JP2015035354A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery whose safety is more secured, capable of quickly generating the amount of gas enough to operate a current interrupt device (CID).SOLUTION: The nonaqueous electrolyte secondary battery includes: a positive electrode; a negative electrode; a separator; a nonaqueous electrolyte; and a CID that interrupts a conductive path when detecting predetermined pressure. The nonaqueous electrolyte includes a first overcharge additive at a saturation amount at room temperature that generates gas when overcharged. The separator includes a second overcharge additive that generates gas when overcharged.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery including a pressure sensing type current interruption mechanism (CID).

  Non-aqueous electrolyte secondary batteries such as lithium secondary batteries are preferably used for so-called portable power supplies, high output power supplies for vehicles, and the like because they are lighter and have higher energy density than existing batteries. Such a nonaqueous electrolyte secondary battery is generally used in a controlled state so as to be within a predetermined voltage range. However, when an excessive current is supplied to the battery due to an erroneous operation or the like and the battery is overcharged, there is a possibility that problems such as decomposition of the electrolyte and generation of gas in the battery case may occur. Therefore, for the purpose of preventing such problems and obtaining higher safety, a battery provided with a current interruption mechanism (CID) that interrupts current when an increase in battery internal pressure associated with an overcharge state is detected has been proposed. ing. Further, in order to quickly realize the operation of the CID at the time of overcharge, an overcharge additive that is oxidatively decomposed to generate gas at the time of overcharge is also added to the non-aqueous electrolyte (for example, Patent Documents). 1-2).

JP 2006-324235 A JP 2013-004305 A

By the way, an overcharge additive such as cyclohexylbenzene (CHB) or biphenyl (BP) activates a polymerization reaction on the surface of the positive electrode active material during overcharge to generate hydrogen gas. However, as the battery is repeatedly charged and discharged, the polymerization reaction of the anti-charge additive is suppressed, and oxidative decomposition is less likely to occur. That is, even if the battery is overcharged, the oxidative decomposition reaction of the gas generating additive at the positive electrode does not proceed rapidly, and it is difficult to ensure the amount of gas necessary for CID operation at an early stage. This problem can be addressed by increasing the amount of overcharge additive in the non-aqueous electrolyte, but if the amount of overcharge additive is simply increased, the internal resistance of the battery There was a problem of rising.
The present invention has been made in view of such circumstances, and it is possible to promptly generate a gas amount capable of operating the CID even after repeated charging and discharging, while suppressing an increase in internal resistance, thereby ensuring more safety. It is an object to provide a method for producing a non-aqueous electrolyte secondary battery.

Overcharge additives such as CHB and BP, as described above, when the battery falls into an overcharged state, a polymer film is formed on the surface of the positive electrode to increase the internal resistance of the battery, stop further charging, or oxidative decomposition Gas is generated and the progress of the overcharge state is suppressed. Here, according to the knowledge of the present inventors, in order for these overcharge additives to exhibit their functions, it is effective to exist in the non-aqueous electrolyte at a certain concentration or more. That is, the above functions can be more effectively exhibited by being present at a high concentration in the non-aqueous electrolyte. However, in practice, the overcharge additive in the non-aqueous electrolyte can be decomposed and consumed by the fluctuating load that occurs during normal battery use (particularly during normal use at high rates). That is, since a polymerized film can be formed even when a normal battery is used, the internal resistance is increased, and the deterioration of cycle characteristics is promoted. Also, overcharge additives are consumed during overcharge, making it difficult to quickly generate a sufficient amount of gas.
In view of the above circumstances, the present invention provides a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and a current blocking mechanism that blocks a conductive path when a predetermined pressure is sensed. A water electrolyte secondary battery is provided. In such a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte includes a first overcharge additive that generates a gas at the time of overcharge in a saturated amount at room temperature, and the separator generates a gas at the time of overcharge. It is characterized by including a second overcharge additive.

