Battery pack with thermoplastic barrier between cells

Abstract

The invention discloses a battery pack having: a cell group wherein the cell group comprises cells each defining a cylindrical body wherein the cells are enclosed in respective sleeves wherein the cells are further enclosed in thermoplastic spacers such that the cells are axially parallel to each other and distributed in a planar array, and wherein adjacent ones of the cells are laterally spaced apart from each other by a thermal barrier defining a pitch formed by thermoplastic spacers.

Description

Technical Field

[0001] Aspects herein relate to multi-cell battery packs and more particularly to battery packs having thermoplastic barriers between cells of the battery pack. Background Art

[0002] In a battery pack, a short circuit between battery electrodes of opposite polarity, such as between a lithium anode and a cathode, can lead to a thermal runaway reaction or thermal anomaly, which can sometimes produce unexpected temperatures in a short period of time. Excessive local thermal energy may cause adjacent cells of a multi-cell battery that are not short-circuited or otherwise damaged to spontaneously begin to react in a similar manner. This may cause a phenomenon where one cell in thermal runaway may cause an adjacent cell to enter thermal runaway. This can lead to a cascading effect between cells. Such a phenomenon can damage component parts of the battery and even cause a full-scale fire in the battery pack. Therefore, it is desirable to limit the transfer of thermal energy between cells in order to prevent or reduce such runaway reactions.

[0003] WO2022072641 discloses a lithium-ion battery assembly, which includes a plurality of battery cells arranged in a spaced-apart and substantially parallel manner, each of the battery cells extending along a central axis and having a first end with a negative terminal and a second end with a positive terminal. The assembly includes a first capture plate and a second capture plate, wherein at least the first capture plate defines a capture plate opening corresponding to the plurality of battery cells, the first capture plate being spaced apart from the second capture plate and oriented substantially parallel to the second capture plate. Each of the plurality of battery cells extends between the first capture plate and the second capture plate, and is coaxially arranged with one of the capture plate openings in the first capture plate. The assembly optionally includes a body between the capture plates, the body defining a gap for each battery cell.

[0004] US20180069208A1 discloses a battery pack having cells arranged in an array, but fails to address thermal runaway between cells other than simply spacing the cells out of contact with each other. The disclosed arrangement has low thermal mass between cells.

[0005] WO2011149075A1 discloses cell carriers that are sufficient to hold cells in a fixed position, but these cell carriers are thin, have low thermal capacity or thermal mass, and therefore do not appear to address thermal runaway between cells.

[0006] US20170301905A1 discloses a cell carrier that positions cells very close to each other, has little thermal resistance between cells, and therefore cannot adequately attenuate thermal runaway between cells.

[0007] US20130236759A1 discloses a cell carrier that only partially covers the cells and therefore cannot adequately attenuate thermal runaway between cells. Summary of the invention

[0008] To address these shortcomings, thermal barriers or firewalls can be placed between cells, however firewalls may not provide adequate insulation or have too low a thermal mass to prevent thermal runaway between cells, or they may require undesirable cell spacing, such as excessive spacing, to provide adequate thermal resistance.

[0009] What is needed is a battery pack construction that selects materials with specific thermal capacities so that during combustion (e.g., oxidation), cells that are closely spaced together to provide the desired enclosure also provide reduced thermal runaway. This can be provided by limiting the heat flow, such as by absorbing the heat, so that a thermal anomaly in one cell does not cause an adjacent cell to go into thermal runaway. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following is a brief description of the drawings, in which like elements have like numbers and which are presented for the purpose of illustrating exemplary aspects disclosed herein and not for the purpose of limiting such aspects.

[0011] Figure 1A is a perspective view of a battery pack according to the present disclosure, and the figure identifies section 1B;

[0012] Figure 1B yes Figure 1A A cross section of a battery pack shown in;

[0013] Figure 2 is a top view of a battery pack according to the present disclosure;

[0014] Figure 3 is a flow chart illustrating a method of constructing a battery pack according to the present disclosure; and

[0015] Figure 4 is a perspective view of a thermoplastic encapsulant for a battery pack according to the present disclosure.

[0016] Figure 5A A top view of the unit test device without the cover is shown.

[0017] Figure 5B A side view of the unit testing apparatus of FIG. 5 is shown, shown in cross-section taken along line BB, with the cover shown in hidden lines.

[0018] Figure 6 An experimental cell carrier is shown with no air gaps between cells.

[0019] Figure 7 An experimental cell carrier is shown with air gaps between cells.

[0020] Figure 8An experimental cell carrier is shown in which spaced-apart cells are arranged in thermoplastic cell spacers.

[0021] Fig. 9A A top view of an experimental thermoplastic cell separator is shown.

[0022] Fig. 9B Shows Fig. 9A Side view of an experimental thermoplastic cell separator.

[0023] Fig.10 Pressure measurements for Tests 1-4 as discussed herein are shown.

[0024] Fig.11 Temperature measurements for Tests 1-4 as discussed herein are shown.

[0025] Fig.12 Pressure measurements for Tests 5-7 as discussed herein are shown.

[0026] Fig.13 Temperature measurements for Tests 5-7 as discussed herein are shown.

[0027] Fig.14 Pressure measurements for Tests 8-10 as discussed herein are shown.

[0028] Fig.15 Temperature measurements for Tests 8-10 as discussed herein are shown.

[0029] The images in Figures 5-15 were provided by Underwriters Laboratory, LLC. DETAILED DESCRIPTION

[0030] A detailed description of one or more aspects of the disclosed apparatus and methods is presented herein by way of example and not limitation with reference to the accompanying figures.

[0031] In a multi-cell battery pack (e.g., a battery pack having groups of cells), a short circuit of a battery cell, such as a lithium (Li) battery cell, can result in a runaway reaction that produces temperatures exceeding 600° C. within 20 to 30 seconds. The temperature can cause adjacent cells to ignite, such as by causing a short circuit, resulting in a cascade that destroys the cell and ignites the battery housing. Utilizing a heat sink, which may be made of aluminum, to increase thermal diffusivity and capacity, along with utilizing low thermal conductivity fillers such as silicone to limit heat propagation, may not be sufficient to minimize the heat transferred between cells during these runaway reactions.

