A ceramic separator for energy storage device and method of manufacture

Abstract

The present invention relates to ceramic separators for high performance electrochemical devices such as secondary batteries and methods of manufacture said ceramic separators. The ceramic separator in the form of a cup having side walls and a bottom wall. The ceramic separator is made of kaolin (Al2O3 and SiO2) powder material. An average diameter of the powder material is up to 5 microns, and a thickness (Hwall) of the side walls and the bottom wall of the ceramic separator is in the range of 0.5 to 1 millimetres.

Description

[0001] A CERAMIC SEPARATOR FOR ENERGY STORAGE DEVICE AND METHOD OF MANUFACTURE

[0002] Field of the invention

[0003] The present invention relates to ceramic separators for high performance electrochemical devices such as secondary batteries and methods of manufacture said ceramic separators.

[0004] Background of the invention

[0005] High-capacity, fast-charging energy storage devices such as capacitors and batteries are used in a wide range of applications, including portable electronics, medical, transportation, grid- connected industrial energy storage, renewable energy, energy storage, and uninterruptible power supply. Alkaline batteries are one of the popular types of rechargeable energy storage devices. Alkaline batteries work more efficiently under high load, do not corrode, and are not subject to sudden heating when overloaded.

[0006] An alkaline battery usually consists of a positive electrode (anode) and a negative electrode (cathode) in an electrolyte bath. As a rule, the electrodes are insulated with a porous separator, the main role of which is to eliminate any contact between the electrodes while keeping them at a minimum distance (for example, a few microns) from each other. The separator prevents short circuits of the electrodes, preventing the growth of dendrites and reducing the precipitation of metal oxides and hydroxides. The separator is usually made from a microporous material based on polymers, ceramics (US3861963A), as well as their combinations (layering (US20120082884A1) or composites (US8852787B2)), as well as fibrous nonwoven material of natural or artificial origin (EP2802026B1). During electrochemical reactions, i.e. charging and discharging, the metal ions (Li+, Na+, etc.) in the electrolyte are transported through the pores in the separator between the two electrodes through the electrolyte. Thus, high porosity is desirable to increase ionic conductivity. However, separators with high porosity are sensitive to short circuits due to the growth of pure metal dendrites formed during cyclic operation, as well as to a significant decrease in mechanical strength, which makes the membranes unsuitable for practical use. The separators currently in use have a number of disadvantages. Membrane materials are often expensive, and a typical battery system will include relatively large volumes of separator material, the cost of membranes can represent a significant portion of overall battery costs. Inexpensive battery separator membrane materials may not be effective in preventing the formation of dendritic bridges and, therefore, such separators must be sufficiently thick. The thickness of the separator, on the other hand, increases the internal resistance of the battery, thereby reducing its efficiency, and also increases the size of the battery. Thus, there is a need for a separator configuration that is efficient, inexpensive, safe, and easy to use.

[0007] Hence it is necessary to create a separator that overcomes aforementioned drawbacks.

[0008] Mainly, the separator shall be easy to manufacture, ensuring the efficiency of the process and minimal deviations from the standard, including deformation during sintering. It has to have high porosity with a small value of the average pore diameter, and has to have high mechanical strength, as well as structural integrity, ensuring safe handling during cell assembly, maintenance, and ease of replacement.

[0009] Summary of the invention

[0010] Aim is reached by a design of ceramic in the form of a cup having side walls and a bottom wall. The ceramic separator is made of A12O3 and SiO2 powder material. The average diameter of said powder material according to D50 is up to 5 microns. The D50 is the mean or average particle size of a mineral. So “D50 = 5 microns” means the average particle size of that mineral is 5 microns. It also means that 50% of the particles are smaller than 2 microns, and 50% are bigger. A thickness of the side walls and the bottom wall is in the range of 0.5 to 1 millimetres.

