RU161876U1 - LITHIUM ION BATTERY - Google Patents

Abstract

1. A lithium-ion battery containing a positive electrode including an electrically conductive substrate with an active layer deposited thereon, and a negative electrode including an electrically conductive substrate with an active layer deposited on it, including silicon particles, a separator impregnated with a non-aqueous electrolyte and placed between the opposite layers of the opposite electrodes, characterized in that as silicon particles included in the active layer of the negative electrode, fibrous silicon with a transverse fiber size is used t 100 nm to 300 nm and a specific surface area of 30-135 m / g, obtained by electrolytic reduction of silicon from a melt of a mixture of alkali metal halides, with the following composition of the active layer of the negative electrode (wt.%): fibrous silicon - 60-80, conductive additive - 15-25 and a binder - 5-15.2. The lithium-ion battery according to claim 1, characterized in that silicon fibers are used with a longitudinal to transverse ratio lying in the range of 0.95-1.05.

Description

The utility model relates to the electrical industry, in particular, to devices for the direct conversion of chemical energy into electrical energy, and specifically to a lithium-ion battery based on a new electrochemical system.

Lithium-ion batteries based on the traditional electrochemical system are known and widely used [see, for example, B. Scrosati, J. Garche. Lithium batteries: Status, prospects and future. Journal of Power Sources, 2010, V. 195, P. 2419-2430); Chemical Current Sources: Reference / Edited by N.V. Korovin and A.M. Skundina. - M: Publishing House MPEI, 2003, p. 740]. In a traditional electrochemical system, negative electrodes are made of graphite or other carbon material, positive electrodes are made of lithium cobalt, nickel or manganese oxides, or of lithium iron phosphate.

Recently, attempts have been made to use silicon as the active substance of the negative electrodes of lithium-ion batteries. Silicon has the ability to incorporate a much larger amount of lithium than graphite (theoretically - 11 times), which allows to increase the specific energy of the entire battery by reducing the mass of the active substance on the negative electrode. However, when lithium is introduced into silicon, a significant, more than threefold, increase in volume occurs. This leads to the fact that in the cyclic process of charging / discharging the battery, volumetric changes in the active material of the electrode cause its degradation and loss of contact with the collector. To overcome this drawback, it was proposed to use thin-film, including multilayer electrodes made, for example, by magnetron sputtering or chemical vapor deposition (e.g., US Pat. 6,685,804, February 3, 2004, Sanyo Electric Co., Ltd. ; US Pat. 6,887,511, May 3, 2005, Sanyo Electric Co., Ltd .; US Pat. 7,192,673, March 20, 2007, Sanyo Electric Co., Ltd .; US Pat. 7,410,728, August 12, 2008, Sanyo Electric Co ., Ltd.). Silicon-based thin-film electrodes have a specific capacity (per unit mass of the active layer) that does not differ much from theoretical values, and good cyclability if the film thickness of the active material is tens or hundreds of nanometers. Since such active films are deposited on metal substrates with a thickness of at least 10 μm, the specific capacity per unit surface area is much less than that of conventional batteries with a carbon negative electrode, where the thickness of the active layer is 40-50 μm. An increase in the thickness of silicon or a silicon-containing composite in order to increase the specific capacity per unit surface area leads to a sharp increase in degradation during cycling.

An alternative to electrodes with continuous thin films could be electrodes made of finely dispersed silicon, manufactured by the standard "spread" technology. In this case, the active mass (in the form of a suspension, paste, "ink", etc.), consisting of a powder of the active material, a binder and (if necessary) other additives, is applied ("spread") onto the substrate in the form of a foil, plate or mesh . This technology, which is fully justified in the manufacture of negative electrodes from carbon materials, is hardly applicable for the manufacture of electrodes made of silicon powder, precisely because of the strong expansion of silicon during the introduction of lithium. There are much fewer patents devoted to such plated electrodes than patents for thin-film electrodes. The first such patent, filed in 1997 and published in 2000 [US Pat. 6,042,969, March 28, 2000, Sony Corporation], was essentially an umbrella patent. It declared the fundamental possibility of using elemental silicon, and the first example of this patent describes an electrode made of single-crystal silicon powder with a size of less than 38 microns. (Subsequent work showed that such material does not withstand cycling). As examples of other umbrella patents, where the possibility of using silicon powder (along with many other dispersed materials) is only declared, patents can be cited: US Pat. 6,300,013, Oct. 9, 2001, Sony Corp .; US Pat. 6,432,585, Aug. 13, 2002, Canon; US Pat. 7,479,351, Jan. 20, 2009, Samsung SDI; US Pat. 7,851,086, Dec. 14, 2010, Samsung SDI; US Pat. 8,080,335, Dec. 20, 2011, Canon.

