METHOD AND SYSTEM FOR LIFE EXTENSION OF BATTERY CELL

Abstract

A method for life extension of a battery cell, provided with charge/discharge terminals to which a charging voltage can be applied with a flowing charging current, comprises: applying to terminals of the battery cell a plurality of constant voltage stages, each stage comprising intermittent voltage plateaus, letting the charging current go to zero for a rest period until an ending condition is reached, collecting data on previous discharge capacities measured during previous charge cycles, calculating a relative variation of the discharge capacity, comparing the calculated relative capacity variation to a predetermined threshold, if the calculated relative capacity variation exceeds the threshold, modifying at least one charge parameter among a selection of charge parameters including the duration of the voltage plateau, the variation of the voltage stage, and the rest time, so as to bring back the relative capacity variation below the threshold.

Claims

1. A method for extending life of a battery cell provided with charge/discharge terminals to which a charging voltage can be applied with a flowing charging current, the method comprising: applying, to the terminals of the battery cell, a plurality of constant voltage stages Vj, where Vj+1>Vj, j=1, 2 . . . , k, each voltage stage comprising intermittent nj voltage plateaus; between two successive voltage plateaus within a voltage stage, letting the charging current go to zero for a rest period R.sub.j.sup.p, 1pnj, until any one of the following conditions is reached: a pre-set charge capacity or state of charge (SOC) is reached, the battery cell temperature exceeds a pre-set limit value T.sub.lim, or the battery cell voltage has exceeded a pre-set limit value V.sub.lim; collecting data on at least two previous measured discharge capacities; calculating a relative variation (Q/Q) of the discharge capacity, from the collected data; comparing the calculated relative variation (Q/Q) of the discharge capacity to a predetermined threshold (); and if the calculated relative variation (Q/Q) of the discharge capacity exceeds the predetermined threshold (), modifying at least one charge parameter among a selection of charge parameters including a duration of the voltage plateau, the voltage stage shift, and the rest time, so as to bring the calculated relative capacity variation (Q/Q) below the predetermined threshold ().

2. The method of claim 1, further comprising: between two successive current rest times R.sub.j.sup.p-1 and R.sub.j.sup.p within a voltage stage Vj, and a pending voltage plateau, detecting flowing pulse-like charging current dropping from an initial value I.sub.j,p.sup.ini to a final value I.sub.j,p.sup.fin, where 1pnj, ending the pending voltage plateau, so that the flowing pulse-like charging current drops to zero for a rest time R.sub.j.sup.p, with the voltage departing from Vj, and after the rest time R.sub.j.sup.p has elapsed, applying back the voltage to Vj.

3. The method of claim 2, wherein a transition from a voltage stage Vj to the following stage Vj+1 is initiated when I.sub.j,p.sup.fin, p=nj reaches a threshold value I.sub.j,nj.sup.Thr.

4. The method of claim 3, further comprising calculating the following stage Vj+1 as =Vj+DV(j), with DV(j) relating to the current change DI(j)=I.sub.j,p.sup.iniI.sub.j,p.sup.fin, p=nj.

5. The method of claim 1, further comprising, prior to applying, to the terminals of the battery cell, the plurality of constant voltage stages Vj, determining a K-value and a charge step from inputs including charging instructions for C-rate, voltage and charge time.

6. The method of claim 5, further comprising detecting a Cshift threshold, followed by determining a shift voltage by applying a non-linear voltage equation and using the K-value and a C-rate.

7. The method of claim 1, wherein the method is applied to a plurality of battery cells arranged in series and/or in parallel.

8. The method of claim 7, wherein the plurality of battery cells are connected in series, and the method further comprises providing intrinsic balancing between the battery cells of the plurality.

9. The method of claim 1, wherein the collecting of the data comprises collecting previously stored voltage, current and capacity data.

10. A system for extending the life of a battery cell provided with charge/discharge terminals to which a charging voltage can be applied with a flowing charging current, the system comprising an electronic converter connected to a power source and configured for applying a charging voltage to the terminals of a battery cell, the electronic converter being controlled by a charging controller configured to process battery cell flowing current and cell voltage measurement data and charging instruction data, wherein the system further comprises: means for collecting data on at least two previous discharge capacities measured or estimated during previous charge cycles for the battery cell, means for calculating a relative variation (Q/Q) of the discharge capacity from the collected data, means for comparing the calculated relative variation (Q/Q) of the discharge capacity to a predetermined threshold () and for delivering information when the predetermined threshold () is exceeded, and wherein the charging controller is programed to modify at least one charge parameter among a selection of charge parameters including a duration of a voltage plateau, a voltage stage shift, and the rest time, so as to bring back the calculated relative variation (Q/Q) of the discharge capacity below the predetermined threshold ().

