Electrode composition for lithium ion secondary battery and manufacturing process thereof

Abstract

To provide a cathode electrode for a lithium ion battery, a process for preparing the electrode, and a high rate capability lithium ion battery comprising the electrode.SOLUTION: A cathode electrode is prepared with an active substance along with a high interfacial area carbon-fused metal- and heteroatom-doped MWCNT prepared from petroleum refinery feedstock, where the metal is transition metal such as Co, Mn and Fe, and the heteroatom is nitrogen, sulfur, oxygen, phosphorus, or the like. The active substance is selected from NMC, LFP, NCA, LNMO, LCO, LMO, or a combination thereof. Lithium ion 2032 full coin cells employing the material for a cathode and employing a graphite anode have high rate capability allowing delivery of capacity up to the 5 C rate, deliver specific capacity of 80-100 mAhg-1 at the 1 C rate and exhibit good cycling stability at the same rate when cycled between 2.75 and 4.2 V.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to the fabrication of high-rate lithium-ion batteries using carbon-fused metal- and heteroatom-doped multi-walled carbon nanotubes and the process for fabricating such electrodes. More specifically, the present invention relates to a cathode electrode for lithium-ion batteries and the process for fabricating such electrodes. The cathode is prepared using carbon black as the active material and uniquely prepared carbon-fused metal- and heteroatom-doped multi-walled carbon nanotubes (MWCNTs). The MWCNTs are prepared from petroleum-refined feedstocks. The MWCNTs are metal- and heteroatom-doped CNTs, where the metals are transition metals such as Co, Mn, Fe, and Ni, and the heteroatoms are nitrogen, sulfur, oxygen, and phosphorus. A polymer binder is also used in the composition for fabricating the cathode electrode. [Background technology]

[0002] Carbon with a high surface area plays an important role in battery performance. In general, the interfacial surface area between the carbon and the active material affects the interparticle internal resistance, rate capability, and other properties of the electrode. The adhesive properties of the carbon, along with its surface area, are crucial for improving the battery's life cycle without degradation of the active material or capacity loss. While much effort has been devoted to improving battery performance using various types of high-surface-area carbon materials, there is still a need to develop lithium-ion batteries that offer improved rate capability, power density, and long cycle life without sacrificing capacity.

[0003] MWCNTs possess many unique properties due to their small size, cylindrical graphitic structure, and high aspect ratio. Carbon nanotubes have very high tensile strength, high elastic modulus, excellent chemical and environmental stability, and high thermal and electrical conductivity. Carbon nanotubes have found many applications, including the preparation of conductive, electromagnetic, and high-strength composite materials and energy storage systems. In batteries, MWCNTs function as the conductive agent in cathode and anode electrodes. MWCNTs also function as the anode active material in lithium-ion batteries.

[0004] Carbon-fused metal and heteroatom-doped MWCNTs have a large interfacial surface area, which allows them to connect with the active material, leading to higher electrode conductivity and adhesion performance, which are necessary for stable, high-rate cathode electrodes in lithium-ion batteries.

[0005] US Patent Application Publication No. 2014 / 0093769 provides a nanoelement-based electrode material for rechargeable batteries. The electrode is based on a carbon nanotube (CNT) scaffold and is coated with a thin layer of electrochemically active material in the form of nanoparticles. The use of alternating layers of CNTs and active nanoparticles further improves the power density and rate of the battery.

[0006] U.S. Patent No. 8,540,902 describes a carbon nanotube-based paste and its method of manufacture and use. The carbon nanotubes are dispersed by milling, and the resulting paste has a Hegman scale greater than 7. The paste can be used as a conductivity enhancer for electronic devices such as batteries, capacitors, electrodes, or other devices requiring a highly conductive paste.

[0007] U.S. Patent Application Publication No. 2007 / 0190422 relates to energy storage devices. In particular, the disclosure relates to a lithium-ion battery having two active electrodes made of carbon nanotube (CNT) material, with lithium metal powder dispersed in the CNT material of the anode.

[0008] EP 3786110 A1 relates to a carbon nanotube dispersion liquid having excellent dispersibility and storage stability of carbon nanotubes. The present disclosure also relates to a battery electrode mixture layer and a lithium ion secondary battery containing the carbon nanotube dispersion liquid.

[0009] U.S. Patent No. 8,822,078 relates to freestanding carbon nanotube paper containing purified carbon nanotubes, wherein the purified carbon nanotubes form the freestanding carbon nanotube paper and carbon particles are embedded inside or present on the surface of the carbon nanotube paper. The present disclosure also relates to lithium ion batteries, capacitors, supercapacitors, battery / capacitors, and fuel cells that contain the freestanding carbon nanotube paper as an electrode.

[0010] US Patent Application Publication No. 2005 / 0181282 discloses a carbon nanofiber-based (CNT - carbon nanotube) electrically high-performance battery, which includes a cell trough filled with an electrolyte, a spring coil locked in the cell trough, an anode / cathode substrate installed in the cell trough with a separator membrane, and a cathode terminal and an anode terminal installed outside a cell cap that connects to the anode / cathode substrate, respectively.

[0011] U.S. Patent Application Publication No. 2009 / 0246625 relates to lithium-ion batteries in general, and more particularly to lithium-ion batteries based on aligned graphene ribbon anodes, V2O5 graphene ribbon composite cathodes, and ionic liquid electrolytes, which have excellent performance metrics such as cell voltage, energy density, and power density.

[0012] U.S. Patent Application Publication No. 2011 / 0256451 discloses an electronic device comprising a carbon nanotube film having a plurality of carbon nanotubes, an inorganic coating on the carbon nanotube film, and a conductive electrode coupled to the carbon nanotube film for conducting electrical current therethrough.

