JP5650418B2 - Electrically conductive nanocomposites containing sacrificial nanoparticles and open porous nanocomposites produced therefrom - Google Patents

Description

  The present invention relates to an electrode material for an electrode of a rechargeable lithium battery based on a nanoparticulate lithium compound incorporated in a nanocomposite. The invention also relates to a method for the production of such an electrode material.

  Rechargeable lithium batteries are particularly used in portable electronic devices such as telephones, computers and video equipment, and more recently in electric bicycles and cars such as automobiles. In these applications, the demands on these batteries are severe. In particular, they need to store the maximum amount of energy per given volume or weight. They also need to be reliable and environmentally compatible. Therefore, high energy density and high specific energy are two basic requirements imposed especially on the electrode material of such batteries.

  A further important requirement for such electrode materials is cycle resistance. Here, each cycle includes one charge and discharge process. Cycle resistance substantially determines the specific charge available after several cycles. Even assuming 99% cycle endurance per cycle, the available specific charge after 100 cycles is only 37% of the initial value. Therefore, such a relatively high value of 99% is generally insufficient. Therefore, a rechargeable suitable high-performance battery of the type mentioned above not only needs to be able to store a certain amount of energy with as little weight and volume as possible, but also has the ability to discharge and charge this energy several hundred times. It is necessary to have. The critical factor here is the electrode material to a considerable extent.

  Due to the great economic importance of such batteries, numerous efforts have been made to find electrode materials that fully meet the above requirements.

  To date, the materials used for the anode of rechargeable lithium batteries have been in particular transition metal oxides or transition metal sulfides, organic molecules and polymers. In particular, transition metal oxides and sulfides have been shown to be successful in practical use. Such materials are referred to as insertion electrode materials and are found in many batteries that can be charged at room temperature. The reason why such materials are becoming more widespread is the fact that the electrochemical insertion reaction is topochemical and therefore partly structure-retaining.

The idea of a rechargeable battery based on the lithium insertion reaction developed in the 1970s. Meanwhile, a number of electrodes based on this principle have been proposed and implemented. The charging capacity of a lithium cell is mainly based on the dimensional stability of the guest material during Li ⁺ insertion and removal.

  As described above, several transition metal oxides, sulfides, phosphates and halides are known as highly reversible anode materials. They include in particular lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide and lithium vanadium oxide, copper oxyphosphate, copper sulfide, lead sulfide and copper sulfide, iron sulfide, copper chloride and the like. However, these materials are somewhat unsuitable. That is, for example, lithium cobalt oxide is relatively expensive and not particularly environmentally compatible. From the viewpoint of environmental compatibility, lithium manganese oxide is particularly preferable. However, it has been found that these oxides generally have a spinel structure so that they have a lower specific charge or are less stable under cycles for lithium exchange. Tests have also shown that orthorhombic lithium manganese oxides have a spinel structure upon removal of lithium. Regarding the prior art, the publication “Insertion Electrode Materials for Rechargeable Lithium Batteries” by Martin Winter, Juergen O. Besenhard, Michael E. Sparh and Petr Novak, ADVANCED MATERIALS 1998, October, November, no. 10, pages 725-763, and the article ETH no. 12281, “Synthese und Charakterisierung neuartiger Oxide, Kohlenstoffverbindungen, Silicide sowie nanostrukturierter Materialien und deren elektro- und magnetochemische Untersuchung” (“Synthesis and characterization of new types of oxides, carbon compounds, silicides and nano-structured materials and their electro- and magneto- and See "chemical analysis").

  Therefore, there is still a great need for batteries that are particularly improved in terms of high specific energy and high power density.

WO01 / 41238 US Patent Application Publication US 2007 10054187 A1

Publication "Insertion Electrode Materials for Rechargeable Lithium Batteries" by Martin Winter, Juergen O. Besenhard, Michael E. Sparh and Petr Novak, ADVANCED MATERIALS 1998, October, October, no. 10, pages 725-763 A paper by M.E.Spahr ETH no. 12281, `` Synthese und Charakterisierung neuartiger Oxide, Kohlenstoffverbindungen, Silicide sowie nanostrukturierter Materialien und deren elektro- und magnetochemische Untersuchung '' (`` Synthesis and characterization of new types of oxides, carbon compounds, silicides and nano-structured materials and their electro-magnetic chemical analysis ") Yong-Jun Li, Wei-Jun Huang, and Shi-Gang Sun. Angew. Chem. 118, 2599, (2006) Padhi, A. K., Nanjundaswamy, K. S. & Goodenough, J. B. J. Electrochem. Soc., 144, 1188 (1997) S. Franger, F. Le Cras, C. Bourbon and H. Rouault, Electrochem.Solid-State Lett., 5, A231 (2002) S. Yang, P. Y. Zavalij and M. S. Whittingham, Electrochem. Commun., 3, 505 (2001). S. Franger, F. Le Cras, C. Bourbon and H. Rouault, J. Power Sources, 119, 252 (2003) Chung, S.-Y., Bloking, J. T. & Chiang, Y.-M.Nature Mater., 1, 123 (2002) S. Y. Chung and Y.-M. Chiang, Electrochem.Solid-State Lett., 6, A278 (2003) F. Croce, A. D. Epifanio, J. Hassoun, A. Deptula, J. Olczac, and B. Scrosati, Electrochem. Solid-State Lett., 5, A47 (2002) A. Yamada, S. C. Chung and K. Hinokuma, J. Electrochem. Soc., 148, A224, (2001) Zhaohui Chen and J. R. Dahn, J. Electrochem. Soc., 149, A1184 (2002) Prosini, P. P., Zane, D. & Pasquali, M. Electrochim. Acta., 46, 3517 (2001) G. Heywang and F. Jonas, Adv. Mater., 4, 116 (1992) L. B. Groenendaal, F. Jonas, D. Freitag, H. Pielartzik, and J. R. Reynolds, Adv. Mater. Weinheim, Ger., 12, 481 (2000) H. Yamato, M. Ohwa and W. Wernet. J. Electroanal. Chem., 397, 136 (1995) I. Winter, C. Reese, J. Hormes, G. Heywang and F. Jonas. Chem. Phys., 194, 207 (1995)

