Titanium niobium composite oxide, electrodes using the same, and lithium-ion secondary battery

Abstract

To provide a titanium-niobium complex oxide in which the mixing of TiO2 and Ti2 Nb10O29 and the fibrous growth of crystal grains are suppressed, and to provide an electrode and a lithium-ion secondary battery using the same.SOLUTION: A titanium-niobium complex oxide according to the present invention contains less than 0.30 atm% of alkali metal elements and at least one element of Al, Y, La, Ce, Pr and Sm. A ratio of a total atomic weight of Al, Y, La, Ce, Pr and Sm to a total atomic weight of Ti and Nb is 0.001 or more.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] This invention relates to a titanium-niobium composite oxide, and more particularly to an electrode using the titanium-niobium composite oxide as an electrode active material, and to a lithium-ion secondary battery using this electrode as a positive or negative electrode. [Background technology]

[0002] Titanium niobium composite oxides are expected to be used as active materials for lithium-ion secondary batteries because they have high electrical capacity and excellent cycle capacity retention (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2010-287496 [Patent Document 2] Japanese Patent Publication No. 2014-225474 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] For example, when synthesizing titanium niobium composite oxides by solid-phase reaction, if the calcination temperature is too low and the reaction is insufficient, in addition to the desired product TiNb2O7, TiO2 and Ti2Nb may also be produced. 10 O 29 These are mixed together. TiO2 and Ti2Nb are contained in the titanium niobium composite oxide. 10 O 29 This causes a decrease in the charge-discharge performance of titanium niobium composite oxides.

[0005] On the other hand, TiO2 and Ti2Nb 10 O 29 If the firing temperature is increased to allow the reaction to proceed sufficiently in order to suppress the presence of other elements, crystal grains (primary grains) will grow. This growth of crystal grains can cause a decrease in the rate characteristics of lithium-ion secondary batteries that use titanium niobium composite oxide as the electrode active material.

[0006] Therefore, it is conceivable to improve the reactivity of titanium niobium composite oxide by adding alkali metal elements so that a sufficient reaction can be obtained even at low firing temperatures (see, for example, Patent Document 2). However, simply adding alkali metal elements can lead to adverse effects such as the growth of fibrous crystal grains and a decrease in the active material packing density of electrodes using titanium niobium composite oxide as the electrode active material.

[0007] In view of the above problems, the present invention relates to TiO2 and Ti2Nb 10 O 29 The objective is to provide a titanium-niobium composite oxide in which the coexistence of various materials and the fibrous growth of crystal grains are suppressed, as well as electrodes and lithium-ion secondary batteries using the same. [Means for solving the problem]

[0008] To achieve the above objective, the titanium niobium composite oxide according to the first aspect of the present invention contains 0.05 atomic% or more and less than 0.30 atomic% of alkali metal elements, contains at least one of the elements Al, Y, La, Ce, Pr, and Sm, contains the elements Ti, Nb, and O, the remainder being impurities, and the total atomic content of Ti and Nb is % Total atoms of Al, Y, La, Ce, Pr, and Sm % The first configuration is one in which the ratio is 0.001 or greater.

[0009] Furthermore, in the titanium niobium composite oxide of the first configuration described above, the total number of atoms of Ti and Nb % Total atoms of Al, Y, La, Ce, Pr, and Sm % It is preferable that the ratio of is 0.002 or greater (second configuration).

[0010] Furthermore, in the titanium niobium composite oxide having the first or second configuration described above, the total number of atoms of Ti and Nb % Total atoms of Al, Y, La, Ce, Pr, and Sm %It is preferable that the ratio is less than 0.024 (the third configuration).

[0011] In order to achieve the above object, the titanium niobium composite oxide according to the second aspect of the present invention contains an alkali metal element of 0.05 atomic% or more and less than 0.30 atomic%, contains at least one element of Al, Y, La, Ce, Pr, and Sm, and the total atoms of Ti and Nb % The total atoms of Y relative to % The ratio is a configuration (the fourth configuration) of 0.001 or more and 0.011 or less.

[0012] In order to achieve the above object, the titanium niobium composite oxide according to the third aspect of the present invention contains an alkali metal element of 0.05 atomic% or more and less than 0.30 atomic%, contains at least one element of Al, Y, La, Ce, Pr, and Sm, and the total atoms of Ti and Nb % The total atoms of Al, Y, La, Ce, Pr, and Sm relative to % The ratio is 0.001 or more, and when the aspect ratio represented by the ratio of the long axis length to the short axis length of the primary particles of the titanium niobium composite oxide is represented by a logarithmic normal distribution based on volume, the ratio of the primary particles having an aspect ratio exceeding 3 is 11% by volume or less (the fifth configuration).

[0013] In order to achieve the above object, the titanium niobium composite oxide according to the fourth aspect of the present invention contains an alkali metal element of 0.05 atomic% or more and less than 0.30 atomic%, contains at least one element of Al, Y, La, Ce, Pr, and Sm, and the total atoms of Ti and Nb % The total atoms of Al, Y, La, Ce, Pr, and Sm relative to % The ratio is 0.001 or more, and when the long axis length of the primary particles of the titanium niobium composite oxide is represented by a logarithmic normal distribution based on volume, the ratio of the primary particles having a long axis length exceeding 3 μm is 5% by volume or less (the sixth configuration).