  For example, the internal temperature of the battery that has begun to fall into an overcharge state starts to rise (for example, about 70 ° C. or higher). Therefore, the overcharge additive that cannot be completely dissolved in the non-aqueous electrolyte at room temperature is previously contained in the separator as the second overcharge additive. Then, (1) when the first overcharge additive abundantly contained in the nonaqueous electrolyte is oxidatively decomposed and the dissolved amount of the overcharge additive falls below the saturation amount, and (2) the battery is overcharged. When the internal temperature rises and the solubility of the overcharge additive of the non-aqueous electrolyte increases, the second overcharge inhibitor contained in the separator is dissolved in the non-aqueous electrolyte. Thereby, the overcharge additive can be maintained at a high concentration (preferably a saturated concentration) in the non-aqueous electrolyte, and the function of the overcharge additive during overcharge can be suitably expressed. In addition, the 1st overcharge additive and the 2nd overcharge additive may be comprised from the same compound in part or all, and may be comprised from a different compound. Desirably the same compound.

  In a preferred aspect of the non-aqueous electrolyte secondary battery disclosed herein, the positive electrode includes a positive electrode active material containing at least tungsten (W). For example, it is known that a battery using a positive electrode active material containing W has good output characteristics and suppresses an increase in internal resistance. On the other hand, for a positive electrode active material containing W, particularly a positive electrode active material having a high W concentration on the particle surface, the reaction field between the overcharge additive and the positive electrode is reduced, and the amount of gas generated during overcharge is reduced. It is also known that it can. On the other hand, according to the non-aqueous electrolyte secondary battery having the above configuration, the reaction efficiency between the overcharge additive and the positive electrode is sufficiently increased, so that the amount of gas generated during overcharge can be secured quickly, and the battery An increase in internal resistance can be suppressed.

(A) (B) is the graph which illustrated the relationship between the charge depth of the nonaqueous electrolyte secondary battery before and after a durability test, and the battery case internal pressure, respectively.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than the matters specifically mentioned in the present specification (for example, overcharge additive blending form, etc.) and matters necessary for the implementation of the present invention (for example, general structure and manufacturing process of the battery) Can be understood as a design matter of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  The non-aqueous electrolyte secondary battery disclosed herein includes, as a basic configuration, a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and a current blocking mechanism that blocks a conductive path when a predetermined pressure is sensed. Yes. The non-aqueous electrolyte includes a first overcharge additive that generates gas at the time of overcharge in a saturated amount at room temperature, and the separator includes a second overcharge additive that generates gas at the time of overcharge. Yes. Each component will be described below.

  The positive electrode is typically configured by providing a positive electrode active material layer on a positive electrode current collector. The positive electrode active material layer is not particularly limited as long as it includes a positive electrode active material, but typically, the positive electrode active material is bonded together with a conductive material together with a binder (binder), and is fixed to the positive electrode current collector. It can be in the form of Such a positive electrode includes, for example, a positive electrode paste obtained by dispersing a positive electrode active material, a conductive material, and a binder (binder) in an appropriate solvent (for example, N-methyl-2-pyrrolidone). And then dried to remove the solvent. As the positive electrode current collector, a conductive member made of a metal having good conductivity (for example, aluminum, nickel, titanium, stainless steel, etc.) can be preferably used.

The positive electrode active material is not particularly limited, and various kinds of materials that can be used as the positive electrode active material of the non-aqueous electrolyte secondary battery are used singly or in combination of two or more. Can be used. As a suitable example, lithium composite metal oxides such as layered and spinel (for example, LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiCrMnO ₄ , LiFePO ₄ Etc.). Among these, lithium nickel cobalt manganese composite oxide having a layered structure (typically a layered rock salt structure belonging to a hexagonal system) containing Li, Ni, Co, and Mn as constituent elements can be preferably used. For example, specifically, so-called ternary lithium transition metal composite oxides such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ are excellent in thermal stability and can realize a high energy density. Preferred as a positive electrode active material. Here, the lithium-nickel-cobalt-manganese composite oxide is not only an oxide containing only Li, Ni, Co and Mn as a constituent metal element, but also magnesium (Mg), calcium (Ca), strontium (Sr), titanium ( Ti), zirconium (Zr), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo), tungsten (W), iron (Fe), rhodium (Rh), palladium (Pb), platinum ( Pt), copper (Cu), zinc (Zn), boron (B), aluminum (Al), gallium (Ga), indium (In), tin (Sn), lanthanum (La), cerium (Ce) An oxide containing one or more of them is also included. The amount of these additional metal elements is not particularly limited, but is usually 0.01% by mass to 5% by mass (typically 0.05% by mass to 2% by mass, for example, 0.1% by mass to 0.8% by mass). Mass%).