  Therefore, the problem to be solved by the present invention is that the polarization during the cycle is low or non-polar, preferably has a good electrochemical response / high discharge capacity, and is also preferably relatively environmentally compatible It is to provide an electrode material for both the anode and the cathode, preferably for the cathode.

This problem is a nanocomposite, solved by an improved electrolyte and an electrode material having large pores for the transfer of ions, e.g. lithium, said nanocomposite comprising:
An open porous material having pores, preferably pores having at least nanoparticle dimensions, preferably in the range of 200 nm to 500 nm, in particular in the range of 300 nm to 500 nm,
-Electronic conductivity.

In one embodiment, the nanocomposite electrode material is for an anode or cathode of a rechargeable lithium battery, the electrode material is a nanocomposite, and the nanocomposite is a uniformly distributed nanoparticulate electronic activity An open porous material comprising a material and a nanoparticulate electronically conductive binder material, wherein the average particle size of the nanoparticles of the electronically active material and the average particle size of the nanoparticulate electronically conductive binder material are:
Both differ by less than +100% /-50% and / or both are in the range of less than 500 nm,
Said nanocomposite electrode material comprises pores in the range of 200 nm to 500 nm, in particular in the range of 300 nm to 500 nm.

By open porous material is meant that the pores are so large and interconnected that diffusion of the electrolyte and Li ⁺ is readily possible. The porosity of the material, such as the presence of large pores due to the removal of the sacrificial particles, can be determined, for example, by electron microscopy.

Currently, surprisingly, electron active materials (EAM), such as electrons and Li ⁺ emitting or electron and Li ⁺ accepting materials, were interconnected by nanoparticles of an electron conductive binder (CB) of approximately the same particle size. An open porous material can be easily obtained when in the form of nanoparticles, and when the nanoparticles are mixed with additional types of nanoparticles that are ultimately removed in creating the electrode. It has been found that it can be done. In the context of the present invention, such additional particles are called sacrificial particles (SP). Such nanocomposites may contain additional components such as conductive fillers and conductive nanofibers.

After removal of the sacrificial nanoparticles, the pores remain in the material and promote the diffusion of electrolyte and Li ⁺ ions.

As the EAM for the cathode of the present invention, materials having low conductivity in the form of coarse particles, or even insulators can be used, provided that they are in the form of nanoparticles (hereinafter referred to as nanoparticulate). Used only if they can emit electrons and Li ⁺ ions if they are provided with a conductive coating.

Suitable EAMs are all compounds that already have Li ⁺ ions or that can form Li-containing compounds during the first duty cycle. The production of Li-containing compounds during loading is advantageous in the case of Li-containing compounds that are poorly stable or more unstable.

  Examples of EAM are not only transition metal and main group metal oxides, nitrides, carbides, borates, phosphates, sulfides, halides, etc., and mixtures thereof, but also in the state of the art, eg WO01 / All EAMs listed in 41238.

  Nanoparticles used herein generally have an average primary particle size in the range of 5 nm to 500 nm, preferably in the range of 5 nm to 400 nm, more preferably in the range of 20 nm to 300 nm.

Preferred EAMs are Li _x V ₃ O ₈ and Li _x H _n V ₃ O ₈ , with LiFePO ₄ being particularly preferred at present.

Suitable EAMs for the anode material are silicon, alloys such as Li _x AlSi _n , Li _x SiSn _n and nitrides such as Li _x VN.

  According to the present invention, these EAMs in nanoparticulate form are electrically conductive binders which are also in nanoparticulate form and have a similar average particle size, and optionally have a similar particle size. Mixed with filler. Although it is possible to have CB in the form of fibers, nanotubes, etc., nanostubs or substantially spherical nanoparticles are currently preferred for cost reasons.

