Abstract
An energy storage device comprising: a container, a mandrel, at least one sheet of separator material, and two or more electrodes. The container comprises a base and an inner surface forming an internal space. The mandrel is positioned in the container and is spaced apart from the inner surface to define a cavity within the container. The sheet of separator material is arranged about the mandrel to provide a plurality of discrete separator layers within the cavity. At least one electrode is provided between each of the discrete separator layers, and at least a portion of an external surface of a container has a curved profile.
Claims
1. An energy storage device comprising: a container comprising a base and an inner surface forming an internal space, the internal space having a first side and a second side opposite the first side; a mandrel positioned in the container at the first side away from the second side, wherein the mandrel and the inner surface are spaced apart to define a cavity within the container at the second side, the mandrel having a center longitudinal axis; at least one sheet of separator material arranged within the cavity wholly to provide a plurality of discrete separator layers, the plurality of discrete separator layers wounded about a winding axis separate from the center longitudinal axis such that the winding axis is positioned between the mandrel and the second side of the container; and a plurality of discrete electrodes comprising a plurality of discrete positive electrodes and a plurality of discrete negative electrodes, wherein the plurality of discrete electrodes occupies space between adjacent discrete separator layers of the plurality of discrete separator layers, and at least a portion of an external surface of the container has a curved profile.
2. The device of claim 1, wherein the mandrel comprises a first face that is curved.
3. The device of claim 2, wherein the mandrel comprises a second face.
4. The device of claim 3, wherein the second face of the mandrel is curved such that a cross-section of the mandrel has an elliptical shape.
5. The device of claim 4, wherein at least one wall of the container has a concave inner surface which is opposite the first face or the second face of the mandrel.
6. The device of claim 5, wherein the concave inner surface is formed due to the curved profile of the at least a portion of an external surface of the container.
7. The device of claim 6, wherein at least one of the first face and the second face of the mandrel is concentric with the curve of the internal surface of the container.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) In order to better understand the present invention, and to show more clearly how embodiments of the invention may be put into effect, embodiments will now be described, by way of example, with reference to the following drawings:
(2) FIG. 1 is an exploded view of a schematic of an energy storage device of the present invention, according to some embodiments;
(3) FIGS. 2a-2d are schematics of separator material and mandrel within the energy storage device, according to some embodiments;
(4) FIGS. 3a-3c are schematics of energy storage devices of the present invention, according to some embodiments; and
(5) FIGS. 4a and 4b are schematics of arrays of alternative container shapes, according to some embodiments.
DETAILED DESCRIPTION OF THE INVENTION
(6) FIG. 1 shows an energy storage device 1 comprising a container 2, a compressible mandrel 3, separator material 4, and discrete electrodes 5. The container 2 has a casing 6, a base 7 and a cap 8 that together form the shell of the energy storage device 1. The casing 6 is formed of robust material to avoid external objects from piercing or rupturing the device 1. The casing 6 could be deep drawn/rolled/shaped and formed with the base 7 and cap 8 so as to form an internal space 9 for holding the electrochemical cell components, namely the compressible mandrel 3, separator material 4, and electrodes 5. The casing 6 has an inner surface 10 facing into the space 9. The base 7 and cap 8 are provided over the open ends of the casing 6 to enclose the electrochemical cell components 3, 4, 5 within the container 2. Although the base 7 and cap 8 are shown as separate parts from the casing 6, it is conceivable that the casing 6 may include, or be attached to, a preformed base 7 and cap 8.
(7) The mandrel 3 has a first mandrel surface 11 and second mandrel surface 12 connected by an arm 13. The mandrel 3 is formed from a single piece of pliable material, such as a plastic or metal. The cross section of the mandrel 3 generally has the shape of an S and its outline is elliptical. The mandrel 3 has a longitudinal axis L which is normal to the S shape formed by the curved surfaces 11, 12 and the arm 13. The mandrel 3 extends along its longitudinal axis L such that it is similar in length to the container 2. The general cross-sectional shape of the mandrel 3 is the same along the entire length of its longitudinal axis L.
(8) The mandrel 3 is formed so that it can be placed in the internal space 9 of the container 2. When the mandrel 3 is positioned within the internal space 9, a cavity 9a remains between the mandrel surfaces 11, 12 and the inner surface 10 of the container 2. Due to the shape of the mandrel 3, columns of hollow dead space exist between the mandrel surfaces 11, 12 and the arm 13 which extend along the longitudinal axis L. The hollow columns allow space for the mandrel 3 to collapse, as well as providing access for welding to at least part of the base 7 when the electrochemical cell components 3, 4, 5 are placed within the container 2.
(9) The mandrel 3 is compressible in the direction of a packing axis P, which will be described in more detail in relation to the separator material 4. Generally speaking, the mandrel 3 can compress and/or deform such that the general elliptical shaped outline of its cross section decreases in size. The volume of the space 9 taken up by the mandrel 3 decreases as the mandrel 3 compresses. Furthermore, the mandrel surfaces 11, 12 can deform under extreme pressure such that the curvature or arc can change according to compression forces applied to the surface.
(10) The separator material 4 as presented in FIG. 1 is a continuous sheet of electronically insulating porous material. The separator material 4 is rolled and positioned within the cavity 9a between the container 2 and the mandrel 3. The separator material 4 is wound around the mandrel 3 about a winding axis W which overlies the longitudinal axis L of the mandrel 3 when the electrochemical cell container 1 is in its complete form. As the sheet of separator material 4 is wound about winding axis W, layers of separator material are formed as the sheet rolls over itself. In the complete energy storage device 1, the separator material 4 is arranged in the container 2 to provide a plurality of separator layers placed along the packing axis P. This creates spaces 14 between layers of the separator material 4.
