Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
  • G01R31/392—Determining battery ageing or deterioration, e.g. state of health
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
  • G01R31/382—Arrangements for monitoring battery or accumulator variables, e.g. SoC
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
  • H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
  • H01M10/486—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte for measuring temperature
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention pertains to methods, devices, and systems to determine certain thermal properties of an electrochemical device that contains an electrolyte, and from that to determine useful information about the electrochemical device. For instance, the invention can be used to determine the state -of-health of lithium ion batteries and other electrochemical devices. Background
• the state-of -health of a lithium ion battery measures the fraction of life that remains should the battery continue to be operated in the same way, for example for a battery in a portable phone or a battery in an electric vehicle.
• the fraction of life remaining can be defined by the ratio of the number of remaining charge -discharge cycles (to occur in the future) to the total number of charge -discharge cycles that will occur over the entire life of the battery.
• the fraction of life remaining can be defined by the ratio of the remaining time (to occur in the future) that the battery will be useful to the total time that that battery will be useful.
• the state -of-health of any rechargeable or secondary electrochemical device can defined in a similar way.
• Li-ion batteries Measuring or estimating the state-of-health of an arbitrary Li-ion battery is very difficult to do.
• proposals to take Li-ion batteries from used electric vehicles and re-use them for grid energy storage In such an enterprise, it will be important to know if some batteries are expected to have, e.g. 10% life remaining while others have, e.g. 90% remaining, so that when these are connected in an energy storage facility the batteries can be connected appropriately to ensure ease of replacement at an appropriate time.
• batteries in electric vehicles age at different rates depending on numerous factors including temperature history, driving habits, charging potential, chemistry of the Li-ion cells selected, etc., so it is important to know their state-of-health before re-using or replacing them.
• US 8,415,926 discloses impedance measurements to estimate state- of-health.
• US 8,937,459 discloses comparisons of voltage and current to a look-up table on batteries of known degree of degradation to estimate battery state-of-health.
• US 8,427,166 discloses electrical measurements of battery capacity and voltage to determine state-of-health.
• US 8,589,097 discloses a method that compares the voltage of a battery under load and after elimination of load (open circuit) to estimate state-of-health.
• US 8,680,815 discloses a method involving comparisons of dQ/dV (differential capacity) vs V (voltage) of the battery under load to those of a reference anode and cathode.
• US 8,116,998 discloses a method in which internal resistances of batteries are compared to a predetermined critical resistance threshold.
• US 7,554,294 discloses a method in which a full AC impedance spectrum is used to characterize battery health.
• US 6,456,043 discloses a method of monitoring of voltage and capacity during storage periods to determine state-of-health of the battery. All the aforementioned prior art references use some sort of electrical measurement to determine the state-of-health and require prior knowledge of the battery behaviour throughout its lifetime.
• US Patent Application 2014/0107949 discloses a method in which a stress/strain sensor mounted on the battery is used to determine the state-of-health of a battery by comparison to previously measured stress/strain data for batteries at a different state of charge and different state-of- health. This method involves substantial prior knowledge of the battery behaviour throughout its entire lifetime.
• liquid electrolytes in Li-ion battery cells react with the charged electrode materials during operation, solid, polymeric and gaseous reaction products are created and the amount of liquid electrolyte remaining within the cells decreases.
• liquids like water and sea water, freeze when the temperature is lowered below the freezing point and ice melts when the temperature is increased above the melting point.
• the same logic can be applied to a lithium ion battery cell which has been cooled to a point where the electrolyte has frozen.
• the more liquid electrolyte remaining in the cell the longer the cell will remain at the electrolyte melting point as the cell warms.
• the magnitudes of the thermal features associated with such phase transitions are easily measured with instruments such as a differential scanning calorimeter (DSC) or a differential thermal analyzer (DTA).
• DSC differential scanning calorimeter
• DTA differential thermal analyzer
• a specialized differential thermal analyzer is preferably used that can perform DTA measurements on an entire Li- ion cell without compromising the integrity of the cell.
• the fraction of liquid electrolyte remaining in the Li-ion cell is directly related to the state -of-health of the cell. Therefore, a DTA that can perform non-invasive measurements on a complete Li-ion cell to determine the fraction of electrolyte remaining (in-situ) can determine the state -of-health of the Li-ion cell. Further, a DTA system designed to take measurements on full Li-ion cells can also be used to determine or infer electrolyte composition.