  The nanocomposites of the present invention are well mixed with each other, preferably stabilized by mixed storage and sufficient viscosity of the binder at the temperature of use, by pressure treatment with or without heating, or by solvent evaporation, EAM and CB nanoparticles, and optionally sacrificial nanoparticles and / or conductive filler nanoparticles and / or conductive nanofibers. A thermoplastic material with a low glass transition point of the conductive binder is preferred not only for particle bonding, but also for bonding the nanocomposite to a conductor, usually an aluminum electrode / substrate.

  The nanocomposites of the present invention that further comprise sacrificial nanoparticles are intermediate nanocomposites that can further react to become final nanocomposites by removal of the sacrificial nanoparticles, eg, thermal or chemical removal.

  Electroconductive polymers include polyacetylene, polyaniline, polypyrrole and polythiophene. These polymers may be substituted or unsubstituted depending on the desired characteristics. A presently preferred binder is poly (3,4-ethylenedioxythiophene), hereinafter referred to as PEDOT. This polymer is electrically conductive, has a suitable viscosity and can be easily produced in nanoparticulate form.

  In certain embodiments, CB nanoparticles are present in an amount of 4% to 10%, based on the weight of the final, i.e., nanocomposite free of sacrificial particles.

  As already mentioned above, if the EAM particles are particles of an insulating material, or in order to improve their conductivity, the nanoparticles are coated with a conductive layer, in particular a carbon / graphite / graphene layer.

  The sacrificial nanoparticles are thermal and / or chemical reactions that do not affect the rest of the nanocomposite as long as such materials can be formed as nanoparticles having a particle size generally from 200 nm to 500 nm, preferably 300 nm to 500 nm. Any material particles can be used as long as they can be removed.

  Non-limiting examples of nanoparticulate sacrificial materials are, for example, polystyrene, polyethylene, polyvinyl acetal, and polyethylene glycol.

  Polystyrene is commercially available in several particle sizes in the desired range and is soluble as described above. Polystyrene is soluble in some organic solvents such as acetone.

  Polyethylene glycol is available in different chain lengths and can optionally be etherified and / or esterified to match its solubility.

  Polyvinyl acetals such as polyvinyl butyral can be removed by treatment with nitric acid, for example nitric acid vapor.

  Polyethylene can be removed by oxidation at 300 ° C. in an oxygen rich atmosphere.

  Polystyrene and polyethylene glycol are compatible with many electron conducting polymers, but polyethylene is preferred for use with polyacetylene and polyvinyl acetal is preferred for use with polypyrrole.

  A large amount of sacrificial particles can be advantageous because a very porous structure is usually desirable. The preferred amount of sacrificial polymer, based on the intermediate composite, is 40% to 60% by weight, but even in smaller amounts, for example in the range 0.5% to 10%, already in a small volume with increased porosity. Provides high density EAM. Thus, all amounts from 0.5% to 60% can be used to provide different feature optimizations.

  A method for producing nanoparticulate EAM, a method for coating nanoparticulate EAM, a method for producing nanoparticulate CB, and a method for producing the intermediate and final nanocomposites of the present invention. This will be described below.

EAM can be prepared by thermal decomposition in the case of oxides, nitrides, etc., or by solvothermal synthesis, especially in the case of LiFePO ₄ . The solvothermal process offers many advantages, such as controlling the modification of the synthesized particle morphology and size distribution. The inert gas required to protect the material is unnecessary or negligible in solvothermal synthesis, and the process is generally much faster and more energy efficient than conventional convenient synthesis, Good for particle formation. LiFePO ₄ samples are preferably prepared by optimized solvothermal synthesis as described by Nuspl et al. US Pat.
FeSO ₄ + H ₃ PO ₄ + 3LiOH.H ₂ O → LiFePO ₄ + Li ₂ SO ₄ + 11H ₂ O

  Carbon coating of nanoparticulate EAM can be performed by carbon deposition by pyrolysis of various organic precursors such as sugars or ketones.

Nanoparticulate electronically conductive polymers such as PEDOT can be prepared using the reverse microemulsion technique as described by Sun et al. For PEDOT synthesis, a microemulsion is prepared containing an emulsified oxidant containing particles / droplets such as FeCl ₃ / bis (2-ethylhexyl) sulfosuccinate particles as polymerization aids.

  In order to form the nanocomposites of the present invention, the nanoparticulate CP is optionally combined with nanoparticulate electronically conductive fillers such as carbon black and graphite, conductive nanofibers and sacrificial nanoparticles, preferably acetonitrile or the like. Suspended in a suitable solvent, then nanoparticulate (if EAM itself is not sufficiently electronically conductive) carbon-added EAM is added, the mixture is homogenized, dried and optionally compressed with or without heating Is done. Alternatively, sacrificial nanoparticles may be added with or after the EAM.

  From the following detailed description of the invention, the invention will be better understood and objects other than those set forth above will become apparent. Such description refers to the accompanying drawings.

