Method and system for fast-charging an electrochemical cell and fast-charging controller implemented in this system

Abstract

A method for fast-charging an electrochemical cell comprises the steps of: —providing the electrochemical cell, the electrochemical cell presenting an initial state of charge (SOC), and—providing a time-varying charging voltage to the electrochemical cell, thereby generating a charging current resulting in charging of the electrochemical cell from the initial SOC up to a target value SOC.sub.f for the state of charge. The step of providing a time-varying charging voltage involves applying N bundles of current pulses in such a way that: each bundle k (1≤k≤N) comprises a variable number P.sub.k of i.sub.k pulses (1≤i.sub.k≤P.sub.k), each i.sub.k pulse in a k bundle being defined by a C-rate equal to n.sub.i,k.Math.C and a duration τ.sub.i,k. at each pulse i.sub.k, the state of charge (SOC) is increased by δ.sub.ik (%)=n.sub.i,k.Math.τ.sub.i,k/M, with M as a predetermined parameter.

Claims

1. A method for fast-charging an electrochemical cell, the method comprising the steps of: providing the electrochemical cell, the electrochemical cell presenting an initial state of charge (SOC), and providing a time-varying charging voltage to the electrochemical cell, thereby generating a charging current resulting in charging of the electrochemical cell from the initial SOC up to a target value SOC.sub.f for the state of charge, real-time determining the state of charge (SOC) of said electrochemical cell, wherein the step of providing a time-varying charging voltage involves applying N bundles of current pulses in such a way that: each bundle k (1≤k≤N) comprises a variable number P.sub.k of i.sub.k pulses (1≤i.sub.k≤P.sub.k), each i.sub.k pulse in a k bundle being defined by a C-rate equal to n.sub.i,k.Math.C and a duration τ.sub.i,k, with n.sub.i,k as the ratio of the charging current of said i.sub.k pulse to the nominal capacity of said cell, at each pulse i.sub.k, the state of charge (SOC) is increased from said determined state of charge by δ.sub.ik (%)=n.sub.i,k.Math.τ.sub.i,kM, with M as a predetermined parameter, two successive current pulse ik and ik+1 in a bundle are separated by a rest time ρ.sub.i,k and two successive bundles are separated by a rest time ω.sub.k.

2. The charging method of claim 1, wherein parameters N, M, Pk, i.sub.k, n.sub.i,k, τ.sub.i,k, are selected so that: at each complete bundle k, the state of charge (SOC) is increased by an amount δ.sub.K (%)=Σ.sub.i=1.sup.i=Pδ.sub.Pi,k; and Σ.sub.k=1.sup.k=Nδ.sub.k=SOC.sub.f.

3. The charging method of claim 2, wherein τ.sub.i,k is between 1 s and 120 s.

4. The charging method of claim 2, wherein the M parameter is determined as equal to 36.

5. The charging method of claim 2, wherein the amount of SOC increase is in a range extending from 20% to 100%.

6. The charging method of claim 2, wherein the parameters N, M, P.sub.k, i.sub.k, n.sub.i,k, τ.sub.i,k are selected so that a total charge time (t.sub.charge) computed as
t.sub.charge=Σ.sub.k=1.sup.k=NΣ.sub.i=1.sup.i=P.sup.k(τ.sub.i,k+ρ.sub.i,k)+Σ.sub.k=1.sup.k=Nω.sub.k is between 2 hours and 2 minutes, with ω.sub.k being a rest time between two successive bundles.

7. The charging method of claim 1, wherein the SOC determination step comprises implementing a SOC determination method among a group comprising Coulomb counting, Kalman filter, extended Kalman filter, neural networks or thermodynamics.

8. The charging method of claim 1, wherein the SOC determination step is at least partially implemented by an electronic circuit close to or within the electrochemical cell.

9. The charging method of claim 1, wherein the SOC determination step is at least partially implemented by an electronic circuit close to or within a fast-charging system implementing the charging method.

10. The method of claim 1, wherein the electrochemical cell is a secondary battery.

11. The method of claim 10, wherein the electrochemical cell belongs to the group consisting of lithium ion batteries, Sodium ion batteries, Nickel cadmium batteries, lithium polymer batteries, solid state lithium batteries, sodium-sulfur batteries, metal-air batteries, sodium-nickel chloride batteries, nickel metal hydride batteries, lead-acid batteries, or redox-flow batteries.

12. The method of claim 11, wherein the electrochemical cell is a metal-air battery, and wherein a metal in the metal-air battery comprises at least one element selected from among the group consisting of lithium, sodium, magnesium, zinc, aluminum and a combination thereof.

