BACKGROUND
FIELD OF THE INVENTION
The present invention relates to a capacity balancing battery cell, more particularly related to lithium based batteries which includes lithium-ion, lithium-polymer and solid-state lithium batteries. Apart from the usual cathode and anode, these battery cells consists of a capacity balancing electrode (CBE) which helps the cell regain its lost capacity or remove its excess capacity.
DISCUSSION OF THE PRIOR ART
The deliverable capacity of conventional lithium based batteries containing non-pre lithiated carbonaceous or non-carbonaceous anodes (graphene Si, Sn, etc.); is measured by the amount of recyclable lithium the cathode can hold. However, in the case of lithium batteries which consists of lithium metal anode and lithium-ion batteries consisting of pre-lithiated anodes (Li4Ti50I2, pre-lithiated graphene, pre-lithiated silicon, etc.); the lithium content in cathode corresponds to only a part of the entire cell capacity.
The three main reasons for the loss of capacity in lithium based batteries are loss of recyclable Li+ (lithium ion), loss of active material, and structural change of the active material. Loss of active material occurs due to its dissolution into the electrolyte either as a result of parasitic reactions, exposure of the cell to high temperature operation or wear and tear of the electrode surface as a result of repeated cycling. Prolonged cycling also results in structural deformation of the active materials which effects the cell capacity either by trapping some of the recyclable Li+ inside its interstitials which can no longer be extracted or structural changes which can no longer intercalate Lf into them. The capacity loss occurring as a result of all the above mentioned causes cannot be compensated for during the cell operation. However, such impacts can be minimized by suitable material selection or synthesis and cell operation under optimum conditions.
The capacity loss occurring as a result of loss of Lf alone can be recovered by supplying extra Li+ to the electrodes. The loss of Li+ occurs primarily due to the formation of SEI (Solid Electrolyte Inter-phase) layer on the anode surface and other side reactions. Although formation of SEI layer is also a side reaction where Li+ combines with the electrolyte to form a passive layer on anode surface; its formation is necessary for stable cell operation and prevents the anode from further side reactions. The Li+ bonded in the SEI layer cannot be extracted for further cycling.
There are various ways suggested in the literature to regain the lost capacity of the lithium-ion batteries, they may be broadly classified into two categories: (a) In-situ: Wherein the excess lithium is already placed in the electrode prior to cell assembly either inside the electrode body or on its surface. This method witnesses the use of pre-lithiated electrodes, (b) Ex-situ: Wherein the excess lithium source is present in the form of an additional electrode which is separated from the primary electrodes and Li+ can be moved to and from this electrode by closing an external circuit between the additional electrode and the desired primary electrode (anode/cathode).
A number of patents have been reported in state-of-the art on ways of incorporating supplemental lithium to the electrodes in order to make up for the lost capacity of the cell based on both in-situ and ex-situ techniques.
US 6,335,115 Bl titled "Secondary lithium-ion cell with an auxiliary electrode"
discloses a lithium-ion secondary cell arrangement consisting of a lithium rich auxiliary electrode that replenishes the lost Li+ as a result of SEI formation on the anode surface or parasitic reactions during cycling. The secondary lithium-ion cell with an auxiliary electrode proposed by the described invention requires the cell orientation to be changed for capacity replenishment. This kind of architecture limits the applicability of the battery for various applications where changing the battery orientation is either impractical or not feasible. Also, the possibility of electrolyte leakage cannot be ruled out. The capacity balancing cell disclosed in
the present invention does not require any change in alignment or orientation for capacity replenishment.
US 2011/0081563Al titled "Lithium reservoir system and method for rechargeable lithium-ion batteries" outlines the arrangement of a secondary lithium-ion cell consisting of a lithium reservoir electrode (LRE) which can replenish the lost capacity of the cell arising as a result of loss of LF as well as store the excess capacity generated as a result of loss of active material. The BMS (Battery Management System) of the cell calculates the SOC of the working electrodes, closes a switch to complete the circuit between the working electrodes and the auxiliary electrode in case cell rebalancing or renewal is required and opens the switch in the event of completion of the LF distribution process to avoid excess Li+ insertion or extraction. The BMS also controls the direction and rate of transfer of the LF by controlling variable load resistors.
