JP2014192069A - Lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion battery which is arranged so as to suppress the rapid rise in battery temperature resulting from the reaction of a positive electrode active material and a nonaqueous electrolytic solution with internal short circuit caused by the nail pricking or the like, and which is superior in battery performance, especially low-temperature output characteristic.SOLUTION: A lithium ion battery comprises: a positive electrode including a positive electrode active material; and a nonaqueous electrolytic solution which is a liquid nonaqueous electrolyte. The nonaqueous electrolytic solution includes 0.06-0.3 mol/L of lithium bisoxalate borate(LiBOB) to the nonaqueous electrolytic solution. The positive electrode active material includes a lithium-containing transition metal oxide, and 0.01-3 wt.% of a phosphate compound to the lithium-containing transition metal oxide. The phosphate compound is deposited on the surface of a particle of the lithium-containing transition metal oxide.

Description

  The present invention relates to a lithium ion battery.

  In lithium-ion batteries, lithium bisoxalate borate (LiBOB) added to non-aqueous electrolytes, which are liquid non-aqueous electrolytes, has been studied as one of the additives considered to have an effect of improving battery performance. Has been. In Patent Document 1, the output characteristics are improved by using a nonaqueous electrolytic solution containing about 0.05 mol / L to 0.3 mol / L of LiBOB with respect to the nonaqueous electrolytic solution together with the lithium-containing transition metal composite oxide. Is disclosed.

JP 2010-50079 A

  However, when LiBOB is contained in the non-aqueous electrolyte at a high concentration as disclosed in Patent Document 1, there arises a problem that the battery temperature rapidly increases in the nail penetration test. The nail penetration test is a test in which an internal short circuit is caused by passing a sharp object such as a nail through the battery, and the battery temperature, battery voltage, and the like at that time are measured. In such a test, when an internal short circuit occurs, a large current flows in the battery, Joule heat is generated in the vicinity of the current collector, and this Joule heat induces a reaction between the positive electrode active material and the non-aqueous electrolyte. The battery temperature tends to increase rapidly.

  An object of the present invention is to provide a lithium ion battery excellent in battery performance by suppressing a rapid rise in battery temperature due to an internal short circuit.

  A lithium ion battery according to the present invention includes a positive electrode containing a positive electrode active material and a non-aqueous electrolyte that is a liquid non-aqueous electrolyte, and the non-aqueous electrolyte uses lithium bisoxalate borate (LiBOB) for non-aqueous electrolysis. The positive electrode active material is contained in an amount of 0.01% by weight to 3% by weight with respect to the lithium-containing transition metal oxide and the lithium-containing transition metal oxide. The following phosphoric acid compound is included, and the phosphoric acid compound is deposited on the surface of the lithium-containing transition metal oxide particles.

  The lithium ion battery according to the present invention suppresses a rapid increase in battery temperature due to an internal short circuit, and is excellent in battery performance, particularly low temperature output characteristics.

It is a figure which shows a mode that a phosphoric acid compound is adhered to the particle | grain surface of the lithium containing transition metal oxide in an example of embodiment of this invention. It is a schematic diagram of the cylindrical battery in an example of embodiment of this invention.

  Hereinafter, embodiments according to the present invention will be described in detail. In the lithium ion battery according to the embodiment of the present invention, for example, an electrode body in which a positive electrode and a negative electrode are wound or stacked with a separator interposed therebetween and a nonaqueous electrolyte solution that is a liquid nonaqueous electrolyte are contained in a battery outer can. It has the structure made. Below, each structural member of a lithium ion battery is explained in full detail.

[Positive electrode]
A positive electrode is comprised by positive electrode collectors, such as metal foil, and the positive mix layer formed on the positive electrode collector, for example. As the positive electrode current collector, a metal foil that is stable in the potential range of the positive electrode or a film in which a metal that is stable in the potential range of the positive electrode is arranged on the surface layer is used. As the metal stable in the potential range of the positive electrode, it is preferable to use aluminum.