[0014] Further, in the titanium niobium composite oxide having any of the above first to sixth configurations, it is preferable that a part of the surface of the titanium niobium composite oxide is coated with a carbon material (seventh configuration).

[0015] To achieve the above object, the electrode according to the present invention includes an electrode active material, and at least a part of the electrode active material is a titanium niobium composite oxide having any of the above first to seventh configurations (eighth configuration).

[0016] To achieve the above object, the lithium ion secondary battery according to the present invention includes a positive electrode and a negative electrode, and either the positive electrode or the negative electrode is an electrode having the above eighth configuration (ninth configuration).

Effects of the Invention

[0017] According to the present invention, it is possible to provide a titanium niobium composite oxide in which the mixing of TiO2 and Ti2Nb 10 O 29 and the fibrous growth of crystal grains are suppressed, and an electrode and a lithium ion secondary battery using the same.

Brief Description of the Drawings

[0018] [Figure 1A] Analysis results of titanium niobium composite oxides of Examples 1 to 13 and Comparative Examples 1 to 3 [Figure 1B] Analysis results of titanium niobium composite oxides of Examples 14 to 19 [Figure 1C] Analysis results of titanium niobium composite oxides of Examples 20 to 21 [Figure 1D] Analysis results of titanium niobium composite oxides of Examples 22 to 24 [Figure 1E] Analysis results of titanium niobium composite oxides of Examples 25 to 27 [Figure 1F] Analysis results of titanium niobium composite oxides of Examples 28 to 30 [Figure 2] SEM image of the titanium niobium composite oxide of Example 3 [Figure 3] SEM image of the titanium niobium composite oxide of Comparative Example 1 [Figure 4] Volume-based log-normal distribution of the long axis length (L) for the titanium niobium composite oxide of Example 3 [Figure 5] Volume-based log-normal distribution of the long axis length (L) for the titanium niobium composite oxide of Comparative Example 1 [Figure 6] Volume-based log-normal distribution of aspect ratio (L / D) for the titanium niobium composite oxide of Example 3 [Figure 7] Volume-based log-normal distribution of aspect ratio (L / D) for titanium niobium composite oxide in Comparative Example 1 [Figure 8] Schematic diagram of a 2032 type coin cell [Modes for carrying out the invention]

[0019] The following describes embodiments of the titanium niobium composite oxide according to the present invention.

[0020] <Overview> The titanium niobium composite oxide according to the present invention contains less than 0.30 atomic percent of alkali metal elements, and includes at least one of the elements Al, Y, La, Ce, Pr, and Sm, with a total of Ti and Nb atoms. % Total atoms of Al, Y, La, Ce, Pr, and Sm % The ratio is 0.001 or greater.

[0021] The titanium niobium composite oxide according to the present invention contains alkali metal elements, so TiO2 and Ti2Nb 10 O 29 The presence of these elements is suppressed. However, if alkali metal elements are present in amounts exceeding 0.30 atomic percent, fibrous growth of crystal grains becomes excessive, and even substitution of at least one of the elements Al, Y, La, Ce, Pr, and Sm described below will not sufficiently suppress fibrous growth of crystal grains.

[0022] The titanium niobium composite oxide according to the present invention contains at least one element of Al, Y, La, Ce, Pr, and Sm, and the total number of atoms of Ti and Nb is...% Total atoms of Al, Y, La, Ce, Pr, and Sm % The ratio is 0.001 or greater. This suggests that some of the Ti and Nb sites in the titanium-niobium composite oxide are substituted with at least one of the elements Al, Y, La, Ce, Pr, and Sm, and that such substitution suppresses the fibrous growth of the crystal grains.

[0023] However, the ratio of the total atomic weights of Al, Y, La, Ce, Pr, and Sm to the total atomic weights of Ti and Nb is 0.025 exceeding Therefore, it is estimated that the total atomic weights of Al, Y, La, Ce, Pr, and Sm exceed the substitution limits for some of the Ti and Nb seats, potentially inhibiting the reaction-promoting effect of alkali metal elements. Consequently, the ratio of the total atomic weights of Al, Y, La, Ce, Pr, and Sm to the total atomic weights of Ti and Nb is 0.025. below That is preferable.

[0024] <Example of manufacturing method> The titanium-niobium composite oxide according to the present invention can be synthesized, for example, by a solid-phase reaction method. An example of a method for synthesizing the titanium-niobium composite oxide according to the present invention by a solid-phase reaction method is described below.

[0025] The titanium niobium composite oxide according to this embodiment is synthesized (manufactured) by a solid-phase reaction method including a mixing step and a calcination step.

