Cathode for high-voltage lithium-ion secondary battery and dry manufacturing method thereof

Abstract

A cathode for a high voltage lithium ion secondary battery is described, comprising an electrode layer having an electrode composition containing cathode active particles, a fluoropolymer binder, and conductive carbon. The cathode active particles are a high voltage lithium transition metal oxide, the fluoropolymer binder is a fibrillated tetrafluoroethylene polymer having a high melt creep viscosity, and the conductive carbon is a fluoropolymer having a melt creep viscosity of about 50 m. 2 The carbon fibers have a specific surface area of ​​0.1 μm to 10 μm / g. The carbon fibers and fluoropolymer binder form a conductive structural web that electronically connects the cathode active particles and allows electronic conductivity through the electrode layer. The electrode layer is adhered to a current collector comprising aluminum having a surface roughness and substantially free of a carbon surface coating other than the conductive carbon of the electrode layer. Additionally, a dry binder process for fabricating such cathodes and the utility of such cathodes in high voltage lithium ion secondary batteries are described.

Description

[Technical field]

[0001] The present disclosure relates to lithium-ion secondary battery cathodes for high voltage operation, dry manufacturing methods for such cathodes, and high voltage lithium-ion batteries implementing such cathodes. [Background technology]

[0002] LiCoO 2 (LCO), LiNi x Mn y Co z O 2 (x+y+z=1)(NMC), LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA), LiFePO 4 (LFP), and LiMn 2 O 4 A variety of Li-ion battery (LIB) cathode materials have been successfully commercialized over the past two decades, including LiNi (LMO). With increasing demand for electric vehicles (EVs) and electronic devices, both higher energy density and lower manufacturing costs are commercially desirable features for the next generation of secondary lithium-ion batteries. 0.5 Mn 1.5 O 4 (LNMO) is considered one of the most promising cathode candidates due to its high operating voltage (~4.7V) and absence of cobalt. The high average operating voltage of LNMO can effectively reduce the number of cells for a battery pack system, thus providing a higher volumetric energy density. Unlike conventional cobalt-containing cathode materials such as LCO, NMC, and NCA, the removal of expensive and toxic cobalt makes LNMO one of the most cost-effective cathode materials for electrification applications.

[0003] Despite its high energy density and low cost, LNMO faces various challenges for commercialization. For example, a well-known drawback of LNMO is its low cycling stability in battery systems. Due to the high working potential of LNMO (about 4.7 V), the cathode and electrolyte must be capable of operating in an extremely oxidizing environment. In particular, when using commercially available hydrocarbon carbonate-based electrolytes with low oxidative stability, the violent electrolyte decomposition and large amounts of parasitic reaction products would cause rapid collapse or even safety issues for the battery system. Another challenge of LNMO is its inherently low electronic conductivity (about 10 -6 The conductivity of the conductive carbon is 1-2 orders of magnitude lower than that of commercial NMC, NCA, and LCO. As a result, more than 5 wt.% of conductive carbon has been used in published results to maintain an efficient conductive network. However, this reduces the energy density of the battery system due to the increased content of inactive components. Furthermore, the additional conductive carbon may catalyze additional side reactions that exacerbate the capacity fade. One of the most important side reactions is the reaction of the salt decomposition product PF with traces of water to form the strong acid HF. 5 This reaction is highly corrosive to the electrodes and interphase.

[0004] To improve the performance of LNMO, efforts have been made to address and mitigate potential problems. Developing new electrolytes with additives is the most common strategy to stabilize the interfacial phases of both the cathode and anode. Among the improvements observed in full cells, the 20 mg / cm 2Apart from a few that have demonstrated longer cycle life using less than 1000 cycles, most are limited to 200 cycles, making the improvements less compatible with industrial applications. Material doping is another strategy to stabilize the cathode electrolyte interphase (CEI) while mitigating its decomposition by HF. However, the addition of expensive transition metals inevitably increases the manufacturing cost. Surface coatings applied on the material or electrodes are another method that has been explored to reduce the degradation of the cathode surface and extend the cell cycle. Uniform coating and appropriate coating thickness can help to form a more robust CEI and prevent the dissolution of transition metals. However, the scale-up of sophisticated synthesis processes is a significant industrial challenge. Moreover, the cost of equipment and precursors in surface coating techniques on electrodes, such as atomic layer deposition (ALD), reduces their usefulness in large-scale manufacturing.

[0005] Of the progress made to improve the performance of LNMO, few have considered the compatibility of the proposed strategies with thick electrodes, the most important criterion for practical use. For LNMO, a thick electrode with a capacity of at least 3 mAh / cm per side is required to achieve roughly 300 Wh / kg. 2 (approx. 21mg / cm 2 ) may be required. Previous work to achieve this level of loading has been limited by either low cycle numbers (less than 300 cycles) or low capacity utilization. Therefore, to realize the potential of LNMO under industrially practical conditions, high loading must be achieved in conjunction with other modifications.

[0006] Effective fabrication of thick cathodes is an ongoing technical challenge in the Li-ion battery field. In slurry-based electrode fabrication, N-Methyl-2-pyrrolidone (NMP) is widely used as a solvent due to its excellent chemical and thermal stability, as well as its ability to dissolve polyvinylidene fluoride (PVDF) binder, which provides high mechanical and electrochemical stability in cathode operation. The drying process of thick cathodes can cause the migration of binder and carbon to the top surface of the electrode due to convective and capillary forces generated during the process. This results in poor adhesion between the electrode and current collector, which can lead to severe electrode cracking. For this reason, great efforts have been made to explore effective thick electrode fabrication processes, such as using repeated co-extrusion / assembly to create artificial channels to reduce tortuosity and improve ion flow, dispersing single-wall carbon nanotubes (SWCNTs) to fabricate 800 μm thick electrodes, and utilizing novel binders such as polyacrylonitrile (PAN) to enable high loading. However, these methods have very complicated fabrication procedures or are limited to laboratory-scale processing. Another negative feature of NMP is its toxicity and the need for expensive solvent recycling equipment, making the slurry-based fabrication process even more expensive.

[0007] Unlike the above-mentioned methods, fabrication using binder fibrillation is a dry process, and fibrillizable polytetrafluoroethylene (PTFE) is the known binder utilized. In this process, PTFE particles are shear mixed and, under these conditions, become adhesive fibrils that can bond both conductive carbon and active materials, and such dry electrodes have recently generated increasing industrial interest. Compared to slurry-based methods, this dry process has the potential to fabricate roll-to-roll electrodes with unlimited thickness and minimal cracks. More importantly, the elimination of toxic NMP and solvent recirculation equipment makes the dry process a cost-effective and environmentally friendly electrode manufacturing strategy. Summary of the Invention [Means for solving the problem]

[0008] The present invention provides a wide range of high load (>3mAh / cm 2 This invention addresses the shortcomings of this prior work by providing a dry binder fibrillation process for fabricating cathodes for high voltage lithium ion secondary batteries at low temperature (>4.7V) levels, and demonstrates improved long cycle performance in high voltage (>4.7V) secondary lithium ion battery applications. The stable cycling stability of secondary lithium ion batteries utilizing the cathodes of the invention can be attributed, in part, to the combined factors of reduced parasitic reactions, robust mechanical properties, and a conductive structural web that electronically connects the cathode active particles to enable electronic conductivity through the electrode layer. In one embodiment, the invention provides a cathode for a high voltage lithium ion secondary battery, comprising an electrode layer comprising an electrode composition comprising cathode active particles, a fluoropolymer binder, and conductive carbon, wherein the cathode active particles comprise a lithium transition metal oxide having an electrochemical potential vs. Li / Li+ of at least about 4.5 V, and the fluoropolymer binder has a conductivity of at least about 1.8×10 11 The fluoropolymer binder is fibrillated, and the conductive carbon is about 50 μm. 2 / g or less, wherein the carbon fibers and fibrillated fluoropolymer binder form a conductive structural web that electronically connects the cathode active particles to enable electronic conductivity through the electrode layer, and the electrode layer is adhered to a current collector comprising aluminum having a surface roughness and substantially free of a carbon surface coating other than the conductive carbon of the electrode layer.

[0009] In another embodiment, the present invention provides a high voltage lithium ion secondary battery, comprising a cathode comprising an electrode layer comprising an electrode composition comprising cathode active particles, a fluoropolymer binder, and conductive carbon, wherein the cathode active particles comprise a lithium transition metal oxide having an electrochemical potential vs. Li / Li+ of at least about 4.5 V, and the fluoropolymer binder has a conductivity of at least about 1.8×10 11 The fluoropolymer binder is fibrillated and the conductive carbon is about 50 μm thick. 2 a cathode comprising carbon fibers having a specific surface area of ​​0.1 μm to 1 μm / g, wherein the carbon fibers and fibrillated fluoropolymer binder form a conductive structural web that electronically connects the cathode active particles to enable electronic conductivity through the electrode layer, the electrode layer being adhered to a current collector comprising aluminum having a surface roughness and substantially free of a carbon surface coating other than the conductive carbon of the electrode layer; An anode; a separator between the cathode and the anode; an electrolyte in communication with the cathode, the anode, and the separator.

