from Step 1) was heated at 385 °C for 8 hours under an oxygen atmosphere followed by grinding and sieving to obtain CEX1 .2.

[0120] CEX1 .3 was obtained through the following process:

[0121] 1) Mixing: The CEX1.1 was mixed with SWCNTs (Tuball manufactured by OCSiAl) having diameter between 1 to 3 nm in NMP solvent to produce a mixture comprising 0.06 wt% SWCNTs.

[0122] 2) Drying: The mixture obtained from Step 1) was dried at 130 °C for 12 hours followed by grinding and sieving to obtain CEX1 .3

[0123] Examples 1 to 3

[0124] EX1 was obtained through the following process:

[0125] 1) Mixing: CEX1.2 was mixed with SWCNTs in NMP solvent to obtain a mixture comprising 0.06 wt% SWCNTs.

[0126] 2) Drying: The mixture obtained from Step 3) was dried at 130 °C for 12 hours followed by grinding and sieving to obtain EX1 .

[0127] Figure 2 is the SEM image of EX1 showing SWCNTs covering the surface of a positive electrode active material particle. Figure 4 is the EDS mapping of carbon for the corresponding SEM image in Figure 2 showing carbon detection on the surface of the particle. EX2 was prepared according to the same method as EX1 , except that MWCNTs (BT1001 manufactured by LG Chem) having diameter between 5 to 15 nm in NMP solvent was used in step 1) to obtain a mixture comprising 0.9 wt% MWCNTs.

[0128] EX3 was prepared according to the same method as EX1 , except that SWCNTs in water was used in step 1) to obtain a mixture comprising 0.09 wt% SWCNTs.

[0129] Results

[0130] Table 2. Summary of the properties of example and comparative example

[0131] N / A : Not applicable

[0132] 'wt% : relative to total weight of a positive electrode active material

[0133] "at% : relative to total atomic contents of Ni, Mn, Co, Al and S

[0134] ””ppm : relative to total weight of a positive electrode composite material

[0135] Table 2 summarizes the properties of examples and comparative example. Al was detected in CEX1.2, EX1 , EX2 and EX3, and the contents of S and soluble S in CEX1 .2, EX1 , EX2 and EX3 were greater than those in CEX1 .1 and CEX1 .3. Thus, addition of Al2(SO4)3 during the preparation of positive electrode active materials is confirmed by the contents of Al, S and soluble S. The contents of carbon in CEX1 .3, EX1 , EX2, and EX3 were much greater than those in CEX1 .1 and CEX1 .2. Thus, addition of CNTs, i.e., SWCNTs and MWCNTs during the preparation of positive electrode active materials are recognized by the content of carbon.

[0136] Comparing CEX1 .1 with CEX1 .2 reveals that mixing Al2(SO4)3 solution with a lithiated material, followed by heating, grinding and sieving the mixture, increases the cycle-life at 45 °C of a battery. In contrast, comparing CEX1.1 with CEX1.3 reveals that mixing CNTs with a lithiated material, followed by heating, grinding and sieving the mixture, deteriorates the cycle-life at 45 °C of a battery. Surprisingly, the battery with EX1 , prepared by applying both Al2(SO4)3 solution and CNTs — i.e., mixing the material treated by CNTs with Al2(SO4)3 solution, followed by heating, grinding and sieving the mixture — had a cycle-life at 45 °C greater than that of the battery with CEX1 .2. It is an unexpected effect that the positive electrode composite material, prepared by applying both Al2(SO4)3 solution and CNTs, exhibits an increased cycle- life at 45 °C compared to the positive electrode composite material, prepared by applying only Ah(SO4)3 solution, although the application of only CNTs worsens the cycle-life at 45 °C.

[0137] The cycle-life at 45 °C of the battery with EX2 was smaller than that of the battery with EX1 , even though the added amount of MWCNTs to EX2 was much greater than the added amount of SWCNTs to EX1.

[0138] Accordingly, SWCNTs could lead to a greater increase in cycle-life at 45 °C than MWCNTs.

[0139] In addition, CQ1s of the batteries with CEX1.1 and CEX1.3 were identical, and CQ1 of the battery with CEX1 .2 was higher than those of CEX1 .1 and CEX1 .3. Thus, applying Al2(SO4)3 solution enhanced CQ1 , whereas applying CNTs did not. Nevertheless, CQ1 of the battery with EX1 was higherthan CQ1 of CEX1.2.

[0140] It is an unexpected effect that applying both Al2(SO4)3 solution and CNTs enhances CQ1 to a greater extent than applying only Al2(SO4)3 solution.

[0141] Accordingly, it is obviously observed that the positive electrode composite material according to the present disclosure can achieve the object of the present disclosure, which is to provide a battery with a prolonged cycle-life.

Claims

CLAIMS1. A positive electrode composite material comprising a positive electrode active material and carbon nanotubes, wherein the positive electrode active material comprises lithium, M’, and oxygen, wherein M’ comprises:Ni in a content x, wherein 50 at% < x < 95 at%, relative to M’;Mn in a content y, wherein 0 at% < y < 30 at%, relative to M’;Co in a content z, wherein 0 at% < z < 20 at%, relative to M’;Al in a content a, wherein 0 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 0.5 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 60 at% < x < 95 at%, preferably 70 at% < x < 93 at%, more preferably 75 at% < x < 90 at%.

3. The positive electrode composite material according to claim 1 or 2, wherein 1 at% < y < 25 at%, preferably 5 at% < y < 20 at%, more preferably 7 at% < y < 15 at%.

4. The positive electrode composite material according to any of the previous claims, wherein 1 at% < z< 18 at%, preferably 5 at% < z < 15 at%, more preferably 7 at% < z < 13 at%.

5. 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 0.6 at% < c < 3 at%, preferably 0.65 at% < c < 2 at%, more preferably 0.7 at% < c < 1 .5 at%.

7. 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.

8. 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 600 ppm < d < 15000 ppm,preferably 1000 ppm < d < 12000 ppm, more preferably 1500 ppm < d < 11000 ppm, relative to a total weight of the positive electrode composite material, as measured by carbon analyzer.

9. The positive electrode composite material according to claim 8, wherein the carbon nanotubes are single walled carbon nanotubes, and 600 ppm < d < 5000 ppm, preferably 1000 ppm < d < 4000 ppm, more preferably 1500 ppm < d < 3500 ppm.

10. The positive electrode composite material according to any of the previous claims, wherein a content of soluble sulfur ranges from 0.35 at% to 1.5 at%, preferably from 0.5 at% to 1 at%, more preferably from 0.6 at% to 0.9 at%, as measured by ICP, wherein the content of soluble sulfur is equal to a decrease of a content of S relative to M’ as measured by ICP after having contacted the positive electrode composite material into deionized water for at least 5 minutes at 25 °C to form a slurry, filtered the slurry to form a filtered slurry, and dried the filtered slurry.

11. A method for preparing a positive electrode composite material, wherein the method comprises consecutive steps of: preparing a lithium transition metal-based oxide compound; mixing the lithium transition metal-based oxide compound with a solution comprising aluminum sulfate to obtain a first mixture; heating the first mixture in an oxidizing atmosphere in a furnace at a temperature between 250°C and 500°C, preferably between 300°C and 400°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 sulfate of the solution is dissolved in water.

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

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

15. The battery according to claim 14, wherein the battery has a cycle-life at 45°C of about 450 or greater, about 475 or greater, about 500 or greater.

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

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