KR20170036321A - Safety Unit Comprising Bypass Configured to Allow Electric Current to Flow Only When Discharging Battery Cell - Google Patents

Abstract

The present invention relates to a safety unit for a battery pack, which blocks an electric current when the temperature of a battery cell rises above a critical temperature in a charging and discharging process. The safety unit for a battery pack comprises: a first node electrically connected to a battery cell; a second node electrically connected to an external device; a main path which is electrically connected to the first node and the second node under a critical temperature and cut off at a threshold temperature or more by a switching element; and a bypass which electrically connects the first node and the second node and is configured to allow an electric current to flow only during discharge.

Description

(Safety Unit Comprising Bypass Configured to Allow Electric Current to Flow Only When Discharging Battery Cell)

The present invention relates to a safety unit including a detour path configured to allow a current to flow only when a battery cell is discharged.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most active field of research is electric power generation and storage.

At present, a typical example of an electrochemical device utilizing such electrochemical energy is a secondary battery, and the use area thereof is gradually increasing.

2. Description of the Related Art [0002] Recently, as the development and demand for portable devices such as portable computers, portable phones, cameras, and the like are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Many studies have been made on lithium secondary batteries, which exhibit high energy density and operating potential, have a long cycle life and low self-discharge rate among such secondary batteries, and have been widely used for commercialization.

However, despite the above advantages, the lithium secondary battery has a fundamental problem that safety is low. For example, when the battery is overcharged, the decomposition reaction of the electrolytic solution at the electrode is promoted to generate a flammable gas, and the overcurrent caused by various causes such as an internal short-circuit increases the temperature of the battery, cause. Such generation of gas due to overcharging, overcurrent, or the like causes the battery to ignite, and in some cases, the battery may explode. In addition, even if it is not an overcurrent, the temperature rise due to other causes causes similar problems as described above. Therefore, a battery pack including a lithium secondary battery as a power plant has various safety units built in to solve such a problem.

Typical examples of such a safety unit include a PTC (Positive Temperature Coefficient), a fuse, and a thermal cutoff (TCO). PTC is a safety unit that cuts off the current by increasing the resistance when the temperature rises due to the overcurrent. The fuse is also a safety unit that cuts off the current when the temperature rises due to overcurrent. TCO is a safety unit that reversibly disconnects the electrical connection when the temperature rises due to other causes.

These safety units are the same in that a current is cut off by sensing a temperature abnormality upon charging and discharging the battery pack. However, although the criteria for safety of the battery pack during charging and discharging are different, these safety units cut off the current according to the same standard, so that it is difficult to sufficiently exhibit the performance of the battery pack during discharging.

Therefore, there is a high need for a technique capable of sufficiently exhibiting the performance of the battery pack during discharging, while ensuring safety in charging and discharging the battery pack.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments, and have found that, as will be described later, since the first node and the second node are electrically connected to each other, It has been confirmed that the discharge performance of the battery pack can be improved while ensuring safety in charging and discharging the battery pack, and the present invention has been accomplished.

Accordingly, a safety unit for a battery pack according to the present invention comprises: a first node which cuts off a current when a battery cell rises above a critical temperature in a charging / discharging process, and is electrically connected to a battery cell; A second node electrically connected to the external device; A main path which is electrically connected to the first node and the second node by a switching element at a temperature lower than a critical temperature and is cut off at a threshold temperature or more; And a bypass path electrically connecting the first node and the second node and configured to allow a current to flow only during discharging.

Although the temperature of the battery pack generally rises during charging and discharging, when the temperature rises above the critical temperature, the current should be cut off because the risk of ignition and explosion due to abnormal operation of the battery pack is high.

However, since the operation mechanism of the battery pack differs between charging and discharging, it is preferable that the criterion for judging abnormal operation is also applied differently.

Specifically, since a constant current is applied from the charger during charging, when the normal charging progresses, the temperature rarely rises above the critical temperature. Therefore, when the temperature rises sharply at the time of charging, it is determined that there is an abnormality in the battery pack, and it is necessary to immediately cut off the current.