The LRE described here is placed at the bottom of the cell. In this case, the effective area of LF transfer to/from LRE during the cell renewal or replenishment is very small (i.e. the cross sectional area of the anode/cathode) as compared to the active surface area. Also, this arrangement is not very practical as placing the LRE horizontally at the bottom of the cell across its width would lead to complications in cell assembly. The cell arrangement disclosed in the present invention can be easily rolled into a cylinder or wounded into a prismatic/pouch cell. Also, the lithium transfer between the capacity balancing electrode (CBE) and the cathode occurs across the entire surface area of the anode and hence the capacity balancing is much faster.
US 8,241,793 B2 titled "Secondary lithium-ion battery containing a prelithiated anode" discloses a lithium-metal or lithium-ion battery with anode containing pre­lithiated and pre-pulverized active material. The anode contains very fine particles (average particle size < 1 um) of a first non-carbonaceous active material which has been pre-pulverized and pre-lithiatedand. dispersed in the matrix of a,second carbonaceous active material reinforced with a nano-scidejd.ffller such as carbon
nano-tube (CNT) or nano-graphene platelet (NGP). As disclosed in the invention, such anodes have several advantages which includes; (a) Performance: Anodes with nano-particles demonstrate better rate capacity and rapid charging due to significant reduction in the travelling distance of the Lf and electrons during insertion and extraction to and from the active materials, (b) Cycle-life: Unlike lithiated anodes, pre-lithiated and pre-pulverized anode materials do not undergo any further pulverization or structural change on repeated cycling. In case of shrinkage of volume also, the active materials does not lose contact with the conductive additives and current collector resulting in higher cycle life, (c) Capacity enhancement: In the case of pre-lithiated anodes; the cathode need not pre-store any lithium which enhances the battery capacity by 10-20%which is lost in conventional batteries due to the formation of SEI layer, (d) Safety: Pre-lithiated non-carbonaceous anodes are more unstable in normal operating conditions than pre-lithiated carbonaceous anodes.
US 2012/0107680 Al titled "-Lithium-ion battery with supplemental lithium"
discloses various ways to replenish the lost capacity of secondary lithium-ion battery electrodes and methods to generate lithium-replenished electrodes. One way to do so is by using a sacrificial electrode (either lithium foil and/or supplemental lithium source supported by a polymer binder) and loading supplemental lithium from this electrode to the anode by closing an external circuit. A different way is to incorporate supplemental lithium source into the electrodes (anode/cathode) in the form of a lithium-source bonded in a polymer matrix, inside the electrode body, or by providing a thin Li-foil as supplemental lithium source either on the electrode surface or between the electrode and the respective current collector. Third method is to use a pre-lithiated electrode for the cell operation. The invention also discloses ways of preparation of electrodes with sacrificial lithium as well as ways of performing lithiation on electrode surface. A number of experimental evidences have also been provided to demonstrate the superior performance of pre-lithiated anodes. In the described invention, various
ways of balancing the lost capacity of the electrodes of the lithium-ion batteries is also discussed.
Of the various methods suggested, the one with a supplemental lithium source on the electrode surface is unfeasible. In case the supplemental lithium-source is a lithium-foil as disclosed, it is similar to handling lithium metal anode and may have safety issues as a result of formation of dendrites. In another embodiment, an electrode stack is disclosed with cathode containing supplemental lithium source embedded within the cathode active material and anode consisting of an optional sacrificial electrode. Here, the nature of the anode current collector material is not mentioned and in case a metal foil is used; there would be no path for the LiT to move to the anode from the sacrificial electrode. Under this circumstance, Li+ would start plating onto the anode current collector once the external circuit between the anode and the sacrificial electrode is closed. The present invention disclosed herein uses a porous substrate as the cathode current collector which can provide an easy path for the intercalation of Li+ from the capacity balancing electrode (CBE) into the cathode and vice versa.
The present invention discloses a capacity balancing cell design primarily for lithium based batteries consisting of a capacity balancing electrode (CBE) apart from the usual anode and cathode. .The CBE provides Li+ to the cathode in case of capacity loss as a result of loss of recyclable Li+, hereafter referred to as negative capacity fade, C and extracts Li+ from the cathode in case of excess cell capacity due to the loss of electrode active material, hereafter referred to as positive capacity fade, C+. This is done once the circuit between the cathode and the CBE is closed.
