The present disclosure relates to a method for detecting internal short-circuit (ISC) in batteries. It also relates to a system and battery cells implementing the detection method.
A battery cell consists of an anode (negative pole), a cathode (positive pole), an electrolyte and a separator, among other constituents. During normal operation such as discharge only for a primary battery (disposable) and charge and discharge for a secondary (rechargeable) battery ions and electrons are flowing simultaneously. Ions are flowing inside the cell between anode and cathode owing to the electrolyte, whereas electrons are flowing outside the cell into a load (such as a cellphone) during discharge and into a charger during charge.
There should be no electrons flowing inside the cell between anode and cathode. For this reason, a separator is used between anode and cathode to avoid any physical contact between them. Should electrons flow inside the cell, this leads to self-discharge and capacity loss of the cell, which is undesirable.
An internal short-circuit (ISC) occurs in a battery cell when anode and cathode get in direct electrical contact with each other inside the cell.
Because of the existing difference in voltage between anode and cathode, ΔV (in Volts (V)) an electrical contact between anode and cathode will generate an electric current I (in Amperes (A)), generally called an ISC current or internal leak current.
An ISC has an ohmic resistance between anode and cathode, R (in Ohms (a)).
The current flowing between anode and cathode is given by the Ohm's law:
ΔV=RI (1).
In Eq. (1), ΔV and R vary with time and so does the ISC current I.
When a current I flows into a resistance R a heat power is generated given by the Joule's law
P(W)=R·I2 (2)
Because of the internal heat generated due to the ISC, the local temperature may rise, eventually trigging a thermal event in the cell such as a thermal runaway.
Accordingly, an ISC raises a safety issue in a battery cell.
ISC is considered one of the major root causes of battery thermal events such as thermal runaway, gassing, fire and explosion.
The main reasons an ISC occurs in a battery cell are:
1) Metal dendrite growth on anode surfaces, which eventually crosses the separator causing a short-circuit. Growth of dendrites has been reported for Li and Zn chemistry-based anodes,
2) Metal and other electrically conducting materials particles in the cell due to manufacturing defects, electrode disintegration and dissolution/precipitation processes,
3) Rupture in the separator between anode and cathode due to fatigue and/or mechanical pressure within the cell, and
4) Defective cell design
Should one cell in a battery pack undergo a thermal runaway, the heat generated propagates to the neighbor cells, which in turn may undergo a thermal runaway leading to a catastrophic chain of thermal events. During thermal runaway of a lithium ion battery, for instance, cells temperature may rise above 1000° C. causing metal melting and emission of hot metal particles.
Because of serious safety risks caused by an ISC, it is important to develop methods and systems able to detect the early stages of an ISC formation before a thermal event may take place in a battery cell.
The present disclosure provides a method and a system to detect ISC in a battery cell, and is about using thermodynamics and kinetics data to detect an ISC in a battery cell.
The method applies to any type of batteries, including but not limited to lithium ion battery cells (LIB), nickel cadmium cells (NiCd), nickel metal hydride cells (NIMH), lead acid batteries (LAB), Zinc-air cells, Zinc manganese dioxide cells, redox flow batteries, lithium manganese oxide cells, lithium sulfur and lithium air cells.
Useful thermodynamics data in the present disclosure include but not limited to open-circuit voltage (OCV), entropy (ΔS) and enthalpy (ΔH) data and combinations thereof.
Useful kinetics data include, but not limited to: cell voltage, cell temperature, cell internal resistance and current and combinations thereof.
Thermodynamics data and kinetics data can be measured and processed online owing to an integrated circuit including a smart chip to manage a single cell and a plurality of cells (cell modules, cell packs).
ΔS and ΔH are determined from the OCV and from the temperature dependence of OCV using equations (3), (4):
where E0 is the OCV, x=state of charge, T=temperature, p=pressure and F=the Faraday constant.
OCV, ΔS and ΔH data are plotted vs. the cell charge and discharge capacity (Ah) and/or vs. the cell state of charge (SOC) and/or the cell state of discharge (SOD, SOD=100−SOC).
