Energy storage

Abstract

A DC battery such as a Sodium ion cell battery is disclosed having positive (4) and negative (3) terminals and further comprising or including a main array of electro-chemical cells (1) connected in series, the first cell in the main array being connected to the negative terminal of the battery via a battery management circuit (2) and the last cell in the main array being connected, directly or indirectly, to the positive terminal of the battery, at least one charge booster cell connected to the final cell in the main array and being further connected to a charge sensing and controlling means (8) operable to sense the charge in each cell in the main array whereby to selectively add charge to each cell in the main array from the or each booster cell and maintain output voltage for the battery from the main array at or above a desired level. The invention also extends to energy storage systems using this concept.

Description

DescriptionTitle of Invention: ENERGY STORAGE

[0001] This invention relates to electro-chemical cell energy storage systems, Sodium ion (Na+) systems and in particular, but not exclusively, to 12 and 24 Volt batteries, for use in stationery applications such as in buildings to provide emergency power at normal line voltage, and batteries for use in vehicles on land or water having either electric traction / drive motors or loads relying on deep-cycle, long life and high lifecycle electrical energy storage capacity for power generation and high current loads such as for air conditioners, stabilizers, DC to AC power inverters, pumps, and electronics such as radar, computers, Navigation and the like, BACKGROUND OF THE INVENTION

[0002] It is well-known that conventional 12 V lead acid batteries are very heavy and their manufacture and subsequent disposal can have significantly harmful environmental consequences. Such batteries require constant maintenance and also suffer from low charging rates such that they are slow to recharge, last for only a few hundred discharge and recharge cycles, and do not perform well in sub-zero temperatures.

[0003] In recent years high energy Lithium ion (Li+) batteries have become popular, particularly for powering road-going vehicles, because they weigh about half that of lead acid batteries and the power density is much greater, meaning that electrically powered roadgoing vehicles are capable of travelling hundreds of miles before recharging becomes necessary. However, at around freezing point Lithium ion batteries stop working efficiently and in the event that they are recharged at such low temperatures serious damage to the battery may occur. A further, more serious, problem is that they are prone to thermal runaway and self-ignition, causing fires that are difficult to extinguish and which usually result in the destruction of the vehicle in which they are installed and sometimes catastrophic consequences to any building within which the vehicle is parked and hence danger to any occupants. It is for this reason that many insurers are unwilling to provide insurance, particularly if the batteries are installed in marine vessels such as motorised boats and yachts, where escape from danger may be difficult or impossible.

[0004] More recently, Lithium Iron Phosphate (LiFePO4) batteries have been developed that marginally reduce some of the thermal runaway problems associated with Lithium ion batteries but still suffer from low temperature operation and runaway thermal ignition if overcharged, undercharged, overheated or punctured in an accident.

[0005] A further problem with Lithium based battery technologies is that the individual battery cells cannot be allowed to discharge completely, otherwise they are likely tofail internally and will often either not assume a normal charge again, or ignite due to the usually dangerous thermal runaway.

[0006] Sodium ion (Na+) batteries (SIB’s) are a relatively new technology and are being exploited as a solution to the shortcomings of Lithium chemistries. Such batteries do not suffer from the disadvantages of Lithium based battery technologies and their popularity or favour is largely furthered by their manufacture not involving the extraction of rare raw materials such as Lithium, Cobalt and Copper, at ever increasing cost and drain on the Earth’s resources. Sodium ion Batteries can also be fully discharged without causing problems, making them safe to operate and to transport in bulk, since they become inert when fully discharged. They can also last for circa 3,000 or more discharge cycles, similar to Lithium technologies, which represents about six times longer life than batteries using lead based chemistries.

[0007] A single Sodium ion cell typically delivers about 2 to 4 Volts and when four such cells are arranged in series to form a nominally “12V” battery that, when fully charged, delivers power suitable for use on most electrically powered vehicles and other electrical devices. Unfortunately, it is found that such a four-cell battery has an inconveniently wide Voltage range from about 8 V to 16 V, in which only about 45% of the battery’s electrical energy is deliverable within a Voltage range above the nominal 12 V. However, since many 12 V devices do not operate well below 12 V, only about 45% to 50% of the energy of a fully charged battery can be used before it requires recharging.