13. A system for fast-charging an electrochemical cell, comprising: two or more electrodes for making an electrical connection to terminals of an electrochemical cell having an initial state of charge (SOC.sub.i); a power supply positioned in electrical communication with the two or more electrodes for providing a controllable time-varying charging voltage to the two or more electrodes; and a processor for controlling the charging voltage provided by the power supply, wherein the processor provides a time-varying charging voltage to the electrochemical cell, thereby generating a charging current resulting in charging of the electrochemical cell from the initial state of charge (SOC.sub.i) to a state-of-charge target value (SOC.sub.f), means for real-time determining the state of the charge (SOC) of the electrochemical cell, wherein the power supply is controlled to apply N bundles of current pulses in such a way that: each bundle k (1≤k≤N) comprises a variable number P.sub.k of i.sub.k pulses (1≤i.sub.k≤P.sub.k) each i.sub.k pulse in a k bundle being defined by a C-rate equal to n.sub.i,k.Math.C and a duration τ.sub.j,k, with n.sub.ik, as the ratio of the charging current of said i.sub.k pulse to the nominal capacity of said cell, at each pulse i.sub.k, the state of charge (SOC) is increased from said determined state of charge by δ.sub.ik (%)=n.sub.i,k.Math.τ.sub.i,k/M with M as a predetermined parameter, two successive current pulse ik and ik+1 in a bundle are separated by a rest time ρ.sub.i,k and two successive bundles are separated by a rest time ω.sub.k.

14. The charging system of claim 13, wherein the SOC-determination means comprise an electronic circuit close to or within the electrochemical cell.

15. The charging system of claim 13, wherein the SOC-determination means comprise an electronic circuit close to or within the power supply.

16. A secondary battery charging controller comprising a control circuit for controlling a charging voltage provided by a power supply for charging a secondary battery, wherein the control circuit controls the charging voltage to provide a time-varying charging voltage to an electrochemical cell, thereby generating a charging current resulting in charging of the electrochemical cell from an initial state of charge (SOC.sub.i) to a state-of-charge target value (SOC.sub.f), wherein the charging controller is programmed to apply N bundles of current pulses in such a way that: each bundle k (1≤k≤N) comprises a variable number P.sub.k of i.sub.k pulses (1≤i.sub.k≤P.sub.k) each i.sub.k pulse in a k bundle being defined by a C-rate equal to n.sub.i,k.Math.C and a duration τ.sub.i,k, with n.sub.ik as the ratio of the charging current of said i.sub.k pulse to the nominal capacity of said cell, at each pulse i.sub.k, the state of charge (SOC) is increased from a determined state of charge by δ.sub.ik (%)=n.sub.i,k.Math.τ.sub.i,k/M with M as a predetermined parameter, two successive current pulse ik and ik+1 in a bundle are separated by a rest time ρ.sub.i,k and two successive bundles are separated by a rest time ω.sub.k.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features and advantages of the present disclosure will become better understood with regards to the following description, appended claims, and accompanying drawings wherein:

(2) FIG. 1 is a functional scheme of a fast-charging system implementing the Cascade Pulse Charging (CPC) protocol according to the present disclosure,

(3) FIG. 2 is an illustration of a charging current profile during bundles, within the charging process according to the present disclosure,

(4) FIG. 3 illustrates a typical voltage profile during a current pulse, observed in the charging process according to the present disclosure,

(5) FIG. 4 illustrates current and voltage profiles during a bundle within the charging process according to the present disclosure,

(6) FIG. 5 illustrates current and voltage profiles measured during a first 10-minute charging test with the charging method according to the present disclosure,

(7) FIG. 6 illustrates an evolution of the charging voltage vs time during the first 10-minute charging test,

(8) FIG. 7 illustrates an evolution of the charging voltage vs the discharge capacity during the first 10-minute charging test,

(9) FIG. 8 illustrates a polarization profile measured during the first 10-minute charging test,

(10) FIG. 9 illustrates a polarization resistance profile measured during the first 10-minute charging test,

(11) FIG. 10 illustrates voltage and current profiles measured at a 50% SOC during a second 10-minute charging test,

(12) FIG. 11 illustrates the evolution of voltage vs time during the second 10-minute charging test,

(13) FIG. 12 illustrates the evolution of current vs time during the second 10-minute charging test,

(14) FIG. 13 illustrates the evolution of charge capacity vs time during the second 10-minute charging test,

(15) FIG. 14 illustrates the evolution of voltage vs discharge capacity during the second 10-minute charging test,

(16) FIG. 15 illustrates a polarization profile measured during the second 10-minute charging test,

(17) FIG. 16 illustrates a polarization resistance profile measured during the second 10-minute charging test,

(18) FIG. 17 illustrates voltage and current profiles measured during a first 15-minute charging test,

(19) FIG. 18 illustrates a charging profile measured during the first 15-minute charging test,

(20) FIG. 19 illustrates an evolution of voltage vs discharge capacity measured during the first 15-minute charging test,

(21) FIG. 20 illustrates a polarization profile measured during the first 15-minute charging test,