On the other hand, at the time of discharging, the power required by the external device is variable. If the power required by the external device is large, even if the battery pack operates normally, the temperature of the battery pack may instantaneously rise due to a sudden current increase. Particularly, heat can be generated by the electric resistance of the elements located in the safety unit. In such a case, the necessity of blocking the current is low because the temperature rise does not threaten the safety of the battery pack. Further, when the power required by the external device is lowered again, no serious problem occurs.

Furthermore, when the battery pack is charged, energy is stored in the battery pack, so that there is a serious problem in safety when the battery pack is abnormally operated. On the other hand, when the battery pack discharges energy, energy is released in the battery pack, so that even when the battery pack operates abnormally, the energy stored in the battery pack is not so large, so there is less concern about safety.

Therefore, when the same stability criterion is applied at the time of discharging and at the time of charging, it is determined that the battery pack operates abnormally even though the battery pack operates normally, or that there is a problem with safety, so that the performance of the battery pack can not be fully exhibited.

As a result, in order to improve the discharging performance of the battery pack, it is necessary to evaluate with a safety standard different from that at the time of charging.

There is a problem in that the performance of the battery pack can not be sufficiently exhibited since currents flow in the same path during charging and discharging and the current is cut off by the same switching element as in the related art, .

In order to apply different stability standards during charging and discharging, it is possible to consider a configuration in which a path through which current flows during charging and a path through which current flows during charging are separately formed, and a separate switching element is included in each path However, in this case, the circuit configuration of the safety unit becomes complicated, the number of necessary parts increases, the cost increases, and the heat generation due to the electrical resistance of the elements at the time of discharge is the same.

According to the present invention, a current flows in both charging and discharging processes, including a main path disconnected at a constant temperature reference, so that the circuit configuration is simple, and only one switching element is required. In addition, the amount of current flowing through the main path at the time of discharging can be reduced through the bypass path configured to allow the current to flow only during discharging, thereby reducing heat generation due to the current flowing in the main path at the time of discharging. As a result, the discharge performance of the battery pack can be remarkably improved while ensuring stability in discharging.

An external device electrically connected to the second node may be understood as a concept including a charger in addition to a device supplied with power from the battery pack.

In one specific example, the bypass path may include a semiconductor device that allows current to flow only from the first node to the second node, in order to allow current to flow only during discharging.

The semiconductor element is not particularly limited as long as it can control the direction of the current, but may be, for example, a rectifying diode.

In one specific example, the switching element may be composed of a bimetal to which metal plates having different thermal expansion coefficients are bonded.

More specifically, the switching element may have a structure in which the concave shape of the disk is inverted according to a change in temperature to block the current flowing through the main path.

In addition, the main path may be configured to reversibly energize or deenergize the first node and the second node in accordance with a change in the concave disc shape of the switching element.

As described above, when the switching element has a disk shape, it is easy to maintain a concave disk shape even if it is repeatedly inverted, so that it is excellent in durability and excellent in operation reliability to cut off the energization compared with a general plate shape.

On the other hand, the effective operating temperature of the switching device may be 80 to 150 degrees Celsius, more specifically, 100 to 140 degrees Celsius. When the effective operating temperature range is less than 80 degrees Celsius, the current blocking time is too fast to allow the battery pack to exhibit sufficient performance. If the effective operating temperature range is over 150 degrees Celsius, the risk of ignition and explosion increases due to abnormal operation of the battery pack. can do.

In one specific example, the safety unit is configured such that, at the time of discharging under a critical temperature condition, the current limiting resistor for adjusting the relative amount of the current flowing in the main path and the current flowing in the bypass path is further included in the bypass path .

The current limiting resistor may have an electrical resistance value such that a ratio of a current flowing in the main path to a current flowing in the bypass path at the time of discharging is 4: 1 to 1: 2. If the current flowing in the main path is too large beyond the relative range of the current, the current flowing in the bypass path is relatively small and the discharge performance of the battery pack does not increase significantly. If the current flowing in the main path is too small, The current can not be blocked even when the battery pack is in a stable state.

On the other hand, the bypass path may be configured such that current flows through a safety element that interrupts the current when the temperature rises. When the safety element is included, the current flowing through the bypass path can be blocked at the same time when the current flowing in the main path at the time of discharging exceeds the critical temperature, thereby further improving the safety of the battery pack.

