METHOD FOR INCREASING THE DISCHARGE CAPACITY OF A BATTERY CELL AND CHARGE SYSTEM ADAPTED TO SUCH METHOD

Abstract

A method is used for increasing the discharge capacity (Qdisch) of a battery cell provided with charge/discharge terminals to which a charging voltage can be applied with a flowing charging current. The method involves applying a plurality of charge cycles to the battery cell, each of which comprises applying a plurality of constant voltage stages each comprising intermittent voltage plateaus, and monitoring current flow. The temperature of the battery cell is monitored and maintained under a predetermined limit temperature, and the charge cycles are performed until the discharge capacity reaches a predetermined target capacity greater than the rated capacity.

Description

TECHNICAL FIELD

The present disclosure relates to a method for increasing the discharge capacity of a battery cell. It also relates to a charge system adapted to such method.

BACKGROUND

As compared to other rechargeable batteries operating at the ambient temperatures such as alkaline-electrolyte and acid-electrolyte based batteries, lithium-ion batteries (LIB) show the best combined performances in terms of energy density (Ea), power density (Pa), life span, operation temperature range, lack of memory effect, lower and lower costs and recyclability.

The LIB market is expanding exponentially to cover the three main applications: a) mobile electronics (ME) (cellphones, handhold devices, laptop PCs . . . ), b) electromobility (EM) (e-bikes, e-cars, e-buses, drones, aerospace, boats, . . . ), and c) stationary energy storage systems (ESS) (power plants, buildings/houses, clean energy (solar, wind, . . . )), industry, telecom . . . .

The fastest growing market segment of LIB is the electromobility market.

In electromobility, energy density goes with the operation time and driving range of any electric vehicle (EV). Higher E_d provides longer driving range when using a battery pack of a fixed weight (kg) and volume (l).

The energy density of LIB has been steadily improved since their commercialization. However, recent years showed a slowdown in Ea increase with a plateau around 250 Wh/kg and 700 Wh/l at the cell level.

Because of Ea and Pa limitations, current EV, which are mostly LIB powered, have a driving range of about 250 km to 650 km per full charge and a full charging time above 60 min.

Current internal combustion cars can fill a tank in 5-10 min and provide a driving range up to 900 km.

To ensure success public acceptance of EV for the coming energy transition the most serious option today is fast charging. Current fast charging stations for EV provide a limited amount of charge below 60 min because of: 1) overheating (reaching a safety temperature limit), and/or 2) overcharging (reaching a safety voltage limit).

Common charging methods for Lithium-Ion Batteries are disclosed in the Journal of Energy Storage 6 (2016) 125-141, as shown by Prior Art FIG. 1.

Except for the “voltage trajectory” method, all other LIB charging methods apply a constant current and/or a constant voltage in at least a step of the charging process.

There is no indication of cell cycle life nor of the cell temperature profile when these methods are used for 0-100% full charging of a LIB in less than 60 minutes (fast charging). There is no indication the methods apply to any battery chemistry

With reference to Prior Art FIG. 2 the typical CCCV (Constant Current-Constant voltage) charging and Constant Current discharge profile, during the Constant Current step, the voltage increases from its initial value to a set voltage value (up to 4.4V). During the Constant Voltage step, up to 4.4V, the current drops to a set value (here 0.05 C or C/20).

During the rest time, current is nil, and voltage drops to reach an open-circuit voltage (OCV).

During the CC discharge, the current is fixed, and voltage drops to a limit (here 2.5V).

During the following rest time, current is nil, and voltage increases to a new OCV value.

With reference to Prior Art FIG. 3 that features multistage constant current charge profile (MSCC), two charge currents have been applied successively to the cell, I1 and I2, (where in general I1>I2).

I1 is applied until voltage reaches a first value V1, then I2 is applied until voltage reaches a value of V2, and so on.

Other currents Ij can be applied until a voltage Vj is reached, where V1>V2>V3> . . . Vj>Vj+1.

The MSCC charge process ends when either the target capacity is reached, or a voltage high limit is reached or temperature limit is reached.

CCCV and MSCC are the most popular charging methods used in lithium-ion batteries today. CCCV and MSCC are simple and convenient methods if the full charging time is above 2 hours.

Both CCCV and MSCC are based on applying one or several charging constant current(s) (CC) up to preset voltage limit(s), then for CCCV by applying a constant voltage (CV).