Schematic of a composite with particles of similar particle size of EAM (black filled circles), conductive binder (pentagon shaded gray), sacrificial particles (dotted ellipses), and conductive fibers (black lines) is there. It is the schematic of the composite material after destroying a sacrificial particle. It is an XRD pattern of LiFePO ₄ with and without carbon coating. It shows a comparison of the particle size distribution of carbon coated and untreated LiFePO _4. Carbon-coated LiFePO _4, it is a SEM photograph of the battery composite consisting of graphite and a standard binder. FIG. 3 shows the product of synthesis by reverse microemulsion of PEDOT resulting in the formation of a nano-sized mesh with a porous structure formed from the aggregation of individual PEDOT nanostubs. Ratio of 20 mA (about 0.1 C) of three samples: LiFePO ₄ combined with conventional binder and filler, carbon-coated LiFePO ₄ combined with conventional binder and filler, and composition of the present invention The initial discharge capacity after cycling with current is shown. FIG. 7a compares the performance of carbon-coated LiFePO ₄ combined with conventional (LC) and inventive (LP) binders at a specific current of 135 mA (approximately 0.8 C), FIG. The discharge curves after the 50th and 100th cycles are shown, and FIG. 7b shows the discharge curves after the 10th, 50th and 100th cycles for LP. Both LC and LP samples for the next 100 cycles compared to LC of 56 mAh / g are shown. FIG. 4 shows the discharge potential as a function of the number of cycles at various currents.

The invention will now be further described with respect to a system of LiFePO ₄ , PEDOT, sacrificial nanoparticles and conductive filler particles (including nanofibers). Such compositions, i.e. intermediate composite and final composite, are shown schematically in FIG.

LiFePO ₄ is a very promising EAM because it can be produced from inexpensive precursors, is non-toxic, environmentally friendly and has excellent chemical and thermal stability. This material promotes extremely fast lithium ion mobility, which makes it desirable for high power applications (Non-Patent Document 4). However, the low intrinsic electronic conductivity of this material greatly limits the electrochemical response (Non-Patent Document 4). Reduction of particle size (Non-Patent Documents 5 to 7), coating with ultra-thin carbon, doping with super multivalent ions (Non-Patent Documents 8 and 9), addition of metal particles to electrode composite (Non-Patent Document 10) Several attempts have been made to improve its properties, all of which are some of the methods that have not led to acceptable results, let alone good results.

The greatest improvement in the performance of LiFePO ₄ is obtained by surface coating it with carbon deposited by pyrolysis of various organic precursors such as sugars. It is also known that the rated capacity of a battery can be greatly improved by a decrease in particle size that results in improved solid diffusion of lithium in the electrode material (Non-Patent Document 11). However, due to the increased surface due to the small particle size, a greater amount of carbon / graphite and binder in the electrode composite is required, which leads to a significant reduction in battery tap density, so nanostructured EAM Problems arise from the use of (Non-Patent Documents 11 to 13). Therefore, in order to design an optimal electrode composition, it is necessary to make a good adjustment between the particle size and the amount of conductive additive and other additives added. Polymeric binders such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyisobutene are currently employed to bind graphite, carbon black and active materials (eg LiFePO ₄ ) to each other and to the current collector. ing. The net amount of binder and other conductive additives for nanospherical particles typically amounts to greater than 20% by weight in the electrode. In addition, the binders currently used are electrochemically and electronically inert, and therefore the specific energy and reaction rate of the cathode can be reduced by adding additional weight and reducing the conductivity of the cathode composite, respectively. Substantially lower. Overall, this results in diminishing the attractiveness of the material for high power applications.

The inventors have found that nanostructured polymer binders, which can be double utilized as effective conductive additives and binders in electrode composites, alleviate this problem and further increase the battery's high rate performance. I thought that there is a possibility to increase. Such nanostructured polymer binders have now been found to have several advantages. If a suitable nanoparticle size and shape is used, the binder will mix uniformly with the nanoparticulate EAM. Due to the particulate structure, pores that promote Li ⁺ diffusion are formed, and the presence of nanoparticles or pores, respectively, reduces the amount of binder required, thereby reducing weight. At the same time, electrochemical characteristics, that is, power density and specific energy are improved.

  Includes additional sacrificial nanoparticles that are later removed to leave the structure with improved porosity that facilitates diffusion of electrolytes and ions, thereby allowing the formation of thicker electrodes than previously possible Additional improvements can be made if the electrodes are first formed with nanocomposites.

Poly (3,4-ethylenedioxythiophene) (PEDOT) is an attractive candidate as a conductive polymer binder. In addition to the advantages of high chemical and environmental stability, the synthesis of PEDOT in various particle sizes and forms has been extensively studied so far (Non-Patent Documents 13-17). The monomer 3,4-ethylenedioxythiophene exhibits higher hydrophobicity and slower reaction rate than pyrrole, which makes it relatively simple for PEDOT as nanostubs or nanoparticles, as opposed to forming a tubular structure Synthesis is brought about. This form has been found to be beneficial for nanoparticles such as LiFePO ₄ particles that are synthesized with the same particle size and conformation and thus can be mixed together in a uniform composite.