[0032] In view of the above considerations, Figure 1A-1BA battery pack 100 is shown that may include a cell group 110. The cell group 110 may include one or more cells 120 that each define a cylindrical body 126. The present subject matter is not limited to cylindrical cells and may be applicable to prismatic cells, but cylindrical cells provide a useful description. Each cell 120 may define an exterior having a height surface extending between an upper base surface and a lower base surface. Multiple cells, including cell 120 may be arranged in the cell group 110 so that the respective lower base surfaces are aligned parallel to each other, as shown. Each of the cells is associated with a thermal runaway potential and a thermal runaway ignition energy including the heat capacity of the cell. In the example, the thermal runaway ignition energy of the cell is 37kJ.

[0033] The cells 120 may be enclosed in respective sleeves 125. The sleeve may be a sleeve or sleeve-shaped or define a sleeve. The cells 120 may be further enclosed in a carrier system 105 including a thermoplastic spacer 150. The thermoplastic matrix 150 may be overmolded on the sleeve 125 so that the carrier system 105 is easily assembled into a battery pack. The cells 120 may be axially parallel to each other and distributed in a planar array. Adjacent cells in the cells 120 may be laterally spaced apart from each other by a thermal barrier that defines a spacing D2 that may be formed by the thermoplastic spacer 150. The sleeve 125 is optional.

[0034] An example may include a unit carrier system 105, which may include a plurality of sleeves 125, each sleeve 125 having a sleeve thickness D1, wherein each of the plurality of units is disposed in the sleeve, wherein each sleeve 125 is associated with a sleeve thermal resistance, and the sleeve thermal resistance is associated with a sleeve thermal capacity. The example may include a thermoplastic spacer 150 formed of a thermoplastic and joined to the plurality of sleeves to define the unit carrier, wherein the thermoplastic spacer includes a thermoplastic thermal resistance associated with a pre-thermolysis heat capacity and a pyrolysis heat capacity including a latent heat of fusion. In one example, the unit carrier may define a unit-to-unit spacing D2 between adjacent units, and for each unit, a respective base surface is exposed, while a respective height surface is shielded by the unit carrier from a height surface of an adjacent unit. This example can be characterized in that the sleeve, sleeve thickness D1, cell-to-cell spacing D2, and thermoplastic spacers are selected so that the sleeve thermal resistance and the thermoplastic thermal resistance provide a combined thermal resistance to limit the heat flow from a cell in thermal runaway to one or more adjacent cells so that the thermal runaway potential energy of the cell in thermal runaway (as limited) is less than the thermal runaway ignition energy of one or more adjacent cells during a thermal runaway event.

[0035] The units 120 may be of the same size and shape as one another. In a multi-component design, a housing 160 may surround the thermoplastic spacer 150. The housing 160 may be of the same material as the sleeve 125. The housing 160 may be a different material than the sleeve 125. The housing 160 may be snap-fit ​​to the carrier, adhered to, or otherwise secured to the unit carrier system 105. The material properties of the thermoplastic spacer 150 may include one or more of the following: a melting point of 110°C to 300°C, or 110°C to 270°C, such as 130°C; a heat capacity of 1400 to 2400 kilojoules per kilogram Kelvin (kJ / kg K), such as 2200 kJ / kg K; a heat of fusion of at least 120 joules per gram (J / g); or a pyrolysis temperature of at least 300°C.

[0036] The thermoplastic spacer 150 may be formed of a polymer composition comprising a thermoplastic polymer. The thermoplastic polymer is not particularly limited and may include at least one of polyacetal, polyacrylic polymer, polycarbonate, polystyrene, polyester, polyamide, polyamideimide, polyarylate, polyarylsulfone, polyethersulfone, polyphenylene sulfide, polysulfone, polyimide, polyetherimide, fluoropolymer (e.g., polytetrafluoroethylene), polyetherketone, polyetheretherketone, polyetherketoneketone, polybenzoxazole, polyoxadiazole, polybenzimidazole, polyacetal, polyanhydride, poly(vinyl ether), poly(vinyl sulfide), poly(vinyl alcohol), poly(vinyl ketone), poly(vinyl halide), poly(vinyl nitrile), poly(vinyl ester), polysulfonate, polysulfide, polysulfonamide, polyurea, or polyphosphazene. Thermoplastic polymers may include polyolefins, polycarbonates, polysulfones, polyetherimides, polyamides, polyesters such as poly(ethylene terephthalate) or poly(butylene terephthalate), polystyrenes, polyethers such as polyetherketones or polyetheretherketones, or polyacrylates such as poly(methyl methacrylate).

[0037] The thermoplastic polymer may include a polyolefin. The polyolefin may include at least one of a homopolymer or a copolymer. The polyolefin may have a general structure: n H 2n , wherein n can be 2 to 20. The polyolefin can include at least one of polyethylene, polypropylene, polyisobutylene or polynorbornene. Examples of polyethylene include linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and medium density polyethylene (MDPE). The polyolefin can include polyolefin copolymers, such as ethylene and propylene, 1-butene, 1-octene, 1-decene, 4-methylpentene-1,2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, 3-hexene, norbornene or diene (e.g., 1,4-hexadiene, monocyclic or polycyclic diene) copolymers. The polyolefin copolymer can include heterophasic polyolefins. The thermoplastic polymer can include polyethylene.

[0038] Thermoplastic compositions can include additives. The additives can include at least one of a blowing agent, a flame retardant, an impact modifier, a flow modifier, a filler (e.g., granular polytetrafluoroethylene (PTFE), glass, carbon, mineral, or metal), a reinforcing agent (e.g., glass fiber), an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet (UV) light stabilizer, a UV absorbing additive, a plasticizer, a lubricant, a release agent (e.g., a mold release agent), an antistatic agent, an antifogging agent, an antimicrobial agent, a colorant (e.g., a dye or pigment), a surface effect additive, a radiation stabilizer, an anti-drip agent (e.g., PTFE-encapsulated styrene-acrylonitrile copolymer (TSAN)), or a combination thereof. For example, a combination of a heat stabilizer, a mold release agent, and an ultraviolet light stabilizer can be used. Typically, additives are used in a commonly known effective amount.