Both CCCV and MSCC cannot realistically be used to charge a battery in less than one hour because of: 1) excess heat generation, 2) lithium metal plating on the anode side, which may create an internal short circuit and thermal runaway event, 3) the reduction of the battery life due to accelerated ageing.

Moreover, when used for charging battery cells connected in series, CCCV requires cell balancing, as discussed, for example, in the paper “Implementation of a LiFePO4 battery charger for cell balancing application,” by Amin et al./Journal of Mechatronics, Electrical Power, and Vehicular Technology 9 (2018)81-88.

Active cell balancing, which is required for high power applications, has the disadvantage of slow balancing speed and thus time-consuming, complex switching structures. Active cell balancing also needs advanced control techniques for switch operation.

Fast charging (FC) protocols are reviewed in the paper “Lithium-ion battery fast charging: a review” published in eTransportation 1 (2019) 100011. Issues of fast-charging are identified for fast-charging with charging time<1 h: heat generation, lithium plating, materials degradation, limited charge uptake within tch (ΔSOC<100%), reduced cycle life, safety, and thermal runaway.

The paper in Journal of Energy Storage 29 (2020) 101342 recites CCCV limitations in fast charging and discloses that cycle life decreases when the Total Charge Time (TCT)=CCCT+CVCT decreases.

As recited in eTransportation 1 (2019) 100011, to date, no reliable onboard methods exist to detect the occurrence of crucial degradation phenomena such as lithium plating or mechanical cracking. Techniques for detecting lithium plating based on the characteristic voltage plateau are promising for online application, but fully reliable methods to distinguish lithium stripping from other plateau-inducing phenomena, or to detect plating where no plateau is observed, have not yet been reported.

Many studies on fast charging protocols have been of empirical or experimental nature, and therefore their performance has only been assessed for a limited range of cell chemistries, form factors, and operating conditions. Such results cannot be easily extended to other cell types or ambient temperatures, as supported by the often-conflicting findings reported by different authors.

The rated capacity of a battery cell is usually determined by charging the battery cell with a CCCV process and then discharging it very slowly (typically 10 hs).

Presently, many research programs are implemented worldwide for increasing the capacity of LIB. Considerable budgets are committed to these programs, while the actual capacities of existing batteries have not yet been explored.

A main objective of the present disclosure is to propose an alternative to this costly trend by proposing a new method for increasing the discharge capacity of a battery cell beyond its own rated capacity, in order to get an augmented battery.

Main Symbols and Definitions

i, I=Electric current intensity (A, mA . . . )

v, V=Cell voltage (in Volt, V)

Q_ch, q_ch=charge capacity (Ah, mAh . . . )

Q_dis, q_dis=discharge capacity (Ah, mAh . . . )

Q_nom=cell nominal capacity (Ah, mAh . . . )

C-rate=current intensity relative to the charge time in hour

• • 1C-rate is the current intensity needed to achieve Q_nom in 1 h
  • 2C-rate is the current intensity needed to achieve Q_nom in 0.5 h
  • 0.5C-rate is the current intensity needed to achieve Q_nom in 2 h

SOC=state of charge relative to Q_nom (in %)

SOH=state of health is the actual full capacity of the cell relative to the initial Q_nom

SOS=state of safety estimated risk of thermal runaway

A=The time derivative of voltage

$\left(A=\frac{\partial V}{\partial t}\mathrm{in}V.s^{-1}\right)$

t_s=step time (in s)

t_ch=charge time (in min)

BRIEF SUMMARY

The goal of getting an augmented battery is reached with a method for increasing the discharge capacity (Q_disch) of a battery cell having a rated capacity and provided with charge/discharge terminals to which a charging voltage can be applied with a flowing charging current, the method comprising:

• • implementing a plurality of charge cycles to the battery cell, each of the charge cycle comprising the steps of:
    • applying to a plurality of constant voltage stages V_j, where V_j+1>V_j, j=1, 2 . . . , k, each voltage stage comprising intermittent n_j voltage plateaus,
    • between two successive voltage plateaus within a voltage stage, letting the charging current going to rest (I=0 A) for a rest period R_j^p, 1≤p≤n_j,
    • between two successive current rest times R_j^p−1 and R_j^p within a voltage stage V_j, and a pending voltage plateau, detecting the flowing pulse-like current dropping from an initial value I_j,pⁱⁿⁱ reaches a final value I_j,p^fin where 1≤p≤n_j,
    • ending the pending voltage plateau, so that the flowing pulse-like current drops to zero for a rest time R_j^p, with the voltage departing from V_j,
    • after the rest time R_j^p is elapsed, applying back the voltage to V_j.
    • initiating a transition from a voltage stage V_j to the following stage V_j+1 when, I_j,p^fin, p=n_j reaches a threshold value I_j,nj^Thr,
    • calculating the following stage V_j+1 as =V_j+DV(j), with fin DV(j) relating to the current change DI(j)=I_j,pⁱⁿⁱ˜I_j,p^fin, p=n_j, and ΔV/Δt a function of the following parameters i, V, Δi/Δt, T, SoC (State of Charge), SOH (State of Health),
  • monitoring the temperature of the battery cell under a predetermined limit temperature,
  • proceeding the charge cycles until the discharge capacity reaches a predetermined target capacity greater than the rated capacity.

The calculating step implements parameters such as the upper voltage limit, and/or the step time, and/or voltage step DV and/or ΔI/Δt for the voltage step transition.

The charge cycles are proceeded until either one of the following conditions is reached:

• • a pre-set charge capacity or state of charge (SOC) is reached,
  • the cell temperature exceeds a pre-set limit value T_lim, and
  • the cell voltage has exceeded a pre-set limit value V_lim.

The method of the present disclosure can further comprise an initial step for determining a K-value and a charge step from inputs including charging instructions for C-rate, voltage and charge time, and a step for detecting a Cshift threshold, leading to a step for determining a shift voltage, by applying a non-linear voltage equation and using K-value and ΔC-rate.

This method can be applied to a combination of battery cells arranged in series and/or un parallel.

The method of the present disclosure can further comprise a step for collecting in the battery cell data related to the rated capacity for the battery cell, and this collect step can include reading a QR code on the battery cell.

According to another aspect of the present disclosure, there is proposed a system for fast-charging a battery cell having a rated discharge capacity, implementing the method as described herein, the system comprising an electronic converter connected to a power source and designed for applying a charging voltage to the terminals of a battery cell, the electronic converter being controlled by a charging controller designed to process battery cell flowing current and cell voltage measurement data and charging instruction data, characterized in that the charging controller is further designed to control the electronic converter so as to proceed a plurality of charge cycles, each charge cycle comprising steps for;

• • applying to terminals of the battery cell a plurality of constant voltage stages Vj, where V_j+1>V_j, j=1, 2 . . . , k, each voltage stage comprising intermittent n_j voltage plateaus,
  • between two successive voltage plateaus within a voltage stage, letting the charging current going to rest (1=0 A) for a rest period R_p^j, 1≤p≤n_j,
  • until the discharge capacity reaches a predetermined target capacity greater than the rated capacity.

The charge cycles can be proceeded until either one of the following conditions is reached:

• • the cell temperature exceeds a pre-set limit value T_lim, and
  • the cell voltage has exceeded a pre-set limit value V_lim.

In a specific embodiment of a charge system according to the present disclosure, this charge system includes a control device for entering a request for extra-charge of a battery cell or a battery system.

The extra-charge system of the present disclosure can also be automated by reading the QR code attached to a battery.

The main characteristics of the extra-charge system of the present disclosure implementing Voltage Staged Intermittent Pulse charge method, are:

• • The total full (100% ΔSOC) charging time is below 60 min, and may be below 30 min,
  • VSIP fully charges a battery (SOC=100%) in a time lower than 30 min,
  • The charging time is even lower if ΔSOC<100% (partial charge such as, for example, from 20 to 100%, ΔSOC=80%),
  • The cell voltage during VSIP may exceed 4.5V in LIB, 2V in of alkaline cells and 3V in lead acid batteries,
  • During VSIP none of the voltage and current is constant for a period higher than 3 min.,
  • The temperature difference between the cell temperature Tcell and the ambient temperature Tamb remains below 25° C. (Tcell−Tamb<25° C.) during VSIP,
  • The VSIP operating parameters are adjustable according to the cell SOC, SOH and SOS,
  • VSIP parameters adjustment can be performed using artificial intelligence (AI, such as machine learning, deep learning . . . ),
  • VSIP applies to individual battery cells as well as to cells arranged in series and in parallel (battery modules, battery packs, power wall, . . . ), and
  • Two successive VSIP current and voltage profiles can be different from each other.