A further advantage is the viscosity of PEDOT, good interparticle adhesion when pressed at pressures from 0.5 bar to 2 bar, ie from 5 · 10 ⁴ Pa to 2 · 10 ⁵ Pa and from 20 ° C. to 90 ° C., respectively. And sufficient substrate adhesion is obtained.

  Depending on the desired stability, heating can be unnecessary because the microparticles are sticky due to increased surface reactivity and van der Waals forces.

Nanocomposites such as PEDOT, sacrificial nanoparticles and LiFePO ₄ nanocomposites can be successfully synthesized using the inverse microemulsion technique. The unique beneficial effects of nanostructured poly (3,4-ethylenedioxythiophene) synthesized by inverse microemulsion and the structural properties of such composites have been studied and their electrochemical properties are bare And carbon coated LiFePO ₄ .

Thereby, it has been found that a further improved characteristic is obtained by a composite of a nanoparticle-form conductive coating with EAM, ie LiFePO ₄ , with a nanoparticle-form conductive polymer binder.

  These features can be further improved if the structure becomes more porous by removing previously added sacrificial particles.

  For further improvement of the characteristics, the nanoparticulate binder can be combined with an electronically conductive nanoparticulate filler such as carbon black and / or graphite, for example 2% to 10% by weight of the total electrode material, preferably about 5%. % Can also be mixed. Furthermore, conductive nanofibers can be added, preferably in an amount of 0.1% to 2%.

Experiment I. Material Preparation I. 1. Lithium iron phosphate Lithium iron phosphate samples were prepared by optimized solvothermal synthesis. Starting materials were FeSO ₄ .7H ₂ O (Aldrich, purity 99%) with a stoichiometric ratio of 1: 1: 3, H ₃ PO ₄ (Aldrich, purity> 85%), LiOH (Aldrich) , Purity> 98%). First, aqueous solutions of FeSO ₄ and H ₃ PO ₄ were prepared and mixed together. The mixture is transferred to a Parr autoclave, which is washed several times with nitrogen. A solution of LiOH is slowly pumped into the reaction mixture and then the autoclave is sealed. The reaction mixture is deagglomerated and heated at 160 ° C. overnight. The resulting precipitate is filtered and washed thoroughly with water to remove any excess salt. The wet precipitate is then dried in vacuo overnight to form a dry olive green solid powder of LiFePO ₄ .

I. 2. Carbon coated samples LiFePO ₄ was coated with carbon using several carbon-containing organic precursors. Separate batches of carbon-coated LiFePO ₄ were synthesized using polyacrylonitrile (PAN), 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid) and lactose, respectively. In a typical experiment, a certain amount of precursor (Table 1) was mixed with 100 mg LiFePO _{4 in a} liquid medium to form a highly dispersed suspension. The suspension was dried and subsequently calcined by heating to 650 ° C. at a rate of 2.5 ° C./min and maintaining at that temperature. The total firing time (excluding the heating time) was 6 hours. In order to avoid oxidation of Fe ⁺² to Fe ⁺³ , the heat treatment was performed under an inert nitrogen environment or under vacuum.

Table 1 shows the weight of the initial amount of organic precursor added relative to the weight of LiFePO ₄ and the final carbon content of the coated sample. The amount of carbon was determined by thermogravimetric analysis.

In addition, propylene gas was thermally decomposed in a flow oven to deposit carbon on LiFePO ₄ . The oven temperature was set at 700 ° C. The gas flow rate was 20 ml / min and the process was carried out for 4 hours. The amount of carbon deposited was about 0.1% by weight. The XRD patterns of all carbon coated samples are completely consistent with the untreated LiFePO ₄ and the presence of carbon does not interfere with the crystallinity at all. FIG. 1 shows the RD pattern of LiFePO ₄ carbon coated with lactose compared to untreated LiFePO ₄ . The particle size distribution of the carbon-coated sample obtained after annealing is wider than that of the as-synthesized untreated LiFePO ₄ . This may have occurred due to Ostwald ripening of primary particles at high temperatures. However, the particle size distribution remains sufficiently narrow so that lithium ions can still be effectively diffused by the LiFePO ₄ / FePO ₄ volume, and the discharge capacity is not affected even at a high exchange rate.

A comparison of the particle size distribution of the carbon-coated sample prepared with the lactose composition with untreated uncoated LiFePO ₄ is shown in FIG. The D80 value of the carbon-coated sample was found to be 30 μm or less, but it has grown about 3 times compared to the original sample.

A very thin amorphous layer of carbon around the carbon coated LiFePO ₄ particles can be delineated by high resolution TEM (not shown). The average layer thickness was found to be about 2 nm. The layer appeared to be very porous, but this should facilitate the easy diffusion of lithium ions into and out of the active material. In a clear TEM image, a distance of about 3 mm between the [301] separated portions of olivine-type LiFePO ₄ is observed.