[0039] The thermoplastic composition may include, for example, a blowing agent that foams at about 240°C. The presence of a blowing agent may be used to absorb thermal energy to potentially prevent thermal runaway or prevent oxygen from contacting the surface of the polymer during combustion (expansion). The blowing agent may include a solid blowing agent, a liquid blowing agent, or a supercritical blowing agent. The blowing agent may be solid at room temperature and produce a gas (e.g., nitrogen, carbon dioxide, or ammonia) when heated to a temperature above its decomposition temperature, such as azodicarbonamide, a metal salt of azodicarbonamide, 4,4′-oxybis(benzenesulfonylhydrazide), sodium bicarbonate, ammonium carbonate, etc. The blowing agent may include at least one of an inorganic agent or an organic agent. Examples of inorganic blowing agents include carbon dioxide, nitrogen, argon, water, air, nitrogen, ammonia, and inert gases such as helium and argon. Examples of organic agents include aliphatic hydrocarbons having 1 to 9 carbon atoms, aliphatic alcohols having 1 to 3 carbon atoms, and fully and partially halogenated aliphatic hydrocarbons having 1 to 4 carbon atoms. Examples of aliphatic hydrocarbons include methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, neopentane, etc. Examples of aliphatic alcohols include methanol, ethanol, n-propanol, and isopropanol. Examples of fully and partially halogenated aliphatic hydrocarbons include fluorocarbons, chlorocarbons, and chlorofluorocarbons. Examples of fluorocarbons include fluoromethane, perfluoromethane, fluoroethane, 1,1-difluoroethane, 1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane, pentafluoroethane, difluoromethane, perfluoroethane, 2,2-difluoropropane, 1,1,1-trifluoropropane, perfluoropropane, dichloropropane, difluoropropane, perfluorobutane, perfluorocyclobutane, etc. Examples of partially halogenated chlorocarbons and chlorofluorocarbons include methyl chloride, dichloromethane, ethyl chloride, 1,1,1-trichloroethane, 1,1-dichloro-1-fluoroethane, 1-chloro-1,1-difluoroethane, chlorodifluoromethane, 1,1-dichloro-2,2,2-trifluoroethane, 1-chloro-1,2,2,2-tetrafluoroethane, etc. Examples of fully halogenated chlorofluorocarbons include trichloromonofluoromethane, dichlorodifluoromethane, trichlorotrifluoroethane, 1,1,1-trifluoroethane, pentafluoroethane, dichlorotetrafluoroethane, chloroheptafluoropropane, and dichlorohexafluoropropane. Examples of other chemical agents include azodicarbonamide, azobisisobutyronitrile, benzenesulfonylhydrazide, 4,4-oxobenzenesulfonylsemicarbazide, p-toluenesulfonylsemicarbazide, barium azodicarboxylate, N,N′-dimethyl-N,N′-dinitrosoterephthalamide, trihydrazinotriazine, and the like.

[0040] The thermoplastic composition may include a flame retardant. Useful flame retardants include organic compounds containing chlorine, bromine or phosphorus. The flame retardant may include at least one of a halogenated flame retardant, a phosphorus-containing flame retardant or an inorganic flame retardant. For regulatory reasons, non-brominated and non-chlorinated phosphorus-containing flame retardants may be preferred in certain applications, such as organic phosphates and organic compounds containing phosphorus-nitrogen bonds.

[0041] Examples of halogenated flame retardants include bisphenols represented by the following: 2,2-bis-(3,5-dichlorophenyl)-propane; bis-(2-chlorophenyl)-methane; bis-(2,6-dibromophenyl)-methane; 1,1-bis-(4-iodophenyl)-ethane; 1,2-bis-(2,6-dichlorophenyl)-ethane; 1,1-bis-(2-chloro-4-iodophenyl)-ethane; 1,1-bis-(2-chloro-4-methylphenyl)-ethane; 1,1-bis-(3,5-dichlorophenyl)-ethane; 2,2-bis-(3-phenyl-4-bromophenyl)-ethane; 2,6-bis-(4,6-dichloronaphthyl)-propane; and 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane, 2,2-bis-(3-bromo-4-hydroxyphenyl)-propane. Other halogenated materials include 1,3-dichlorobenzene, 1,4-dibromobenzene, 1,3-dichloro-4-hydroxybenzene and biphenyls, such as 2,2'-dichlorobiphenyl, polybrominated 1,4-diphenoxybenzene, 2,4'-dibromobiphenyl and 2,4'-dichlorobiphenyl and decabromodiphenyl oxide, as well as oligomeric and polymeric halogenated aromatic compounds, such as bisphenol A and tetrabromobisphenol A and carbonate precursors, such as copolycarbonates of phosgene. Metal synergists, such as antimony oxide, can also be used with the flame retardant. When present, the halogen-containing flame retardant can be present in an amount of 1 to 25 parts by weight or 2 to 20 parts by weight based on 100 parts by weight of the total composition excluding any filler.

[0042] Alternatively, the thermoplastic composition can be substantially free of chlorine and bromine. "Substantially free of chlorine and bromine" is defined as having a bromine or chlorine content of less than or equal to 100 parts per million (ppm), less than or equal to 75 ppm, or less than or equal to 50 ppm, based on the total weight of the composition excluding any filler.

[0043] The flame retardant may include a phosphorus-containing flame retardant. Flame retardant aromatic phosphates include triphenyl phosphate, tricresyl phosphate, isopropylated triphenyl phosphate, phenyl bis(dodecyl) phosphate, phenyl bis(neopentyl) phosphate, phenyl bis(3,5,5'-trimethylhexyl) phosphate, ethyl diphenyl phosphate, 2-ethylhexyl di(p-tolyl) phosphate, bis(2-ethylhexyl) p-tolyl phosphate, tricresyl phosphate, bis(2-ethylhexyl) phenyl phosphate, tri(nonylphenyl) phosphate, bis(dodecyl) p-tolyl phosphate, dibutylphenyl phosphate, 2-chloroethyl diphenyl phosphate, p-tolyl bis(2,5,5'-trimethylhexyl) phosphate, and 2-ethylhexyl diphenyl phosphate. Difunctional or polyfunctional aromatic phosphorus-containing compounds are also useful, such as resorcinol tetraphenyl diphosphate (RDP), bis(diphenyl) phosphate of hydroquinone and bis(diphenyl) phosphate of bisphenol A, and their oligomeric and polymeric counterparts. Flame retardant compounds containing phosphorus-nitrogen bonds include chlorophosphazene, phosphorus ester amides, phosphoric acid amides, phosphonic acid amides, phosphinic acid amides and tris(aziridine)phosphine oxide. Aromatic phosphates can include difunctional or polyfunctional compounds or polymers. When used, the phosphorus-containing flame retardant can be present in an amount of 0.1 to 30 parts by weight or 1 to 20 parts by weight based on 100 parts by weight of the total composition not including any filler.