(22) FIG. 21 illustrates a polarization resistance profile vs SOC measured during the first 15-minute charging test,

(23) FIG. 22 illustrates voltage variation vs time, measured during a second 15-minute charging test,

(24) FIG. 23 illustrates an evolution of voltage vs discharge capacity during the second 15-minute charging test,

(25) FIG. 24 illustrates a polarization profile with a delay time of 0.5 s, during the second 15-minute charging test,

(26) FIG. 25 illustrates a polarization resistance profile with a delay time of 0.5 s, during the second 15-minute charging test,

(27) FIG. 26 illustrates voltage vs time, measured during a third 15-minute charging test,

(28) FIG. 27 illustrates voltage variation vs discharge capacity measured during the third 15-minute charging test,

(29) FIG. 28 illustrates a polarization profile measured during the third 15-minute charging test,

(30) FIG. 29 illustrates a polarization resistance profile measured during the third 15-minute charging test,

(31) FIG. 30 illustrates a cycle capacity profile measured during the third 15-minute charging test.

DETAILED DESCRIPTION

(32) With reference to FIG. 1, a charger system 1 is provided for charging for charging a battery (cell, pack) 2 via an electric connection 3. The charger system 1 implements an Adaptive Control Protocol (ACP) algorithm or a Cascade Pulse Charging (CPC) algorithm 4. The battery 2 is monitored by a measurement system 5 for measuring Voltage, Temperature and Current. From these measurement, Data 6 on Entropy, Enthalpy and Open-Circuit Voltage (OCV) are calculated and then processed by means of SOC, SOH Algorithms 8 to deliver Data 7 on State of Charge (SOC) and State of Health (SOH) of the battery 2. SOC and SOH Data 7 are processed by the charger system 1.

(33) In this description, the battery 2 includes cylindrical LIB cells of about 700 mAh nominal capacity. Cells have been subjected to the following tests:

(34) 1. Cells are first cycled 3 times. a) CCCV charging (CC=C/2 rate, 350 mA; CV=4.2 V) b) Discharge C/2 rate to 2 V c) Last step is a discharge to 2.5 V

(35) 2. Cells at step c) are charged using the CPC protocol.

(36) 3. Cells are discharged under C/2 rate (350 mA) to 2.5V. Discharge capacity is then determined.

(37) During the CPC protocol; the activation polarization η.sub.a(I,k) (mV) and activation resistance R.sub.a(i,k) are determined for each pulse I,k using the equations:

(38) ${\eta }_a\left(i,k\right)=e\left({\tau }_{i,k}-t_0\right)-e\left(t_0\right)$$R_a\left(i,k\right)=\frac{{\eta }_a\left(i,k\right)}{I\left(i,k\right)}$

(39) Where e(t) is the cell voltage during pulse, t.sub.0 is a delay time and I (i,k) is the current in A. R.sub.a(i,k) is in mΩ. Here 0.5 s<t.sub.0<2 s.

(40) TABLE-US-00001 Range Parameter Symbol/unit low high Total number of bundles k 1 50 Number of pulses in a bundle P.sub.k: (1 ≤ i ≤ P.sub.k) 1 10 C-rate of a pulse (i, k) n.sub.i,k 0.1 20 Time duration of pulse (i, k) τ.sub.i,k (seconds) 1 30 Rest time duration between two pulses ρ.sub.i,k (seconds) 2 60 Rest time duration between two bundles ω.sub.i,k (seconds) 2 60 Increase in SOC at pulse (i, k) δ.sub.i,k (%) 1 25 Increase in SOC at bundle k δ.sub.k (%) 3 50 Total charge time duration 5 300 Activation polarization −50 200 Charge voltage limit 3.6 5 Note: *C-rate is defined as the ratio of the charge current of a pulse 1.sub.ik (in A) to the nominal capacity of the cell (Q in Ah): $n_{i,k}=\frac{1_{i,k}}{Q}\left(h{r}^{-1}\right)$Examples: n.sub.ik = 2 and n.sub.i,k = 0.33 correspond to a charge in 0.5 hour and in 3 hours, respectively. The C-rate definition applies likely to charge and to discharge rates.

(41) FIG. 2 illustrates a charging current profile during bundles, measured during the implementation of the CPC charging method according to the present disclosure, where n.sub.iC is the C-rate of the i.sup.th pulse (A), τ.sub.i is duration of the i.sup.th pulse (s) and ρ.sub.i is the duration of the i.sup.th rest time (s).

(42) A corresponding typical voltage profile during a current pulse is represented in FIG. 3, where τ.sub.i,k is the pulse duration (s), to is a delay time (s), I is the pulse current (A) and R.sub.1, R.sub.2 are ohmic resistances of the cell.

(43) Current and voltage profiles during a bundle are illustrated by FIG. 4.