  In a preferred procedure, carbon coated samples were made by heat treatment in the presence of lactose (15% by weight) in an inert environment. After drying, the powder was calcined at 650 ° C. for 6 hours (excluding the heating time at a rate of 2.5 ° C./min) and then subjected to a grinding or deagglomeration process. The amount of carbon was determined to be less than 3 wt% by thermogravimetric analysis.

I. 3. Preparation of PEDOT nanostubs by synthesis with inverse emulsion PEDOT nanoparticles were synthesized using the inverse microemulsion technique described in Sun et al. First, 8.5 g (19.12 mmol) of sodium bis (2-ethylhexyl) sulfosuccinate (AOT) was dissolved in 70 ml of n-hexane in an ultrasonic bath with 100% output (410 W). A mixture of 1.6 g (10.00 mmol) anhydrous FeCl _{3 in} 1 ml distilled water was then added dropwise with a Pasteur pipette. Once all the oxidizing agent was added, the resulting solution was removed from the ultrasonic bath and gently shaken by hand until a cloudy yellow precipitate appeared. Then 0.38 ml of ethylenedioxythiophene (EDOT) was added to the emulsion all at once. The resulting mixture was then maintained at 10 ° C. for 1 hour in a rotary evaporator. Polymerization started when the temperature of the water bath reached about 20 ° C. Thereafter, the temperature of the water bath was maintained at 30 ° C. for 3 hours. Meanwhile, the reaction mixture turned green and subsequently black. The product was then filtered off with suction and washed with ethanol and acetone. When dried at 100 ° C. overnight, a blue / black PEDOT nanopowder was obtained.

II. Chemical, electrochemical and structural characterization Due to the strong fluorescence of iron, a Bragg-Bentano type arranged powder X-ray diffractometer Bruker using λCuKα1 = 1.54056 Å irradiation (40 mA, 40 kV) and a germanium monochromator AXS mod. D8 Advance was used. The sample was placed on a rotating plate holder. A quartz sample was used as an external standard.

  Scanning electron microscope (SEM) analysis was performed using a Zeiss Gemini 1530 with an operating voltage of 1 kV. The material was deposited on a perforated carbon foil supported on a copper grid for measurement by transmission electron microscopy (TEM). The TEM inspection was performed using a C30ST microscope (manufactured by Philips; LaB6 cathode, operating voltage 300 kV, point resolution about 2 mm). Conductivity was measured using a four point conductivity test method.

III. Electrochemical measurements The composition of the three samples analyzed is summarized in Table 2, where L1 indicates the reference material obtained with untreated LiFePO ₄ and LC is the reference material with carbon-coated LiFePO ₄ And LP represents a mixture of carbon-coated LiFePO ₄ and PEDOT nanoparticles, which are materials of the present invention.

  For electrochemical measurements, the electrodes were made by mixing L1 and LC with carbon black, graphite and polyisobutene-based polymer binders. Active materials: Ensaco 250 (manufactured by TIMCAL): Graphite SFG6 (manufactured by TIMCAL): Oppanol (manufactured by BASF) = 75: 18: 6: 2 The components were mixed. The active material and additives were mixed and ground together by hand in a mortar until an apparent mechanical homogenization was obtained (35 minutes). The mortar was warmed to 90 ° C. and a 0.2% Opanol solution in n-hexane was added to the mixture. The suspension was mixed until n-hexane was completely evaporated. Next, 15 to 30 mg of sample was manually compressed into a pill (diameter 13 mm), and then the prepared cathode was dried. The mixed LP used as the electrode uses only 5% carbon and no graphite.

For the preparation of LP samples, PEDOT nanoparticles were dispersed in acetonitrile solution and then mixed with untreated LiFePO ₄ at 10% by weight. To obtain a higher pore volume, the sacrificial particles can be mixed and removed as soon as the “front electrode” is dry.

The cell was assembled in an argon filled glove box using lithium metal foil as the counter electrode. The electrolyte used was MERCK Selectipur, LP30, consisting of a 1M solution of LiPF ₆ in a 1: 1 (weight ratio) mixture of ethylene carbonate and dimethyl carbonate.

All electrochemical measurements were performed using a computer controlled charging system provided by Astrol Electronic AG (Switzerland). The cell was subjected to a constant current cycle in the range of 1.5 to 4.0 V vs. Li / Li ⁺ at a specific current based on the weight of the active material (LiFePO ₄ ) in the composite.