• Changes in thermal behaviour can be used to learn about the degradation modes of the Li-ion cell in addition to determining the fraction of electrolyte remaining. Furthermore, should changes to the electrolyte occur when Li-ion cells are operated outside manufacturer's specifications, then these could be detected using DTA measurements on Li-ion cells. Such measurements may be useful in determining if use of Li-ion batteries has voided a warranty or if battery management systems may have allowed overcharge, for example, at some point during battery operation.
• any battery or other electrochemical device incorporating liquid electrolyte which can be frozen and where the liquid electrolyte is depleted over time during battery operation can be characterized with the instant invention.
• the thermal signatures of a PEO-based (polyethylene oxide-based) electrolyte (Bathium cell) may change with state-of -health. In cases where the depletion of the liquid electrolyte leads to cell degradation, state-of-health can be determined.
• battery chemistries include Na-ion, Mg-ion, Ca-ion, Li-S and dual graphite.
• the invention is not limited to batteries and is applicable to many electrochemical devices. For example, electrochemical supercapacitors and carbon-carbon ultracapacitors can be so characterized.
• the present invention includes a method of determining a state-of-health property of an electrochemical device comprising an appropriate liquid and/or polymer electrolyte.
• the method comprises measuring the thermal features associated with transitions of portions of the liquid electrolyte or polymer electrolyte, comparing the measured thermal features to those of a reference electrochemical device, and deducing the state-of-health property from the comparison.
• the state-of-health property of the electrochemical device which can be determined in such a manner includes but is not limited to cycle life, lifetime, electrolyte composition, exposure to overcharge abuse, and operation outside of manufacturer specifications.
• the method is suitable for use with electrochemical devices including batteries, supercapacitors, and ultracapacitors.
• the method is particularly suitable for use in determining the lifetime of a rechargeable lithium ion battery.
• the thermal features are measured as the temperature of the electrochemical device is varied.
• the measuring step can comprise differential thermal analysis or differential scanning calorimetry.
• the invention also includes thermal feature measuring devices (e.g. differential scanning calorimetry or differential thermal analysis devices) for measuring the state-of-health property of an electrochemical device according to the aforementioned methods.
• thermal feature measuring devices e.g. differential scanning calorimetry or differential thermal analysis devices
• a particularly suitable differential thermal analysis device is for measuring thermal features of a rechargeable lithium ion battery.
• the invention includes a differential thermal analysis system for measuring the state-of-health property, in which the system comprises the aforementioned differential thermal analysis device.
• Figure 1 shows a diagram of an exemplary cell holder used to mount 402035 -size pouch type Li-ion cells in a DTA of the invention.
• the detailed views show an expanded view of the RTD.
• Figure 2 shows a side view for a diagram of the cell holder of Figure 1 with 402035 -size pouch cells mounted.
• Figure 3 shows a side view diagram of the cryostat can.
• Figure 4 shows a top view diagram for the cryostat can.
• Figure 5 shows an exemplary assembled inventive DTA device.
• Figure 6 shows a block diagram of an entire exemplary DTA device of the invention.
• Figure 7 shows the temperature versus time plots for the cryostat can (curve 1), the reference cell (curve 2) and the sample cell (curve 3) in one of the Examples.
• Figure 8a shows the temperature difference between the sample cell and the reference cell plotted versus temperature in one of the Examples.
• Figure 8b shows a DSC experiment on the same electrolyte as in the sample cell.
• Figure 9 shows the difference between sample cell and reference cell temperatures (T samp ie - T reference ) during heating for cells of the Examples containing different amounts of liquid electrolyte.
• Figure 10 shows the peak area from Figure 9 plotted versus electrolyte mass.
• Figure 11 shows a schematic diagram of an exemplary cell holder for a DTA device designed to measure the remaining electrolyte in 18650-size Li-ion cells.
• a relevant electrolyte may be a liquid or a polymer electrolyte and has a density greater than 400 kg/m 3 . Further, a relevant electrolyte is characterized by at least one transition including for instance a melting transition, other phase transition, or a glass transition.
• a relevant liquid electrolyte includes those commonly defined as a fluid which flows to conform to the walls of a container in which it is placed.
