Refilled negative electrodes for secondary batteries

Abstract

To provide a secondary battery capable of recovering capacity lost due to SEI formation or the like.SOLUTION: A method for activating a secondary battery including a negative electrode having anode active silicon or an alloy thereof, a positive electrode, and a microporous separator impregnated with a carrier ion-containing electrolyte between the negative electrode and the positive electrode includes transporting carrier ions from the positive electrode to the negative electrode to at least partially charge the secondary battery, and transporting carrier ions from the auxiliary electrode to the positive electrode to give the secondary battery a positive electrode discharge end voltage Vpos,eod and a negative electrode discharge end voltage Vneg,eod when the cell is at a predetermined Vcell,eod value. The Vpos,eod value corresponds to the voltage when the state of charge of the positive electrode is at least 95% of its coulombic capacity, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates generally to methods for refilling energy storage devices and to refilled energy storage devices, such as secondary batteries. [Background technology]

[0002] In a rocking chair battery cell, both the positive and negative electrodes have a material into which carrier ions, such as lithium, can be inserted and extracted. When the cell is discharged, carrier ions are extracted from the negative electrode and inserted into the positive electrode. When the cell is charged, the reverse process occurs; carrier ions are extracted from the positive electrode and inserted into the negative electrode.

[0003] Silicon has become a promising candidate to replace carbonaceous materials as the anode for ultra-high capacity secondary batteries. A large volume increase of over 300% has been observed in bulk silicon upon insertion of carrier ions (e.g., lithium ions). This volume increase, together with cracking and shattering associated with charge-discharge cycling, has practically limited the use of bulk silicon anodes.

[0004] When an energy storage device such as a secondary battery is assembled, the amount of carrier ions available to circulate between the anode and cathode is often initially provided to the cathode, since cathode active materials such as lithium cobalt oxide are relatively stable (e.g., against oxidation) in ambient air compared to lithiated anode materials such as lithiated graphite. When a secondary battery is charged for the first time, carrier ions are extracted from the cathode and introduced into the anode. As a result, the anode potential is significantly lowered (towards the potential of the metal carrier ions) and the cathode potential is further raised (becomes more positive). These changes in potential can cause parasitic reactions on both electrodes, but sometimes more significant reactions on the anode. For example, decomposition products containing lithium (or other carrier ions) and electrolyte components, known as solid electrolyte interphases (SEI), easily form on the surface of carbon anodes. These surface or coating layers are carrier ion conductors that establish ionic bonds between the anode and the electrolyte and prevent further reactions from proceeding.

[0005] Although the formation of the SEI layer is necessary for the stability of the half-cell system including the anode and electrolyte, some of the carrier ions introduced into the cell through the cathode are irreversibly bound and therefore removed from the cyclic operation, i.e., from the capacity available to the user. As a result, during the first discharge, fewer carrier ions are transferred back from the anode to the cathode than were initially provided by the cathode during the first charge operation, resulting in irreversible capacity loss. During each subsequent charge-discharge cycle, the capacity loss due to mechanical and / or electrical degradation to the anode and / or cathode tends to be much less per cycle. However, even if the loss of carrier ions per cycle is relatively small, the energy density and cycle life are significantly reduced as the battery ages. In addition, chemical and electrochemical degradation can occur on the electrodes, causing capacity loss.

[0006] Among the various aspects of the present disclosure is the provision of energy storage devices, such as secondary batteries, fuel cells, and electrochemical capacitors, in which capacity lost as a result of SEI formation and / or mechanical or electrical degradation of the negative and / or positive electrodes can be restored. Advantageously, the energy storage devices of the present disclosure provide extended cycle life, enhanced energy density, and / or increased discharge rates. Summary of the Invention

[0007] Briefly, therefore, one aspect of the present disclosure relates to a method for compensating for loss of carrier ions due to the formation of a solid electrolyte interphase in a secondary battery during an initial or subsequent charging cycle of the battery. The secondary battery comprises a negative electrode, a positive electrode, a microporous separator between the negative electrode and the positive electrode, impregnated with a carrier ion-containing electrolyte in ionic contact with the negative electrode and the positive electrode, and a control unit programmed to cycle the secondary battery between a predetermined cell end-of-charge voltage Vcell,eoc value and a predetermined cell end-of-discharge voltage Vcell,eod value; the negative electrode comprises an anode-active silicon or an alloy of the anode-active silicon and has a coulombic capacity for the carrier ions; the positive electrode includes a cathode active material and has a coulombic capacity for the carrier ions; The coulombic capacity of the negative electrode exceeds the coulombic capacity of the positive electrode. The above method is using an auxiliary electrode including a source of carrier ions and electrolytically coupled to the negative electrode and the positive electrode through the separator, while measuring the voltage of the positive electrode relative to the auxiliary electrode and the voltage of the negative electrode relative to the auxiliary electrode; (i) transporting carrier ions from the positive electrode to the negative electrode during a first or subsequent charging cycle to at least partially charge the secondary battery, thereby forming a solid electrolyte interphase at a surface of the negative electrode during such transport; the above Through the separator the above When the cell is at the predetermined Vcell,eod value, the positive electrode For the auxiliary electrodeDischarge end voltage Vpos,eod, the negative electrode For the auxiliary electrode and (ii) transporting the positive electrode to a discharge end voltage Vneg,eod, the value of Vpos,eod corresponding to a voltage at which the state of charge of the positive electrode is at least 95% of the coulombic capacity of the positive electrode, and until Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0008] Another aspect of the present disclosure is a method for activating a secondary battery. The secondary battery has a negative electrode, a positive electrode, a microporous separator between the negative electrode and the positive electrode, impregnated with a carrier ion-containing electrolyte in ionic contact with the negative electrode and the positive electrode, and a control unit; the positive electrode comprises a cathode active material and has a reversible coulombic capacity for the carrier ions; The negative electrode comprises anodically active silicon or an alloy of the anodically active silicon and has a reversible coulombic capacity for the carrier ions that exceeds the coulombic capacity of the positive electrode. The above method is (i) transporting carrier ions from the positive electrode to the negative electrode to at least partially charge the secondary battery, during which a solid electrolyte interphase is formed on a surface of the negative electrode; (ii) after step (i), transporting carrier ions from the auxiliary electrode to said positive electrode; (iii) after step (ii), transporting carrier ions from the positive electrode to the negative electrode to charge the secondary battery; and (iv) programming the control unit to set a cell discharge end voltage, Vcell,eod; The activated secondary battery is characterized in that it has a positive electrode end-of-discharge voltage Vpos,eod and a negative electrode end-of-discharge voltage Vneg,eod when the cell is at Vcell,eod, the value of Vpos,eod corresponding to the voltage at which the positive electrode state of charge is at least 95% of its coulombic capacity, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0009] Another aspect of the present disclosure is a method for charging a secondary battery. The secondary battery has a negative electrode, a positive electrode, and a microporous separator between the negative electrode and the positive electrode, the microporous separator being impregnated with a carrier ion-containing electrolyte in ionic contact with the negative electrode and the positive electrode; The negative electrode comprises an anode active silicon or an alloy of the anode active silicon, The positive electrode comprises a cathode active material, The ratio of the coulombic capacity of the negative electrode to the coulombic capacity of the positive electrode, in that order, is at least 1.2:1. The above method is (i) transporting carrier ions from an auxiliary electrode to the positive electrode; and (ii) charging the negative electrode with the carrier ions transported from the auxiliary electrode to the positive electrode, thereby charging the secondary battery; The charged secondary battery has a discharge end voltage Vcell,eod and a negative electrode discharge end voltage Vneg,eod, and is characterized in that when Vcell,eod is reached, Vneg,eod is less than 0.9 V (vs. Li) and at least 0.4 V (vs. Li).

[0010] Another aspect of the present disclosure is a secondary battery having a negative electrode, a positive electrode, a microporous separator between the negative electrode and the positive electrode and impregnated with a carrier ion-containing electrolyte in ionic contact with the negative electrode and the positive electrode, and a control unit. The positive electrode includes a cathode active material and has a coulombic capacity for the carrier ions. The negative electrode comprises anodically active silicon or an alloy of the anodically active silicon and has a coulombic capacity for the carrier ions that exceeds the coulombic capacity of the positive electrode. The control unit includes a controller and a sensor electrically coupled to the controller; The sensor measures a cell voltage of the secondary battery during operation of the secondary battery, and detects a source of carrier ions in the negative electrode through the separator. and the positive electrode to a removable auxiliary electrode electrolytically bonded to the positive electrode and the negative electrode relative to the auxiliary electrode. The device is configured to measure a voltage The controller is programmed to perform a charge / discharge cycle between a predetermined cell charging end voltage Vcell,eoc value and a predetermined cell discharging end voltage Vcell,eod value, i.e., to terminate the charging operation of the secondary battery when a cell charging end voltage Vcell,eoc is detected, and to terminate the discharging operation of the secondary battery when a cell discharging end voltage Vcell,eod is detected. moreover, During a first or subsequent charging cycle, carrier ions are transported from the positive electrode to the negative electrode to at least partially charge the secondary battery, forming a solid electrolyte interphase at the surface of the negative electrode during the transport; and When the cell is at the predetermined Vcell,eod value, the positive electrode is charged by carrier ion transport from the removable auxiliary electrode. For the auxiliary electrode Discharge end voltage Vpos,eod, the negative electrode is For the auxiliary electrode Each of the positive electrodes has an end-of-discharge voltage Vneg,eod, the value of Vpos,eod corresponding to a voltage at which the state of charge of the positive electrode is at least 95% of the coulombic capacity of the positive electrode, and the Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0011] Other objects and features will be in part apparent and in part pointed out hereinafter. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 shows a typical charge / discharge cycle for a silicon-containing negative electrode.

[0013] [Figure 1A] FIG. 2 shows a typical charge / discharge cycle for a positive electrode matched to a silicon-containing electrode with the discharge capacity of the silicon-containing electrode of FIG.

[0014] [Diagram 2] FIG. 1 shows a typical charge / discharge cycle for a silicon-containing negative electrode.

[0015] [Figure 2A] FIG. 3 shows a typical charge / discharge cycle for a positive electrode matched to a silicon-containing electrode with the discharge capacity of the silicon-containing electrode of FIG.

[0016] [Diagram 3] FIG. 1 shows a typical charge / discharge cycle for a silicon-containing negative electrode.

[0017] [Figure 3A] FIG. 4 shows a typical charge / discharge cycle for a positive electrode matched to a silicon-containing electrode with the discharge capacity of the silicon-containing electrode of FIG.

[0018] [Figure 4] FIG. 1 shows a typical charge / discharge cycle for a silicon-containing negative electrode.

[0019] [Figure 4A] FIG. 5 shows a typical charge / discharge cycle for a positive electrode matched to a silicon-containing electrode with the discharge capacity of the silicon-containing electrode of FIG.

[0020] [Diagram 5] 1 is a schematic diagram showing a secondary battery according to an embodiment of the present disclosure.

[0021] [Figure 6] FIG. 2 is a schematic diagram showing a secondary battery according to another embodiment of the present disclosure.

[0022] [Figure 7] FIG. 2 is a schematic diagram showing a secondary battery according to another embodiment of the present disclosure.

[0023] [Figure 8] FIG. 2 is an exploded view of a secondary battery according to an embodiment of the present disclosure.