[0008] In contrast, Lithium Iron Phosphate batteries have a much narrower and more usable voltage range of between about 12 V - 13.5 V and although the wide voltage range of four-cell Sodium ion batteries can theoretically be managed with solid-state circuitry or by altering the design characteristics of the devices they power e.g. electric motors, both solutions are expensive and very wasteful in terms of battery power by being converted to heat that then needs to be safely dissipated, and such energy is therefor wasted. The inconveniently wide voltage range of Sodium ion batteries has therefore lessened the impact that they have had on many potential applications and explains why they have not been commercially available as alternatives to standard 12 V lead acid batteries or 12 V Lithium batteries.

[0009] However, with shortages of raw materials such as Lithium and Cobalt, many Lithium based manufacturers are now converting to Sodium based chemistries where possible because Sodium ion batteries are manufactured using only Sodium compounds available from sea water and common aluminium metal foil and so do not generally contain the far more valuable Cobalt, Copper or Lithium.

[0010] The potential benefits that Sodium ion chemistries offer therefore require solutions to the problem of the inconveniently broad voltage range they provide when used in batteries and it is an object of the invention to address these problems.SUMMARY OF THE INVENTION

[0011] The present invention is derived from the realisation that there is a need to obviate the aforesaid disadvantages of using e.g. arrays of electro-chemical cells such as Sodium ion cells to create an ostensibly 12 V battery with such a wide and unwanted voltage range, to instead provide a battery with a narrower and more usable voltage range in a cost-effective manner.

[0012] According to a first aspect of the invention there is provided a DC battery having positive (4) and negative (3) terminals and further comprising or including a main array of electro-chemical cells (1) connected in series, the first cell in the main array being connected to the negative terminal of the battery via a battery management circuit (2) and the last cell in the main array being connected, directly or indirectly, to the positive terminal of the battery, at least one charge booster cell connected to the final cell in the main array and being further connected to a charge sensing and controlling means (8) operable to sense the charge in each cell in the main array whereby to selectively add charge to each cell in the main array from the or each booster cell and maintain output voltage for the battery from the main array at or above a desired level.

[0013] With this arrangement, by way of example, a nominally 12 V Sodium ion battery having a main array of four cells can include an extra cell acting as a booster cell for charging each of the cells in the main array when required to effectively extend the usable voltage range of the main array rather than adding to the total voltage output of the array such that most of the battery energy can be discharged from the main array at or above a usable voltage. Similarly, a Sodium Ion battery with two main arrays of eight cells in total can be used with one or more booster cells to create a nominally 24 V battery with extended usable voltage range characteristics.

[0014] Preferably, a battery management system included in the battery monitors and manages abnormal voltage, current and individual cell temperatures.

[0015] Conveniently, the ECU is controlled by a digital microprocessor (MCU) or, more simply, can be made from discrete linear components including relays, diodes, switches and sensing circuits.

[0016] The switch means can conveniently be a mechanical bistable latching relay that holds its contacts in either an open or closed position after initial electrical activation, or it can be a solid-state switch using high current MOSFETS or similar means.

[0017] Preferably, for a nominally 12 V Sodium ion battery with an array of four main cells and a booster cell, when the ECU senses the B+ (battery positive load terminal) voltage to be at the actual 12 V lower usable limit, it activates the Latch switch means to the closed position, thereby boosting the B+ output voltage by the voltage from the booster cell which, at this point, is usually held between 3.8 to 4 V, meaning that the combined output range of the battery is now between about 15.8 to 16 V. The continuing discharge by the load advantageously reduces the 5 S cell series array from about 15.8 V, until it reaches 12 V, being the point at which the battery energy has been depleted by over 90%.

[0018] Preferably, the charger simultaneously and independently provides charge to all the cells in the battery by means of Internally controlled diodes and switches in the ECU, until such time as the voltage of a five series cells reaches about 16.1 volts and when the ECU senses this it opens the latch relay switch that disconnects the booster cell, thereby returning the B+ load voltage to between 12 V and 15.8 V.

