Battery unit and method for discharging the same

Abstract

The present application concerns a battery unit, comprising one or more positive electrodes, a plurality of negative electrodes and an electrolyte comprising lithium ions, arranged in between the one or more positive electrodes and the plurality of negative electrodes. The battery unit is configured to generate an output current by intermittently allowing the negative electrodes from the plurality of negative electrodes to discharge to a corresponding positive electrode from the one or more positive electrodes. The present application further concerns a method for discharging such a battery unit.

Description

[0001] BATTERY UNIT AND METHOD FOR DISCHARGING THE SAME

[0002] FIELD

[0003] The present disclosure relates to a battery unit. The present disclosure further relates to a method for discharging such a battery unit.

[0004] BACKGROUND

[0005] Rechargeable lithium-ion batteries are known in the art. A lithium-ion battery comprises a positive electrode, a negative electrode and an electrolyte comprising lithium ions, Li+1, in between. The battery generates a current when the negative electrode discharges to the positive electrode. The positive electrode is sometimes referred to as the cathode and the negative electrode is sometimes referred to as the anode.

[0006] It is well known that the quality of state-of-the-art rechargeable lithium-ion batteries deteriorates during use. The quality of such a battery can be described using its output voltage, maximum depth of discharge or charge capacity. Every cycle of charging and discharging the battery, these aspects decrease. The expected lifetime of lithium-ion batteries is therefore sometimes described in cycles.

[0007] This deterioration is, in part, attributed to lithium trapping. Not wishing to be bound by theory, the applicant found that, in the art, there are various explanations of what exactly happens when the lithium is trapped. One such explanation is schematically shown in Fig. 2A-D. In each of these figures, part of a negative electrode at an interface I with the electrolyte E is shown as well as a graph, together illustrating the distribution of lithium throughout said section of the negative electrode. In said graphs, the x-axis represents a depth into the negative electrode, i.e. a distance of a point in the negative electrode to interface I. The y-axis indicates an amount of lithium at said point in the negative electrode.

[0008] When a lithium-ion battery is charged for the first time, the distribution of lithium may be similar to what is shown in Fig. 2A. The lithium ions Li+1in the electrolyte E absorb electrons, cross the interface I between the electrolyte and the negative electrode and form an alloy. Depending on an extent to which the battery is charged, lithium becomes part of the negative electrode up to a certain depth. Here, that depth is indicated as dl.

[0009] When discharging a lithium-ion battery, lithium in the negative electrode rejects electrons, crosses the interface, and is absorbed into the electrolyte as lithium ions. Discharging of the negative electrode is sometimes also referred to as ‘delithiation’, i.e., the removal of lithium from said electrode. The rejected electrons form an output current. The lithium ions move through the electrolyte, forming an internal displacement of positive charge. However, in state-of-the-art Li-ion batteries, even when the battery is fully discharged, lithium stays behind, trapped in the alloyforming electrode material. As is shown in Fig. 2B, part of the negative electrode is not completely stripped of lithium, specifically a part between depths d2 and dl.

[0010] This effect worsens upon further use; as shown in Fig. 2C, charging the battery again reintroduces lithium into the negative electrode to form the alloy, starting from the interface I. As part of the negative electrode is occupied by the trapped lithium, newly introduced lithium becomes part of the electrode up to depth d3. The previously trapped lithium may even move further into the negative electrode in the process. Even if no unused electrode is left, the concentration of trapped lithium can increase. When said negative electrode is discharged, more lithium will be trapped and remain in the electrode than before. Some theories suggest that one big volume of trapped lithium is formed and other suggest that various separate volumes of trapped lithium are formed - the latter is shown here in Fig. 2D, specifically in a part between depths d4 and d3.

[0011] Lithium trapping reduces the amount of lithium that can move between the electrolyte and the negative electrode, meaning the maximum capacity of the battery decreases.

[0012] SUMMARY

[0013] It is an object of the present application to provide a battery unit with an increased lifetime, which maintains its quality longer over increasing amounts of charge and discharge cycles, in which the capacity decrease per charge / discharge cycle is smaller and in which lithium trapping occurs less than in state-of-the-art batteries.

[0014] According to a first aspect of the present disclosure, a battery unit is provided which comprises one or more positive electrodes, a plurality of negative electrodes comprised of an alloyforming material, and an electrolyte comprising lithium ions, arranged in between the one or more positive electrodes and the plurality of negative electrodes. The battery unit further comprises switching means arranged to allow or disallow each of the negative electrodes from the plurality of negative electrodes to discharge, and a controller configured to control the switching means so as to generate a continuous output current by intermittently allowing the negative electrodes from the plurality of negative electrodes to discharge to a corresponding positive electrode from the one or more positive electrodes.

[0015] When a negative electrode is allowed to discharge, lithium at its interface rejects electrons and is absorbed into the electrolyte. This does not happen to lithium deeper into the negative electrode, so a lithium-gradient occurs in the negative electrode. At and near the interface, a lithium- poor volume is formed, while lithium that is deeper into the negative electrode remains. Not wishing to be bound by theory, the applicant found that lithium trapping occurs when the battery unit is discharged faster than the rate at which diffusion of lithium in the alloy can undo the occurring gradient. Because, during normal discharge conditions, the diffusion speed of lithium in the alloy is low with respect to the rate at which lithium is absorbed into the electrolyte, the gradient increases while the negative electrode is allowed to discharge.