[0024] [Figure 9] FIG. 8 is a schematic diagram showing an electrode assembly included in the secondary battery of FIG. 7, partially cut away to reveal the internal structure.

[0025] [Figure 10] FIG. 2 is an exploded view of a secondary battery according to another embodiment of the present disclosure.

[0026] [Figure 11] FIG. 2 is a schematic diagram of an electrode assembly according to another embodiment included in a secondary battery of the present disclosure.

[0027] [Figure 12] FIG. 2 is a schematic diagram of another embodiment of an electrode assembly stack included in a secondary battery of the present disclosure.

[0028] Corresponding reference characters indicate corresponding parts throughout the drawings. [Definition]

[0029] As used herein, "a," "an," and "the" (i.e., singular) refer to plural referents unless the context clearly dictates otherwise. For example, in one example, a reference to "an electrode" includes both a single electrode and a plurality of similar electrodes. The terms "comprising," "including," and "having" are inclusive and mean that there may be additional elements other than the listed elements.

[0030] As used herein, "about" and "approximately" refer to ±10%, 5%, or 1% of the stated value. For example, in one example, about 250 μm includes 225 μm to 275 μm. As a further example, in one example, about 1000 μm includes 900 μm to 1100 μm. Unless otherwise indicated, all numbers expressing quantities (e.g., measurements, etc.) used in the specification, claims, etc. should be understood in all instances as being modified by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and the appended claims are approximations. Each numerical parameter should be construed at least in accordance with the number of reported significant digits and by applying ordinary rounding techniques.

[0031] "State of charge" as used herein in the context of the state of a secondary battery refers to a state in which a secondary battery is charged to at least 75% of its rated capacity. For example, the battery may be charged to at least 80% of the rated capacity, at least 90% of the rated capacity, at least 95% of the rated capacity, up to 100% of the rated capacity, etc.

[0032] As used herein, the term "discharge capacity" in relation to the negative electrode means the amount of carrier ions available for extraction from the negative electrode and insertion into the positive electrode during a battery discharge operation, between a predetermined set of cell end-of-charge and end-of-discharge voltage limits.

[0033] As used herein in the context of the state of a secondary battery, a "discharged state" refers to a state in which a secondary battery is discharged to less than 25% of its rated capacity. For example, the battery may be discharged to less than 20% of the rated capacity, less than 10% of the rated capacity, less than 5% of the rated capacity, 0% of the rated capacity, etc.

[0034] "Rated capacity" as used herein in the context of secondary batteries refers to the ability of a secondary battery to deliver current over a measured period of time under standard temperature conditions (25°C). For example, rated capacity may be measured in ampere-hours (Ah) by determining the current output for a specified time, or by determining the time for which that current can be output for a specified current, and taking the product of the current and time. For example, for a battery rated for 20 amp-hours, when the current is specified for the rating at 2 amps, the battery may be understood to provide that current output for 10 hours. Conversely, if the time is specified for the rating at 10 hours, the battery may be understood to output 2 amps for 10 hours.

[0035] The term "reversible coulombic capacity" as used herein in reference to an electrode (i.e., positive electrode, negative electrode, or auxiliary electrode) means the total capacity of the electrode for carrier ions available for reversible exchange with the counter electrode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Among the various aspects of the present disclosure, it may be noted that the cell design and formation methods for secondary batteries provide various advantages including, for example, improved cycle life, greater energy density, greater charge rate, and / or greater discharge rate. Generally, secondary batteries have cell voltage limits for the charge-discharge cycles of the secondary battery, the positive electrode (cathode) and the negative electrode (anode), and the reversible coulombic capacity of the positive electrode is matched to the discharge capacity of the negative electrode after formation of the battery (i.e., after the first charge / discharge cycle).

[0037] As mentioned above, the formation of a solid electrolyte interphase (SEI) during the first charge / discharge cycle reduces the amount of carrier ions available for reversible cycling. Mechanical and / or electrical degradation during cycling of the battery can further reduce the amount of carrier ions available for reversible cycling. Therefore, to compensate for the formation of the SEI (or other carrier ion consumption mechanisms such as mechanical and / or electrical degradation of the negative electrode), additional or supplemental carrier ions can be provided from an auxiliary electrode after formation of the battery.

[0038] In general, a secondary battery and the voltage limits of the positive and negative electrodes of that secondary battery are related as follows. Vcell,eoc = Vpos,eoc - Vneg,eoc [1] Vcell,eod = Vpos,eod - Vneg,eod [2] Here, Vcell,eoc is the end-of-charge voltage for the cell, Vpos,eoc is the end-of-charge voltage for the positive electrode, Vneg,eoc is the end-of-charge voltage for the negative electrode, Vcell,eod is the end-of-discharge voltage for the cell, Vpos,eod is the end-of-discharge voltage for the positive electrode, and Vneg,eod is the end-of-discharge voltage for the negative electrode.

[0039] In general, Vcell,eoc is a maximum in that the cell voltage is ideally always below this value, while Vcell,eod is a minimum in that the cell voltage is ideally always above this value. By design, the cell voltage limits, Vcell,eoc and Vcell,eod, are fixed for the life of the battery, while the voltage limits of the individual electrodes may vary. Thus, as used herein, it should be understood that the specification of the positive and negative electrode voltage limits at the end of charge or end of discharge refers to a charge or discharge cycle after formation of the battery, i.e., after the first charge / discharge cycle.

[0040] The end-of-charge voltage Vpos,eoc for positive active materials used in secondary batteries is at most 5V (vs. Li), typically in the range of about 4.3V to 4.5V (vs. Li), and the end-of-discharge voltage Vpos,eod for positive active materials typically used in secondary batteries is typically at least 2.5V (vs. Li). For silicon-containing negative electrodes, the end-of-charge voltage Vneg,eoc is typically 0.1V (vs. Li), and the end-of-discharge voltage is a design choice programmed and controlled by the battery's control unit. Thus, according to equations [1] and [2], the cell end-of-charge voltage Vcell,eoc for cells containing such materials is typically at least about 4.2V, at least about 4.4V (vs. Li), or greater. The cell discharge end voltage Vcell,eod for such materials typically has a value determined by the difference between 2.5V and Vneg,eod (vs. Li) (ie, Vcell,eod=2.5V−Vneg,eod).

[0041] In one embodiment of the present disclosure, when the secondary battery reaches the cell discharge end voltage Vcell,eod during the discharge cycle of the secondary battery (after the initial charge / discharge cycle in which the SEI is formed), the negative electrode discharge end voltage Vneg,eod is less than 0.9V (vs. Li) and greater than 0.4V (vs. Li). Thus, for example, in one such embodiment, when the secondary battery reaches the cell discharge end voltage Vcell,eod during the discharge cycle of the secondary battery (i.e., when the battery is under a discharge load), the negative electrode discharge end voltage Vneg,eod is in the range of about 0.5V (vs. Li) to about 0.8V (vs. Li). As a further example, in one such embodiment, when the secondary battery reaches the cell discharge end voltage Vcell,eod during the discharge cycle of the secondary battery (i.e., when the battery is under a discharge load), the negative electrode discharge end voltage Vneg,eod is in the range of about 0.6V (vs. Li) to about 0.8V (vs. Li). In one such embodiment, when the secondary battery reaches the cell discharge end voltage Vcell,eod during the secondary battery's discharge cycle (i.e., when the battery is under a discharge load), the negative electrode discharge end voltage Vneg,eod is in the range of about 0.6 V (vs. Li) to about 0.7 V (vs. Li).

[0042] 1-4 show exemplary charge / discharge cycles for silicon-containing negative electrodes. The silicon-containing negative electrodes have a charge cut-off voltage Vneg,eoc of 0.1 V (vs. Li) and a discharge cut-off voltage Vneg,eod of 0.9 V (FIG. 1), 0.8 V (FIG. 2), 0.7 V (FIG. 3), or 0.6 V (FIG. 4) (vs. Li). The discharge capacity of the silicon-containing electrodes having these charge / discharge limits is given by Ca (FIG. 1), Cb (FIG. 2), Cc (FIG. 3), and Cd (FIG. 4). Comparing the discharge capacity of the silicon-containing electrodes illustrated in each of FIGS. 1-4, it can be observed that the discharge capacity of the electrodes decreases as the value of the discharge cut-off voltage Vneg,eod decreases (when the reversible coulombic capacity is constant).

[0043] As shown in Figures 1-4, an end-of-discharge voltage value of less than 0.4V (vs. Li) reduces the overall cell energy density and is less preferred. A Vneg,eod value of at least 0.9V (vs. Li) significantly improves the overall cell energy density, but tends to reduce cycle life and is generally less preferred. According to one aspect of the present disclosure, the end-of-discharge voltage Vneg,eod for a lithium-ion battery including a silicon-containing electrode is less than 0.9V (vs. Li). For example, in one such embodiment, Vneg,eod does not exceed 0.8V (vs. Li). As a further example, in one such embodiment, Vneg,eod does not exceed 0.7V (vs. Li). As a further example, in one such embodiment, Vneg,eod does not exceed 0.6V (vs. Li). As a further example, in one such embodiment, Vneg,eod does not exceed 0.5V (vs. Li). In one such exemplary embodiment, Vneg,eod is greater than 0.4V but less than 0.9V relative to Li. By way of further example, in one such embodiment, Vneg,eod is in the range of about 0.5V to about 0.8V relative to Li. By way of further example, in one such embodiment, Vneg,eod is in the range of about 0.6V to about 0.8V relative to Li. In one such exemplary embodiment, Vneg,eod is in the range of about 0.6V to about 0.7V relative to Li.

[0044] In general, the positive electrode of the secondary battery of the present disclosure preferably has a reversible coulombic capacity that matches the discharge capacity of the negative electrode. In other words, the cathode is sized to have a reversible coulombic capacity that corresponds to the discharge capacity of the negative electrode, which in turn is a function of the negative electrode end-of-discharge voltage Vneg,eod (see Figures 1-4). For example, with reference to Figures 1A-4A, the reversible coulombic capacity of a positive electrode sized to match the discharge capacity of a negative electrode having the end-of-discharge voltage limits of Figures 1-4 is given by Ce (Figure 1A), Cf (Figure 2A), Cg (Figure 3A) and Ch (Figure 4A). Comparing Figures 1A-4A, the reversible coulombic capacity of the positive electrode matched to the discharge capacity of the negative electrode decreases as the value of the end-of-discharge voltage Vneg,eod for the negative electrode (which has a constant reversible coulombic capacity) decreases.