[0011] The separator is a thin porous ceramic insulating material with high ionic permeability (< 10 Ohm), good mechanical strength (<250 MPa) and long-term stability (more then 50 000 of charging / discharging) against aggressive substances that are in the system (salts, oxides, metal hydroxides, and alkalis). The ceramic separator is designed for complete electronic and physical isolation of the cathode from the anode in batteries.

[0012] In order to form a ceramic separator according to necessary characteristics a crucial step is its manufacture. A method for manufacture of the ceramic separator comprises the following steps:

[0013] - providing A12O3, SiO2 and kaolin;

[0014] - mixing A12O3, SiO2, kaolin and water to form an aqueous suspension;

[0015] - burning the aqueous suspension while stirring in result of which a calcined kaolin powder is obtained, wherein the step of burning is accomplished by gradually increasing a temperature up to 1100 °C, and wherein the gradual increase of temperature is in the range of 8°C / min to 12°C / min, preferably 10 °C / min;

[0016] - crushing the calcined powder up to particle size of about 5 pm;

[0017] - formation of an aqueous suspension from the crushed calcined powder and additional kaolin;

[0018] - pouring the aqueous suspension into a mold, wherein the mold is in a shape to allow to form a cup;

[0019] - settling of the poured aqueous suspension into the mold at a temperature of 45°C on air, in result of which a cup is formed; and

[0020] - burning the cup at a temperature of 1100°C so that the ceramic separator in the form of the cup is formed.

[0021] The result of the present invention is a safe, high performance ceramic separator for batteries, as well as a method for its manufacture. The ceramic separator is thermally stable at temperatures of minus 50°C to plus 250°C or even higher.

[0022] In other embodiments of the invention, the ceramic separator may be in the form of a thin ceramic plate (for direct use as a separator for unit cell modifications).

[0023] Brief description of the drawings

[0024] Fig. l is a block scheme of a manufacturing process of a ceramic separator.

[0025] Fig. 2A is a photo showing molds for manufacture ceramic separators.

[0026] Fig. 2B illustrates a ceramic separator with its main dimensions.

[0027] Fig. 3 A illustrates an anode / cathode cup enclosed by a ceramic separator having round crosssection. Types of ceramic separation electrode (anode / cathode) nozzles.

[0028] Fig. 3B illustrates an anode / cathode cup enclosed by a ceramic separator having hexagonal cross-section. Fig. 3C illustrates an anode / cathode cup enclosed by a ceramic separator having rectangular cross-section.

[0029] Fig. 4 illustrates an electrochemical cell formed by two anode / cathode cups as seen in Fig. 3B.

[0030] Fig. 5A illustrates an assembly of a secondary battery comprising a number of electrochemical cells.

[0031] Fig. 5B is a close-up view of part of the assembly as seen in Fig. 5A.

[0032] Fig. 6 is a micrograph of a ceramic porous material used in a ceramic separator.

[0033] Fig. 7 illustrates a ceramic porous material (plate) of a ceramic separator and a wetting angle of said ceramic porous materials (plate).

[0034] Fig. 8 is a hodograph of a ceramic porous material.

[0035] Detailed description of the invention

[0036] A technological process of manufacture of ceramic separators is represented as a block diagram in Fig. 1. In one embodiment of the invention, which is also the technological process, at the first stage, thin ceramic plates are formed from liquid raw materials. The liquid raw materials are aqueous suspension of kaolin with a composition of 60% A12O3 and 40% SiO2. The liquid raw materials are watered and further fired at a temperature of 900 - 1100 °C.

[0037] In other embodiments of the invention, single thin ceramic sheets are used as interelectrode separators. In other embodiments of the invention, the ceramic sheets are subject to crushing to form a fine powder with particles of up to 5 microns. Further, the resulting powder is added to said aqueous suspension of kaolin. The addition of fired ceramic particles contributes to the mechanical strength of the final product and the required porosity. In addition, to increase the mechanical strength, particles of kaolin powder calcined at a temperature of 1100°C are added to the aqueous suspension. Additional ceramic material with particle size of up to 5 microns is added in an amount equal to the original powder. The introduction of uncalcined powder provides strength before the sintering operation, and also gives the finished samples the necessary sintering ability. After burning, the ceramic acquires mechanical strength and has a strong hygroscopicity.