Further, the present invention discloses a strategy for determining the type of capacity fade by measuring SOC of the individual electrodes and thereby performing capacity balancing of the cell.
SUMMARY OF THE INVENTION
The present invention relates to a capacity balancing cell design primarily for lithium based batteries including lithium-ion, lithium-polymer, lithium-air, or solid state lithium batteries which can restore the lost Li+ content as well as withdraw the excess Li+ in the cell.
One of the important aspects of the present invention is that the capacity balancing cell consists of an additional capacity balancing electrode (CBE) apart from the usual anode and cathode. Thus, the present invention discloses an ex-situ technique of capacity balancing of the cell.
One of the important aspects of the present invention is that the CBE consists of a lithium intercalation compound which may or may not have the similar chemical composition as that of the cathode and is less than half of its thickness.
Another important aspect of the present invention is that the lithium content in the cathode is balanced during the entire life of the cell, thereby enhancing the cell performance as well as its longevity.
One of the embodiments of the present invention discloses the use of a porous cathode substrate made of nickel foam, nickel-plated steel foam, copper foam, or the like, which also acts as the current collector for the cathode. The porous nature of the substrate aids in the movement of Li+to and from the cathode.
Another embodiment of the present invention discloses a strategy to determine whether the capacity loss has occurred as result of negative capacity fade (C ) or positive capacity fade (C+) based on the State-of-Charge (SOC) of the individual electrodes as well as amount of Li+ that needs to be intercalated into the cathode or extracted from it in order to balance the capacity of the cell.
One important aspect of the present invention discloses that Lf can be transferred between the CBE and the cathode and vice versa once the circuit between the
cathode and the CBE is closed. The closing and opening of this circuit is controlled by the cell controller.
Another embodiment of the present invention discloses the architecture of a finished wounded prismatic cell consisting of an anode containing non-pre lithiated carbonaceous or non-carbonaceous compound along with the anode current collector. Cathode active material is held by a porous electrode substrate, CBE along with its current collector and three separator films disposed between the anode and the cathode, cathode and the CBE, and the anode current collector and the CBE current collector. The final cell consists of three terminals arising out of the tabs of the anode current collector, porous cathode substrate, and the CBE current collector.
Brief description of the drawings accompanying the provisional specification.
Figure 1 shows the cross-sectional view of the capacity balancing cell.
Figure 2 shows the schematic representation of the final wounded capacity balancing cell.
Figure 3 shows the schematic representation of the various layers inside the final wounded capacity balancing cell.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 is the schematic representation of the cross-sectional view of a capacity balancing cell 100. The cell 100 consists of an anode 103 with anode active material coated onto an anode current collector film 101. The anode active material consists of a non-pre-lithiated compound that is either carbonaceous (graphene, carbon black, Meso carbon micro beads (MCMB), etc.) or non-carbonaceous (Si, Sn, etc.) along with a conductive additive and binder. The cathode, comprising of lithium intercalating active materials pressed onto an porous cathode substrate 107. The cathode active material may consist of either LiFeP04, LiMn204, Li(NiCoMn),/302, LiCo02 or Li(Nio.5Co0.2Mno.3)02 or the
like. The porous cathode substrate 107 may be nickel foam, nickel-plated steel foam, copper foam, or the like. A separator film 105 is placed between the anode 103 and the porous cathode substrate 107. An active material of a CBE 113 is coated onto a CBE current collector 115 that may have similar or dissimilar chemical composition as that of the cathode. The capacity balancing electrode (CBE) 113 is an alternate lithium source mostly in the form of a secondary cathode consisting of a lithium intercalation compound which may or may not have the same chemical composition as the primary cathode 109. Also, the thickness of the CBE 113 is less than half of the thickness of the primary cathode 109. An another separator film 111 is placed between the porous cathode substrate 107 and the CBE 113. The separator films 105 and the separator film 111 are polymer membranes mostly poly-tetra-fluoro-ethylene or poly-propylene membrane or the like. For example, aluminium and nickel foils can be used as CBE current collector 115 whereas copper foil is used as the anode current collector 101.