VSIP is a universal charging technology that applies to all types of rechargeable batteries, including lead acid, alkaline, lithium ion, lithium polymer and solid-state lithium cells and for any application, including but not limited to ME, EM and ESS.

VSIP fully charges batteries (from 0 to 100% SOC) below 60 min and below 30 minutes, while keeping the cell temperature below 50° C. (safety) and providing long life span.

VSIP can apply for quality control (QC) of batteries for specific applications (stress test).

Because VSIP is an adapted charging method it extends the life span of batteries under any operation conditions (power profile, temperature, . . . ).

VSIP increases the energy density of battery cells versus their rated energy density.

Although VSIP is designed for fast charging it also applies to longer charging times tch>60 min.

VSIP 100% SOC charge below 20 min is possible while keeping low temperatures (<45° C.) and long cycle life (>1300 #).

Partial charge (ΔSOC<100%) can be performed in under 10 min.

Voltages above 4.5V can be safely reached under VSIP charge.

No sign of lithium plating during VSIP charge.

Over 1000 charge-discharge cycles can be achieved with ΔSOC<100% with VSIP charge.

VSIP can be used for: 1) cell's quality control. 2) single cells and for cells arranged in series and in parallel, 3) storage capacity enhancement,

Fast charging performance index can be used as a metrics to compare fast charge protocols.

Furthermore, with the NLV based fast-charge method according to the present disclosure, it is no longer necessary to provide cell balancing for the charging of battery cells connected in series, since it is the charging voltage that is now controlled. Thus, the fast-charging method of the present disclosure provides intrinsic balancing between the battery cells.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures illustrating Prior Art:

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

FIG. 2 illustrates Typical CCCV charging and CC discharge profile;

FIG. 3 illustrates Multistage constant current charge profile (MSCC);

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

Figures illustrating the present disclosure:

FIG. 6 illustrates typical voltage and current profiles during VSIP charge and CC discharge cycles;

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

FIG. 8 illustrates typical voltage and current profiles during VSIP charge;

FIG. 9 illustrates typical voltage profile during MVSC with a plurality of voltage stages Vj (here total charge time is about 35 min);

FIG. 10 illustrates detailed voltage and current profiles during VSIP charge showing voltage and current intermittency;

FIG. 11 illustrates detailed voltage and current profiles during VSIP charge showing rest time;

FIG. 12 illustrates Voltage and current profiles during rest time showing a voltage drop;

FIG. 13 shows current profile at stage j;

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

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

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

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

FIG. 18 illustrates linear voltammetry vs VSIP;

FIG. 19 illustrates two successive VSIP charge profiles can be different from each other;

FIG. 20 illustrates VSIP charge voltage and current profiles (60 min);

FIG. 21 illustrates VSIP charge voltage and current profiles (45 min);

FIG. 22 illustrates VSIP charge voltage and current profiles (30 min);

FIG. 23 illustrates VSIP charge voltage and current profiles (20 min);

FIG. 24 illustrates 80% partial charge with VSIP in ˜16 min;

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

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

FIG. 27 shows VSIP enhances cell's capacity;

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

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

FIG. 32 illustrates a Cycle performance index;

FIG. 33 is a VSIP flow diagram: Bayesian optimization;

FIG. 34 is a schematic diagram of a fast-charge system implementing the method for increasing the discharge capacity of the present disclosure;

FIG. 35 shows a NLV augmented batteries C-rate profile vs time;

FIG. 36 shows an augmented battery V profile vs time;

FIG. 37 shows an augmented discharge profile vs time;

FIG. 38 shows an augmented battery T profile vs time;

FIG. 39 shows a NLV augmented cell capacity vs the number of cycles;

FIG. 40 shows 4 cells-in-series voltage profiles measured during a NLV charge in about 30 min.

