Enclosure for battery cells comprising nanoprecipitation strengthened steel

Abstract

The invention relates to a housing for a battery cell comprising nano-precipitation strengthened steel. A method for manufacturing a tubular housing for a battery cell includes bending a steel sheet into a tubular body. The steel comprises iron; 0.01 wt% to 0.1 wt% of carbon; 0.01 to 0.2% by weight of niobium, titanium, and vanadium; and at least one of the first group and the second group. The first group comprises 0.01 wt% to 2.0 wt% of copper; 1 to 6.0 wt% of nickel; 0.1 to 1.0 wt% of aluminum; 0.1 to 1.0 wt% of manganese; and 0.1 to 2.0 wt% of molybdenum. The second group comprising 0.1 to 1.5 wt% of titanium; and 0.1 to 1.5 wt% of silicon. The edges of the tubular body are welded and the tubular body is age hardened.

Description

Technical Field

[0001] The present disclosure relates to battery cells, and more particularly to housings for battery cells comprising nanoprecipitation strengthened steel. Background Art

[0002] The information provided in this section is for the purpose of generally introducing the background of the present disclosure. No admission is made, either explicitly or implicitly, that the work of the presently named inventors described in this section is prior art to the present disclosure, nor is it admitted that the work is prior art to the present disclosure with respect to the specification that may not have been otherwise identified as prior art at the time of filing.

[0003] Electric vehicles (EVs), such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and / or fuel cell vehicles, include one or more motors and a battery system, which includes one or more battery cells, modules, and / or packs. A power control system is used to control the charging and / or discharging of the battery system during charging and / or driving.

[0004] The battery cell includes one or more cathode electrodes, an anode electrode, and a separator disposed in a battery cell housing. The cathode electrode includes a cathode active material layer disposed on a cathode current collector. The anode electrode includes an anode active material layer disposed on an anode current collector. Summary of the Invention

[0005] A method for manufacturing a tubular casing for a battery cell includes bending a sheet of steel into a tubular body having one of a cylindrical and a prismatic shape. The steel comprises iron (Fe); 0.01 to 0.1 weight percent carbon; 0.01 to 0.2 weight percent niobium, titanium, and vanadium; and at least one of a first group and a second group. The first group comprises 0.01 to 2.0 weight percent copper; 1 to 6.0 weight percent nickel; 0.1 to 1.0 weight percent aluminum; 0.1 to 1.0 weight percent manganese; and 0.1 to 2.0 weight percent molybdenum. The second group comprises 0.1 to 1.5 weight percent titanium; and 0.1 to 1.5 weight percent silicon. The method includes welding opposing edges of the tubular body to form a weld and age-hardening the tubular body after welding.

[0006] In other features, the method includes attaching a bottom portion to one end of the tubular housing. The steel comprises the first group and the second group. The weight ratio of Ni / Cu is greater than 0.3. The weight ratio of Ni / Al is between 2 and 5. The weight ratio of Ni / Mn is between 1 and 3. The weight ratio of Si / Ti is between 1.5 and 3.

[0007] In other features, the steel comprises the second group A. Si / Ti weight ratio is 1 to 3.

[0008] In other features, the steel comprises the first group: a Ni / Cu weight ratio greater than 0.3; a Ni / Al weight ratio of 2 to 5; and a Ni / Mn weight ratio of 1 to 3.

[0009] In other features, the tubular body is age-hardened by heating to a temperature of 400° C. to 600° C. for a predetermined soaking time. The steel has a precipitation fraction of 2% to 20% by volume. The precipitate particle size is 1 nm to 100 nm.

[0010] Among other features, the steel comprises nanoprecipitates of Cu, Ni / Al / Ti intermetallic compounds, and Fe2SiTi intermetallic compounds. The steel has a thermal conductivity greater than 40 W / mK. The steel has a yield strength greater than 700 MPa at room temperature and maintains a yield strength greater than 200 MPa at 600°C.