[0016] Interrupting the discharge process for individual negative electrodes introduces rest periods and allows redistribution of lithium in said negative electrodes to take place. The amount of lithium that becomes trapped in a negative electrode when it is discharged intermittently, is much smaller than when the negative electrode is discharged under continuous load. Therefore, in the battery unit according to claim 1 , less lithium is lost to lithium trapping in the negative electrode. Such battery units have smaller capacity decrease per charge / discharge cycle, meaning it maintains its quality longer and has an increased lifetime.

[0017] With the switching means and controller of the battery unit in accordance with the present disclosure, and the presence of a plurality of negative electrodes that are individually switchable by the switching means, it is possible to intermittently allow and disallow negative electrodes to discharge while nevertheless providing a continuous output current. Thus, lithium trapping in the negative electrodes can be prevented or at least reduced without interrupting power delivery by the battery unit.

[0018] In a preferred embodiment, the one or more positive electrodes may comprise one positive electrode for each negative electrode from the plurality of negative electrodes, in which case there is a one-to-one relationship between the negative electrodes from the plurality of negative electrodes and the positive electrodes from the one or more positive electrodes.

[0019] Specifically, the controller may be further configured to allow a first negative electrode from the plurality of negative electrodes to discharge for a first amount time and subsequently disallow the first negative electrode from the plurality of negative electrodes to discharge for a second amount of time. The second amount of time may for example be at least 1 second, or in an order of magnitude of seconds. Embodiments are conceivable in which the first amount of time may be between about 1 minute and about 10 minutes, preferably about 5 minutes. Additionally or alternatively, the second amount of time may be between 1 minute and about 30 minutes, preferably about 15 minutes. Additionally or alternatively, a ratio between the first amount of time and the second amount of time may be between 10:1 and 1:10, and preferably about 1:3.

[0020] It will be appreciated by those skilled in the art that the second amount of time - i.e., the time for which the negative electrode is disallowed from discharging and thus allowed to ‘rest’ - may in practice depend on various factors. For example, since redistribution of lithium during the second amount of time is a diffusion process, temperature and / or dimensions of the electrodes may play a role. Moreover, the time needed for lithium to adequately redistribute may also be a factor of the extent to which lithium has accumulated deep into the negative electrode, and may thus depend on the first amount of time and the discharge current during said first amount of time. Such factors can however be taken into account when selecting a suitable second amount of time, for example by means of manual testing and selection, simulations, and / or neural network training.

[0021] To intermittently discharge the negative electrodes, the controller may be further configured to pulse-width-modulate the discharging of the negative electrodes from the plurality of negative electrodes. In such embodiments, a duty cycle of each negative electrode is equal to one over the number of negative electrodes in the plurality of negative electrodes. In such embodiments, the negative electrodes discharge in a current pulse having either a rectangular shape, a sine or cosine shape (i.e., a sinusoidal shape), or a triangular shape.

[0022] The output current that the battery unit according to the invention is able to provide may be a constant output current.

[0023] In some embodiments, the battery unit may comprise a positive terminal and a negative terminal. The positive terminal may then ne electrically connected or connectable to the one or more positive electrodes, and the negative terminal may be electrically connected or connectable to the plurality of negative electrodes.

[0024] In a preferred embodiment, the battery unit may be configured to generate current from the negative terminal, through the discharging negative electrode and the corresponding positive electrode, to the positive terminal. In such embodiments, the switching means may be arranged to electrically connect the positive terminal to one or more of the one or more positive electrodes and / or the negative terminal to one or more of the plurality of negative electrodes.

[0025] The negative electrodes may be made of various alloy-forming materials, preferably comprising silicon (Si), gold (Ag), aluminium (Al), antimony (Sb), tin (Sn), or zinc (Zn).

[0026] The one or more positive electrodes, the plurality of negative electrodes, and the electrolyte may be included in one housing and may together act as one battery cell. Alternatively, in the case that the battery unit comprises a plurality of said positive electrodes, the battery unit may include a plurality of cells, each cell including: one or more positive electrodes from among the plurality of positive electrodes; one or more negative electrodes from among the plurality of negative electrodes; and a respective portion of the electrolyte between said one or more positive electrodes and said one or more negative electrodes.

[0027] The plurality of cells may be divided into one or more groups each including multiple cells, wherein the multiple cells within each group are connected in series or in parallel.

[0028] In an example, the one or more groups may include a first group and a second group, and the multiple cells of the first group may be connected in series with the multiple cells of the second group. In another example, the one or more groups may include a first group and a second group, and the first group may be connected in parallel with the second group.

[0029] In yet another example, the one or more groups may include a first group and a second group, and the controller may be configured to control the switching means to generate the continuous output current using the first group, and to generate a second continuous output current using the second group by intermittently allowing the negative electrodes of the multiple cells in the second group to discharge to a corresponding positive electrode of the multiple cells in the second group.

[0030] Each cell among the plurality of cells may be included (e.g., enclosed) in a respective cell housing.

[0031] Each group among the one or more groups may be included (e.g., enclosed) in a respective housing. That is, the cells of the one or more groups may be collectively housed in a single housing.

[0032] According to a second aspect of the present disclosure, a method for discharging a battery unit is provided as defined in appended claim 25. This battery unit comprises one or more positive electrodes, a plurality of negative electrodes comprised of an alloy-forming material, an electrolyte comprising lithium ions arranged in between the one or more positive electrodes and the plurality of negative electrodes, and switching means arranged to allow or disallow each of the negative electrodes from the plurality of electrodes to discharge. The method comprises controlling the switching means so as to generate a continuous output current by intermittently allowing the negative electrodes from the plurality of negative electrodes to discharge to a corresponding positive electrode from the one or more positive electrodes.