In a preferred embodiment of the present invention, the positive electrode active material contains W. For example, specifically, a mode in which any of the above lithium composite metal oxides contains W is exemplified. More preferably, W may be arranged on the surface of the granular positive electrode active material. Although not particularly limited, for example, average composition _formula: is represented by _{Li x Ni a Co b Mn c} W d O 2, a lithium composite metal oxide forms W are unevenly distributed on the surface is exemplified The In the formula, 1.0 ≦ x ≦ 1.25, 0.95 ≦ a + b + c + d ≦ 1.05 and 0 <d ≦ 0.05. The positive electrode active material having W on the surface can be produced by a conventionally known method. Although not particularly limited, for example, an aqueous solution containing a metal component other than the Li component (typically a transition metal component and a W component) in a stoichiometric ratio according to a desired positive electrode active material composition is prepared. By neutralizing such an aqueous solution under pH control, these metal element hydroxides are crystallized. A mixture of the composite hydroxide thus obtained and an appropriate lithium salt (lithium carbonate, lithium hydroxide, etc.) is calcined, for example, at about 700 to 800 ° C. for about 1 to 12 hours, and then 800 to 1000 A positive electrode active material in which W is segregated on the surface can be obtained by baking at about 0 ° C. for about 2 to 24 hours. By using such a positive electrode active material, an effect of reducing the internal resistance of the nonaqueous electrolyte secondary battery can be obtained.
A preferable average particle size (which may be a secondary particle size) as the positive electrode active material may be, for example, about 3 μm to 7 μm. The specific surface area is preferably in the range of 0.5 to 1.8 m ² / g. As the conductive material, a carbon material such as carbon black (for example, acetylene black or ketjen black) can be employed.

  As the negative electrode, it is possible to use a negative electrode active material layer in which a negative electrode active material is deposited on a negative electrode current collector as a composition together with a binder or the like. As the negative electrode current collector, a conductive material made of a metal having good conductivity (for example, copper) can be suitably used. As the negative electrode active material, for example, a carbon material such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), etc. can be used. A material whose surface is coated with amorphous carbon can be suitably employed. As the binder, for example, various polymer materials such as styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polytetrafluoroethylene (PTFE) can be adopted.

As the non-aqueous electrolyte, typically, a non-aqueous solvent containing a supporting salt can be used. As the supporting salt, for example, a lithium salt, a sodium salt, a magnesium salt, or the like can be used, and among them, a lithium salt such as LiPF ₆ or LiBF ₄ can be preferably used. As the non-aqueous solvent, for example, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones and lactones can be used. Of these, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be preferably used.

And in this non-aqueous electrolyte, the 1st overcharge additive which generate | occur | produces a gas at the time of overcharge other than the nonaqueous solvent and support salt which were mentioned above is contained by the saturated amount in normal temperature. As such a first overcharge additive, various compounds that react to generate gas when the voltage exceeds a preset voltage for the target nonaqueous electrolyte secondary battery can be considered. For example, a compound having an oxidation potential lower than the decomposition potential of the electrolytic solution can be preferably used. Preferable examples of the above compound include biphenyl compounds, alkylbenzene derivatives, cycloalkylbenzene derivatives and the like. Examples of the biphenyl compound include biphenyl, 4-fluorobiphenyl, 4-methylbiphenyl, 2-fluorobiphenyl, 3,3′-difluorobiphenyl, 4,4′-difluorobiphenyl, and the like. Examples of alkylbenzene derivatives include cumene, 1,3-diisopropylbenzene, 1,4-diisopropylbenzene, 1-methylpropylbenzene, 1,3-bis (1-methylpropyl) benzene and the like. Examples of the cycloalkylbenzene derivative include cyclohexylbenzene (CHB) and cyclopentylbenzene. Such compounds may be used singly or in combination of two or more. Among these, it is more preferable to use one of cyclohexylbenzene (CHB) and biphenyl (BP), or a combination thereof. These CHB and BP are easily conjugated and easily exchanged with electrons, and can be suitably oxidized and decomposed during overcharge to generate a large amount of hydrogen gas. Therefore, the CID can be operated more quickly, and the reliability of the battery can be improved. The addition amount of such an overcharge additive can be grasped as, for example, the solubility at 25 ° C. and 1 atm in the solubility curve of the nonaqueous solvent to be used. For example, for a non-aqueous solvent in which EC, EMC, and DMC are mixed at a volume ratio of 3: 4: 3, the solubility of CHB and BP may generally be about 10% by mass in total. it can.
In addition to the above-described overcharge additive, the non-aqueous electrolyte includes, for example, a film forming agent that suitably forms an electrolyte / electrode interface (SEI: Solid Electrolyte Interface) film on the surface of the electrode due to charge and discharge, etc. These various additives can also be added as appropriate.