[0038] In some embodiments of the invention, the interelectrode separators can be formed in ceramic porous thin-walled cups. The cups are formed by pouring the aqueous suspension into pre- formed molds, further degassing and further burning. Rigid ceramic cups for use as an interelectrode separator in an electrochemical cell are obtained by burning the aqueous suspension of the ceramic material at a temperature of 900 - 1100°C. At the same time, the selected firing temperature affects both the porosity of the ceramic and the average pore size. So, during burning at 940 - 950°C, the porosity is 80% of pores 20 - 25 pm. At 1000°C the porosity is 50% with pores up to 5 - 15 pm. During firing at 1100°C, the porosity is 30 - 40% with an average pore size of 1 - 5 pm.

[0039] Thus, the aforementioned manufacturing method provides the ability to control the pore size and provides high-performance interelectrode membranes with the required porosity, satisfactory mechanical strength.

[0040] In some cases, for the production of ceramic cups as seen in Fig. 2B, casting molds can be used, designed according to the required dimensions of the final cups and representing an antislit design as seen in Fig. 2A.

[0041] The design of the cups can be made in one of three ways: Type 1 with round cross-section as seen in Fig. 3A; type 2 with regular hexagon cross-section as seen in Fig. 3B; and type 3 with square cross-section as seen in Fig. 3C.

[0042] Fig. 4 illustrates a elementary battery cell (60) as a block structure or package. The elementary battery cell (60) comprises two electrodes: an anode (20) and a cathode (30). The anode (20) comprises an active composite anode material impregnated with electrolyte (21) and an electrically conductive insert - current lead (22). The cathode (30) comprises an active composite cathode material impregnated with electrolyte (31) and a current lead (32). The elementary battery cell (60) comprises a ceramic separation cups (40), in which the anode and cathode materials are placed. In this embodiment of the invention, the ceramic cups with anode and cathode material are tightly attached to each other. The anode (20) comprising the active composite anode material impregnated with the electrolyte (21) and the cathode (30) comprising the active composite cathode material impregnated with the electrolyte (31) are pressed into cells or into the ceramic porous separation cups (50) to ensure ion exchange between the anode and cathode and isolation between anodic and cathodic material. Current collectors (22) and (32) are mounted in the active anode and cathode materials respectively. The current collectors (22) and (32) are made in the form of metal or graphite rods commensurate with the length of the cells (see Fig 4).

[0043] Battery cells (60) can be bundled (71) according to required power, current or potential difference in one construction (70) as seen in Figs. 5A and 5B. The bundle (71) is packaged in a polymer case (72). The electrolyte, in some cases sodium hydroxide solutions, preparing as a gel by adding of silica nanoparticles is filling a polymer case with anode and cathode caps. The current collectors (22) and (32) are connected in turn to insure required current or potential difference. Connection system comprises a polymer isolation plate (73) and metallic connecting plates (75). Battery external connectors (76) and (77) taken out of the plastic housing for the possibility of connecting an external current consumer.

[0044] In another embodiments of the inventions the active anode material (21) and cathode material (31) are made of electrically conductive particles of microporous sheet carbon (MSC) with an increased specific surface, respectively, the contact area with inclusions of conglomerates of anode metal nanoparticles. The size of nanoparticles is in the range of 50-100 nm. To increase efficiency, the anode material (21) and cathode material (31) are impregnated with an electrolyte.

[0045] The invention is directed to a rechargeable electrochemical alkaline cell having an anode containing mechanical mixture of zinc / zinc oxide and MSC in 9: 1 by mass and a cathode containing mechanical mixture of copper oxide (Cu2O) or copper hydroxide (Cu(OH)2) and MSC in 9: 1 by mass. If copper oxide is used in the cathode mixture, it is desirable that its purity be at least 80% by weight. MSC is added to the cathode mixture, which contributes to an increase in the conductivity of the electrode layer, and contributes to an increase in the capacitance and voltage of the element.

