Active material for a positive electrode of a battery cell, positive electrode and battery cell

Abstract

Positive active material (A) (42) for a positive electrode (22) of a battery cell (2), comprising a first component (A1) which includes a compound of general formula (III): Li 2-z N / a z MnO 3-y N y (III) where 3 > y > 0; and 2 > z > 0.

Description

[0001] The invention relates to an active material (A) for a positive electrode of a battery cell, comprising a first component (A1) containing Li2MnO3 doped with nitrogen ions. The invention also relates to a positive electrode of a battery cell comprising an active material (A) according to the invention, and to a battery cell comprising at least one positive electrode according to the invention. State of the art

[0002] The storage of electrical energy has become increasingly important in recent decades. Electrical energy can be stored using batteries. Batteries convert chemical reaction energy into electrical energy. A distinction is made between primary and secondary batteries. Primary batteries are only functional once, while secondary batteries, also known as accumulators, are rechargeable. A battery comprises one or more battery cells.

[0003] Lithium-ion battery cells are primarily used in accumulators. These are characterized, among other things, by high energy density, thermal stability, and extremely low self-discharge.

[0004] Lithium-ion battery cells have a positive electrode and a negative electrode. Each positive and negative electrode includes a current collector onto which a positive or negative active material is applied, respectively.

[0005] The positive and negative active material is characterized in particular by its ability to reversibly store and release lithium ions.

[0006] The active material for the negative electrode is, for example, amorphous silicon, which can form intercalation compounds with lithium atoms. Carbon compounds, such as graphite, are also commonly used as active materials for negative electrodes. Lithium atoms are embedded within the active material of the negative electrode.

[0007] The active material for the positive electrode is typically a lithium-containing metal oxide or a lithium-containing metal phosphate. Particularly in applications requiring high energy density, so-called high-energy materials such as HE (high-energy)-NCM (nickel-cobalt-manganese) electrodes (e.g., LiMO2 : Li2MnO3 with M = Ni, Co, Mn) are used. A battery of this type that uses such an HE-NCM electrode is known, for example, from DE 10 2012 208 321 A1.

[0008] During operation of the battery cell, i.e., during a discharge process, electrons flow in an external circuit from the negative electrode to the positive electrode. Inside the battery cell, lithium ions migrate from the negative electrode to the positive electrode during discharge. In this process, the lithium ions are reversibly deposited from the active material of the negative electrode, a process also known as lithiation. During a charging process, the lithium ions migrate from the positive electrode to the negative electrode. In this process, the lithium ions are reversibly deposited back into the active material of the negative electrode, a process also known as lithiation.

[0009] The electrodes of the battery cell are foil-like and wound into an electrode coil with a separator in between, which separates the negative electrode from the positive electrode. Such an electrode coil is also called a jelly roll. The electrodes can also be stacked on top of each other.

[0010] The two electrodes of the electrode winding or electrode stack are electrically connected to the terminals of the battery cell via commutators. A battery cell typically comprises one or more electrode windings or electrode stacks. The electrodes and the separator are surrounded by an electrolyte, usually a liquid. This electrolyte is conductive for lithium ions, enabling their transport between the electrodes.

[0011] EP 2 728 660 A deals with positive active materials for high-energy lithium-ion batteries based on HE-NCM materials.

[0012] US 2014 / 0099559 A1 discloses an electrode for a battery which incorporates an active material selected from LiCoO2, LiMn2O4, Li2MnO3, LiNiO2, LiMn 1.5 Ni 0.5 O4, LiFePO4, Li2FePO4F, Li3CONiMnO6, Li(Li a Ni x Mn y Co z The material comprises O2 and mixtures thereof. It can also be doped with other metals. Furthermore, a coating of the electrode with a nitrogen-containing carbon composition is disclosed.

[0013] Conventional HE-NCMs are characterized by the fact that they deliver high cell voltages at the beginning of the cell's lifetime, which, however, are subject to significant losses over time (so-called voltage fade). The same applies to the cell's capacity (so-called capacity fade). The object of this invention is therefore to provide an active material for a positive electrode that exhibits high cell voltage and capacity even after a long cell lifetime.