[0044] Inorganic flame retardants include C 1-16 Alkyl sulfonates, such as potassium perfluorobutanesulfonate (Rimar salt), potassium perfluorooctanesulfonate, tetraethylammonium perfluorohexanesulfonate, and potassium diphenylsulfonesulfonate; salts such as Na 2 CO 3 , K 2 CO 3 MgCO 3 、CaCO 3 and BaCO 3 , or fluoride anion complexes such as Li 3 AlF 6 ,BaSiF 6 KBF 4 , K 3 AlF 6 , KAlF 4 , K 2 SiF 6 Or Na 3 AlF 6 When present, the inorganic flame retardant salt may be present in an amount of 0.01 to 10 parts by weight or 0.02 to 1 part by weight, based on 100 parts by weight of the total composition excluding any filler.

[0045] The thermoplastic composition can have a UL94 flame retardancy rating of V0 or better at a non-limiting thickness of 3.5 millimeters (mm), preferably 2 mm, or 1.5 mm, or 1 mm or less, as measured in accordance with Underwriter's Laboratory Bulletin 94 (UL94), entitled "Tests for Flammability of Plastic Materials for Parts in Devices and Appliances" (ISBN 0-7629-0082-2), Fifth Edition, dated October 29, 1996 (incorporating revisions up to and including December 12, 2003).

[0046] In some examples discussed in more detail below, the thermoplastic spacer 150 can be formed of a spacer 205 of a thermoplastic composition that defines cylindrical recesses 210 that are each configured to receive the cells 120. Test results with reference to spacers without sleeves are provided herein, see e.g. Figure 8 In any case, the test results are useful for indicating the underlying potential heat capacity of the thermoplastic spacer.

[0047] The sleeves 125 can be formed of cylindrical walls 145, respectively, which define a wall thickness D1 having a sleeve size or material thickness. In some examples, D2>D1. D2 can be at least 2.5 millimeters (mm). The sum of these thicknesses can be considered to be DT, that is, DT=D1+D2 ( Figure 1B ). D1 can be 0.5 to 1.5 mm, for example 0.8 mm. D2 can be at least 3.5 mm. Figure 1B More clearly shown in . Figure 1B Represents a repeating pattern in the battery pack 100, and illustrates areas of the battery pack 100 for applying calculations of D2 and DT. In some aspects, D2, representing the contribution from the thermoplastic spacer 150, is the primary variable in calculations involving absorption of thermal energy from a runaway cell. Thus, in some instances, D2 defines the minimum thickness for forming the battery pack 100 and the minimum thickness for meeting flame retardancy requirements. For some aspects, between adjacent cells of the cell 120, the thermoplastic spacer 150 and the sleeve 125 may together form a combined heat capacity of at least 37 kJ. The sleeve 125 may be formed of aluminum. The sleeve 125 may be formed of anodized aluminum.

[0048] In the above disclosed aspects, the sleeve 125 is used to accommodate a plurality of units 120, which may be cylindrical or occupy other envelopes (or, for example, for stacking prismatic or soft-pack units). Therefore, the disclosed aspects relate to filling the space between the units 120 with a thermoplastic of a thermoplastic spacer 150. The thermoplastic spacer 150 can provide thermal capacity to absorb heat. The ability to absorb heat during unit runaway can be increased by the latent heat of thermoplastic melting. For example, if / when the temperature exceeds its pyrolysis temperature, i.e., at least 300°C, it is increased by pyrolysis heat. It may be advantageous to use a sleeve 125 (e.g., anodized aluminum) to diffuse heat and contain molten plastic. The carrier system 105 can be manufactured by molding a spacer of a thermoplastic composition and then forming an opening, such as by drilling, to receive the unit 120. Conversely, the thermoplastic composition can be molded in a form that defines an opening. The sleeve 125 may be present during formation of the carrier system 105, for example in the mold during injection of the thermoplastic composition, or may be added subsequently to the opening, for example by adding a preformed metal layer to the cylindrical wall 145 or by depositing a metal layer (e.g., by sputter coating) onto the cylindrical wall.

[0049] The heat generated by the runaway cell was measured to be approximately 36 kilojoules (kJ), which was generated by electrochemical heat measured to be approximately 9.5 kJ and decomposition heat measured to be approximately 26.8 kJ. To prevent or minimize heat propagation, the combined heat capacity of the thermoplastic spacer 150 and sleeve 125 can allow energy to be absorbed. The heat capacity of the thermoplastic spacer 150 and sleeve 125 can be calculated using thermodynamic equations and, for example, the latent heat of the thermoplastic.

[0050] The heat of pyrolysis represents an additional safety factor against heat transfer during a runaway reaction of the cell. Pyrolysis occurs by carbonization of the molten thermoplastic and can be a function of the rate of temperature change experienced by the molten thermoplastic from the runaway cell. If the rate of temperature change is within a sufficient range, the carbonization process can result in absorption of the energy released from the cell.

[0051] For example, the thermoplastic composition can have a melting point of 110° C. to 270° C., for example, 130° C., as determined according to ASTM F2625-10 (2016). The thermoplastic composition can have a heat capacity of 1400 to 2400 kJ / kg K, for example, 2200 kJ / kg K, as determined according to ASTM E1269-11 (2018). The thermoplastic composition can have a heat of fusion of at least 120 J / g, as determined according to ASTM F2625-10 (2016). The thermoplastic composition can have a pyrolysis temperature of at least 300° C., as determined according to ASTM D7309-20.