[0026] In the mixing process, titanium raw materials (e.g., titanium oxide or titanium compounds that produce titanium oxide upon heating), niobium raw materials (e.g., niobium oxide or niobium compounds that produce niobium oxide upon heating), alkali metal raw materials (e.g., alkali metal carbonates), and raw materials of at least one of the following elements (e.g., alumina, yttria, lanthanum oxide, cerium oxide, praseodymium oxide, samarium oxide) are weighed to the desired content and then uniformly ground and mixed.

[0027] Furthermore, niobium raw materials containing alkali metals as impurities may be used. Similarly, titanium raw materials containing alkali metals as impurities may be used. If the necessary alkali metals can be supplied solely from the aforementioned impurities, then no additional alkali metal raw materials should be added. On the other hand, if the necessary alkali metals are insufficient from the aforementioned impurities, the amount of alkali metal raw material should be determined considering the amount of impurities.

[0028] In the mixing process, it is preferable to use grinding and mixing equipment such as a ball mill, vibratory mill, or bead mill. To prevent the mixture from adhering to the grinding and mixing equipment when using it, alcohol (e.g., ethanol) may be added to the raw materials as an auxiliary agent.

[0029] The above-mentioned auxiliary agents may also use raw materials of at least one element from aluminum, yttrium, lanthanum, cerium, praseodymium, and samarium that are soluble in the aforementioned auxiliary agents (for example, aluminum halide, yttrium halide, lanthanum halide, cerium halide, praseodymium halide, samarium halide, etc.). Furthermore, raw materials of at least one element from aluminum, yttrium, lanthanum, cerium, praseodymium, and samarium that are soluble in the above-mentioned auxiliary agents may be used together with raw materials of at least one element from aluminum, yttrium, lanthanum, cerium, praseodymium, and samarium that are not soluble in the above-mentioned auxiliary agents.

[0030] In the firing process, the mixture obtained in the mixing process is held at an appropriate temperature range for an appropriate time and fired in the atmosphere. This makes it possible to obtain a titanium-niobium composite oxide in which the primary particles are sintered.

[0031] The appropriate temperature range and time described above are values ​​that yield high-quality crystals without excessive grain growth. The appropriate temperature range is preferably 1000°C to 1300°C, more preferably 1100°C to 1200°C. The appropriate time is preferably 1 to 24 hours, more preferably 2 to 6 hours. The mixture may also be calcined in an atmosphere other than air (for example, a nitrogen atmosphere).

[0032] The following describes embodiments of the present invention in more detail, but the present invention is not limited to the embodiments described below. In other words, it goes without saying that the content can be appropriately modified without being limited in any way to the embodiments described below, as long as it is possible to apply known general techniques such as the various processing methods and granulation methods described below. [Examples]

[0033] <Example 1> 100.0 g of titanium dioxide (TiO2) powder, 355.3 g of niobium oxide (Nb2O5) powder, 0.6 g of potassium carbonate (K2CO3) powder, and 2.5 g of alumina (Al2O3) powder were mixed with ethanol as an additive and ground using a vibratory mill.

[0034] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0035] <Example 2> 100.0 g of titanium dioxide powder, 349.2 g of niobium oxide powder, 0.9 g of potassium carbonate powder, and 1.5 g of alumina powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0036] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0037] <Example 3> 100.0 g of titanium dioxide powder, 359.7 g of niobium oxide powder, 1.4 g of potassium carbonate powder, and 2.4 g of alumina powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0038] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0039] <Example 4> 100.0g of titanium dioxide powder, 348.2g of niobium oxide powder, and 1.4g of potassium carbonate powder were mixed with ethanol containing 7.6g of aluminum chloride (AlCl3) powder as an auxiliary agent, and then ground and mixed using a vibrating mill.

[0040] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0041] <Example 5> 100.0 g of titanium dioxide powder, 352.6 g of niobium oxide powder, 1.6 g of potassium carbonate powder, and 2.7 g of alumina powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0042] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0043] <Example 6> 100.0 g of titanium dioxide powder, 353.9 g of niobium oxide powder, 2.4 g of potassium carbonate powder, 0.2 g of sodium carbonate (Na2CO3) powder, and 2.8 g of alumina powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0044] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0045] <Example 7> 100.3g of titanium dioxide powder containing potassium (K) as an impurity, 340.3g of niobium oxide powder, and 1.3g of yttria (Y2O3) powder were mixed with ethanol as an additive and then pulverized using a vibratory mill.

[0046] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0047] <Example 8> 100.0 g of titanium dioxide powder, 341.7 g of niobium oxide powder, 0.8 g of potassium carbonate powder, 0.1 g of alumina powder, and 1.3 g of yttria powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0048] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0049] <Example 9> 100.0 g of titanium dioxide powder, 338.1 g of niobium oxide powder, 1.3 g of potassium carbonate powder, 0.1 g of alumina powder, and 1.2 g of yttria powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0050] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0051] <Example 10> 100.0 g of titanium dioxide powder, 343.8 g of niobium oxide powder containing potassium and sodium (Na) as impurities, 0.1 g of alumina powder, and 0.5 g of yttria powder were mixed with ethanol as an additive and ground using a vibratory mill.