[0013] Chinese Patent Application Publication No. 105375009 discloses a stable nitrogen-doped carbon nanopipe and iron oxide composite negative electrode material based on nitrogen-doped carbon nanopipes, characterized in that the outer surface loading of the described nitrogen-doped carbon nanopipes has iron oxide particles, iron oxide is the main component, and the loading capacity of iron oxide accounts for 10 to 90% of the total mass of the iron oxide particles and nitrogen-doped carbon nanopipes.

[0014] US Patent Application Publication No. 2016 / 0020466 relates to a dispersion comprising a dispersion medium, a polymeric dispersant, and carbon nanotubes dispersed in the dispersion medium.

[0015] US Patent No. 10,622,631 includes a negative active material crystalline carbon consisting of natural graphite, artificial graphite, expandable graphite, graphene, carbon nanotubes, or a combination thereof, together with silicon-carbon secondary particles.

[0016] EP 3404747 A1 describes a composition for producing an expander-free electrode for lead-acid batteries and its performance. The paper deals with the use of heteroatoms, such as nitrogen and sulfur embedded carbon nanotubes (H-CNTs), as a multifunctional additive for producing lead-acid battery electrodes, replacing the expanding agents vanisperse, Dynel fiber, barium sulfate, and carbon black.

[0017] Ruan, Boyang, et al., "Carbon-encapsulated Sn@N-doped carbon nanotubes as anode materials for SIB applications," ACS applied materials & interfaces 9.43(2017):37682-37693, discloses carbon-fused Sn@N-doped carbon nanotubes as anode materials for sodium-ion battery applications.

[0018] Due to the low conductivity of the conductive carbon used in the electrodes of lithium-ion batteries, problems still remain with the high-rate performance and cycle life of lithium-ion batteries. Furthermore, safety issues remain. Therefore, there remains an urgent need to solve the drawbacks associated with lithium-ion batteries.

[0019] A first object of the present invention is to provide a lithium ion battery with high rate performance. Another object of the present invention is to disclose a process for fabricating electrodes thereof using carbon-fused metal and heteroatom-doped multi-walled carbon nanotubes. Summary of the Invention

[0020] The present invention, as embodied and broadly described herein, provides a cathode electrode composed of carbon-fused metal- and heteroatom-doped MWCNTs prepared from a refined feed, active material, carbon black, and a polymer binder. The electrode obtained through the process of the present invention effectively overcomes the high-rate performance and cycle life problems of lithium-ion batteries / cells caused by the low electrical conductivity of conductive carbons used in lithium-ion battery electrodes. Furthermore, the use of MWCNTs with high thermal conductivity allows for proper heat dissipation throughout the electrode, avoiding thermal runaway, a common problem in lithium-ion batteries, thereby improving the safety of lithium-ion batteries.

[0021] The present invention provides a) carbon-fused metal and heteroatom doped multi-walled carbon nanotubes (MWCNTs); b) an active material; and c) carbon black; d) a polymer binder; A cathode electrode for a lithium-ion battery is provided.

[0022] In one aspect of the present invention, the cathode active material present in the cathode electrode composition is in the range of 85 to 95 wt% of the composition, the carbon-fused metal and heteroatom-doped MWCNTs present in the cathode electrode composition are in the range of 0.5 to 6 wt% of the composition, the carbon black is in the range of 0.5 to 6 wt% of the composition, and the polymer binder is in the range of 1 to 5 wt% of the composition.

[0023] The present invention also provides a process for fabricating a cathode for a lithium ion battery, which includes preparing metal and heteroatom doped MWCNTs from purified raw materials, followed by preparing higher interfacial carbon fused metal and heteroatom doped MWCNTs, followed by preparing a cathode electrode slurry, and finally preparing a cathode electrode.

[0024] The present invention also provides a) preparing metal and heteroatom doped MWCNTs from purified raw materials; b) preparing carbon-fused metal- and heteroatom-doped MWCNTs from the metal- and heteroatom-doped MWCNTs obtained above; c) preparing a cathode electrode slurry by mixing 85 to 95 wt% of the active material with 0.5 to 6 wt% of the carbon-fused metal and heteroatom doped MWCNTs, and then mixing with 0.5 to 6 wt% of carbon black to obtain a mixture, and then adding 1 to 5 wt% of a polymer binder to the mixture; d) preparing a cathode electrode; The present invention provides a process for fabricating a cathode electrode for a lithium ion battery, comprising:

[0025] In another aspect, the present invention provides a method for manufacturing a semiconductor device comprising: a) a cathode electrode consisting of an active material, carbon fused metal and heteroatom doped MWCNTs, carbon black and a polymer binder; b) a graphite anode; A lithium-ion battery comprising:

[0026] The present invention also provides a novel electrode composition for lithium ion batteries that has high rate capability and long cycle life.

[0027] Carbon-fused metal-doped heteroatomic MWCNTs have good adhesion properties that lead to a stable life cycle without capacity fade.

[0028] Carbon-fused metal-doped heteroatomic MWCNTs are uniquely produced from crude oil, and the product is less costly than MWCNTs prepared by pure gas molecules. [Brief explanation of the drawings]

[0029] The invention will be best understood when read in conjunction with the accompanying drawings, in which: Figure embodiments are described herein.