[0052] According to an example, the configuration of high-density polyethylene as an olefinic thermoplastic in an aluminum sleeve of 0.8 mm thickness (D1 in FIG. 1 ) and the calculation of its properties (heat capacity of 2200 kJ / kg K and heat of fusion of 135 J / g) show that a heat capacity (Cp) of 37 kJ can be achieved if the minimum thickness of the plastic (D2 in FIG. 1 ) is 3.5 mm and the local temperature is below the pyrolysis temperature of 400° C. For reference, the total thickness considering the heat absorption of the battery pack is DT=D1+D2( Figure 3 ), is 4.3 mm. This heat capacity will be sufficient to absorb the 36 kJ of thermal energy released by the runaway unit. It should be noted that the values ​​of the material properties identified herein are obtained from, for example, Handbook of Polyethylene, Andrew Peacock, Marcel Dekker Inc, New York 2000, and / or CRC Handbook of Chemistry and Physics, 97th Edition, CRC Press, Boca Raton 2017.

[0053] According to another example, a more general calculation is shown below in Table 1, which lists the material properties of the battery cell, aluminum heat sink (or sleeve), and thermoplastic barrier of relatively high density material. In this case, the minimum thickness is reduced to 2.5 mm. It should be noted that this example is provided only as an example and is not intended to limit the current battery pack in any way.

[0054] Table 1

[0055]

[0056] In the table, a cylindrical battery cell with the listed diameter (Dia), height (Ht) and volume (Vol) can release 36 kJ of energy. The sleeve has a material thickness D1 ( Figure 1A ), and based on the size of the encapsulated cell, the listed volume of the sleeve per cell is provided. The thickness D2 of the thermoplastic ( Figure 1A ) is 2.5 mm, which is the minimum thickness achieved between two adjacent cells. Based on the dimensions of the thermoplastic encapsulating the battery cells and the sleeve, this thickness D2 of the thermoplastic provides the listed volume of thermoplastic between adjacent cells. Thickness DT ( Figure 1B ) represents the combination of D1 and D2, which as a reference is 3.3 mm (total). The respective densities (Den) of the sleeve and the thermoplastic are listed, as well as the respective masses (Mass) due to the volumes indicated.

[0057] The specific heat capacity (cp) of the sleeve and thermoplastic is listed, indicating their respective ability to absorb heat while maintaining the solid phase. The melting temperature (Tm) of the sleeve and thermoplastic is listed. As indicated, the total temperature change (400°C) during the battery cell runaway event can be less than the melting temperature (700°C) of the sleeve. Therefore, the sleeve will absorb 6kJ of thermal energy during the cell runaway event while remaining in its solid phase. However, thermoplastics have a lower melting temperature and will melt as expected, allowing them to absorb additional heat due to their enthalpy heat (dH). Thermoplastics will absorb 24kJ of thermal energy in the solid state and then absorb another 9kJ when they are converted to the liquid (molten) phase. Therefore, the combination of sleeve and thermoplastic can absorb up to 39kJ of thermal energy (6kJ+24kJ+9kJ), which is higher than the 36kJ of thermal energy released from the runaway unit (approximately 3kJ). It will be appreciated that this configuration can prevent thermal energy from one runaway battery cell from impacting adjacent battery cells.

[0058] A sleeve (not shown) may be provided between the cells 120 and the sleeve 125. The size and thickness of the thermoplastic spacer 150 may be a primary design parameter for the battery pack 100. The sleeve 125 may be as thin as possible under manufacturing constraints, which may be a function of the heat transfer properties of the sleeve material. Therefore, calculations involving DT consider only the size of the thermoplastic spacer 150, which may be sized to absorb a desired portion of the thermal energy generated by one or more cells 120 during a runaway event.

[0059] Now refer to Figures 1 and Figure 2 Both, the impact barrier 170 can be formed by the thermoplastic spacer 150 along the lateral outer boundary 180 of the cell group 110. The impact barrier 170 can be formed along one or more outer boundary sides 200 of the battery pack 100. The impact barrier 170 can define a third lateral impact spacing D3, where D3>D2. The impact barrier 170 can define one or more empty cylindrical recesses 190, wherein each of the one or more empty cylindrical recesses 190 is sized to accommodate one of the cells. The impact barrier 170 can enable absorption of external impact energy that might otherwise be transferred to the cell 120, which can further reduce the likelihood of a cascading runaway reaction.

[0060] Go to Figure 3, a flow chart illustrates a method of configuring the battery pack 100 disclosed above. As shown in box 510, the method includes providing a cell group 110. As shown in box 520, the method may include encapsulating the cells 120 in respective sleeves 125. As shown in box 530, the method may include further encapsulating the cells 120 in thermoplastic spacers 150 so that the cells 120 are axially parallel to each other and distributed in a planar array. As indicated, adjacent cells of the cells 120 are laterally spaced apart from each other by a thermal barrier that defines a spacing D2 that can be formed by the thermoplastic spacer 150.

[0061] like Figure 4 As shown in FIG. 1 , a carrier system 105 ( Figure 1A-1B ) may include a thermoplastic spacer 150, also referred to as a cell spacer or cell spacer, which forms a group of cylindrical recesses 210, each of which is configured to receive a cylindrically shaped cell 120 ( Figure 1A-1B ). The thermoplastic spacer 150 can be block-shaped. The cylindrical recesses 210 are axially parallel to each other and distributed in a planar array. Adjacent cylindrical recesses in the cylindrical recesses 210 are laterally spaced apart from each other by a thermal barrier defining a spacing D2 between the cylindrical recesses 210. In some instances, D2 is at least 2.5 mm. The carrier system 105 can be formed of a monolithic thermoplastic. The carrier system 105 can be molded in a single shot. The recess can be machined or molded. In the case of molding, the recess 210 may include a draft angle. The recess 210 may include two draft angles, similar to an hourglass shape. The cross-section of the recess 210 may define a truncated conical shape, wherein the larger base is coplanar with the main surface of the carrier system 105. The size of the central vertex of the cylinder can be set to an interference fit with the unit. The interior of the recess 210 may include a unit retaining feature, such as a detent, a rib, a wedge, etc. An axial channel may be provided along the inner surface of the recess.

[0062] The cylindrical recesses 210 may be of the same size and shape as one another.An outer shell 160 may surround the thermoplastic spacer 150, wherein the outer shell 160 is formed by the sleeve 125 identified above. The carrier system 105 may be formed without an outer shell.

[0063] The thermoplastic spacer 150 may be formed of olefinic thermoplastics. The thermoplastic spacer 150 may include polyethylene. The thermoplastic spacer 150 may include a foaming agent that foams at about 240° C. to absorb thermal energy.