[0052] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0053] <Example 11> 100.0g of titanium dioxide powder, 367.7g of niobium oxide powder containing potassium and sodium as impurities, 0.1g of alumina powder, and 5.0g of yttria powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0054] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0055] <Example 12> 100.0 g of titanium dioxide powder, 341.4 g of niobium oxide powder, 0.5 g of potassium carbonate powder, and 0.1 g of alumina powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0056] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0057] <Example 13> 100.0 g of titanium dioxide powder, 350.5 g of niobium oxide powder, 1.5 g of potassium carbonate powder, and 4.8 g of alumina powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0058] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0059] <Example 14> 100.0 g of titanium dioxide powder, 346.9 g of niobium oxide powder, 0.8 g of potassium carbonate powder, 0.1 g of alumina powder, and 1.2 g of lanthanum oxide (La2O3) powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0060] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0061] <Example 15> 100.0 g of titanium dioxide powder, 344.4 g of niobium oxide powder, 1.4 g of potassium carbonate powder, 0.1 g of alumina powder, and 3.6 g of lanthanum oxide powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0062] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0063] <Example 16> 100.0 g of titanium dioxide powder, 348.3 g of niobium oxide powder, 1.8 g of potassium carbonate powder, and 7.9 g of lanthanum oxide powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0064] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0065] <Example 17> 100.0g of titanium dioxide powder, 347.8g of niobium oxide powder, 2.1g of potassium carbonate powder, and 8.0g of lanthanum oxide powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0066] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0067] <Example 18> 100.0g of titanium dioxide powder, 339.5g of niobium oxide powder, 1.1g of potassium carbonate powder, 0.1g of alumina powder, 0.1g of sodium carbonate powder, and 12.0g of lanthanum oxide powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0068] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0069] <Example 19> 100.0g of titanium dioxide powder, 347.0g of niobium oxide powder, 1.1g of potassium carbonate powder, 0.1g of alumina powder, and 15.0g of lanthanum oxide powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0070] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0071] <Example 20> 100.0g of titanium dioxide powder, 345.6g of niobium oxide powder, 0.8g of potassium carbonate powder, 0.2g of sodium carbonate powder, 1.9g of yttria powder, and 2.5g of lanthanum oxide powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0072] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0073] <Example 21> 100.0g of titanium dioxide powder, 349.6g of niobium oxide powder, 2.7g of potassium carbonate powder, 0.5g of alumina powder, 1.6g of yttria powder, and 2.5g of lanthanum oxide powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0074] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0075] <Example 22> 100.0g of titanium dioxide powder, 339.3g of niobium oxide powder, 1.6g of potassium carbonate powder, 0.1g of alumina powder, and 2.0g of cerium oxide (CeO2) powder were mixed with ethanol as an additive and ground using a vibratory mill.

[0076] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0077] <Example 23> 100.0g of titanium dioxide powder, 349.7g of niobium oxide powder, 2.0g of potassium carbonate powder, 0.1g of alumina powder, and 3.3g of cerium oxide powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0078] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0079] <Example 24> 100.0g of titanium dioxide powder, 344.1g of niobium oxide powder, 1.0g of potassium carbonate powder, 0.1g of alumina powder, 0.2g of sodium carbonate powder, and 0.9g of cerium oxide powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0080] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0081] <Example 25> 100.0 g of titanium dioxide powder, 343.7 g of niobium oxide powder, 2.1 g of potassium carbonate powder, and 0.5 g of praseodymium oxide (Pr2O3) powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0082] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0083] <Example 26> 100.0g of titanium dioxide powder, 343.3g of niobium oxide powder, 1.1g of potassium carbonate powder, 0.3g of sodium carbonate powder, 0.1g of alumina powder, and 1.9g of praseodymium oxide powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0084] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0085] <Example 27> 100.0g of titanium dioxide powder, 342.6g of niobium oxide powder, 0.9g of potassium carbonate powder, 0.3g of sodium carbonate powder, 0.1g of alumina powder, and 0.3g of praseodymium oxide powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0086] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0087] <Example 28> 100.0g of titanium dioxide powder, 347.0g of niobium oxide powder, 1.0g of potassium carbonate powder, and 2.1g of samarium oxide (Sm2O3) powder were mixed with ethanol as an additive and ground using a vibratory mill.

[0088] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0089] <Example 29> 100.0g of titanium dioxide powder, 352.0g of niobium oxide powder, 1.2g of potassium carbonate powder, 0.1g of alumina powder, and 4.1g of samarium oxide powder were mixed with ethanol as an additive and ground using a vibratory mill.

[0090] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0091] <Example 30> 100.0 g of titanium dioxide powder, 346.8 g of niobium oxide powder, 2.0 g of potassium carbonate powder, and 10.9 g of samarium oxide powder were mixed with ethanol as an additive and then ground and mixed using a vibrating mill.