The separator includes a second overcharge additive that generates gas during overcharge. For example, a configuration in which various materials conventionally used as separators of this type of non-aqueous electrolyte secondary battery are used as a base material, and a second overcharge additive is disposed on the surface or inside of the base material. Can be considered.
As an arrangement form of the second overcharge additive, for example, in an environment where the battery operates normally, even if it contacts the nonaqueous electrolyte at room temperature, it does not dissolve in the nonaqueous electrolyte. It may be in a form that can be dissolved in the non-aqueous electrolyte in an overcharged state. Specifically, for example, the first overcharge additive described above may be directly disposed on the base material of the separator in a solid state such as a powder. According to such a configuration, the solubility of the overcharge additive in the non-aqueous electrolyte increases as the temperature of the battery in the overcharge state increases, and the second overcharge additive disposed in the separator becomes the non-aqueous electrolyte. Can dissolve gradually.

  Further, as another example of the arrangement form of the second overcharge additive, for example, a substance that generates a gas at the time of overcharge (gas generating substance) is placed on the separator substrate in a state of being encapsulated in the microcapsule. It may be set. In this case, the gas generating substance may be in any state such as solid, liquid, gas, and gel. Such a microcapsule can be considered to be composed of a material that is decomposed by an increase in potential or temperature of a battery in an overcharged state, or a material that bursts due to gas pressure generated in the microcapsule. Such a microcapsule is made of a polymer having a structure including an acrylic chain, an olefin chain, a methylene chain, a paraffin chain, etc., and has a diameter of the order of micrometers (that is, an average diameter (D50) of about 1 μm to 1000 μm) or less ( That is, a microparticulate capsule having an average diameter of 1 μm or less (on the order of nanometers) can be considered. Examples of the solid gas generating substance include the first overcharge additive in the powder state. Preferable examples of the liquid gas generant include, for example, 1,1,2,2,3,3,4-heptafluorocyclopentane (boiling point 82.5 ° C.), 1,1,2,2,3, Examples thereof include liquid fluorine-based liquids having a boiling point of 70 ° C. or higher, such as 4,4-octafluorocyclopentane (boiling point 79 ° C.).

The second overcharge additive (including those encapsulated in microcapsules) can be applied to the separator by spraying the second overcharge additive onto the separator substrate and placing it in the separator holes. It can be arranged. Or you may make it prepare the paste containing a 2nd overcharge additive and a binder, and supply it to the surface of a separator base material.
With this configuration, even if the first overcharge additive contained in the nonaqueous electrolyte is consumed during overcharge, the second overcharge additive is supplied into the nonaqueous electrolyte. The concentration of the overcharge additive therein can be maintained at a high value, and the amount of gas generated necessary for the operation of CID can be secured early. In the embodiment in which the second overcharge additive is directly disposed on the separator substrate, even when the first overcharge additive is consumed during normal battery use, The second overcharge additive is supplied so that the concentration of the overcharge additive becomes a saturated concentration. Therefore, it is preferable in that a large amount of gas can be generated more quickly when the battery is overcharged.