[0010] In another embodiment, the present invention provides a method for producing a cathode for use in a high voltage lithium ion secondary battery, comprising the steps of: I.) i) Conductive carbon comprising carbon fibers, in a preferred embodiment the carbon fibers are about 50 m 2 / g or less of a specific surface area, ii) cathode active particles comprising a lithium transition metal oxide having an electrochemical potential vs. Li / Li+ of at least about 4.5 V; iii) at least about 1.8 × 10 11 and a fluoropolymer binder comprising a tetrafluoroethylene polymer having a melt creep viscosity of 100 poise; forming a powdered dry cathode mixture, the dry milling fibrillating the fluoropolymer binder and forming a conductive structural web comprising the fluoropolymer binder and conductive carbon, the conductive structural web electronically connecting the cathode active particles to enable electronic conductivity throughout the cathode; II.) Calendering the powdered dry cathode mixture to form a dry cathode electrode layer; III.) Adhering the dried cathode electrode layer to a current collector comprising aluminum having a surface roughness and being substantially free of any carbon surface coating other than the conductive carbon of the cathode electrode layer.

[0011] In another embodiment, the present invention provides a conductive structural web interconnecting conductive particles, comprising: Carbon fiber, and at least about 1.8×10 11 comprising a tetrafluoroethylene polymer having a melt creep viscosity in poise; the carbon fibers and tetrafluoroethylene polymer are combined in the form of a conductive structural web that electronically connects the conductive particles to provide structural reinforcement and electrical conductivity through a solid structure that includes the conductive particles; a portion of the tetrafluoroethylene polymer and a portion of the carbon fibers in the web are (A.) a composite in the form of conductive reinforcing strands comprising a continuous tetrafluoroethylene polymer matrix and a plurality of carbon fibers; The carbon fibers are embedded in and adhered to a tetrafluoroethylene polymer matrix comprising strands; the longitudinal axes of the carbon fibers are substantially aligned with the longitudinal axes of the strands; The strands are randomly interwoven and interconnected throughout the volume between the conductive particles that comprise the solid structure, with the strands contacting the conductive particles. [Brief description of the drawings]

[0012] [Figure 1] 1 is a plan view image of the surface of this electrode layer by SEM at 6.71K magnification. [Diagram 2] 1 is a plan view image of the surface of this electrode layer by SEM at 14.04K magnification. [Diagram 3] 1 is a plan view image of the surface of this electrode layer by SEM at 22.19K magnification. [Figure 4] 1 is a plot of C / 10 rate half-cell performance (voltage (V)) versus specific capacity (mAh / g) of the half-cell battery using dry process LNMO cathodes of the present invention with areal loadings of 3, 4, 6, and 9.5 mAh / cm2. [Diagram 5] 1 is a plot of C / 10 rate half-cell performance (voltage (V)) versus specific capacity (mAh / g) of the half-cell battery using comparative slurry LNMO cathodes with areal loadings of 3 and 4 mAh / cm2. [Figure 6] 1 is a cross-sectional SEM image of an LNMO cathode fabricated by the dry method of the present invention in this Example 1, with an areal capacity of 9.5 mAh / cm2 corresponding to a thickness of about 240 μm. [Figure 7] 1 is a cross-sectional SEM image of an LNMO cathode made by the comparative solvent slurry method of this Comparative Example 1, having an areal capacity of 4 mAh / cm2 corresponding to a thickness of about 110 μm. [Figure 8] FIG. 1 is a plot of extended cycling (up to 1,000 cycles) performance (specific capacity (mAh / g) and coulombic efficiency (%) vs. cycle number) at C / 3 rate of full-cell batteries using LMNO cathodes prepared by the dry process of the present invention compared to similar comparative full-cell batteries using LMNO cathodes prepared by the slurry process, each cathode having an areal loading of 3 mAh / cm2. [Figure 9]1 is a plot of average charge voltage (V) and average discharge voltage (V) versus cycle number over 300 cycles for a full-cell battery using a dry process LMNO cathode of the present invention compared to a similar full-cell battery using a LNMO cathode prepared by a slurry process, each cathode having an areal loading of 3 mAh / cm2. [Figure 10] FIG. 13 is a dQ / dV plot (dQ / dV (mAh / g v-1) vs. voltage (V)) of a full cell battery of the present invention using a LMNO cathode prepared by a dry process of the present invention with an areal loading of 3 mAh / cm2. [Figure 11] FIG. 13 is a dQ / dV plot (dQ / dV (mAh / g v-1) versus voltage (V)) of a comparative full cell battery using a LNMO cathode prepared by the comparative slurry method with an areal loading of 3 mAh / cm2. [Figure 12] FIG. 13 is a Nyquist plot (-Z″ / Ω vs. Z′ / Ω) generated by Electrical Impedance Spectroscopy (EIS) for a full cell battery of the invention using a LMNO cathode prepared by the dry method of the invention and a comparative full cell battery using a cathode prepared by the comparative slurry method, after 50 and 100 cycles, each cathode having an areal loading of 3 mAh / cm2. [Figure 13] FIG. 1 is a plot of energy density (Wh / kg) and energy efficiency (%) versus cycle number over 300 cycles for a full cell battery using a dry process LMNO cathode of the present invention and a similar comparative full cell battery using a cathode prepared by the comparative slurry process. [Figure 14] 1 is a plot comparing the performance (specific capacity (mAh / g) and coulombic efficiency (%) versus cycle number) of a full cell battery using a dry process prepared LMNO cathode of the present invention using Gen2 electrolyte and a similar dry process prepared LMNO cathode of the present invention using a fluorinated (FEC-FEMC) electrolyte. [Figure 15]FIG. 1 is a plot of energy density (Wh / kg) and energy efficiency (%) versus cycle number over 200 cycles for a full cell battery using a dry-process prepared LMNO cathode of the present invention using Gen2 electrolyte, and a similar dry-process prepared LMNO cathode of the present invention using a fluorinated (FEC-FEMC) electrolyte, each cathode having an areal loading of 3 mAh / cm2. [Figure 16] 1 is a plot of average charge voltage (V) and average discharge voltage (V) versus cycle number over 200 cycles for a full cell battery using a dry process prepared LMNO cathode of the present invention using Gen2 electrolyte, and a similar dry process prepared LMNO cathode of the present invention using a fluorinated (FEC-FEMC) electrolyte, each cathode having an areal loading of 3 mAh / cm2. [Figure 17] FIG. 1 is a plot of discharge capacity (mAh / g) and coulombic efficiency (%) versus cycle number for a full cell battery using a dry process prepared LMNO cathode of the present invention on a current collector comprising aluminum substantially free of a carbon coating (other than the conductive carbon contained in the electrode layer) on the aluminum surface in contact with the electrode layer, and a similar dry process prepared LMNO cathode on a current collector comprising aluminum with a carbon coating, each cathode having an areal loading of 3 mAh / cm2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Cathode The electrode layer comprises an electrode composition comprising, in part, relatively high voltage operable cathode active particles comprising a lithium transition metal oxide. The cathode active particles have an electrochemical potential vs. Li / Li+ of at least about 4.5 V, and in some embodiments, at least about 4.6 V vs. Li / Li+. Exemplary high voltage capable cathode active particles comprising lithium transition metal oxides are known in the art and are described in the art as LNMO (e.g., LiNi x Mn 2-x O 4), and lithium nickel manganese oxide, also known in the art as LRLO (e.g., Li 1.098 Mn 0.533 Ni 0.113 Co 0.138 O 2 ) are also known as lithium-rich layered oxides. 0.5 Mn 1.5 O 4 , LiNi 0.45 Mn 1.45 Cr 0.1 O 4 , LiCr 0.5 Mn 1.5 O 4 , LiCrMnO 4 , LiCu 0.5 Mn 1.5 O 4 , LiCoMnO 4 , LiFeMnO 4 , LiNiVO 4 , LiNiPO 4 , LiCoPO 4 , and Li 2 CoPO 4 Examples include F.

[0014] The electrode layer comprises an electrode composition comprising, in part, conductive carbon containing carbon fibers. The carbon fibers have a length of about 10 micrometers to about 200 micrometers. In some embodiments, the carbon fibers have a diameter of about 0.1 micrometers to about 0.2 micrometers. The carbon fibers have a length of about 50 micrometers to about 200 micrometers. 2 In some embodiments, the carbon fibers have a specific surface area of ​​about 40 m 2 / g or less, or about 30m 2 / g or less, or about 20m 2 In some embodiments, the electrode layer has a specific surface area of ​​about 50 m 2 / g or about 40m 2 / g or more than 30m 2 / g or about 20m 2The conductive carbon is substantially free of conductive carbon having a specific surface area greater than 1 / g. Examples of such relatively low specific surface area conductive carbon containing carbon fibers include materials known as vapor grown carbon fibers, also referred to in the art as VGCF.

[0015] The inventors have discovered that conductive carbons having a relatively high surface area relative to the present conductive carbons result in decreased battery cycling performance and coulombic efficiency when the batteries of the present invention are operated at high voltages due to decomposition of conventional electrolytes that is believed to be catalyzed by such high surface area carbon during high voltage operation.