[0014] The study of the influence of 10 cationic (Mg, Ti, V, Nb, Fe, Ru, Co, Ni, Cu and Al) and 2 anionic dopants (N and F) on the phase stability, redox potential and ionic and electronic conductivity of Li2MnO3 and LiMnO2 using density functional theory is known from the publication by Kong, F.; Longo, RC; Park, M.-S.; Yoon, J.; Yeon, O.-H.; Park, J,-H; Wang, W.-H.; “Ab initio study of doping effects on LiMnO2 and Li2MnO3 cathode materials for Li-ion batteries”, Journal of Materials Chemistry A, Vol. 3, 2015, pp. 8489-8500.

[0015] It is known from US 2007 / 065723 A1, Li 2-x A x MO3, which is created by replacing lithium in Li2MO3 with a layered structure by an alkali metal with an ionic radius larger than that of lithium, is to be used as an active electrode material.

[0016] Particles are known from WO 2013 / 120724 A1 which are a mixed oxide of the general formula (I) Li1+a Ni b Co c Mn d O z (I) include. as well as a method for producing these particles and a use of these particles.

[0017] US patent 2005 / 0281727 A1 discloses the reduction of the specific resistance of an active material to drastically decrease the amount of a conductive auxiliary material, thus obtaining a secondary battery with a non-aqueous electrolyte and high capacity. The active material is a material with the composition formula Li x MeO y N z used, where 0 ≤ x ≤ 2, 0.1 ≤ y ≤ 2.2, 0 < z < 1.4, and Me is at least one element from the group Ti, Co, Ni, Mn, Si, Ge and Sn.

[0018] From CN 1 02 694 164 A is a positive electrode active material based on lithium manganese oxide which contains nitrogen, comprising Li 2-z N / a z MnO 3-x N y known for z=0.

[0019] From US patent 2010 / 0 086 853 A1, positive electrode materials are known that exhibit a very high specific discharge capacity at room temperature and a moderate discharge rate. Some materials have the formula Li 1+x Ni α Mn β Co γ O2, where x is in the range of about 0.05 to about 0.25, α is in the range of about 0.1 to about 0.4, β is in the range of about 0.4 to about 0.65 and γ is in the range of about 0.05 to about 0.3. Disclosure of the invention

[0020] An active material (A) for a positive electrode of a battery cell, in particular for a lithium-ion battery cell, is proposed, comprising a first component (A1) containing a metal oxide of formula (I): Li2MnO3 (I)

[0021] According to the invention, the first component (A1) of the active material (A) has a doping with nitrogen ions N 2- on.

[0022] The doping preferably introduces a proportion of between 0.1% and 15 mol% of oxygen ions O₂ 2- of the metal oxide Li2MnO3 of the first component of the active material (A) of the positive electrode by the nitrogen ions N 2- replaced. In particular, a proportion of 1% and 10 mol% of the oxygen ions O is preferred. 2- of Li2MnO3 by nitrogen ions N 2- replaced.

[0023] The component (A1) according to the invention thus comprises at least one compound which can be represented by the following formula (II): Li2MnO 3-y N y (II) where 3 > y > 0. Preferably 1.5 ≥ y > 0, in particular 0.5 ≥ y > 0.

[0024] According to an advantageous embodiment of the invention, component (A1) is additionally doped with sodium ions, wherein a portion of the lithium ions in component (A1) are replaced by sodium ions. This positively influences the rate capability of the active material (A). The advantageous embodiment therefore comprises a component (A1) of the general formula (III): Li 2-z N / a z MnO 3-y N y (III) where y has the previously defined meaning and 2 > z ≥ 0. Preferably, 1 ≥ z ≥ 0,1.

[0025] Preferably, the active material (A) comprises a second component (A2) containing LiMO2. M is a transition metal, preferably selected from the elements nickel, cobalt, and manganese. The active material (A), comprising components (A1) and (A2), enables a relatively large battery cell capacity combined with a relatively high voltage.