  The positive electrode mixture layer includes a positive electrode active material, a conductive agent, a binder, an additive, and the like. These are mixed with an appropriate solvent to form a positive electrode slurry, and this positive electrode slurry is applied onto the positive electrode current collector. Then, it is a layer obtained by drying and rolling.

  The positive electrode active material has, for example, a particle shape, and includes an oxide containing lithium (Li) and a transition metal element, or an oxide in which a part of the transition metal element is substituted with a different element. The transition metal element includes at least one selected from the group consisting of scandium (Sc), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), yttrium (Y), and the like. Various transition metal elements can be used. Of these transition metal elements, Ni, Co, Mn, etc. are preferably used. The different element is selected from the group consisting of magnesium (Mg), aluminum (Al), zirconium (Zr), tungsten (W), molybdenum (Mo), lead (Pb), antimony (Sb), boron (B) and the like. At least one kind of different elements can be used. Among these different elements, Mg, Al, Zr, W, etc. are preferably used.

Specific examples of such oxides include the general formula Li _a Ni _x Co _y Mn _z M _(1-xyz) O _{2 + a / 2} (0.5 <a <1.2, 0.3 ≦ x <1.0, 0 <y ≦ 0.5, 0 <z ≦ 0.7, x + y + z ≦ 1, M is from Na, K, Mg, Ca, Fe, Cu, V, Zr, W, Mo, etc. A lithium-containing transition metal oxide having a layered rock salt type crystal structure represented by at least one element selected from the group consisting of:

  When the Li content a is larger than 0.5, the output characteristics can be improved. However, since the residual alkali on the surface of the lithium-containing transition metal oxide is increased to 1.2 or more, gelation of the positive electrode slurry occurs in the battery manufacturing process, and the amount of the transition metal that performs the oxidation-reduction reaction decreases. Capacity may be reduced. Therefore, the Li content a is preferably greater than 0.5 and less than 1.2.

In addition, LiCoO ₂ can be cited as a positive electrode active material that has been put into practical use, but from the viewpoint of cost and high capacity, LiNiO ₂ is desired, so that the amount of Ni is preferably large. Therefore, the Ni content x is preferably 0.3 or more and less than 1.0. Further, it is preferable that the amount of Co is small from the viewpoint of cost. Therefore, the Co content y is preferably greater than 0 and 0.5 or less. Further, from the viewpoint of cost and safety, it is preferable to contain Mn. Therefore, the Mn content z can be greater than 0 and 0.7 or less, but it is preferably larger within the above range.

  Such a positive electrode active material can be charged at a high voltage. Therefore, a battery including a positive electrode containing such a positive electrode active material preferably has a charge end voltage of 4.3 V or higher, and more preferably 4.35 V or higher. The upper limit of the end-of-charge voltage is not particularly limited, but is preferably not more than a voltage at which the non-aqueous solvent contained in the non-aqueous electrolyte is not decomposed.

  Here, in the present embodiment, the battery performance is improved by adding lithium bisoxalate borate (LiBOB) to a non-aqueous electrolyte that is a liquid non-aqueous electrolyte. However, as described above, when LiBOB is added to the non-aqueous electrolyte at a high concentration, the battery temperature rapidly increases in the reaction between the positive electrode active material and the non-aqueous electrolyte induced by Joule heat in the internal short circuit. There is a risk. Therefore, measures against temperature rise due to internal short circuit are required.

  As a result of diligent research on this point, the present inventor has applied a phosphoric acid compound to the particle surface of the lithium-containing transition metal oxide as the positive electrode active material, so that the battery temperature at the internal short circuit when LiBOB is high in concentration. The present embodiment has been devised by discovering that it is possible to suppress the increase of the above.