[0092] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0093] <Comparative Example 1> 100.0 g of titanium dioxide powder, 344.4 g of niobium oxide powder, 1.5 g of potassium carbonate powder, and 0.1 g of alumina powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0094] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0095] <Comparative Example 2> 100.0 g of titanium dioxide powder, 342.4 g of niobium oxide powder, 2.9 g of potassium carbonate powder, and 5.3 g of alumina powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0096] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0097] <Comparative Example 3> 100.0g of titanium dioxide powder, 332.4g of niobium oxide powder, 2.7g of potassium carbonate powder, 0.4g of alumina powder, and 4.3g of yttria powder were mixed with ethanol as an additive and ground using a vibrating mill.

[0098] The resulting mixture was placed in an alumina crucible and calcined in an electric furnace (processing temperature: 1100°C, processing time: 2 hours) to obtain a titanium niobium composite oxide.

[0099] <Analyzer> The analytical instruments used for the analysis of the titanium niobium composite oxides in Examples 1-30 and Comparative Examples 1-3 are as follows. X-ray diffractometer: Rigaku Corporation, Ultima4, measurement using Cu-Kα rays X-ray fluorescence analyzer: Rigaku Corporation, ZSX PrimusIII+ Scanning electron microscope: JEOL Ltd., JSM-6510

[0100] <Analysis results> Figure 1A shows the analysis results of the titanium niobium composite oxides from Examples 1-13 and Comparative Examples 1-3. Figure 1B shows the analysis results of the titanium niobium composite oxides from Examples 14-19. Figure 1C shows the analysis results of the titanium niobium composite oxides from Examples 20-21. Figure 1D shows the analysis results of the titanium niobium composite oxides from Examples 22-24. Figure 1E shows the analysis results of the titanium niobium composite oxides from Examples 25-27. Figure 1F shows the analysis results of the titanium niobium composite oxides from Examples 28-30. Note that "0.000" in Figures 1A-1F is a value obtained by rounding to the fourth decimal place, and therefore does not mean a perfect zero. Furthermore, in Examples 7, 11, and 14-30, there were no primary particles with a major axis length (L) of 3 μm or more among the 100 measurements. However, it cannot be definitively stated that there are absolutely no primary particles with a major axis length (L) of 3 μm or more in the population. Rather, it can only be said that, based on the normal distribution, the probability of primary particles with a major axis length (L) of 3 μm or more is close to zero. In other words, the "0.0%" in Figures 1A-1F does not mean exactly zero.

[0101] The atomic percentages of Ti, Nb, K, Na, total alkali metals, Al, Y, La, Ce, Pr, and Sm in each titanium-niobium composite oxide were determined from the results of X-ray fluorescence analysis. % The ratios Al / (Ti+Nb), Y / (Ti+Nb), La / (Ti+Nb), Ce / (Ti+Nb), Pr / (Ti+Nb), Sm / (Ti+Nb), and (Al+Y+La+Ce+Pr+Sm) / (Ti+Nb) were determined from the atomic percentages mentioned above.

[0102] The shape of the primary particles of each titanium-niobium composite oxide was determined from observations using a scanning electron microscope. Examples of SEM images of the titanium-niobium composite oxides are shown in Figures 2 and 3. Figure 2 is an SEM image of the titanium-niobium composite oxide of Example 3, and Figure 3 is an SEM image of the titanium-niobium composite oxide of Comparative Example 1.

[0103] SEM images (20,000x magnification) of each titanium-niobium composite oxide were scanned laterally, and the long axis length (L) and short axis length (D) of 100 primary particles located on a line parallel to the horizontal direction were measured sequentially for each titanium-niobium composite oxide. During the measurement, the magnification was changed up to a maximum of 40,000x depending on the size of the primary particles, and the angle of the sample stage was changed according to the orientation of the primary particles.

[0104] Assuming the primary particle's shape is cylindrical, the volume of each primary particle was determined by measuring its major axis length (L) and minor axis length (D). Specifically, the major axis length (L) was considered the height of the cylinder, and the minor axis length (D) was considered the diameter of the cylinder.

[0105] Then, using the volume of the primary particles as the basis rather than the number of primary particles, the distribution of the major axis length (L) of the population (the entire titanium-niobium composite oxide) was estimated from the measured values ​​of 100 primary particles. Examples of the estimation results of the volume-based log-normal distribution of major axis length (L) for titanium-niobium composite oxide are shown in Figures 4 and 5. Figure 4 is the volume-based log-normal distribution of major axis length (L) for titanium-niobium composite oxide in Example 3, and Figure 5 is the volume-based log-normal distribution of major axis length (L) for titanium-niobium composite oxide in Comparative Example 1. Figures 1A to 1F show the volume-based percentage of primary particles with a major axis length (L) of 3 μm or more.

[0106] Furthermore, instead of using the number of primary particles as the basis, the volume of the primary particles was used as the basis to estimate the distribution of the aspect ratio (L / D) of the population (the entire titanium-niobium composite oxide) from the measured values ​​of 100 primary particles. Examples of volume-based log-normal distributions of aspect ratio (L / D) for titanium-niobium composite oxides are shown in Figures 6 and 7. Figure 6 is the volume-based log-normal distribution of aspect ratio (L / D) for titanium-niobium composite oxides in Example 3, and Figure 7 is the volume-based log-normal distribution of aspect ratio (L / D) for titanium-niobium composite oxides in Comparative Example 1. Figures 1A to 1F show the volume-based proportion of primary particles with an aspect ratio (L / D) of 3 or more.