[0064] The impact barrier 170 may be formed by the thermoplastic spacer 150 along the lateral outer boundary 180 of the group of cylindrical recesses 210. The impact barrier 170 may be formed along one or more outer boundary sides 200 of the thermoplastic spacer 150. The impact barrier 170 may define a lateral impact spacing D3, where D3>D2. The impact barrier 170 may enable absorption of external impact energy that may otherwise be transferred to the unit 120, which may further reduce the possibility of a cascading runaway reaction. Energy absorbing features such as honeycomb shapes, ribs, etc. may be defined in the impact barrier 170 to meet the desired extrusion dynamics.

[0065] Figure 5A A top view of the unit test device without the cover is shown. Figure 5B A side view of the unit test apparatus of FIG5 is shown, shown in cross section taken at line BB, with the cover shown in hidden lines. The test apparatus 500 consists of a five-sided steel housing 502 and a steel cover 504, the design of which allows for measurement of housing pressure and temperature conditions as well as specific cell temperatures within an array of cells. The apparatus includes restricted flow holes in the housing wall to regulate pressure and provide ventilation for combustion of gases ejected from the cell during thermal runaway.

[0066] The internal volume of the device 500 is designed to accommodate a 5×5 array of 18650 format cells and variable separation between each cell. The top 506 of the device 500 is manufactured with a square flange 508 and a 3 / 8" threaded hole. The flange forms a mating surface for a 1 / 4" thick cover plate, which is bolted to the housing with a high temperature gasket (not shown) placed between the two mating surfaces. The cover 504 includes a threaded connection for temperature and pressure measuring instruments. The 16mm threaded hole is inserted into the 2" NPT hole 511 on the side of the housing. The presence of the threaded hole can generate a thrust to push the test housing. Therefore, the test housing is manufactured with a bracket for bolting the housing to a rigid surface, such as a heavy workbench.

[0067] Three different cell carriers were mounted to the test equipment, corresponding to three different test arrangements. Each carrier included 25 Panasonic NCR18650B lithium-ion cells arranged in a 5×5 arrangement. The cells were in 18650 format with a nickel-cobalt-aluminum (NCA) cathode chemistry. The cells used have been characterized as entering thermal runaway at approximately 180°C with a ramp rate of 6°C / min. In all test arrangements, the cells were not electrically interconnected and were charged to 100 states of charge (SOC).

[0068] The following measurements were taken during each test: the internal pressure developed during the test, the internal cavity temperature developed during the test, as measured with a sheathed thermocouple, the surface temperature of the two initiating cells driven into thermal runaway, and the bottom surface temperature of a selected target cell in the cell array.

[0069] A 0-250psig diaphragm pressure sensor 512 and a sheathed K-type thermocouple 514 were mounted into an NPT pipe fitting that was connected to the cover plate 504 via a 1 / 2" NPT fitting. A second NPT fitting was connected to an epoxy sealed instrument through hole 516. Through holes 516 were used to route a series of 30AWG K-type thermocouples and two sets of heated power leads into the test equipment. The through holes were sealed to pressure leaks using two part epoxy. The 30AWG thermocouples were mounted on the bottom of a subgroup of cells within the cell array using spot welding to connect the junction to the cell shell, and instant adhesive was used to add strain relief to the thin wires forming the junction. Two power leads supply current to two membrane heaters used to drive the two initiation cells into thermal runaway. Two additional 30AWG K-type thermocouples were used to control the heating of the initiation cells and measure their surface temperature.

[0070] When the cell array is placed in the test enclosure, the cells and their respective 30AWG thermocouples are connected in Figure 5A The layout is shown in Figure 1. Units numbered 1-15 are equipped with thermocouples. Unnumbered units are not equipped with thermocouples. The two units near the center of the unit array, labeled H1 and H2, are equipped with 28V, 10W / in 2 The two cells were heated simultaneously using a parallel heater circuit. Control of the two initiation cells in the cell array was achieved using a PID feedback system consisting of a National Instruments cDAQ data module, a DC power supply, and software. The approach of using two adjacent initiation cells is based on established practice for initiating thermal runaway propagation in a 5×5 cell array in accordance with UL 2596: Test Method for Thermal and Mechanical Performance of Battery Enclosure Materials.

[0071] During testing, the cell array was placed on 1 / 8" ceramic fiber insulation and all thermocouple leads extended from the bottom of the cell, up the sides of the enclosure volume, and out of the epoxy sealed through holes. In addition to the 1 inch gap between the cell array and the enclosure wall with threaded holes, the additional space around the cell array was filled with ceramic fiber insulation. Non-combustible gaskets were used to maintain the 1 inch gap. This gap was provided to allow for exhaust ventilation through the threaded holes.

[0072] Figure 6The experimental cell carrier is shown with no air gaps between cells. This configuration includes an array of 25 cells, all nested as closely together as possible. The array of 25 cells is contained within a wire mesh cage on four sides to keep the cells in as close contact as possible. This configuration was used for Tests 1-4 discussed below.

[0073] Figure 7 An experimental cell carrier is shown with air gaps between cells. This configuration consists of an array of 25 cells with a 2 mm air gap between all cells. The array of 25 cells is mounted in a fixture consisting of two 1 / 16" steel plates and four threaded rods. The steel plates are machined to provide through holes for the cells and to keep them 2 mm apart (measured from the outermost points of the circumference of adjacent cells). This configuration was used for Tests 5-7 discussed below.

[0074] Figure 8 An experimental cell carrier is shown in which spaced-apart cells are arranged in thermoplastic cell spacers. Fig. 9A Shows Figure 8 Top view of the experimental thermoplastic cell separator. Fig. 9B Shows Fig. 9A 904 is placed adjacent to the cell slots where the initiating cell can potentially be placed to allow for heater leads and thermocouples. The center cell slot and the cell slots directly adjacent to the center slot are used to locate the location where the initiating cell goes into thermal runaway. This configuration was used for Tests 8-10 discussed below.

[0075] Tested in the device of Figure 5 Figure 6-8 The arrangements shown in were used to generate comparative data. They are shown in perspective for reference. Figure 6 and Figure 7 The purpose of the arrangement is to provide Figure 8 The performance of the thermoplastic separators was compared to a baseline. The severity of the thermal runaway in terms of enclosure conditions and the extent of thermal runaway propagation (the number of cells in the array that were driven into thermal runaway) were compared between the three test types. Figure 5A and Figure 5B The test arrangements shown in are consistent. At least three trials of each test type were performed. A total of ten tests were performed, in which at least three replicates of each test type were completed. Table 2 shows the test matrix.