[0045] In one embodiment, the reversible capacity of the positive electrode is matched to the discharge capacity of the negative electrode, such that when Vcell,eod is reached, the positive electrode has a Vpos,eod value corresponding to a voltage at which the positive electrode's state of charge is at least 95% of its reversible coulombic capacity, and Vneg,eod is at least 0.4V (vs. Li) but less than 0.9V (vs. Li). For example, in one such embodiment, when Vcell,eod is reached, the positive electrode has a Vpos,eod value corresponding to a voltage at which the positive electrode's state of charge is at least 96% of its reversible coulombic capacity, and Vneg,eod is at least 0.4V (vs. Li) but less than 0.9V (vs. Li). By way of further example, in one such embodiment, when Vcell,eod is reached, the positive electrode has a Vpos,eod value corresponding to a voltage at which the positive electrode's state of charge is at least 97% of its reversible coulombic capacity, and Vneg,eod is at least 0.4V (vs. Li) but less than 0.9V (vs. Li). By way of further example, in one such embodiment, when Vcell,eod is reached, the positive electrode has a Vpos,eod value corresponding to a voltage at which the positive electrode's state of charge is at least 98% of its reversible coulombic capacity, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li). By way of further example, in one such embodiment, when Vcell,eod is reached, the positive electrode has a Vpos,eod value corresponding to a voltage at which the positive electrode's state of charge is at least 99% of its reversible coulombic capacity, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0046] According to one aspect of the present disclosure, the negative electrode is designed to have a reversible coulombic capacity that significantly exceeds the reversible coulombic capacity of the positive electrode. For example, in one embodiment, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in this order, is at least 1.2:1. As a further example, in one embodiment, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in this order, is at least 1.3:1. As a further example, in one embodiment, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in this order, is at least 2:1. As a further example, in one embodiment, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in this order, is at least 3:1. As a further example, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in this order, is at least 4:1. As a further example, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 5:1. Advantageously, the excess coulombic capacity of the negative electrode provides a source of anode active material to allow the battery to operate reversibly within a certain voltage that inhibits the formation of crystalline phases (containing carrier ions) on the negative electrode. Crystalline phases on the negative electrode reduce the cycle life of the negative electrode (and therefore the battery) as a result of cycling the battery. Furthermore, the excess anode coulombic capacity and the reduced voltage of the negative electrode upon discharge provide a battery with a higher energy density (as a result of a higher average voltage).

[0047] In general, the carrier ion may be any carrier ion suitable for use in a secondary battery. In one preferred exemplary embodiment, the secondary battery utilizes carrier ions selected from, for example, lithium ions, sodium ions, potassium ions, calcium ions, magnesium ions, and aluminum ions, which circulate between the member elements of the population of the electrode and the counter electrode as the secondary battery is charged and discharged. For example, in one such embodiment, the carrier ion is a lithium ion. As a further example, in another such embodiment, the carrier ion may be a magnesium ion. As a further example, in another such embodiment, the carrier ion may be an aluminum ion.

[0048] Referring now to FIG. 5, there is illustrated one embodiment of a two-dimensional battery of the present disclosure, generally designated 10. Battery 10 includes within battery enclosure 11 at least one positive electrode structure 20, at least one negative electrode structure 22, an auxiliary electrode 24 that may be selectively electrically connected or coupled (e.g., by switch 32) to positive electrode structure 20, and a control unit (not shown). Auxiliary electrode 24 is shown in the headspace of battery 10, but may be provided elsewhere as desired. Tabs 26, 28, 30 allow the positive, negative, and auxiliary electrodes to be connected to battery terminals (not shown) for connection to an energy source or consumer, and switch 32 allows electrical connection between positive electrode structure 20 and auxiliary electrode 24. The control unit includes sensors for sensing cell voltage (i.e., voltage between the positive and negative electrodes) as well as sensing the voltage of the positive, negative, or both positive and negative electrodes relative to the auxiliary electrode. The control unit further includes a controller that controls the charge and discharge cycles of the battery in response to the voltage sensed by the sensor.

[0049] Battery enclosure 11 may be constructed from any of a range of materials conventionally employed in secondary batteries. For example, in one embodiment, battery enclosure 11 may be constructed from a plastic material or a plastic foil laminate material (e.g., aluminum foil intermediate layers of polyolefin and polyester). Alternatively, battery enclosure 11 may be constructed from stainless steel, titanium, aluminum, or other metals or alloys thereof.

[0050] In one embodiment, the positive electrode structure 20 includes any of a range of cathode active materials capable of storing lithium or other carrier ions. For example, the positive electrode may selectively use cathode active materials selected from transition metal oxides, transition metal sulfides, transition metal nitrides, lithium transition metal oxides, lithium transition metal sulfides, and lithium transition metal nitrides. The transition metal elements of these transition metal oxides, transition metal sulfides, and transition metal nitrides may include metal elements with d-shells or f-shells. Specific examples of such metal elements are Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pb, Pt, Cu, Ag, and Au. Additionally, the cathode active materials may include LiCoO2, LiNi 0.5 Mn 1.5 O4, Li(Ni x Co yExamples of cathode active materials include Al2)O2, LiFePO4, Li2MnO4, V2O5, molybdenum oxysulfide, phosphates, silicates, and vanadates, and combinations thereof. The cathode active materials may be deposited to form the positive electrode structure by any of a range of techniques, including, for example, electrophoretic deposition, electrodeposition, co-deposition, or slurry deposition. In an exemplary embodiment, one or a combination of the aforementioned cathode active materials are electrophoretically deposited in particulate form. In another exemplary embodiment, a cathode active material such as V2O5 is electrodeposited. In another exemplary embodiment, one or a combination of the aforementioned cathode active materials are co-deposited in particulate form into a conductive matrix such as polyaniline. In another exemplary embodiment, one or a combination of the aforementioned cathode active materials are slurry deposited in particulate form.

[0051] The negative electrode structure 22 includes a silicon-containing anode active material. In one embodiment, the negative electrode structure 22 includes silicon, a silicon alloy, a mixture of silicon with other anode active materials, a mixture of silicon with electrochemically inactive materials, or a combination thereof. For example, in one exemplary embodiment, the negative electrode structure 22 includes silicon, or a combination of silicon with carbon, germanium, selenium, nickel copper, tin, manganese, bismuth, silver, gold, zinc, lead, and / or lead. By way of further example, in one such exemplary embodiment, the negative electrode structure 22 includes silicon, silicon and germanium, silicon and carbon, silicon and selenium, silicon, selenium and carbon, a mixture of silicon with nickel and / or copper, or a combination thereof. In one exemplary embodiment, the negative electrode structure 22 includes silicon or an oxide or nitride thereof, a fluoride thereof, or other alloy thereof. In another exemplary embodiment, the negative electrode structure 22 includes silicon or an alloy thereof. In each of the embodiments and embodiments described in this paragraph, the negative electrode structure 22 may be a granular aggregate electrode or a monolithic electrode. The negative electrode structure 22 may be formed or otherwise fabricated using methods such as electrodeposition, electrophoretic deposition, vapor deposition, catalyst-based growth such as vapor-liquid-solid techniques, gel casting, tape casting, patterning and slurry deposition, and subsequently densified by methods such as sintering, bonding, and the like.

[0052] In one embodiment, the anode structure 22 includes a microstructured silicon-containing active material having a significant void volume fraction to accommodate volume expansion and contraction as carrier ions are incorporated into or leave the anode structure 22 during charge and discharge cycles. In general, the void volume fraction of the anode active material is 0.1 or more. Typically, however, the void volume fraction of the anode active material is 0.8 or less. For example, in one embodiment, the void volume fraction of the anode active material is about 0.15 to about 0.75. As a further example, in one embodiment, the void volume fraction of the anode active material is about 0.2 to about 0.7. As a further example, in one embodiment, the void volume fraction of the anode active material is about 0.25 to about 0.6.

[0053] Depending on the composition of the microstructured anode active material and its method of formation, the microstructured anode active material may comprise a macroporous, microporous or mesoporous material layer, or a combination thereof, such as, for example, microporous and mesoporous, or mesoporous and macroporous. Microporous materials are typically characterized by pore dimensions of less than 10 nm, wall dimensions of less than 10 nm, pore depths of 1-50 micrometers, and pore morphology generally characterized by a "spongy" irregular appearance, non-smooth walls, and branched pores. Mesoporous materials are typically characterized by pore dimensions of 10-50 nm, wall dimensions of 10-50 nm, pore depths of 1-100 micrometers, and pore morphology generally characterized by more or less well-defined branched or dendritic pores. Macroporous materials are typically characterized by pore dimensions greater than 50 nm, wall dimensions greater than 50 nm, pore depths between 1 and 500 micrometers, and pore morphologies that can be linear, branched, or dendritic, and smooth or rough-walled. Furthermore, the void volume can include open or closed voids, or a combination thereof. In one embodiment, the void volume includes open voids. That is, the anode active material includes voids that have openings on the side of the anode active material (i.e., the surface facing the separator and the cathode active material). Through the voids, lithium ions (or other carrier ions) can enter or leave the anode active material. For example, lithium ions can enter the anode active material through the void openings after leaving the cathode active material. In another embodiment, the void volume includes closed voids. That is, the anode active material includes voids that are surrounded by the anode active material. In general, open porosity provides a larger interfacial surface area for carrier ions, whereas closed porosity tends to be less susceptible to solid electrolyte interlayer ("SEI"). Together, open and closed porosity each provide room for the anode active material to expand upon intrusion of carrier ions. Thus, in certain embodiments, it is preferred that the anode active material include a combination of open and closed porosity.

[0054] In one embodiment, the anode structure 22 comprises porous silicon or an alloy thereof. The porous silicon layer may be formed, for example, by anodization, etching (e.g., by depositing a precious metal such as gold, platinum, silver or gold / palladium on the (100) face of single crystal silicon and etching the surface with a mixture of hydrofluoric acid and hydrogen peroxide), or other methods known in the art such as patterned chemical etching. Additionally, the porous anode active material generally has a void volume fraction of at least about 0.1 but less than 0.8, as discussed above.

[0055] In another embodiment, the anode structure 22 includes fibers of silicon or alloys thereof. The individual fibers can have a diameter (thickness dimension) of about 5 nm to about 10,000 nm. The silicon fibers (nanowires) can be formed by chemical vapor deposition or other techniques known in the art, such as, for example, vapor-liquid-solid (VLS) growth and solid-liquid-solid (SLS) growth. Additionally, the anode active material 22 generally has a void volume fraction of at least about 0.1 but less than 0.8, as previously described.

[0056] In one embodiment, the positive and negative electrodes are dimensioned such that the reversible coulombic capacity of the negative electrode is at least 120% of the reversible coulombic capacity of the positive electrode when cycled against a reference electrode after formation. For example, in one such embodiment, the positive and negative electrodes are dimensioned such that the reversible coulombic capacity of the negative electrode is at least 130% of the reversible coulombic capacity of the positive electrode when cycled against a reference electrode after formation. As a further example, in one such embodiment, the positive and negative electrodes are dimensioned such that the reversible coulombic capacity of the negative electrode is at least 200% of the reversible coulombic capacity of the positive electrode when cycled against a reference electrode after formation. As a further example, in one such embodiment, the positive and negative electrodes are dimensioned such that the reversible coulombic capacity of the negative electrode is at least 300% of the reversible coulombic capacity of the positive electrode when cycled against a reference electrode after formation. By way of further example, in one such embodiment, the positive and negative electrodes are sized such that, after formation, the reversible coulombic capacity of the negative electrode is at least 400% of the reversible coulombic capacity of the positive electrode when cycled against a reference electrode. By way of further example, in one such embodiment, the positive and negative electrodes are sized such that, after formation, the reversible coulombic capacity of the negative electrode is at least 500% of the reversible coulombic capacity of the positive electrode when cycled against a reference electrode. By way of further example, in one such embodiment, the positive and negative electrodes are sized such that, after formation, the reversible coulombic capacity of the negative electrode is about 120% to about 175% of the reversible coulombic capacity of the positive electrode, or about 120% to about 150% of the reversible coulombic capacity of the positive electrode when cycled against a reference electrode.

