KR102123672B1 - Safety Unit Comprising Bypass Configured to Allow Electric Current to Flow Only When Discharging Battery Cell - Google Patents

Abstract

The present invention is a safety unit for a battery pack that cuts off the current when the battery cell rises above a critical temperature during a charge/discharge process, the first node being electrically connected to the battery cell; A second node electrically connected to an external device; A main path in which the first node and the second node are electrically connected below the threshold temperature and cut off above the threshold temperature by the switching element; And a bypass path configured to electrically connect the first node and the second node and to allow current to flow only when discharged.

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 bypass path configured to allow 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 or clean energy is increasing, and as a part, the most actively researched field is the field of electricity generation and electricity storage using electrochemistry.

At present, a representative example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is gradually expanding.

Recently, as technology development and demand for portable devices such as portable computers, portable telephones, and cameras have increased, demand for secondary batteries as an energy source has rapidly increased. Among these secondary batteries, many studies have been conducted on lithium secondary batteries exhibiting high energy density and operating potential, long cycle life, and low self-discharge rate, and are also commercially used and widely used.

However, despite the above advantages, lithium secondary batteries have a fundamental problem of low safety. For example, when the battery is overcharged, the decomposition reaction of the electrolyte at the electrode is promoted to generate combustible gas, and the overcurrent caused by various causes such as internal short circuit increases the temperature of the battery to decompose the battery components. cause. The generation of gas due to such overcharge, overcurrent, etc., causes the battery to ignite, and in some cases, the battery may explode. In addition, even if it is not overcurrent, the temperature rise due to other causes causes a similar problem to the above. Accordingly, various safety units are built in a battery pack including a lithium secondary battery as a power plant as a solution to this problem.

Typical examples of such safety units include PTC (Positive Temperature Coefficient), fuses, and thermal cut-off (TCO). PTC is a safety unit that cuts off current when the temperature rises due to overcurrent, etc., and the fuse is also a safety unit that cuts off current when temperature rises due to overcurrent, etc. TCO is a safety unit that reversibly cuts off electrical connections when temperature rises due to other causes.

These safety units are the same in that they detect an abnormal temperature during charging and discharging of the battery pack and cut off the current. However, despite the different standards for the safety of the battery pack during charging and discharging, since these safety units block current according to the same standard, it is difficult to sufficiently exhibit the performance of the battery pack during discharge.

Accordingly, there is a high need for a technology capable of sufficiently exerting the performance of the battery pack while discharging while ensuring safety during charging and discharging of the battery pack.

The present invention aims to solve the problems of the prior art as described above and the technical problems requested from the past.

The inventors of the present application have undergone in-depth research and various experiments, and as described later, the first node and the second node are electrically connected, and the safety includes a bypass path configured to allow current to flow only during discharge. When using the unit, while ensuring safety during charging and discharging of the battery pack, it was confirmed that the discharge performance of the battery pack can be improved, and the present invention has been completed.

Accordingly, the safety unit for a battery pack according to the present invention includes a first node that blocks a current when a battery cell rises above a threshold temperature during a charge/discharge process and is electrically connected to the battery cell; A second node electrically connected to an external device; A main path in which the first node and the second node are electrically connected below the threshold temperature and cut off above the threshold temperature by the switching element; And a bypass path configured to electrically connect the first node and the second node, and to allow current to flow only during discharge.

The battery pack generally increases in temperature during charging and discharging, but if the temperature rises above the critical temperature, the risk of ignition and explosion due to abnormal operation of the battery pack is high, so the current must be cut off.

However, since the operation mechanism (mechanism) of the battery pack is different at the time of charging and discharging, it is preferable to apply different criteria for determining whether the operation is abnormal.

Specifically, since a constant current is applied from the charger during charging, the temperature rarely rises above a critical temperature when normal charging is performed. Therefore, it is necessary to immediately cut off the current by determining that there is an abnormality in the battery pack when the temperature rises rapidly during charging.