[0016] The electrode layer includes an electrode composition that includes, in part, a fluoropolymer binder. The fluoropolymer binder has at least about 1.8×10 11 In another embodiment, the tetrafluoroethylene polymer has a melt creep viscosity of at least about 2.0×10 11 In another embodiment, the tetrafluoroethylene polymer has a melt creep viscosity of at least about 3.0×10 11 In a preferred embodiment, the tetrafluoroethylene polymer has a melt creep viscosity of at least about 4.0×10 11 The melt creep viscosity (MCV) is measured in Poise by the method described in Ebnesajjad, Sina, (2015), Fluoroplastics, Volume 1-Non-Melt Processible Fluoropolymers-The Definitive User's Guide and Data Book (2nd Edition), Appendix 5, Melt Creep Viscosity of Polytetrafluoroethylene, pp. 660-661, with reference to U.S. Pat. No. 3,819,594.

[0017] The tetrafluoroethylene polymer is a polymer containing repeating units of tetrafluoroethylene monomer, also referred to in the art as TFE, and has a molecular weight of at least about 1.8×10 11 It has a melt creep viscosity of Poise. At such high melt viscosity, the polymer does not flow in the molten state and is therefore not melt processable. In one embodiment, the tetrafluoroethylene polymer is a tetrafluoroethylene homopolymer consisting of repeating units of tetrafluoroethylene monomer, also known in the art as polytetrafluoroethylene and abbreviated as PTFE. In another embodiment, the tetrafluoroethylene polymer is a "modified" PTFE, which refers to a copolymer of TFE and a low concentration of comonomer such that the melting point of the resulting polymer is not substantially lowered below the melting point of homopolymer PTFE. The concentration of such comonomer in the modified PTFE is less than 1% by weight, preferably less than 0.5% by weight. Generally, a minimum amount of at least about 0.05% by weight is used to have a significant effect. Exemplary comonomers in the modified PTFE include perfluoroolefins, particularly hexafluoropropylene (HFP) or perfluoro(alkyl vinyl ether) (PAVE), perfluoro(ethyl vinyl ether) (PEVE), and perfluoro(propyl vinyl ether) (PPVE), in which the alkyl group contains 1 to 5 carbon atoms, and chlorotrifluoroethylene (CTFE), perfluorobutyl ethylene (PFBE), or other similar monomers that introduce relatively bulky side groups into the polymer chain.

[0018] The tetrafluoroethylene polymer is fibrillizable, meaning that the tetrafluoroethylene polymer is capable of forming fibrils of at least one dimension of nano-size (i.e., <100 nm width) that can vary in length from submicrometers to several micrometers to tens of micrometers when the tetrafluoroethylene polymer is subjected to shear forces, for example, during the performance of the method.

[0019] The electrode layer includes an electrode composition including cathode active particles, a fluoropolymer binder, and conductive carbon, and in one embodiment, contains about 1 to about 10 weight percent conductive carbon, about 0.5 to about 5 weight percent fluoropolymer binder, and the remainder cathode active particles, based on the combined weight of the fluoropolymer binder, the cathode active particles, and the conductive carbon. In another embodiment, the electrode composition contains about 2 to about 7 weight percent conductive carbon, about 1 to about 3 weight percent fluoropolymer binder, and the remainder cathode active particles. In a preferred embodiment, the electrode composition contains about 5 weight percent conductive carbon and about 2 weight percent fluoropolymer binder.

[0020] The electrode layer is adhered to a current collector comprising aluminum having a surface roughness. In one embodiment, the surface roughness of the aluminum current collector, expressed as Sa (arithmetic mean height), is at least about 260 nm. In another embodiment, the surface roughness of the aluminum current collector is at least about 280 nm. In a preferred embodiment, the surface roughness of the aluminum current collector is at least about 300 nm.

[0021] The cathode has a concentration of at least about 10 to about 90 mg / cm 2 The cathode active particles have a loading level on the current collector that is

[0022] The electrode layer is adhered to a current collector comprising aluminum that is substantially free of a carbon coating on the aluminum surface in contact with the electrode layer other than the conductive carbon contained in the electrode layer. Conventional aluminum foil current collectors have a carbonaceous coating for the purpose of protecting the aluminum current collector. The present aluminum current collector is substantially free of such a carbonaceous coating. The inventors have discovered that the presence of a carbon coating on the aluminum surface in contact with the electrode layer results in a decrease in battery cycling performance and coulombic efficiency in the high voltage compatible battery of the present invention. Without wishing to be bound by theory, the inventors believe that this is due to the decomposition of conventional electrolytes that is believed to be catalyzed by such high surface area carbon coatings during high voltage operation.

[0023] The electrode layer can have a selected thickness suitable for a certain battery application. The thickness of the electrode layer as provided herein can be greater than that of the electrode layer prepared by conventional processes. This increase in the thickness of the electrode layer is made possible by the carbon fibers and fibrillated fluoropolymer binder in the electrode layer that form a conductive structural web that electronically connects the cathode active particles to enable electronic conductivity through the relatively thicker electrode layer. In some embodiments, the electrode layer can have a thickness of at least about 60 micrometers, about 70 micrometers, about 80 micrometers, about 90 micrometers, about 100 micrometers, about 110 micrometers, about 115 micrometers, about 120 micrometers, about 130 micrometers, about 135 micrometers, about 140 micrometers, about 145 micrometers, about 150 micrometers, about 155 micrometers, about 160 micrometers, about 170 micrometers, about 180 micrometers, about 190 micrometers, about 200 micrometers, about 250 micrometers, about 260 micrometers, about 265 micrometers, about 270 micrometers, about 280 micrometers, about 290 micrometers, about 300 micrometers, about 350 micrometers, about 400 micrometers, about 450 micrometers, about 500 micrometers, about 750 micrometers, about 1 mm, or about 2 mm, or any range of values ​​therebetween. The thickness of the electrode layer can be selected to correspond to a desired areal capacity, specific capacity, areal energy density, energy density, or specific energy density of the high voltage lithium ion secondary battery of the invention.

[0024] In the present cathodes for high voltage lithium ion secondary batteries, the carbon fibers and fibrillated fluoropolymer binder form a conductive structural web that electronically connects the cathode active particles to allow electronic conductivity through the electrode layer and also maintains structural integrity in the electrode layer by fixing the cathode active particles in place.

[0025] In one embodiment, the invention provides a cathode for a lithium ion secondary battery comprising a cathode active layer comprising a conductive structural web connecting substantially spherical cathode active particles in a cathode active layer of the lithium ion secondary battery cathode, the conductive structural web comprising a PTFE binder and conductive carbon fibers; A. a portion of the PTFE and a portion of the carbon fibers in the web are combined in the form of conductive strands comprising a continuous PTFE matrix and a plurality of carbon fibers, the carbon fibers being embedded in and adhered to the PTFE matrix comprising the strands, the longitudinal axes of the carbon fibers being substantially aligned with the longitudinal axes of the strands, and the strands being randomly interwoven and interconnected throughout the volume between and in contact with the cathode active particles; B. a portion of the PTFE and a portion of the carbon fibers in the web are combined in the form of discontinuous randomly matted regions positioned adjacent to and attached to the cathode active particles, the carbon fibers being embedded in and adhered to the PTFE comprising regions; C. a portion of the PTFE in the web is in the form of free PTFE fibrils (i.e., PTFE fibrils that are substantially free of carbon fibers); D. a portion of the PTFE in the web is in the form of a PTFE coating layer covering a portion of the surface of some of the cathode active particles; E. A portion of the carbon fibers in the web are free of conductive carbon fibers (i.e., carbon fibers substantially free of PTFE); The conductive strands (A.), discontinuous random matted regions (B.), free fluoropolymer fibrils (C.), PTFE coating layer (D.), and no conductive carbon fibers (E.) are randomly interconnected with each other throughout the electrode layer and are in contact with the surfaces of the cathode active particles, thereby forming a conductive structural web that electrically connects and secures the cathode particles in place.

[0026] FIG. 1 is a plan view image of the surface of this electrode layer by SEM at 6.71K magnification. 101 is a conductive strand comprising PTFE and carbon fiber (A.). 102 is a discontinuous matted area of ​​PTFE and carbon fiber located between and attached to cathode active particles 103 (B.). 104 is PTFE in the form of free fluoropolymer fibrils (C.). 105 is PTFE in the form of a coating layer covering a portion of the cathode particles 103 (D.). 106 is free carbon fiber.

[0027] Figure 2 is a plan view image of the surface of this electrode layer by SEM at 14.04K magnification, further enlarging a portion of the image of Figure 1. 101 is a conductive strand comprising PTFE and carbon fiber (A.). 102 is a discontinuous matted area of ​​PTFE and carbon fiber located between and attached to the cathode active particles 103 (B.). 104 is PTFE in the form of free fluoropolymer fibrils (C.). 105 is PTFE in the form of a coating layer covering a portion of the cathode particles 103 (D.). 106 is free carbon fiber.

[0028] 3 is a plan view image of the surface of this electrode layer by SEM at 22.19 K magnification. 301 are two conductive strands comprising PTFE and carbon fiber (A.) in a volume between and in contact with cathode active particles 302. The PTFE phase is clearly visible at 303.