  Regarding the deposition of a phosphoric acid compound on the surface of particles of the positive electrode active material, Japanese Patent Application Laid-Open No. 2008-16235 discloses a positive electrode active material including a surface layer having phosphorus and magnesium. However, this is intended to increase the capacity and improve the charge / discharge cycle characteristics, and is not intended to suppress the rise in battery temperature due to the internal short circuit. For this reason, there is no suggestion that when the concentration of LiBOB is high, an attempt is made to suppress an increase in battery temperature due to an internal short circuit by depositing a phosphoric acid compound on the surface of the positive electrode active material particles.

  In the present embodiment, hereinafter, a lithium transition metal oxide is used as a base material of a positive electrode active material, and a phosphoric acid compound deposited on the surface of lithium-containing transition metal oxide particles is referred to as a positive electrode active material. To.

  The deposition amount of the phosphate compound to be deposited on the particle surface of the lithium-containing transition metal oxide is preferably 0.01% by mass or more and 3% by mass or less with respect to the lithium-containing transition metal oxide. More preferably, the content is 01% by mass or more and 2% by mass or less. If the amount is less than the above range (0.01) mass%, the amount of the phosphoric acid compound deposited on the surface of the lithium-containing transition metal oxide particles is small, so it is considered that the characteristics are not affected. Moreover, when it exceeds the said range (3) mass%, since content of the lithium containing transition metal oxide contained in a positive mix layer reduces, battery capacity may reduce and it is unpreferable.

The phosphoric acid compound is not particularly limited, but Li, Mg, Al, Si, Ca, Ga, Ge, Y, Zr, Nb, Mo, Sn, W, Bi, La, Ce, Nd, Sm, Eu, It is preferable to include at least one element selected from the group consisting of Ho and Er. The phosphate compound is preferably an inorganic phosphate containing at least one element selected from the group consisting of magnesium (Mg), aluminum (Al), zirconium (Zr), and tungsten (W). Magnesium or aluminum phosphate is more preferable, and magnesium phosphate is more preferable. Examples of magnesium phosphate include, but are not limited to, Mg ₃ (PO ₄ ) ₂ and Mg ₂ P ₂ O ₇ .

  Here, FIG. 1 shows a step of obtaining a positive electrode active material in which a phosphoric acid compound is deposited on a lithium-containing transition metal oxide. Although details will be described later in the preparation of the positive electrode active material, the positive electrode active material 10 that satisfies the above requirements is, for example, an alkali metal phosphate such as disodium hydrogen phosphate 12 on the particle surface of the lithium-containing transition metal oxide 11. And Li, Mg, Al, Si, Ca, Ga, Ge, Y, Zr, Nb, Mo, Sn, W, Bi, La, Ce, Nd, Sm, Eu, Ho, and Er. An adhesion step A in which an aqueous solution 13 containing at least one element chloride is adhered and dried to obtain a precursor 14 in which a phosphoric acid compound 15 is deposited on the particle surface of the lithium-containing transition metal oxide 11; It can be manufactured by a method including a baking step B of baking the precursor 14.

  The conductive agent is a conductive powder or particle, and is used to increase the electronic conductivity of the positive electrode mixture layer. As the conductive agent, a conductive carbon material, metal powder, organic material, or the like is used. Specifically, examples of the carbon material include acetylene black, ketjen black, and graphite, aluminum as the metal powder, potassium titanate and titanium oxide as the metal oxide, and a phenylene derivative as the organic material. These conductive agents may be used alone or in combination of two or more.

  The binder is, for example, a polymer having a particle shape or network structure, maintains a good contact state between the particle shape positive electrode active material and the powder or the particle shape conductive agent, and the surface of the positive electrode current collector. It is used to enhance the binding property of the positive electrode active material and the like. As the binder, a fluorine polymer, a rubber polymer, or the like can be used. Specifically, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or modified products thereof as the fluorine-based polymer, ethylene-propylene-isoprene copolymer, ethylene-propylene- Examples thereof include butadiene copolymers. The binder may be used in combination with a thickener such as carboxymethyl cellulose (CMC) or polyethylene oxide (PEO).