[0033] In preferred embodiments of this method, generating the current may comprise allowing a first negative electrode from the plurality of negative electrodes to discharge for a first amount time and subsequently disallowing the first negative electrode from the plurality of negative electrodes to discharge for a second amount of time. For example, the second amount of time may be at least 1 second.

[0034] The ratio between the first amount of time and the second amount of time may be between 10:1 and 1:10, and may preferably be about 1:3.

[0035] In an example, the first amount of time may be between about 1 minute and about 10 minutes, preferably about 5 minutes. Additionally or alternatively, the second amount of time may be between 1 minute and about 30 minutes, preferably about 15 minutes. Additionally or alternatively,

[0036] The approach to allowing the negative electrodes to discharge may also be considered pulsewidth modulation of the discharging of the negative electrodes from the plurality of negative electrodes.

[0037] Further aspects, embodiments, and / or advantageous effects of embodiments according to the present disclosure may become apparent from the ensuing detailed description below. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Next, the present disclosure will be described in more detail referring to the appended drawings, wherein:

[0039] Fig. 1A - 1C each show an embodiment of a battery unit according to the invention;

[0040] Fig. 2A - 2D illustrate lithium-trapping in a negative electrode in state-of-the-art rechargeable lithium-ion batteries;

[0041] Fig. 3A - 3H illustrate lithium trapping in a negative electrode in a battery unit according to the invention;

[0042] Fig. 4A and 4B each show how currents from different cells can combine to a continuous current;

[0043] Fig. 5A shows a layout for electrodes as may be used in an embodiment according to the invention;

[0044] Fig. 5B shows a layout for terminals as may be used for a layout of electrodes as shown in Fig. 5A; and

[0045] Fig. 6A - 6C each show an embodiment of the battery unit in accordance with the present disclosure.

[0046] DETAILED DESCRIPTION

[0047] Hereinafter, reference will be made to the appended drawings. It should be noted that identical reference signs will be used to refer to identical or similar components. Moreover, unless explicitly stated otherwise, various elements shown in the appended drawings may not be drawn to scale, and parts may be exaggerated or omitted for convenience of explanation.

[0048] Fig. 1A - C each shown an embodiment of a battery unit 100 according to the invention. Unit 100 comprises silicon negative electrodes 10A, 10B, 10C, ... lOn and positive electrodes 11 A, 11B, 11C, ... lOn, in between which electrolyte E is arranged. The silicon negative electrodes are made of and the positive electrodes can be made of any one of a number of well-known materials. Electrolyte E is arranged between corresponding negative and positive electrodes and contains lithium ions.

[0049] In Fig. 1A - 1C, each battery unit 100 comprises a common negative terminal 14 and a common positive terminal 15 to function as electrical connections. Embodiments are also conceivable in which this electrical connection is provided for differently. The various silicon negative electrodes and positive electrodes may each have their own terminal, or may be divided into any other number of groups. In Fig. 1A - 1C specifically, there is a one-to-one relationship between the silicon negative electrodes and positive electrodes. Each pair of electrodes 10A / 11 A, 10B / 1 IB, 10C / 11C, . . . 10n / l In, form what may also be referred to as an electrode pair or an anode-cathode pair. For example, each anode-cathode pair may form a respective cell Cl, C2, . . . Cn of battery unit 100 as shown in Fig. 1A - 1C. In these embodiments, all pairs are combined to effectively act as one cell. However, embodiments are also conceivable in which the electrode pairs are included in multiple cells. Embodiments are also conceivable in which the relationship between silicon negative electrodes and positive electrodes is not one-to-one.

[0050] In Fig. 1 A - 1C specifically, battery unit 100 comprises switches 12 A, ... 13n and a controller 101. Such switches can be implemented by any appropriate switching means such as transistors, e.g. MOSFET’s.

[0051] In these embodiments, the components can be included in one housing and together perform as if they are one battery cell. However, the present disclosure is not limited thereto. For example, each cell of the battery unit may comprise a respective housing and at least some cells may not be arranged inside a common housing. Furthermore, controller 101 may be included inside the housing but may also be external to the housing. For example, controller 101 may be a microcontroller arranged externally to the battery cells.

[0052] In Fig. 1 A, switches 12A, 12B, 12C, . . . 12n, are arranged between silicon negative electrodes 10A, 10B, 10C, ... lOn and common negative terminal 14, and switches 13A, 13B, 13C, . . . 13n, are arranged between positive electrodes 11 A, 1 IB, 11C, ... 1 In and common positive terminal 15.

[0053] In Fig. IB, switches 12A, 12B, 12C, ... 12n, are arranged between the silicon negative electrodes 10A, 10B, 10C, ... lOn and the common negative terminal 14.

[0054] In Fig. 1C, switches 13A, 13B, 13C, ... 13n are arranged between positive electrodes positive electrodes 11 A, 11B, 11C, ... l ln and the common positive terminal. In each of these embodiments, each switch is arranged between one electrode and the corresponding common terminal.

[0055] In each of Fig. 1 A - 1C, an output current is generated by allowing the silicon negative electrode 10A to discharge. Controller 101 has closed the corresponding switch or switches, forming an electrical path from common negative terminal 14, via silicon negative electrode 10A, via positive electrode 11 A, to common positive terminal 15. Discharge of the further silicon negative electrodes 10B, 10C, . . . lOn is disallowed. Controller 101 has opened the corresponding switch or switches.