[0029] The conductive structural web of the present invention, comprising fibrillated PTFE binder and conductive carbon fibers, allows for the formation of electrodes that are much thicker than conventional electrodes with excellent electrical conductivity throughout the entire volume of such relatively thick electrodes. The electrical conductivity can be assessed by conventional methods, such as two-point probe and four-point probe electrical conductivity methods. In some embodiments, the thickness of the present electrode layer is at least about X micrometers, and the two-point probe electrical conductivity is at least about 1×10 -2S / cm and the four-point probe conductivity is at least about 1×10 -2 As used herein, X is selected from the group consisting of the following values: 60, 70, 80, 90, 100, 110, 115, 120, 130, 135, 140, 145, 150, 155, 160, 170, 180, 190, 200, 250, 260, 265, 270, 280, 290, 300, 350, 400, 450, 500, 750, 1,000 (i.e., 1 mm), and 2000 (i.e., 2 mm), and any range of values ​​therebetween.

[0030] In one embodiment, the present invention provides a conductive structural web interconnecting conductive particles, comprising: Carbon fiber, and at least about 1.8×10 11 may be described as a conductive structural web comprising a tetrafluoroethylene polymer having a melt creep viscosity in poise; the carbon fibers and tetrafluoroethylene polymer are combined in the form of a conductive structural web that electronically connects the conductive particles to provide structural reinforcement and electrical conductivity through a solid structure that includes the conductive particles; a portion of the tetrafluoroethylene polymer and a portion of the carbon fibers in the web are (A.) a composite in the form of conductive reinforcing strands comprising a continuous tetrafluoroethylene polymer matrix and a plurality of carbon fibers; The carbon fibers are embedded in and adhered to a tetrafluoroethylene polymer matrix comprising strands; the longitudinal axes of the carbon fibers are substantially aligned with the longitudinal axes of the strands; The strands are randomly interwoven and interconnected throughout the volume between the conductive particles that comprise the solid structure, with the strands contacting the conductive particles.

[0031] In one embodiment, the conductive structural web comprises: B. a portion of the tetrafluoroethylene polymer and a portion of the carbon fibers in the web are combined in the form of discontinuous random matted regions located adjacent to and attached to the conductive particles, the carbon fibers being embedded in and adhered to the tetrafluoroethylene polymer comprising the regions; C. a portion of the tetrafluoroethylene polymer in the web is in the form of free tetrafluoroethylene polymer fibrils; D. a portion of the tetrafluoroethylene polymer in the web is in the form of a tetrafluoroethylene polymer coating layer covering a portion of the surface of some of the conductive particles; and E. a portion of the carbon fibers in the web are free of conductive carbon fibers; The conductive reinforcing strands (A.), discontinuous random matted regions (B.), free fluoropolymer fibrils (C.), tetrafluoroethylene polymer coating layer (D.), and no conductive carbon fibers (E.) are randomly interconnected with each other throughout the conductive structural web and are in contact with the surfaces of the conductive particles, thereby forming a conductive structural web that electrically connects the conductive particles and secures them in place.

[0032] In a preferred embodiment, the conductive structural web includes all of elements A, B, C, D, and E described above.

[0033] In one embodiment of the conductive structural web, the carbon fibers (conductive carbon) are about 50 m 2 In an alternative embodiment of the conductive structural web, the carbon fibers have a specific surface area of ​​about 40 m 2 In an alternative embodiment of the conductive structural web, the carbon fibers have a specific surface area of ​​about 30 m 2 In an alternative embodiment of the conductive structural web, the carbon fibers have a specific surface area of ​​about 20 m 2 / g or less.

[0034] In one embodiment of the conductive structural web, the carbon fibers have a length of about 10 micrometers to about 200 micrometers. In one embodiment of the conductive structural web, the conductive carbon fibers have a diameter of about 0.1 micrometers to about 0.2 micrometers.

[0035] In one embodiment of the conductive structural web, the tetrafluoroethylene polymer has a viscosity of at least about 2.0×10 11 In an alternative embodiment of the conductive structural web, the tetrafluoroethylene polymer has a melt creep viscosity of at least about 3.0×10 11 In an alternative embodiment of the conductive structural web, the tetrafluoroethylene polymer has a melt creep viscosity of at least about 4.0×10 11 It has a melt creep viscosity of poise.

[0036] In one embodiment, the conductive structural web is formed by a solvent-free process. In an alternative embodiment, the conductive structural web is formed by dry blending the particles, tetrafluoroethylene polymer, and carbon fibers to form an electrode composition, and applying a shear force to the electrode composition in the absence of a solvent to form the conductive structural web.

[0037] In one embodiment of the conductive structural web, the conductive carbon fibers comprise vapor grown carbon fibers (VGCF).

[0038] In one embodiment of the conductive structural web, the particles are active particles comprising a lithium transition metal oxide having an electrochemical potential vs. Li / Li+ of at least about 4.5 V. In an alternative embodiment of the conductive structural web, the particles are active particles comprising a lithium transition metal oxide having an electrochemical potential vs. Li / Li+ of at least about 4.6 V. In one embodiment of the conductive structural web, the lithium transition metal oxide is LiNi x Mn 2-x O 4 (LNMO) and Li 1.098 Mn 0.533 Ni 0.113Co 0.138 O 2 (Li-rich layered oxide (LRLO)). In one embodiment of the conductive structural web, the lithium transition metal oxide is selected from the group consisting of LiNi 0.5 Mn 1.5 O 4 , LiNi 0.45 Mn 1.45 Cr 0.1 O 4 , LiCr 0.5 Mn 1.5 O 4 , LiCrMnO 4 , LiCu 0.5 Mn 1.5 O 4 , LiCoMnO 4 , LiFeMnO 4 , LiNiVO 4 , LiNiPO 4 , LiCoPO 4 and Li 2 CoPO 4 F.

[0039] In one embodiment of the conductive structural web, the tetrafluoroethylene polymer is fibrillated so that the conductive structural web is self-supporting.

[0040] In one embodiment, the conductive structural web has a thickness of from about 60 micrometers to about 250 micrometers. In an alternative embodiment, the conductive structural web has a thickness of from about 80 micrometers to about 120 micrometers. In an alternative embodiment, the conductive structural web has a thickness of at least about 240 micrometers.

[0041] battery In one embodiment, the invention is a high voltage lithium ion secondary battery comprising a cathode as defined hereinabove, an anode, a separator between the cathode and the anode, and an electrolyte in communication with the cathode, the anode, and the separator.

[0042] Anodes of the present invention include those capable of continuous high voltage operation of the cell, examples include graphite anodes, pure silicon anodes, or lithium metal anodes.

[0043] In one embodiment, the anode of the battery is a graphite anode. In one embodiment, the graphite anode comprises about 80% to about 98% by weight of active material and has a specific capacity of at least about 300 to about 370 mAh / g at a discharge rate of at least about C / 20 to about 2C, and has a specific capacitance of at least about 5 to about mg / cm. 2 Following activation of the battery in the first charge cycle, the negative electrode has a specific discharge capacity of at least about 300 to about 370 mAh / g based on the weight of the negative electrode active material at a rate of at least about C / 20 to about 2C, the battery has a discharge energy density of at least about 260 to about 340 Wh / kg at a rate of at least about C / 20 to about 5C, and the battery has a discharge energy density at the 100th charge / discharge cycle that is at least about 90% of the discharge energy density at the 3rd cycle.

[0044] In one embodiment, the anode is a pure silicon anode, and the battery has a discharge energy density of at least about 340 to about 650 Wh / kg at a rate of at least about C / 20 to about 5C, and the battery has a discharge energy density at the 100th charge / discharge cycle that is at least about 90% of the discharge energy density at the 3rd cycle.

[0045] In one embodiment, the anode is a lithium metal anode, and the battery has a discharge energy density of at least about 300 to about 560 Wh / kg at a rate of at least about C / 20 to about 5C, and the battery has a discharge energy density at the 100th charge / discharge cycle that is at least about 90% of the discharge energy density at the 3rd cycle.

[0046] The separator of the present high voltage lithium ion secondary battery invention includes conventional separators for lithium ion secondary batteries that allow for continuous high voltage operation of the battery. The separator is configured to electrically insulate two adjacent electrodes on either side of the separator while allowing ionic communication between the two adjacent electrodes. The separator can include a suitable porous, electrically insulating material. In some embodiments, the separator can include a polymeric material. For example, the separator can include a cellulosic material (e.g., paper), a polyethylene resin, a polypropylene resin, and / or a mixture thereof.

[0047] The electrolyte of the high voltage lithium ion secondary battery invention includes conventional electrolytes for lithium ion secondary batteries that allow for continuous high voltage operation of the battery. The electrolyte facilitates ionic communication between the electrodes of the battery and is typically in contact with the cathode, anode, and separator. In one embodiment, the battery uses a suitable lithium-containing electrolyte, such as a lithium salt and a solvent, such as a non-aqueous or organic solvent, or a fluorinated organic solvent. Generally, the lithium salt includes an anion that is redox stable. In some embodiments, the anion can be monovalent. In some embodiments, the lithium salt is hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO 2 CF 3 ) 2 ), lithium trifluoromethanesulfonate (LiSO 3 CF 3), lithium bis(oxalato)borate (LiBOB), and combinations thereof. In some embodiments, the electrolyte can include a quaternary ammonium cation and an anion selected from the group consisting of hexafluorophosphate, tetrafluoroborate, and iodide. In some embodiments, the salt concentration can be about 0.1 mol / L (M) to about 5 M, about 0.2 M to about 3 M, or about 0.3 M to about 2 M. In further embodiments, the salt concentration of the electrolyte can be about 0.7 M to about 1 M. In some embodiments, the salt concentration of the electrolyte can be about 0.2 M, about 0.3 M, about 0.4 M, about 0.5 M, about 0.6 M, about 0.7 M, about 0.8 M, about 0.9 M, about 1 M, about 1.1 M, about 1.2 M, or any range of values ​​therebetween.