(11) Electrodes 5 are positioned along the packing axis P within the spaces 14 of the wound separator material 4. For simplicity, only two electrodes 5 (one anode and one cathode along with the separator material 4 forming a cell) are shown in FIG. 1. However, an electrochemical cell container 1 of embodiments of the present invention may contain many electrodes 5, forming multiple electrochemical cells.
(12) The electrodes 5 each comprise a tab 15a, 15b which can be secured to the internal surfaces of the base 7 and cap 8. By providing a tabs 15a, 15b on each electrode 5, the current path length for each electrode 5 is reduced and the internal resistance of the cell decreases.
(13) As the cells charge/discharge, the electrodes 5 may expand and contract. As the electrodes 5 expand and occupy more volume within the internal space 9, the mandrel 3 compresses. Similarly, as the electrodes contract, the mandrel 3 expands to re-occupy the volume whilst also providing a constant compressive force along the packing axis P between the separator material 4 and the electrodes 5. The curved mandrel surfaces 11, 12 ensure that a uniform pressure over the surface of the electrodes 5 is maintained.
(14) Various electrochemical cell container 1 arrangements that are within the scope of the present invention are shown schematically in FIGS. 2a-2d. The electrochemical cell containers 1 are shown in cross section along the longitudinal axis L of the mandrel 3, and without electrodes 5 for simplicity. Each electrochemical cell container 1 is shown in an over simplified manner as a squared container 2. However, it is appreciated that the separator material 4 would curve to occupy the internal space 9 of the container 2.
(15) In FIG. 2a, two sheets of separator material 4 are wound about the mandrel 3. The mandrel 3 is positioned along the winding axis W of the separator materials 4. The sheets of the separator material 4 are concentric about the longitudinal axis L of the mandrel 3. A multitude of layers 14 is provided between the layers of the wound separator material 4 for housing electrodes 5. The electrodes 5 are arranged along the packing axis P.
(16) In FIG. 2b, a mandrel 3 is provided with a single curved surface 11. The mandrel arm 13 rests against an internal surface 10 of the container 2. One sheet of separator material 4 is provided in the internal space 9 and is wound around a winding axis W. The winding axis W does not overlie the longitudinal axis L of the mandrel 3. Discrete layers 14 are provided in the roll of separator material 4 for housing electrodes. The electrodes 5 are arranged along the packing axis P.
(17) FIGS. 2c and 2d illustrate embodiments of the present invention, where rolls or folds of separator material sheets 4 are positioned in the cavities 9a about the mandrel 3, the separator 4 is not wound about the mandrel 3. The device in FIG. 2c comprises two rolled sheets of separator material 4 in each cavity 9a. In FIG. 2d, the sheets of separator material 4 are folded in the cavity 9a. Electrodes 5 would be placed within the spiral or folds of the separator material 4. In these cases, the mandrel 3 is merely functioning to absorb expansion of the electrode 5 within the device 1, and not providing a bobbin for material 4, 5 to be wound around.
(18) The container 2 in FIG. 1 is shown as cylindrical but could also form the shape of any prismatic cell. Cross-sectional schematics are shown in FIGS. 3a-3c of device 1. The layers of separator material 4 are shown as concentric rings instead of a continuous rolled sheet in the cavity 9a merely as a way of simplifying the drawing. Electrodes 5 are shown schematically as broken lines and can be positioned anywhere within the layers 14 between the rolled sheets of separator material 4. FIG. 3a shows a simplified cross sectional view of the complete device 1 of FIG. 1. The inner surface 10 is one continuous surface, and the mandrel surfaces 11, 12 face different regions of the same inner surface 10.
(19) FIG. 3b illustrates a device 1 that has a generally cuboid shaped container 2, wherein the inner surfaces 10 facing the mandrel faces 11, 12 are concave. The separator material 4 is folded or wound so that fills the cavities 9b between the mandrel surfaces 11, 12 and the inner surface 10 of the container 2. The separator material 4 is arranged to provide layers 14 along the packing axis P, the layers being filled with electrodes 5. The curvature of the concave inner surface 10 similar to the curvature of the mandrel surfaces 11, 12 such that a uniform pressure is applied across the surface of the electrodes 5 within the layers 14 of separator material 4.
(20) FIG. 3c illustrates a device 1 that has a generally cuboid shaped container 2, wherein the device 1 has only one cavity 9c which is filled with electrochemical cells. The inner surface 10 facing the mandrel face 11 is concave. The separator material 4 is folded or wound so that fills the cavity 9c between the mandrel surfaces 11, 12 and the inner surface 10 of the container 2. The separator material 4 is arranged to provide layers 14 along the packing axis P, the layers being filled with electrodes 5. The curvature of the concave inner surface 10 similar to the curvature of the mandrel surfaces 11, 12 such that a uniform pressure is applied across the surface of the electrodes 5 within the layers 14 of separator material 4.
(21) In the examples shown in FIGS. 3a-3c, the curvature of the external casing matches the concave shape of the inner surfaces 10, the external casing may be flatted to provide an external cuboid shape. However, it may be beneficial to keep the curvature of the casing 6.
(22) FIGS. 4a and 4b show an array of energy storage devices 1 according to FIGS. 3b and 3c respectively. The curvature of the casing 6 allows for gaps 16 between the containers 2 when arranged in an array. The curved casing 6 ensures that physical contact between adjacent containers 2 is reduced. A fluid such as air can be provided in the gaps 16 between the containers 2. The reduced contact between the containers 2 ensures that low heat transfer occurs between adjacent devices 1. In addition, fluid is free to flow over the array of containers and act as a coolant to remove any excess heat given off by the cells within the devices 1.