[0030] [Figure 1] 1 shows Raman shift graphs of carbon-fused metal and heteroatom doped MWCNTs. [Figure 2] 1 shows XRD graphs of carbon fused metal and heteroatom doped MWCNTs. [Figure 3] 1 shows TGA graphs of carbon fused metal and heteroatom doped MWCNTs. [Figure 4]

[0023] Figure 1 shows cyclic voltammetry graphs of LiFePO4 cathodes doped with carbon fused metal and heteroatom doped MWCNTs. [Figure 5] Low-resolution TEM images (low magnification) of carbon-fused metal and heteroatom doped MWCNTs are shown. [Figure 6]HR-TEM images (high magnification) of carbon-fused metal and heteroatom-doped MWCNTs are shown. [Figure 7] 1 is a graph comparing the rate performance of NMC811 cathodes doped with carbon fused metal and heteroatom doped MWCNTs and a control. [Figure 8] 1 is a graph comparing the rate performance of a carbon fusion metal doped NCA cathode and heteroatom doped MWCNT. [Figure 9] 1 is a graph showing a life cycle comparison of NMC811 cathodes doped with carbon fused metal and heteroatom doped MWCNTs with a control and commercial MWCNTs. DETAILED DESCRIPTION OF THE INVENTION

[0031] While exemplary implementations of embodiments of the present disclosure are set forth below, it should be understood at the outset that the present disclosure may be implemented using any number of technologies, whether currently known or existing. The present disclosure should in no way be limited to the exemplary implementations, drawings, and technologies set forth below, including the exemplary designs and implementations shown and described herein, but may be modified within the scope of the appended claims along with their full range of equivalents.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0033] The terms and structures used herein are intended to describe, teach, and highlight certain embodiments and their specific features and elements, but are not intended to limit, restrict, or reduce the scope of the claims or their equivalents.

[0034] The term "doctor blade" as used in the present invention is a tool for coating an electrode material to a desired thickness.

[0035] The "active material" as defined in the present invention is the material responsible for the capacity of the battery, ie, the lithium-based metal oxide.

[0036] As defined herein, "crude oil-related products" or "refinery feedstocks" refer to heavy naphtha, light naphtha, and combinations thereof.

[0037] The "ID / IG" ratio used in the present invention is used to define the defects of the carbon sample. If the ID / IG ratio is large, there are many defects in the carbon sample, and vice versa.

[0038] The present invention provides a) carbon-fused metal and heteroatom doped multi-walled carbon nanotubes (MWCNTs); b) an active material; and c) carbon black; d) a polymer binder; and The present invention provides a cathode electrode for a lithium ion battery, which comprises:

[0039] In one aspect of the invention, the carbon fused metal and heteroatom doped MWCNTs are present in the range of 0.5 to 6 wt %.

[0040] In another aspect of the invention, the active material is selected from lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminum oxide (NCA) and lithium iron phosphate (LFP), lithium nickel manganese spinel (LNMO), lithium manganate (LMO) and lithium cobalt oxide (LCO) and is present in the range of 85 to 95 wt %.

[0041] In yet another aspect of the invention, the carbon black is present in the range of 0.5 to 6% by weight.

[0042] In yet another aspect of the invention, the polymer binder is polyvinylidene fluoride and is present in the range of 1 to 5 weight percent.

[0043] The present invention also provides a) preparing metal and heteroatom doped MWCNTs from purified raw materials; b) preparing carbon-fused metal- and heteroatom-doped MWCNTs from the metal- and heteroatom-doped MWCNTs obtained above; c) preparing a cathode electrode slurry by mixing 85 to 95 wt% of the active material with 0.5 to 6 wt% of the carbon-fused metal and heteroatom doped MWCNTs, and then mixing with 0.5 to 6 wt% of carbon black to obtain a mixture, and then adding 1 to 5 wt% of a polymer binder to the mixture; d) fabricating a cathode electrode;

[0009] A process for making a cathode electrode for a lithium ion battery is provided.

[0044] In one aspect of the invention, step (a) of the process comprises: I. reducing the catalyst using hydrogen gas in a reactor operating at three different temperature ranges of about 620-640°C, 645-665°C, and 670-690°C and a pressure of about 1 atmosphere; II. feeding purified feedstock into a reactor at a flow rate of 25-45 ml / hr for 10 hours in the presence of nitrogen carrier gas; III.0.1~1 g's adding the doped MWCNTs and dilute sulfuric acid (50-550 ml) and dispersing for 0.5-1 hour to obtain a mixture; IV. Refluxing the mixture of step III at 80-100°C for 2-6 hours at a rotation speed of 200-500 rpm to obtain a reaction mixture; V. adding distilled water to the reaction mixture of step IV, holding for 10-15 minutes, decanting, and filtering; VI. Repeating step V 4-5 times, the resulting mixture is washed to a neutral pH, then dried at 100-120°C for 8-12 hours, and weighed to obtain metal- and heteroatom-doped MWCNTs.

[0045] In another aspect of the present invention, step (b) of the process for preparing a cathode electrode for a lithium ion battery comprises: I.80~99 g's 1-20 with metal and heteroatom doped MWCNTs g's grinding the carbon black to obtain a powder; II. Ultrasonicating the powder obtained in step I in NMP solvent for 0.5-1 hour to obtain the resulting mixture; III. filtering the resulting mixture, followed by drying and calcining to obtain carbon-fused metal and heteroatom-doped MWCNTs.

[0046] In yet another aspect of the present invention, step (c) of the process for preparing a cathode electrode for a lithium ion battery comprises: I. mixing carbon-fused metal and heteroatom-doped MWCNTs with an active material, and then adding carbon black to obtain a mixture, wherein the active material is selected from NMC, NCA, LFP, LNMO, LMO, and LCO, and combinations thereof; II. Polymer binder in NMP solvent to The dissolved , and stirring for 2 to 8 hours to obtain a homogeneous cathode electrode slurry. Includes:

[0047] In yet another aspect of the present invention, step (d) of the process for preparing a cathode electrode for a lithium ion battery comprises: I Thickness 100~300 μm of Using an applicator coating the cathode electrode slurry onto an aluminum foil; II. Drying the cathode electrode of step I in a vacuum oven at 100-120 ° C overnight to obtain a cathode for a lithium ion battery; Includes:

[0048] In yet another aspect of the present invention, the metal and heteroatom doped MWCNTs consist of 0.01-3100 ppm Co, 0.01-800 ppm Mn, 0.01-400 ppm Fe, 0.001-1 wt % S, and 0.01-2000 ppm N.