[0026] In general, the doping of the first component (A1) of the active material (A) of the positive electrode, which contains the metal oxide Li2MnO3, with the nitrogen ions N 2- a material according to formula (III).

[0027] The initially inactive first component (A1) of the active material (A) of the positive electrode, which contains the metal oxide Li₂MnO₃, is activated during battery cell formation by irreversible release of oxygen. Battery cell formation occurs when a defined voltage is applied to the battery cell for the first time and a defined current flows through it for the first time. Such a method for forming a battery cell, in which formation currents are introduced to activate electrochemical processes in the battery cell, is known, for example, from German patent application DE 10 2012 214 119 A1.

[0028] The doping of the first component (A1), containing the metal oxide Li₂MnO₃, takes place before the aforementioned formation and activation of the battery cell. During doping, oxygen ions O₂ are added proportionally. 2- of the metal oxide Li2MnO3 by the nitrogen ions N 2- replaced. The nitrogen ions are able to have both the -2 (N₂) oxidation state. 2- ) as well as the oxidation state -1 (N -The nitrogen ions are redox-active and can be absorbed at sufficient voltage. This allows them to participate in charge compensation during the charging and discharging of the battery cell. The proposed doping of the positive active material with nitrogen ions reduces irreversible oxygen loss. Since this reduces defects in the material, it also reduces the destabilization of the material structure caused by rearrangements and migrations of transition metals within the positive active material. This leads to a stabilization of the capacity and voltage, as the active material is subject to fewer changes.

[0029] Furthermore, the nitrogen ions N 2- Sufficiently electronegative to bind electrons to itself and not donate them to neighboring manganese. This prevents the formation of electrochemically undesirable Mn⁻. 3+-ions are inhibited. Furthermore, it is assumed that the doping of the positive active material (A) with nitrogen anions according to the invention stabilizes the oxygen, particularly at high charge states. This also stabilizes the overall voltage of the cell. Another advantage of nitrogen ions is their relatively low price and low weight, which has a positive effect on the specific capacity.

[0030] The allocation is proportionally O 2 -ions of the metal oxide Li2MnO3 by nitrogen ions N 2-The doping is replaced. Preferably, the properties of the composition are not negatively affected. For example, doping is carried out using nitrogen compounds of lithium or manganese. Nitrogen-oxygen compounds or other element-nitrogen compounds are also conceivable, provided that the introduced elements do not negatively affect the properties of the active material and / or can be removed from the active material.

[0031] In general, the aforementioned doping produces an active material (A) of the positive electrode with a first component (A1) containing the nitrogen-doped metal oxide Li2MnO3 and a second component (A2) containing the NCM compound LiMO2 according to the following formula (IV): x(LiMO2):1-x(Li 2-z N / a z MnO 3-y N y ) (IV) where M, z, and y have the previously defined meanings and 1 > x ≥ 0. Preferably, 1 > x > 0, in particular 0.8 ≥ x ≥ 0.2.

[0032] A positive electrode of a battery cell is also proposed, which comprises an active material (A) according to the invention.

[0033] According to an advantageous embodiment of the invention, a coating containing aluminum fluoride (AlF3) is applied to the active material (A) of the positive electrode. A coating of the active material (A) of the positive electrode with aluminum fluoride has a positive effect on the capacity of the battery cell.

[0034] In particular, the coating in question prevents or reduces contact between the active material (A) of the positive electrode and the electrolyte composition contained in the battery cell. This also prevents or reduces the leaching of transition metals from the active material (A) of the positive electrode and the migration of leached transition metals to the negative electrode of the battery cell.

[0035] According to a further advantageous embodiment of the invention, a coating containing carbon is applied to the active material (A) of the positive electrode. Such a coating ensures homogeneous electronic contact of the positive electrode.

[0036] The aforementioned AlF3-containing coating and the aforementioned carbon-containing coating can also be applied together to the active material (A) of the positive electrode, in particular one on top of the other, i.e. layer by layer.