ΔS and ΔH data are also usually plotted vs. the cell OCV.
OCV, ΔS and ΔH profiles vary with the battery ageing, which relates to the cell state of health (SOH)
The cell voltage varies with the SOC. It increases during charging and decreases during discharging.
When a cell is at rest after charge or discharge—no external current is flowing in the cell—the cell OCV vs. time profile varies with SOC, SOH and temperature ‘T’:
OCV(t)=f(SOC,SOH,T) (5)
a process called cell voltage relaxation.
At fixed SOC and T the OCV vs. time tends to stabilize toward equilibrium OCV.
OCV varies with T enabling ΔS and ΔH to be measured at well-defined SOC and measured OCV as in shown in Eq. (3) and (4).
Thermodynamics and kinetics data comparative analysis enables early stage detection of an ISC.
At fixed cell OCV, the ΔS and ΔH data are significantly different when cell has a ISC as compared when a cell doesn't have an ISC.
At a defined cell's SOC/SOD, the OCV relaxation profile following a charge or discharge is different in cells having an ISC and cells not having an ISC.
The measured differences in the thermodynamics and kinetics data between cells having and not having an ISC are greater than the error bar, which enables an ISC to be detected.
A method and a system has been developed by the Applicant based on thermodynamics and kinetics data collection and analysis to detect an ISC in a battery cell.
Three fitting parameters are computed: U0, A1 and t1
Parameters vary according to cells with and without ISC, especially the t1 parameter.
These and other features and advantages of the present disclosure will become better understood with regard to the following description, appended claims, and accompanying drawings wherein:
Two series of tests have been conducted on lithium ion batteries of about 600 mAh rated capacity from two different origin and chemistry, cells A and cells B.
With reference to
To simulate an ISC, cells A and cells B are loaded with external resistances (REx) (as in the schematics).
For cells A:
Cells without resistance (case infinite) are tested as base cells
For cells B:
(CHn=test channel ‘n’ of the BA3000 machine, 1≤n≤6)
Prior to attaching (or not attaching) an external resistance to the cells, cells are either fully charged or fully discharged at the ambient temperatures (˜25° C.) using an Arbin battery cycler (at C/6 rate, here 100 mA).
Once a cell is fully charged or discharged a resistance is then attached to the cell, then cell is transferred to the BA 3000 machine for immediate thermodynamics and kinetics data measurements under the following protocol:
Fully charged cells are discharged from 100% SOC to 0% SOC by 5% steps. In each step discharge current of 100 mA is applied for 18 minutes followed by rest. Discharging was continued until cell voltage reached 2.5 V cut-off voltage.
Fully discharged cells are charged from 0% SOC to 100% SOC to by 5% steps. In each step charge current of 100 mA is applied for 18 minutes followed by rest. Charging was continued until cell voltage reached 4.2 V cut-off voltage.
After each charge and discharge step OCV is monitored at the ambient temperatures until OCV stabilized (voltage relaxation typically takes about 30 min).
Temperature was then deceased by 5° C. steps from the ambient 25° C. to 20° C., 15° C. and 10° C. then back to ambient. At each temperature OCV was measured until it stabilized (here voltage relaxation typically takes about 20 minutes).
The OCV vs. T data enable entropy and enthalpy to be measured according to Equations (3) and (4).
Experimental for Thermodynamics Data
Thermodynamics data consist of OCV, entropy and enthalpy data plots versus discharge capacity, SOC/SOD for the OCV and versus SOC and OCV for entropy and enthalpy, including (entropy, enthalpy, SOC) 3D plots. This is illustrated in
OCV Profiles
The OCV vs. capacity of
Enthalpy (ΔH) Profiles
Enthalpy vs. OCV profiles are illustrated in
Enthalpy vs. SOC profiles are illustrated in
The difference in the enthalpy profiles both vs. OCV and vs. SOC between cells with simulated ISC and without ISC is significantly larger than in the OCV profiles presented above. Accordingly, enthalpy profile analysis is useful for ISC detection.