[0057] The positive and negative electrode structures 20, 22 may be provided as flat or planar components of the battery 10, and may be wound in a spiral or other configuration, or may be provided in a folded form. For example, the electrodes may be wound around a relatively rectangular mandrel to form an elliptically wound coil for insertion into a relatively prismatic battery case.

[0058] The auxiliary electrode comprises a source of carrier ions to replenish lost energy capacity after the formation of the battery (i.e., to compensate for the loss of carrier ions during the formation of the SEI and other carrier ion losses during the first charge and / or discharge cycle). The auxiliary electrode can comprise a foil of carrier ions in metallic form (e.g., lithium, magnesium or aluminum foil), or any of the aforementioned positive or anode active materials in their carrier ion-containing forms. For example, the auxiliary electrode can comprise lithiated silicon or lithiated silicon alloy. The auxiliary electrode is formed by placing an electrode made of the desired material in an inactive area of ​​the battery cell, but still electrolytically bonded to the negative and / or positive electrodes through the separator. Alternatively, the auxiliary electrode can be formed by depositing the desired auxiliary electrode material using techniques such as electrochemical deposition, electroless deposition, electrophoretic deposition, vacuum-assisted filling, stencil-assisted filling, dip coating, and the like.

[0059] In one embodiment, the auxiliary electrode is dimensioned to provide at least 15% of the reversible coulombic capacity of the positive electrode. For example, in one such embodiment, the auxiliary electrode is dimensioned to include sufficient carrier ions (e.g., lithium ions, magnesium ions, or aluminum ions) for it to provide at least 30% of the reversible coulombic capacity of the positive electrode. As a further example, in one such embodiment, the auxiliary electrode is dimensioned to include sufficient carrier ions for it to provide at least 100% of the reversible coulombic capacity of the positive electrode. As a further example, in one such embodiment, the auxiliary electrode is dimensioned to include sufficient carrier ions for it to provide at least 200% of the reversible coulombic capacity of the positive electrode. As a further example, in one such embodiment, the auxiliary electrode is dimensioned to include sufficient carrier ions for it to provide at least 300% of the reversible coulombic capacity of the positive electrode. As a further example, in one such embodiment, the auxiliary electrode is dimensioned to include sufficient carrier ions for it to provide about 100% to about 200% of the reversible coulombic capacity of the positive electrode.

[0060] Once the cell is assembled, it is charged by transporting carrier ions from the positive electrode to the negative electrode. When the positive electrode reaches the design value of Vpos,eoc, charging is stopped. During the initial charging cycle, the SEI easily forms on the surface of the negative electrode structure. Referring again to FIG. 5, to compensate for the loss of carrier ions to the SEI, the positive electrode structure 20 can be replenished by closing the switch 32 and applying a voltage between the auxiliary electrode 24 and the positive electrode structure 20 to transport carrier ions from the auxiliary electrode to the positive electrode. Once the transport of carrier ions from the auxiliary electrode to the positive electrode is completed, the negative electrode is charged again, this time with carrier ions transferred from the auxiliary electrode, until a Vcell,eoc value is reached. This typically corresponds to a Vneg,eoc value of 0.1 V and a Vpos,eoc value equal to the sum of Vcell and 0.1 V (vs. Li).

[0061] In yet another embodiment, the positive electrode can be replenished with carrier ions by simultaneously transporting carrier ions from the auxiliary electrode to the positive electrode while simultaneously transporting carrier ions from the auxiliary electrode to the positive electrode. Referring to FIG. 5, a voltage is applied between the positive electrode structure 20 and the negative electrode structure 22 to transport carrier ions from the positive electrode structure 20 to the negative electrode structure 22. While the carrier ions are being transported from the positive electrode structure 20 to the negative electrode structure 22, the switch 32 may be closed to apply a voltage between the auxiliary electrode 24 and the positive electrode structure 20 to transport carrier ions from the auxiliary electrode 24 to the positive electrode structure 20. In this manner, carrier ions are transported from the auxiliary electrode 24 to the positive electrode structure 20 at the same time that carrier ions are transported from the positive electrode structure 20 to the negative electrode. That is, a voltage sufficient to transport carrier ions from the auxiliary electrode 24 to the positive electrode structure 20 is maintained between the positive electrode structure 20 and the negative electrode structure 22 at the same time that a voltage sufficient to transport carrier ions from the auxiliary electrode to the positive electrode structure is maintained between the auxiliary electrode 24 and the positive electrode structure 20. In one embodiment, a voltage may be applied between the positive electrode structure 20 and the negative electrode structure 22 to start transporting carrier ions to the negative electrode structure at t0, and then at a time t1, which is a predetermined time later, the switch 32 may be closed to apply a voltage between the auxiliary electrode 24 and the positive electrode structure 20 to transport carrier ions to the positive electrode structure 20. That is, the start of transport of carrier ions from the positive electrode structure 20 to the negative electrode structure 22 begins at the initial time t0, the start of transport of carrier ions from the auxiliary electrode 24 to the positive electrode structure 20 begins at time t1, which is a predetermined time after time t0, and at times after time t1, carrier ions are transported from the auxiliary electrode 24 to the positive electrode structure 20 simultaneously with the transport of carrier ions from the positive electrode structure to the negative electrode structure 22. In another embodiment, the start of transport of carrier ions from the auxiliary electrode 24 to the positive electrode structure 20 may begin at time t0 simultaneously with the start of transfer of carrier ions from the positive electrode structure 20 to the negative electrode structure 22.Similarly, in one embodiment, the transport of carrier ions from the auxiliary electrode 24 to the positive electrode structure 20 is stopped at time t2, simultaneously with the time that the transport of carrier ions from the positive electrode structure 20 to the negative electrode structure 22 is stopped, and / or the transport of carrier ions from the auxiliary electrode 24 may be stopped at time t2, a predetermined time before time t3, at which the transport of carrier ions from the positive electrode structure 20 to the negative electrode structure 22 is stopped.

[0062] In one embodiment, the transport rate of carrier ions from the positive electrode structure 20 to the negative electrode structure 22 is equal to or greater than the transport rate of carrier ions from the auxiliary electrode 24 to the positive electrode structure 20, thereby allowing a good overall transport rate of carrier ions from the auxiliary electrode 24 to the negative electrode structure 22 through the positive electrode structure 20. That is, the relative transport rates between the positive electrode structure 20 and the negative electrode structure 22 and between the auxiliary electrode 24 and the positive electrode structure 20 can be maintained such that the overall capacity of the positive electrode structure 20 for additional carrier ions is not exceeded. In this manner, the positive electrode structure 20 can be maintained in a state capable of accepting new carrier ions from the auxiliary electrode 24, thereby allowing the continued transport of carrier ions to the negative electrode structure 22. For example, in one embodiment, the voltage applied between the positive electrode structure 20 and the negative electrode structure 22 and the voltage applied between the auxiliary electrode 24 and the positive electrode structure 20 are selected to provide a transport rate of carrier ions between the positive electrode structure 20 and the negative electrode structure 22 that is equal to or greater than the transport rate of carrier ions between the auxiliary electrode 24 and the positive electrode structure 20. The transport rate of carrier ions between the electrodes is related to the current between the electrodes, which can be measured, for example, using a sensor. Thus, in one example, the current between the auxiliary electrode 24 and the positive electrode structure 20 is smaller than the current between the positive electrode structure 20 and the negative electrode structure 22, reflecting a lower transport rate of carrier ions between the auxiliary electrode 24 and the positive electrode structure 20 compared to the transport rate of carrier ions between the positive electrode structure 20 and the negative electrode structure 22. For example, in one embodiment, the current between the auxiliary electrode 24 and the positive electrode structure 20 may be 80% or less of the current between the positive electrode structure 20 and the negative electrode structure 22. Furthermore, in one embodiment, the current between the auxiliary electrode 24 and the positive electrode structure 20 may be 60% or less of the current between the positive electrode structure 20 and the negative electrode structure 22. As yet another example, in one embodiment, the current between the auxiliary electrode 24 and the positive electrode structure 20 may be 50% or less of the current between the positive electrode structure 20 and the negative electrode structure 22. As yet another example, in one embodiment, the current between the auxiliary electrode 24 and the positive electrode structure 20 may be 30% or less of the current between the positive electrode structure 20 and the negative electrode structure 22 .As yet another example, in one embodiment, the current between the auxiliary electrode 24 and the positive electrode structure 20 may be 20% or less of the current between the positive electrode structure 20 and the negative electrode structure 22 .

[0063] In one embodiment, without being limited to a particular theory, carrier ions are transported from the auxiliary electrode 24 to the positive electrode structure 20 as part of the replenishment of the negative electrode structure 22 (as opposed to direct transport from the auxiliary electrode 24 to the negative electrode structure 22). This is because the positive electrode structure 20 can receive carrier ions uniformly across its surface, and therefore the carrier ions can participate more uniformly in their transport between the positive electrode structure 20 and the negative electrode structure 22. In contrast, for certain materials used to form the negative electrode structure 22, such as silicon-containing materials, direct transport of carrier ions from the auxiliary electrode 24 to the negative electrode structure 22 leads to a non-uniform accumulation of carrier ions on the surface of the negative electrode structure, such as on the surface of the negative electrode structure 22 closest to the auxiliary electrode 24. Thus, the ability of the accumulated carrier ions to participate uniformly in the transport between the positive electrode structure 20 and the negative electrode structure 22 during the charge and discharge process is limited. Thus, transporting carrier ions from the auxiliary electrode 24 to the positive electrode structure 20 allows for more uniform transport of carrier ions to the negative electrode structure 22, improving the overall performance of the battery having the replenished negative electrode structure 22.

[0064] In general, the amount of carrier ions transported from the auxiliary electrode to the positive electrode (and then, ultimately, the negative electrode) is sufficient to match the reversible capacity of the positive electrode to the discharge capacity of the negative electrode (wherein the negative electrode end-of-discharge voltage Vneg,eod is greater than 0.4 V (vs. Li) and less than 0.9 V (vs. Li) when the secondary battery reaches the cell discharge end-of-discharge voltage Vcell,eod). In one embodiment, the amount of carrier ions transported from the auxiliary electrode to the positive electrode is at least 10% of the reversible capacity of the positive electrode. For example, in one such embodiment, the amount of carrier ions transported from the auxiliary electrode to the positive electrode is at least 15% of the reversible coulombic capacity of the positive electrode. As a further example, in one such embodiment, the amount of carrier ions transported from the auxiliary electrode to the positive electrode is at least 20% of the reversible coulombic capacity of the positive electrode. As a further example, in one such embodiment, the amount of carrier ions transported from the auxiliary electrode to the positive electrode is at least 25% of the reversible coulombic capacity of the positive electrode. As a further example, in one such embodiment, the amount of carrier ions transported from the auxiliary electrode to the positive electrode is at least 30% of the reversible coulombic capacity of the positive electrode. As a further example, in one such embodiment, the amount of carrier ions transported from the auxiliary electrode to the positive electrode is at least 40% of the reversible coulombic capacity of the positive electrode. As a further example, in one such embodiment, the amount of carrier ions transported from the auxiliary electrode to the positive electrode is at least 50% of the reversible coulombic capacity of the positive electrode.