(44) The following examples are given to illustrate the CPC concept. In these examples: the number of pulses in each bundle is P.sub.k=3 the C-rate of each pulse n.sub.i,k is either increasing, decreasing or constant the increase in SOC (State of Charge) after each pulse is

(45) ${\delta }_{i,k}\left(\%\right)=n_{i,k}\frac{{\tau }_{i,k}}{36}=\frac{5}{3}\%$ the increase in SOC after each bundle is d.sub.k(%)=5% the number of bundles to achieve full charge from 0 to 100% SOC is N=20 the end of charge voltage is <4.9 V

(46) CPC test data illustrated below include Bundles parameters Discharge profile Polarization profiles Polarization resistance profile

(47) A first 10-minute charging test implementing the charging method according to the present disclosure is now described with reference to FIGS. 5-9, with the following test condition:

(48) TABLE-US-00002 Total Rest Time Rest time Discharge Charge Test Time taken after every after every Capacity Capacity Efficiency Time 9 C 9 C 9 C C-rate 5% (mAh) (mAh) (%) ~10 min 6.67 s 6.67 s 6.67 s 2.5 s 5 s 711 700 101.57

(49) A second 10-minute charging test implementing the charging method according to the present disclosure is now described with reference to FIGS. 10-16, with the following test condition:

(50) TABLE-US-00003 Total Rest Time Rest time Discharge Charge Cell Test Time taken after every after every Capacity Capacity Efficiency Number Time 12 C 9 C 7 C C-rate 5% (mAh) (mAh) (%) 50 ~10 min 5 s 6.67 s 8.57 s 3 s 6 s 704 700 100.57

(51) The following table summarizes the main experimental results obtained with the two above-cited tests:

(52) TABLE-US-00004 Discharge capacity Test # C1 C2 C3 Q.sub.d (MAh) 1-1  9C 9C 9C 709 1-2 12C 9C 7C 704

(53) A group of experimental tests corresponding to 15 minutes charging is now described with reference to FIGS. 17-21.

(54) A first 15-minute charging test has been done with the following test conditions:

(55) TABLE-US-00005 Rest Time Rest time Time taken after every after every Total Test Time 1C 3C 6C C-rate 5% ~15 minutes 17 s 13 s 4 s 3.666 s 7.333 s

(56) A second 15-minute charging test has been done with the following test conditions:

(57) TABLE-US-00006 Rest Time Rest time Time taken after every after every Total Test Time 6C 6C 6C C-rate 5% ~15 minutes 10 s 10 s 10 s 3.75 s 7.5 s

(58) A third 15-minute charging test has been done with the following test conditions:

(59) TABLE-US-00007 Rest Time Rest time Time taken after every after every Total Test Time 6C 9C 12C C-rate 5% ~15 minutes 10 s 6.67s 5s 5.75s 11.5 s

(60) A fourth 15-minute charging test has been done with the following test conditions:

(61) TABLE-US-00008 Rest Time Rest time Time taken after every after every Total Test Time 12C 9C 6C C-rate 5% ~15 minutes 10 s 6.67s 5s 5.75s 11.5 s

(62) The following Table summarizes the main results obtained from these four tests and illustrated by FIGS. 22-30.

(63) TABLE-US-00009 Summary-2 Discharge capacity Test # C1 C2 C3 Q.sub.d (MAh) 2-1  1C 3C  6C 362 2-2  6C 6C  6C 703 2-3  6C 9C 12C 696 2-4 12C 9C  6C 701

(64) Another group of tests has been done with the CPC method according to the present disclosure with charging times varying from about 5 hours to 20 minutes, and the main results are summarized in the table below.

(65) TABLE-US-00010 Summary-3 Rest Time Rest time Total after each after every Discharge Test Charge Pulse duration τ.sub.i, k Pulse, 5%, Capacity # Time 1 C 3 C 6 C ρ.sub.i, k ω.sub.i, k (mAh) 3-1 ~5 hours 17 s 13 s 4 s 3.75 minutes 7.5 minutes 710 3-2 ~2.5 hours 17 s 13 s 4 s 1.88 minutes 3.75 minutes 708 3-3 ~1.25 hours 17 s 13 s 4 s 56 s 1.9 minutes 711 3-4 ~37.5 minutes 17 s 13 s 4 s 28 s 56 s 717 3-5 ~20 minutes 17 s 13 s 4 s 8.7 s 17.3 s 716

(66) The experimental tests implementing the CPC charging protocol according to the present disclosure show, in comparison with the convention CCCV protocol, that identical cells were charged in 15 minutes using the CPC protocol, and in 20 minutes using the CCCV protocol at 3 C-rate. CPC charging in 15 minutes is safer than CCCV charging in 20 minutes, since with a CCCV charging, cells inflated at 18 cycles and exploded at 20 cycles.