[0049] The present invention also provides a) a cathode consisting of an active material, carbon fused metal and heteroatom doped MWCNTs, carbon black and a polymer binder; b) a graphite anode; A lithium-ion battery comprising:

[0050] As a feature of the present invention, the lithium-ion battery provides capacity up to 5C rate, and the cell provides 80-100mAhg at 1C rate. -1 The cells exhibit excellent cycling stability when cycled between 2.75 and 4.2 V.

[0051] This disclosure relates to the fabrication of high-rate lithium-ion batteries using carbon-fused, metal- and heteroatom-doped multi-walled carbon nanotubes, as well as the fabrication process for the electrodes. The cathode was fabricated using carbon black as the active material and proprietary carbon-fused, doped multi-walled carbon nanotubes (MWCNTs). The MWCNTs were prepared from petroleum-refined feedstocks. The MWCNTs are metal- and heteroatom-doped carbon nanotubes, with metals including transition metals such as Co, Mn, Fe, and Ni, and heteroatoms including nitrogen, sulfur, oxygen, and phosphorus. The cathode electrode also uses a polymer binder.

[0052] In one embodiment, the present invention discloses a process and composition for fabricating a lithium-ion battery electrode. The cathode active material present in the cathode electrode composition ranges from 85 to 95% by weight of the composition. The carbon-fused metal and heteroatom-doped MWCNTs present in the cathode electrode composition ranges from 0.5 to 6% by weight of the composition. The carbon black is present in a range from 0.5 to 6% by weight of the composition. The polymer binder is present in a range from 1 to 5% by weight of the composition.

[0053] The refining feedstock in the present invention comprises low sulfur crude oil, high sulfur crude oil and mixtures thereof.

[0054] In another embodiment, the present invention includes the following process for fabricating a cathode electrode.

[0055] 1) Preparing metal and heteroatom doped MWCNTs from purified raw materials, comprising:

[0056] 1a) The catalyst was reduced in a reactor using hydrogen gas. Then, crude oil-related products were fed into the reactor. The reactor was operated at three temperature ranges: 630°C, 655°C, and 680°C. The reactor was operated at approximately 1 atmosphere. The catalyst used in this process was an alumina-supported Fe-Co catalyst or Fe-Mo catalyst.

[0057] Metal and heteroatom doped MWCNTs with OD (outer diameter) 20-40 nm, ID (inner diameter) 5-17 nm, and 15-40 or more layers can be prepared from refinery feedstocks by the process shown below.

[0058] 8 g of alumina-supported catalyst is loaded into the center of a vibrating reactor. The flow rates of the carrier gas and reduction gas are controlled by electronic mass flow meters, and the catalyst and reactor temperatures are measured by thermocouples. The catalyst is then heated to 700 °C in the presence of nitrogen carrier gas. After reaching the desired temperature of 700 °C, hydrogen gas (75 sccm) is introduced into the reactor to reduce the catalyst, and the reduction process continues for 4 hours. After the catalyst reduction is complete, the reactor temperature is reduced to 600 °C under a nitrogen atmosphere. At this stage, high-sulfur crude oil with a sulfur content of more than 1 wt% is fed into the reactor at a flow rate of 14 g / h with 50 sccm of nitrogen carrier gas for 430 minutes. The product gas stream is further analyzed using a refinery gas analyzer. The chromatogram shows the yield patterns of gases such as hydrogen, nitrogen, methane, and other light hydrocarbons. After the run is completed, the reactor is cooled under a nitrogen atmosphere, and solid carbon nanotubes are recovered to estimate the yield.

[0059] 1b) The required amount of doped MWCNTs (0.1–1 gm) prepared by the above method was added to a round-bottom glass flask and diluted sulfuric acid (50–550 ml) was added. The MWCNTs were dispersed in an ultrasonic bath for 0.5–1 hour. The mixture was then refluxed on a hot plate at 200–500 rpm at 80–100°C for 2–6 hours. Distilled water was then added, the mixture was allowed to stand for 10–15 minutes, and then decanted and filtered through a membrane filter. This process was repeated 4–5 times. The mixture was then washed to a neutral pH, dried at 100–120°C for 8–12 hours, and weighed to obtain the desired metal- and heteroatom-doped MWCNTs. (Co: 0.01–3100 ppm, Mn: 0.01–800 ppm, Fe: 0.01–400 ppm, S: 0.001–1 wt%, N: 0.01–2000 ppm).

[0060] 2) Preparing high-interface carbon-fused metal and heteroatom doped MWCNTs.

[0061] 2a) 10 gm of carbon black was milled with 90 gm of metal and heteroatom doped MWCNTs in ethanol solvent using a planetary ball mill at room temperature at a speed of 500 rpm for 1-4 hours. 2b) The resulting mixture was filtered, and the mixture was kept in a vacuum oven at 200°C for 6 to 10 hours. 2c) The powder was placed in a heating furnace at 1000 to 1400°C in an inert atmosphere. The temperature was increased to 1000 to 1400°C at a rate of 200°C / hr, held for 2 to 4 hours, and then naturally cooled to room temperature. 2d) The flow rate of argon gas was kept at 100 ml / hr throughout the entire process.

[0062] 3) preparing a cathode electrode slurry;

[0063] 3a) Cathode active material (NMC / NCA / LFP, LNMO, LCO, LMO, etc.) was mixed at 85-95 wt% of the composition with 0.5-6 wt% of carbon-fused metal- and heteroatom-doped MWCNTs using a mortar and pestle / vacuum mixer for 15 min to 1 hour. The resulting powder mixture was then further mixed with 0.5-6 wt% of carbon black and milled for 15 min to 1 hour. 3b) 1-5 wt% of the total composition of polymer binder polyvinylidene fluoride (PVDF) in NMP (N-methyl-2-pyrrolidone) solution was added to the above and stirred with a magnetic stirrer for 2-8 hours to obtain a uniform slurry.

