Energy storage device

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 an inner surface. The mandrel comprises a mandrel surface, and is positioned within the container so that the mandrel surface is spaced apart from the inner surface to define a cavity within the container. The container has a packing axis that passes through the cavity, the mandrel surface, and the inner surface. The mandrel is compressible in the direction of the packing axis, the at least one sheet of separator material is arranged in the cavity to provide a plurality of separator layers along the packing axis, and an electrode is provided between the separator layers.

Claims

1. An energy storage device comprising: a container comprising a first inner surface and a second inner surface disposed opposite the first inner surface; a mandrel comprising a first mandrel surface and a second mandrel surface, the mandrel positioned within the container such that the first mandrel surface is spaced apart from the first inner surface to define a first cell cavity within the container and the second mandrel surface is spaced apart from the second inner surface to define a second cell cavity within the container; at least one sheet of separator material; a first plurality of discrete electrodes; and a second plurality of discrete electrodes; wherein: the container has a packing axis that passes through the first cell cavity, the mandrel, and the second cell cavity, the mandrel is compressible in the direction of the packing axis, a first sheet of separator material of the at least one sheet of separator material is arranged in the first cell cavity wholly to provide a first plurality of separator layers along the packing axis, a second sheet of separator material of the at least one sheet of separator material is arranged in the second cell cavity wholly to provide a second plurality of separator layers along the packing axis, the first plurality of discrete electrodes comprises a first plurality of discrete positive electrodes and a first plurality of discrete negative electrodes, the second plurality of discrete electrodes comprises a second plurality of discrete positive electrodes and a second plurality of discrete negative electrodes, the first plurality of discrete electrodes is distributedly disposed along the packing axis and wholly within the first cavity, the second plurality of discrete electrodes is distributedly disposed along the packing axis and wholly within the second cavity, the first plurality of discrete electrodes occupies space between adjacent separator layers of the first plurality of separator layers, and the second plurality of discrete electrodes occupies space between adjacent separator layers of the second plurality of separator layers.

2. The device of claim 1, wherein at least one of the first inner surface or the second inner surface is concave.

3. The device of claim 1, wherein the mandrel is positioned centrally along the packing axis so that the first plurality of separator layers and the second plurality of separator layers are arranged symmetrically about the mandrel.

4. The device of claim 1, wherein the mandrel is positioned centrally along the packing axis so that the first sheet of separator material in the first cell cavity and the second sheet of separator material in the second cell cavity are arranged symmetrically about the mandrel.

5. The device of claim 4, wherein the at least one sheet separator material includes a first plurality of sheets of separator material arranged in the first cell cavity wholly and a second plurality of sheets of separator material arranged in the second cell cavity wholly.

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 alternative layouts of separator material and mandrel within the energy storage device, according to some embodiments;

(4) FIGS. 3a-3c are schematics of some embodiments of energy storage devices of the present invention; 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 which are occupied by the electrodes.

(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 some embodiments 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 alternative 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 further 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 layers or the folds of the separator material 4. In some embodiments, 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.