[0011] A tubular casing for a battery cell, comprising a tubular body made of steel sheet and including a weld. The steel comprises iron (Fe); 0.01 to 0.1 weight percent carbon; 0.01 to 0.2 weight percent niobium, titanium, and vanadium; and at least one of a first group and a second group. The first group comprises 0.01 to 2.0 weight percent copper; 1 to 6.0 weight percent nickel; 0.1 to 1.0 weight percent aluminum; 0.1 to 1.0 weight percent manganese; and 0.1 to 2.0 weight percent molybdenum. The second group comprises 0.1 to 1.5 weight percent titanium; and 0.1 to 1.5 weight percent silicon. A bottom portion is attached to one end of the tubular body.

[0012] In other features, the tubular body is age hardened for a predetermined soaking time.

[0013] In other features, the steel comprises the first group and the second group, wherein the weight ratio of Ni / Cu is greater than 0.3, the weight ratio of Ni / Al is between 2 and 5, the weight ratio of Ni / Mn is between 1 and 3, and the weight ratio of Si / Ti is between 1.5 and 3.

[0014] In other features, the steel comprises the second group A. Si / Ti weight ratio is 1 to 3.

[0015] In other features, the steel comprises the first group: a Ni / Cu weight ratio greater than 0.3; a Ni / Al weight ratio of 2 to 5; and a Ni / Mn weight ratio of 1 to 3.

[0016] In other features, the tubular body is age-hardened by heating to a temperature of 400° C. to 600° C. for a predetermined soaking time. The steel has a precipitation fraction of 2% to 20% by volume. The precipitate particle size is 1 nm to 100 nm.

[0017] Among other features, the steel comprises nanoprecipitates of Cu, Ni / Al / Ti intermetallic compounds, and Fe2SiTi intermetallic compounds. The steel has a thermal conductivity greater than 40 W / mK. The steel has a yield strength greater than 700 MPa at room temperature. The steel maintains a strength greater than 200 MPa at 600°C.

[0018] The present invention discloses the following solutions:

[0019] Solution 1. A method for manufacturing a tubular housing for a battery cell, comprising:

[0020] bending a sheet made of steel into a tubular body having one of a cylindrical shape and a prismatic shape,

[0021] wherein the steel comprises:

[0022] Iron (Fe);

[0023] 0.01 to 0.1 wt% carbon;

[0024] 0.01 to 0.2 weight percent niobium, titanium, and vanadium; and

[0025] at least one of the first group and the second group,

[0026] The first group comprises:

[0027] 0.01 to 2.0 wt. % copper;

[0028] 1 to 6.0 wt. % nickel;

[0029] 0.1 to 1.0 wt. % aluminum;

[0030] 0.1 to 1.0 wt. % manganese; and

[0031] 0.1 to 2.0 wt. % molybdenum;

[0032] The second group comprises:

[0033] 0.1 to 1.5 wt. % titanium; and

[0034] 0.1 to 1.5 wt% silicon;

[0035] welding opposing edges of the tubular body to form a weld; and

[0036] The tubular body is age hardened after welding.

[0037] Option 2. The method of Option 1, further comprising attaching a bottom portion to one end of the tubular housing.

[0038] Option 3. The method according to Option 1, wherein:

[0039] The steel comprises the first group and the second group,

[0040] The weight ratio of Ni / Cu is greater than 0.3,

[0041] The weight ratio of Ni / Al is 2 to 5,

[0042] The weight ratio of Ni / Mn is 1 to 3, and

[0043] The weight ratio of Si / Ti is 1.5 to 3.

[0044] Option 4. The method according to Option 1, wherein:

[0045] said steel comprises said second group, and

[0046] The weight ratio of Si / Ti is 1 to 3.