And an electrode body can be comprised by laminating | stacking said positive electrode and negative electrode through a separator. The electrode body may be, for example, a stacked electrode body in which a plurality of positive electrodes and negative electrodes are stacked, or a wound electrode body in which a long positive electrode sheet and a negative electrode sheet are stacked and wound. Also good. The capacity ratio (C _N / C _P ) calculated as the initial capacity ratio of the positive and negative electrodes, that is, the ratio of the initial charge capacity (C _N ) of the negative electrode to the initial charge capacity (C _P ) of the positive electrode is not particularly limited, For example, it can be set to about 1.0 to 2.1.
Such an electrode body is accommodated in a battery case together with a non-aqueous electrolyte. Specifically, the positive electrode of the electrode body is electrically connected to a positive electrode external connection terminal disposed outside the battery case via a positive electrode current collecting terminal. The negative electrode of the electrode body is typically electrically connected to a negative external connection terminal disposed outside the battery case via a negative current collector terminal. The positive and negative external connection terminals are typically arranged while maintaining insulation on the battery case lid, and the electrode body is fixed to the lid as described above, so that electricity can be smoothly input and output. At the same time, the position in the battery case is stabilized. The electrode body is inserted into the case main body of the battery case, and the opening of the case main body is closed by a lid and sealed by welding or the like. As the battery case, for example, a lightweight metal case such as an aluminum alloy can be preferably used. In addition, a battery case (typically a lid) has a safety valve communicating with the outside of the case when the internal pressure of the battery case exceeds a predetermined value, a liquid injection port for injecting a non-aqueous electrolyte, and a note for sealing the same. A liquid spout or the like may be provided. Typically, a CID that operates when the internal pressure of the battery case exceeds a predetermined value is provided between the external connection terminal and the current collecting terminal. As long as the CID can block the conductive path at a predetermined operating pressure, the specific configuration or the like is not limited. Since the specific configuration of the CID is not related to the essence of the present invention, a detailed description thereof will be omitted.

The non-aqueous electrolyte secondary battery constructed as described above can be provided as a product having a predetermined charge / discharge performance after performing an appropriate conditioning process or aging process.
As described above, the non-aqueous electrolyte secondary battery disclosed herein includes the overcharge additive at a saturated concentration in the non-aqueous electrolyte and the separator also includes the overcharge additive. Yes. Therefore, the concentration of the overcharge additive in the non-aqueous electrolyte can be maintained at a high value (for example, a saturated concentration) even after repeated charge / discharge (particularly charge / discharge at a high rate). The decomposition reaction of the overcharge additive on the surface of the positive electrode active material can be performed satisfactorily. Therefore, for example, as shown in FIG. 1 (A), a predetermined amount of gas can be quickly generated at the time of overcharge, and as quickly as the initial stage before repeated charge / discharge (for example, a lower SOC state). CID) can be activated. For example, in a conventional secondary battery, if the decomposition reaction of the overcharge additive on the surface of the positive electrode active material is suppressed after repeated charge and discharge, it takes a long time to generate a predetermined amount of gas. there were. As a result, for example, as shown in FIG. 1 (B), it takes time to operate the CID during overcharge, and the CID operates if the overcharge is more advanced (for example, in a higher SOC state). A situation that couldn't have happened. Such a delay in the operation of the CID is not preferable in terms of safety because it may cause a rapid temperature increase of the battery. Thus, the non-aqueous electrolyte secondary battery disclosed herein is provided as a product that ensures safety during overcharging over a long period of time.
Such a non-aqueous electrolyte secondary battery can be particularly suitably used for applications that require long-term high output characteristics, high durability, and safety. Among them, high capacity type batteries having a theoretical capacity of about 10 to 100 Ah, batteries for applications that repeatedly charge and discharge at a high rate, and the like, such as plug-in hybrid vehicles (PHV), are specifically mounted. It is suitable as a power source (drive power source) for a motor. In such applications, a plurality of non-aqueous electrolyte secondary batteries can be used in the form of an assembled battery in which a plurality are electrically connected to each other.

Hereinafter, the nonaqueous electrolyte secondary battery disclosed here was produced as a specific example. It should be noted that the present invention is not intended to be limited to those shown in the specific examples.
<Example 1>
Lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) powder as a positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder ) Was mixed with N-methylpyrrolidone (NMP) so that the mass ratio was 94: 3: 3 to prepare a slurry composition. This composition was applied to a long aluminum foil (positive electrode current collector) having a thickness of about 15 μm to form a positive electrode active material layer. The obtained positive electrode was dried and pressed to produce a sheet-like positive electrode.

  Next, the ion-exchange of amorphous coated graphite powder as the negative electrode active material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) so that the mass ratio is 98.3: 1.0: 0.7. A slurry-like composition was prepared by mixing with water. This composition was applied to a long copper foil (negative electrode current collector) having a thickness of about 10 μm to form a negative electrode active material layer. The obtained negative electrode was dried and pressed to produce a sheet-like negative electrode.

  As the separator, a microporous sheet having a three-layer structure in which a polypropylene (PP) layer is laminated on both sides of a polyethylene (PE) layer is used as a base material, and an overcharge additive is dispersedly arranged on the surface of the base material. Was used. Such an overcharge additive-containing separator was prepared by spraying powdery BP as an overcharge additive on a microporous sheet as a base material and arranging the powdery BP in the holes of the sheet. Is.