[0056] To discharge silicon negative electrode 10A intermittently, controller 101 can interrupt the discharge by open the corresponding switch or switches, breaking the electrical path between the common terminals through said silicon negative electrode. While discharge is interrupted, lithium in silicon negative electrode 10A diffuses and redistributes, thus preventing trapping. One possible definition of silicon negative electrode 10A being discharged intermittently is that the discharge of silicon negative electrode 10A, for example when during discharge of the battery unit, the discharge to said silicon negative electrode 10A is interrupted at least one.

[0057] Not wishing to be bound by theory, one possible description and / or explanation of this redistribution of lithium in a silicon negative electrode (e.g. negative electrode 10A) is given in Fig. 3A-3E. Each of these figures shows part of a silicon negative electrode at an interface I with the electrolyte E and a graph, together illustrating the distribution of lithium throughout said section of the silicon negative electrode. In said graphs, the x-axis represents the depth into the silicon negative electrode, i.e. the distance of a point in the silicon negative electrode to interface I. The y-axis indicates the amount of lithium at said point in the silicon negative electrode.

[0058] Fig. 3A shows a lithium distribution in a silicon negative electrode that may occur after a battery unit is charged for the first time. Lithium forms an alloy with the silicon in volume 1, up to depth dl. Beyond depth dl, a volume of silicon 2 remains.

[0059] Fig. 3B shows a lithium distribution in a silicon negative electrode that may occur while a silicon negative electrode is allowed to discharge. As seen in the graph of Fig. 3B, a lithium- gradient forms at interface I. To avoid a volume of lithium-poor silicon being formed and to avoid lithium from getting trapped, discharge of the silicon negative electrode should be interrupted.

[0060] Fig. 3C shows a lithium distribution in a silicon negative elective that may occur after the discharge of the silicon negative electrode was interrupted. The time for which the discharge is interrupted may be referred to as the rest time. In Fig. 3C, there is no more lithium-gradient at interface I. The overall level of lithium in the negative electrode, i.e. the level of lithium from interface I up to dl is reduced. While in this embodiment, the rest time is long enough for the gradient to disappear completely, this is not necessary. The lithium trapping can already be reduced by interrupting the discharge by a rest time long enough for the gradient to lessen, i.e. at least be less prevalent than at the time the discharge is interrupted.

[0061] Fig. 3D and Fig. 3E show lithium distributions in a silicon negative elective that may occur after a second discharge time and after a second rest time, respectively. In Fig. 3D, a lithium- gradient is formed again and in Fig. 3E, the lithium-gradient has disappeared and the overall level of lithium is reduced.

[0062] Fig. 3F shows a lithium distribution that can be achieved in a battery unit according to the invention, and / or using a method for discharging according to the invention. Only a very small amount of lithium remains in the silicon and therefore the performance of the battery unit is not affected by trapping. Fig. 3G and Fig. 3H show lithium distributions after the battery unit 100 is recharged and discharged, respectively. As shown here, no substantial amounts of lithium become trapped in the negative electrode.

[0063] Fig. 4A and Fig. 4B illustrate methods for discharging battery units according to the invention. Both figures illustrate how four cells enumerated 1, 2, 3, and n can generate currents intermittently. In these embodiments specifically, the cells generate current one by one. Generating current in other orders is possible as well. The sum of the currents generated by the individual cells achieves a constant or continuous common output current, while also providing each cell (or, more specifically, the silicon negative electrode or electrodes in said cell) with rest time. Each cell can be said to provide current in a pulse during a discharge time. The rest time may also be referred to as relaxation time.

[0064] In Fig. 4A, during the discharge time cell 1, indicated with “current,” said cell provides a constant current, i.e. a rectangular pulse. Because the current is equally high over the discharge time, and one cell is sufficient to provide the desired output current, discharge times of the various cells do not have to overlap. Embodiments are conceivable in which cells discharge with rectangular pulses and in which discharge times do overlap. The group of cells (or more specifically, the plurality of negative electrodes) is preferably capable of providing a constant output current. The rest time of cell 1, indicated with “rest,” is as long as the discharge time of cells 2, 3, and n combined. The discharge time and the rest time of one cell together can be said to form one period, as after the rest time, the next discharge time commences. Unless the battery unit is turned off or common output current demand is halted completely, in which case there is not necessarily a next discharge time.

[0065] The applicant found that in some practical embodiments, the discharge time can be anywhere between 1-10 minutes, such as 5 minutes. The rest time can be anywhere between 1-30 minutes, such as 15 minutes. However, discharge times and rest times in the order of seconds are also possible. The relation between the discharge time and the rest time can also be expressed as ratio’s. The applicant found that in some practical embodiments, the ratio discharge time : rest time can be anywhere between 10:1, 1:1, 1:2, 1:3, 1:10, or even 1:100. However, depending on the particulars of an embodiment, other amounts of time and ratios can also be achieved.

[0066] The methods for discharging illustrated in Fig. 4A and Fig. 4B are advantageous when applied to battery cells that are similar or the same, or are at least similar in operation. The cells are discharged according to the same, or at least similar, discharge times and rest times.

[0067] The skilled person will appreciate that the reduction in lithium trapping can be optimized for a particular output current. Aspects that can be considered are the number of available cells, the specific types of cells, appropriate discharge times and rest times, etc. In the embodiment shown in Fig. 4A, the method for discharging may also be described as a sort of pulse width modulation. In this context, the discharge time can be considered the pulse width. The ratio [discharge time / (discharge time + rest time)] can be considered the duty cycle. In the embodiment shown in Fig. 4A, there are four battery cells having identical discharge times and rest times, making the duty cycle of each battery cell one over four or 25%. This can be done for any number of negative electrodes. Generally, the duty cycle of each negative electrode is preferably equal to one over the number of negative electrodes in the battery unit.