On the other hand, the electric power required by the external device is variable during discharge. When the power required by the external device is large, even if the battery pack operates normally, the temperature of the battery pack may rise instantaneously due to a sudden increase in current. In particular, heat may be generated by electrical resistance of elements located in the safety unit, and in this case, since the temperature rise does not threaten the safety of the battery pack, the need to cut the current is low. In addition, when the power required by the external device is lowered again, there is no big problem.

Moreover, since energy is accumulated in the battery pack when charging the battery pack, it may be a serious problem in safety when the battery pack is operated abnormally. On the other hand, when the battery pack is discharged, energy is released in the battery pack, so even if the battery operates abnormally, the energy accumulated in the battery pack is not large, and thus there is relatively little concern about safety.

Therefore, when the same stability criteria are applied at the time of discharging and charging, it is determined that there is a problem in safety or abnormal operation even when the battery pack is operating normally, and thus there is a problem that the performance of the battery pack cannot be fully exhibited.

As a result, in order to improve the discharge performance of the battery pack, it is necessary to evaluate the safety standards different from when charging.

As in the prior art, when charging and discharging, current flows through the same path, and when the current is cut off by the same switching element, the standard for stability is also completely the same, so there is a problem that the performance of the battery pack cannot be sufficiently exhibited. .

In addition, in order to apply different stability criteria during charging and discharging, it is possible to consider a configuration in which a path through which a current flows during charging and a path through which a current flows during discharging are separately included, and a separate switching element is included in each path. However, in this case, since the circuit configuration of the safety unit is complicated, the required components increase, the cost increases, and the heat generation according to the electrical resistance of the elements during discharge cannot be significantly improved.

According to the present invention, current flows in both charging and discharging processes, including a main path that is cut off at a constant temperature reference, the circuit configuration is simple, and only one switching element is required, thereby reducing cost. In addition, through a bypass path configured to allow current to flow only during discharge, the amount of current flowing through the main path during discharge can be reduced, and heat generation due to the current flowing through the main path during discharge can be reduced. For this reason, it is possible to significantly improve the discharge performance of the battery pack while securing stability during discharge.

The 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 a battery pack.

In one specific example, the bypass path may include a semiconductor device that allows current to flow only in the direction of the first node to the second node, so that current flows only during discharge.

The semiconductor device 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 bimetals in which metal plates having different thermal expansion coefficients are joined.

In detail, the switching element may have a disc shape having a concave surface on one side, and more specifically, the switching element may have a structure in which a concave disc shape is inverted according to a temperature change to block energization of the main path.

In addition, the main path may be configured to reversibly energize or cut the first node and the second node according to changes in the concave disk shape of the switching element.

As described above, when the switching element forms a disc shape, it is easy to maintain a concave disc shape even if it is repeatedly inverted, and has excellent durability, and has excellent operational reliability in blocking energization compared to a general plate shape.

On the other hand, the effective operating temperature of the switching element may be 80 degrees to 150 degrees Celsius, specifically, 100 degrees to 140 degrees Celsius. When the effective operating temperature range is less than 80 degrees Celsius, the time at which the current is cut off is too fast, so it is difficult for the battery pack to exhibit sufficient performance, and when it exceeds 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 to further include, in the bypass path, a current limiting resistor for controlling a relative amount of current flowing in the main path and current flowing in the bypass path upon discharge under a threshold temperature. Can be.

The current limiting resistor may have an electrical resistance value in which the ratio of the current flowing in the main path and the current flowing in the bypass path during discharge is 4:1 to 1:2. If the current flowing in the main path outside the relative range of these currents is too large, the current flowing in the bypass path is relatively small, so the increase in the discharge performance of the battery pack is not large, and if the current flowing in the main path is too small, the battery malfunctions. Even when the current is not blocked, the stability of the battery pack may deteriorate.