Patents devoted to electrodes based on finely dispersed silicon proper include rather complicated technological methods for powder production, as well as rather complicated, laborious, and lengthy special preparation of the surface of the collector substrate. So, in accordance with US Pat. 8,734,991, May 27, 2014, Sanyo Electric Co. the active part of the electrode is prepared from silicon powder with characteristic sizes from 20 to 100 nm, synthesized by pyrolysis of silane at a temperature of 1000 ° C in a fluidized (boiling) layer, and additionally doped with boron, phosphorus or arsenic (with an alloying element from 0.1 to 100 ppm, i.e. from 0.00001% to 0.01%); for such doping, silicon powder is annealed in a non-oxidizing atmosphere containing diborane, phosphine or arsine at a temperature of 1000 ° C.

In accordance with the aforementioned US Pat. 7,479,351 and US Pat. 7,851,086 highly dispersed silicon powder is prepared by leaching the active component from a silicon alloy with alkali or alkaline earth metals, boron, aluminum, zinc, etc. Thus, in this case we are talking more about skeletal silicon.

US Pat. 8,101,298, Jan. 24, 2012, Nexeon Ltd. and GB 2,464,158, 04/14/2010, Nexeon Ltd. describe a highly dispersed silicon powder consisting of cylindrical single-crystal silicon particles having a diameter of from 80 to 500 nm and an aspect ratio of more than 40. Such particles are obtained by selective etching of a silicon wafer, followed by separation from the substrate by ultrasonic treatment.

US Pat. No. 7,597,997, Oct. 06, 2009, Panasonic Corp. provides that each particle of silicon powder is covered with a thin layer of tin, indium, gallium, lead, or bismuth, and the thickness of this layer should be about 10% of the diameter of the silicon particle. Such a coating, according to the author, improves the electrical contact between silicon particles, as well as between these particles and the collector.

In the patent EP 2,056,381, 05/06/2009, Panasonic Corp. It is proposed to improve the adhesion between the down conductor substrate and the active layer (consisting of silicon powder) on a flat surface of the substrate to create a regular network of primary protrusions with a height of 3 to 15 μm, on the surface of which there are smaller secondary protrusions.

Known lithium-ion battery containing deposited on a substrate of titanium foil, one of which is coated with a positive electrode made of a material in the form of a paste based on lithium ferrophosphate, and the second negative electrode made of amorphous silicon (RF patent 128014, cl. H01M 4/12, op. 05/10/2013).

The disadvantage of this battery is its low specific capacity.

Closest to the claimed one is a lithium-ion battery containing a positive electrode including an electrically conductive substrate with an active layer deposited thereon, and a negative electrode including an electrically conductive substrate with an active layer deposited on it containing silicon particles or a mixture of such particles with carbon particles, a separator impregnated with a non-aqueous electrolyte and placed between the active layers of unlike electrodes (RF patent No. 129301, class H01M 10/52, op. 20.06.2013)

The specific capacity of the battery with a silicon-containing negative electrode described in this patent is from 1.1 to 1.6 mAh / cm ² and is fundamentally limited from above. Since, as follows from the above description, the specific capacity of the electrodes per unit of surface area is a key indicator of the battery, it is desirable to increase it in every way.

The objective of this utility model is to create a lithium-ion battery with a negative electrode of the smeared design based on highly dispersed silicon with a significant simplification of the electrode design and manufacturing technology and, as a result, with a significant increase in the specific capacitance of the electrode per unit area while maintaining low labor costs for production batteries.

The technical result achieved by the utility model is to increase the specific capacity of the battery while maintaining the salted technology of its manufacture, characterized by low labor costs in its application.

The indicated technical result is achieved in that in a lithium-ion battery containing a positive electrode including an electrically conductive substrate with an active layer deposited thereon, and a negative electrode including an electrically conductive substrate with an active layer deposited on it, including silicon particles, a separator impregnated with a non-aqueous electrolyte and placed between the active layers of unlike electrodes, fiber silicon is used as silicon particles included in the active layer of the negative electrode minutes with a transverse dimension of the fibers of from 100 to 300 nm and a specific surface area of 30-135 m ² / g obtained by electrolytic reduction of silicon from a melt mixture of alkali metal halides, with the following composition of the negative electrode active layer (wt.%): silicon fiber - 60 -80, conductive additive - 15-25 and a binder - 5-15.

In the particular case, to increase the repeatability of the negative electrode properties of the lithium-ion battery from one instance to another, silicon fibers with a longitudinal to transverse ratio lying in the range of 0.95-1.05 can be used in the active layer of the indicated electrode.