In one specific example, the safety element may be a PTC device that cuts off current by increasing the electrical resistance at a temperature rise

The effective operating temperature of the safety element may be between 80 and 150 degrees Celsius, more specifically between 100 and 140 degrees Celsius. When the effective operating temperature range is less than 80 degrees Celsius, the current blocking time is too fast to allow the battery pack to exhibit sufficient performance. If the effective operating temperature range is over 150 degrees Celsius, the risk of ignition and explosion increases due to abnormal operation of the battery pack. can do.

The PTC device may include a polymer material and a conductive material.

Specifically, the polymeric material may be, for example, a thermoplastic polymer, provided that the polymeric material is low in electrical conductivity and bulky at the time of temperature rise to cut off the electric path, although it is not particularly limited.

The thermoplastic polymer may be a semi-crystalline material, since it may be easier to obtain PTC properties in a semi-crystalline material when compared to an amorphous thermoplastic material. The semi-crystalline thermoplastic material may have a crystallinity of 5% or more, specifically 10% or more, more specifically 15% or more.

The thermoplastic polymer is not particularly limited as long as it meets the above-mentioned characteristics. Examples of the thermoplastic polymer include high density polyethylene, linear low density polyethylene, low density polyethylene, medium density polyethylene, maleic anhydride functionalized polyethylene, maleic anhydride functionalized (Such as EXXELOR VA1801 and VA1803 from ExxonMobil), ethylene butene copolymer, ethylene octene copolymer, ethylene acrylate, ethylene ethyl acrylate and ethylene butyl acrylate copolymer (PE), polypropylene (PP), maleic anhydride functionalized polypropylene, glycidyl methacrylate modified polypropylene, glycidyl methacrylate modified polypropylene, modified poly Propylene (glycidyl methacrylate modified p but are not limited to, polypropylene, polypropylene, polypropylene, polypropylene, polypropylene, olypropylene, polyvinyl chloride, polyvinyl acetate, polyvinyl acetyl, acrylic resins, syndiotactic polystyrene (sPS) Polyimide, polyethylene vinyl acetate (EVA), polyvinylidene fluoride (PVA), polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride, polyimide, polyamide, polytetrafluoroethylene (PTFE), polybutylene terephthalate (PMMA), polyisobutylene, polyvinylidene chloride, polyvinylidene fluoride (PVDF), polymethyl acrylate, polyacrylonitrile, polyvinylidene fluoride (PET), poly-8-aminocaprylic acid, polyvinyl alcohol (PVA), and polycaprolactone, all of which are made up of nitrile, polybutadiene, polyethylene terephthalate It may be at least one selected from the group.

It is needless to say that the above-described substrate is only one example, and a PTC device can be manufactured using a thermosetting polymer in addition to the thermoplastic polymer.

The content of the polymer material may be 1 to 60 wt%, particularly 5 to 50 wt%, based on the total weight of the PTC device.

If the content of the polymer material is less than 1 wt%, the volume expansion of the PTC material is not large at the time of temperature rise, and it is difficult to effectively block the current. On the other hand, if the content of the polymer substance is more than 60% by weight, the polymer material does not exist in the form of particles dispersed and aggregates and exists in a large lump shape, and thus the PTC characteristics are deteriorated.

The content of the conductive material may be 1 to 60 wt%, particularly 5 to 50 wt%, based on the total weight of the PTC device.

If the content of the conductive material is less than 1% by weight, the resistance of the electrode may be high even in a low temperature state. If the content of the conductive material is more than 60% by weight, .

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The PTC device may further include other materials such as a binder.

The binder is not particularly limited as long as it can provide sufficient adhesion without causing chemical changes. Examples of the binder include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and a variety of polyolefins such as polyethylene, polypropylene, Or a copolymer thereof.

The present invention provides a battery pack including the safety unit and at least one battery cell.

In addition, the battery pack may further include a battery management unit (BMU) that cuts off current in an overcurrent and an overvoltage state.

The battery pack according to the present invention includes both the safety unit and the battery management unit, and can cut off current in an abnormal state due to high temperature, overcurrent, and overvoltage, thereby remarkably improving the safety of the battery pack.

The battery cell may be a rechargeable secondary battery, specifically, a lithium secondary battery.