In case of the porous electrode substrate 107, the entire depth of the active material is in contact with the current collector which significantly reduces the travelling distance of the electrons from the current collector to the active material particles. This results in much reduced charge transfer resistance thereby aiding in faster charging, higher power output, and improved charge-discharge capacity of the cell 100. The porous electrode substrate 107 also helps in effective utilization of the active materials and more uniform current distribution across the entire depth of the electrode active material. The porous substrate 107 is electronically conductive and hence eliminates the need to use any extra current collector. The porous substrate also provides mechanical stability to the active material against structural deformations and reduces active material loss by dissolution into the electrolyte. Apart from the advantages mentioned above, the porous substrate provides two additional benefits applicable to the present invention. First, it provides a path for the movement of LiT between the cathode 109 and the CBE 113, which would not have been possible in the event of use of a metallic foil
collector. Secondly, the porous material is compressible and provides an adaptive contact with the active material. Hence, it can accommodate for storing certain amount of excess capacity (Li+) without negatively affecting the cell performance.
A number of prior arts are available demonstrating the use of porous current collectors and establishing their superior performance as compared to metallic foil current collectors. A 3D porous aluminium current collector is used in the case of a battery, capacitor, and lithium-ion capacitor containing non-aqueous electrolytes [1]. Another electrochemical cell has used porous current collectors both for the cathode and the anode which are disposed into the respective semi solid suspension of active material [2]. The graphite based porous carbon current collector with a total porosity of 60% is used as the current collector for both positive as well as negative electrode in a lead-acid battery has demonstrated significantly lower electrical resistivity [3]. Another 3D micro-porous current collector made of foamed polyurethane and nickel-chromium alloy that is utilized as the positive electrode substrate for a LiFeP04 battery cell demonstrated a significant reduction in the charge transfer resistance as well as superior high-rate discharge capabilities as compared to cells containing Al-foil as current collector [4].
During the usual cell operation, an external circuit 119 remains closed and an alternate circuit 121 remains open. The transfer of Li+ between the cathode 109 and the CBE 113 for the purpose of capacity balancing is carried out by closing the alternate circuit 121 during which the external circuit 119 remains open. The Li+ is transferred between the cathode 109 and the CBE 113 is based on the individual SOC of the electrodes which can be measured by various methods like impedance spectroscopic techniques, extended Kalman filter based methods, etc. The SOC of the full cell (SOCcen) is equal to the SOC of the anode (SOC ). The SOCceii refers to the amount of charge remaining in the anode for discharge, i.e.
SOCCell = SOC
Also, SOCof the cathode (SOC+) and SOC of the anode (SOC ) must be equal to 100,
SOC++ SOC = 100
In case of positive capacity fade (C+), excess recyclable Lf resides within the electrodes whereas in case of negative capacity fade (C ), LF is lost due to SEI layer and by products formation as a result of side reactions. Capacity fade (Co), as a result of either of these phenomena can be determined as
Capacity fade, C0 = (SOC++ SOC ) -100
Capacity fade less than 0, i.e. C0< 0, indicates negative capacity fade (C ) and LiT needs to be transferred from the CBE 113 to the cathode 109. In case capacity fade is greater than 0, i.e. Co> 0 it indicates a positive capacity fade (C+) and Li+ needs to be transferred from the cathode 109 to the CBE 113.Three examples are presented to demonstrate the strategy used for balancing the amount of Li+ in the cell 100.
Example 1: Capacity balancing is performed for a new cell exhibiting negative capacity fade (C ) and the various steps for the same are mentioned in Table 1 (Annexure 'A').
Step 1.1 shows the SOC of the anode 103, cathode 109 and the CBE 113 of a new cell 100 prior to cell formation stage and does not exhibit any capacity loss. Step 1.2 shows the SOC of the electrodes at a point during the first charge where 15% of the recyclable Li+ is lost as a result of SEI formation resulting in negative capacity fade (C ) of-15.
At the end of charging in step 1.3, the capacity loss is increased to -20. In step 1.4, capacity balancing of the cell is performed by providing the amount of LFto the cathode 109 from the CBE113 to account for the negative capacity
fade (C ) of the cell by closing the alternate circuit 121. The alternate circuit 121 is reopened once the required amount of Li+ is intercalated into the cathodel09. The cell 100 is fully charged after the capacity balancing at step 1.5. After capacity balancing the anode active material is fully utilized, improving the SOC of the cell, SOCceii from 80 to 100.