[0065] Referring again to FIG. 5, porous separators (not shown) are disposed between the positive electrode structure 20 and the negative electrode structure 22, and between the auxiliary electrode 24 and the positive electrode structure and / or the negative electrode structure. The porous separator material can include any of the porous materials conventionally used as secondary battery separators, including, for example, microporous polyethylene, polypropylene, TiO2-polymer composites, SiO2, Al2O3, and the like (P. Arora and J. Zhang, "Battery Separators," Chemical Reviews, 2004, vol. 104, pp. 4419-4462). Such materials can be deposited, for example, by electrophoretic deposition of a granular separator material, slurry deposition (including spin or spray coating) of a granular separator material, or sputter coating of an ionically conductive granular separator material. In one embodiment, the porous separator material comprises pores having a diameter of at least 50 Å, more typically about 2500 Å, and a void volume fraction in the range of about 25% to about 75%, more typically about 35 to 55%.

[0066] The porous separator material is impregnated with a non-aqueous electrolyte that serves as a medium for conducting carrier ions between the positive electrode, the negative electrode, and the auxiliary electrode. In general, the non-aqueous electrolyte may be any of a series of non-aqueous electrolytes suitable for use as secondary battery electrolytes. Typically, the non-aqueous electrolyte includes a salt of a carrier ion, such as a magnesium, aluminum, or lithium salt, dissolved in an organic solvent. Exemplary lithium salts include inorganic lithium salts such as LiClO4, LiBF4, LiPF6, LiAsF6, LiCl, LiBr, LiB(C6H5)4, LiN(SO2CF3)2, LiN(SO2CF3)3, LiNSO2CF3, LiNSO2CF5, LiNSO2C4F9, LiNSO2C5F 11 ,LiNSO2C6F 13 ,LiNSO2C7F 15Exemplary organic solvents for dissolving lithium salts include cyclic esters, linear esters, cyclic ethers, and linear ethers. Specific examples of cyclic esters include propylene carbonate, butylene carbonate, γ-butyrolactone, vinylene carbonate, 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, and γ-valerolactone. Specific examples of linear esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl butyl carbonate, methyl propyl carbonate, ethyl butyl carbonate, ethyl propyl carbonate, butyl propyl carbonate, alkyl propionates, dialkyl malonates, and alkyl acetates. Specific examples of cyclic ethers include tetrahydrofuran, alkyltetrahydrofuran, dialkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, and 1,4-dioxolane. Specific examples of chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, and tetraethylene glycol dialkyl ether. Specific examples of cyclic ethers include tetrahydrofuran, alkyltetrahydrofuran, dialkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, and 1,4-dioxolane. Further examples include alkoxy solutions with carrier ions, dichloro complex electrolytes, organoborates, organohalates, organohaloaluminates, Grignard organohaloaluminates, borohydrides, phenolates, and halooxides.

[0067] The auxiliary electrode is a component of the completed secondary battery, as shown in Figure 5. In an alternative embodiment, the auxiliary electrode is removed from the secondary battery cell after replenishment with the positive or negative electrodes but before final packaging.

[0068] The inclusion of an auxiliary electrode in a secondary battery cell has important advantages in battery monitoring and maintenance. For example, the auxiliary electrode can act as a reference electrode and be used for accurate measurement of state of charge and state of health, allowing measurement of changes in the relationship of cell voltage versus state of charge over time, or when the cell voltage is relatively independent of the state of charge. For example, the auxiliary electrode can act as a reference electrode to shut off the discharge when the voltage at the negative electrode exceeds a certain limit relative to the auxiliary electrode. In one such embodiment, this can be accomplished by using a sensor to detect the voltage at the negative electrode relative to the auxiliary electrode, and a controller isolates the cell from the circuit that was supplying power when a predetermined voltage limit is exceeded.

[0069] In one embodiment, when the state of charge of one of the electrodes is outside of a predetermined range, the auxiliary electrode can be accessed to transport carrier ions to the positive electrode and / or the negative electrode to restore the state of charge of the predetermined state of charge. For example, if at some point in the life of the secondary battery the control unit detects that the negative electrode has an end-of-discharge voltage Vneg,eod value greater than 0.9 V (vs. Li), the control unit can activate the transport of carrier ions from the auxiliary electrode to the positive electrode and / or the negative electrode to restore Vneg,eod to a value less than 0.9 V (vs. Li). As a further example, if at some point in the life of the secondary battery the control unit detects that the negative electrode has an end-of-discharge voltage Vneg,eod value greater than 0.8 V (vs. Li), the control unit can activate the transport of carrier ions from the auxiliary electrode to the positive electrode and / or the negative electrode (as described above) to restore Vneg,eod to a value less than 0.8 V (vs. Li). As a further example, if at some point in the life of the secondary battery the control unit detects that the negative electrode has an end-of-discharge voltage Vneg,eod value greater than 0.7 V (vs. Li), the control unit can activate the transport of carrier ions from the auxiliary electrode to the positive and / or negative electrodes (as described above) to restore Vneg,eod to a value less than 0.7 V (vs. Li). As a further example, if at some point in the life of the secondary battery the control unit detects that the negative electrode has an end-of-discharge voltage Vneg,eod value greater than 0.6 V (vs. Li), the control unit can activate the transport of carrier ions from the auxiliary electrode to the positive and / or negative electrodes (as described above) to restore Vneg,eod to a value less than 0.6 V (vs. Li).

[0070] In an alternative embodiment, carrier ions can be transported from the positive electrode to the auxiliary electrode to restore a predetermined state of charge or to balance the electrodes. For example, some positive electrode materials have a first cycle loss that significantly exceeds the first cycle of the negative electrode of the cell. In such an embodiment, the difference in the first cycle losses of the positive and negative electrodes can be compensated for by providing a negative electrode with a reversible coulombic capacity that significantly exceeds the reversible coulombic capacity of the positive electrode. Alternatively, or in addition, the difference in the first cycle losses can be accommodated by transporting carrier ions from the positive electrode to the auxiliary electrode during formation of the battery.

[0071] Referring to FIG. 6, in one alternative embodiment, a secondary battery 10 includes a plurality of positive electrode structures 20, a plurality of negative electrode structures 22, an auxiliary electrode 24, a control unit 27, and a substrate 29 supporting the positive and negative electrode structures. Each positive electrode structure includes a positive electrode current collector 21 and a cathode active material 120 overlying and in direct contact with the positive electrode current collector 21. Each negative electrode structure also includes a negative electrode current collector 23 and an anode active material 122 overlying and in direct contact with the negative electrode current collector 23. When the secondary battery 10 includes a plurality of positive electrode structures 20 as shown in FIG. 6, the positive electrode structures may be electrically coupled to each other. Similarly, when the secondary battery 10 includes a plurality of negative electrode structures 22 as shown in FIG. 6, the negative electrode structures may be electrically coupled to each other. The control unit 27 includes sensors for sensing the cell voltage (i.e., the voltage difference between the positive and negative electrodes) and for sensing the voltage difference between the auxiliary electrode and each of (i) the positive electrode, (ii) the negative electrode, or (iii) the positive and negative electrodes. The control unit further includes a controller in communication with the sensors for controlling the charging and discharging operations of the battery and the transport of carrier ions from the auxiliary electrode to the positive and / or negative electrodes, as described elsewhere herein.

[0072] In one embodiment, the anode active material 122 is in the form of a layer having a thickness of about 1 to about 100 micrometers. For example, in one embodiment, the anode active material 122 comprises porous silicon, has a thickness of about 5 to about 100 micrometers, and has a void volume fraction of about 0.15 to about 0.75. By way of further example, in one such embodiment, the anode active material 122 comprises porous silicon, has a thickness of about 10 to about 80 micrometers, and has a void volume fraction of about 0.15 to about 0.7. By way of further example, in one such embodiment, the anode active material 122 comprises porous silicon, has a thickness of about 20 to about 50 micrometers, and has a void volume fraction of about 0.25 to about 0.6. By way of further example, in one embodiment, the anode active material 122 comprises a porous silicon alloy (such as nickel silicide), has a thickness of about 5 to about 100 micrometers, and has a void volume fraction of about 0.15 to about 0.75.

[0073] In another embodiment, the anode active material 122 comprises silicon nanowires, has a thickness of about 5 to about 100 micrometers, and has a void volume fraction of about 0.15 to about 0.75. For example, in one such embodiment, the anode active material 122 comprises silicon nanowires, has a thickness of about 10 to about 80 micrometers, and has a void volume fraction of about 0.15 to about 0.7. By way of further example, in one such embodiment, the anode active material 122 comprises silicon nanowires, has a thickness of about 20 to about 50 micrometers, and has a void volume fraction of about 0.25 to about 0.6. By way of further example, in one embodiment, the anode active material 122 comprises silicon alloy (such as nickel silicide) nanowires, has a thickness of about 5 to about 100 micrometers, and has a void volume fraction of about 0.15 to about 0.75.

[0074] The negative electrode current collector 23 is typically at least about 10 3 For example, in one such embodiment, the negative electrode current collector 23 has a conductivity of at least about 10 4By way of further example, in one such embodiment, the negative electrode current collector 23 has a conductivity of at least about 10 5 Negative electrode current collector 23 has a conductivity of 1000 siemens / cm. Generally, negative electrode current collector 23 can include any metal or other conductor conventionally used as a current collector material for negative electrodes, such as carbon, cobalt, chromium, copper, nickel, titanium, or one or more alloys thereof. Negative electrode current collector 23 can be fabricated by processes such as electrodeposition, electroless deposition, immersion deposition, physical vapor deposition, chemical vapor deposition, and the like.

[0075] The separator 25 surrounds and electrically isolates each member element 20 of the positive electrode structure assembly from each member element 22 of the negative electrode structure assembly, and comprises a microporous separator material that may be impregnated with a non-aqueous electrolyte as described above. For example, in one embodiment, the microporous separator material includes pores with diameters of at least 50 Å, more typically about 2500 Å, and has a void volume fraction in the range of about 25% to about 75%, more typically in the range of about 35% to about 55%.

[0076] Separator 25 also electrically insulates auxiliary electrode 24 from positive and negative electrode structures 20, 22. As shown, separator 25 can include the same microporous material in the region between auxiliary electrode 24 and negative and positive electrode structures 20, 22 as in the region between positive electrode structure 20 and negative electrode structure 22. Alternatively, separator 25 can include a microporous material in the region between auxiliary electrode 24 and negative and positive electrode structures 20, 22 that is compositionally different from the microporous material in the region between positive electrode structure 20 and negative electrode structure 22.

[0077] In embodiments in which the voltage difference between the auxiliary electrode and the positive electrode is greater than the voltage difference between the auxiliary electrode and the negative electrode between the charge and discharge limits, the positive electrode may be replenished more rapidly than the negative electrode. Furthermore, in embodiments in which the transport of carrier ions involves a phase change reaction, i.e., converting crystalline silicon to amorphous silicon, transporting carrier ions directly from the auxiliary electrode to the negative electrode may result in uneven concentration of carrier ions in the negative electrode (the carrier ions tend to concentrate closest to the auxiliary electrode). Thus, in such embodiments, it may be preferable to replenish the secondary battery by transporting carrier ions from the auxiliary electrode to the positive electrode and then to the negative electrode, rather than directly from the auxiliary electrode to the negative electrode. Nevertheless, there are some embodiments in which it may be advantageous to electrically couple the auxiliary electrode 24 to the negative electrode structure 22 instead of (or in addition to) the positive electrode structure 20 (and as otherwise shown in FIG. 6). For example, in one such embodiment, the auxiliary electrode 24 is electrically coupled to the negative electrode structure 22 and has the ability to function as an auxiliary negative electrode. The combination of the negative electrode structure 22 and the auxiliary negative electrode can achieve better performance than the negative electrode alone.