[0047] Option 5. The method according to Option 1, wherein:

[0048] said steel comprising said first group,

[0049] The weight ratio of Ni / Cu is greater than 0.3,

[0050] The weight ratio of Ni / Al is 2 to 5, and

[0051] The weight ratio of Ni / Mn is 1 to 3.

[0052] Option 6. The method of Option 1, wherein the tubular body is age-hardened by heating to a temperature of 400° C. to 600° C. for a predetermined soaking time.

[0053] Option 7. The method according to Option 1, wherein:

[0054] The steel has a precipitation fraction of 2% to 20% by volume, and

[0055] The particle size of the precipitate is 1 nm to 100 nm.

[0056] Option 8. A method according to Option 1, wherein the steel contains nanoprecipitates of Cu, Ni / Al / TI intermetallic compounds and Fe2SiTi intermetallic compounds.

[0057] Option 9. The method according to Option 1, wherein the thermal conductivity of the steel is greater than 40 W / mK.

[0058] Option 10. The method according to Option 1, wherein:

[0059] The steel has a yield strength greater than 700 MPa at room temperature, and

[0060] The steel maintains a yield strength greater than 200 MPa at 600°C.

[0061] Solution 11. A tubular housing for a battery cell, comprising:

[0062] A tubular body made of steel plate and including welds,

[0063] wherein the steel comprises:

[0064] Iron (Fe);

[0065] 0.01 to 0.1 wt% carbon;

[0066] 0.01 to 0.2 weight percent niobium, titanium, and vanadium; and

[0067] at least one of the first group and the second group,

[0068] The first group comprises:

[0069] 0.01 to 2.0 wt. % copper;

[0070] 1 to 6.0 wt% nickel;

[0071] 0.1 to 1.0 wt% aluminum;

[0072] 0.1 wt% to 1.0 wt% manganese; and

[0073] 0.1 to 2.0 wt% molybdenum;

[0074] The second group comprises:

[0075] 0.1 to 1.5 wt% titanium; and

[0076] 0.1 wt% to 1.5 wt% silicon; and

[0077] A bottom portion is attached to one end of the tubular body.

[0078] Item 12. The tubular housing of Item 11, wherein the tubular body is age hardened for a predetermined soaking time.

[0079] Option 13. The tubular housing of Option 11, wherein:

[0080] The steel comprises the first group and the second group,

[0081] The weight ratio of Ni / Cu is greater than 0.3,

[0082] The weight ratio of Ni / Al is 2 to 5,

[0083] The weight ratio of Ni / Mn is 1 to 3, and

[0084] The weight ratio of Si / Ti is 1.5 to 3.

[0085] Option 14. The tubular housing of Option 11, wherein:

[0086] said steel comprises said second group, and

[0087] The weight ratio of Si / Ti is 1 to 3.

[0088] Option 15. The tubular housing of Option 11, wherein:

[0089] said steel comprising said first group,

[0090] The weight ratio of Ni / Cu is greater than 0.3,

[0091] The weight ratio of Ni / Al is 2 to 5, and

[0092] The weight ratio of Ni / Mn is 1 to 3.

[0093] Item 16. The tubular housing of Item 11, wherein the tubular body is age-hardened by heating to a temperature of 400° C. to 600° C. for a predetermined soaking time.

[0094] Option 17. The tubular housing of Option 11, wherein:

[0095] The steel has a precipitation fraction of 2% to 20% by volume, and

[0096] The particle size of the precipitate is 1 nm to 100 nm.

[0097] 18. The tubular housing of 11, wherein the steel comprises nanoprecipitates of Cu, Ni / Al / TI intermetallic compounds, and Fe2SiTi intermetallic compounds.

[0098] Option 19. The tubular housing of Option 11, wherein the thermal conductivity of the steel is greater than 40 W / mK.

[0099] Option 20. The tubular housing of Option 11, wherein:

[0100] The steel has a yield strength greater than 700 MPa at room temperature, and

[0101] The steel maintains a strength greater than 200 MPa at 600°C.