[Negative electrode]
If a negative electrode is conventionally used as a negative electrode of a lithium ion battery, it can be used without limitation. Such a negative electrode includes a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. The negative electrode mixture layer is a layer obtained by, for example, mixing a negative electrode active material and a binder with water or a suitable solvent, applying the mixture to a negative electrode current collector, drying, and rolling.

  The negative electrode active material is a material that can occlude and release lithium ions. As such a negative electrode active material, for example, carbon materials, metals, alloys, metal oxides, metal nitrides, carbon in which lithium is occluded in advance, silicon, and the like can be used. Examples of the carbon material include natural graphite, artificial graphite, and pitch-based carbon fiber. Specific examples of the metal or alloy include lithium (Li), silicon (Si), tin (Sn), germanium (Ge), indium (In), gallium (Ga), lithium alloy, silicon alloy, tin alloy, and the like. It is done. A negative electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type.

  As the binder, as in the case of the positive electrode, a fluorine-based polymer, a rubber-based polymer, or the like can be used. However, a styrene-butadiene copolymer (SBR) that is a rubber-based polymer, or a modified product thereof. Is preferably used. The binder may be used in combination with a thickener such as carboxymethylcellulose (CMC).

  As the negative electrode current collector, a metal foil that hardly forms an alloy with lithium in the potential range of the negative electrode or a film in which a metal that hardly forms an alloy with lithium in the potential range of the negative electrode is disposed on the surface layer is used. As a metal that hardly forms an alloy with lithium in the potential range of the negative electrode, it is preferable to use copper that is easy to process at low cost and has good electronic conductivity.

[Non-aqueous electrolyte]
The nonaqueous electrolytic solution includes a nonaqueous solvent and an electrolyte salt that dissolves in the nonaqueous solvent. Furthermore, an additive may be appropriately contained for the purpose of improving battery performance.

  As the non-aqueous solvent, cyclic carbonates, chain carbonates, nitriles, amides, and the like can be used. As the cyclic carbonate, a cyclic carbonate, a cyclic carboxylic acid ester, a cyclic ether, or the like can be used. As the chain carbonate, a chain ester, a chain ether, or the like can be used. More specifically, ethylene carbonate (EC) or the like is used as the cyclic carbonate, γ-butyrolactone (GBL) or the like is used as the cyclic carboxylic acid ester, and ethyl methyl carbonate (EMC) or dimethyl carbonate (DMC) is used as the chain ester. Can do. Moreover, the halogen substituted body which substituted the hydrogen atom of the said non-aqueous solvent with halogen atoms, such as a fluorine atom, can be used. Among them, it is preferable to use a mixture of EC as a cyclic carbonate that is a high dielectric constant solvent and EMC and DMC as a chain carbonate that is a low viscosity solvent.

As the electrolyte salt, a lithium salt generally used as a supporting salt in a lithium ion secondary battery can be used. As the lithium salt, LiPF ₆ , LiBF ₄ , LiClO ₄ or the like can be used. These lithium salts may be used alone or in combination of two or more.

  In addition, the non-aqueous electrolyte contains lithium bisoxalate borate (LiBOB) as an additive for the purpose of forming a film with excellent lithium ion conductivity on the positive electrode surface and obtaining high output characteristics at low temperatures. Is preferable. For the above purpose, LiBOB preferably contains 0.06 mol / L or more and 0.3 mol / L or less, more preferably 0.08 mol / L or more and 0.12 mol / L or less with respect to the nonaqueous electrolytic solution. . If the value is smaller than the lower limit (0.06), the effect as an additive cannot be obtained, which is not preferable. Moreover, in the upper limit (0.3) or less, lithium ion conductivity becomes smoother and excellent battery performance is obtained.