11. The system of claim 10, wherein the charging controller is further configured to control the electronic converter so as to: apply to the terminals of the battery cell a plurality of constant voltage stages Vj, where Vj+1>Vj, j=1, 2 . . . , k, each voltage stage comprising intermittent nj voltage plateaus, between two successive voltage plateaus within a voltage stage, let the charging current go to zero for a rest period R.sub.j.sup.p, 1pnj, until one of the following conditions is reached: a pre-set charge capacity or state of charge (SOC) is reached, the battery cell temperature exceeds a pre-set limit value T.sub.lim, or the battery cell voltage has exceeded a pre-set limit value V.sub.lim.

12. The system of claim 10, further comprising a plurality of battery cells connected in series, wherein the charging controller is further configured to provide intrinsic balancing between the battery cells of the plurality.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0128] Figures showing Prior Art:

[0129] FIG. 1 is a schematic description of prior art charging methods;

[0130] FIG. 2 shows Typical CCCV charging and CC discharge profile;

[0131] FIG. 3 shows Multistage constant current charge profile (MSCC);

[0132] FIG. 4 and FIG. 5 show The CCCV limitations in fast charging;

[0133] Figures showing the present disclosure:

[0134] FIG. 6 shows typical voltage and current profiles during VSIP charge and CC discharge cycles;

[0135] FIG. 7 shows typical voltage and current profiles during VSIP charge and CC discharge (here full charge time is 26 min);

[0136] FIG. 8 shows typical voltage and current profiles during VSIP charge;

[0137] FIG. 9 shows typical voltage profile during VSIP with a plurality of voltage stages Vj (here total charge time is about 35 min);

[0138] FIG. 10 shows detailed voltage and current profiles during VSIP charge showing voltage and current intermittency.

[0139] FIG. 11 shows detailed voltage and current profiles during VSIP charge showing rest time;

[0140] FIG. 12 shows Voltage and current profiles during rest time showing a voltage drop;

[0141] FIG. 13 shows current profile at stage j;

[0142] FIG. 14 shows current profile at sub-step j,p;

[0143] FIG. 15 shows Typical V(j)=Vj+1Vj vs. Time profile during VSIP charging in 17 min over many cycles;

[0144] FIG. 16 shows voltage and gained capacity during VSIP charge in 26 mn;

[0145] FIG. 17 shows discharge profile of 12 Ah cell after VSIP charge in 26 mn;

[0146] FIG. 18 shows linear voltammetry vs VSIP;

[0147] FIG. 19 shows two successive VSIP charge profiles can be different from each other;

[0148] FIG. 20 shows VSIP charge voltage and current profiles (60 min);

[0149] FIG. 21 shows VSIP charge voltage and current profiles (45 min);

[0150] FIG. 22 shows VSIP charge voltage and current profiles (30 min);

[0151] FIG. 23 shows VSIP charge voltage and current profiles (20 min);

[0152] FIG. 24 shows 80% partial charge with VSIP in 16 min;

[0153] FIG. 25 shows Temperature profile during VSIP charge in 30 min: Stress test for LIB quality control (QC);

[0154] FIG. 26 shows Temperature profile during VPC in 20 min of a good quality cell;

[0155] FIG. 27 shows VSIP enhances cell's capacity;

[0156] FIGS. 28 and 29 show VSIP applies to multi-cell systems in parallel;

[0157] FIGS. 30 and 31 show VSIP applies to multi-cell systems in series;

[0158] FIG. 32 shows a Cycle performance index;

[0159] FIG. 33 is a flow diagram of an embodiment of the extended-life fast-charge method, including a Bayesian optimization;

[0160] FIG. 34 is a schematic view of an extended-life fast-charge system implementing the fast-charge method of FIG. 33;

[0161] FIG. 35 shows 4 cells-in-series voltage profiles measured during a NLV charge in about 30 min.

DETAILED DESCRIPTION

[0162] For programming a controller implementing the fast-charging method according to the present disclosure, with an artificial intelligence (AI)-based approach, a list of duty criteria is proposed: [0163] fixing the charging time tch [0164] reaching the target capacity in tch [0165] keeping temperature under control (<60 C.) [0166] achieving the target cycle number [0167] insuring battery safety [0168] enhancing capacity

[0169] The variables in the fast-charging method according to the present disclosure are: [0170] the VSIP governing equation A=V/t=f(i, V, i/t, T, SOC, SOH) [0171] the charge current limits [0172] the current trigger for next voltage step [0173] the rest time [0174] the temperature limit [0175] the voltage limit [0176] the target capacity limit

[0177] A Bayesian optimization is used to adjust the Non Linear Voltammetry (NLV) variables.