[0019] A preferred embodiment of the invention utilizes switch means in the form of a linear voltage controller and electronic current switching instead of a latching relay. This voltage controller regulates the voltage from the or each booster cell linearly and dynamically, once the B+ voltage in the main cell array reaches the lowest acceptable limit, such as about 12 V. This operates like a “Buck and Boost” converter enabling the B+ load terminal to sustain a steady nominal output voltage during the complete boost cycle. In that regard, it will be understood that components for such linear control are usually large and cumbersome and cannot be readily fitted within casing of a 5 S battery, thus making them impractical in most applications., but the use of a latching relay or switch provides a more compact arrangement. Accordingly, although the voltage output range for such a latch relay operated battery at the B+ load terminal is between about 12 V and about 16 V it makes it suitable for use as a direct replacement for conventional 12 V lead acid or 12 V Lithium batteries. It will further be understood that multiple arrays of such cells may be connected together in series to provide higher voltages, such as 24 V, 36 V, and so on. Such batteries may also be wired externally in parallel, thereby retaining an ostensibly 12 V system but doubling or tripling the current capacity and hence energy content.

[0020] With this arrangement it can be seen, for example, that by adding a single 4 V Sodium ion cell to a four cell 12 V Sodium ion battery, the nominal output voltage can be boosted and held above 12 V, thereby allowing over 90% of the energy to be discharged from the battery, instead of the initial 45% from a 4 cell sodium ion array, while maintaining 12 V or higher at the battery output B+ terminal. In turn, this also means that the current running through the wires is correspondingly reduced suchthat thinner wires, at lower cost, can be used and battery energy through heat loss is reduced.

[0021] Accordingly, with the addition of one extra Sodium ion cell, for example, to an array of four such cells but using the extra cell as a voltage booster for each cell in the main array, it can produce a result that would normally require the doubling of the battery size and available capacity in terms of Ampere-hours in order for it to deliver the same energy at the required voltage, as compared to the conventional four cell lead acid battery arrangement which only discharges about 45% of its full energy capacity at the required 12 V or higher.The compactness of the solution provided by the invention therefore provides a size of battery that generally matches a conventional 12 V Lead or Lithium battery size for size, that would otherwise need to be implemented with a bulky, heavy, heat dissipating buck / boost regulating converter that would normally have to be housed externally to the battery casing.

[0022] Conveniently, the battery of the first aspect of the invention also includes a battery charging circuit connected or connectable to the or each booster cell for receiving DC charge from a dedicated charging terminal or port (CC+) on or in the battery casing. The charging port may conveniently have reverse current protection from external charging devices and the charging voltage may optionally be connected directly to either the charging port CC+ or, if the load is not voltage sensitive, to the B+ and CC + terminals by bridging them together and charging them as one. However, since the charging voltage will always need to be high enough to charge all five cells in a 12 V Sodium ion battery with a booster cell, a battery charger capable of delivering the sum of the booster and main cells voltages, is needed as these are internally charged as a five cell group by the charging circuitry.

[0023] The invention also extends to the ability to synchronize multiple such Sodium ion batteries into series and parallel configurations, using a common control bus such as a CAN bus, NMEA bus or similar protocols over cable or Blue-tooth wireless, so that a multi-battery group can come under a single control protocol. This improves the charging algorithm when larger battery banks are working together as the multiple series or parallel batteries can be closely managed so that all loads and charge currents are shared equally and safely.

[0024] Advantageously, where batteries of the invention are used at multiple locations within a motorised sailing vessel, for example, they can have a common CAN style communications bus connected to the vessel's main electrical management system and also over an Internet connection, to an Artificial Intelligence Application Program Interface ( API) and application platform, database, which can be further utilized in managing, troubleshooting and supporting services for the sailing vessel or other installation or application. For this purpose, the ECU, embedded computer or MCUmay include programmable voltage presets to thereby enable battery performance figures to be modified, improved and controlled over the link / Blue-tooth etc.

[0025] Advantageously, the charging algorithm included in the ECU, in combination with the BMS, which are also part of the battery, further provides the ability to maintain the individual battery cells in as close to a balanced state as possible. This is achieved by utilizing active balancing circuitry that continually monitor the voltage of each cell and directs charge from the highest voltage cells to the lower voltage cells and is important in such a management system because the booster cell is purposely made to be out of balance to the main cell array. The various charging algorithms described herein manage this function so as to not permit cell damage or for voltage parameters and limitations to be exceeded during operation.