DETAILED DESCRIPTION

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:

• • Fixing the charging time t_ch
  • Reaching the target capacity in t_ch
  • Keeping temperature under control (<60° C.)
  • Achieving the target cycle number
  • Insuring battery safety
  • Enhancing capacity

The variables in the fast-charging method according to the present disclosure are:

• • The VSIP governing equation A=ΔV/Δt=f(i, V, Δi/Δt, T, SOC, SOH)
  • The charge current limits
  • The current trigger for next voltage step
  • The rest time
  • The temperature limit
  • The voltage limit
  • The target capacity limit

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

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

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

With reference to FIGS. 6 and 7, in a first 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.

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, . . . , V_j,V_j+1, . . . V_k including constant voltage plateau.

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.

During a rest time, as illustrated by FIG. 12 showing detailed current and voltage profile, the voltage can be controlled so that ΔV/Δt has a constant negative value calculated as above described.

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

During a voltage plateau V_j, the current at sub-step j,p decreases from I_j,pⁱⁿⁱ to I_j,p^fin shown in FIG. 15.

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

During a voltage charge VSIP sequence lasting 26 min full charge time as shown in FIG. 16, the charge capacity Q_ch 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 Q_dis decreases with the voltage applied to the terminals of the battery cell.

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.

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. 20-23. 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).

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

With reference to FIG. 25, during a VSIP charge in 30 min, 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.

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.

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.

With reference to FIG. 27, by adjusting the VSIP parameters such as the upper voltage limit, the step time, ΔV and ΔI/Δt for the voltage step transition, the discharge capacity can be improved without compromising safety and life span.

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.

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.

As shown in FIG. 40, the profiles of the voltages V1, V2, V3 and V4, corresponding to 4 cells connected in series and measured during a NLV charge in about 30 min, are very close to each other, which avoids cell balancing.

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

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 Φ can be calculated as:

$\Phi =\sum _{i=1}^n\frac{Q_{disch}^i/Q_{nom}}{t_i}$

• • with
  • Φ=normalized cycle performance index
  • i=cycle number
  • t_i=charge time @ i^th cycle (hr)
  • Q_dischⁱ discharge capacity @ i^th cycle (Ah)
  • Q_nom=nominal capacity (Ah)

With reference to FIGS. 33 and 34, an example of an augmented-battery fast-charging system, along with the implemented VSIP charging method, is now described. This augmented-battery fast-charging system 30 includes a VSIP charge system 10 comprising 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.

The VSIP system 10 further includes a VSIP controller 1 designed for receiving and processing:

• • 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,
  • instruction data collected from a user interface, including inputs such as an expected C-Rate, a charge voltage instruction and a charge time instruction.

The user interface 6 is designed to receive as inputs, information on a rated capacity value for the battery cell B and a target capacity value, and a “extra charge” signal from a physical or virtual button 32.

The VSIP controller 1 is further designed to control power electronics components within the converter 11 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.

The augmented-battery fast-charge method implements a VSIP method 100 receiving inputs data including the rated-capacity value 20 and the target-capacity value 21.

These VSIP termination criteria 5 include:

• • minimum C-Rate cut-off,
  • safety voltage exceeded,
  • charge capacity reached, and
  • over temperature.

From inputs “C-Rate,” “Voltage” and “elapsed charge Time,” which can be entered as instructions 6 by an user, the VSIP controller 1 first determines an initial K value and a charge step.

Provided that no charge termination 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-Rate—which is an image of the current flowing into the battery cell—is measured.

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.

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 ΔC-rate. The calculated shift voltage is then applied for applying a new voltage stage to the battery cell.

A step 22 for determining or estimating the discharge capacity is proceeded at the end of each VSIP charge cycle. The value of the discharge capacity is then compared (step 23) to the target capacity. As long as the discharge capacity has not reached the target capacity, a new VSIP charge cycle is proceeded. When the target capacity is reached, the augmented-battery charge method (step 24) of the present disclosure is ended.

With reference to FIGS. 35 to 39, A commercial LIB designed for Electric Vehicle (EV) application was charged in 20 minutes with NLV from 0 to 100% SOC and discharged at 1C-rate to 2.7V.

The cell was then charged with NLV with target capacity 7%, 10%, 13% and 27% higher than its initial rated capacity.

Cell was discharged at same 1C-rate to 2.7V, the discharge capacity was then determined.