[0102] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims and drawings.The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0103] The present disclosure will be more fully understood from the detailed description and accompanying drawings, in which:

[0104] Figure 1 is a functional block diagram of an example of a battery cell including a battery cell stack including an anode electrode, a cathode electrode, and a separator arranged in a housing made of nanoprecipitation strengthened steel according to the present disclosure;

[0105] Figure 2A and Figure 2B is a perspective view of an example of a prismatic battery cell housing made of nanoprecipitation strengthened steel according to the present disclosure; and

[0106] Figure 3 is a side cross-sectional view of an example of a cylindrical battery cell made of nanoprecipitation strengthened steel according to the present disclosure;

[0107] Figure 4 is a side view of an example of a tube during induction welding according to the present disclosure;

[0108] Figure 5 is a flow chart of an example of a method for manufacturing a housing for a battery cell according to the present disclosure;

[0109] Figure 6 is a scanning electron microscope image of an example of a tubular shell before age hardening;

[0110] Figure 7A and Figure 7B is a simulation indicating estimated phase volume fractions as a function of temperature for an example of an enclosure according to the present disclosure; and

[0111] Figure 8A and 8B Improvements in weld quality according to the present disclosure are shown after welding and after age hardening, respectively.

[0112] In the drawings, reference numerals may be repeated to designate similar and / or identical elements. DETAILED DESCRIPTION

[0113] Although battery pack enclosures according to the present disclosure are illustrated herein in the context of electric vehicles, the battery pack enclosures may be used in stationary and / or other applications.

[0114] A battery cell comprises a stack of anode electrodes, cathode electrodes, and separators arranged in a battery cell stack. The battery cell stack is arranged in a housing. For cylindrical and prismatic battery cells, respectively, the housing is typically made of a metal material, such as steel or aluminum.

[0115] The melting temperature of steel (approximately 1500-1530 degrees Celsius) is approximately 2.5 times higher than that of aluminum (approximately 600-600 degrees Celsius). Using steel to manufacture the enclosure helps maintain the integrity of the enclosure during thermal runaway events, when the enclosure temperature can reach high temperatures (600-800 degrees Celsius) that can cause complete melting of the aluminum enclosure.

[0116] Although steel has improved strength at room temperature compared to aluminum and has a higher melting temperature than aluminum, the sidewalls of the enclosure may still fail during thermal runaway. For example, sidewall failures may occur in battery cells with thin steel walls (e.g., 0.2 mm to 0.3 mm thick). Sidewall failures can be mitigated by increasing the thickness of the enclosure steel walls. However, increasing the thickness of the steel walls reduces the gravimetric energy density (Wh / kg) of the battery cells.

[0117] During thermal runaway, the internal temperature of the enclosure can rise to over 800°C, and the steel enclosure can be heated to temperatures between 500°C and 800°C. Mild steel softens significantly above 500°C, and its tensile strength at around 800°C is approximately 1 / 10 of its room temperature strength. Therefore, the heating of the steel enclosure during thermal runaway is sufficient to soften the steel casing, which can trigger sidewall rupture.

[0118] The casing can also fail due to increased exhaust pressure and softening of the casing. For example, during thermal runaway, increased exhaust pressure can occur when the safety vent fails and is unable to release the generated exhaust gas.

[0119] The present disclosure relates to casings for cylindrical and prismatic battery cells that utilize a steel composition having high high-temperature strength due to nanoprecipitation strengthening of Cu, Ni / Al / Ti intermetallic compounds, and / or Fe2SiTi intermetallic compounds. The nanoprecipitates resist coarsening and dissolve only at high temperatures, above 750 to 800°C. The nanoprecipitates in the steel matrix soften the steel more gradually than mild steel alloys without precipitates. Because the steel is designed with a lean alloy content, it has a high thermal conductivity (e.g., above 40 W / mK, similar to mild steel).