[0068] The approach shown in Fig. 4A may also be described as alternatingly discharging each of the negative electrodes from the plurality of negative electrodes. The cells 1, 2, 3, n can be said to be discharged in a particular order, or can be said to be discharged according to a particular rotation. The order in which the battery cells are discharged can be the same over the time that the battery unit as a whole is discharged, but embodiments are also conceivable in which that order is changed over time, perhaps giving priority to allowing some battery cells to discharge again, or delaying having to discharge others.

[0069] However, the invention is not limited thereto. Embodiments are also conceivable in which the battery cells differ from one another and the methods for discharging them can be adapted based thereon, assigning different discharge and rest times different battery cells, or even vary the discharge and test times assigned to a battery cell over time. For example, if it is detected that quality of a battery has already deteriorated, perhaps due to lithium-trapping resulting from earlier operation not according to the invention, the discharge time may be reduced for that cell, rest time may be increased for that cell, or the ratio discharge time : rest time may be reduced. In the context of this application, ‘different’ battery cells may mean that the cell has a different, or even multiple silicon negative electrodes; the battery cells may comprise different electrolytes; or the battery cells may be of identical make, while one has been through more cycles than the other, meaning that forms of degradation are more present. The skilled person will be aware of how such varying discharge times may be scheduled.

[0070] In Fig. 4B, the individual battery cells 1, 2, 3, n provide current per pulse having a sine (or cosine) pulse. Other shapes can be used as well, such as a triangle shape. It will however be appreciated by the skilled person that this does not mean that the current provided by said cell overall has the shape of a sine or cosine. In this embodiment, to provide a continuous common output, the discharge times of the cells do overlap. The discharge time for cell 1 is approximately indicated by “C” and the rest time is approximately indicated by “R.” In this case, the discharge time and the rest time may for example be distinguished by a threshold value in output current, such as about 10%. However, as the current provided by individual cells increases and decreases smoothly over time, where the discharge time ends and the rest time begins is more of a grey area. The rectangular pulse of Fig. 4A and the sine pulse of Fig. 4B are both what can be described as current profiles. Embodiments are also conceivable in which other current profiles are used.

[0071] Of course, while the present disclosure particularly relates to the above-described intermittent discharging process, this does not mean that the battery unit can solely provide a current based on this process. Rather, the battery unit is configured and thus able to do so. For example, in some applications, more power may be required which renders it impossible to use the intermittent discharging process.

[0072] To that end, the battery unit may be configured to be operable in an intermittent discharging mode and in a normal discharging mode. In the intermittent discharging mode, the controller may control the switching means so as to generate a continuous output current while intermittently allow negative electrodes to discharge, which provides rest periods for some negative electrodes without interrupting the required power delivery to the load. In the normal discharging mode, some or all cells of the battery unit may be active without performing the intermittent discharging process. This may for example be employed in situations where maximum power delivery is required and prioritized over the prevention of lithium trapping.

[0073] It will additionally be appreciated by those skilled in the art that the present disclosure is not limited to any particular length of time of the discharging and length of time of the ‘rest period’ , as this will depend on the application and the implementation of the battery unit. For example, a suitable rest period may be selected in dependence of the required discharging current for the particular application, the number of cells available in the battery unit, the selected, optimal or suitable discharging time for each cell before being interrupted by the rest period, the dimensions and / or material implementations of the cells and in particular the electrodes, and the like. Suitable rest periods and discharging periods may be determined based on an optimization process, for example using computer simulations or a neural network based approach.

[0074] In the embodiment shown in Fig. 5 A and 5B, the battery unit according to the invention comprises one positive electrode and four negative electrodes. Any other plurality of negative electrodes may be provided as well. These figures show an embodiment in which these electrodes are provided in one battery cell.

[0075] Fig. 5A shows a configuration of four silicon negative electrodes 10A, 10B, 10C, 10D and one positive electrode 11. In between, electrolyte E is arranged. Each of the four silicon negative electrodes is electrically connected to a corresponding terminal T1-T4. The common positive electrode 11 is electrically connected to terminal T5.

[0076] Fig. 5B shows the outside of the battery cell, and shows that in this embodiment battery unit 100 further comprises a housing. The terminals T1-T5 can be electrically connected to from outside of the housing and allow for electrical connection to the corresponding electrode. Fig. 6 A - 6C illustrate battery unit 100 according to various embodiments of the present disclosure.

[0077] As shown in Fig. 6A, battery unit 100 may have a plurality of cells. In this embodiment, three cells C1-C3, though battery unit 100 may similarly comprise two or more than three cells.

[0078] Similarly to the embodiments of Fig. 1 A - 1C, each cell in Fig. 6 A may include one or more positive electrodes from among the plurality of positive electrodes of battery unit 100, one or more negative electrodes form among the plurality of negative electrodes of battery unit 100. Between said one or more positive and one or more negative electrodes, an electrolyte is provided that enables the battery operation. For convenience of explanation, the positive electrode(s), negative electrode(s), and electrolyte are not illustrated in Fig. 6 A but may be represented by each of cells Cl -C3.