Hereinafter, other components of the secondary battery will be described.

The secondary battery includes a positive electrode, a negative electrode, and a separator. The positive electrode may be manufactured by, for example, applying a positive electrode mixture mixed with a positive electrode active material, a conductive material, and a binder to a positive electrode collector, A filler may further be added to the positive electrode mixture.

The cathode current collector is generally formed to a thickness of 3 to 201 탆 and is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium , And a surface treated with carbon, nickel, titanium or silver on the surface of aluminum or stainless steel can be used. Specifically, aluminum can be used. The current collector may form fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The cathode active material may be, for example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiV ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide expressed by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and x = 0.01 to 0.3); Formula _{LiMn 2-x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the positive electrode material mixture containing the positive electrode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples thereof include carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, Carbon black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder contained in the positive electrode is added to the binder in an amount of 1 to 30% by weight, based on the total weight of the mixture containing the positive electrode active material, as a component that assists in bonding between the active material and the conductive material and bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

On the other hand, the negative electrode may be manufactured by applying a negative electrode mixture containing a negative electrode active material and a binder to a negative electrode collector, and may further include a dispersant, a filler, and the like selectively.

The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

In the present invention, the thickness of the anode current collector may be the same within the range of 3 to 201 [mu] m, but may have different values depending on the case.

The negative electrode active material is, for example, the natural graphite, artificial _{graphite, Li x Fe 2 O 3 (} 0≤x≤1), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me ': Al, B, P, Si, Group 1, Group 2 and Group 3 elements of the periodic table, ; 1? Z? 8); Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based material, or the like may be used.

In one specific example, the separation membrane may be a polyolefin-based film commonly used in the art, and may be, for example, high density polyethylene, low density polyethylene, linear low density polyethylene, ultra high molecular weight polyethylene, polypropylene, polyethylene terephthalate polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyetheretherketone, A sheet made of at least one selected from the group consisting of polyethersulfone, polyphenylene oxide, polyphenylenesulfrode, polyethylene naphthalene, and mixtures thereof.

The separation membrane may be made of the same material but is not limited thereto and may be made of materials different from each other depending on safety, energy density, and overall performance of the battery cell.

The pore size and porosity of the separation membrane are not particularly limited, but the porosity may be in the range of 10 to 95% and the pore size (diameter) may be 0.1 to 50 탆. When the pore size and porosity are 0.1 μm or less and 10% or less, respectively, it acts as a resistive layer. If the pore size and porosity are more than 50 μm and 95%, it is difficult to maintain the mechanical properties.

The electrolyte solution may be a non-aqueous electrolyte containing a lithium salt, and the non-aqueous electrolyte containing a lithium salt is composed of a non-aqueous electrolyte and a lithium salt. Non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, The present invention is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile , Nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, Tetrahydrofuran derivatives, ether, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride A polymer containing an acid dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a substance that is soluble in the nonaqueous electrolyte and includes, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate lithium, lithium tetraphenylborate, and imide.

The nonaqueous electrolyte may contain, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride and the like may be added have. In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

In one specific _{example, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing nonaqueous electrolyte.

The present invention also provides a device including such a battery pack as a power source.

The device may be, for example, a notebook computer, a netbook, a tablet PC, a mobile phone, MP3, a wearable electronic device, a power tool, an electric vehicle (EV), a hybrid electric vehicle (HEV) , A plug-in hybrid electric vehicle (PHEV), an electric bike (E-bike), an electric scooter (E-scooter), an electric golf cart, However, the present invention is not limited thereto.

The structure and manufacturing method of such a device are well known in the art, so a detailed description thereof will be omitted herein.

As described above, the safety unit for a battery pack according to the present invention includes a detour path electrically connected to a first node and a second node and configured to allow a current to flow only during discharging, It is possible to improve the discharge performance of the battery pack while securing safety at the time of use.

Current flows in both charging and discharging processes, including the main path disconnected at a constant temperature reference, the circuit configuration is simple, and only one switching element is required, thereby reducing the cost.

It is possible to reduce the amount of current flowing through the main path at the time of discharging and reduce the heat generation due to the current flowing in the main path at the time of discharging through the bypass path configured to allow the current to flow only at the time of discharging, The discharge performance of the battery pack can be remarkably improved.