[0120] The manufacturing method according to the present disclosure uses age hardening to increase the yield strength of steel. Age hardening relies on the temperature-dependent change in solid solubility, producing nanoprecipitates of impurity phases within the steel matrix. Impurity phases hinder the movement of dislocations or defects in the crystal lattice. Since dislocations are typically the primary carriers of plasticity, impurity phases harden the steel.

[0121] Now refer to Figure 1 The battery cell 10 includes C cathode electrodes 20, A anode electrodes 40, and S separators 32 arranged in a predetermined order in the battery cell stack 12, where C, S, and A are integers greater than zero. The C cathode electrodes 20-1, 20-2, ..., and 20-C include a cathode active material layer 24 arranged on one or both sides of a cathode current collector 26. The A anode electrodes 40-1, 40-2, ..., and 40-A include an anode active material layer 42 arranged on one or both sides of an anode current collector 46. In some examples, the A anode electrodes 40 and the C cathode electrodes 20 exchange lithium ions during charge / discharge.

[0122] In some instances, the cathode active material layer 24 and / or the anode active material layer 42 comprises a coating applied to the current collector (e.g., using a wet or dry roll-to-roll process) comprising one or more active materials, one or more conductive additives, and / or one or more adhesive materials, although other manufacturing methods may be used. In some instances, the cathode current collector 26 and / or the anode current collector 46 comprises a metal foil, a metal mesh, a perforated metal, a 3D metal foam, and / or an expanded metal. In some instances, the current collector is made of one or more materials selected from copper, stainless steel, brass, bronze, zinc, aluminum, and / or their alloys. The outer tabs 28 and 48 are connected to the current collectors of the cathode electrode and the anode electrode, respectively, and can be arranged on the same side or different sides of the battery cell stack 12. The outer tabs 28 and 48 are connected to the terminals of the battery cell stack 12.

[0123] Now refer to Figure 2A and Figure 2B , the battery cell 58 includes a housing 60. In some examples, the housing 60 has a prismatic shape with a rectangular cross-section in the x-axis, y-axis, and z-axis planes. In some examples, the housing 60 includes a housing body 61, which includes a side 80 corresponding to a narrow side and a side 82 corresponding to a wide side. The housing body 61 is defined as a rectangular parallelepiped with one end open. In some examples, the housing 60 includes a cover portion 84 and a bottom portion 86. In other examples, the bottom portion 86 is attached after the housing body 61 is formed. The edge 83 is arranged between the side surfaces 80 and 82, between the side surfaces 80 and 82 and the cover portion 84, and between the side surfaces 80 and 82 and the bottom 86.

[0124] A cover portion 84 and an optional bottom portion 86 are attached to the housing body 61 to respectively close the top and bottom openings of the housing body 61. The battery cells 58 include external terminals 62 and 64 extending through the cover portion 84. The battery cell stack 12 of C cathode electrodes 20, A anode electrodes 40, and S separators 32 is arranged in the housing 60.

[0125] External terminals 62 and 64 are connected to the outer tabs 28 and 48 of the C cathode electrodes 20 and the A anode electrodes 40, respectively. Figure 2A In the embodiment, the cover portion 84 does not include a pressure-based vent cover. Figure 2B , the cover portion 84 (and / or the bottom portion 86) includes a pressure-based vent cap 66. The pressure-based vent cap 66 is configured to release venting when the pressure within the inner housing is greater than a predetermined pressure.

[0126] Now refer to Figure 3 , a cylindrical battery cell 110 includes a tubular housing 114, a cover portion 118 including a cathode terminal 120, and a bottom portion 122. A battery cell stack 126 (e.g., a jelly roll) is arranged in the tubular housing 114. External tabs 128 and 132 connect the cathode electrode and the anode electrode to the cathode terminal 120 and the anode terminal (e.g., on the bottom portion 122).