[0107] In the analysis method described above, the shape of the primary particles was assumed to be cylindrical, but the same estimation results can be obtained even if the shape of the primary particles is assumed to be a rectangular prism with a square base.

[0108] Figures 1A to 1F show the intensity (relative value) of peaks in the X-ray diffraction spectra of each titanium niobium composite oxide in Examples 1 to 30 and Comparative Examples 1 to 3, where peaks exist in the diffraction angle 2θ ranges of 26.2° to 26.4°, 24.8° to 25.1°, and 27.2° to 27.6°, respectively. The peaks in the diffraction angle 2θ range of 26.2° to 26.4° are due to the crystal structure of the target product, TiNb2O7. The peaks in the diffraction angle 2θ range of 24.8° to 25.1° are due to Ti2Nb 10 O 29 These peaks are due to the crystal structure. Peaks with diffraction angles 2θ in the range of 27.2° to 27.6° are due to the rutile-type TiO2 crystal structure.

[0109] Furthermore, Figures 1A to 1F show, as percentages, the ratio of the peak intensity in the diffraction angle 2θ range of 24.8° to 25.1° to the peak intensity in the diffraction angle 2θ range of 26.2° to 26.4°, and the ratio of the peak intensity in the diffraction angle 2θ range of 27.2° to 27.6° to the peak intensity in the diffraction angle 2θ range of 26.2° to 26.4°.

[0110] Furthermore, Figures 1A to 1F also show the full width at half maximum (FMAX) of peaks in the diffraction angle 2θ range of 26.2° to 26.4°. The smaller the FMAX of peaks in the diffraction angle 2θ range of 26.2° to 26.4°, the higher the quality of the desired product, TiNb2O7 crystals.

[0111] In each of the titanium-niobium composite oxides in Examples 1 to 30, the volume-based proportion of primary particles with an aspect ratio (L / D) of 3 or more is 11% by volume or less, more precisely 10.8% by volume or less. On the other hand, in each of the titanium-niobium composite oxides in Comparative Examples 1 to 30, the volume-based proportion of primary particles with an aspect ratio (L / D) of 3 or more is 16% by volume or more, more precisely 16.7% or more. In other words, the fibrous grain growth of primary particles is suppressed in each of the titanium-niobium composite oxides in Examples 1 to 30 compared to each of the titanium-niobium composite oxides in Comparative Examples 1 to 3.

[0112] Each of the titanium niobium composite oxides in Examples 1-30 contains less than 0.30 atomic percent of alkali metal elements, and includes at least one of the elements Al, Y, La, Ce, Pr, and Sm, with a total of Ti and Nb atoms. % Total atoms of Al, Y, La, Ce, Pr, and Sm % While the composition has a ratio of 0.001 or higher, the titanium niobium composite oxides in Comparative Examples 1 to 3 do not have such a composition. Furthermore, it is preferable that the alkali metal element content is between 0.05 atomic% and 0.28 atomic%.

[0113] The titanium niobium composite oxide of Comparative Example 1 has a total atom count of Ti and Nb. % Total atoms of Al, Y, La, Ce, Pr, and Sm % Because the ratio is too small, the fibrous grain growth of the primary particles is not sufficiently suppressed, and as a result, it is thought that the aspect ratio (L / D) of the primary particles tends to be larger than that of the titanium niobium composite oxides in Examples 1 to 30. The titanium niobium composite oxides in Comparative Examples 2 and 3 have too much alkali metal element content, so the fibrous grain growth of the primary particles is not sufficiently suppressed, and as a result, it is thought that the aspect ratio (L / D) of the primary particles tends to be larger than that of the titanium niobium composite oxides in Examples 1 to 30.

[0114] In each of the titanium-niobium composite oxides in Examples 1-11 and 13-30, the volume-based proportion of primary particles with a long axis length (L) of 3 μm or more is 5 volume% or less, more precisely 4.0 volume% or less. On the other hand, in the titanium-niobium composite oxide of Example 12, the volume-based proportion of primary particles with a long axis length (L) of 3 μm or more is 10 volume% or more, more precisely 10.8 volume%. %in Yes. In other words, the growth of primary particles is suppressed in each of the titanium niobium composite oxides in Examples 1-11 and 13-30 compared to the titanium niobium composite oxide in Example 12.

[0115] Each of the titanium niobium composite oxides in Examples 1-11 and 13-30 is the total number of Ti and Nb atoms. % Total atoms of Al, Y, La, Ce, Pr, and Sm % While the configuration has a ratio of 0.002 or higher, the titanium niobium composite oxide of Example 12 does not have such a configuration.