Example 2: Capacity balancing is performed when cell 100 is relatively old after repeated cycling hence exhibiting positive capacity fade(C+) due to the loss of anode active material as a result of structural deformation and parasitic reactions in addition to the negative capacity fade(C J.The various steps for the same are mentioned in Table 2 (Annexure 'A').
Step 2.1 shows the SOC of the anode 103, cathode 109 and the CBE 113 of a fully discharged old cell 100 which exhibits a negative capacity fade (C ) of-30.
Step 2.2 shows the SOC of the electrodes at a point during the charging of the cell 100 where 15% of the capacity is lost as a result of loss of anode active material resulting in a positive capacity fade(C+) of+15 in addition to the existing negative capacity fade(C ) of -30. Due to the reduction in the anode active material, a lesser amount of LP fills all the interstitial sites of the anode resulting in 100% SOC of the cell with lesser amount of Li+. The excess amount of Li+ remains within the cathode and must be extracted out, since in the event of overcharging; the excess LP would start to plate onto the anode surface resulting in the formation of dendrites.
At the end of charging step 2.3, 15% excess SOC remains in the cathode even after full charge of the cell.
In step 2.4, capacity balancing of the cell 100 is performed by extracting the excess LP from the cathode 109 and intercalating it into the CBE 113 by closing the alternate circuit 121. After the removal of the excess capacity, the cathode
SOC (SOC+) becomes 0 and the SOC of the CBE 113 (SOCcbe) is increased from 70 to 85. This eliminates the positive capacity fade(C+) from +15 to 0.
Example 3: Capacity balancing is performed after cell 100 is relatively old after repeated cycling hence exhibiting positive capacity fade (C+) as a result of loss of cathode active material in addition to negative capacity fade(C_). The various steps for the same are mentioned in Table 3 (Annexure 'A').
Step 3.1 shows the SOC of the anode 103, cathode 109 and the CBE 113 of a fully charged old celllOO which exhibits a negative capacity fade (C ) of-30.
Step 3.2 shows the SOC of the electrodes at a point during the discharging of the cell 100 where 10% of the capacity is lost as a result of loss of cathode active material resulting in a positive capacity fade(C+) of+10.
At the end of discharging step 3.3, 10% excess SOC remains in the anode 103 even after complete discharge of the cell. Due to the reduction in the cathode active material, a lesser amount of Li+ fills all the interstitial sites of the cathode 109 resulting in 100% SOC of the cathode 109 with lesser amount of Lf. The cathode 109 is no longer capable of accepting more Li+ and in the event of over-discharge: the impedance of the cell would increase drastically due to concentration polarization on cathode surface which may also lead to structural deformation of the cathode active material.
In step 3.4, capacity balancing of the cell 100 is performed by extracting the excess Li+from the cathode 109 and intercalating it into the CBE 113 by closing the alternate circuit 121. Balancing of the cell 100 increases the SOC of the CBE 113 (SOCcbe) from 70 to 80 and eliminates the positive capacity fade (C+) from +10 to 0.
After the removal of the excess capacity, the balanced cell 100 is again fully discharged in step 3.5 resulting in cathode SOC, SOC+ = 100 and anode SOC, SOC. = 0.
It is possible that at any given time, the capacity loss of a cell 100 occurs as a result of both positive capacity fade (C+) as well as negative capacity fade (C_). However, the dominant of the two phenomena decides whether the overall capacity fade is positive or negative. The SOC measurements and closing and opening of circuits 119 and 121 for usual cell operation and cell balancing respectively are controlled by the cell controller. Capacity balancing of the cell 100 needs to be performed after the first charge cycle and thereafter only at certain fixed intervals determined by the cell controller. Capacity balancing needs to be performed in case of prolonged exposure to high temperature environments as well as after a long idle period. Too frequent capacity balancing may negatively impact the cell performance and cycle life as the cell remains in operation during balancing as well.
Figure 2 shows the final wounded capacity balancing cell 100 as per one of the embodiment, consisting of three terminals T+, T. and Tcbe each arising out of the tabs connected to the porous cathode substrate 107, anode current collector 101 and the CBE current collector, 115 respectively. In the case of the metallic film type of current collectors (e.g. negative and the CBE current collectors), the tabs are connected to the current collector foils by welding means for example, spot welding. However, in case of porous foam kind of electrode substrates, performing spot welding is not very effective.