[0127] Now refer to Figure 4 A flat steel sheet of the desired composition is roll-formed into a tube 210 and welded. Opposite sides of the tube 210 are rolled and welded using resistance welding, induction welding, friction stir welding, or other types of welding to close the open ends along the length of the sheet, thereby forming a hollow rectangular tube.

[0128] A tube 210 is shown during induction welding. The tube 210 may have an open-ended cylindrical or (rectangular) prismatic cross-section. During the welding of the weld, current flows through an induction coil 224 wrapped around the tube 210 to generate a time-varying magnetic field that heats the tube 210. Welding rollers 226 press and weld the opposing sides 212 of the tube 210 together to form a weld 230.

[0129] Mild steel typically contains carbon (up to 0.1 wt%), manganese (e.g., 0.16 wt%), phosphorus (e.g., 0.008 wt%), chromium (e.g., 0.056 wt%), copper (e.g., 0.012 wt%), molybdenum (e.g., 0.002 wt%), vanadium (e.g., 0.003 wt%), titanium (e.g., 0.003 wt%), and cobalt (e.g., 0.006 wt%). Although mild steel can be replaced with stainless steel to provide increased heat resistance, stainless steel has a lower thermal conductivity.

[0130] In some examples, tube 210 is formed using mild steel with a lean alloy content. While the steel is soft, it is roll-formed and welded into a rectangular / cylindrical tube, prior to any age-hardening treatment to produce nanoprecipitates. Once the tube is formed, the steel is age-hardened to form nanoprecipitates within the steel matrix, enhancing strength and heat resistance. In some examples, tube 210 is made from a low-alloy steel with increased heat resistance and lean alloying (for reduced cost, improved weldability, thermal conductivity, and formability).

[0131] Depending on the design goals, different steel compositions can be used. In some instances, the steel used for the battery pack housing is optimized for thermal conductivity, cost, and high-temperature strength, and its chemical composition includes 0.01 to 0.1% by weight of carbon, 0.01 to 0.2% by weight of niobium, titanium, and vanadium, 0.1 to 2.0% by weight of copper, 1.0 to 6.0% by weight of nickel, 0.1 to 1.0% by weight of aluminum, 0.1 to 1.0% by weight of manganese, 0.1 to 2.5% by weight of molybdenum, 0.1 to 1.5% by weight of titanium, 0.5 to 3.0% by weight of silicon, and iron (Fe) (and other optional materials) as the balance. In some instances, the weight ratio of Ni / Cu is greater than 0.3, the weight ratio of Ni / Al (by weight) is 2 to 5, the weight ratio of Ni / Mn is 1 to 5, and the weight ratio of Si / Ti is 1.5 to 3.

[0132] In other examples, the steel used for the battery pack housing is optimized for cost and high temperature strength and has a chemical composition including 0.01 to 0.1 weight percent carbon, 0.01 to 0.2 weight percent niobium, titanium, and vanadium, 0.1 to 1.5 weight percent titanium, 0.5 to 3.0 weight percent silicon, and iron (Fe) (and other optional materials) as the balance. In some examples, the weight ratio of Si to Ti is 1 to 3.

[0133] In another example, the steel used for the battery pack housing is optimized for thermal conductivity and has a chemical composition including 0.01 to 0.1% carbon by weight, 0.01 to 0.2% niobium, titanium, and vanadium by weight, 0.1 to 2.0% copper by weight, 1.0 to 6.0% nickel by weight, 0.1 to 1.0% aluminum by weight, 0.1 to 1.0% manganese by weight, 0.1 to 2.5% molybdenum by weight, and iron (Fe) (and other optional materials) as the balance. The Ni / Al ratio (by weight) is 2 to 5, and the Ni / Mn ratio is 1 to 3.

[0134] Carbon, niobium, titanium, and vanadium provide carbides for grain refinement and precipitation hardening. Copper, nickel, aluminum, manganese, molybdenum, and titanium support the coprecipitation of Cu-Ni-Al-Ti. Mn and Mo control precipitate size and distribution. Iron, titanium, and silicon form Fe2SiTi nanoprecipitates.