In addition to the LiBOB, the non-aqueous electrolyte can contain an additive used for the purpose of forming a film having excellent ion permeability on the surface of the positive electrode or the negative electrode. Here, the surfaces of the positive electrode and the negative electrode mean the surface of the mixture layer and the surface of the active material. As the additive, vinylene carbonate (VC), ethylene sulfite (ES), cyclohexylbenzene (CHB), lithium difluorophosphate (LiPO ₂ F ₂ ), and modified products thereof can be used. An additive may be used individually by 1 type and may be used in combination of 2 or more type. The ratio of the additive in the nonaqueous electrolytic solution is not particularly limited, but is preferably about 0.05 to 10% by mass with respect to the total amount of the nonaqueous electrolytic solution.

[Separator]
As the separator, for example, a porous film having ion permeability and insulating properties disposed between the positive electrode and the negative electrode is used. Examples of the porous film include a microporous thin film, a woven fabric, and a non-woven fabric. The material used for the separator is preferably polyolefin, and more specifically, polyethylene (PE), polypropylene (PP) and the like are suitable. These may be used alone or in combination of two or more. As such an example, a PP / PE / PP laminated film having a three-layer structure in which polyethylene (PE) and polypropylene (PP) are laminated can be used.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples. Below, the lithium ion battery used for Examples 1-3 and Comparative Examples 1-3 was produced in order to evaluate the effect which made the phosphate compound 15 adhere to the particle | grain surface of the lithium containing transition metal oxide 11. FIG. A specific method for manufacturing the lithium ion battery is as follows.

<Example 1>
[Preparation of positive electrode active material]
As the base material of the positive electrode active material 10, a lithium-containing transition metal oxide 11 was used. The lithium-containing transition metal oxide 11 was produced as follows. First, Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ and Li ₂ CO ₃ as raw materials were mixed, and this mixture was fired in an air atmosphere at 900 ° C. for 20 hours to produce a lithium-containing transition metal oxide 11. . The composition of the obtained lithium-containing transition metal oxide 11 was Li _1.03 Ni _0.50 Co _0.20 Mn _0.30 O _{2 as} measured by inductively coupled plasma (ICP) emission spectroscopy. Moreover, when the crystal structure was analyzed by the powder X-ray diffraction method, it was confirmed that it had a crystal structure belonging to the space group R3m.

Next, the process shown in FIG. 1 was performed for the purpose of depositing magnesium phosphate as the phosphate compound 15 on the particle surface of the obtained lithium-containing transition metal oxide 11. First, the lithium-containing transition metal oxide 11 and about 200 ml of water 16 were placed in a suitable container 17 and dispersed. Next, 4.38 g of disodium hydrogen phosphate (Na ₂ HPO ₄ ) 12 is placed in the container 17, and 25 vol% nitric acid (HNO ₃ ) 18 or sodium hydroxide ( (NaOH) was added to obtain dispersion 19.

Separately, a filtrate 13 of MgCl ₂ solution in which 1.75 g of magnesium chloride (MgCl ₂ ) is dissolved in 50 g of water, and NaOH 20 in which 0.48 g of sodium hydroxide (NaOH) is dissolved in 50 g of water. Were prepared in containers each having a volume of 100 ml. Then, the container 17 is placed on the stirring device 21, the stirrer 22 accommodated in the container 17 is rotated, and the dispersion liquid 19 in the container 17 is stirred at 900 rpm, while the filtrate 13 of the MgCl ₂ solution and NaOH aqueous solution 20 was added dropwise at 50 ml / min. At this time, when there was a pH change such that the dispersion 19 had a pH of 7, it was adjusted with an aqueous NaOH solution 20 (or 10 vol% HNO ₃ ). After completion of the dropping, the container in which the MgCl ₂ solution was placed was washed with distilled water, and the washing liquid was also dropped into the dispersion liquid 19.

  Next, as the attachment step A, the previous dispersion 19 was vacuum filtered. During vacuum filtration, the process of washing the filtered solid with water and filtering again was repeated twice. The obtained filtered solid was dried at 110 ° C. to obtain the precursor 14.