[0037] A battery cell is also proposed which comprises at least one positive electrode according to the invention.

[0038] A battery cell according to the invention is advantageously used in an electric vehicle (EV), a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), a power tool, or a consumer electronics product. Tools in this context include, in particular, home and garden tools. Consumer electronics products include, in particular, mobile phones, tablet PCs, or notebooks. Advantages of the invention

[0039] By partially replacing the oxygen ions O 2- in the metal oxide of the first component (A1) of the active material (A) of the positive electrode by nitrogen ions N 2-An active material (A) is provided which, when used in a lithium-ion battery cell, ensures a stable voltage over a relatively long period and a high number of cycles. Likewise, the capacity of the lithium-ion battery cell remains stable over a relatively long period and a high number of cycles. Voltage and capacity loss are significantly reduced. This increases the battery's lifespan, thus enabling commercial use, particularly of lithium-ion batteries with an NCM compound in the active material (A) of the positive electrode. Brief description of the drawings

[0040] Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0041] They show: Fig. 1 a schematic representation of a battery cell and Fig. 2 a schematic representation of a modification of the battery cell made of Fig. 1. Embodiments of the invention

[0042] In Fig. Figure 1 shows a schematic representation of a battery cell 2. The battery cell 2 comprises a cell housing 3, which is prismatic, in this case cuboid. The cell housing 3 is electrically conductive and, for example, made of aluminum. However, the cell housing 3 can also be made of an electrically insulating material, such as plastic.

[0043] Battery cell 2 comprises a negative terminal 11 and a positive terminal 12. A voltage supplied by battery cell 2 can be accessed via terminals 11 and 12. Furthermore, battery cell 2 can also be charged via terminals 11 and 12. Terminals 11 and 12 are spaced apart from each other on a top surface of the prismatic cell housing 3.

[0044] Within the cell housing 3 of the battery cell 2, an electrode winding is arranged, comprising two electrodes, namely a negative electrode 21 and a positive electrode 22. The negative electrode 21 and the positive electrode 22 are each made of foil and wound into the electrode winding with a separator 18 in between. It is also conceivable that several electrode windings are provided in the cell housing 3. Instead of the electrode winding, for example, an electrode stack could also be provided.

[0045] The negative electrode 21 comprises a negative active material 41, which is designed in a foil-like form. The negative active material 41 consists of silicon or a silicon-containing alloy as its base material.

[0046] The negative electrode 21 further comprises a current collector 31, which is also designed as a foil. The negative active material 41 and the current collector 31 are laid flat against each other and connected to one another. The current collector 31 of the negative electrode 21 is electrically conductive and made of a metal, for example, copper. The current collector 31 of the negative electrode 21 is electrically connected to the negative terminal 11 of the battery cell 2.

[0047] The positive electrode 22 is a high-energy (HE) NCM (nickel-cobalt-manganese) electrode. The positive electrode 22 comprises a positive active material (A) 42, which is in particle form. Additives, in particular conductive carbon black and binders, are arranged between the particles of the positive active material (A) 42. The positive active material (A) 42 and the aforementioned additives form a composite, which is arranged in a film-like manner.

[0048] The positive active material (A) 42 has a first component (A1) containing Li2MnO3. The first component of the positive active material (A) 42 is further doped with nitrogen ions N 2- on, which contain at least some of the oxygen ions O 2- The component Li2MnO3 can be replaced. The first component (A1) can additionally be doped with sodium ions, so that some of the lithium ions are replaced by sodium ions.

[0049] The positive active material (A) 42 further comprises a second component (A2) containing an NCM compound, namely LMO2. M is a transition metal, in particular selected from nickel, cobalt, and manganese. Other components of the positive active material (A) 42 are, in particular, PVDF binder, graphite, and carbon black.

[0050] The positive electrode 22 also includes a current collector 32, which is also designed as a foil. The assembly of the positive active material (A) 42 and the additives and the current collector 32 are laid flat against each other and connected to one another. The current collector 32 of the positive electrode 22 is electrically conductive and made of a metal, for example, aluminum. The current collector 32 of the positive electrode 22 is electrically connected to the positive terminal 12 of the battery cell 2.