[0064] 4) Fabricating a cathode electrode.

[0065] 4a) The cathode slurry prepared as above is applied to a film having a thickness of 100 to 300 mm. μm The cathode electrode was then placed in a vacuum oven at 100-120°C overnight to dry.

[0066] In one of its many embodiments, the present invention discloses the use of low grade carbon black, a very inexpensive conductive material available on the market, in conjunction with metal-doped heteroatomic MWCNTs in lithium ion battery applications.

[0067] In another embodiment, the present invention discloses the use of 30 to 40 layer carbon fused metal and heteroatom doped MWCNTs with ID / IG: 0.740±0.1 along with carbon black in the electrodes to fabricate a full lithium ion cell with high rate capability.

[0068] In yet another embodiment, the present invention provides a method for producing a lithium ion battery with a BET surface area of ​​120±10 m with carbon black in the electrode to produce a full lithium ion battery with high rate capability. 2 The use of carbon-fused metal and heteroatom doped MWCNTs is disclosed.

[0069] In more embodiments, the present invention discloses the use of highly purified carbon-fused metal and heteroatom doped MWCNTs (confirmed by TGA) along with carbon black in electrodes to produce full lithium ion batteries with high rate capabilities.

[0070] In yet another embodiment, the present invention discloses the use of highly graphitic carbon fused metal and heteroatom doped MWCNTs (confirmed by XRD) along with carbon black in electrodes to produce full lithium ion batteries with high rate capabilities.

[0071] According to one aspect of the subject matter, in the above embodiment, the carbon-coated metal-doped heteroatomic MWCNTs have a larger interfacial surface area (confirmed by CV electrochemical studies) and thereby also connect the active materials leading to higher electrode conductivity and adhesion properties necessary for highly stable and high rate capable cathode electrodes in lithium ion batteries.

[0072] In yet another embodiment, the present invention provides for the formation of lithium ion batteries with high coulombic efficiency.

[0073] According to one aspect of the subject matter, in the above embodiment, the optimized composition of carbon-fused metal and heteroatom-doped MWCNTs in the cathode electrode avoids irreversible capacity loss.

[0074] In one preferred embodiment, the present invention discloses the fabrication of full lithium ion coin cells with high power density and high rate capability.

[0075] In another preferred embodiment, the present invention discloses the preparation of a cathode using carbon-fused MWCNTs prepared from petroleum-refined feedstocks. The MWCNTs are metal- and heteroatom-doped CNTs, where the metals are heavy metals such as Co, Mn, Fe, and Ni, and the heteroatoms are nitrogen, oxygen, sulfur, and phosphorus.

[0076] In a further preferred embodiment, the present invention discloses the fabrication of a full cell 2032 coin battery using the above materials, which is capable of delivering high rate capacity up to 5C rate and 80 to 100mAhg at 1C rate. -1 and exhibits excellent cycling stability when cycled between 2.75 and 4.2 V.

[0077] Advantages and Improvements of the Present Invention Over Existing Methods 1. Carbon-fused metal- and heteroatom-doped MWCNTs prepared from petroleum-refined feedstocks can be used with low-quality, inexpensive carbon black that is not suitable for lithium-ion battery applications. 2. Carbon-fused metal and heteroatom-doped MWCNT particles are compatible with low-quality carbon black, resulting in high interfacial interaction between the particles and the active material particles. 3. This interaction also helps to improve the adhesion properties of the active material leading to a high rate, high life cycle stable cathode. [Example]

[0078] The invention will now be illustrated by the following non-limiting examples. Example 1 Preparation of desired metal and heteroatom doped MWCNTs from purified raw materials

[0079] Hydrogen gas was used to reduce the catalyst in the reactor. The reactor was operated at three temperature ranges: 630°C, 655°C, and 680°C. The reactor was operated at a pressure of approximately 1 atmosphere. Crude oil-related products were fed into the reactor at a flow rate of 35 ml / hr for 10 hours in the presence of nitrogen carrier gas to obtain metal- and heteroatom-doped MWCNTs. 0.1–1 gm of the resulting doped MWCNTs and dilute sulfuric acid (50–550 ml) were added to a round-bottom glass flask, and the MWCNTs were dispersed in an ultrasonic bath for 0.5–1 hour. The mixture was then refluxed on a hot plate at 80–100°C and a rotation speed of 200–500 rpm. Distilled water was then added, and the mixture was left to stand for 10 to 15 minutes, followed by decantation and filtration of the sample through a membrane filter. This process was repeated 4 to 5 times, after which the mixture was washed to a neutral pH, dried at 100 to 120°C for 8 to 12 hours, and weighed to obtain the desired metal- and heteroatom-doped MWCNTs (Co: 0.01 to 3100 ppm, Mn: 0.01 to 800 ppm, Fe: 0.01 to 400 ppm, S: 0.001 to 1 wt%, N: 0.01 to 200 ppm).

[0080] Example 2 Preparation of highly interfacial carbon-fused metal and heteroatom-doped MWCNTs

[0081] 1. 10 gm of carbon black and 90 gm of metal- and heteroatom-doped MWCNTs were ground using a planetary ball mill at room temperature at 500 rpm for 1 to 3 hours, and the resulting powder was ultrasonically treated in NMP solvent for 0.5 to 1 hour. 2. The resulting mixture was filtered and kept in a vacuum oven at 200°C for 6 to 10 hours. 3. The obtained powder was placed in a heating furnace at 1000 to 1400°C in an inert atmosphere. It was heated at a rate of 200°C / hr until it reached 1000 to 1400°C, held there for 2 to 4 hours, and then naturally cooled to room temperature. 4. The flow rate of argon gas was kept at 100 ml / hr throughout the entire process.