[0076] Table 2

[0077]

[0078]

[0079] Each test follows the same procedure. The test procedure will simultaneously start data collection at 10 Hz and heating of the initiation units. The test will heat both initiation units at a set rate of 6°C / min using a parallel circuit, using the thermocouple on H1 as a reference thermocouple, until thermal runaway is observed in both initiation units. The test procedure will continue until all measured temperatures within the test enclosure have dropped below the ventilation temperature of the unit. The unit test equipment will then be turned on and the unit inspected.

[0080] Table 3 provides an overview of the metrics from each test performed. Figure 10-15 The descriptions provide details about the results of each test type.

[0081] Table 3:

[0082]

[0083] Fig.10 Pressure measurements for Tests 1 to 4 are shown. Fig.11 Temperature measurements for Tests 1-4 are shown. Four baseline tests were performed using tightly nested cells. Tests 1-4 resulted in full thermal runaway propagation throughout the cell array. Full propagation was indicated by all measured cell temperature increases exceeding 180°C, increased case pressure, and visual inspection of the cells after the test. Immediately after the thermal runaway propagation, the cell array temperature was approximately 900°C.

[0084] Test 3 included an erroneously high ramp rate that induced cell temperatures above 6° C. per second. Although the increased rate did not significantly affect the test results regarding thermal runaway severity, an additional test (Test 4) was performed with the correct cell heating rate.

[0085] Fig.12 Pressure measurements for Tests 5-7 are shown. Fig.13 Temperature measurements for Tests 5-7 are shown. Three baseline tests were performed with a 2 mm air gap. Tests 5-7 resulted in full thermal runaway propagation throughout the cell array. Full propagation was indicated by all measured cell temperature increases exceeding 180°C, increased case pressure, and visual inspection of the cells after the test. Immediately after the thermal runaway propagation, the cell array temperature was approximately 800°C.

[0086] Peak sheath thermocouple temperatures and case pressures were lower in the air gap test series compared to the tightly nested cell baseline test series. Peak cell array temperatures were also lower by approximately 100°C on average. However, in terms of the number of cells entering thermal runaway, the 2mm air gap did not impede the progression of cascading thermal runaway compared to the tightly nested cells.

[0087] Fig.14 Pressure measurements for Tests 8-10 are shown. Fig.15 Temperature measurements for Tests 8-10 are shown. Three tests were conducted with the test material. Peak case pressure and sheath thermocouple measurements were lower than the two baseline test series. Based on the cell array thermocouple data, case pressure data, and visual inspection of the cells after testing, Tests 8 and 9 did not result in thermal runaway propagation beyond the two initiating cells. Cell temperatures did not rise above 150°C for all equipped cells 1-15 for either Test 8 or Test 9. During Test 9, user error caused a brief interruption in heater system data acquisition. Acquisition was restarted with no observable impact.

[0088] The cell array thermocouple data from test 10 gave completely different temperature results compared to the cell array thermocouple data from tests 8 and 9. The data for cells 3, 6, 7, 9, 11, 12, and 14 showed sharp spikes in temperature, but the decay distribution was inconsistent with the thermal runaway temperatures in the baseline test. The data for cells 1, 2, 4, 5, 8, 10, 13, and 15 showed similar temperature distributions as the target cells in tests 8 and 9. Inspection of the target cells after the test did not indicate signs of thermal runaway in cells other than the two initiating cells, such as cell shell cracks. One possible reason for the difference in the data is electrical interference caused by the initiating cell going into thermal runaway. At the point of thermal runaway, an overload condition was induced in the cell heater power supply and data system. Air gaps or material separation distances below or above 2 mm or different cell layouts, such as a honeycomb pattern, may produce different results.

[0089] The above disclosed aspects involve utilizing thermoplastic melting latent heat enthalpy as a thermal barrier that can absorb the energy of a battery cell short circuit and prevent further propagation in a cell pack (eg, a group of cells). The pyrolysis heat of the thermoplastic will provide a second safety barrier for further propagation.

[0090] As used herein, "a kind of", "one", "the" and "at least one / kind" do not represent quantitative restrictions, and are intended to cover both the singular and the plural, unless the context clearly indicates otherwise. For example, unless the context clearly indicates otherwise, "a kind of element" has the same meaning as "at least one element". The term "combination" includes blends, mixtures, alloys, reaction products, etc. In addition, "at least one / kind" means that the list includes each individual element, and a combination of two or more elements in the list, and a combination of at least one element of the list with unnamed similar elements. "Or" means "and / or". As used herein, the suffix "(s)" is intended to include both the singular and the plural of the term it modifies, thereby including one or more (for example, the film includes one or more films) in the term. References to "an aspect", "another aspect", "aspects", etc. throughout the specification mean that the specific elements (for example, features, structures and / or characteristics) described in conjunction with the aspect are included in at least one aspect described herein, and may or may not be present in other aspects. In addition, it should be understood that the described elements can be combined in any suitable manner in various aspects.

Claims

1. A battery pack (100), comprising: a plurality of cells (120), each cell defining an exterior having a height surface extending between an upper base surface and a lower base surface, the plurality of cells (120) being arranged in a cell group (110) such that the respective lower base surfaces are aligned parallel to each other, wherein each of the cells is associated with a thermal runaway potential energy and a thermal runaway ignition energy comprising a thermal capacity of the cell; and A unit carrier comprising: a plurality of sleeves (125), each sleeve having a sleeve thickness D1, wherein each of the plurality of cells is disposed in the sleeve, wherein each sleeve (125) is associated with a sleeve thermal resistance, the sleeve thermal resistance being associated with a sleeve thermal capacity; and a thermoplastic spacer (150) formed of thermoplastic and engaged with the plurality of sleeves to define the unit carrier, wherein the thermoplastic spacer includes a thermoplastic thermal resistance associated with a pre-thermal decomposition heat capacity and a thermal decomposition heat capacity including a latent heat of fusion, wherein the cell carrier defines a cell-to-cell spacing D2 between adjacent cells, and for each cell, the respective base surface is exposed while the respective height surface is shielded by the cell carrier and the height surface of the adjacent cell, Features: The distance D2 between the units is greater than the thickness D1 of the sleeve. Each of the plurality of cells is encapsulated in the sleeve (125) and further encapsulated in the thermoplastic spacer (150); The sleeve (125) is formed of aluminum; The thermoplastic spacer (150) is formed of thermoplastic plastic and a foaming agent; An impact barrier (170) is formed by the thermoplastic spacer (150) along the lateral outer boundary (180) of the cell group (110) and along the outer boundary side (200) of the battery pack (100), and the impact barrier (170) defines a third lateral impact distance D3, wherein D3>D2; and The barrier (170) defines one or more hollow cylindrical recesses 190, in: The material properties of the thermoplastic spacer (150) include one or more of the following: A melting point of 110°C to 270°C as determined according to ASTM F2625-10(2016); Heat capacity of 1400 to 2400 kJ / kg K as determined according to ASTM E1269-11(2018); A heat of fusion of at least 120 J / g as determined according to ASTM F2625-10 (2016); and A pyrolysis temperature of at least 300°C as determined according to ASTM D7309-20.