Results and discussion Effect of Structure and Morphology FIG. 2 shows the XRD pattern of L1, which is consistent with an orthorhombic crystal structure with space group Pnma. The pattern perfectly corresponds to the theoretical pattern of LiFePO ₄ and no impurities were detected. The XRD pattern of the carbon-coated sample LC is completely consistent with the naked sample L1, and the presence of carbon does not inhibit the crystallinity at all. The primary particle size is calculated using the Scherrer equation d = 0.9λ / βcos θ, where β is the half width of the XRD line and λ is the wavelength in angstroms. The single crystal diameter estimated using the width obtained from the XRD (020) line is 31.6 nm. The LC1 SEM image (not shown) shows that the particles had a clear elliptical shape with an average particle size of 200 nm. The LC form showed no significant difference from L1. A high resolution TEM image of LC (not shown) shows a very thin amorphous layer of carbon around the LiFePO ₄ particles. The average layer thickness was measured to be about 2 nm. The layer appeared to be very porous, but this should facilitate easy diffusion of lithium ions within the active material. The inter-surface distance was found to be about 3 mm, which is very similar to olivine's [301] inter-surface distance. The carbon coated sample had a conductivity in the range of 10 ⁻⁴ S / cm, which is several orders of magnitude higher than that of untreated LiFePO ₄ (10 ⁻⁹ S / cm). A SEM photo (not shown or FIG. 4) of a battery composite consisting of LC, graphite and standard binder should ideally serve as a conductive interconnect between insulating LiFePO ₄ particles. It shows that micro-sized graphite is completely out of range compared to nano-sized active materials. This remains as isolated islands in the matrix and is unlikely to be beneficial to the electronic percolation network, while greatly contributing to the weight of the electrode composite. This problem was successfully solved in LP. Synthesis of PEDOT with a reverse microemulsion results in the formation of a nano-sized mesh (shown in FIG. 5). A porous structure is formed from the aggregation of individual PEDOT nanostubs. The PEDOT particle conductive porous nanomesh (Nanomesh) completely encapsulates the LiFePO ₄ particles, which makes the entire composite even more conductive. PEDOT particles also function as a binder that bonds the electrode components to each other and to the current collector. This eliminates the need for the use of any separate binder, thus reducing the inert content from the bulk of the electrode.

II. Electrochemical results This electrochemical property of all samples was systematically investigated. FIG. 6 shows the initial discharge capacities of all three samples imposed on the cycle at a specific current of 20 mA (about 0.1 C). All samples have a significant flat voltage level. At this relatively low current, both the carbon coated sample (LC) and the polymer composite sample (LP) have a capacity of about 166 mAh / g, very close to the theoretical capacity of LiFePO ₄ 170 mAh / g. The uncoated sample (L1) has a starting capacity of 110 mAh / g which is much lower than the other two samples. In all three samples, the discharge capacity at this current remains stable for a very large number of cycles. This difference in performance clearly shows the effect of conductivity on the performance of the electrode.

  Since the difference in performance between the coated and uncoated active materials was clear and significant, we proceeded only with the higher current tests of LC and LP. Figures 7a and 7b compare the performance of LC and LP at a specific current of 135mA (about 0.8C). The initial discharge capacity of LP is 158.5 mAh / g. FIG. 7a shows the discharge curves after the 10th, 50th and 100th cycles. The capacities in these cycles are 158 mAh / g, 159 mAh / g and 141 mAh / g, respectively. This represents a drop of about 0.17 mAh / g per cycle, suggesting that 90% of the initial discharge capacity is maintained after 100 cycles. On the other hand, sample LC has an initial discharge capacity of 145 mAh / g, which is 128 mAh / g, 112 mAh / g and 97 mAh / g for the 10th, 50th and 100th cycles, respectively. This represents a drop of about 0.33 mAh / g per cycle and only 67% of the original capacity is maintained after 100 cycles. Thus, for LP, both the starting capacity and capacity retention are significantly better than LC. As shown in FIG. 8, for the next 100 cycles, both samples show a substantially linear drop at the same rate. The final discharge capacity of LP after 200 cycles is 130 mAh / g against 56 mAh / g of LC.

The inset of FIG. 7a shows the differential specific capacity plot (DSCP) of both these samples in the corresponding 10th, 50th and 100th discharge cycles. The peaks of these differential specific capacity plots correspond to the anode and cathode horizontal regions of lithium intercalation / deintercalation from the active material. Both anode and cathode peaks occur around 3.4 V, which is the lithium extraction / insertion potential in LiFePO ₄ . The main difference between the two plots is the polarization gap between the anode and cathode peaks and the intensity of the peaks. For LP, the spacing is about 0.1V, while for LC it is 0.6V. This spacing indicates the amount of overpotential in the electrode mix and mainly suggests higher electrode resistance in the LC. The peak intensity of the polymer composite LP is much higher than that of LC, indicating a better Li insertion reaction rate than the latter.

  Samples were tested at a range of current densities to investigate the effects of more stringent conditions on LP. FIG. 9 shows the discharge potential as a function of the number of cycles at various currents. At C / 5, the sample shows a theoretical capacity of 170 mAh / g. This value gradually decreases with increasing current, but a relatively stable discharge capacity of about 130 mAh / g is observed even under high current corresponding to 10C. After the current drops to its initial value, most of the original capacity is retained.

The performance of the PEDOT and LiFePO ₄ composites was significantly better compared to bare and carbon coated LiFePO ₄ . The composite containing the conductive polymer outperforms the other two samples, while its total additive content is only 50% of the electrode weight.

  While presently preferred embodiments of the invention have been shown and described, it should be clearly understood that the invention is not limited thereto and can be embodied and practiced in various other ways within the scope of the following claims. .