[0048] In some embodiments, the electrolyte of the present high voltage lithium ion secondary battery invention comprises a liquid solvent. In further embodiments, the solvent can be an organic solvent. In some embodiments, the solvent can comprise one or more functional groups selected from carbonates, ethers, and / or esters. In some embodiments, the solvent can comprise a carbonate. In further embodiments, the carbonate can be selected from cyclic carbonates such as, for example, ethylene carbonate (EC), propylene carbonate (PC), vinyl ethylene carbonate (VEC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), methyl (2,2,2-trifluoroethyl) carbonate (FEMC), and combinations thereof, or acyclic carbonates such as, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and combinations thereof. In an embodiment, the electrolyte can include LiPF6 and one or more carbonates. Exemplary organic solvent electrolytes include those known in the art as "Gen2" electrolytes, which are 1.0 M LiPF in ethylene carbonate (EC) and ethyl methyl carbonate (EMC). 6 and the weight ratio of EC:EMC is 3:7. In a preferred embodiment, the electrolyte used in the present high voltage lithium ion secondary battery invention is a fluorinated organic solvent electrolyte. For example, a fluorinated electrolyte called FEC-FEMC is 1M LiPF in fluoroethylene carbonate (FEC) and methyl (2,2,2-trifluoroethyl) carbonate (FEMC) with a volume ratio of FEC:FEMC of 1:9. 6 It is.

[0049] In one embodiment, the lithium ion secondary battery is capable of an energy density of at least about 350 Wh / kg at a rate of at least about C / 20. In another embodiment, the lithium ion secondary battery is capable of an energy density of at least about 400 Wh / kg at a rate of at least about C / 20. In another embodiment, the lithium ion secondary battery is capable of an energy density of at least about 450 Wh / kg at a rate of at least about C / 20. In another embodiment, the lithium ion secondary battery is capable of an energy density of at least about 500 Wh / kg at a rate of at least about C / 20. In another embodiment, the lithium ion secondary battery is capable of an energy density of at least about 550 Wh / kg at a rate of at least about C / 20. In another embodiment, the lithium ion secondary battery is capable of an energy density of at least about 600 Wh / kg at a rate of at least about C / 20. In another embodiment, the lithium ion secondary battery is capable of an energy density of at least about 650 Wh / kg at a rate of at least about C / 20.

[0050] method In one embodiment, the present invention relates to a method for producing a cathode as defined hereinbefore for use in a high voltage lithium ion secondary battery, comprising the steps of: I.) i) Length of about 10 micrometers to about 200 micrometers and about 50 m 2 / g or less of a specific surface area of ​​a conductive carbon containing carbon fibers; ii) cathode active particles comprising a lithium transition metal oxide having an electrochemical potential vs. Li / Li+ of at least about 4.5 V; iii) at least about 1.8 × 10 11and a fluoropolymer binder comprising a tetrafluoroethylene polymer having a melt creep viscosity of poise to form a powdered dry cathode mixture, the dry milling fibrillating the fluoropolymer binder and forming a conductive structural web comprising the fluoropolymer binder and conductive carbon, the conductive structural web electronically connecting the cathode active particles to enable electronic conductivity throughout the cathode; II.) Calendering the powdered dry cathode mixture to form a dry cathode electrode layer; III.) Adhering the dried cathode electrode layer to a current collector comprising aluminum having a surface roughness and being substantially free of any carbon surface coating other than the conductive carbon of the cathode electrode layer.

[0051] This dry milling process substantially homogeneously distributes a relatively small mass of carbon fibers and fluoropolymer binder with a relatively large mass of cathode active particles.

[0052] In one embodiment, I.) the carbon fibers subjected to the dry-grinding step are in the form of agglomerates, and the dry-grinding is sufficient to substantially deagglomerate such agglomerates, resulting in single carbon fibers and / or relatively small clusters of carbon fibers.

[0053] The method forms the electrode layer in a solvent-free manner. In one embodiment of the method, the electrode layer is formed by dry mixing the cathode active particles, the fluoropolymer binder, and the conductive carbon in the absence of an organic solvent or water to form a dry electrode composition, and applying a shear force to the dry electrode composition in the absence of a solvent to form the electrode layer.

[0054] In one embodiment, the fluoropolymer binder is fibrillated such that the cathode electrode layer is self-supporting, meaning that the cathode electrode layer has sufficient tensile strength and tear and puncture resistance such that it can be fabricated and handled as a self-supporting film without a backing or support film, and manipulated and applied to a current collector without suffering damage (e.g., cracking, tearing, wrinkling, buckling, stretching, etc.).

[0055] In one embodiment of the method, I.) the dry-grinding step further includes dry-grinding a mixture including conductive carbon and dry cathode active particles under first conditions to result in a first dry mixture, then adding a dry fluoropolymer binder to the first dry mixture to form a second dry mixture, and dry-grinding the second dry mixture under second conditions to form a powdered dry cathode mixture in which the fluoropolymer binder is fibrillated.

[0056] This dry-grinding step I.) is carried out at room temperature to elevated temperatures. In one embodiment, the dry-grinding is carried out at a temperature of about 40°C to about 150°C.

[0057] This dry-grinding step I.) is carried out by applying a shear force to the materials being ground. In embodiments where the conductive carbon, cathode active particles and fluoropolymer binder are combined and then ground together at one time, the shear applied is sufficient to homogenously distribute the materials and fibrillate the fluoropolymer binder without substantially destroying the conductive carbon fibers or cathode active particles.

[0058] In one embodiment where the conductive carbon fibers are initially obtained from the supplier as agglomerates, it is preferred to dry-mill the conductive carbon sufficiently to substantially deagglomerate the agglomerates to result in single carbon fibers and / or clusters of relatively small carbon fibers. In this embodiment, the conductive carbon fibers can be dry-milled alone or, in a preferred embodiment, together with the cathode active particles, so that the conductive carbon results in single carbon fibers or clusters of relatively small carbon fibers, and the conductive carbon is uniformly dispersed throughout the cathode active particles. In this embodiment, a fluoropolymer binder is then subsequently added to the ground mixture of the conductive carbon and the cathode active particles, and the mixture can then be further ground to homogenously distribute all the materials and fibrillate the fluoropolymer binder without substantially destroying the conductive carbon fibers or the cathode active particles.

[0059] In one embodiment, the dry milling is performed by rolling, such as in a bottle roller or, for example, in a rotary drum mixer, to impart sufficient shear force such that the fluoropolymer binder is fibrillated and the carbon fibers are substantially unbroken and homogeneously distributed throughout the powdered dry cathode active particles, and to result in the formation of a conductive structural web comprising the fluoropolymer binder and the conductive carbon. In one embodiment, the rolling can be performed at a rotation speed of about 30 to about 150 rpm. In a preferred embodiment, the rolling is performed at a rotation speed of about 70 to about 90 rpm. In a preferred embodiment, the rolling is performed at a rotation speed of from about 80 rpm. In one embodiment, the rolling can be performed for a duration of at least about 1 hour. In one embodiment, the rolling is performed at room temperature to an elevated temperature. In one embodiment, the rolling is performed at a temperature of about 70° C. to about 250° C. In a preferred embodiment, the rolling is performed at a temperature of about 80° C.

[0060] In one embodiment, dry milling is carried out using a mortar and pestle at an elevated temperature (e.g., 80°C) for a period of time and applying sufficient shear force to result in homogenous mixing of the materials, fibrillation of the PTFE, and formation of the conductive structural web. In the mortar and pestle milling method, care must be taken not to impart excessive shear on the mixture as this may undesirably substantially fragment (shorten) the fibers of the VGCF and / or substantially fragment the LNMO. In one embodiment, dry milling is carried out using a mortar and pestle at an elevated temperature of about 30°C to about 150°C. In one embodiment, dry milling is carried out using a mortar and pestle for a period of about 10 minutes to about 1 hour.

[0061] The method includes step II.) of calendering the powdered dry cathode mixture to form a dry cathode electrode layer. In one embodiment, the calendering step II.) is carried out at room temperature to an elevated temperature. In one embodiment, the calendering is carried out at a temperature of about 70° C. to about 250° C. In one embodiment, the calendering step II.) is carried out under pressure. In one embodiment, the applied pressure is about 1 metric ton to about 10 metric ton.