[0079] Battery unit 100 further comprises controller 101, and first switches 12 and / or second switches 13 forming the switching means, in a similar manner to the embodiments shown in Fig. 1A - 1C. In this illustrative embodiment, cells C1-C3 together form a single group having a positive terminal 15 and a negative terminal 14 between which cells C1-C3 are coupled. If present, first switches 12 may be coupled between positive terminal 15 and the positive electrode(s) of respective cells C1-C3, and second switches 13 may be coupled between negative terminal 14 and the negative electrode(s) of respective cells C1-C3. In accordance with the present disclosure, controller 101 is configured to control first switches 12 and / or second switches 13 so as to generate a continuous output current while intermittently allowing the negative electrodes of cells C1-C3 to discharge to corresponding positive electrodes. The continuous output current is configured to flow through an external load coupled between positive terminal 15 and negative terminal 14.

[0080] In other words, controller 101 is configured to control first switches 12 and / or second switches 13 so as to intermittently activate and deactivate some of cells C1-C3 while maintaining at least one of the cells in an activated state at any time to ensure that the output current is continuous. For example, when cell C2 is active by means of its corresponding switch(es), cell Cl and / or cell C3 may be switched to an inactive or ‘rest’ state to allow redistribution of lithium in their negative electrodes. After some time, cell Cl and / or cell C3 may be activated and cell C2 may be deactivated. This can be done alternatingly and with various combinations of activated and deactivated cells, depending on the required current for the application.

[0081] Cells C1-C3 may be included in a first group Gl. In an embodiment, each cell C1-C3 has a respective cell housing encapsulating its components, i.e., the electrodes and electrolyte. Additionally or alternatively, the first group is included in a housing that houses cells C1-C3. Controller 101 may be included in said housing of the first group or may be external to the housing. For example, controller 101 may be a microcontroller that is external to the cell portion of battery unit 100. Now referring to Fig. 6B, this embodiment differs from the one shown in Fig. 6 A in that battery unit 100 may include a second group G2 which has its own cells C4-C6 that are identical or similar to cells C1-C3. Each group Gl, G2 includes respective first switches 12-1, 13-1 and second switches 12-2, 13-2.

[0082] In this embodiment, the plurality of cells C1-C6 of battery unit 100 may be divided into first group Gl including cells C1-C3 and second group G2 including cells C4-C6. In this particular embodiment, first group Gl and second group G2 are coupled in series between positive terminal 15 and negative terminal 14 and therefore are able to cooperatively generate the continuous output current as controlled by controller 101. First group Gl and second group G2 may for example each have a respective housing, or may be included in a single housing.

[0083] Although first group Gl and second group G2 are illustrated to be connected in series, it is equally envisaged that they are coupled in parallel to each other.

[0084] Of course, the cells within first group Gl and the cells within second group G2 do not need to be identical to each other in structure, dimensions, composition, or the like. For example, the cells within each group and / or cells between groups may differ in electrode material, number of positive and / or negative electrodes, dimensions of electrodes, and the like.

[0085] Furthermore, first group Gl and second group G2 do not need to have the same number of cells included therein. For example, instead of first group Gl and second group G2 both having three respective cells, one or both groups may have only two cells or more than three cells.

[0086] Even further, although only two groups Gl, G2 are shown in Fig. 6B, it will be appreciated that battery unit 100 according to the present disclosure may include any feasible number of groups that are connected in series and / or in parallel. Similarly to the above, these groups may be identical for simplicity of control and design, but it is equally envisaged that the groups differ in number of cells and / or implementation of cells.

[0087] In the embodiment shown in Fig. 6B, controller 101 may apply the control for intermittent discharging of negative electrodes individually per group, such that during operation each group always has at least one cell that is activated by switching means. Of course, if first group Gl and second group G2 are in parallel, the continuous output current can be ensured even if all cells of one group are deactivated, provided that at least one cell in the other group(s) is active.

[0088] Now referring to Fig. 6C, this embodiment differs from the one shown in Fig. 6B in that first group Gl provides the continuous output current to a first load LI, whereas second group G2 is controlled to provide a second continuous output current to a second load L2 in a similar fashion. In that case, first group Gl may have a positive terminal 15-1 and a negative terminal 14-1 between which cells C1-C4 are coupled, and second group G2 may have a separate, second positive terminal 15-2 and a separate, second negative terminal 14-2 between which its cells C4-C6 are coupled and to which second load L2 can be connected. First group Gl and second group G2 may be configured to individually provide power to respective loads, and controller 101 may control each of said groups individually using the intermittent discharging control.

[0089] Again, although only two groups Gl, G2 are shown in Fig. 6C, any feasible number of groups may be included to individually (as shown in Fig. 6C) and / or cooperatively (as shown in Fig. 6B) drive one or more loads, and these groups do not need to be mutually identical in cell number or cell implementation.

[0090] The above examples are not intended to be limiting, and merely illustrate the different configurations in which the invention can operate. Depending on the need, the number of cells (e.g., in each group) can be varied as can the type and number of series and / or parallel connections of cells. A single controller may control some or all of the switches within one cell, and several or all cells within one or multiple groups of cells in the battery unit. The battery unit may power one or multiple loads. The exact implementation and configuration of the battery unit may be determined by the application. The skilled person will appreciate that the negative electrodes can also be made of other materials than silicon. Negative electrodes can be made of any material that can form an alloy with lithium. Examples are gold (Ag), aluminium (Al), antimony (Sb), tin (Sn), zinc (Zn). Other examples are silicon-oxide (e.g. SiO2) or tin-oxide (e.g. SnO). The negative electrodes do not have to be made from this alloy-forming material alone, but may be made of a composition incorporating one of these materials. An example thereof is a negative electrode made of Si-C, a composite of silicon and carbon.