[0082] Example 3 Fabrication of NMC811 cathode electrode

[0083] 1.8 gm of cathode active material NMC811 (lithium nickel-manganese-cobalt oxide) was taken and mixed with 68 mg of carbon-fused metal- and heteroatom-doped MWCNTs using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour. Then, 24 mg of carbon black was added and ground for 15 minutes to 2 hours. Next, 52 mg of polymer binder (based on the total composition weight) was added to 2.7 ml of NMP solution and stirred with a magnetic stirrer for 2 to 8 hours to obtain a uniform slurry. The cathode electrode was then cut into a 16 mm diameter disk.

[0084] Example 4 Fabrication of NMC811 cathode electrode

[0085] 1.8 gm of cathode active material NMC811 (lithium nickel-manganese-cobalt oxide) was taken and mixed with 88 mg of carbon-fused metal- and heteroatom-doped MWCNTs using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour. Then, 32 mg of carbon black was added and ground for 15 minutes to 2 hours. Next, 82 mg of polymer binder (based on the total composition weight) was added to 2.7 ml of NMP solution and stirred with a magnetic stirrer for 2 to 8 hours to obtain a uniform slurry. The cathode electrode was then cut into a 16 mm diameter disk.

[0086] Example 5 Fabrication of NCA cathode electrode

[0087] 1.8 gm of cathode active material (NCA) was taken and mixed with 68 mg of carbon-fused metal- and heteroatom-doped MWCNTs using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour. Then, 24 mg of carbon black was added and ground for 15 minutes to 2 hours. Next, 82 mg of polymer binder was added to 2.7 ml of NMP solution and stirred with a magnetic stirrer for 2 to 8 hours to obtain a uniform slurry. The cathode electrode was then cut into a 16 mm diameter disk.

[0088] Example 6 Fabrication of NCA cathode electrode

[0089] 1.8 gm of cathode active material (NCA) was taken and mixed with 88 mg of carbon-fused metal- and heteroatom-doped MWCNTs using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour. Then, 32 mg of carbon black was added and ground for 15 minutes to 2 hours. Next, 82 mg of polymer binder was added to 2.7 ml of NMP solution and stirred with a magnetic stirrer for 2 to 8 hours to obtain a uniform slurry. The cathode electrode was then cut into a 16 mm diameter disk.

[0090] Example 7 Fabrication of LiFePO4 cathode electrode

[0091] 1.8 gm of LiFePO4 cathode (lithium iron phosphate) (LFP) was taken and mixed with 68 mg of carbon-fused metal- and heteroatom-doped CNTs using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour. Then, 24 mg of carbon black was added and ground for 15 minutes to 2 hours. Next, 82 mg of polymer binder (based on the total composition weight) was added to 2.7 ml of NMP solution and stirred with a magnetic stirrer for 2 to 8 hours to obtain a uniform slurry. The cathode electrode was then cut into a 16 mm diameter disk.

[0092] Example 8 Fabrication of LiFePO4 cathode electrode

[0093] 1.8 gm of LiFePO4 cathode (lithium iron phosphate) (LFP) was taken and mixed with 88 mg of carbon-fused metal- and heteroatom-doped MWCNTs using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour. 32 mg of carbon black was added and ground for 15 minutes to 2 hours. Next, 82 mg of polymer binder was added to 2.7 ml of NMP solution and stirred with a magnetic stirrer for 2 to 8 hours to obtain a uniform slurry. The cathode electrode was then cut into a 16 mm diameter disk.

[0094] Example 9 Fabrication and testing of lithium-ion 2032 full coin cells using carbon-fused metal and heteroatom-doped MWCNT-based NMC811 cathodes

[0095] 9a) Preparation of the cathode electrode 1.8 gm of cathode active material NMC811 (lithium nickel-manganese-cobalt oxide) was taken and mixed with 48 mg of carbon-fused metal- and heteroatom-doped MWCNTs using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour. Then, 70 mg of carbon black was added and ground for 15 minutes to 2 hours. Next, 82 mg of polymer binder (based on the total composition weight) was added to 2.7 ml of NMP solution and stirred with a magnetic stirrer for 2 to 8 hours to obtain a uniform slurry. The cathode electrode was then cut into a 16 mm diameter disk.

[0096] 9b) Preparation of the anode electrode The anode active material, 85 to 90 wt% graphite (total composition), was taken and mixed with 6 wt% carbon black using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour. A polymer binder was added to the NMP solution at 1 to 5 wt% of the total composition, and the mixture was stirred overnight with a magnetic stirrer to obtain a homogeneous slurry. The anode electrode was then cut into a 16 mm diameter disk.

[0097] 9c) Fabrication of Lithium-ion 2032 Full Coin Cells Full CR2032 coin cells were assembled in an argon-filled glove box using a graphite anode, NMC811 (prepared above) as the cathode, polypropylene Celgard polymer as the separator, and 1 to 1.22 M lithium hexafluorophosphate with various ratios of EC / EMC / DMC organic solvents and vinylene carbonate (VC) as an additive. The coin cells were cycled between 2.75 and 4.2 V in a Biologic BCS805 battery cycler. The fabricated full 2032 coin cells were tested at various rates for rate performance studies.

[0098] [Table 1] Doped MWCNTs prepared from purified raw materials exhibited high rate capability in lithium-ion 2032 full coin cells.

[0099] Example 10 Life cycle comparison of doped MWCNTs with commercial MWCNTs and controls in full lithium-ion batteries

[0100] Anode and cathode electrodes were fabricated in a manner similar to that described in Example 1. CR2032 full coin cells were assembled in an argon-filled glove box using a graphite electrode (prepared above) as the anode, polypropylene Celgard polymer as the separator, and 1 to 1.22 M lithium hexafluorophosphate and organic solvents with various ratios of EC / EMC / DMC as the electrolyte, with vinylene carbonate (VC) as the additive. The coin cells were cycled between 2.75 and 4.2 V in a Biologic BCS805 battery cycler. The fabricated 2032 full coin cells were tested for life cycle studies. The observed capacities at a 1C rate during cycling of the fabricated full cells are shown below.