[0078] As described above, the secondary battery 10 includes a population of negative electrode structures 22 and a population of positive electrode structures 20. As shown in FIG. 6, in one embodiment, the member elements of the two populations are stacked together in an alternating order (i.e., negative electrode structures, positive electrode structures, negative electrode structures, positive electrode structures, ...). For ease of illustration, in FIG. 6, the population of positive electrode structures includes four member elements 20, and the population of negative electrode structures includes three member elements 22. However, in practice, the population of negative electrode structures and the population of positive electrode structures may each include a greater or lesser number of member elements. For example, in one embodiment, the population of negative electrode structures and the population of positive electrode structures included in the secondary battery of the present disclosure may each include at least five member elements. As a further example, in one embodiment, the population of negative electrode structures and the population of positive electrode structures each include at least 10 member elements. As a further example, in one embodiment, the population of negative electrode structures and the population of positive electrode structures each include at least 50 member elements. By way of further example, in one embodiment, the population of negative electrode structures and the population of positive electrode structures each include at least 100 member elements.

[0079] 6, each member element 22 of the negative electrode population is between two member elements 20 of the positive electrode structure population, with the interdigitated series beginning with a positive electrode structure 20 and ending with a positive electrode structure 20, and each negative electrode structure 22 being between two positive electrode structures 20 (e.g., the series of electrodes has the following repeating order: positive electrode, negative electrode, positive electrode, negative electrode, positive electrode, ...). For example, in one such embodiment, the negative electrode structure population has N member elements and the positive electrode structure population has N+1 member elements, each negative electrode is between two positive electrodes, and N is at least 5, at least 10, at least 25, at least 50, or at least 100.

[0080] In one alternative embodiment, with one exception, each member element 22 of the population of negative electrode structures is between two member elements 20 of the population of positive electrodes, and with one exception, each member element 20 of the population of positive electrodes is between two member elements 22 of the population of negative electrodes. More generally, in one embodiment, the population of positive electrode structures and the population of negative electrode structures each have N member elements, each of the N-1 positive electrode structures is between two negative electrode structures, and each of the N-1 negative electrode structures is between two positive electrode structures, and N is at least 2. For example, in one embodiment, N is at least 4 (as shown in FIG. 4), at least 5, at least 10, at least 25, at least 50, or even at least 100.

[0081] In another alternative embodiment, for example, each member element 20 of the population of positive electrode structures is between two member elements 22 of the population of negative electrode structures, such that the interdigitated series begins with a negative electrode structure 22 and ends with a negative electrode structure 22, with each positive electrode structure 20 being between two negative electrode structures 22 (e.g., comprising a series of electrodes having the following repeating sequence: negative, positive, negative, positive, negative, ...). In one such embodiment, the population of positive electrode structures has N member elements and the population of negative electrode structures has N+1 member elements, with each positive electrode structure being between two negative structures, and N being at least 5, at least 25, at least 50, or even at least 100.

[0082] As shown in FIG. 6, the auxiliary electrode 24 is shown as a single element. In certain embodiments, the auxiliary electrode can include multiple auxiliary electrode elements or portions. For example, in one embodiment, the auxiliary electrode can include a lithium metal layer deposited (e.g., sputter deposited) on a positive electrode current collector, a negative electrode current collector, a substrate supporting a positive electrode structure, a substrate supporting a negative electrode structure (see, e.g., FIG. 6), or other surfaces or structures within a secondary battery, such as, for example, a battery enclosure. Additionally, the auxiliary electrode can be consumed within the battery formation process, or after formation, the auxiliary electrode can contain sufficient lithium such that it can be accessed to provide additional lithium to the positive or negative electrode structures.

[0083] Referring now to FIG. 7, in one alternative embodiment, the secondary battery 10 includes an electrode assembly stack 74 and a control unit 27. In this embodiment, the electrode assembly stack 74 includes two electrode assemblies 75, each including a population of positive electrode structures 20, a population of negative electrode structures 22, a substrate 29 supporting the positive and negative electrode structures, and an auxiliary electrode 24. In this embodiment, the electrode assemblies are stacked relative to each other in a direction perpendicular to the planar substrate 29. The populations of positive and negative electrode structures are stacked relative to each other in each electrode assembly 75 in a direction parallel to the planar substrate 29. The control unit 27 is electrically connected to the positive electrode structures, the negative electrode structures, and the auxiliary electrode, and is operable to replenish each electrode assembly 75 with carrier ions as previously described. For ease of illustration, each of the electrode assemblies 75 includes two populations of negative electrode structures and two populations of positive electrode structures. In practice, each of these populations may include more member elements. Additionally, in certain embodiments, substrate 29 may be omitted, in which case the stacking direction (as described in this paragraph) is relative to an imaginary plane parallel to substrate 29.

[0084] 8, in one embodiment, the secondary battery 10 of the present disclosure includes a battery enclosure 72, an electrode assembly stack 74, an auxiliary electrode 24, a negative electrode tab 41 and a positive electrode tab 42 for electrically connecting the electrode assembly stack 74 to an external energy source or consumer (not shown), and a control unit (not shown) including sensors and controllers as previously described. The electrode assembly stack 74 includes a group of six electrode assemblies 75 stacked vertically relative to one another, with the stacking direction perpendicular to the stacking direction of the positive and negative electrodes in each electrode assembly 75 (see FIG. 9). The number of electrode assemblies 75 in the electrode assembly stack 74 is not critical and can range from 1 to 50, for example, with 2 to 20 electrode structures in one electrode stack being typical. After filling the battery enclosure with non-aqueous electrolyte, the battery enclosure 72 may be sealed by folding the lid 72A at hinge 72B and adhering the lid 72A to the top surface 72C. As described in more detail below, the auxiliary electrode 24 may be incorporated within (i.e., as a component of) the sealed secondary battery. Alternatively, it may be accessed during formation of the secondary battery and removed prior to sealing, as previously described.

[0085] Negative electrode tab extension 25 is electrically connected to each negative electrode structure 22 (see FIG. 9) of each electrode assembly 75, and positive electrode tab extension 26 is electrically connected to each positive electrode structure 20 (see FIG. 8) of each electrode assembly 75. Tab 41 may be electrically connected to negative electrode tab extension 25, for example, using a conductive adhesive, and tab 42 may be electrically connected to positive electrode tab extension 26, for example, using a conductive adhesive. Alternatively, tabs 41 and 42 may be folded-over ends of negative electrode tab extension 25 and positive electrode tab extension 26, respectively.

[0086] 9, each electrode assembly 75 includes a population of negative electrode structures 22, a population of positive electrode structures 20, and a porous separator (not shown), as described in more detail with respect to Figures 5 and 6. The member elements of the two populations are interdigitated and stacked in alternating order in the D direction, which is perpendicular to the stacking direction of the electrode assemblies 75 in the electrode assembly stack 74 (see Figure 7).

[0087] 10, in one alternative embodiment, a secondary battery 10 of the present disclosure, as described elsewhere with respect to FIG. 9, includes two auxiliary electrode structures on the top and bottom of a stack 74. A control unit (not shown) included with the battery is operable to replenish each of the electrode assemblies 75 from one or the other, or both, of the auxiliary electrodes, as described above.

[0088] 11, in another embodiment, an electrode assembly 75 includes an auxiliary electrode 24 and a population of positive and negative electrode structures 20 and 22, each including a positive and negative electrode backbone 80 and 82, respectively. Also in this embodiment, each member element 20 of the population of positive electrode structures includes a current collector 21 disposed between the backbone 80 and the cathode active material 120. Each member element 22 of the negative electrode structure includes a current collector 23 on a surface of the member element (i.e., at the interface between the anode active material 122 and the separator 25). The backbone 80 and the negative electrode backbone 82 provide mechanical stability for the cathode active material layer 120 and the anode active material layer 122, respectively. Typically, the backbones have a thickness of at least 1 micrometer. Depending on the application, the positive and negative electrode backbones 80 and 82 may be independently conductive or insulating.

[0089] 12, in this alternative embodiment, the electrode assembly stacks 74 are as described elsewhere with respect to Figures 7 and 11, but in this embodiment, the electrode assembly stacks 74 include more auxiliary electrode structures 24 than there are electrode assemblies in the electrode assembly stacks. A control unit (not shown) included with the battery is operable to replenish each electrode assembly 75 from one or more auxiliary electrode structures, as previously described.

[0090] In further embodiments numbered 1-84 below, aspects of the disclosure include the following:

[0091] EMBODIMENT 1 A method for activating a secondary battery, comprising the steps of: The secondary battery has a negative electrode, a positive electrode, a microporous separator between the negative electrode and the positive electrode, impregnated with a carrier ion-containing electrolyte in ionic contact with the negative electrode and the positive electrode, and a control unit; the negative electrode comprises an anode-active silicon or an alloy of the anode-active silicon and has a coulombic capacity for the carrier ions; the positive electrode includes a cathode active material and has a coulombic capacity for the carrier ions; the coulombic capacity of the negative electrode exceeds the coulombic capacity of the positive electrode; The above method is (i) transporting carrier ions from the positive electrode to the negative electrode to at least partially charge the secondary battery, during which a solid electrolyte interphase is formed on a surface of the negative electrode; (ii) after step (i), transporting carrier ions from the auxiliary electrode to said positive electrode; (iii) after step (ii), transporting carrier ions from the positive electrode to the negative electrode to charge the secondary battery; and (iv) programming the control unit with a predetermined cell discharge end voltage Vcell,eod value; the activated secondary battery has a positive electrode end-of-discharge voltage Vpos,eod and a negative electrode end-of-discharge voltage Vneg,eod when the cell is at the predetermined Vcell,eod value, the value of Vpos,eod corresponding to a voltage at which the positive electrode state of charge is at least 95% of its coulombic capacity, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0092] EMBODIMENT 2 In the method of embodiment 1, when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 95% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0093] EMBODIMENT 3 In the method of embodiment 1, when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 96% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0094] EMBODIMENT 4 In the method of embodiment 1, when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 97% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0095] EMBODIMENT 5 In the method of embodiment 1, when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 98% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0096] EMBODIMENT 6 In the method of embodiment 1, when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 99% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0097] EMBODIMENT 7 In any one of the methods of embodiments 1 to 6, The method, wherein when the cell is at Vcell,eod, Vneg,eod is at least 0.4V (vs. Li) but less than 0.8V (vs. Li).

[0098] EMBODIMENT 8 In any one of the methods of embodiments 1 to 6, The method, wherein when the cell is at Vcell,eod, Vneg,eod is at least 0.5V (vs. Li) but less than 0.8V (vs. Li).

[0099] EMBODIMENT 9 In any one of the methods of embodiments 1 to 6, The method, wherein when the cell is at Vcell,eod, Vneg,eod is at least 0.4V (vs. Li) but less than 0.7V (vs. Li).