Enthalpy profiles of cells A and cells B both vs. OCV and vs. SOC are significantly different due to differences in cells A and B chemistry and/or construction.
Entropy (ΔS) Profiles
Entropy vs. OCV profiles are illustrated in
Entropy vs. SOC profiles are illustrated in
The difference in the entropy profiles both vs. OCV and vs. SOC between cells with simulated ISC and without ISC is significantly larger than in the OCV profiles presented above. Accordingly, entropy profile analysis is useful for ISC detection.
Here too entropy profiles of cells A and cells B both vs. OCV and vs. SOC are significantly different due to differences in cells A and B chemistry and/or construction.
Entropy (ΔS), Enthalpy (ΔH), SOC Profile
Entropy (ΔS), Enthalpy (ΔH), SOC 3D full profiles of cells B #1 to #6 with ISC and without ISC are shown in
Entropy (ΔS), Enthalpy (ΔH), SOC 3D zoom profiles of cells B #1 to #6 with ISC and without ISC are shown in
Entropy (ΔS), Enthalpy (ΔH), SOC profiles 2D projection on the (Entropy, Enthalpy) plane of cells B #1 to #6 with ISC and without ISC are shown in
Here it should be emphasized that the specific OCV and SOC values useful for ISC online detection are: 1) average values within an OCV domain and an SOC domain, 2) cells chemistry and state of health (SOH) dependent.
Accordingly, for a specific cell's chemistry and cell's SOH, a method for ISC detection may consist of driving the cell voltage to one of the average OCV values such as 3.7V, 3.8V, 3.92V and 3.96V for cells B and measure entropy and enthalpy data around that specific OCV value. If the difference in entropy is higher than an error bar, then it is very highly likely the cell has an ISC. Similarly, another method for ISC detection consists of the driving the cell to a specific SOC and measure entropy and enthalpy at that SOC. If the difference in entropy is higher than an error bar, then it is very highly likely the cell has an ISC.
An illustration of embodiments of the present disclosure on the ISC detection method and system is illustrated in
Δ(ΔS(OCV))=|ΔSISC(OCV)−ΔSno-ISC(OCV)| (8),
SOC Vs. Entropy (ΔS) and Enthalpy (ΔH)
In a patent application PCT/IB2018/059751, a method and system are disclosed for online determination of the SOC of primary and rechargeable batteries using and empirical Equation:
SOC=α+βΔS+γΔH (7),
where α, β and γ coefficients are specific to a battery chemistry and SOH.
Here the SOC of cells B with and without ISC are fitted with Eq. (7).
TABLE 1 below summarizes the achieved fitting data together with the coefficient of determination R2. It can be seen that the α, β and γ coefficients are different according to the presence or the absence of an ISC. Accordingly, the SOC fit with Eq. 7 can be used as a method and system to detect an ISC in a battery cell. α, β and γ coefficients can be used individually or in combination to detect an ISC by comparing with a standard cell without ISC.
Experimental for Kinetics Data
The OCV time dependence with temperature is illustrated in
Another embodiment of the present disclosure is the data analysis and simulation of isothermal voltage relaxation profile following discharge at a specific SOC and OCV of cells with and without ISC.
where U(t)=time ‘t’ dependent OCV, U0=Equilibrium OCV (t=∞), A1=pre-exponential coefficient and t1=time constant.
Of course, the present disclosure is not limited to the above-described detailed embodiments and numerous other versions of the ISC detection method and system according to the present disclosure can be implemented without departing from the scope of the present invention as defined by the claims.
Number | Date | Country | Kind |
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10201804493S | May 2018 | SG | national |
This application is a national phase entry under 35 U.S.C. § 371 of International Patent Application PCT/IB2019/054411, filed May 28, 2019, designating the United States of America and published as International Patent Publication WO 2019/229651 A1 on Dec. 5, 2019, which claims the benefit under Article 8 of the Patent Cooperation Treaty to Singapore Patent Application Serial No. 10201804493S, filed May 28, 2018.
Filing Document | Filing Date | Country | Kind |
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PCT/IB2019/054411 | 5/28/2019 | WO | 00 |