[0178] The NLV variables are adjusted at each cycle to meet the criteria:

[00003]$A=\frac{V}{t}=f\left(i,V,\frac{i}{t},T,\mathrm{SOC},\mathrm{SOH}\right)$

[0179] With reference to FIGS. 6 and 7, in a fist embodiment, the fast charging (VSIP) method according to the present disclosure is implemented during charge sequences within VSIP charge, CC discharge cycles. In these profiles, the C-rate is representative of the current in the battery cell.

[0180] As shown in FIGS. 8 and 9, a VSIP charge sequence, which has a duration of about 26 min, includes a number of increasing voltage stages, each voltage stage V1, . . . , Vj, Vj+1, . . . Vk including constant voltage plateau.

[0181] A shown in FIGS. 10 and 11, during each voltage plateau in a VSIP charging sequence, the voltage profile is constant and decreases to a low constant voltage between two successive plateaus, while the C-rate profile includes a decrease during each plateau and decreases to zero during the rest period between two plateaus.

[0182] During a rest time, as illustrated by FIG. 12 showing detailed current and voltage profile, the voltage can be controlled so that

[00004]$\frac{V}{t}$

has a constant negative value calculated as above described.

[0183] As shown in FIG. 13, a voltage stage j includes current impulsions 1,2,3, . . . nj in response to voltage plateaus applied to the terminal of a battery cell.

[0184] During a voltage plateau Vj, the current at sub-step j,p decreases from I.sub.j,p.sup.ini to I.sub.j,p.sup.fin as shown in FIG. 15.

[0185] For a large number of charging cycles operated with the fast-charging method according to the present disclosure, the voltage variations V experienced between the successive voltage plateau within successive voltage stages Vj, Vj+1. globally decrease with time, as shown in FIG. 15.

[0186] During a voltage charge VSIP sequence lasting 26 min full charge time as shown in FIG. 16, the charge capacity Qch continuously increases while the corresponding voltage profile includes successive voltage stages each comprising voltage plateau with rest times. As shown in FIG. 17, during a following discharge sequence, the discharge capacity Qd is decreases with the voltage applied to the terminals of the battery cell.

[0187] The VSIP fast charging method according to the present disclosure clearly differs from a conventional Linear Voltammetry (LV) method, with respective distinct voltage and current profiles shown in FIG. 18. The respective current and voltage profiles can differ from a charge/discharge VSIP cycle to another, as shown in FIG. 19.

[0188] The variability of voltage and current profiles is also observed when the charge time is modified, for example, from 60 min, 45 min, 30 min to 20 min, with reference to respective FIGS. 20, 21, 22 and 23. For a 60 min charge time, the charge sequence includes 4 voltage stages (FIG. 20), and for a 45 min charge time the charge sequence includes 8 voltage stages (FIG. 21). For a 30 min charge time, the charge sequence includes 10 voltage stages (FIG. 22) and for a 20 min charge time, the charge sequence includes 4 voltage stages (FIG. 23).

[0189] As shown in FIG. 24, the VSIP charging method according to the present disclosure allows an 80% partial charge of a Lithium-Ion battery cell in about 16 min.

[0190] With reference to FIG. 25, during a VSIP charge in 30 mm, cells A, B and D had temperature raising above the safety limit of 50 C. These battery cells didn't pass the VSIP stress test. Only cell C passed the stress test. It means that all LIB cells can't be fast charged.

[0191] Thus, the VSIP charging method according to the present disclosure can also be used as stress quality control (QC) test before using a cell in a system for fast charging.

[0192] With reference to FIG. 26, during a charge sequence of an excellent quality LIB cell, the full charge is reached in about 20 min and the temperature of the cell does not exceed 32 C.

[0193] With reference to FIG. 27, by adjusting the VSIP parameters such as the upper voltage limit, the step time, V and I/t for the voltage step transition, the discharge capacity can be improved without compromising safety and life span.

[0194] The VSIP charging method according to the present disclosure can be implemented for charging 4 LIB cells assembled in parallel in about 35 min, as shown in FIG. 28 with a CC discharge and in FIG. 29, which is a detailed view of the voltage and current profiles during the VSIP charge sequence of FIG. 28,

[0195] With reference to FIGS. 30 and 31, the VSIP charging method according to the present disclosure can also be applied for charging 4 e-cig cells in series, in about 35 min.