Meanwhile, the bypass path may be configured such that current flows through a safety element that blocks current when the temperature rises. When the safety element is included, when the current flowing in the main path is cut off at a threshold temperature or higher during discharge, the current flowing through the bypass path can also be blocked together, further improving the safety of the battery pack.

In one specific example, the safety element may be a PTC element that cuts the current by increasing the electrical resistance when the temperature rises.

The effective operating temperature of the safety element may be 80 degrees to 150 degrees Celsius, specifically 100 degrees to 140 degrees Celsius. When the effective operating temperature range is less than 80 degrees Celsius, the time at which the current is cut off is too fast, so it is difficult for the battery pack to exhibit sufficient performance, and when it exceeds 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.

In detail, the polymer material is not particularly limited as long as the electrical conductivity is low and the volume expands when the temperature rises to cut off the electrical passage, but may be, for example, a thermoplastic polymer.

The thermoplastic polymer can be a semi-crystalline material because it can 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, and more specifically 15% or more.

The thermoplastic polymer is not particularly limited as long as it satisfies the above properties, for example, high density polyethylene, linear low density polyethylene, low density polyethylene, medium density polyethylene, maleic anhydride functionalized polyethylene, maleic anhydride functionalized Ethylene acrylics such as elastomers, ethylene copolymers (e.g. EXXELOR VA1801 and VA1803 from ExxonMobil), ethylene butene copolymers, ethylene octene copolymers, ethylene methyl acrylate, ethylene ethyl acrylate and ethylene butyl acrylate copolymers Late copolymers, polyethylene (PE) including glycidyl methacrylate modified polyethylene, polypropylene (PP), maleic anhydride functionalized polypropylene, glycidyl methacrylate modified poly Contains propylene (glycidyl methacrylate modified polypropylene), polyvinyl chloride (PVC), polyvinyl acetate, polyvinyl acetyl, acrylic resin, alternating polystyrene (sPS), PA6, PA66, PA11, PA12, PA6T, PA9T , But not limited to, polyamide, poly-tetra-fluoroethylene (PTFE), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polyamideimide, polyimide, polyethylene vinyl acetate (EVA), glycidyl methacrylate modified polyethylene vinyl acetate, polyvinyl alcohol, polymethyl methacrylate (PMMA), polyisobutylene, polyvinylidene chloride, polyvinylidene fluoride (PVDF), polymethyl acrylic Rate, polyacrylonitrile, polybutadiene, polyethylene-terephthalate (PET), poly8-aminocaprylic acid, polyvinyl alcohol (PVA), and polycaprolactone.

The substrate is only an example, and it is needless to say that a PTC device may be manufactured using a thermosetting polymer in addition to the thermoplastic polymer.

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

If the content of the polymer material is less than 1% by weight, the volume expansion of the PTC material is not large when the temperature rises, so it is difficult to effectively block the current. On the other hand, if the content of the polymer material is more than 60% by weight, the polymer material does not exist dispersed in the form of particles, but aggregates with each other to exist in a large lump form, and thus there is a problem that PTC characteristics are deteriorated.

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

When the content of the conductive material is less than 1% by weight, the resistance of the electrode may be high even when the temperature is low, and when it is more than 60% by weight, the increase in resistance may not be large when the temperature is increased, resulting in a decrease in PTC characteristics. There is.

The conductive material is not particularly limited as long as it has conductivity without inducing a chemical change, 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 fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder, 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 may 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, for example, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl Cellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, and various other It may be one or more selected from the group consisting of copolymers.

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 blocks current in an overcurrent and overvoltage condition.

The battery pack according to the present invention includes both the safety unit and the battery management unit, and cuts the current in an abnormal state according to high temperature, overcurrent, and overvoltage to significantly improve the safety of the battery pack.

The battery cell may be a secondary battery capable of charging and discharging, and in particular, 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, and the positive electrode may be manufactured by coating, for example, a positive electrode mixture in which a positive electrode active material, a conductive material, and a binder are mixed in a positive electrode current collector, if necessary A filler may be further added to the positive electrode mixture.