Various ways of making electrical connection of the cell by joining current collector tabs to porous current collectors have been disclosed previously. A way of making electrical connections to the graphite based porous carbon current collector with tabs also made of carbon foam which are actually extensions of the original porous current-collector is illustrated in the present invention. In order to make the tabs conductive to high currents, a carbon-metal interface is established
by thermally spraying a conductive metal (e.g. Ag) onto the tab such that the conductive metal penetrates through the porous carbon. Thereafter, a second conductive material (e.g. Pb) is coated onto the carbon-metal surface to complete the electrical connection [2]. Further, methods of connecting a metal conductor in the form of metal strip to an electrode substrate having foam or fiber kind of structure are revealed. Either a single metal strip or two metal strips are used which is secured to the main core across its entire length by performing electric seam welding or spot welding in respective cases. The core material mostly consists of either nickel foam or polyurethane felt [5].
Figure 3 describes a schematic representation of the various layers inside the final wounded capacity balancing cell 100 according to an embodiment. The cell consists of an anode 103 with anode active material coated onto the anode current collector film 101. The cathode 109 comprising of lithium intercalating active material is pressed onto a porous foam based cathode substrate 107 coated on the cathode 109. A separator film 105 is placed between the anode 103 and the porous cathode substrate 107. A CBE 113 is coated onto a CBE current collector 115. A separator film 111 is placed between the porous cathode substrate 107 and the CBE 113 whereas another separator film 117 is placed between the CBE current collector 115 and the anode current collector film 101. Various layers are placed over one another and wounded either manually for example, using a flat blade or the like or using a winding machine.
REFERENCES
US 2012/0288757 Al, Hosoe et.al
US 2004/0002006 Al, Kelley et.al,
US 2013/0065122, Chiang et.al,
Masaru Yao etal, "LiFePC>4 based electrode using micro-porous current collector for high power lithium-ion battery", Journal of Power Sources, 173 (2007) 545-549.
US 5667915, Loustau et.al
WE CLAIM:
1. A capacity balancing lithium based battery cell 100 comprising of an additional capacity balancing electrode CBE 113 that helps the cell regain its lost capacity and remove its excess capacity providing an ex-situ technique of capacity balancing of the cell to enhance performance and longevity of the cell comprising (a) the cell 100, (b) an anode current collector film 101, (c) the anode 103, (d) one or more separator films 105, 111, 117 (e) a porous foam based cathode substrate 107, (f) a primary cathode 109, (g) the capacity balancing electrode (CBE) 113, (h) a CBE current collector 115, (i) an external circuit 119, and (j) an alternate circuit 121 wherein: i. The anode 103 comprises of an anode active material coated onto
the anode current collector film 101; ii. The separator film 105 is placed between the anode 103 and the
porous cathode substrate 107; iii. The porous cathode substrate 107 is made of nickel foam, nickel-plated steel foam, copper foam, or the like, which also acts as the current collector for the cathode 109; iv. The primary cathode 109 comprises of lithium intercalating active materials or the like pressed onto porous foam based cathode substrate 107; v. The separator film 111 is placed between the porous cathode
substrate 107 and the CBE 113; vi. The CBE 113 is an alternate lithium source in the form of a
secondary cathode coated onto a CBE current collector 115; vii. The separator film 117 is placed between the CBE current collector
115 and the anode current collector film 101; viii. The external circuit 119 remains closed and the alternate circuit 121 remains open during the cell operation; and
ix. The closing and opening of the circuit is controlled by the cell controller.
The capacity balancing lithium based battery cell as in 1 wherein, the anode active material of the anode 103 comprises of non-pre-lithiated compound made up of one or more carbonaceous compounds including graphene, carbon black and Meso carbon micro beads (MCMB) along with a conductive additive and binder.
The capacity balancing lithium based battery cell as in 1 wherein, the anode active material of the anode 103 comprises of non-pre-lithiated compound made up of one or more non-carbonaceous compounds including Silicon and Tin along with a conductive additive and binder.
The capacity balancing lithium based battery cell as in 1 wherein, the cathode active material of the primary cathode 109 is includes at least one of LiFeP04, LiMn204, Li(NiCoMn)i/302, LiCoC>2 and
Li(Ni0.5Coo.2Mno.3)02.