• liquid electrolytes in this application include typical Li- ion battery electrolytes such as 1M LiPF 6 ethylene carbonate:ethyl methyl carbonate and typical electrolytes found in a carbon-carbon ultracapacitors such as tetrabutylammonium phosphorus hexafluoride dissolved in acetonitrile.
• Some electrochemical devices may have electrolytes which are polymeric at their operating temperature but become liquid at higher temperature.
• Some electrochemical devices may have gel polymer electrolytes or polymers plasticized by liquid electrolytes. Such devices can also be characterized by the present invention.
• Electrolytes of Li-ion batteries are known to freeze and melt according to their phase diagrams as published in the scientific literature.
• Ding et al. [J. Electrochem. Soc. 147 18688 (2000) and J. Electrochem. Soc. 148 A299 (2001)] used DSC to measure the phase diagram of various solvent mixtures commonly found in Li-ion batteries as electrolyte solvent.
• Figure 1 in Ding et al. [J. Electrochem. Soc. 147 18688 (2000)] shows a typical DSC experiment on a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) which shows thermal features (thermal anomalies) at the temperatures of the liquidus and solidus points in the phase diagram.
• EC ethylene carbonate
• DMC dimethyl carbonate
• DSC experiments are typically made on very small samples of 2 - 20 mg.
• Differential Thermal Analysis is a similar technique which can also measure thermal features (thermal anomalies) associated with transitions (e.g. phase transitions) and is also normally practiced on small samples of a few milligrams.
• thermal features thermal anomalies
• transitions e.g. phase transitions
• a typical 402035 pouch cell contains approximately 900 mg of electrolyte.
• the size of the thermal feature is proportional to the mass of the sample undergoing the transition.
• a DSC instrument manufactured by TA Instruments is the Q1000, which is used in numerous laboratories around the world.
• DSC instruments heat a sample, which shows a transition, and a reference sample, which does not have a transition, at a fixed rate while measuring the heat flow to the sample and to the reference required to provide the desired heating rate.
• a transition like melting or other phase transition
• additional heat is applied to the sample to provide the latent heat of fusion compared to the heat provided to the reference sample.
• DSC instruments could be built to satisfy the requirement of the inventive method, but they are more complex than DTA instruments.
• One early scientific paper describing differential thermal analysis (DTA) is that of M. Void [Analytical Chemistry, 21, 683 (1949)]. In the DTA method, the sample and a reference (which does not show a transition) are heated by contact with air in an appropriate device.
• One embodiment of the present invention includes DTA systems designed to measure the fraction of liquid electrolyte remaining in Li-ion cells which can be used as a state-of -health indicator.
• a DTA system designed to take measurements on full Li-ion cells can also be used to determine or infer electrolyte composition.
• Figures 2 through 11 of Ding et al. [J. Electrochem. Soc. 147 18688 (2000)] and Figures 1 through 6 of Ding et al. [J. Electrochem. Soc, 148, A299 (2001)] show that the phase diagrams of Li-ion battery binary electrolyte solvents depend on the solvents and upon the ratio of solvents used. For example, the liquidus lines are strongly dependent on solvent ratio while both the solidus and liquidus lines are strongly affected by salt content.
• FIG. 1 shows a diagram of a cell holder used to mount 402035-size pouch type Li-ion cells in the inventive DTA.
• the cell holder consists of polypropylene frame 1 with two 100 ⁇ Pt resistance temperature devices (e.g. RTD - US Sensor - Pt. PPG101A1) 2 mounted slightly "proud" of the surface of the polypropylene frame.
• the polypropylene frame is attached to a piece of 1 ⁇ 4" diameter thin-walled stainless steel tubing 3.
• RTDs 2 were soldered directly to 36AWG Phosphorus-Bronze alloy QuadLead cryogenic wire from Lakeshore (Lake shore --QL36). These leads complete a full wrap of the "I" shaped profile of the frame and are heat sunk to frame 1 using a layer of GE varnish and Kim wipe before switching to 24AWG copper wire which is fed up through the inside of the stainless steel tubing. This is done to avoid thermal noise from the lab environment from corrupting the temperature signal.
• the 24 AWG copper wires were fed through the inside of the stainless steel tubing.
• Detailed view A shows an expanded view of RTD 2.
• Detailed view B shows an expanded side view of RTD 2.