2. The battery pack according to claim 1, wherein: The units 120 have the same size and shape as each other; and The housing 160 surrounds the thermoplastic spacer 150 .

3. A battery pack according to any preceding claim, wherein: The thermoplastic spacer (150) comprises a polyolefin and a foaming agent.

4. A battery pack according to any preceding claim, wherein: The thermoplastic spacer (150) is formed of a thermoplastic spacer (205), and the spacer (150) includes cylindrical recesses (210) respectively configured to receive the cells (120).

5. A battery pack according to any preceding claim, wherein: D2 is at least 2.5 mm; and D1 is 0.5 to 1.5 mm.

6. A battery pack according to any preceding claim, wherein: D2 is at least 3.5 mm.

7. A battery pack according to any preceding claim, wherein: Each of the units is cylindrical; and Each of the one or more hollow cylindrical recesses (190) is sized to house one of the cells.

8. A method for configuring the battery pack (100) according to claim 1, comprising: providing the unit set (110), wherein the unit group (110) includes units (120) each defining a cylindrical body (126); Enclosing the units (120) in respective sleeves (125); and further encapsulating the units (120) in the thermoplastic spacer (150) such that the units 120 are axially parallel to each other and distributed in a planar array, and Adjacent ones of the cells (120) are laterally spaced apart from each other by a thermal barrier defining a spacing D2 formed by the thermoplastic spacer (150).

9. A vector system comprising: a thermoplastic spacer (150) forming a set of cylindrical recesses (210) each configured to receive a cylindrically shaped unit (120); wherein the cylindrical recesses (210) are axially parallel to each other and are distributed in a planar array, and wherein adjacent ones of the cylindrical recesses (210) are laterally spaced apart from each other by a thermal barrier, the thermal barrier defining a spacing D2 between the cylindrical recesses (210), D2 is at least 2.5 mm, and; Features: The thermoplastic spacer (150) is formed of thermoplastic plastic and a foaming agent; Each of the plurality of recesses encloses one of a plurality of sleeves (125) formed of aluminum; a ballistic barrier (170) formed by said thermoplastic spacer (150) along a lateral outer boundary (180) of the set of cylindrical recesses (210); The impact barrier (170) is formed along one or more outer boundary sides (200) of the thermoplastic spacer (150); and The impact barrier (170) defines a lateral impact spacing D3, wherein D3>D2, and the impact barrier (170) defines one or more hollow cylindrical recesses (190).

10. The system of claim 9, wherein: The cylindrical recesses (210) have the same size and shape as each other; and An outer shell (160) surrounds the thermoplastic spacer (150).

11. The system according to any one of claims 9 to 10, wherein The material properties of the thermoplastic spacer (150) include one or more of the following: A melting point of 110°C to 270°C as determined according to ASTM F2625-10(2016); Heat capacity of 1400 to 2400 kJ / kg K as determined according to ASTM E1269-11(2018); A heat of fusion of at least 120 J / g as determined according to ASTM F2625-10 (2016); and A pyrolysis temperature of at least 300°C as determined according to ASTM D7309-20.

12. A battery pack (100), comprising: a plurality of cells (120), each cell defining a cylindrical exterior having a cylindrical height surface extending between a pair of opposing base surfaces, the plurality of cells (120) being arranged in a cell group (110) such that each cell central axis is parallel to a central axis of an adjacent cell, wherein each of the cells is associated with a thermal runaway potential energy and a thermal runaway ignition energy comprising a thermal capacity of the cell; a thermoplastic spacer (150) formed of thermoplastic and defining a plurality of cylindrical recesses, each of a plurality of sleeves being disposed in the plurality of recesses and defining a cell-to-cell spacing D2 between adjacent cells, wherein for each cell, a respective base surface is exposed and a respective cylindrical height surface is shielded from other cylindrical height surfaces by the thermoplastic spacer, and a plurality of sleeves (125), each sleeve having a sleeve thickness D1, wherein each of the plurality of cells is disposed in the sleeve defining an air gap between the thermoplastic spacer and each respective cell; and wherein the air gap is related to the air gap thermal resistance, which is related to the air gap thermal capacitance, and wherein the sleeve (125) is associated with a sleeve thermal resistance, which is associated with a sleeve thermal capacity, and It is characterized in that The distance D2 between the units is greater than the thickness D1 of the sleeve. Each of the plurality of cells is encapsulated in the sleeve 125 and further encapsulated in the thermoplastic spacer (150); The thermoplastic spacer (150) is formed of thermoplastic plastic and a foaming agent; An impact barrier (170) is formed by the thermoplastic spacer (150) along the lateral outer boundary (180) of the cell group (110) and along the outer boundary side (200) of the battery pack 100, and the impact barrier 170 defines a third lateral impact distance D3, wherein D3>D2; and The impact barrier (170) defines one or more hollow cylindrical recesses (190), in: The material properties of the thermoplastic spacer (150) include one or more of the following: A melting point of 110°C to 270°C as determined according to ASTM F2625-10(2016); Heat capacity of 1400 to 2400 kJ / kg K as determined according to ASTM E1269-11(2018); A heat of fusion of at least 120 J / g as determined according to ASTM F2625-10 (2016); and A pyrolysis temperature of at least 300°C as determined according to ASTM D7309-20.

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