[0101] [Table 2]

[0102] Example 11 Capacity retention comparison of novel doped MWCNTs with control and commercially available MWCNTs in lithium-ion batteries

[0103] The anode and cathode electrodes were fabricated in the same manner as in Example 1. CR2032 coin cells were assembled in an argon-filled glove box using a graphite electrode (prepared above) as the anode, a polypropylene Celgard polymer as the separator, and 1 to 1.22 M lithium hexafluorophosphate, various organic solvents with EC / EMC / DMC ratios, and vinylene carbonate (VC) as an additive. The coin cells were cycled between 2.75 and 4.2 V using a Biologics cycler.

[0104] BCS805 Battery Cycler. Fabricated 2032 full coin cells were tested for life cycle studies. The total capacity retention observed at 1C rate during cycling of the fabricated full cells is shown below.

[0105] [Table 3]

[0106] Example 12 Rate performance of NCA cathode compared with a control

[0107] The cathode active material, lithium nickel-cobalt-aluminum oxide (NCA), was mixed with 60–100 mg of carbon-fused metal- and heteroatom-doped MWCNTs at 85–95 wt% of the composition using a mortar and pestle / vacuum mixer for 15 min–1 h. Next, 1–5 wt% of the polymer binder was added to the NMP solution and stirred overnight with a magnetic stirrer to obtain a uniform, homogeneous slurry. The cathode electrode was then cut into 16 mm diameter disks. CR2032 half-coin cells were assembled in an argon-filled glovebox using a lithium foil anode, a polypropylene Celgard polymer separator, and a 1 M lithium hexafluorophosphate electrolyte with various EC / EMC organic solvents and vinylene carbonate (VC) additive. The coin cells were cycled between 2.75 and 4.2 V using a Biologic BCS805 battery cycler. The fabricated 2032 half coin cells were tested at various rates for rate performance studies.

[0108] [Table 4] Doped MWCNTs prepared from purified raw materials exhibited high rate capability in lithium-ion 2032 half coin cells.

[0109] Example 13 Fabrication and testing of lithium-ion 2032 full coin cells using carbon-fused metal and heteroatom-doped MWCNTs

[0110] 13a) Preparation of the cathode electrode The cathode active material, lithium nickel cobalt aluminum oxide (NCA), was mixed at 85-95 wt% of the composition with 0.5-6 wt% carbon-fused metal- and heteroatom-doped MWCNTs using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour, followed by 0.5-6 wt% carbon black and grinding for 15 minutes to 2 hours. Next, 1-5 wt% of a polymer binder was added to the NMP solution, based on the total composition weight, and the mixture was stirred overnight with a magnetic stirrer to obtain a uniform slurry. The cathode electrode was then cut into a 16 mm diameter disk.

[0111] 13b) Preparation of the anode electrode The anode active material, 85 to 90 wt% graphite (total composition), was mixed with 6 wt% carbon black using a mortar and pestle / vacuum mixer for 15 minutes to 1 hour. A polymer binder was added to the NMP solution at 1 to 5 wt% of the total composition, and the mixture was stirred overnight with a magnetic stirrer to obtain a homogeneous slurry. The anode electrode was then cut into a 16 mm diameter disk.

[0112] 13c) Fabrication of Lithium-ion 2032 Full Coin Cells

[0113] CR2032 full coin cells were assembled in an argon-filled glove box using a graphite electrode as the anode, NMC811 (prepared above) as the cathode, polypropylene Celgard polymer as the separator, and 1 to 1.22 M lithium hexafluorophosphate with various ratios of EC / EMC / DMC organic solvents and vinylene carbonate (VC) as an additive as the electrolyte. The coin cells were cycled between 2.75 and 4.2 V in a Biologic BCS805 battery cycler. The fabricated 2032 full coin cells were tested at various rates for rate performance studies.

[0114] [Table 5]

[0115] Example 14 High electrical conductivity of carbon fusion-doped MWCNTLiFePO4 cathodes (lithium iron phosphate) and comparison with controls

[0116] Cathode slurries were prepared by mixing 85 to 95 wt% LiFePO4 (lithium iron phosphate) cathode active material with 0.5 to 6 wt% carbon-fused metal- and heteroatom-doped MWCNTs and 0.5 to 6 wt% carbon black. Cathode slurries were then fabricated using 1 to 5 wt% polymer binder in NMP solution. Prior to slurry preparation, the carbon black was dispersed in NMP for 10 minutes to 0.5 hours. The cathode electrodes were then cut into 16 mm diameter disks. In an argon-filled glove box, the cathode working electrode area was 1.77 cm. 2 CR2032 coin cells with different compositions of neat metal and heteroatom-doped MWCNTs were assembled using a lithium foil counter electrode, a Celgard polymer separator, and an electrolyte solution consisting of 1 to 1.22 M lithium hexafluorophosphate dissolved in various organic solvents (ethylene carbonate / diethylene carbonate). Cyclic voltammetry (CV) tests showed a 0.1 mVs voltage drop between 2.5 and 4.0 V. -1 The scan rate was 100 s. The anodic and cathodic peak currents (mA / g) observed from different ratios of neat metal and heteroatom-doped MWCNTs are shown below.

[0117] [Table 6]

[0118] The CV profile of the carbon-fused MWCNT-LFP electrode showed higher anodic and cathodic peak currents than the control. The potential difference between the two redox peaks of the LFP-MWCNT electrode was smaller than that of the control, reflecting lower polarization, higher lithium ion diffusivity, and lower internal resistance. The superior electrical conductivity of the carbon-fused MWCNT electrode facilitates electron transfer and reduces resistance during the reversible lithium ion reaction.