• Figure 2 shows a side view for a diagram of the cell holder of Figure 1 with sample and reference 402035-size pouch cells installed.
• Figure 2 shows reference Li-ion cell 4a mounted on one side of the frame such that it is pressed firmly against reference RTD 2 and sample Li-ion cell 4b mounted on the other side of the frame such that it is firmly pressed against sample RTD 2.
• the cells are held in position by wrapping two "bread bag” twist ties around the cells and frame and tightening them firmly.
• FIG. 3 shows a side view diagram of an exemplary aluminum cryostat can 5 complete with top flange 6 and o-ring groove 7.
• a 28 W electric band heater 8 (Electroflex - EFH KH-2X6-2.5-28A) is wrapped around the outside of the can.
• Control RTD 9 is attached to the inside of can 5 so that the cryostat can temperature can be monitored while it is controlled by, for instance, a Lakeshore Cryotronics model 340 temperature controller.
• Control RTD 9 is held in place using a thermally insulating layer of Stycast (2850FT and Cat24LV) around the rear and sides of the sensor to promote thermal coupling to the cryostat can alone.
• Cryostat can 5 is mounted and removed to install cells on the cell holder, and thus the control RTD wires are attached to female electrical connector 10 (TE Connectivity— 66105-4) for ease of installation.
• control RTD 9 is heat sunk using QuadLead cryogenic wire that wraps around the inner circumference of the cryostat before switching to copper wire for feeding out.
• the walls of cryostat can 5 are wrapped with a layer of alumina wool insulation 11 and a plastic sheet to hold the alumina wool in place. No insulation is applied to the bottom of the cryostat can.
• Figure 4 shows a top view diagram of cryostat can 5. The labelling of parts is the same as in Figure 3.
• FIG. 5 shows an assembled inventive DTA device.
• a "cut-away" in cryostat can 5 allows the cell holder and pouch cells (as in Figure 2) to be observed.
• Stainless steel cryostat lid 12 is silver soldered to thin walled stainless steel tubing 3 supporting the polypropylene frame 1.
• Silicone o-ring 13 seals cryostat can 5 from air in order to prevent condensation of water on the cells under measurement.
• Cryostat can 5 is continuously flushed with a small volume flow of helium gas, ⁇ 80 seem at a small overpressure of 40kPa, (Praxair UHP grade) so helium gas inlet 14 and helium gas outlet 15 are provided accordingly.
• the male electrical connector for control RTD 16 (TE Connectivity— 66103-4) is attached to wires which are fed within the thin walled stainless steel tubing.
• the entire DTA device is designated as item 17 so that it can be described with respect to the entire DTA system in Figure 6.
• FIG. 6 shows a block diagram of an entire exemplary DTA system including the aforementioned DTA device 17.
• Hollow copper platform 18 is fabricated from 2.5" diameter copper pipe with 1 ⁇ 4" wall thickness.
• a 3" diameter (1/4" thick) disc-shaped copper top is soldered to the copper pipe and several 5.65 mm diameter holes are drilled in the sides of the copper pipe just under the copper disc.
• the copper platform is placed within liquid nitrogen dewar 19 (Cryofab— CF 4515).
• Rotameter 20 (Matheson— FM1051V) is used to control the flow of helium within helium gas lines 21 connected to a helium cylinder).
• the necessary electrical connections 22 from DTA device 17 to Lakeshore temperature controller 23 and control computer with VB.NET control software and IEEE-GPIB interface card 24 are also included.
• cryostat can 5 is flushed with a slow steady stream of He gas.
• the liquid nitrogen dewar is filled with liquid nitrogen to the level of the top of the copper platform.
• the jack stand connected to DTA device 27 is used to lower the DTA device cryostat can onto the top of the copper platform.
• the thermal coupling between the cold copper platform (-196°C) and cryostat can 5 is sufficient to cool DTA device 27 to temperatures as low as -120°C in a reasonable period of time.
• DTA device 27 is lifted off the copper platform.
• the heater, temperature controller and computer with control software are used to stabilize the temperature at the desired starting point.
• the heater and temperature controller are instructed to heat the cryostat can 5 at a fixed rate (e.g. l°C/minute) while the sample cell and reference cell temperatures are monitored versus time.