[0062] The method involves III.) applying a dry cathode electrode layer to a current collector comprising aluminum having a surface roughness and substantially free of a carbon surface coating other than said conductive carbon of said electrode layer. In one embodiment, this applying step III.) is carried out at room temperature to an elevated temperature. In one embodiment, such applying is carried out at a temperature of about 70° C. to about 250° C. In one embodiment, this applying step III.) is carried out under pressure. In one embodiment, the applied pressure is from about 1 metric ton to about 10 metric ton.

[0063] This III.) applying step can be carried out by preparing the cathode electrode layer and applying the cathode electrode layer to the current collector under elevated temperature and pressure. In an alternative embodiment, this III.) applying step can be carried out simultaneously with II.) calendering step, where the cathode electrode layer is formed and applied to the current collector in a single calendering step. EXAMPLES

[0064] Example 1 - Dry method for preparing a cathode of the present invention The materials used to prepare the cathodes of the present invention are commercially available battery grade materials: lithium nickel manganese oxide (LNMO) cathode active from Haldor Topsoe, 50 ml 2 vapor grown carbon fiber (VGCF) conductive carbon manufactured by Sigma Aldrich having a surface area of ​​less than about 1.8×10 / g; and vapor grown carbon fiber (VGCF) conductive carbon manufactured by Chemours FC LLC having a surface area of ​​less than about 1.8×10 / g. 11 The binder was a polytetrafluoroethylene (PTFE) fluoropolymer binder with a melt creep viscosity of 100 poise. All materials were used dry (i.e., not containing, dissolved in, or supported / dispersed in water or organic solvents) and otherwise as obtained from the manufacturer. The cathode active materials were stored and handled in an oxygen-free drybox under an Ar atmosphere. The PTFE fluoropolymer binder is stored at 0° C. prior to use.

[0065] The materials were combined in the desired weight ratio in an appropriately sized rolling vessel (bottle) and rolled using a bottle roller at 80 rpm and a temperature of 80° C. for 24 hours to thoroughly mix the materials, fibrillate the PTFE, and form a conductive structural web.

[0066] In an alternative preferred embodiment, the cathode active material (LNMO) and conductive carbon (VGCF) were combined and first ground in the absence of a fluoropolymer binder (PTFE) for a period of time sufficient to substantially break up VGCF agglomerates, separate the fibers of the VGCF, and homogenously mix the VGCF and LNMO. The PTFE was then added and the mixture was further rolled using a bottle roller to homogenously mix the PTFE with the previously ground VGCF and LNMO and fibrillate the PTFE to form the milled dry cathode powder comprising the present conductive structural web.

[0067] The resulting milled dry cathode powder LNMO, VGCF and PTFE mixture was then calendered to form a dry cathode electrode layer of desired thickness. Calendering is carried out in an MTI rolling press under conditions of temperature of 70-200°C and pressure of 1-10 metric tons for 5-40 seconds to result in a dry cathode active layer of desired thickness. The dry cathode active layer of the present invention is self-supporting, meaning that it can be handled and manipulated as a self-supporting film without the need for a backing or support film, and has sufficient strength (e.g., tensile, tear, and fracture resistance) so that it can be manipulated (e.g., rolled, slit, etc.) and applied to a current collector without suffering failure (e.g., cracking, tearing, breaking, wrinkling, buckling, stretching, etc.).

[0068] The resulting cathode active layer was then adhered to an aluminum current collector having a surface roughness, expressed as Sa (arithmetic mean height), of at least about 260 nm and no carbon surface coating. Adhesion of the cathode active layer and the aluminum current collector was carried out under pressure at a temperature of about 70° C. to about 250° C., at room temperature to elevated temperatures, and at an applied pressure of about 1 metric ton to about 10 metric tonnes, resulting in the formation of the present cathode.

[0069] Comparative Example 1 - Preparation of Comparative Cathode Using Solvent Slurry Method The materials used to prepare the cathode using the comparative solvent slurry method were commercially available battery grade materials: Lithium Nickel Manganese Oxide (LNMO) cathode active material from Haldor Topsoe, Super C65 (C65) conductive carbon from MTI Corporation, and HSV-900 polyvinylidene fluoride (PVDF) from Arkema. After weighing the materials in the designed weight ratio, the PVDF was transferred to N-methyl-2-pyrrolidone (NMP, from Sigma Aldrich) solvent in a jar. A Thinky mixer (ARE-310) was used to mix and dissolve the PVDF. Then, LNMO and SC65 were added to the mixture and mixing was continued for another hour without any grinding beads. The slurry was then cast onto a current collector using a film casting doctor blade (Futt Brand). The cast slurry was dried in a vacuum oven (MTI Corporation) at 80° C. for 24 hours. The dried electrodes were calendered using a rolling press (MTI Corporation) to reduce the porosity to approximately 35%.

[0070] Example 2 - Electronic Conductivity of Cathodes of the Invention with Different Areal Capacities Cathode with various cathode layer areal capacity and thickness was prepared using the dry method and materials described in Example 1. The weight ratio of LNMO:PTFE:VGCF in the cathode electrode layer is 93:2:5. The conductivity of the cathode was measured by two-point probe conductivity method and four-point conductivity method, and the results are reported in Table 1.

[0071] The two-point and four-point conductivity test methods are generally known to those skilled in the art as typical methods for evaluating the electronic conductivity of electrodes in the battery field, and are disclosed in references such as i) Park, Sang-Hoon, et al., "High areal capacity battery electrodes enabled by segregated nanotube networks," Nature Energy 4.7 (2019): 560-567; ii) Liu, G., et al., "Effects of various conductive additive and polymeric binder contents on the performance of a lithium-ion composite cathode," Journal of The Electrochemical Society 155.12 (2008): A887; and iii) Entwistle, Jake, et al., "Carbon binder domain networks and electrical conductivity in lithium-ion battery electrodes: A critical review.," Renewable and Sustainable Energy Reviews 166 (2022): 112624.

[0072] [Table 1]

[0073] The cathodes of the present invention with different areal loadings show the same order of electronic conductivity by four-point probe conductivity method. Without wishing to be bound by theory, the inventors believe that this is related to in-plane conductive carbon twisting. The electronic conductivity by two-point probe method shows a tendency to increase as the areal loading increases. Without wishing to be bound by theory, the inventors believe that this is due to the reduction in thickness of the cathode layer during the calendaring process, which disperses the carbon fibers and results in fewer carbon fibers per unit volume in the resulting thinner cathode (i.e., the cathode composition is calendared to reduce the cathode layer film thickness, resulting in a larger area of ​​the cathode layer film).

[0074] Example 3 - Electronic conductivity of cathodes of the present invention with varying conductive carbon (VGCF) content Similar areal capacity (3mAh / cm 2 ) and thickness of cathodes were prepared by the dry method and materials described in Example 1. The weight ratio of LNMO:PTFE:VGCF in the electrode layer was varied as shown in Table 2. The conductivity of the cathodes was measured by a four-point conductivity method and the results are reported in Table 2.

[0075] [Table 2]

[0076] These results indicate that reducing the amount of VGCF, especially below 3 wt%, has a relatively large effect on the conductivity as measured by four-point probe conductivity. Without being bound by theory, the inventors believe that electrodes of the invention containing less than 3 wt% VGCF are less able to connect the cathode active particles and form an effective electronically conductive structural web. Below this amount, the measured conductivity appears to correspond essentially to that of the LNMO cathode active particles, and is approximately 1×10 -6 S / cm.

[0077] Example 4 - Electronic Conductivity of Cathode of the Invention Made by Different Cathode Electrode Composition Milling Methods To prepare an electrode composition containing cathode active particles, a fluoropolymer binder, and conductive carbon, three different grinding methods were investigated: a Thinky mixer method, a bottle roller method, and a mortar and pestle method.

[0078] The Thinky mixer method involved the use of a Thinky planetary centrifugal mixer model ARE-310 to mix the LNMO:PTFE:VGFE compositions described in Table 3. The mixer was operated under the following conditions: 2000 rpm for 30 minutes. What was prepared was a dry powder LNMO:PTFE:VGCF cathode electrode mixture.

[0079] The bottle roller mixing method generally followed that described in Example 1. Approximately 2 g quantities of the LNMO:PTFE:VGCF mixture were placed in 20 mL glass vials and rolled on a bottle mixer at 80 rpm and 80° C. for 24 hours, with no grinding beads in one trial and four grinding beads in another trial, to prepare a dry powder LNMO:PTFE:VGCF cathode mixture. The use of grinding beads in the bottle roller mixing method was found to be undesirable as the presence of the grinding beads undesirably resulted in substantially fragmented (shortened) fibers of VGCF and / or substantially fragmented LNMO particles. Bottle roller mixing at relatively low mixing speeds (less than 80 rpm) was found to not adequately disperse the VGCF, but rather to result in agglomeration of the VGCF.

[0080] The mortar and pestle mixing method generally followed that of this Example 1. A dry powder LNMO:PTFE:VGCF cathode electrode mixture was prepared by placing a quantity of the LNMO:PTFE:VGCF mixture into a mortar and pestle and gently mixing by hand while heating to 80° C. until the powder mixture was visually uniform.

[0081] Cathode of similar areal capacity was prepared by this dry method using dry powder LNMO:PTFE:VGCF cathode electrode mixture prepared by the mixing method described above and materials as described in this Example 1. The weight ratio of LNMO:PTFE:VGCF in the electrode layer is reported in Table 3. The conductivity of the cathode was measured by four-point conductivity method and the results are reported in Table 3.