The positive electrode current collector is generally manufactured to a thickness of 3 to 201 μm, and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium , And one of the surface treatment with carbon, nickel, titanium or silver on the surface of aluminum or stainless steel may be used, and specifically aluminum may be used. The current collector may also increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, and various forms such as film, sheet, foil, net, porous body, foam, and nonwoven fabric are possible.

The positive electrode active material may include, 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 the formula Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; 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 ; Ni-site type lithium nickel oxide represented 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, Zn or Ta, x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like, but are not limited to these.

The conductive material is usually added in 1 to 30% by weight based on the total weight of the positive electrode mixture containing the positive electrode active material. The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, etc. Carbon black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder, 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 may be used.

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

The filler is selectively used as a component that suppresses the expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. For example, olefinic 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 prepared by applying a negative electrode mixture containing a negative electrode active material and a binder to the negative electrode current collector, and thus, a dispersant and a filler may be optionally further included.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, on the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used. In addition, like the positive electrode current collector, it is also possible to form fine irregularities on the surface to enhance the bonding force of the negative electrode active material, and may 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 negative electrode current collector may be all the same within the range of 3 to 201 μm, but may have different values depending on the case.

The negative 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, 2, 3 elements of the periodic table, halogen; 0<x≤1; 1≤y≤3 Metal composite oxides such as 1≤z≤8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; 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 materials or the like can also be used.

In one specific example, the separator may be a polyolefin-based film commonly used in the art, 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, It may be a sheet of one or more selected from the group consisting of polyethersulfone, polyphenyleneoxide, polyphenylenesulfidro, polyethylenenaphthalene, and mixtures thereof.

The separator may be made of the same material as each other, but is not limited thereto, and may be made of different materials according to safety, energy density, and overall performance of the battery cell.

The pore size and porosity of the separator are not particularly limited, but the porosity may range from 10 to 95%, and the pore size (diameter) may be 0.1 to 50 μm. When the pore size and porosity are less than 0.1 μm and 10%, respectively, it acts as a resistive layer, and when the pore size and porosity exceeds 50 μm and 95%, it becomes difficult to maintain mechanical properties.

The electrolyte solution may be a lithium salt-containing non-aqueous electrolyte, and the lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt, and the non-aqueous electrolyte includes a non-aqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte. It is not limited to.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma. -Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxyfuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxorun, formamide, dimethylformamide, dioxorun, acetonitrile , Nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxoren derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate can be used.

The organic solid electrolyte includes, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and ions. A polymerization agent containing a sex dissociating group and the like can be used.

The inorganic solid electrolyte is, for example, 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 , Li ₄ nitrides such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , halides, sulfates, and the like can be used.

The lithium salt is a material that is soluble in the non-aqueous electrolyte, 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 lithium carboxylate, lithium 4-phenyl borate, imide, and the like.

In addition, non-aqueous electrolytes are used for the purpose of improving charge/discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme (glyme), hexaphosphate triamide, Nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. have. In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, or carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-Ethylene) Carbonate), PRS (Propene sultone), and the like may be further included.

In one specific example, lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , and LiN(SO ₂ CF ₃ ) ₂ are formed of a cyclic carbonate of EC or PC as a highly dielectric solvent and DEC, DMC or EMC of a low viscosity solvent. A lithium salt-containing non-aqueous electrolyte may be prepared by adding it to a mixed solvent of linear carbonate.

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

The device includes, for example, a notebook computer, a netbook, a tablet PC, a mobile phone, an MP3, wearable electronic devices, a power tool, an electric vehicle (EV), and a hybrid electric vehicle (HEV). It can be a plug-in hybrid electric vehicle (PHEV), electric bike (E-bike), electric scooter (E-scooter), electric golf cart, or power storage system. However, it goes without saying that they are not limited to these.

Since the structure and manufacturing method of such a device are known in the art, detailed description thereof is omitted in this specification.