[0116] Each of the titanium-niobium composite oxides in Examples 1-11 and 13-30 has a higher total atom content of Ti and Nb than the titanium-niobium composite oxide in Example 12. % Total atoms of Al, Y, La, Ce, Pr, and Sm % Because the ratio is large, the growth of primary particles can be suppressed more effectively than in the titanium-niobium composite oxide of Example 12. As a result, it is considered that the primary particles tend to have a smaller major axis length (L) than the titanium-niobium composite oxide of Example 12.

[0117] In the titanium-niobium composite oxides of Examples 1-11, 14-17, and 20-30, the ratio of the peak intensity in the diffraction angle 2θ range of 27.2°-27.6° to the peak intensity in the diffraction angle 2θ range of 26.2°-26.4° is 7% or less, more precisely 6.8% or less. On the other hand, in the titanium-niobium composite oxides of Examples 13, 18, and 19, the ratio of the peak intensity in the diffraction angle 2θ range of 27.2°-27.6° to the peak intensity in the diffraction angle 2θ range of 26.2°-26.4° is 8% or more, more precisely 8.5% or more. In other words, the titanium-niobium composite oxides of Examples 1-11, 14-17, and 20-30 have suppressed TiO2 inclusion compared to the titanium-niobium composite oxides of Examples 13, 18, and 19.

[0118] The total atoms of Ti and Nb in each of the titanium niobium composite oxides in Examples 1-11, 14-17, and 20-30 are % Total atoms of Al, Y, La, Ce, Pr, and Sm % While the ratio of is less than 0.020, the titanium niobium composite oxides in Examples 13, 18, and 19 do not have such a configuration. Note that the total atoms of Ti and Nb % Total atoms of Al, Y, La, Ce, Pr, and Sm % The ratio is preferably less than 0.020, and more precisely, 0.018 or less.

[0119] Unlike the titanium niobium composite oxides in Examples 1-11, 14-17, and 20-30, the total atoms of Ti and Nb differ in the titanium niobium composite oxides in Examples 13, 18, and 19. % Total atoms of Al, Y, La, Ce, Pr, and Sm % Because the ratio is not too large, it is thought that the presence of TiO2 can be suppressed more effectively than in the titanium niobium composite oxides of Examples 13, 18, and 19.

[0120] Each of the titanium niobium composite oxides in Examples 7-11 is the total number of Ti and Nb atoms. % Total atoms of Y %While the ratio of the two components is between 0.001 and 0.011, the titanium niobium composite oxide of Example 13 does not have such a configuration.

[0121] Each of the titanium niobium composite oxides in Examples 7-11 has a moderate Y content and a total atom content of Ti and Nb. % Total atoms of Y % Since the ratio is within an appropriate range, it is considered that the presence of TiO2 can be suppressed more effectively than in the titanium niobium composite oxide of Example 13, which has an excessively high Al content.

[0122] <Applications to lithium-ion secondary batteries> For example, electrodes can be prepared using any of the titanium niobium composite oxides from Examples 1 to 30 as the active material. Specifically, 10 parts by weight of polyvinylidene fluoride can be dissolved in N-methyl-2-pyrrolidone, then 10 parts by weight of conductive carbon and 100 parts by weight of any of the titanium niobium composite oxides from Examples 1 to 13 can be added as conductive additives, and the mixture can be kneaded in a rotary-orbiting agitator to create a coating. This coating can then be applied to aluminum foil, vacuum-dried at 120°C, pressed, and then punched out in a circular shape.

[0123] Using the electrodes fabricated as described above, a 2032-type coin cell 1, as shown in Figure 8, can be assembled. The 2032-type coin cell 1 shown in Figure 8 is an example of a lithium-ion secondary battery. The 2032-type coin cell 1 is fabricated by sandwiching the electrode 2, counter electrode 3, non-aqueous electrolyte 4, and separator 5 between the upper case 6a and the lower case 6b, and sealing the perimeter of the upper case 6a and the lower case 6b with a gasket 7.

[0124] For the counter electrode 3, for example, metallic lithium foil may be used. For the non-aqueous electrolyte 4, for example, a solution of ethylene carbonate:dimethyl carbonate 1:1 v / v% with 1 mol / L of LiPF6 dissolved in it may be used. For the separator 5, for example, a porous polypropylene membrane may be used.

[0125] Furthermore, an electrode in which at least a portion of the electrode active material is the titanium-niobium composite oxide according to the present invention may be used as the positive electrode of a lithium-ion secondary battery, or as the negative electrode of a lithium-ion secondary battery.

[0126] <Other> Although embodiments of the present invention have been described above, the configuration of the present invention is not limited thereto, and various modifications can be made without departing from the spirit of the invention. That is, the above embodiments should be considered in all respects to be illustrative and not restrictive, and the technical scope of the present invention is indicated by the claims and should be understood to include all modifications that fall within the meaning and scope equivalent to the claims.