[0082] [Table 3]

[0083] Example 5 - Electrochemical performance of half-cell and full-cell batteries using LNMO cathodes prepared by the dry coating method of the present invention and cathodes prepared by the comparative solvent slurry method The cathodes were prepared according to the bottle roller mixing method of Example 1 and the solvent slurry method of Comparative Example 1. The dry process LNMO cathodes of the present invention were prepared with capacities of 3, 4, 6 and 9.5 mAh / cm 2 Comparative solvent slurry LNMO cathodes were prepared with areal loadings of 3 and 4 mAh / cm. 2 The plate was prepared with an area load of 100 μm.

[0084] Half-cell coin cell batteries were constructed using these cathodes, lithium metal anodes, Celgard 2325 separators, and Gen2 electrolyte (Gen2 electrolyte is 1.0 M LiPF in ethylene carbonate (EC) and ethyl methyl carbonate (EMC)). 6 The cathode, anode, Gen2 electrolyte, and Celgard 2325 separator were used to assemble a full-cell coin cell battery. The anode is a graphite anode obtained from Ningbo Institute of Materials Technology and Engineering. The graphite used is synthetic graphite, and the weight percentage is 95%.

[0085] Figure 4 shows the results for 3, 4, 6 and 9.5 mAh / cm2 FIG. 5 is a plot of C / 10 rate half-cell performance (voltage (V)) versus specific capacity (mAh / g) for half-cell batteries using the present dry process LNMO cathode with areal loadings of 3 and 4 mAh / cm. 2 1 is a plot of C / 10 rate half-cell performance (voltage (V)) versus specific capacity (mAh / g) for half-cell batteries using comparative slurry LNMO cathodes with areal loadings of 1000 mAh / cm. The dry LNMO half-cell maintains consistently good performance even as the areal loading is tripled, while the slurry LNMO performs better at an areal loading of 4 mAh / cm. 2 shows a significant decrease in performance when the conductivity is increased to 1. The inventors believe that the excellent conductive carbon network helped to achieve this performance.

[0086] Figure 6 shows a 9.5 mAh / cm2 charge, which corresponds to a thickness of approximately 240 μm. 2 7 is a cross-sectional SEM image of the LNMO cathode fabricated by the dry method of the present invention in this Example 1, having an areal capacity of 4 mAh / cm, corresponding to a thickness of about 110 μm. 2 1 is a cross-sectional SEM image of an LNMO cathode fabricated by the comparative solvent slurry method of this Comparative Example 1, having an areal capacity of 1000 nm. A dense electrode layer was achieved in the LNMO cathode fabricated by the dry method of the present invention. No peeling was found between either the electrode layer or the current collector.

[0087] FIG. 8 is a plot showing a comparison of the performance (specific capacity (mAh / g) and coulombic efficiency (%) vs. cycle number) at C / 3 rate over extended cycling (through 1,000 cycles) of a full cell battery using a dry process LMNO cathode of the present invention and a similar comparative full cell battery using a slurry process LMNO cathode, with each cathode achieving a 3 mAh / cm 2The dry process LNMO cathode of the present invention resulted in a full cell battery with an average coulombic efficiency of 99.88% over 1000 cycles and 67% retention of specific discharge capacity over 700 cycles. A similar full cell battery using a comparative slurry process LMNO cathode resulted in a comparative full cell battery that suffered a significant reduction in coulombic efficiency and specific discharge capacity after only 300 cycles. The inventors believe that the reduction in low specific surface area and elimination of the carbon coating helps reduce parasitic reactions at high voltages.

[0088] FIG. 9 is a plot showing the average charge voltage (V) and average discharge voltage (V) versus cycle number over 300 cycles for a full cell battery using a dry process LMNO cathode of the present invention and a similar full cell battery using a slurry coated cathode, these cathodes having a 3 mAh / cm 2 The cells using the cathodes of the present invention exhibit a relatively lower average charge voltage and a relatively higher average discharge voltage over 300 cycles than similar comparative full-cell cells using slurry-coated cathodes. The low and stable voltage hysteresis in the cells using the cathodes of the present invention indicates a much slower impedance growth in the cells along the cycles.

[0089] FIG. 10 shows the dQ / dV plot (dQ / dV(mAh / g v -1 ) vs. voltage (V). Figure 11 shows the dQ / dV plot (dQ / dV(mAh / g v -1 (vs. voltage (V)) and these cathodes have a capacity of 3 mAh / cm 2 The oxidation and reduction peak positions from the full cell battery using the dry process LMNO cathode of the present invention are well preserved. These results show a dramatic impedance rise and severe Li inventory loss in the full cell using the comparative slurry coated cathode.

[0090] FIG. 12 shows Nyquist plots (-Z″ / Ω vs. Z′ / Ω) obtained by electrical impedance spectroscopy (EIS) for full-cell batteries using the dry process LMNO cathode of the present invention and the comparative slurry-coated cathode after 50 and 100 cycles, which show that these cathodes have a 3 mAh / cm 2 During 100 cycles, a significant impedance increase can also be observed in the full cell battery using the comparative slurry coated cathode.

[0091] Figure 13 shows the 21.2 mg / cm 2 A full cell battery using the dry process LMNO cathode of the present invention with an LNMO loading of 21.2 mg / cm 2 1 is a plot showing energy density (Wh / kg) and energy efficiency (%) versus cycle number over 300 cycles for a similar full cell battery using a slurry coated cathode with an LNMO loading of 1000. Energy density levels can be well maintained even after extended cycling in full cell batteries using the dry process LMNO cathode of the present invention.

[0092] Example 6 - Electrochemical performance of a full cell battery using a cathode prepared by the dry coating method of the present invention and using a fluorinated electrolyte Using LNMO cathode active material, 3mAh / cm 2 A cathode having an areal loading of 1.0 g was prepared according to the bottle roller drying method of Example 1.

[0093] Full cell batteries were assembled using these cathodes, graphite anodes, and Dreamweaver Gold 20 separators. In one example battery, the electrolyte used was Gen2 electrolyte (Gen2 electrolyte is 1.0 M LiPF in ethylene carbonate (EC) and ethyl methyl carbonate (EMC)). 6In another exemplary cell, the electrolyte used is a fluorinated electrolyte called FEC-FEMC (FEC-FEMC electrolyte is 1M LiPF in fluoroethylene carbonate (FEC) and methyl (2,2,2-trifluoroethyl) carbonate (FEMC)). 6 (The FEC:FEMC volume ratio is 1:9.) The anode is a graphite anode obtained from Ningbo Institute of Materials Technology and Engineering. The graphite used is artificial graphite, and the weight percentage is 95%.

[0094] FIG. 14 is a plot showing a comparison of performance (specific discharge capacity (mAh / g) and coulombic efficiency (%) versus cycle number) for a full cell battery using the dry process LNMO cathode of the present invention with Gen2 electrolyte and an essentially identical full cell battery using FEC-FEMC electrolyte. A coulombic efficiency of 99.9% can be reached in approximately 50 cycles. This cell system can be quickly stabilized at such high voltage operation.

[0095] 15 is a plot showing energy density (Wh / kg) and energy efficiency (%) versus cycle number over 200 cycles for a full cell battery using a dry process LNMO cathode of the present invention with Gen2 electrolyte and an essentially identical full cell battery using FEC-FEMC electrolyte. Energy density levels can be well maintained even after extended cycling in the full cell battery using a dry process LMNO cathode of the present invention with FEC-FEMC electrolyte.

[0096] 16 is a plot showing the average charge voltage (V) and average discharge voltage (V) versus cycle number over 200 cycles for a full cell battery using a dry process LNMO cathode of the present invention with Gen2 electrolyte and an essentially identical full cell battery using FEC-FEMC electrolyte. The low and stable voltage hysteresis in the battery using the full cell battery using a dry process LMNO cathode of the present invention with FEC-FEMC electrolyte indicates a much slower impedance growth in the cell along the cycles.

[0097] Example 7 - Electrochemical performance of full cell batteries using cathodes made by the dry coating method of the present invention attached to aluminum current collectors with and without a carbon coating Using LNMO cathode active material, 3mAh / cm 2 A cathode having an areal loading of 1000 nm was prepared according to the mortar and pestle mixing method and the calendaring method of Example 1. In one exemplary embodiment, the resulting cathode layer film was adhered to an aluminum current collector having a surface roughness expressed as Sa (arithmetic mean height) of at least about 260 nm and having no carbon surface coating. The aluminum was 20um Etched Aluminum Foil for Supercapacitor manufactured by Tob New Energy. In a comparative embodiment, the resulting cathode layer film was adhered to a carbon-coated aluminum current collector foil. The carbon-coated aluminum current collector foil was Conductive Carbon Coated Aluminum Foil for Battery Cathode Substrate (260mm W x 18um Thick, 80mL / roll), EQ-CC-Al-18u-260 inch manufactured by MTI Corporation.