[0026] In accordance with another preferred aspect of the invention a latching transfer relay may be used instead of a more common ON / OFF contactor latch relay. This type of transfer latch relay can be used to mechanically direct the B+ load to either the main cell array or the booster cell in series to the main array and provides a simpler, all mechanical, transfer of current that does not require considerations as to heat and current capacity that a standard ON / OFF type latch relay requires, with all its attendant components and circuitry..

[0027] Although the battery of the invention, when used as a 12 V DC battery, has an additional cell to the basic four-cell arrangement, which adds approximately 25% by weight and cell cost, it almost doubles the available power available, all of it being at or above the desirable 12 V. This additional power is made available without discharging the main cell array to unnecessarily low voltage levels that would occur if say a Buck / boost DC to DC converter solution were used, thereby prolonging their cycle life i.e. the total number of charge and discharge cycles during the life of the battery. The use of an additional booster cell has further advantages, one being that the provision of an extra charge port or terminal gives the battery separation as between load and charge circuits, which simplifies system management. For example, if a sailing vessel previously had a variety of battery charging sources including a solar panel array, an engine alternator and a shore power supply connection, these can all be connected via to a common charging bus, to an external battery charger and on to the third Sodium ion charging port or terminal. These charging sources will manage themselves according to whichever has the most current / voltage available according to the load being drawn.

[0028] In accordance with a second aspect of the invention there is provided an electrical energy storage and management apparatus and associated control software installed or installable within a storage facility, the apparatus comprising or including arrays of Sodium ion cells and, for each array, at least one extra cell acting as a booster forthat array whereby to boost the voltage in each other cell of the array and maintain a continuous voltage output at or above a required minimum voltage.

[0029] With this arrangement a substantial energy storage system can be assembled for use with electric power generation systems with spare capacity requiring storage instead of wastage of electricity, such as spare capacity from wind turbines, solar panels or combinations thereof, in much the same way as pumped water storage systems can use spare electrical capacity during times of the day and night when energy demand is low.

[0030] DETAILED DESCRIPTION OF THE DRAWINGS

[0031] The invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0032] Figure 1 is a graph showing typical voltage ranges available during discharger of 4 cell lead acid, Lithium Iron phosphate and Sodium ion batteries,

[0033] Figure 2 is a block diagram of a battery arrangement of the invention,

[0034] Figure 3 is a graph showing available voltage ranges for the battery arrangement ofFigure 2,

[0035] Figure 4a shows a simplified circuit diagram of a four-cell nominally 12 V battery array with a fifth, booster cell disconnected from the output load,

[0036] Figure 4b shows the battery arrangement of Figure 4a with the fifth cell connected, and

[0037] Figure 5 shows the general arrangement and placement of multiple such batteries connected or connectable to a variety of battery charging options and the main electrical wiring bus of a motorised sailing vessel with attendant power outlets.

[0038] Figure 1 is a graph showing the voltage distribution of, respectively, four cell ostensibly 12 V lead acid, lithium iron phosphate and Sodium ion batteries when fully charged and when fully discharged. It will be seen that the voltage range for the lead acid battery is relatively narrow, being between about 13 V and 10.5 V with at least half of the energy available being above 12 V. The corresponding curve for the lithium iron phosphate battery is much flatter and begins at around 13.5 V going down to 13 V, meaning that for this type of battery all of the energy available is above 12 V as the battery is being discharged. In contrast, it will be seen that the curve for the Sodium ion battery shows a much wider voltage distribution, starting at around 15.8 V and typically going down to around 7 V when the battery is fully discharged, meaning that only around 45% of the available energy in the battery is above 12 V. Although this wide voltage distribution can be narrowed by means of a voltage regulator and charge controller of the buck and boost type this can be an expensive solution but, more importantly, will not fit into the confined space inside a regular battery enclosure and would generate large amounts of heat that requires dissipation.