  Next, as the firing step B, the obtained precursor 14 is heated at 5 ° C./min, heated to 700 ° C., heated for 5 hours, and then pulverized, so that the magnesium phosphate as the phosphate compound 15 becomes the particle surface. A positive electrode active material 10 deposited on the substrate was obtained. The obtained positive electrode active material 10 was measured by ICP emission spectroscopic analysis for the purpose of confirming the amount of magnesium phosphate deposited. As a result, the magnesium phosphate was 0 with respect to the lithium-containing transition metal oxide 11. 0.07% by mass was deposited.

[Preparation of positive electrode]
A positive electrode was prepared using the positive electrode active material obtained above. As a preparation method, first, the positive electrode active material 10 is mixed to 92 mass%, acetylene black as a conductive agent is 5 mass%, and polyvinylidene fluoride powder as a binder is 3 mass% to obtain a mixture. It was. This mixture was mixed with an N-methyl-2-pyrrolidone (NMP) solution to prepare a positive electrode slurry. This positive electrode slurry was applied to both surfaces of a 15 μm thick aluminum positive electrode current collector to form a positive electrode mixture layer. It dried after that, compressed using the compression roller, and obtained as a positive electrode by attaching a positive electrode current collection lead.

[Production of negative electrode]
As the negative electrode active material, graphite whose surface was coated with amorphous carbon was used. The negative electrode was produced as follows. First, 98.7% by mass of the negative electrode active material, 0.6% by mass of the aqueous dispersion of styrene-butadiene copolymer (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were dissolved. The negative electrode slurry was prepared by mixing so that the aqueous solution was 0.7% by mass. The negative electrode slurry was applied to both surfaces of a copper negative electrode current collector having a thickness of 10 μm to form a negative electrode mixture layer. It dried after that, compressed using the compression roller, and obtained as a negative electrode by attaching a negative electrode current collection lead.

[Preparation of non-aqueous electrolyte]
LiPF ₆ as an electrolyte salt is dissolved at 1.0 mol / L in a non-aqueous solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed at a volume ratio of 3: 3: 4. Further, 0.3% by mass of vinylene carbonate (VC) was added. Thereafter, lithium difluorophosphate was further dissolved to 0.05 mol / L and lithium bisoxalate borate (LiBOB) to 0.12 mol / L to prepare a non-aqueous electrolyte, which was used for battery production. Provided.

[Production of cylindrical lithium-ion battery]
FIG. 2 is a perspective view showing a cylindrical lithium ion battery for evaluation (hereinafter referred to as a cylindrical battery) cut in the vertical direction. Using the positive electrode 23, the negative electrode 24, and the nonaqueous electrolytic solution prepared above, a cylindrical battery 30 for evaluation was manufactured according to the following procedure. First, the positive electrode 23 and the negative electrode 24 produced above were wound through a separator 25 having a three-layer structure of PP / PE / PP to produce a wound electrode body 26. Next, insulating plates 31 and 32 are arranged above and below the wound electrode body 26, respectively, and this wound electrode body 26 is made of steel and serves as a negative electrode terminal. Housed inside. And the negative electrode current collection lead 34 was welded to the inner bottom part of the battery exterior can 33, and the positive electrode current collection lead 35 was welded to the bottom plate part of the current interruption sealing body 36 provided with the safety valve and the current interruption device. A nonaqueous electrolytic solution was supplied from the opening of the battery outer can 33, and then the battery outer can 33 was sealed with a current blocking seal 36 to obtain a cylindrical battery 30. In the cylindrical battery 30, the rated capacity was 1300 mAh.

<Example 2>
In Example 1, the cylindrical battery 30 of Example 2 was obtained in the same manner as in Example 1 except that the LiBOB content was changed from 0.12 mol / L to 0.08 mol / L.

<Example 3>
A cylindrical battery 30 of Example 2 was obtained in the same manner as in Example 1 except that the LiBOB content was changed from 0.12 mol / L to 0.06 mol / L in Example 1.

<Comparative Example 1>
Cylindrical battery of Comparative Example 1 in the same manner as in Example 1 except that the surface of the lithium-containing transition metal oxide 11 was not coated with magnesium phosphate in the production of the positive electrode active material of Example 1. 30 was obtained.