[0098] FIG. 17 is a plot of discharge capacity (mAh / g) and coulombic efficiency (%) versus cycle number for full cell batteries using a dry process prepared LMNO cathode of the present invention on a current collector comprising aluminum substantially free of a carbon coating (other than the conductive carbon contained in the electrode layer) on the aluminum surface in contact with the electrode layer, and a similar dry process prepared LMNO cathode on a current collector comprising aluminum with a carbon coating.

[0099] From this experiment, it is clear that the carbon coating on the current collector has a very detrimental effect on the high voltage cycling performance in terms of coulombic efficiency and capacity retention. When the current collector of the present invention is used, which comprises aluminum having substantially no carbon coating on the aluminum surface in contact with the electrode layer, the cycling stability is significantly improved.

Claims

1. 1. A cathode for a high-voltage lithium-ion secondary battery, comprising: an electrode layer comprising an electrode composition comprising cathode active particles, a fluoropolymer binder, and conductive carbon; the cathode active particles comprise a lithium transition metal oxide having an electrochemical potential vs. Li / Li+ of at least 4.5 V; the fluoropolymer binder is a tetrafluoroethylene polymer having a melt creep viscosity of at least 1.8×10 poise (1.8×10 Pa·S); the fluoropolymer binder is fibrillated; the conductive carbon includes carbon fibers having a specific surface area of ​​50 m 2 / g or less; the carbon fibers and the fibrillated fluoropolymer binder form a conductive structural web that electronically connects the cathode active particles to enable electronic conductivity through the electrode layer; A cathode wherein the electrode layer is adhered to a current collector comprising aluminum having a surface roughness and no carbon surface coating other than the conductive carbon of the electrode layer.

2. The conductive structural web is A. a portion of the tetrafluoroethylene polymer and a portion of the carbon fibers in the web are combined in the form of conductive strands comprising a continuous tetrafluoroethylene polymer matrix and a plurality of carbon fibers, the carbon fibers being embedded in and bonded to the tetrafluoroethylene polymer matrix comprising the strands, the longitudinal axes of the carbon fibers being aligned with the longitudinal axes of the strands, and the strands being randomly interwoven and interconnected throughout the volume between and in contact with the cathode active particles; B. a portion of the tetrafluoroethylene polymer and a portion of the carbon fibers in the web are combined in the form of discontinuous randomly matted regions positioned adjacent to and attached to the cathode active particles, the carbon fibers being embedded in and adhered to the tetrafluoroethylene polymer comprising the regions; C. a portion of the tetrafluoroethylene polymer in the web is in the form of free tetrafluoroethylene polymer fibrils; D. a portion of the tetrafluoroethylene polymer in the web is in the form of a tetrafluoroethylene polymer coating layer covering a portion of the surface of some of the cathode active particles; and E. a portion of the carbon fibers in the web are free of conductive carbon fibers; 2. The cathode of claim 1, wherein the conductive strands (A.), the discontinuous random matted regions (B.), the free fluoropolymer fibrils (C.), the tetrafluoroethylene polymer coating layer (D.), and the no conductive carbon fibers (E.) are randomly interconnected with one another throughout the electrode layer and in contact with the surfaces of the cathode active particles, thereby forming the conductive structural web that electrically connects and secures the cathode particles in place.

3. the electrode composition contains, based on the total weight of the fluoropolymer binder, the cathode active particles, and the conductive carbon, 1 to 10 weight percent conductive carbon, 0.5 to 5 weight percent fluoropolymer binder, and the remainder cathode active particles, and preferably the electrode composition comprises, based on the total weight of the fluoropolymer binder, the cathode active particles, and the conductive carbon, 2 to 7 weight percent conductive carbon, 1 to 3 weight percent fluoropolymer binder, and the remainder cathode active particles, and more preferably 3. The cathode of claim 1, wherein the electrode composition contains 5 weight percent conductive carbon, 2 weight percent fluoropolymer binder, and the remainder cathode active particles, based on the total weight of the fluoropolymer binder, the cathode active particles, and the conductive carbon.

4. 10. The cathode of claim 1, wherein the carbon fibers have a length of from 10 micrometers to 200 micrometers.

5. A cathode as described in claim 1, wherein the electrode layer is substantially free of conductive carbon having a specific surface area of ​​more than 50 m2 / g, or the conductive carbon has a specific surface area of ​​40 m2 / g or less, preferably the electrode layer is substantially free of conductive carbon having a specific surface area of ​​more than 30 m2 / g, or the conductive carbon has a specific surface area of ​​20 m2 / g or less, more preferably the electrode layer is substantially free of conductive carbon having a specific surface area of ​​more than 20 m2 / g.

6. 2. The cathode of claim 1, wherein the tetrafluoroethylene polymer has a melt creep viscosity of at least 2.0×10 poise (2.0×10 10 Pa·S), preferably the tetrafluoroethylene polymer has a melt creep viscosity of at least 3.0×10 11 poise (3.0×10 10 Pa·S), and more preferably the tetrafluoroethylene polymer has a melt creep viscosity of at least 4.0×10 11 poise (4.0×10 10 Pa·S).

7. 2. The cathode of claim 1, wherein the surface roughness of the aluminum current collector, expressed as Sa (arithmetic mean height), is at least 260 nm, preferably the surface roughness of the aluminum current collector, expressed as Sa (arithmetic mean height), is at least 280 nm, and more preferably the surface roughness of the aluminum current collector, expressed as Sa (arithmetic mean height), is at least 300 nm.

8. The thickness of the electrode layer is 60 micrometers to 250 micrometers, preferably the thickness of the electrode layer is between 80 micrometers and 120 micrometers; or 10. The cathode of claim 1, wherein the electrode layer has a thickness of at least 240 micrometers.

9. 2. The cathode of claim 1, wherein the electrode layer has a thickness of at least 80 micrometers, preferably at least 100 micrometers, and more preferably at least 130 micrometers, a two-point probe conductivity of at least 1×10 −2 S / cm, and a four-point probe conductivity of at least 1×10 −2 S / cm.

10. A high-voltage lithium-ion secondary battery, a cathode comprising an electrode layer comprising an electrode composition comprising cathode active particles, a fluoropolymer binder, and conductive carbon, wherein the cathode active particles comprise a lithium transition metal oxide having an electrochemical potential vs. Li / Li+ of at least 4.5 V, the fluoropolymer binder is a tetrafluoroethylene polymer having a melt creep viscosity of at least 1.8×10 poise (1.8×10 Pa·S), the fluoropolymer binder is fibrillated, the conductive carbon comprises carbon fibers having a specific surface area of ​​50 m / g or less, the carbon fibers and the fibrillated fluoropolymer binder electronically connect the cathode active particles to form a conductive structural web to enable electronic conductivity through the electrode layer, and the electrode layer is adhered to a current collector comprising aluminum having a surface roughness and no carbon surface coating other than the conductive carbon of the electrode layer; an anode; a separator between the cathode and the anode; an electrolyte in communication with the cathode, the anode, and the separator.

11. 11. The lithium ion secondary battery according to claim 10, wherein the carbon fibers have a length of 10 micrometers to 200 micrometers.

12. 12. The lithium ion secondary battery according to claim 10 or 11, wherein the electrolyte comprises a fluorinated organic solvent, preferably selected from the group consisting of fluoroethylene carbonate (FEC) and methyl (2,2,2-trifluoroethyl) carbonate (FEMC).

13. 1. A method for manufacturing a cathode for use in a high voltage lithium ion secondary battery, comprising: I.) i) a conductive carbon comprising carbon fibers having a specific surface area of ​​50 m 2 / g or less; ii) cathode active particles comprising a lithium transition metal oxide having an electrochemical potential vs. Li / Li of at least 4.5 V; iii) a fluoropolymer binder comprising a tetrafluoroethylene polymer having a melt creep viscosity of at least 1.8×10 11 poise (1.8×10 10 Pa·S), forming a powdered dry cathode mix, wherein the dry-milling fibrillates the fluoropolymer binder and forms a conductive structural web comprising the fluoropolymer binder and the conductive carbon, the conductive structural web electronically connecting the cathode active particles to enable electronic conductivity throughout the cathode; II.) Calendering the powdered dry cathode mixture to form a dry cathode electrode layer; III.) adhering the dried cathode electrode layer to a current collector comprising aluminum having a surface roughness and no carbon surface coating other than the conductive carbon of the cathode electrode layer.

14. The method of claim 13, wherein the carbon fibers have a length of from 10 micrometers to 200 micrometers.

15. The carbon fibers subjected to the dry milling are in the form of agglomerates, and the dry milling is sufficient to deagglomerate the agglomerates to result in single carbon fibers and relatively small clusters of carbon fibers, and preferably the dry milling is dry-milling a mixture containing the carbon fiber agglomerates and the cathode active particles under first conditions to obtain a first dry mixture; combining the fluoropolymer binder and the first dry mixture to form a second dry mixture; dry-milling the second dry mixture under second conditions, preferably wherein the dry-milling is carried out at a temperature of from 40°C to 150°C, preferably wherein the dry-milling is carried out by the application of shear, preferably wherein the dry-milling is carried out in a bottle roller, preferably wherein the dry-milling includes the application of a shear force such that the fluoropolymer binder is fibrillated and the carbon fibers are substantially unbroken and homogeneously distributed throughout the powdered dry cathode mixture.

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