Next, the positive electrode sheet and the negative electrode sheet produced above were overlapped and wound through a separator to construct a wound electrode body having an elliptical cross-sectional shape. Then, the end of the positive electrode current collector of the wound electrode body is welded to the positive electrode current collector terminal, the end of the negative electrode current collector is welded to the negative electrode current collector terminal, and electrically connected to the positive and negative external connection terminals, respectively. . A pressure sensing type CID mechanism is provided in the conductive path between the positive electrode current collector and the positive electrode external terminal.
This electrode body was accommodated in a battery case and a non-aqueous electrolyte was injected. As the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3: 4: 3, and LiPF ₆ as an electrolyte is about What melt | dissolved in the density | concentration of 1 mol / L, and also dissolved the overcharge additive was used. In this embodiment, BP is used as an overcharge additive to be added to the non-aqueous electrolyte, and the amount of the non-aqueous electrolyte having the above composition is saturated at room temperature (25 ° C.), that is, the entire electrolyte. It adjusted and added so that it might become a density | concentration of about 10 mass% with respect to mass. Then, a total of 40 lithium secondary batteries were manufactured by attaching a lid to the opening of the battery case and welding and joining. The capacity ratio (C _N / C _P ) of these lithium secondary batteries is adjusted to 1.36.

<Example 2>
The positive electrode active material in which tungsten (W) is substituted and compounded at the transition metal site of the lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) used in Example 1 above, In the same manner as in Example 1, 40 lithium secondary batteries were prepared. The positive electrode active material has an average composition (element molar ratio) represented by Li _1.03 Ni _0.33 Co _0.33 Mn _0.33 W _0.03 O _2.06 , and the total amount of transition metal elements Is 100% by mass and contains 3% by mass of tungsten. Such positive electrode active materials are nickel sulfate (NiSO ₄ ), cobalt sulfate (CoSO ₄ ), manganese sulfate (MnSO ₄ ), and ammonium paratungstate [(NH ₄ ) ₁₀ (H ₂ W ₁₂ O ₄₂ ) · 4H as starting materials. ₂ O] is dissolved in water so that the molar ratio of Ni, Co, Mn, and W is 0.33: 0.33: 0.33: 0.03 (stoichiometric ratio). By crystallizing a composite hydroxide of these elements, and further mixing lithium carbonate (LiCO ₃ ) as a lithium source so that Li: (Ni + Co + Mn + W) is 1: 1, firing and solid phase diffusing. It is obtained. In the positive electrode active material thus obtained, W is segregated particularly on the surface of the active material particles (in the case where the particles constitute an aggregate, at the grain boundary).

<Example 3>
Instead of the separator in Example 1 above, a microporous sheet having a three-layer structure in which a polypropylene (PP) layer is laminated on both sides of a polyethylene (PE) layer that does not contain an overcharge additive is used. 40 lithium secondary batteries were prepared in the same manner as in Example 1. That is, a lithium secondary battery was constructed using only the separator substrate of Example 1 as a separator.

<Example 4>
In Example 3, 40 lithium secondary batteries were prepared in the same manner as in Example 3 except that the amount of the overcharge additive added to the non-aqueous electrolyte was increased to 13% by mass. That is, a lithium secondary battery was constructed using only the separator base material of Example 1 as a separator and further setting the amount of the overcharge additive added to the non-aqueous electrolyte to a supersaturated state.

<Example 5>
Instead of the separator in Example 2 above, a microporous sheet having a three-layer structure in which a polypropylene (PP) layer is laminated on both sides of a polyethylene (PE) layer that does not contain an overcharge additive is used. 40 lithium secondary batteries were prepared in the same manner as described above. That is, a lithium secondary battery was constructed by using only the separator base material of Example 1 as a separator and using a positive electrode active material containing tungsten.

<Example 6>
In Example 2, 40 lithium secondary batteries were prepared in the same manner as in Example 3 except that the amount of the overcharge additive added to the non-aqueous electrolyte was reduced to 8% by mass. That is, a lithium secondary battery was constructed by using a positive electrode active material containing tungsten instead of the positive electrode active material of Example 1 and setting the amount of the overcharge additive added to the non-aqueous electrolyte to less than saturation.