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

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

Through a bypass path configured to allow current to flow only during discharge, the amount of current flowing through the main path during discharge can be reduced, thereby reducing heat generation due to the current flowing in the main path during discharge, thereby improving stability during discharge. While securing, it is possible to significantly improve the discharge performance of the battery pack.

In addition, the use of a concave disk-shaped switching element is excellent in durability and excellent in operational reliability to cut off the energization.

1 is a circuit diagram of a typical battery pack safety unit that cuts off the current when the battery cell rises above a critical temperature during the charging and discharging process;
2 is a circuit diagram of a safety unit for a battery pack according to an 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;
4 and 5 are schematic diagrams for explaining the operating principle of the safety unit represented by the circuit diagram of FIG. 3;
6 is a circuit diagram of a battery pack safety unit including a PTC device according to another embodiment of the present invention.

Hereinafter, with reference to the drawings according to an embodiment of the present invention, it is for easier understanding of the present invention, and the scope of the present invention is not limited thereto.

FIG. 1 is a circuit diagram of a general battery pack safety unit that blocks current when a battery cell rises above a critical temperature during a charge/discharge process.

Referring to FIG. 1, the safety unit 100 includes a first node 111 that is electrically connected to a battery cell, a second node 112 that is electrically connected to an external device, and a switching element that blocks current at a threshold temperature or higher. Contains 120.

During discharge, a current flows from the first node 111 to the second node 112, and when charging, a current flows from the second node 112 to the first node 111.

As described above, since the safety unit 100 flows in the same path during charging and discharging, it is determined whether the battery pack is abnormally operated based on the same criteria during charging and discharging. 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, and a switching element blocking current at a threshold temperature or higher. 220, and a diode 230 for rectifying the current to flow in only one direction.

At the time of charging, current flows from the second node 212 toward the first node 211, and is specifically configured in the order of the second node 212, the conductive portion 221, and the first node 211. Current flows along the main path.

During discharge, current flows from the first node 211 toward the second node 212, and current flows along two paths, a main path and a bypass path.

The main path is configured in the order of the first node 211, the conductive portion 221, and the second node 212, and the bypass path is the first node 211, the diode 230, and the second node 212 ).

The switching element 220 ensures safety by cutting the main path at a constant temperature standard. In addition, through a bypass path configured to allow current to flow only during discharge, the amount of current flowing through the main path during discharge can be reduced, and heat generation due to the current flowing through the main path during discharge can be reduced. For this reason, the output performance of the battery pack is significantly improved while securing stability during discharge.

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

Referring to FIG. 3 in comparison with FIG. 2, 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, and a current above a critical temperature It includes a switching element 220 for blocking, a diode 230 for rectifying current flowing in only one direction, and a resistor 250 for limiting current. That is, compared with the safety unit 200 of FIG. 2, the safety unit 200a is different in that it further includes a current limiting resistor 250.

The current limiting resistor 250 adjusts the relative amount of current flowing in the main path and current flowing in the bypass path during discharge. If the current flowing in the main path is too large, the current flowing in the bypass path is relatively small, so the discharge performance of the battery pack is not large, and if the current flowing in the main path is too small, the current cannot be blocked even when the battery is abnormally operated. The problem that the stability of the battery pack is lowered can be prevented.

4 and 5 are schematic diagrams for explaining the operating principle of the safety unit represented by the circuit diagram of FIG. 3.

4 and 5, both the safety unit 200a1 and the safety unit 200a2 conform to the circuit diagram of FIG. 3, and the safety unit 200a1 operates under a critical temperature, and the safety unit 200a2 Shows a typical operation above the critical temperature.

First, in the safety unit 200a1, the switching element 220 is composed of bimetals in which metal plates having different thermal expansion coefficients are joined, and the lower surface has 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 made of a PTC material or an insulating material.

Next, in the safety unit 200a2, the switching element 220 is a disc shape having a concave shape inverted due to an increase in temperature and a concave upper surface.