Further, by using a concave disc-shaped switching element, the durability is excellent and the operation reliability for cutting off the energization is excellent.

1 is a circuit diagram of a safety unit for a general battery pack in which current is shut off when a battery cell rises above a critical temperature in a charging / discharging process;
2 is a circuit diagram of a safety unit for a battery pack according to one embodiment of the present invention;
3 is a circuit diagram of a safety unit for a battery pack including a current limiting resistor according to another embodiment of the present invention;
Figs. 4 and 5 are schematic diagrams for explaining the operation principle of the safety unit represented by the circuit diagram of Fig. 3; Fig.
6 is a circuit diagram of a safety unit for a battery pack including a PTC device according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited by the scope of the present invention.

FIG. 1 is a circuit diagram of a safety unit for a general battery pack in which current is shut off when a battery cell rises above a critical temperature in a charging / discharging process.

Referring to FIG. 1, the safety unit 100 includes a first node 111 electrically connected to a battery cell, a second node 112 electrically connected to an external device, and a switching element (120).

A current flows from the first node 111 to the second node 112 at the time of discharging and a current flows from the second node 112 to the first node 111 at the time of charging.

As described above, since the current flows through the same path during charging and discharging, the safety unit 100 determines whether the battery pack is abnormally operated based on the same criterion both during charging and discharging. Therefore, It is difficult to exhibit sufficient performance.

2 is a circuit diagram of a safety unit for a battery pack according to an embodiment of the present invention.

Referring to FIG. 2, the safety unit 200 includes a first node 211 electrically connected to a battery cell, a second node 212 electrically connected to an external device, a switching element And a rectifier diode 230 for allowing current to flow only in one direction.

The current flows from the second node 212 toward the first node 211. Specifically, the current flows through the second node 212, the conductive section 221, and the first node 211 in this order Current flows along the main path.

At the time of discharging, a current flows from the first node 211 toward the second node 212, and current flows along two paths of the main path and the bypass path.

The main path is composed of a first node 211, a conductive part 221 and a second node 212 in this order. The bypass path includes a first node 211, a diode 230, and a second node 212 ).

The switching element 220 secures safety by disconnecting the main path at a constant temperature reference. In addition, the amount of current flowing through the main path at the time of discharging can be reduced through the bypass path configured to allow the current to flow only during discharging, thereby reducing heat generation due to the current flowing in the main path at the time of discharging. As a result, the output performance of the battery pack is remarkably improved while ensuring stability in discharging.

3 is a circuit diagram of a safety unit for a battery pack including a current limiting resistor according to another embodiment of the present invention.

3, the safety unit 200a includes a first node 211 electrically connected to a battery cell, a second node 212 electrically connected to an external device, A rectifying diode 230 for allowing a current to flow only in one direction, and a current limiting resistor 250. The switching element 220 is connected to the switching element 220, That is, as compared with the safety unit 200 of FIG. 2, the safety unit 200a differs from the safety unit 200 of FIG. 2 in that it further includes a current limiting resistor 250.

The current limiting resistor 250 regulates the relative amount of the current flowing in the main path and the current flowing in the bypass path at the time of discharging. If the current flowing in the main path is too large, the current flowing in the bypass path is relatively small and the discharge performance of the battery pack does not increase significantly. If the current flowing in the main path is too small, The problem that the stability of the battery pack is deteriorated can be prevented.

4 and 5 are schematic diagrams for explaining the operation principle of the safety unit represented by the circuit diagram of Fig.

4 and 5, both the safety unit 200a1 and the safety unit 200a2 are in conformity with the circuit diagram of Fig. 3, and the safety unit 200a1 is configured to operate in a safety unit 200a2, Is schematically shown to operate at a critical temperature or higher.

First, in the safety unit 200a1, the switching element 220 is formed of a bimetal to which metal plates having different thermal expansion coefficients are bonded, and the bottom surface is a concave disc shape. A part of the lower surface of the switching element 220 is connected to the safety element 240. The safety element 240 prevents current from flowing through the switching element 220, and may be composed of a PTC material or an insulating material.