[Conditioning] The lithium secondary batteries prepared in Examples 1 to 6 were subjected to a conditioning process in which constant current (CC) charging was performed at 25C to 1% SOC at 1C. Then, the capacity | capacitance when CC discharge was carried out to 3.0V with the discharge rate of 1 / 5C was made into the initial stage capacity | capacitance, and the measurement result was shown in following Table 1.

[Evaluation of Initial Gas Generation Amount] Of each of the batteries prepared in Examples 1 to 6, the initial gas generation amount was evaluated for 20 batteries. That is, the operating state of the CID when charging at a constant current (CC) up to a high SOC (overcharged state) at 1 C at 60 ° C. was confirmed, and the result is shown in the column of Table 1 below. The column related to the operating status of the CID in Table 1 indicates the symbol “◎” when the CID opens quickly, and the symbol “X” when the CID does not open.

[Evaluation of Durability and Capacity Maintenance Rate] Among the batteries prepared in Examples 1 to 6, the remaining 20 batteries were 4.1 V at a rate of 1/5 C in an environment at a temperature of 25 ° C. After constant current (CC) charging, constant voltage (CV) charging was performed until the current value reached 1/50 C to obtain a fully charged state.
Subsequently, after leaving each battery in a thermostat set at 60 ° C. for 2 hours or longer, the following charge / discharge operations (1) to (2) at a high rate were repeated 500 cycles (endurance test).
(1) CC charge to 4.1V at a rate of 2C and rest for 10 minutes.
(2) CC discharge to 3.0 V at a rate of 2 C and rest for 10 minutes.
Thereafter, the discharge capacity was measured by the same procedure as the above initial capacity measurement method to obtain the capacity after endurance. The capacity retention rate (%) was calculated as a ratio of the capacity after endurance to the initial capacity ((capacity after endurance / initial capacity) × 100 (%)). The obtained values (capacity maintenance ratio) are shown together in Table 1. At the same time, the resistance between the positive and negative electrodes was measured, and the results are shown in Table 1 below together as the resistance after durability.

[Evaluation of gas generation after endurance]
For each battery after the endurance test, the operating status of CID when CC was charged at 60C to 1C at high SOC (overcharged state) was confirmed, and the result is shown in the column of Table 1 below. The column related to the operating status of the CID in Table 1 indicates the symbol “◎” when the CID opens quickly, and the symbol “X” when the CID does not open.

[Evaluation]
The battery of Example 1 contains a saturated amount of an overcharge additive at normal temperature in the non-aqueous electrolyte, and further contains an overcharge additive in the separator. Therefore, both when the secondary battery is overcharged at the initial stage of use and when it is overcharged after repeated charge / discharge (after endurance), the SOC quickly increases. It was confirmed that a sufficient amount of the overcharge additive was oxidized and decomposed to generate gas, and the CID operated quickly. That is, in the initial stage of use of the secondary battery, the overcharge additive in the non-aqueous electrolyte is oxidized and decomposed at the initial stage of overcharge, and the concentration of the overcharge additive is lowered. Rises. Then, the solubility of the overcharge additive in the non-aqueous electrolyte is increased, and the overcharge additive added to the separator is dissolved in the non-aqueous electrolyte, and the overcharge additive in the non-aqueous electrolyte is dissolved. The concentration is kept higher. Thereby, even if overcharge progresses, an overcharge additive having a sufficient concentration is supplied in the non-aqueous electrolyte and then to the surface of the positive electrode, and a sufficient amount of gas can be generated. On the other hand, in the secondary battery after durability, the polymerization of the overcharge additive on the surface of the positive electrode can be suppressed. However, even in such a case, when the battery temperature rises with the progress of charging, the solubility of the overcharge additive in the non-aqueous electrolyte is increased, and the overcharge additive added to the separator becomes non-aqueous electrolysis. Dissolve in the liquid. As a result, the concentration of the overcharge additive in the non-aqueous electrolyte is further increased, more overcharge additive can be supplied to the positive electrode, sufficient gas generation and rapid CID generation can be achieved even in the overcharge state. Operation becomes possible. According to the battery of Example 1 as described above, the CID is activated earlier when the battery is overcharged, the progress of further overcharge is suppressed, and the electrochemical reaction of the secondary battery is stopped in a safer state. Can be made.
In the battery of Example 1, the overcharge additive is supplied in a saturation amount or more at normal temperature only during overcharge, and the internal resistance due to the overcharge additive is not increased more than necessary during normal battery use. I was able to confirm that.