[0135] In some examples, the precipitate fraction is between 2% and 20% by volume. In some examples, the precipitate particle size is between 1 nm and 100 nm. In some examples, the precipitate comprises Cu, Ni / Al / Ti intermetallic compounds, and / or Fe2SiTi intermetallic compounds. In some examples, the steel composition has a high thermal conductivity (e.g., >40 W / mK) due to the lean alloy chemistry (compared to stainless steel). In some examples, the hardness difference between the seam weld and the bulk steel is less than 50 HV (Vickers hardness value).

[0136] In some examples, the steel has a yield strength greater than 700 MPa at room temperature after age hardening and maintains a yield strength greater than 200 MPa at 600° C. In other words, the steel is approximately 4 times stronger than the steel used in 4680 housings and 20 times stronger than conventional aluminum prismatic housings.

[0137] Now refer to Figure 5 , a method for manufacturing a tubular housing is shown. At 310, an unaged nanoprecipitated steel sheet having a desired steel composition is roll-formed into a tube. The housing is formed in an unaged (soft) state when the steel is formable and can be bent into an open-ended cylinder or rectangular prism with sharp corners and no cracks. At 314, the opposing edges of the tube are seam welded to form the open-ended tubular housing.

[0138] At 318, the tubular housing is age-hardened. In some examples, the tubular housing is heated to a temperature of 400°C to 600°C for a predetermined soaking time. In some examples, the predetermined soaking time is between 6 minutes and 10 hours. At 322, the bottom portion is attached to one end of the tubular housing using brazing, crimping, or welding. Subsequently, the battery cell stack is placed in the housing, the terminals are connected, and the cover portion is attached to the opposite end of the tubular housing.

[0139] Age hardening of the steel shell improves strength and corrosion resistance. The shell's steel component balances strengthening and thermal conductivity through the use of lean alloy chemically strengthened nanoprecipitations as described herein. The steel includes nanoprecipitation strengthening with Cu, Ni / Al / Ti intermetallic compounds, and / or Fe2SiTi intermetallic compounds, enabling the shell to withstand increased thermal runaway temperatures of 600°C to 800°C.

[0140] The addition of silicon and titanium (in addition to nano-precipitation strengthening elements) allows Fe-Si-Ti precipitation strengthening to partially replace Ni-based precipitation strengthening, thereby reducing costs. Silicon and titanium delay the austenitization transformation at high temperatures, which further increases the high temperature strength.

[0141] Now refer to Figure 6 , shows a scanning electron microscope image of a tubular housing. In this example, the steel composition includes 0.05 wt% carbon, 5.5 wt% nickel, 1.2 wt% aluminum, and 0.015 wt% niobium. The steel has an ultimate tensile strength of about 1400 MPa and a thermal conductivity of about 40 W / mK. The nanoprecipitates can be Figure 6 Seen as black spots.

[0142] Now refer to Figure 7A and 7B , simulation (e.g., The simulations (Figure 5) show the estimated (equilibrium) phase volume fractions as a function of the shell temperature. The simulations indicate that the precipitated phase remains until the temperature is increased to 800°C (e.g., under equilibrium conditions). Due to the slow diffusion rate of alloying elements, the dissolution temperature in use may be even higher.

[0143]

[0144] For the above example, the aging hardness was 415 HV, 415 HV after 40 minutes at 500°C, 399 HV after 40 minutes at 550°C, and 409 HV after 40 minutes at 600°C.

[0145] Now refer to Figure 8A and 8B , an improvement in weld quality was seen after age hardening the roll-formed housing. Figure 8A In the example, the material in the middle of the weld is melted and hardened at 810. The adjacent area of the weld is affected by the heat 814 (e.g., softened by the heat). The outer area of the shell includes bulk steel 818 that is not affected by the heat. Figure 8B , various regions (810', 814', and 818') of the tubular housing are shown after age hardening and are generally uniform in hardness.