Next, in the safety unit 200a2, the switching element 220 is in the shape of a disc having a concave top surface with a concave shape inverted due to a rise in temperature.

As the shape of the switching element 220 becomes dark, the main path composed of the first node 211, the conductive portion 221, and the second node 212 is cut off.

In this way, when the switching element 220 has a disk shape, it is easy to maintain a concave disk shape even if it is repeatedly inverted, so that it is excellent in durability and excellent in operation reliability to cut off the energization compared with a general plate shape.

6 is a circuit diagram of a safety unit for a battery pack including a PTC device according to another embodiment of the present invention.

6, the safety unit 200b includes a first node 211 electrically connected to a battery cell, a second node 212 electrically connected to an external device, A rectifying diode 230 for allowing a current to flow only in one direction, a PTC element 241, and a current limiting resistor 250. The switching element 220 is connected to the switching element 220, That is, the safety unit 200b differs from the safety unit 200a of FIG. 3 in that the safety unit 200b further includes a PTC element 241 in the detour path.

The current flows from the second node 212 toward the first node 211. Specifically, the current flows through the second node 212, the conductive section 221, and the first node 211, Current flows along the path.

The switching element 220 cuts off the main path when it is above the critical temperature.

At the time of discharging, a current flows from the first node 211 toward the second node 212, and current flows along two paths of the main path and the bypass path.

The main path is composed of a first node 211, a conductive portion 221 and a second node 212 in this order. The bypass path includes a first node 211, a PTC element 241, 250, a diode 230, and a second node 212 in this order.

When the PTC element 241 is included, the current flowing through the bypass path can be blocked at the same time when the current flowing in the main path at the time of discharging exceeds the critical temperature, thereby further improving the safety of the battery pack.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.

Claims (17)

A safety unit for a battery pack in which a current is cut off when a battery cell rises above a critical temperature in a charging / discharging process,
A first node electrically connected to the battery cell;
A second node electrically connected to the external device;
A main path which is electrically connected to the first node and the second node by a switching element at a temperature lower than a critical temperature and is cut off at a threshold temperature or more; And
A bypass path electrically connecting the first node and the second node and configured to allow current to flow only during discharging;
The safety unit comprising: 2. The safety unit of claim 1, wherein the bypass path includes a semiconductor device that allows current to flow only from the first node to the second node. 3. The safety unit according to claim 2, wherein the semiconductor element is a rectifier diode. The safety unit according to claim 1, wherein the switching elements are made of bimetals to which metal plates having different thermal expansion coefficients are bonded. 5. The safety unit according to claim 4, wherein the switching element is in the form of a disc having a concave surface. The safety unit according to claim 5, wherein the switching element is reversed in shape of a concave disc according to a change in temperature, thereby blocking energization of the main path. The safety unit according to claim 6, wherein the main path comprises a structure for reversibly energizing or de-energizing the first node and the second node in accordance with a change in the concave disc shape of the switching element. The safety unit of claim 1, wherein the effective operating temperature of the switching element is in the range of 80 to 150 degrees Celsius. The bypass circuit according to claim 1, further comprising a current limiting resistor for adjusting a relative amount of a current flowing in the main path and a current flowing in the bypass path at the time of discharging under the critical temperature condition Safety unit. The safety unit according to claim 9, wherein the current limiting resistor has an electrical resistance value such that a ratio of a current flowing in the main path to a current flowing in the bypass path at the time of discharging is 4: 1 to 1: 2. The safety unit of claim 1, wherein the bypass path is configured to allow current to flow through a safety element that interrupts the current when the temperature rises. 12. The safety unit according to claim 11, wherein the safety element is a PTC element that increases the electrical resistance when the temperature rises and blocks the current. 12. The safety unit of claim 11, wherein the effective operating temperature of the safety element is in the range of 80 to 150 degrees Celsius. 13. The safety unit of claim 12, wherein the PTC device comprises a polymeric material and a conductive material. A battery pack comprising a safety unit according to claim 1 and at least one battery cell. 16. The battery pack according to claim 15, wherein the battery pack further comprises a battery management unit (BMU) that cuts off current in an overcurrent and an overvoltage condition. A device comprising the battery pack according to claim 15 as a power source.

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