<Comparative Example 2>
A cylindrical battery 30 of Comparative Example 2 was obtained in the same manner as Comparative Example 1.

<Comparative Example 3>
A cylindrical battery 30 of Comparative Example 3 was obtained in the same manner as in Comparative Example 1 except that the LiBOB content was changed from 0.12 mol / L to 0.06 mol / L in Comparative Example 1.

[Discharge capacity evaluation]
In order to evaluate the discharge capacity of each of the cylindrical batteries 30 of Examples 1 to 3 and Comparative Examples 1 to 3, a charge / discharge test was performed at an environmental temperature of 25 ° C. As a test method, each cylindrical battery 30 of Examples 1 to 3 and Comparative Examples 2 to 3 was charged with a constant current of 1C (1300 mA) until the battery voltage reached 4.35 V, and then the current value at a constant voltage. The battery was continuously charged until it reached 0.05 C (65 mA). Next, the battery was discharged at a constant current of 1 C until the battery voltage reached 2.5 V, and then discharged with a constant current of 1/3 C (430 mA) until the battery voltage reached 2.5 V. Moreover, the comparative example 1 changed the said charging voltage from 4.35V to 4.2V, and performed the same discharge capacity evaluation.

[Low temperature output characteristics evaluation]
Next, in order to evaluate the low-temperature output characteristics of Examples 1 to 3 and Comparative Examples 1 to 3, a charge / discharge test was performed at an environmental temperature of 25 ° C. First, the cylindrical batteries 30 of Examples 1 to 3 and Comparative Examples 2 to 3 were charged with a constant current of 1C (1300 mA) until the depth of charge (SOC) reached 50%, and then the temperature was lowered to −30 ° C. Thereafter, discharge was performed for 10 seconds at a current value of 0.02 A at the minimum and 12 A at the maximum. In this test, the current value (Ip) at which the operating voltage 10 seconds after the start of discharge was 2.7 V was obtained, and the output was calculated from the following equation. Output (W) = Ip x (Operating voltage at 2.7 V)

[Nail penetration test]
About Examples 1-3 and Comparative Examples 1-3 for the purpose of grasping the effect which suppresses the rise in the battery temperature in the internal short circuit by depositing magnesium phosphate on the particle surface of the lithium-containing transition metal oxide 11 A nail penetration test was performed on each fully charged cylindrical battery 30. As a test method, first, the battery voltage of each cylindrical battery 30 of Examples 1 to 3 and Comparative Examples 2 to 3 is 4.35 V at a constant current of 1.0 C (1300 mA) at an environmental temperature of 25 ° C. Then, charging was continued until the current value reached 0.05 C (65 mA) at a constant voltage. Next, in an environment where the battery temperature is 65 ° C., the tip of a round nail with a 3 mmφ thickness and a sharp tip is attached to the center of the side surface of each of the cylindrical batteries of Examples 1 to 3 and Comparative Examples 2 to 3. The round nail was pierced along the diameter direction of each cylindrical battery 30 at a speed of 80 mm / sec, and the piercing of the round nail was stopped when the round nail completely penetrated each cylindrical battery 30. And it measured by making a thermocouple contact the battery surface as a behavior of the battery temperature after piercing. As the battery temperature, the highest reached temperature of the battery after piercing was evaluated. In Comparative Example 1, a similar nail penetration test was performed by changing the charging voltage from 4.35V to 4.2V. Table 1 summarizes the results of discharge capacity at 1/3 C, low-temperature output characteristics, and battery temperature in the nail penetration test.