[0196] As shown in FIG. 35, the profiles of the voltages V1, V2, V3 and V4, corresponding to 4 cells connected in series and measured during a NLV charge, are very close to each other, which avoids cell balancing.

[0197] Note that in this configuration, the VSIP charging method is particularly advantageous, compared to CCCV, as it no longer requires a time-consuming and energy-using active cell balancing.

[0198] As shown in FIG. 32, the charge and discharge capacity varies as a function of the number of cycles, A fast charge cycle performance index can be calculated as:

[00005]$=\underset{i=1}{\overset{n}{.Math.}}\frac{Q_{\mathrm{disch}}^i/Q_{nom}}{t_i}$ [0199] with [0200] =normalized cycle performance index [0201] i=cycle number [0202] t.sub.i=charge time @ ith cycle (hr) [0203] Q.sub.disch.sup.i=discharge capacity @ ith cycle (Ah) [0204] Q.sub.nom=nominal capacity (Ah)

[0205] With reference to FIGS. 33 and 34, an example of an extended-life fast-charge system 100, along with the implemented charging method, is now described.

[0206] This extended-life fast-charge system 100 comprises a VSIP controller 1 including a power electronics converter 11 designed for processing electric energy provided by an external energy source E and supplying a variable voltage V(t) to a battery cell B to be charged. Note that this battery cell B can be replaced by a system of battery cells connected in series and/or in parallel.

[0207] The VSIP controller 1 further includes a VSIP controller 1 designed for receiving and processing: [0208] measurement data provided by a current sensor 13 placed in the current circuit between the power electronics converter 11 and the battery cell B, and by a temperature sensor 12 placed on or in the battery cell B, [0209] instruction data collected from a user interface 6, including inputs such as an expected C-Rate, a charge voltage instruction and a charge time instruction.

[0210] The extended-life fast-charge system 100 is further adapted to receive the parameter F as an input 14 to the user interface 6.

[0211] Typically, the parameter F can be equal to 0.002% (average slope of capacity loss per cycle), corresponding to a capacity loss of 20% in 1000 cycles.

[0212] An output 15 can be the number of cycles experienced by the charged battery cell with a relative variation in discharge capacity per cycle Q/Q less than F.

[0213] The VSIP controller 1 is further designed to control power electronics components within the converter 10 so as to generate a charge voltage profile according to the VSIP method until at least of one the termination criteria for ending 9 the charging process are met.

[0214] These VSIP termination criteria 5 include: [0215] minimum C-Rate cut-off, [0216] safety voltage exceeded, [0217] charge capacity reached, [0218] over temperature.

[0219] From inputs C-Rate, Voltage and elapsed charge Time, which can be entered as instructions by a user, the VSIP controller 1 first determines an initial K value and a charge step.

[0220] Provided that no charge termination 7 criterion is met and a predetermined threshold for C-Rate is not reached, the VSIP controller 1 launches a charge sequence 2 by applying voltage for a charge step duration and C-Ratewhich is an image of the current flowing into the battery cellis measured.

[0221] When current reaches a pre-set C-rate value, the VSIP controller 1 commutes to a rest period 3 during which no voltage is applied to the battery cell. The duration of this rest period depends on the measured C-Rate before current decreasing.

[0222] If the C shift reaches the determined threshold 8, the VSIP controller 1 calculates a shift voltage 4 required to maintain a sufficient charge of the battery cell. This calculation is based on the NLV equation using K-value and C-rate. The calculated shift voltage is then applied for applying a new voltage stage to the battery cell.

[0223] In the particular embodiment of the fast-charge method shown in FIG. 33, this fast-charge method comprises, at the output of the above-described VSIP fast-charge process 30, a step 24 for calculating the relative capacity loss Q/Q based on previously collected capacity data 23. These capacity data, that include capacity data collected during two successive charge cycles, may have been collected in different ways: from local storages within the VSIP controller or within the battery cell. The Q/Q value is then compared (step 25) to the threshold F. As long as Q/Q is less than F, the present VSIP charge parameters (step 20) are maintained.

[0224] Temperature T of the battery cell is monitored (step 21) all along the charge process and compared (step 22) to the predetermined limit of temperature Tlim. If measured temperature T exceeds Tlim, the VSIP charge process is ended.

[0225] If Q/Q exceeds F, the VSIP charge parameters (step 20) are then modified and applied to the VSIP charge process 30. Adjustment rules can be easily derived from the equations governing the VSIP process as above described. Artificial Intelligence techniques can also be implemented to process previous capacity loss measures in function of a plurality of VSIP parameters.

[0226] Of course, the present disclosure is not limited to the above-described examples and other embodiments can be considered without departing from the scope of the present disclosure.