• 402035 pouch cells (40 mm high x 20 mm wide x 3.5 mm thick) were obtained dry (without electrolyte) from LiFUN Technologies in China (Li-Fun Technology, Xinma Industry Zone, Golden Dragon Road, Tianyuan District, Zhuzhou City, Hunan province, PRC, 412000, China).
• the sample cells were vacuum filled with various amounts of electrolyte within an argon-filled glove box.
• the electrolyte used in the sample cells was 0.4 M LiPF 6 dissolved in ethylene carbonate: dimethyl carbonate 1 :2 by weight. Additionally, an electrolyte of 1 M LiPF 6 in methyl acetate (MA), which does not freeze above -110°C, was prepared to use in the reference cell.
• the electrolyte salt and the solvents were obtained from BASF.
• Figure 7 shows temperature versus time plots for the cryostat can (curve 1), the reference cell (curve 2) and the sample cell (curve 3) during an experiment where the heating rate was 1.50°C/min.
• the sample 402035 cell contained 0.9 grams of 0.4 M LiPF 6 EC:DMC electrolyte and the reference 402035 cell contained 0.9 grams of 1 M LiPF 6 methyl acetate (Melting point ⁇ -110°C) electrolyte.
• Figure 7 shows that that the cryostat temperature and the reference cell temperature increased linearly in time.
• Figure 7 also shows a clear thermal feature (thermal anomaly) in the response of the sample cell near a temperature of -10°C, as expected based on the results in Figure 2 of Ding et al. [J. Electrochem. Soc. 147 18688 (2000)].
• Figure 8a shows the temperature difference between the sample cell and the reference cell plotted versus the temperature of the sample cell for the results in Figure 7.
• Figure 8b shows the results of a DSC experiment (using a TA Instruments Q1000 DSC) on a few mg of the same electrolyte as in the sample cell which clearly shows the melting of the electrolyte in an analogous manner to that shown in Figure 8a.
• Figures 7, 8a, and 8b clearly prove that the inventive DTA system can detect the melting of the electrolyte within a complete Li-ion cell.
• Figure 9 clearly shows that the size of the feature in ⁇ vs. T increases as the amount of electrolyte within the Li-ion pouch cell increases.
• the inventive DTA system is sensitive to the amount of electrolyte remaining in a Li-ion cell.
• Figure 10 shows the area of the feature in ⁇ vs. T from Figure 9 plotted versus the electrolyte mass.
• the relationship in Figure 10 is linear indicating that the size of the feature in ⁇ vs. T is proportional to the amount of liquid electrolyte in the cell. This proves that the inventive DTA system can quantitatively detect the amount of liquid electrolyte within a Li-ion cell.
• the inventive DTA system as a state-of -health indicator for Li-ion cells the following procedure could be used, for example.
• a fresh sample Li-ion cell would be measured in the DTA system using an identical cell filled with methyl acetate (or a suitable alternative) electrolyte as the reference cell.
• the DTA system would be used to measure an aged (by charge-discharge cycling, storage or use in the field) Li-ion cell of the same type versus the methyl acetate reference cell.
• the magnitude of the thermal feature in the first experiment would be compared to that in the second experiment in order to determine the fraction of liquid electrolyte remaining.
• the melting temperature and the features in the thermal response could also change if the liquid electrolyte composition changed significantly in the aged cell as previously discussed.
• Figure 11 shows a schematic diagram of a cell holder for a DTA device designed to measure the remaining electrolyte in 18650-size Li-ion cells.
• polypropylene frame 1 sample and reference resistance-temperature devices (RTDs) 2
• RTDs resistance-temperature devices
• Sample 18650 cell 27a and reference 18650 cell 27b are also shown.
• the method of the invention is not limited to analyzing Li-ion batteries. Any battery incorporating liquid electrolyte which can be frozen and where the liquid electrolyte is depleted over time during battery operation can be characterized with the instant invention. In cases where the depletion of the liquid electrolyte leads to cell degradation, state-of -health can be determined. Examples of such battery chemistries include Na-ion, Mg-ion, Ca-ion, Li-S and dual graphite. Furthermore, the invention is not limited to batteries and is applicable to many electrochemical devices. For example, electrochemical supercapacitors and carbon-carbon ultracapacitors can be so characterized.

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• 2016
  • 2016-03-14 WO PCT/CA2016/050277 patent/WO2016145519A1/en not_active Ceased
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