  Compared with the battery configuration of Example 1, the battery of Example 2 contains W in the positive electrode active material. Therefore, while maintaining the operating status of the CID and the safety of the battery in an overcharged state (for example, about SOC 140%), the internal resistance is lower, the durability is higher (the capacity retention rate is higher), and the higher performance secondary. It was confirmed that a battery was obtained. If the non-aqueous electrolyte contains a saturated amount of overcharge additive at room temperature, the internal resistance of the battery may increase slightly compared to the case of using a non-aqueous electrolyte with a lower concentration of overcharge additive. It is done. However, by using a positive electrode active material containing W, the increase in internal resistance can be sufficiently suppressed, and a battery that is more excellent in safety and durability can be realized.

  On the other hand, the battery of Example 3 does not contain an overcharge additive in the separator as compared with the battery configuration of Example 1. Therefore, the resistance after endurance and the capacity retention ratio were as good as in Example 1. However, in the initial stage of use, a sufficient amount of gas could be generated to operate the CID in the overcharged state, but the overcharge additive in the non-aqueous electrolyte was consumed with repeated charge and discharge in the durability test. Therefore, after the endurance, a sufficient amount of gas could not be generated to operate the CID in the overcharged state.

  Compared with the battery configuration of Example 1, the battery of Example 4 does not contain an overcharge additive in the separator, and accordingly includes an overcharge additive in a supersaturated state in the nonaqueous electrolyte. . Therefore, in the initial stage of use, a sufficient amount of gas could be generated to operate the CID in the overcharged state. However, in the endurance test, more overcharge additive than in Example 3 forms a film on the surface of the positive electrode, and the film closes the gap between the positive electrode active materials, so that the CID is activated in the overcharged state. A sufficient amount of gas could not be generated. In addition, since a large amount of the polymer film was formed on the positive electrode surface during repeated charging and discharging, the increase in internal resistance was large and the capacity retention rate was also low.

  Compared with the battery configuration of Example 1, the battery of Example 5 contains W in the positive electrode active material and does not contain the overcharge additive in the separator. In the battery of Example 5, since the positive electrode active material contains W, the resistance after endurance is suppressed to the lowest among the batteries of Examples 1 to 6, and the capacity retention rate after endurance is also high. Met. In addition, although W was segregated on the surface of the positive electrode active material, a sufficient amount of gas could be generated to operate the CID at the initial stage of use. However, due to segregation of W on the surface of the positive electrode active material, the positive electrode and the overcharge additive cannot react with high efficiency, and the overcharge additive in the non-aqueous electrolyte is consumed due to repeated charge and discharge in the durability test. Therefore, after the endurance, a sufficient amount of gas could not be generated to operate the CID even in the overcharged state.

  Compared with the battery configuration of Example 1, the battery of Example 6 contains W in the positive electrode active material, and the concentration of the overcharge additive in the non-aqueous electrolyte is set low. In the battery of Example 6, the positive electrode active material contains W, and the concentration of the overcharge additive in the non-aqueous electrolyte is low, so that the CID operates in both the initial use state and the overcharge state. A sufficient amount of gas could not be generated. In addition, since the positive electrode active material contains W, the resistance after endurance was a relatively low value, but it is considered that the capacity retention rate was reduced by elution of W. Since the overcharge additive was contained in the separator, it was confirmed that more gas was generated than in the batteries of Examples 3 to 5 in the overcharged state after durability.

From the above, the non-aqueous electrolyte secondary battery of the present invention is optimally designed for the arrangement of the overcharge additive in the battery, so that after the cycle without increasing the internal resistance It was confirmed that the amount of gas generated can be kept high, the deterioration of battery characteristics is suppressed, and high safety is ensured.
As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

Claims (2)

A positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and a current interruption mechanism that interrupts a conductive path when a predetermined pressure is sensed,
The non-aqueous electrolyte contains a first overcharge additive that generates gas during overcharge in a saturated amount at room temperature,
The separator is a non-aqueous electrolyte secondary battery including a second overcharge additive that generates gas during overcharge.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode includes a positive electrode active material containing at least tungsten.

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