[0039] As shown in Figure 2, the foregoing problem of Sodium ion cells having a very wide voltage distribution can be solved by adding another Sodium ion cell in series to the main array of 4 cells (4S) for an ostensibly 12 V battery but using it to boost voltages in the main cell array as and when needed. The block diagram shows the complete contents of a battery, consisting of consisting of the main cell array (1) of four Sodium ion cells (SI, S2, S3, S4) connected in series to a generally conventional battery management system in the form of a Battery Management System ( BMS) (2) for sensing and balancing voltages across the array (1). As discussed earlier, this arrangement would normally deliver a wide voltage distribution as the array (1) becomes discharged between the negative (3) and positive (4) terminals such that only about 45% of the energy within the four cell array would be available at or above 12 V, and hence 55% of the energy within the array remains unused because it is below the 12 V threshold and therefore unusable for most purposes. However, in accordance with the invention an additional or booster cell (5) (S5) is added in series to the main array (1) and can be selectively connected thereto by switch means (6) such as a latching relay i.e. a relay that is either open or closed and therefore not requiring a constant supply of power to keep it in either condition. The switch means (6) is controlled by the ECU voltage sensing circuit within the ECU (7) operable to monitor the voltage level at the load B+ terminal (4) activating the timely closure of switch means (6) to transition from the 4S array (1) to a boosted 5S array when the B+ load voltage drops to below 12 volts.

[0040] A charge sensing circuit (8) within the ECU (7) monitors the charge levels of the main 4S array (1) and the S5 booster cell (5), providing electronically switched charge control from the battery charge terminal (9) in a manner that provides fast, safe and balanced charge to all the cells (1) and (5).

[0041] Figure 3 shows the dramatic effects of using a fifth cell (S5) to charge the main array of cells (SI, S2, S3 & S4) when the voltage drops to around 12 V in which it will be seen that with this arrangement around 90% of the usable energy becomes available before the battery voltage becomes too low.

[0042] Figures 4a and 4b respectively show the arrangement by which the fifth cell S5 can be selectively connected or disconnected in series to the main array SI - S4. Figure 4a shows a switch means (6), which may be a latching relay or a solid-state bi-stable switch, in its open position whereby to provide a positive load to the circuit shown in Figure 2 via a diode (10) which acts to block and reverse current that could short circuit S5 (5) to itself. In contrast, Figure 4b shows the switch (6) in its closed position whereby the booster cell S5 (5) is connected in series to the main array of cells Sl- S4 and forms part of the overall circuit. Accordingly, upon gradual depletion of thecharge in the array of cells S1-S4 (1) the charge in the booster cell S5 (5) can be used to increase the voltage in those cells by the closure of switch (6).

[0043] Thus, by adding one or more booster cells (5) to a main array of Sodium ion cells (1) in a battery configuration to boost the charge in each of the cells in the main array (1) as and when required, a nominally 12 V Sodium ion battery, for example, can therefore be used as a practical substitute for 12 V lead acid, Lithium ion or Lithium Iron phosphate batteries for use in vehicles, with advantages in terms of cost, safety and greatly reduced environmental impact.

[0044] In Figure 5 there is shown a general arrangement by way of example, in which an array of Sodium ion batteries of the invention can be usefully incorporated as part of the 12 V wiring bus for a motorised sailing vessel in which the or each battery can be optionally recharged via power from the on-shore electricity grid via an AC to DC power supply (12) or charger (13) when the vessel is in port, while one or more onboard solar panels (14) also act to constantly generate DC charge for the array, and by means of an ICE engine alternator (16) and associated engine battery (17) driven by an on-board internal combustion engine (not shown) for powering the drive propeller or screw of the vessel. The electric motor of a bow thruster (18) has a dedicated battery (19) and receives energy from a high output alternator (20) that drives this i.e. it is connected to the internal combustion engine. The charging options therefore include an array of solar panels(14), mains connectors (12,13) for connection to the onshore mains electricity grid when the vessel is in port, and engine-driven alternators (16) for respectively charging a first battery (17), a second battery (19) with both batteries supplying power to the bank of three batteries (22). These selectively supply on-board power to a main wiring bus (23) in which 12V DC electricity is converted to 110 V as used to power on-board devices and appliances. In that regard, it will be appreciated by those skilled in the art that DC to DC converters are known which could, in theory, be used to keep the voltages within a required range from a wide range of voltages that a Sodium ion battery would normally output from fully charged to flat, such as from 16 V to 8 V and thereby capably convert them to a steady 12V, 12.5 V or whatever the output voltage required, these are affordable up to about 60 Amps but become bulky, hot and heavy for larger current ratings, thereby being too large to fit into the casing of a conventional battery case. Accordingly, the invention provides a compact solution to this problem.