5. The capacity balancing lithium based battery cell as in 1 comprises of
at least three terminals arising out of the tabs connected to the porous
cathode substrate 107, anode current collector 101 and the CBE
current collector, 115, wherein:
a. Aluminium and nickel foils function as CBE 113 current collector 115 and copper foil functions as the anode current collector 101; and
b. Li+ is transferred between the CBE 113 and the cathode 109 and vice versa once the circuit 121 between the CBE 113 and the cathode 109 is closed.
6. The capacity balancing lithium based battery cell as in 1 wherein, the CBE 113 is configured to include lithium intercalation compound which may or may not have the same chemical composition as the primary cathode 109 and having a thickness less than half of the thickness of the primary cathode 109.
The capacity balancing lithium based battery cell as in 1 wherein, the separator film 105 and another separator film 111 are made of polymer membranes or the like including poly-tetra-fluoro-ethylene and poly-propylene membrane.
7. The capacity balancing lithium based battery cell as in 1 wherein the capacity balancing lithium based battery cell as in 1 wherein the SOC measurements and closing and opening of circuits 119 and 121 for usual cell operation and cell balancing respectively are controlled by the cell controller where capacity balancing is carried out such that:
The alternate circuit 121 is closed during which the external circuit 119 remains open;
The SOC of individual electrodes is measured by methods of impedance spectroscopic techniques and extended Kalman filter based methods;
The Li+ is transferred between the cathode 109 and the CBE 113 based on the individual SOC of the electrodes measured;
The SOC of the full cell (SOCcen) is equal to the SOC of the anode (SOC ); and
e) The SOC of the cathode (SOC+) and SOC of the anode (SOC ) is equal to 100.
8. The capacity balancing lithium based battery cell as in 1 wherein the
capacity loss of a cell 100 occurs as a result of both positive capacity
fade (C+) as well as negative capacity fade (C ) such that the
dominant of the two phenomena decides whether the overall capacity
fade is positive or negative such that:
Capacity fade value greater than zero indicates a positive capacity fade (C+) during which excess recyclable Li+ resides within the electrodes and is transferred from the cathode 109 to the CBE 113; and
Capacity fade value less than zero indicates a negative capacity fade (C ) during which LF is lost due to SEI layer and by products formation as a result of side reactions and additional Li+ is transferred from the CBE 113 to the cathode 109 to compensate for the lost capacity.
9. The capacity balancing lithium based battery cell as in 1 wherein the
Capacity balancing of the cell 100 is performed at one or more
conditions specified:
After the first charge cycle;
At certain fixed intervals determined by the cell controller;
After prolonged exposure to high temperature environments; and
After a long idle period.
10. A Capacity balancing method of lithium based battery cell 100
consisting of an additional capacity balancing electrode CBE 113
apart from the usual cathode 109 and anode 103 that helps the cell
regain its lost capacity and remove its excess capacity providing an ex-situ technique of capacity balancing of the cell to enhance performance and longevity of the cell comprising (a) the cell 100, (b) an anode current collector film 101, (c) the anode 103, (d) one or more separator films 105, 111, 117 (e) a porous foam based cathode substrate 107, (f) the primary cathode 109, (g) the capacity balancing electrode (CBE) 113, (h) a CBE current collector 115, (i) an external circuit 119, and (j) an alternate circuit 121 having the steps of:
Closing the alternate circuit 121 during which the external circuit 119 remains open;
Measuring the SOC individual electrodes by methods of impedance spectroscopic techniques and extended Kalman filter based methods;
Transferring the Li+ between the cathode 109 and the CBE 113 based on the individual SOC of the electrodes measured;
Making the SOC of the full cell (SOCceii) equal to the SOC of the anode (SOC );
Checking if SOC of the cathode (SOC+) and SOC of the anode (SOC) is equal to 100; and
Deciding whether the overall capacity fade is positive or negative by determining the capacity loss of the cell 100.
11. The capacity balancing method of lithium based battery cell as in 10
wherein the overall capacity fade is positive or negative is decided by
checking value of capacity fade is greater than zero and:
a) Indicating a positive capacity fade (C+), and transferring excess
recyclable Li+ from the cathode 109 to the CBE 113, if the value is
greater than zero; and
b) Indicating a negative capacity fade (C ) and transferring the lost Li+ from the CBE 113 to the cathode 109, if the value less than zero.