[0146] The foregoing description is merely exemplary and is absolutely not intended to limit the present disclosure, its application or use. The broad teachings of the present disclosure can be implemented in various forms. Therefore, although the present disclosure includes specific examples, the true scope of the present disclosure should not be limited thereto, because other modifications will become apparent after studying the drawings, the specification and the following claims. It should be understood that one or more steps within the method may be implemented in a different order (or simultaneously) without changing the principles of the present disclosure. In addition, although the various embodiments are described above as having certain features, any one or more features described with respect to any embodiment of the present disclosure may be implemented in any other embodiment and / or combined with the features of any other embodiment, even if the combination is not explicitly described. In other words, the embodiments are not mutually exclusive, and the mutual replacement of one or more embodiments is still within the scope of the present disclosure.

[0147] Various terms are used to describe the spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.), including "connected," "engaged," "coupled," "adjacent," "next to," "on top of," "over," "under," and "disposed." Unless explicitly described as "directly," when describing a relationship between a first element and a second element in the above disclosure, the relationship can be a direct relationship in which there are no other intervening elements between the first element and the second element, or an indirect relationship in which there are one or more intervening elements (spatially or functionally) between the first element and the second element. The phrase "at least one of A, B, and C" as used herein should be interpreted to mean a logical (A or B or C) using a non-exclusive logical OR, and should not be interpreted to mean "at least one of A, at least one of B, and at least one of C."

Claims

1. A method for manufacturing a tubular housing for a battery cell, comprising: bending a sheet made of steel into a tubular body having one of a cylindrical shape and a prismatic shape, wherein the steel comprises: 0.01 to 0.1 wt% carbon; 0.01 to 0.2 weight percent niobium, titanium, and vanadium; and at least one of the first group and the second group, The first group comprises: 0.01 to 2.0 wt. % copper; 1 to 6.0 wt. % nickel; 0.1 to 1.0 wt. % aluminum; 0.1 to 1.0 wt. % manganese; and 0.1 to 2.0 wt. % molybdenum; The second group comprises: 0.1 to 1.5 wt. % titanium; and 0.1 to 1.5 wt% silicon; welding opposing edges of the tubular body to form a weld; and The tubular body is age hardened after welding. 2 . The method of claim 1 , further comprising attaching a bottom portion to one end of the tubular housing.

3. The method according to claim 1, wherein: The steel comprises the first group and the second group, The weight ratio of Ni / Cu is greater than 0.3, The weight ratio of Ni / Al is 2 to 5, The weight ratio of Ni / Mn is 1 to 3, and The weight ratio of Si / Ti is 1.5 to 3.

4. The method according to claim 1, wherein: said steel comprises said second group, and The weight ratio of Si / Ti is 1 to 3.

5. The method according to claim 1, wherein: said steel comprising said first group, The weight ratio of Ni / Cu is greater than 0.3, The weight ratio of Ni / Al is 2 to 5, and The weight ratio of Ni / Mn is 1 to 3.

6. The method of claim 1, wherein the tubular body is age hardened by heating to a temperature of 400°C to 600°C for a predetermined soaking time.

7. The method according to claim 1, wherein: The steel has a precipitation fraction of 2% to 20% by volume, and The particle size of the precipitate is 1 nm to 100 nm.

8. The method of claim 1, wherein the steel comprises nanoprecipitates of Cu, Ni / Al / TI intermetallic compounds, and Fe2SiTi intermetallic compounds.

9. The method of claim 1, wherein the thermal conductivity of the steel is greater than 40 W / mK.

10. The method according to claim 1, wherein: The steel has a yield strength greater than 700 MPa at room temperature, and The steel maintains a yield strength greater than 200 MPa at 600°C.

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