[0045] In practical terms, although a 12 V battery in accordance with the invention uses five cells instead of four at an extra 25% cost and corresponding increase in battery weight, it enables the battery to provide 40% more energy at or above 12 V and for a 24 V battery for just a 13% increase in terms of cost and weight, assuming only one booster cell is used for all of the other eight cells. It has been found that an additional30% to 40% output energy at or above 24 V is achieved such that, in overall terms, where the batteries are used in applications requiring a usable voltage range it provides a significant saving in terms of cost and weight when compared with conventional 12 V or 24 V batteries made using lead acid or lithium chemistries. In addition, if the batteries of the invention are provided with a third, charging, terminal a simple and practical means for combining legacy Batteries like Lead Acid and Sodium Ion batteries into a traditional installation is safe and possible.

[0046] Accordingly, the invention provides an elegantly simple solution to the problem of providing electrical energy storage using electro-chemical technology which avoids the unwanted characteristic of having a usable voltage range at or below about 50% of the battery energy, to instead provide a battery that is able to extract approximately 90% of that energy at a usable voltage. In addition, it is to be noted that batteries in accordance with the invention can be used in conjunction with conventional lead acid batteries or batteries made using lithium technologies and when the latter have reached the end of their life-cycle they can be systematically replaced by the former such that, over time, where multiple batteries are required for a variety of applications, such as within a motorised sailing vessel, they provide a practical replacement option and a cost- effective and affordable means of gradually converting the original arrangement of conventional batteries to an arrangement based on the much safer and environmentally more responsible Sodium ion technology.

Claims

Claims

1. A DC battery having positive (4) and negative (3) terminals and further comprising or including a main array of electro-chemical cells (1) connected in series, the first cell in the main array being connected to the negative terminal of the battery via a battery management circuit (2) and the last cell in the main array being connected, directly or indirectly, to the positive terminal of the battery, at least one charge booster cell connected to the final cell in the main array and being further connected to a charge sensing and controlling means (8) operable to sense the charge in each cell in the main array whereby to selectively add charge to each cell in the main array from the or each booster cell and maintain output voltage for the battery from the main array at or above a desired level.

2. A battery according to Claim 1 in which the electro-chemical cells are Sodium Ion cells.

3. A battery according to Claim 1 in which the main array (1) comprises four cells (S1-S4).

4. A battery according to Claim 1 in which the cell management system (2) includes means for monitoring and managing abnormal voltage, current and temperature for each cell.

5. A battery according to Claim 1 or Claim 2 further including a battery charging circuit and associated charging port (9) connected or connectable to the or each electro-chemical cell for receiving DC charge.

6. A battery according to Claim 5 wherein the charging circuit includes reverse current protection from external charging devices and the charging voltage is optionally connectable directly to the charging port (9) or, if the load is not voltage sensitive, to the positive (4) and battery charge (9) terminals (4,9) by bridging them together and charging them as one.

7. A battery according to Claim 1 including means to synchronize with other batteries into series and / or parallel configurations, using a common control bus.

8. A battery according to Claim 1 further including means when used with other batteries at multiple locations, to connect with a common communications bus.

9. A battery according to Claim 1 wherein the individual battery cells are managed to a generally balanced state of charge.

10. A battery according to Claim 1 wherein the individual battery cells are charged according to their voltage, prioritising charging to the cells with the lowest voltage.

11. An electrical energy storage and management apparatus and associated control software installed or installable within a storage facility, the apparatus comprising or including arrays of Sodium ion cells and, for each array, at least one extra cell acting as a booster for that array whereby to boost the voltage in each other cell of the array and maintain a continuous voltage output at or above a required minimum voltage.

12. Apparatus according to Claim 11 wherein the or each array of cells is recharged when not in use to a required energy level.

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