[0127] For example, in the above-described embodiment, the alkali metal elements contained in the titanium niobium composite oxide were K and Na, but other alkali metal elements such as Li may also be included. Other alkali metal elements such as Li may be included in the titanium niobium composite oxide that does not contain K and Na, may be included in the titanium niobium composite oxide together with K, or may be included in the titanium niobium composite oxide together with Na. Furthermore, comparing Example 18 and Example 19, there is no significant difference in the content of alkali metal elements between the configuration with one type of alkali metal element and the configuration with two types of alkali metal elements, and the total atoms of Ti and Nb % Total atoms of Al, Y, La, Ce, Pr, and Sm % If there is no significant difference in the ratio, then TiO2 or Ti2Nb 10 O 29 It is considered that the effect of suppressing the mixing and grain growth is of a similar degree. Therefore, for example, for each of Examples 1 to 30, the total atoms of Ti and Nb were kept approximately unchanged. % Total atoms of Al, Y, La, Ce, Pr, and Sm % When the ratio of alkali metal elements is kept constant but the number of alkali metal elements is changed, TiO2 and Ti2Nb are compared to each of Examples 1-30. 10 O 29The effects of suppressing the presence of these substances and the growth of crystal grains are considered to be of similar magnitude.

[0128] For example, in the above-described embodiment, a portion of the surface of the titanium-niobium composite oxide was not coated with a carbon material, but a portion of the surface of the titanium-niobium composite oxide may be coated with a carbon material.

[0129] Here, we will describe an example of a method for producing a titanium-niobium composite oxide in which a portion of the surface is coated with a carbon material. For example, after adding an aqueous solution of polyvinyl alcohol (PVA) to any of the titanium-niobium composite oxides from Examples 1 to 30 so that the PVA content is 13% by weight, the mixture is crushed and mixed using a ball mill, and then dried with a spray dryer. After that, the resulting dried product is heat-treated under a nitrogen atmosphere (treatment temperature: 800°C, treatment time: 4 hours). This makes it possible to obtain a titanium-niobium composite oxide in which a portion of the surface is coated with a carbon material. [Industrial applicability]

[0130] The titanium-niobium composite oxide according to the present invention can be used, for example, as an electrode active material used in the electrodes of lithium-ion secondary batteries. [Explanation of symbols]

[0131] 1. 2032 type coin cell 2 electrodes 3. Opposite 4. Non-aqueous electrolytes 5 Separators 6a Upper case 6b Lower case 7 Gasket

Claims

1. A titanium-niobium composite oxide for electrode active materials in lithium-ion secondary batteries, It contains at least one alkali metal element selected from the group consisting of Li, Na, K, Rb, and Cs in an amount of 0.05 atomic percent or more and less than 0.30 atomic percent. It contains at least one element of Al, Y, La, Ce, Pr, and Sm, It contains the elements Ti, Nb, and O, The remainder is an impurity. The ratio of the total atomic percent of Al, Y, La, Ce, Pr, and Sm to the total atomic percent of Ti and Nb is 0.001 or more and 0.025 or less. In the X-ray diffraction spectrum of the aforementioned titanium-niobium composite oxide, the ratio of the peak intensity in the diffraction angle 2θ range of 27.2° to 27.6° to the peak intensity in the diffraction angle 2θ range of 26.2° to 26.4° is 9.9% or less, and the ratio of the peak intensity in the diffraction angle 2θ range of 24.8° to 25.1° to the peak intensity in the diffraction angle 2θ range of 26.2° to 26.4° is 8.7% or less. When the aspect ratio, which is expressed as the ratio of the major axis length to the minor axis length of the primary particles of the titanium niobium composite oxide, is represented by a volume-based log-normal distribution, the proportion of primary particles with an aspect ratio of 3 or more is 11% by volume or less. When the major axis lengths of the primary particles of the titanium-niobium composite oxide are represented by a volume-based log-normal distribution, the proportion of primary particles with a major axis length of 3 μm or more is 10.8% by volume or less. Titanium-niobium composite oxide for electrode active materials in lithium-ion secondary batteries.

2. The ratio of the total atomic percent of Al, Y, La, Ce, Pr, and Sm to the total atomic percent of Ti and Nb is less than 0.

024. Titanium niobium composite oxide for electrode active material of lithium-ion secondary battery according to claim 1.

3. The ratio of the total atomic percentage of Y to the total atomic percentage of Ti and Nb is 0.001 or more and 0.011 or less. Titanium niobium composite oxide for electrode active material of lithium-ion secondary battery according to claim 2.

4. When the major axis lengths of the primary particles of the titanium niobium composite oxide are represented by a volume-based log-normal distribution, the proportion of primary particles with a major axis length of 3 μm or more is 5 volume% or less. Titanium niobium composite oxide for electrode active material of lithium-ion secondary battery according to any one of claims 1 to 3.

5. A portion of the surface of the aforementioned titanium niobium composite oxide is coated with a carbon material. Titanium niobium composite oxide for electrode active material of lithium-ion secondary battery according to any one of claims 1 to 4.

6. Equipped with an electrode active material, An electrode in which at least a portion of the electrode active material is a titanium-niobium composite oxide for electrode active material of a lithium-ion secondary battery according to any one of claims 1 to 5.

7. Equipped with a positive electrode and a negative electrode, A lithium-ion secondary battery wherein either the positive electrode or the negative electrode is the electrode described in claim 6.

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