[0100] EMBODIMENT 10 In any one of the methods of embodiments 1 to 6, The method, wherein when the cell is at Vcell,eod, Vneg,eod is at least 0.5V (vs. Li) but less than 0.7V (vs. Li).

[0101] EMBODIMENT 11 A secondary battery having a negative electrode, a positive electrode, a microporous separator between the negative electrode and the positive electrode, the microporous separator being impregnated with a carrier ion-containing electrolyte in ionic contact with the negative electrode and the positive electrode, an auxiliary electrode, and a control unit, the positive electrode includes a cathode active material and has a coulombic capacity for the carrier ions; the negative electrode comprises anode-active silicon or an alloy of anode-active silicon and has a coulombic capacity for the carrier ions that exceeds the coulombic capacity of the positive electrode; The control unit includes a controller and a sensor electrically coupled to the controller; The sensor is configured to measure a cell voltage of the secondary battery during operation of the secondary battery and to measure a voltage of the positive electrode or the negative electrode relative to the auxiliary electrode of the secondary battery; the controller has a predetermined cell charging end voltage Vcell,eoc value and a predetermined cell discharging end voltage Vcell,eod value; A secondary battery characterized in that when the cell is at the predetermined Vcell,eod value, the positive electrode has an end-of-discharge voltage Vpos,eod and the negative electrode has an end-of-discharge voltage Vneg,eod, the value of Vpos,eod corresponding to a voltage at which the positive electrode has a state of charge of at least 95% of its coulombic capacity, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0102] EMBODIMENT 12 In the secondary battery of embodiment 11, a controller programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.9 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

[0103] EMBODIMENT 13 In the secondary battery of embodiment 11, a controller programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.8 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

[0104] EMBODIMENT 14 In the secondary battery of embodiment 11, a controller programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.7 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

[0105] EMBODIMENT 15 In the secondary battery of embodiment 11, a controller programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.6 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

[0106] EMBODIMENT 16 In the secondary battery of embodiment 11, a controller programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.5 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

[0107] EMBODIMENT 17 The method according to any one of embodiments 1 to 10 or the secondary battery according to any one of embodiments 11 to 16, The carrier ion is a lithium ion, a sodium ion, a potassium ion, a magnesium ion or an aluminum ion.

[0108] EMBODIMENT 18 The method according to any one of embodiments 1 to 10 or the secondary battery according to any one of embodiments 11 to 16, The carrier ion is a lithium ion, a magnesium ion or an aluminum ion.

[0109] EMBODIMENT 19 The method according to any one of embodiments 1 to 10 or the secondary battery according to any one of embodiments 11 to 16, The carrier ions are lithium ions.

[0110] EMBODIMENT 20 The method according to any one of embodiments 1 to 10 or the secondary battery according to any one of embodiments 11 to 16, The carrier ion is a magnesium ion.

[0111] EMBODIMENT 21 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 1.2:1.

[0112] EMBODIMENT 22 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 1.3:1.

[0113] EMBODIMENT 23 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 1.5:1.

[0114] EMBODIMENT 24 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 2:1.

[0115] EMBODIMENT 25 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 3:1.

[0116] EMBODIMENT 26 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 4:1.

[0117] EMBODIMENT 27 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 5:1.

[0118] EMBODIMENT 28 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 1.2:1.

[0119] EMBODIMENT 29 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 1.3:1.

[0120] EMBODIMENT 30 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 1.5:1.

[0121] EMBODIMENT 31 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 2:1.

[0122] EMBODIMENT 32 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 3:1.

[0123] EMBODIMENT 33 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 4:1.

[0124] EMBODIMENT 34 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 5:1.

[0125] EMBODIMENT 35 The method or secondary battery of any of the above embodiments, The negative electrode comprises a microstructured silicon-containing active material having a significant void volume fraction to accommodate volume expansion and contraction as carrier ions are incorporated into or leave the negative electrode during charge and discharge cycles.

[0126] EMBODIMENT 36 The method or secondary battery of embodiment 35, The anode active material has a void volume fraction of at least 0.1.

[0127] EMBODIMENT 37 The method or secondary battery of embodiment 35 or 36, The anode active material has a void volume fraction of less than 0.8.

[0128] EMBODIMENT 38 The method or secondary battery of embodiment 35 or 36, The anode active material has a void volume ratio of about 0.15 to about 0.75.

[0129] EMBODIMENT 39 The method or secondary battery of embodiment 35 or 36, The anode active material has a void volume ratio of about 0.2 to about 0.7.

[0130] EMBODIMENT 40 The method or secondary battery of embodiment 35 or 36, The anode active material has a void volume ratio of about 0.25 to about 0.6.

[0131] EMBODIMENT 41 The method or secondary battery of embodiment 35 or 36, The microstructured anode active material comprises macroporous, microporous or mesoporous material layers, or a combination of these material layers.

[0132] EMBODIMENT 42 A method for activating a secondary battery, comprising the steps of: The secondary battery has a negative electrode, a positive electrode, a microporous separator between the negative electrode and the positive electrode, impregnated with a carrier ion-containing electrolyte in ionic contact with the negative electrode and the positive electrode, and a control unit programmed with a predetermined cell discharge end voltage Vcell,eod value; the negative electrode comprises an anode-active silicon or an alloy of the anode-active silicon and has a coulombic capacity for the carrier ions; the positive electrode includes a cathode active material and has a coulombic capacity for the carrier ions; the coulombic capacity of the negative electrode exceeds the coulombic capacity of the positive electrode; The above method is (i) transporting carrier ions from the positive electrode to the negative electrode to at least partially charge the secondary battery, during which a solid electrolyte interphase is formed on a surface of the negative electrode; and (ii) transporting carrier ions from an auxiliary electrode to the positive electrode to provide a positive electrode end-of-discharge voltage Vpos,eod and a negative electrode end-of-discharge voltage Vneg,eod to the secondary battery when the cell is at the predetermined Vcell,eod value, the Vpos,eod value corresponding to a voltage at which the state of charge of the positive electrode is at least 95% of its coulombic capacity, and Vneg,eod being at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0133] EMBODIMENT 43 In the method of embodiment 42, A method characterized in that step (ii) is carried out after or simultaneously with step (i).

[0134] EMBODIMENT 44 In the method of embodiment 43, When step (ii) is carried out after step (i), The method further comprises, after step (ii), a step (iii) of transporting carrier ions from the positive electrode to the negative electrode to charge the secondary battery.

[0135] EMBODIMENT 45 In the method of embodiment 43, step (ii) is performed simultaneously with step (i), step (ii) including transporting carrier ions from the auxiliary electrode to the negative electrode at a first rate, and step (i) including transporting carrier ions from the positive electrode to the negative electrode at a second rate; The method, wherein the second speed is greater than the first speed.

[0136] EMBODIMENT 46 In the method of embodiment 42, when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 95% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0137] EMBODIMENT 47 In the method of embodiment 42, when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 96% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0138] EMBODIMENT 48 In the method of embodiment 42, when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 97% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0139] EMBODIMENT 49 In the method of embodiment 42, when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 98% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0140] EMBODIMENT 50 In the method of embodiment 42, when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 99% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0141] EMBODIMENT 51 In any of the methods of embodiments 42 to 50, The method, wherein when the cell is at Vcell,eod, Vneg,eod is at least 0.4V (vs. Li) but less than 0.8V (vs. Li).

[0142] EMBODIMENT 52 In any of the methods of embodiments 42 to 50, The method, wherein when the cell is at Vcell,eod, Vneg,eod is at least 0.5V (vs. Li) but less than 0.8V (vs. Li).

[0143] EMBODIMENT 53 In any of the methods of embodiments 42 to 50, The method, wherein when the cell is at Vcell,eod, Vneg,eod is at least 0.4V (vs. Li) but less than 0.7V (vs. Li).

[0144] EMBODIMENT 54 In any of the methods of embodiments 42 to 50, The method, wherein when the cell is at Vcell,eod, Vneg,eod is at least 0.5V (vs. Li) but less than 0.7V (vs. Li).

[0145] EMBODIMENT 55 A secondary battery having a negative electrode, a positive electrode, a microporous separator between the negative electrode and the positive electrode, the microporous separator being impregnated with a carrier ion-containing electrolyte in ionic contact with the negative electrode and the positive electrode, an auxiliary electrode, and a control unit, the positive electrode includes a cathode active material and has a coulombic capacity for the carrier ions; the negative electrode comprises anode-active silicon or an alloy of anode-active silicon and has a coulombic capacity for the carrier ions that exceeds the coulombic capacity of the positive electrode; The control unit includes a controller and a sensor electrically coupled to the controller; The sensor is configured to measure a cell voltage of the secondary battery during operation of the secondary battery and to measure a voltage of the positive electrode or the negative electrode relative to the auxiliary electrode of the secondary battery; the controller being programmed with a predetermined cell charging end voltage, Vcell,eoc value, and a predetermined cell discharging end voltage, Vcell,eod value; A secondary battery characterized in that when the cell is at the predetermined Vcell,eod value, the positive electrode has an end-of-discharge voltage Vpos,eod and the negative electrode has an end-of-discharge voltage Vneg,eod, the value of Vpos,eod corresponding to a voltage at which the positive electrode has a state of charge of at least 95% of its coulombic capacity, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

[0146] EMBODIMENT 56 In the secondary battery of embodiment 55, a controller programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.9 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

[0147] EMBODIMENT 57 In the secondary battery of embodiment 55, a controller programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.8 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

[0148] EMBODIMENT 58 In the secondary battery of embodiment 55, a controller programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.7 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

[0149] EMBODIMENT 59 In the secondary battery of embodiment 55, a controller programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.6 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

[0150] EMBODIMENT 60 In the secondary battery of embodiment 55, a controller programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.5 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

[0151] EMBODIMENT 61 The method according to any one of embodiments 42 to 54 or the secondary battery according to any one of embodiments 55 to 60, The carrier ion is a lithium ion, a sodium ion, a potassium ion, a magnesium ion or an aluminum ion.

[0152] EMBODIMENT 62 The method according to any one of embodiments 42 to 54 or the secondary battery according to any one of embodiments 55 to 60, The carrier ion is a lithium ion, a magnesium ion or an aluminum ion.

[0153] EMBODIMENT 62 The method according to any one of embodiments 42 to 54 or the secondary battery according to any one of embodiments 55 to 60, The carrier ions are lithium ions.

[0154] EMBODIMENT 63 The method according to any one of embodiments 42 to 54 or the secondary battery according to any one of embodiments 55 to 60, The carrier ion is a magnesium ion.

[0155] EMBODIMENT 64 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 1.2:1.

[0156] EMBODIMENT 65 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 1.3:1.

[0157] EMBODIMENT 66 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 1.5:1.

[0158] EMBODIMENT 67 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 2:1.

[0159] EMBODIMENT 68 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 3:1.

[0160] EMBODIMENT 69 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 4:1.

[0161] EMBODIMENT 70 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 5:1.

[0162] EMBODIMENT 71 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 1.2:1.

[0163] EMBODIMENT 72 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 1.3:1.

[0164] EMBODIMENT 73 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 1.5:1.

[0165] EMBODIMENT 74 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 2:1.