In FIG. Figure 1 shows a graph of the change in the discharge capacity of the negative electrode of a lithium-ion battery during cycling with a current of 250 mA / g in a 1 M LiPF ₆ electrolyte in a mixture of ethylene carbonate-diethyl carbonate-dimethyl carbonate (1: 1: 1 ratio).

In FIG. Figure 2 shows a graph of the change in the discharge capacity of the negative electrode of a lithium-ion battery during cycling with various current densities.

A lithium-ion battery contains a positive electrode including an electrically conductive substrate with an active layer deposited on it, and a negative electrode including an electrically conductive substrate with an active layer deposited on it, including silicon particles, a separator impregnated with a non-aqueous electrolyte and placed between the active layers of unlike electrodes.

The negative electrode has a spread design.

As silicon particles included in the active layer of the negative electrode, fibrous silicon was used with a transverse fiber size of 100 to 300 nm and a specific surface area of 30-135 m ² / g, obtained by electrolytic reduction of silicon from a melt of a mixture of alkali metal halides. Such a material can be characterized as “nanofiber” silicon. The content of fibrous silicon in the active layer of the negative electrode is 60-80 mass. % In addition, the specified active layer contains 15-25 mass. % conductive additives and 5-15 mass. % binder.

In the particular case, to increase the repeatability of the negative electrode properties of the lithium-ion battery from one instance to another, silicon fibers with a longitudinal to transverse ratio lying in the range of 0.95-1.05 can be used in the active layer of the indicated electrode. Such fibers, due to the proximity of their longitudinal and transverse sizes, can be considered as “nanopowder” silicon. Fibers with a specified ratio of longitudinal to transverse size can be obtained from a mixture of fibers of various sizes, usually obtained in the processes of electrolytic reduction of silicon from a melt of a mixture of alkali metal halides, by fractionation by any known method, for example, the method of separation of nanoparticles into fractions using the Faraday magnetic system ( see publication: http://electromeh.npi-tu.ru/assets/files/archive_4_2014.pdf.) or by the method of flow fractionation in a transverse force field (see, for example, publication: http: // http: // ww w.soctrade.com/laboratornoe_oborudovanie/frakcionirovanie-nanochastic.phtml) or by the fractionation method in planetary centrifuges with rotating spiral columns, described, for example, in the dissertation of the candidate of chemical sciences MS Ermolin “Fractionation of nano- and microparticles in rotating spiral columns in the analysis of polydisperse samples”: Institute of Geochemistry and Analytical Chemistry. IN AND. Vernadsky RAS, Moscow, 2013. 67-108.

Highly dispersed silicon obtained by electrolytic reduction of silicon from a melt of a mixture of alkali metal halides has a specific surface area of 30 to 135 m ² / g, which ensures the manufacture of electrodes capable of functioning in a wide range of current loads. Obtained by the indicated technology, fibrous finely dispersed silicon allows the manufacture of electrodes with a sufficiently high content of active substance per unit of space, which provides an increased capacity of the electrodes and the battery as a whole.

The positive electrode of a lithium-ion battery can also be made of a spread structure, i.e. it contains an electrically conductive substrate in the form of a stainless steel grid with a current output welded to it. The active layer in the form of a paste based on lithium ferrophosphate (lithiated iron phosphate) is applied to the grid. Such a paste may include the following ingredients (wt.%): Lithium ferrophosphate - 50-95, an electrically conductive carbon additive - 2-45, a binder - 5-14, and polyvinylidene fluoride can be used as a binder.

Consider an example of the manufacture and operation of a lithium-ion battery with a negative electrode, which uses highly dispersed silicon fiber with a transverse fiber size of 100 to 300 nm and a specific surface area of 30-135 m ² / g, obtained by electrolytic reduction of silicon from a melt of a mixture of alkali metal halides (for example, according to the well-known technology described in RF patent No. 2486290, class С25В 1/00, op. June 27, 2013. Similar technological processes for producing highly dispersed silicon are also described in RF patents No. 2399698 and 2427526)

Example. Silicon powder obtained by electrolytic reduction of silicon from a melt of a mixture of alkali metal halides was mixed with an electrically conductive additive (carbon black) and a solution of a binder (polyvinylidene fluoride) in N-methylpyrrolidone in the ratio (70:20:10). After homogenization on an ultrasonic device UZDN-4, the active mass was deposited on one side of a stainless steel mesh with a current output welded to it. The amount of silicon applied was about 4.5 mg / cm ² , and this is not the limit. Next, the electrodes were pressed with a pressure of 2 t / cm ² . After pressing, the electrodes were placed in a vacuum oven and annealed at a temperature of 120 ° C. After annealing, the electrodes were transferred to a glove box with an atmosphere of dry argon, where they assembled mock-ups of a lithium-ion battery of a plane-parallel design containing negative electrodes of the design described above and standard positive electrodes with an active layer based on lithium ferrophosphate. The electrodes were separated by a non-woven polypropylene separator impregnated with a standard electrolyte - a solution of lithium hexafluorophosphate in an equivalent volume mixture of ethylene carbonate-diethyl carbonate-dimethyl carbonate.