[0051] The negative electrode 21 and the positive electrode 22 are separated from each other by the separator 18. The separator 18 is also film-like. The separator 18 is electronically insulating but ionically conductive, i.e., permeable to lithium ions.

[0052] The cell housing 3 of the battery cell 2 is filled with a liquid aprotic electrolyte composition 15, or with a polymer electrolyte. The electrolyte composition 15 surrounds the negative electrode 21, the positive electrode 22, and the separator 18. The electrolyte composition 15 is also ionically conductive and comprises, for example, a mixture of at least one cyclic carbonate (e.g., ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC)) and at least one linear carbonate (e.g., dimethylene carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC)) as a solvent, as well as a lithium salt (e.g., LiPF6, LiBF4) as an additive.

[0053] In Fig. 2 is a modification of battery cell 2 made of Fig. Figure 1 shows a schematic representation. The modified battery cell 2 also comprises a cell housing 3, which is prismatic, in this case cuboid. Battery cell 2 is largely similar to battery cell 2 from Fig. 1. In the following, particular attention will therefore be paid to the differences compared to battery cell 2. Fig. 1 received.

[0054] A coating 52 is applied to the particles of the positive active material (A) 42. The particles of the positive active material (A) 42 are surrounded by the coating 52. The coating 52 thus encapsulates the particles of the positive active material (A) 42.

[0055] The coating 52 contains aluminum fluoride, i.e., AlF3. The coating 52 prevents or reduces contact between the positive active material (A) 42 and the electrolyte composition 15 contained in the cell housing 3 of the battery cell 2. This also prevents or reduces the leaching of transition metals from the positive active material (A) 42 and the migration of leached transition metals to the negative electrode 21 of the battery cell 2.

[0056] The coating 52 can also contain carbon. Such a coating 52 ensures homogeneous electronic contact of the positive electrode 22. The coating 52 can, in particular, be multilayered and contain, for example, a layer of aluminum fluoride, i.e., AlF3, and a layer of carbon.

[0057] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, within the scope specified by the claims, a multitude of modifications are possible that fall within the bounds of what is considered skilled in the art.

Claims

[1] Positive active material (A) (42) for a positive electrode (22) of a battery cell (2), comprising a first component (A1) which includes a compound of general formula (III): Li 2-z N / a z MnO 3-y N y (III) where 3 > y > 0; and 2 > z > 0. [2] Positive active material (A) (42) according to claim 1, characterized by , that 1.5 ≥ y > 0, in particular 0.5 ≥ y > 0. [3] Positive active material (A) (42) according to claim 1 or 2, characterized by , that 1 ≥ z ≥ 0.

1. [4] Positive active material (A) (42) according to any one of claims 1 to 3, characterized by , that the positive active material (A) (42) comprises a second component (A2) which contains LiMO2, wherein M is a transition metal selected from the elements nickel, cobalt and / or manganese. [5] Positive active material (A) (42) according to claim 4, characterized by , that the positive active material (A) (42) comprises a compound of formula (IV): x(LiMO2):1-x(Li 2-z N / a z MnO 3-y N y ) (IV) where 1 > x ≥ 0; 3 > y > 0; and 2 > z > 0 is. [6] Positive electrode (22) of a battery cell (2) comprising a positive active material (A) (42) according to any one of the preceding claims. [7] Positive electrode (22) according to claim 6, characterized by , that a coating (52) containing aluminium fluoride (AlF3) is applied to the positive active material (A) (42). [8] Positive electrode (22) according to claim 6 or 7, characterized by , that a coating (52) containing carbon is applied to the positive active material (A) (42). [9] Battery cell (2) comprising at least one positive electrode (22) according to any one of claims 6 to 8. [10] Use of a battery cell (2) according to claim 9 in an electric vehicle (EV), in a hybrid vehicle (HEV), in a plug-in hybrid vehicle (PHEV), in a tool or in a consumer electronics product.

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