As the shape of the switching element 220 is spotted, energization of the main path composed of the first node 211, the conductive portion 221, and the second node 212 is blocked.

As described above, when the switching element 220 forms a disc shape, it is easy to maintain a concave disc shape even if it is inverted repeatedly, and has excellent durability, and has excellent operational reliability in blocking energization compared to 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.

Referring to FIG. 6 in comparison with FIG. 3, 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, and a current above a critical temperature It includes a switching element 220 for blocking, a diode 230 for rectifying current flowing in only one direction, a PTC element 241, and a resistor 250 for limiting current. That is, compared with the safety unit 200a of FIG. 3, the safety unit 200b is different in that it further includes a PTC element 241 in the bypass path.

At the time of charging, a current flows from the second node 212 toward the first node 211, and specifically, a note composed in the order of the second node 212, the conductive portion 221, and the first node 211 A current flows along the path.

When the switching element 220 is above a critical temperature, the main path is cut off.

During discharge, current flows from the first node 211 toward the second node 212, and current flows along two paths, a main path and a bypass path.

The main path is composed of the first node 211, the conductive part 221, and the second node 212 in order, and the bypass path includes the first node 211, the PTC element 241, and the current limiting resistor ( 250), a diode 230, and a second node 212 in this order.

When the PTC element 241 is included, when a current flowing in the main path is cut off at a threshold temperature or higher during discharge, the current flowing through the bypass path can also be blocked together, thereby further improving the safety of the battery pack.

Although described above with reference to the drawings according to embodiments of the present invention, those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above.

Claims (17)

As a safety unit for a battery pack that cuts off the current when the battery cell rises above a critical temperature during the charging and discharging process
A first node electrically connected to the battery cell;
A second node electrically connected to an external device;
It is configured such that current flows during charging and discharging, current flows from the second node to the first node during charging, and current flows from the first node to the second node when discharging, and by a switching element, A main path in which the first node and the second node are electrically connected below the critical temperature and are cut off above the critical temperature; And
It is configured to electrically connect the first node and the second node, and include a semiconductor element that flows current only in the direction from the first node to the second node. A bypass path configured to distribute and flow the current flowing through it;
It comprises,
The bypass route,
A current limiting resistor connected in series with the semiconductor element to adjust a relative amount such that a current flowing in a main path and a current flowing in a bypass path have a predetermined ratio when discharging under the threshold temperature; And
A PTC element connected between the first node and the switching element to block current flowing through the bypass path when the current flowing in the main path at a threshold temperature or higher during discharge is blocked by the switching element;
Safety unit comprising a. delete The safety unit according to claim 1, wherein the semiconductor element is a rectifying diode. The safety unit according to claim 1, wherein the switching element is composed of bimetals in which metal plates having different thermal expansion coefficients are joined. The safety unit according to claim 4, wherein the switching element has a concave disc shape on one side. The safety unit according to claim 5, wherein the switching element blocks the energization of the main path by reversing the shape of the concave disc according to the temperature change. 7. The safety unit according to claim 6, wherein the main path is configured to reversibly energize or cut off the first node and the second node according to a change in the concave disk shape of the switching element. The safety unit according to claim 1, wherein the effective operating temperature of the switching element is in the range of 80 degrees to 150 degrees Celsius. delete The safety unit according to claim 1, wherein the current limiting resistor has an electrical resistance value in which the ratio of the current flowing in the main path to the bypass path during discharge is 4:1 to 1:2. delete delete The safety unit according to claim 1, wherein the effective operating temperature of the PTC element is in the range of 80 degrees to 150 degrees Celsius. The safety unit according to claim 1, wherein the PTC element comprises a polymer material and a conductive material. A battery pack comprising the safety unit according to claim 1 and at least one battery cell. 16. The battery pack of claim 15, wherein the battery pack further comprises a battery management unit (BMU) that cuts off current in an overcurrent and overvoltage condition. A device comprising the battery pack according to claim 15 as a power source.

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