TABLE 1
NLV Test Data during augmented capacity tests
Q aug. rate	Max C-rate	Max C-rate	V max	T max
(%)	vs. initial Q	vs. target Q	(V)	(° C.)
0	3.57	3.77	4.40	36.9
7	3.76	3.76	4.45	38.2
10	3.84	3.74	4.48	39
13	3.97	3.77	4.60	41.4
27	4.47	3.77	4.79	46

During NLV charge, the C-rate, Voltage and Temperature profiles varied according to the target capacity, as shown in Table 1.

In all NLV tests the discharge capacity was identical to the target capacity.

During NLV charge tests temperature remained below 50 C.

The maximum C-rate during charge with NLV is almost constant vs. target capacity.

Up to 27% capacity augmentation was achieved with NLV charging with the same battery cell without modifying its composition.

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.

Claims

1. A method for increasing a discharge capacity (Qdisch) of a battery cell having a rated capacity and provided with charge/discharge terminals to which a charging voltage can be applied with a flowing charging current, the method comprising: implementing a plurality of charge cycles to the battery cell, each of the charge cycles comprising the steps of: applying 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 going to rest (I=0 A) for a rest period Rjp, 1≤p≤nj,between two successive current rest times Rjp−1 and Rjp within a voltage stage Vj, and a pending voltage plateau, detecting the flowing pulse-like current dropping from an initial value Ij,pini reaches a final value Ij,pfin in where 1≤p≤nj,ending the pending voltage plateau, so that the flowing pulse-like current drops to zero for a rest time Rjp, with the voltage departing from Vj,after the rest time Rjp is elapsed, applying back the voltage to Vj,initiating a transition from a voltage stage Vj to the following stage Vj+1 when Ij,pfin, p=nj reaches a threshold value Ij,njThr,calculating the following stage Vj+1 as=Vj+ΔV(j), with ΔV(j) relating to the current change ΔI(j)=Ij,pini˜Ij,pfin, p=nj, and ΔV/Δt a function of the following parameters i, V, Δi/Δt, T, SoC (State of Charge), SOH (State of Health),monitoring the temperature of the battery cell under a predetermined limit temperature, andproceeding the charge cycles until the discharge capacity reaches a predetermined target capacity greater than the rated capacity.

2. The method of claim 1, wherein the calculating step implements the upper voltage limit, and/or the step time, and/or voltage step ΔV and/or ΔI/Δt for the voltage step transition.

3. The method of claim 2, wherein the charge cycles are proceeded until any one of the following conditions is reached: a pre-set charge capacity or state of charge (SOC) is reached,the cell temperature exceeds a pre-set limit value Tlim, orthe cell voltage has exceeded a pre-set limit value Vlim.

4. The method of claim 1, further comprising an initial step for determining a K-value and a charge step from inputs including charging instructions for C-rate, voltage and charge time.

5. The method of claim 4, further comprising a step for detecting a Cshift threshold, leading to a step for determining a shift voltage, by applying a non-linear voltage equation and using K-value and ΔC-rate.

6. The method of claim 1, further comprising applying the method to a combination of battery cells arranged in series and/or in parallel.

7. The method of claim 6, implemented to charge a plurality of battery cells connected in series, wherein the method provides intrinsic balancing between the battery cells.

8. The method of claim 1, further comprising collecting battery cell data related to the rated capacity for the battery cell.

9. The method of claim 8, wherein collecting batter cell data includes reading a QR code on the battery cell.

10. A system for increasing a discharge capacity (Qdisch) of a battery cell having a rated capacity and provided with charge/discharge terminals to which a charging voltage can be applied with a flowing charging current, implementing the method according to claim 1, the system comprising an electronic converter connected to a power source and designed for applying a charging voltage to the terminals of the battery cell, the electronic converter being controlled by a charging controller designed to process battery cell flowing current and cell voltage measurement data and charging instruction data, wherein the charging controller is further configured to control the electronic converter so as to proceed perform a plurality of charge cycles, each charge cycle comprising steps for: applying to 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, andbetween two successive voltage plateaus within a voltage stage, letting the charging current go to rest (I=0 A) for a rest period Rjp, 1≤p≤nj,until the discharge capacity reaches a predetermined target capacity greater than the rated capacity.

11. The system of claim 10, wherein the charge cycles are performed until either one of the following conditions is reached: the cell temperature exceeds a pre-set limit value Tlim, orthe cell voltage has exceeded a pre-set limit value Vlim.

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