[0046] Ceramic electrode separators have dimensions X*Y*Z 30*30*280 mm3, wall thickness l±0.2 mm as seen in Fig. 2B.

[0047] The main characteristics of the ceramic separator are as follows: mechanical strength, electrolyte contact angle, ionic conductivity, as well as resistance to cyclic loads. The crosssection of the porous ceramic material displays a microporous structure with pore sizes from 3 to 50 pm, with opened channels. The average pore diameter is 165±3 pm. A morphology of the ceramic materials of the cup is seen in Fig. 6.

[0048] Fig. 7 shows the contact angle of water wetting with a volume at a drop size of 50 pl. An image of a lying drop of liquid was captured using a camera (resolution 600x800 dpi) at lOOx magnification. The determination of the contact angle of wetting of the samples from the obtained images was carried out in the ImageJ program, averaging the values of 5 measurements. The average value of the wetting angle was 49.4±3.5 degrees, which indicates good wetting of the samples.

[0049] Porosity was measured indirectly, by the amount of water adsorbed by dried ceramic plates with an average size of 450±50 mm3.

[0050] The calculation of porosity (open pores) was carried out according to the formula (1): where

[0051] M is the ceramic plate that adsorbed water, kg,

[0052] M0 is the mass of the dry ceramic plate, kg,

[0053] V0 is the measured volume of the plate, m3, and pl is the density of the liquid (water).

[0054] The porosity calculated in this way was 44.1±2.3%.

[0055] The conductivity of the ceramic material of the electrode cups was measured in 0.1 M NaOH electrolyte using carbon electrodes using a galvanostat potentiostat (Corectest, China). The ionic conductivity was 7.1 1 / Ohm*cm2. The hodograph is shown in Fig. 8.

[0056] Life tests under cyclic load (55,000 of charge / discharge cycles) of the assembled elementary cell as seen in Figs. 5 A and 5B, comprising the ceramic electrode separator cups with electrode materials, mentioned above, and with a present of 2.5 M NaOH were carried out. The ceramic separator cups ensured the integrity of electrode materials during charge / discharge cycles, reliable separation of electrode materials, including during the growth of metal dendrites, and also prevented electrode materials from entering the electrolyte. Upon completion of the cyclic tests, the electrolyte was filtered, no sediment of insoluble compounds and electrode materials, as well as ceramic fragments and crumbs of the tested cups, which indicates the absence of mechanical damage to ceramic cups during long-term, use were not found. With low resistance, the separation cups ensured high ionic conductivity, and, accordingly, the battery efficiency in the range of 95-98%.

Claims

CLAIMS1. A ceramic separator for a battery cell in the form of a cup having side walls and a bottom wall, wherein the ceramic separator is made of kaolin (A12O3 and SiO2) powder material, wherein an average diameter of the powder material according to D50 is up to 5 microns, and wherein a thickness (Hwaii) of the side walls and the bottom wall is in the range of 5 to 10 millimetres.

2. A method for manufacture of the ceramic separator according to Claim 1, wherein the method comprises the following steps:- providing kaolin;- mixing kaolin and water to form an aqueous suspension;- burning the aqueous suspension while stirring in result of which a calcined kaolin powder is obtained, wherein the step of burning is accomplished by gradually increasing a temperature up to 1100 °C, and wherein the gradual increase of temperature is in the range of 8°C / min to 12°C / min, preferably 10 °C / min;- crushing the calcined powder up to particle size of about 5 pm;- formation of an aqueous suspension from the crushed calcined powder and additional kaolin;- pouring the aqueous suspension into a mold, wherein the mold is in a shape to allow to form a cup;- settling of the poured aqueous suspension into the mold at a temperature of 45°C on air, in result of which a cup is formed;- burning the cup at a temperature of 1100°C so that the ceramic separator in the form of the cup is formed.

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