L1 Reference material obtained with untreated LiFePO ₄ uncoated;
Reference material with LC carbon coated LiFePO ₄ ;
LP A mixture of carbon-coated LiFePO ₄ and PEDOT nanoparticles, the material of the present invention.

Claims (20)

An intermediate nanocomposite for an anode or cathode of a rechargeable lithium battery, the nanocomposite comprising a uniformly distributed nanoparticulate electroactive material (EAM) and a nanoparticulate electronically conductive binder material (CB) and sacrificial nanoparticles that are finally removed when generating the electrode, and the average particle size of the EAM nanoparticles and the average particle size of the nanoparticulate CB are:
Both differ by +100% /-50% or less, and / or both are in the range of 5 nm to 500 nm, and
The sacrificial nanoparticles are in the range of 200 nm to 500 nm;
Here, the nanoparticulate CB is poly (3,4-ethylenedioxythiophene) (PEDOT), and the intermediate nanocomposite contains no binder other than the nanoparticulate CB,
Nanoparticles E AM is coated with a conductive layer, nanocomposite.   2. The electrode is an anode and the EAM is selected from transition metal and main group metal oxides, nitrides, carbides, borates, phosphates, sulfides, halides, and mixtures thereof. The intermediate nanocomposite described in 1. EAM is LiFePO _4, the intermediate nanocomposite of claim 2. The intermediate nanocomposite of claim 1, wherein the electrode is a cathode and the nanoparticulate EAM is an anode EAM selected from silicon and Li _x VN.   The intermediate nanocomposite according to any one of claims 1 to 4, wherein the conductive layer is a carbon or graphite / graphene layer.   The intermediate nanocomposite according to any one of claims 1 to 5, wherein both the average particle diameter of the CB nanoparticles and the average particle diameter of the EAM nanoparticles are in the range of 5 nm to 400 nm.   The intermediate nanocomposite according to claim 6, wherein the average particle size of the CB nanoparticles and the average particle size of the EAM nanoparticles are both in the range of 20 nm to 300 nm.   The intermediate nanocomposite according to any one of claims 1 to 7, comprising carbon black as a nanoparticulate electronically conductive filler material.   9. The intermediate nanocomposite of claim 8, wherein the amount of carbon black is in the range of 2% to 10% based on the weight of the nanocomposite that does not include sacrificial nanoparticles.   The intermediate nanocomposite according to claim 9, wherein the amount of carbon black is 5%.   11. The intermediate nanocomposite according to any one of claims 1 to 10, wherein the CB nanoparticles are present in an amount of 4% to 10%, based on the weight of the nanocomposite free of sacrificial nanoparticles.   The intermediate nanocomposite according to any one of claims 1 to 11, wherein the sacrificial nanoparticles have a particle size in the range of 300 nm to 500 nm.   The intermediate nanocomposite according to any one of claims 1 to 12, wherein the sacrificial nanoparticles are selected from polyethylene particles, polyethylene glycol particles, polyvinyl acetal particles, polystyrene particles and mixtures thereof.   14. The intermediate nanocomposite according to any one of claims 1 to 13, wherein the sacrificial nanoparticles are present in an amount of at least 0.5% by weight.   15. The intermediate nanocomposite according to claim 14, wherein the sacrificial nanoparticles are present in an amount of 0.5 wt% to 10 wt%.   The intermediate nanocomposite of claim 14, wherein the sacrificial nanoparticles are present in an amount of 40 wt% to 60 wt%. An electrode material for an anode or cathode of a rechargeable lithium battery obtained from the intermediate nanocomposite according to any one of claims 1 to 16 by removing sacrificial nanoparticles, wherein the electrode material is A nanocomposite, the nanocomposite being an open porous material comprising uniformly distributed nanoparticulate EAM and nanoparticulate CB, wherein the mean particle size and nanoparticulate CB of EAM nanoparticles The average particle size of
Both differ by less than +100% /-50%, and / or both are in the range of 5 nm to 500 nm,
The electrode material comprises pores in the range of 200 nm to 500 nm,
An electrode material characterized by that.   A method for producing the electrode material according to claim 17 from the intermediate nanocomposite according to any one of claims 1 to 16, wherein the electrode is formed or after the electrode is formed. During which the sacrificial nanoparticles are removed by heat treatment or chemical reaction. Rechargeable lithium battery anode comprising a nanoparticulate electroactive material (EAM), a nanoparticulate electronically conductive binder material (CB), and sacrificial nanoparticles that are ultimately removed in forming the electrode or a method for generating an intermediate nanocomposite for the cathode, comprising the steps of mixing the nanoparticulate CB, the nanoparticulate EAM and sacrificial nanoparticles, and exposing the mixture to pressure and heat ,
Here, the nanoparticulate CB is poly (3,4-ethylenedioxythiophene) (PEDOT), the intermediate nanocomposite contains no binder other than the nanoparticulate CB, Methods. The process according to claim 19, wherein the pressure is from 0.5 bar to 2 bar (5 · 10 ⁴ to 2 · 10 ⁵ Pa) and the heat corresponds to room temperature.