[0119] Example 15 High interfacial surface area and conductance of carbon fusion-doped MWCNTLiFePO4 (LFP) cathode (lithium iron phosphate) and comparison with controls

[0120] Cathode slurries were prepared by mixing 85 to 95 wt% LiFePO4 (lithium iron phosphate) cathode active material with 0.5 to 6 wt% carbon-fused metal- and heteroatom-doped MWCNTs and 0.5 to 6 wt% carbon black. Cathode slurries were then fabricated using 1 to 5 wt% polymer binder in NMP solution. Prior to slurry preparation, the carbon black was dispersed in NMP for 10 minutes to 0.5 hours. The cathode electrodes were then cut into 16 mm diameter disks. In an argon-filled glove box, the cathode working electrode area was 1.77 cm. 2 CR2032 coin cells with different compositions of neat metal and heteroatom-doped MWCNTs were assembled using lithium foil as the counter electrode, Celgard polymer as the separator, and 1 to 1.22 M lithium hexafluorophosphate dissolved in various organic solvents (ethylene carbonate / diethylene carbonate) as the electrolyte. Cyclic voltammetry (CV) tests showed a 0.1 mVs between 2.5 and 4.0 V. -1 The scan rate was 100 s. The anodic and cathodic peak currents (mA / g) observed from different ratios of neat metal and heteroatom-doped MWCNTs are shown below.

[0121] [Table 7]

[0122] The anodic and cathodic peaks appear at approximately 3.6 V and 3.2 V, respectively, which are due to the Fe 2+ / Fe 3+The peak separation between the oxidation and reduction of the redox couple for the fused-doped cathode electrode was 72 mV smaller than that for the control, indicating that the carbon covering the LFP cathode particles in the fused-doped cathode has a high interfacial surface area, resulting in efficient electron conduction during the electrochemical reaction.

Claims

1. a) carbon-fused metal and heteroatom doped multi-walled carbon nanotubes (MWCNTs); b) an active material; and c) carbon black; and d) a polymer binder; and A cathode electrode for a lithium ion battery comprising:

2. 10. The electrode of claim 1, wherein the carbon-fused metal and heteroatom-doped MWCNTs are present in the range of 0.5 to 6 wt.%.

3. 2. The electrode of claim 1, wherein the active material is selected from lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminate (NCA), and lithium iron phosphate (LFP), lithium nickel manganese spinelate (LNMO), lithium manganate (LMO), and lithium cobalt oxide (LCO) and is present in the range of 85 to 95 wt %.

4. 10. The electrode of claim 1, wherein the carbon black is present in the range of 0.5 to 6% by weight.

5. 10. The electrode of claim 1, wherein the polymer binder is polyvinylidene fluoride and is present in the range of 1 to 5 wt. %.

6. 1. A process for making a cathode electrode for a lithium ion battery, comprising: a) preparing metal and heteroatom doped MWCNTs from purified raw materials; b) preparing carbon-fused metal- and heteroatom-doped MWCNTs from the metal- and heteroatom-doped MWCNTs obtained above; c) mixing 85 to 95 wt% of the active material with 0.5 to 6 wt% of the carbon-fused metal and heteroatom doped MWCNTs, and then mixing with 0.5 to 6 wt% of the carbon black to obtain a mixture, and then adding 1 to 5 wt% of the polymer binder to the mixture; d) fabricating a cathode electrode; Including, Step (a) I. Reducing the catalyst using hydrogen gas in a reactor operating at three different temperature ranges: 620-640°C, 645-665°C, and 670-690°C and a pressure of 1 atmosphere; II. feeding purified feedstock into the reactor at a flow rate of 25 to 45 ml / hr for 10 hours in the presence of nitrogen carrier gas; III. Adding 0.1 to 1 g of doped MWCNTs and dilute sulfuric acid (50 to 550 ml) and dispersing for 0.5 to 1 hour to obtain a mixture; IV. Refluxing the mixture of step III at 80-100°C for 2-6 hours at 200-500 rpm to obtain a reaction mixture; V. adding distilled water to the reaction mixture of Step IV and holding for 10 to 15 minutes, followed by decanting and filtering; VI. Repeating step V 4 to 5 times, the resulting mixture is washed to a neutral pH, then dried at 100 to 120°C for 8 to 12 hours, and weighed to obtain metal and heteroatom doped MWCNTs; Including, Step (b) I. Milling 1 to 20 g of carbon black with 80 to 99 g of metal and heteroatom doped MWCNTs to obtain a powder; II. Sonicating the powder obtained in step I in NMP solvent for 0.5 to 1 hour to obtain a resulting mixture; III. Filtering, drying and calcining the resulting mixture to obtain carbon-fused metal and heteroatom-doped MWCNTs; Including, Step (c) I. Mixing carbon-fused metal and heteroatom-doped MWCNTs with an active material, and then adding carbon black to obtain a mixture, wherein the active material is selected from NMC, NCA, LFP, LNMO, LMO, and LCO, and combinations thereof; II. Adding a polymer binder dissolved in NMP solvent to the mixture obtained in step I and stirring for 2 to 8 hours to obtain a homogeneous cathode electrode slurry; Including, Step (d) I. Coating the cathode electrode slurry onto an aluminum foil using an applicator with a thickness of 100 to 300 μm; II. Drying the cathode electrode of step I in a vacuum oven at 100-120°C overnight to obtain a cathode for a lithium ion battery; A process involving:

7. 7. The process of claim 6, The process wherein the metal and heteroatom doped MWCNTs consist of Co: 0.01 to 3100 ppm, Mn: 0.01 to 800 ppm, Fe: 0.01 to 400 ppm, S: 0.001 to 1 wt % and N: 0.01 to 2000 ppm.

8. a) a cathode electrode consisting of an active material, carbon fused metal and heteroatom doped MWCNTs, carbon black and a polymer binder; b) a graphite anode; A lithium-ion battery comprising:

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