Since the characteristics of the battery depend on the characteristics of both electrodes, for a more complete characterization of the negative electrodes according to the present utility model, experiments were carried out with three-electrode laboratory cells, which made it possible to isolate the characteristics of the negative electrode under study. The cells were mock-ups of a lithium-ion battery containing a working negative electrode, made in the same way as described above, an auxiliary lithium foil electrode and the same lithium reference electrode. All electrodes were separated by a nonwoven polypropylene separator (NPP Ufim, Moscow). As electrolytes, 1 M LiPF ₆ in a mixture of ethylene carbonate-diethyl carbonate-dimethyl carbonate (EK-DEK-DMK) (1: 1: 1) and 1 M LiClO ₄ in a mixture of propylene carbonate-dimethoxyethane (PC-DME) (7: 3) were used. It is known that the electrodes of a lithium-ion battery are very sensitive to traces of moisture in non-aqueous electrolytes. The water content in the electrolyte did not exceed 20 ppm. The galvanostatic cycling of the electrodes was carried out using a computerized charge-discharge stand (LLC Buster, St. Petersburg). Cycling limits ranged from 0.01 to 2 V. Cycling currents ranged from 20 to 4000 mA / g silicon.

After assembling the electrochemical cell and filling it with electrolyte, the potential of the working electrode was about 2.5 V, which corresponds to the current-free potential of silicon relative to lithium metal. During cathodic polarization, lithium was introduced into silicon; during anodic polarization, lithium was extracted.

From the graph in FIG. 1, which shows the change in the discharge capacity of the electrodes during continuous cycling to full depth at a load of 250 mA / g, it follows that the degradation of the negative electrode according to the present utility model is very small. The decrease in capacity from the 3rd to the 19th cycle is only 0.9%, which corresponds to a degradation rate of 0.06% per cycle. Since the cycling of positive electrodes based on lithium ferrophosphate proceeds very stably, the degradation of the entire battery is determined precisely by the degradation of the negative electrode.

From the graph in FIG. 2 shows how the discharge capacity of the negative electrode active layer, wherein silicon is used with the fibrous fiber transverse dimension of 100 to 300 nm and a specific surface area of 30-135 m ² / g obtained by electrolytic reduction of silicon from a melt mixture of alkali metal halides, when cycling with different values of the charge and discharge current. It can be seen that even with a load of 4000 mA / g, which corresponds approximately to 2C mode, the electrode is quite functional, although its capacity is less than 10% of the value at a load of 20 mA / g. The specific capacity per unit area at low loads (i.e., in soft cycling mode) is about 9 mAh / cm ² , and in forced mode it can be from 2 to 5 mAh / cm ² , which significantly exceeds the prototype.

From the above it follows that the use of a lithium-ion battery in the active layer of the negative electrode with electrodes of the spread structure of fibrous silicon with a transverse fiber size of 100 to 300 nm and a specific surface area of 30-135 m ² / g, obtained by electrolytic reduction of silicon from a melt mixture alkali metal halides with a negative electrode (wt.%) in the active layer: 60-80 fibrous silicon, 15-25 conductive additives and 5-15 binder, leads to a noticeable increase in hydrochloric battery capacity while maintaining namaznomu technology of its manufacture.

Claims (2)

1. A lithium-ion battery containing a positive electrode including an electrically conductive substrate with an active layer deposited thereon, and a negative electrode including an electrically conductive substrate with an active layer deposited on it, including silicon particles, a separator impregnated with a non-aqueous electrolyte and placed between the opposite layers of the opposite electrodes, characterized in that as silicon particles included in the active layer of the negative electrode, fibrous silicon with a transverse fiber size is used t 100 nm to 300 nm and a specific surface area of 30-135 m ² / g obtained by electrolytic reduction of silicon from a melt mixture of alkali metal halides, with the following composition of the negative electrode active layer (wt.%): silicon fiber - 60-80, the conductive the additive is 15-25 and the binder is 5-15. 2. The lithium-ion battery according to claim 1, characterized in that silicon fibers with a ratio of longitudinal to transverse size lying in the range of 0.95-1.05 are used.

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