[0091] Further to the above, the present disclosure may relate to any of the following clauses.

[0092] Clause 1. Battery unit, comprising: one or more positive electrodes; a plurality of negative electrodes; an electrolyte comprising lithium ions, arranged in between the one or more positive electrodes and the plurality of negative electrodes; wherein the battery unit is configured to generate an output current by intermittently allowing the negative electrodes from the plurality of negative electrodes to discharge to a corresponding positive electrode from the one or more positive electrodes.

[0093] Clause 2. Battery unit according to clause 1, wherein the one or more positive electrodes comprises one positive electrode for each negative electrode from the plurality of negative electrodes and there is a one-to-one relationship between the negative electrodes from the plurality of negative electrodes and the positive electrodes from the one or more positive electrodes.

[0094] Clause 3. Battery unit according to clause 1 or 2, further comprising: switching means, arranged to allow or disallow each of the negative electrodes from the plurality of negative electrodes to discharge; a controller configured to control the switching means, and configured to generate an output current by intermittently allowing the negative electrodes from the plurality of negative electrodes to discharge. Clause 4. Battery unit according to clause 3, wherein the controller is further configured to allow a first negative electrode from the plurality of negative electrodes to discharge for a first amount time and subsequently disallow the first negative electrode from the plurality of negative electrodes to discharge for a second amount of time.

[0095] Clause 5. Battery unit according to clause 4, wherein the first amount of time is between about 1 minute and about 10 minutes, preferably about 5 minutes.

[0096] Clause 6. Battery unit according to clause 4 or 5, wherein the second amount of time is between 1 minute and about 30 minutes, preferably about 15 minutes.

[0097] Clause 7. Battery unit according to clause 4, 5, or 6, wherein a ratio between the first amount of time and the second amount of time is between 10:1 and 1:10, and preferably around 1:3.

[0098] Clause 8. Battery unit according to any of the clauses 3-7, wherein, to provide the output current, the controller is further configured to pulse-width modulate the discharging of the negative electrodes from the plurality of negative electrodes.

[0099] Clause 9. Battery unit according to clause 8, wherein a duty cycle of each negative electrode is equal to one over the number of negative electrodes in the plurality of negative electrodes.

[0100] Clause 10. Battery unit according to clause 8 or 9, wherein the negative electrodes discharge in a current pulse having either a rectangular shape, a sinus-shape, a cosine-shape, or a triangle-shape.

[0101] Clause 11. Battery unit according to any of the clauses 3-10, wherein the output current is a constant and / or continuous output current.

[0102] Clause 12. Battery unit according to any of the clauses 1-11, further comprising: a positive terminal, electrically connected or connectable to the one or more positive electrodes, and a negative terminal, electrically connected or connectable to the plurality of negative electrodes.

[0103] Clause 13. Battery unit according to clause 12, wherein the battery unit is further configured to generate current from the negative terminal, through the discharging negative electrode and the corresponding positive electrode, to the positive terminal.

[0104] Clause 14. Battery unit according to any of the clauses 3-8, and clause 12 or 13, wherein the switching means are arranged to electrically connect the positive terminal to one or more of the one or more positive electrodes and / or the negative terminal to one or more of the plurality of negative electrodes.

[0105] Clause 15. Battery unit according to any of the clauses 1-14, wherein the negative electrodes are made of an alloy-forming material, preferably comprising one of silicon (Si), gold (Ag), aluminium (Al), antimony (Sb), tin (Sn), and zinc (Zn). Clause 16. Method for discharging a battery unit comprising one or more positive electrodes, a plurality of negative electrodes, and an electrolyte comprising lithium ions, arranged in between the one or more positive electrodes and the plurality of negative electrodes, the method comprising: generating a output current by intermittently allowing the negative electrodes from the plurality of negative electrodes to discharge to a corresponding positive electrode from the one or more positive electrodes.

[0106] Clause 17. Method according to clause 16 wherein generating the current comprises: allow a first negative electrode from the plurality of negative electrodes to discharge for a first amount time and subsequently disallow the first negative electrode from the plurality of negative electrodes to discharge for a second amount of time.

[0107] Clause 18. Method of clause 17, wherein the first amount of time is between about 1 minute and about 10 minutes, preferably about 5 minutes and / or wherein the second amount of time is between 1 minute and about 30 minutes, preferably about 15 minutes.

[0108] Clause 19. Method of clause 17 or 18, wherein a ratio between the first amount of time and the second amount of time is between 10:1 and 1:10, and preferably around 1:3.

[0109] Clause 20. Method of any of the clauses 16-19 wherein generating the current further comprises pulse-width modulate the discharging of the negative electrodes from the plurality of negative electrodes.

[0110] It is to be understood that the invention is not limited to particular embodiments described in the above and that aspects thereof may vary in further conceivable embodiments, while staying within the scope of the claims. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to be limiting. The scope of the present invention will be limited only by the appended claims.

Claims

CLAIMS1. A battery unit, comprising: one or more positive electrodes; a plurality of negative electrodes comprised of an alloy-forming material; an electrolyte comprising lithium ions, arranged in between the one or more positive electrodes and the plurality of negative electrodes; switching means arranged to allow or disallow each of the negative electrodes from the plurality of negative electrodes to discharge; and a controller configured to control the switching means so as to generate a continuous output current by intermittently allowing the negative electrodes from the plurality of negative electrodes to discharge to a corresponding positive electrode from the one or more positive electrodes.