  From Table 1, it was found that when the LiBOB concentration was observed, the higher the concentration, the better the low-temperature output. However, when Comparative Example 2 and Comparative Example 3 are seen, if the LiBOB concentration is high, the battery temperature becomes high in the nail penetration test, and it is not preferable that the LiBOB concentration is high. Thus, looking at Examples 1 to 3 in which magnesium phosphate was deposited on the surface of the lithium-containing transition metal oxide 11, in Examples 1 to 3, all were compared with Comparative Examples 1 to 3 in the nail penetration test. The battery temperature was low and good results were obtained. In addition, what set the charging voltage low shown in the comparative example 1 is unpreferable in the high capacity | capacitance of a battery with small discharge capacity.

  In Table 1, the surface deposition amount is a value measured by ICP emission spectrometry spectroscopy when the positive electrode active material 10 was produced. The positive electrode active material 10 includes a lithium-containing transition metal oxide 11, and 0.01% by weight or more and 3% by weight or less of phosphorus with respect to the lithium-containing transition metal oxide 11 on the particle surface of the lithium-containing transition metal oxide 11. It is preferred to deposit the acid compound. In Examples 1 to 3, the surface deposition amount (0.07% by mass) was within the above range, and it was confirmed that the temperature increase in the internal short circuit was suppressed.

  Thus, LiBOB is contained in the nonaqueous electrolytic solution in an amount of 0.06 mol / L to 0.3 mol / L, and 0.01 wt% to 3 wt% of phosphoric acid on the particle surface of the lithium-containing transition metal oxide 11. The lithium ion battery including the positive electrode active material 11 containing the compound 15 suppresses the reaction between the positive electrode active material and the non-aqueous electrolyte due to an increase in the battery temperature in an internal short circuit such as nail penetration, and has battery performance, particularly low temperature output characteristics. Excellent.

10 cathode active material, 11 lithium-containing transition metal oxide, 12 disodium hydrogen phosphate, 13 filtrate of MgCl ₂ solution, 14 precursor, 15 phosphate compound, 16 water, 17 container, 18 nitric acid, 19 dispersion, 20 Sodium hydroxide (NaOH) aqueous solution, 21 Stirrer, 22 Stirrer, 23 Positive electrode, 24 Negative electrode, 25 Separator, 26 Winding electrode body, 30 Cylindrical battery, 31, 32 Insulating plate, 33 Battery outer can, 34 Negative electrode Current collecting lead, 35 Positive electrode current collecting lead, 36 Current interruption sealing body.

Claims (5)

In a lithium ion battery comprising a positive electrode containing a positive electrode active material and a non-aqueous electrolyte that is a liquid non-aqueous electrolyte,
The non-aqueous electrolyte contains lithium bisoxalate borate (LiBOB) at 0.06 mol / L to 0.3 mol / L with respect to the non-aqueous electrolyte,
The positive electrode active material includes a lithium-containing transition metal oxide and a phosphoric acid compound of 0.01 wt% or more and 3 wt% or less with respect to the lithium-containing transition metal oxide, and particles of the lithium-containing transition metal oxide A lithium ion battery having the phosphoric acid compound deposited on its surface. The lithium ion battery according to claim 1,
The phosphoric acid compound is composed of Li, Mg, Al, Si, Ca, Ga, Ge, Y, Zr, Nb, Mo, Sn, W, Bi, La, Ce, Nd, Sm, Eu, Ho, and Er. A lithium ion battery comprising at least one element selected from the group. The lithium ion battery according to claim 1 or 2,
The lithium ion battery, wherein the phosphate compound is magnesium phosphate. The lithium ion battery according to any one of claims 1 to 3,
The lithium-containing transition metal oxide has a general formula of Li _a Ni _x Co _y Mn _z M _(1-xyz) O _{2 + a / 2} (0.5 <a <1.2, 0.3 ≦ x <1. 0, 0 <y ≦ 0.5, 0 <z ≦ 0.7, x + y + z ≦ 1, M is selected from the group consisting of Na, K, Mg, Ca, Fe, Cu, V, Zr, W, Mo, etc. A lithium ion battery represented by at least one element. The lithium ion battery according to any one of claims 1 to 4,
The end-of-charge voltage is a lithium ion battery having a battery voltage of 4.3 V or higher.

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