[0166] EMBODIMENT 75 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 3:1.

[0167] EMBODIMENT 76 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 4:1.

[0168] EMBODIMENT 77 The method or secondary battery of any of the above embodiments, When cycled against a counter electrode, the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, in that order, is at least 5:1.

[0169] EMBODIMENT 78 The method or secondary battery of any of the above embodiments, The negative electrode comprises a microstructured silicon-containing active material having a significant void volume fraction to accommodate volume expansion and contraction as carrier ions are incorporated into or leave the negative electrode during charge and discharge cycles.

[0170] EMBODIMENT 79 The method or secondary battery of embodiment 78, comprising: The anode active material has a void volume fraction of at least 0.1.

[0171] Embodiment 80 The method or secondary battery of embodiment 78, comprising: The anode active material has a void volume fraction of less than 0.8.

[0172] Embodiment 81 The method or secondary battery of embodiment 78, comprising: The anode active material has a void volume ratio of about 0.15 to about 0.75.

[0173] EMBODIMENT 82 The method or secondary battery of embodiment 78, comprising: The anode active material has a void volume ratio of about 0.2 to about 0.7.

[0174] EMBODIMENT 83 The method or secondary battery of embodiment 78, comprising: The anode active material has a void volume ratio of about 0.25 to about 0.6.

[0175] EMBODIMENT 84 The method or secondary battery of embodiment 78, comprising: The microstructured anode active material comprises macroporous, microporous or mesoporous material layers, or a combination of these material layers.

[0176] Various changes may be made in the above articles, compositions and methods without departing from the scope of the present disclosure, in which it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

Claims

1. 1. A method for compensating for loss of carrier ions due to formation of a solid electrolyte interphase in a secondary battery during a first or subsequent charge cycle of the battery, comprising: The secondary battery comprises a negative electrode, a positive electrode, a microporous separator between the negative electrode and the positive electrode, impregnated with a carrier ion-containing electrolyte in ionic contact with the negative electrode and the positive electrode, and a control unit programmed to cycle the secondary battery between a predetermined cell end-of-charge voltage Vcell,eoc value and a predetermined cell end-of-discharge voltage Vcell,eod value; the negative electrode comprises an anode-active silicon or an alloy of the anode-active silicon and has a coulombic capacity for the carrier ions; the positive electrode includes a cathode active material and has a coulombic capacity for the carrier ions; the coulombic capacity of the negative electrode exceeds the coulombic capacity of the positive electrode; The above method is measuring a voltage of the positive electrode relative to the auxiliary electrode and a voltage of the negative electrode relative to the auxiliary electrode using an auxiliary electrode including a source of carrier ions and electrolytically coupled to the negative electrode and the positive electrode through the separator; (i) transporting carrier ions from the positive electrode to the negative electrode during a first or subsequent charging cycle to at least partially charge the secondary battery, thereby forming a solid electrolyte interphase at a surface of the negative electrode during said transport; and (ii) transporting carrier ions from the auxiliary electrode through the separator until, when the cell is at the predetermined value of Vcell,eod, the positive electrode has an end-of-discharge voltage Vpos,eod relative to the auxiliary electrode and the negative electrode has an end-of-discharge voltage Vneg,eod relative to the auxiliary electrode, the value of Vpos,eod corresponding to a voltage at which the state of charge of the positive electrode is at least 95% of its coulombic capacity and Vneg,eod is at least 0.4 V vs. Li but less than 0.9 V vs. Li.

2. 10. The method of claim 1 , A method characterized in that step (ii) is carried out after or simultaneously with step (i).

3. 3. The method of claim 2, When step (ii) is carried out after step (i), The method further comprises, after step (ii), a step (iii) of transporting carrier ions from the positive electrode to the negative electrode to charge the secondary battery.

4. 3. The method of claim 2, step (ii) is performed simultaneously with step (i), step (ii) including transporting carrier ions from the auxiliary electrode to the negative electrode at a first rate, and step (i) including transporting carrier ions from the positive electrode to the negative electrode at a second rate; The method of claim 1, wherein the second speed is greater than the first speed.

5. 10. The method of claim 1 , when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 95% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

6. 10. The method of claim 1 , when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 96% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

7. 10. The method of claim 1 , when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 97% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

8. 10. The method of claim 1 , when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 98% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

9. 10. The method of claim 1 , when the cell is at Vcell,eod, the value of Vpos,eod corresponds to a voltage where the state of charge of the positive electrode is at least 99% of the coulombic capacity of the positive electrode, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

10. The method according to any one of claims 1 to 9, The method of claim 1, wherein when the cell is at Vcell,eod, Vneg,eod is at least 0.4 V (vs. Li) but less than 0.8 V (vs. Li).

11. The method according to any one of claims 1 to 9, The method of claim 1, wherein when the cell is at Vcell,eod, Vneg,eod is at least 0.5 V (vs. Li) but less than 0.8 V (vs. Li).

12. The method according to any one of claims 1 to 9, The method of claim 1, wherein when the cell is at Vcell,eod, Vneg,eod is at least 0.4 V (vs. Li) but less than 0.7 V (vs. Li).

13. The method according to any one of claims 1 to 9, The method of claim 1, wherein when the cell is at Vcell,eod, Vneg,eod is at least 0.5 V (vs. Li) but less than 0.7 V (vs. Li).

14. A secondary battery having a negative electrode, a positive electrode, a microporous separator between the negative electrode and the positive electrode, the microporous separator being impregnated with a carrier ion-containing electrolyte in ionic contact with the negative electrode and the positive electrode, and a control unit, the positive electrode includes a cathode active material and has a coulombic capacity for the carrier ions; the negative electrode comprises anode-active silicon or an alloy of anode-active silicon and has a coulombic capacity for the carrier ions that exceeds the coulombic capacity of the positive electrode; The control unit includes a controller and a sensor electrically coupled to the controller; the sensor is configured to measure a cell voltage of the secondary battery during operation of the secondary battery, and to measure a voltage of the positive electrode relative to a removable auxiliary electrode including a source of carrier ions and electrolytically coupled to the negative electrode and the positive electrode via the separator, and a voltage of the negative electrode relative to the auxiliary electrode; the controller is programmed to cycle between a predetermined cell charging end voltage Vcell,eoc value and a predetermined cell discharging end voltage Vcell,eod value; During a first or subsequent charging cycle, carrier ions are transported from the positive electrode to the negative electrode to at least partially charge the secondary battery, forming a solid electrolyte interphase at the surface of the negative electrode during the transport; and A secondary battery characterized in that, when the cell is at the predetermined Vcell,eod value due to transport of carrier ions from the removable auxiliary electrode, the positive electrode has an end-of-discharge voltage Vpos,eod relative to the auxiliary electrode and the negative electrode has an end-of-discharge voltage Vneg,eod relative to the auxiliary electrode, the value of Vpos,eod corresponds to a voltage at which the state of charge of the positive electrode is at least 95% of its coulombic capacity, and Vneg,eod is at least 0.4 V (vs. Li) but less than 0.9 V (vs. Li).

15. The secondary battery according to claim 14, The controller is programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.9 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

16. The secondary battery according to claim 14, The controller is programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.8 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

17. The secondary battery according to claim 14, The controller is programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.7 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

18. The secondary battery according to claim 14, The controller is programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.6 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

19. The secondary battery according to claim 14, The controller is programmed to transport carrier ions from the auxiliary electrode to the positive electrode or negative electrode when the value of Vneg,eod exceeds 0.5 V (vs. Li) when the secondary battery is at the predetermined Vcell,eod value at the end of a discharge cycle of the secondary battery.

20. The method according to any one of claims 1 to 13, The method wherein the carrier ions are lithium ions, sodium ions, potassium ions, magnesium ions or aluminum ions.

21. The method according to any one of claims 1 to 13, The method wherein the carrier ions are lithium ions, magnesium ions or aluminum ions.

22. The method according to any one of claims 1 to 13, The method wherein the carrier ions are lithium ions.

23. The method according to any one of claims 1 to 13, The method wherein the carrier ion is a magnesium ion.

24. The method according to any one of claims 1 to 13, The method wherein the ratio of the reversible coulombic capacity of said negative electrode to the reversible coulombic capacity of said positive electrode, when cycled against a counter electrode, in that order, is at least 1.2:

1.

25. The method according to any one of claims 1 to 13, The method wherein the ratio of the reversible coulombic capacity of said negative electrode to the reversible coulombic capacity of said positive electrode, when cycled against a counter electrode, in that order, is at least 1.3:

1.

26. The method according to any one of claims 1 to 13, The method wherein the ratio of the reversible coulombic capacity of said negative electrode to the reversible coulombic capacity of said positive electrode, when cycled against a counter electrode, in that order, is at least 1.5:

1.

27. The method according to any one of claims 1 to 13, The method wherein the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, when cycled against a counter electrode, in that order, is at least 2:

1.

28. The method according to any one of claims 1 to 13, The method wherein the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, when cycled against a counter electrode, in that order, is at least 3:

1.

29. The method according to any one of claims 1 to 13, The method wherein the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, when cycled against a counter electrode, in that order, is at least 4:

1.

30. The method according to any one of claims 1 to 13, The method wherein the ratio of the reversible coulombic capacity of the negative electrode to the reversible coulombic capacity of the positive electrode, when cycled against a counter electrode, in that order, is at least 5:

1.

31. The method according to any one of claims 1 to 13, The method wherein the ratio of the coulombic capacity of said auxiliary electrode to the reversible coulombic capacity of said positive electrode, when cycled against a counter electrode, in that order, is at least 1.2:

1.

32. The method according to any one of claims 1 to 13, The method wherein the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, when cycled against a counter electrode, in that order, is at least 1.3:

1.

33. The method according to any one of claims 1 to 13, The method wherein the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, when cycled against a counter electrode, in that order, is at least 1.5:

1.

34. The method according to any one of claims 1 to 13, The method wherein the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, when cycled against a counter electrode, in that order, is at least 2:

1.

35. The method according to any one of claims 1 to 13, The method wherein the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, when cycled against a counter electrode, in that order, is at least 3:

1.

36. The method according to any one of claims 1 to 13, The method wherein the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, when cycled against a counter electrode, in that order, is at least 4:

1.

37. The method according to any one of claims 1 to 13, The method wherein the ratio of the coulombic capacity of the auxiliary electrode to the reversible coulombic capacity of the positive electrode, when cycled against a counter electrode, in that order, is at least 5:

1.

38. The method according to any one of claims 1 to 13, The negative electrode comprises as an anode active material a microstructured silicon-containing active material having a significant void volume fraction to accommodate volume expansion and contraction as carrier ions are incorporated into or leave the negative electrode during charge and discharge cycles.

39. 39. The method of claim 38, The anode active material has a void volume fraction of at least 0.

1.

40. 39. The method of claim 38, The anode active material has a void volume fraction of less than 0.

8.

41. 39. The method of claim 38, The anode active material has a void volume fraction of 0.15 to 0.

75.

42. 39. The method of claim 38, The anode active material has a void volume fraction of 0.2 to 0.

7.

43. 39. The method of claim 38, The anode active material has a void volume fraction of 0.25 to 0.

6.

44. 39. The method of claim 38, The microstructured anode active material comprises macroporous, microporous or mesoporous material layers, or a combination of such material layers.

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