2. The battery unit according to claim 1, wherein the one or more positive electrodes comprises one positive electrode for each negative electrode from the plurality of negative electrodes and there is a one-to-one relationship between the negative electrodes from the plurality of negative electrodes and the positive electrodes from the one or more positive electrodes.

3. The battery unit according to claim 1 or 2, wherein the controller is further configured to allow a first negative electrode from the plurality of negative electrodes to discharge for a first amount of time and subsequently disallow the first negative electrode from the plurality of negative electrodes to discharge for a second amount of time.

4. The battery unit according to claim 3, wherein the second amount of time is at least 1 second.

5. Battery unit according to claim 3 or 4, wherein a ratio of the first amount of time and the second amount of time is between 10:1 and 1:10.

6. The battery unit according to claim 5, wherein the ratio is and between 1:1 and 1:3.

7. The battery unit according to any of the claims 3-6, wherein the first amount of time is between 1 and 10 minutes, preferably about 5 minutes, and / or wherein the second amount of time is between 1 and 30 minutes, preferably about 15 minutes.

8. The battery unit according to any of the claims 3-7, wherein, to provide the output current, the controller is further configured to pulse-width modulate the discharging of the negative electrodes from the plurality of negative electrodes.

9. The battery unit according to claim 8, wherein a duty cycle of each negative electrode is equal to one over the number of negative electrodes in the plurality of negative electrodes.

10. The battery unit according to claim 8 or 9, wherein the negative electrodes discharge in a current pulse having either a rectangular shape, a sinus-shape, a cosine-shape, or a triangle-shape.

11. The battery unit according to any of the claims 3-10, wherein the output current is a constant output current.

12. The battery unit according to any of the preceding claims, further comprising: a positive terminal, electrically connected or connectable to the one or more positive electrodes; and a negative terminal, electrically connected or connectable to the plurality of negative electrodes.

13. The battery unit according to claim 12, wherein the battery unit is further configured to generate current from the negative terminal, through the discharging negative electrode and the corresponding positive electrode, to the positive terminal.

14. The battery unit according to any of the claims 3-8, and claim 12 or 13, wherein the switching means are arranged to electrically connect the positive terminal to one or more of the one or more positive electrodes and / or the negative terminal to one or more of the plurality of negative electrodes.

15. The battery unit according to any of the preceding claims, wherein the negative electrodes are made of one of silicon, ‘Si’, gold, ‘Ag’, aluminium, ‘Al’, antimony, ‘Sb’, tin, ‘Sn’, and zinc, ‘Zn’.

16. The battery unit according to any of the previous claims, wherein the one or more positive electrodes, the plurality of negative electrodes, and the electrolyte are included in one housing and together act as one battery cell.

17. The battery unit according to any of the claims 1-15, the battery unit comprising a plurality of said positive electrodes, wherein the battery unit includes a plurality of cells, each cell including: one or more positive electrodes from among the plurality of positive electrodes; one or more negative electrodes from among the plurality of negative electrodes; and a respective portion of the electrolyte between said one or more positive electrodes and said one or more negative electrodes.

18. The battery unit according to claim 17, wherein the plurality of cells is divided into one or more groups each including multiple cells, wherein the multiple cells within each group are connected in series or in parallel.

19. The battery unit according to claim 18, wherein the one or more groups include a first group and a second group, and wherein the multiple cells of the first group is connected in series with the multiple cells of the second group.

20. The battery unit according to claim 18, wherein the one or more groups include a first group and a second group, and wherein the first group is connected in parallel with the second group.

21. The battery unit according to claim 18, wherein the one or more groups include a first group and a second group, wherein the controller is configured to control the switching means to generate the continuous output current using the first group, and to generate a second continuous output current using the second group by intermittently allowing the negative electrodes of the multiple cells in the second group to discharge to a corresponding positive electrode of the multiple cells in the second group.

22. The battery unit according to any of the claims 17-21, wherein each cell among the plurality of cells is included in a respective cell housing.

23. The battery unit according to any of the claims 18-22, wherein each group among the one or more groups is included in a respective housing.

24. A method for discharging a battery unit, the battery unit comprising one or more positive electrodes, a plurality of negative electrodes comprised of an alloy-forming material, and an electrolyte comprising lithium ions, arranged in between the one or more positive electrodes and the plurality of negative electrodes, and switching means arranged to allow or disallow each of the negative electrodes from the plurality of negative electrodes to discharge, wherein the method comprises controlling the switching means so as to generate a continuous output current by intermittently allowing the negative electrodes from the plurality of negative electrodes to discharge to a corresponding positive electrode from the one or more positive electrodes.

25. The method according to claim 24, wherein generating the current comprises: allow a first negative electrode from the plurality of negative electrodes to discharge for a first amount time and subsequently disallow the first negative electrode from the plurality of negative electrodes to discharge for a second amount of time.

26. The method according to claim 25, wherein the second amount of time is at least 1 second.

27. The method according to claim 25 or 26, wherein a ratio between the first amount of time and the second amount of time is between 10:1 and 1:10, preferably about 1:3.

28. The method according to any of the claims 25-27, wherein the first amount of time is between 1 and 10 minutes, preferably about 5 minutes, and / or wherein the second amount of time is between 1 and 30 minutes, preferably about 15 minutes.

29. Method of any of the claims 24-27, wherein generating the current further comprises pulse-width modulate the discharging of the negative electrodes from the plurality of negative electrodes.

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